U.S. patent application number 13/577163 was filed with the patent office on 2012-12-06 for nuclear reactor system having natural circulation of primary coolant.
Invention is credited to P. Stefan Anton, Ranga Nadig, Indresh Rampall, Krishna P. Singh.
Application Number | 20120307956 13/577163 |
Document ID | / |
Family ID | 44355832 |
Filed Date | 2012-12-06 |
United States Patent
Application |
20120307956 |
Kind Code |
A1 |
Singh; Krishna P. ; et
al. |
December 6, 2012 |
NUCLEAR REACTOR SYSTEM HAVING NATURAL CIRCULATION OF PRIMARY
COOLANT
Abstract
A nuclear reactor system that, in one embodiment, utilizes
natural circulation (i.e., thermosiphon) to circulate a primary
coolant in a single-phase through a reactor core and a heat
exchange sub-system. The heal exchange sub-system is located
outside of the nuclear reactor pressure vessels and, in some
embodiments, is designed so as to not cause any substantial
pressure drop in the flow of the primary coolant within the heal
exchange sub-system that is used to vaporize a secondary coolant.
In another embodiment, a nuclear reactor system is disclosed in
which the reactor core is located below ground and all penetrations
into the reactor pressure vessel are located above ground.
Inventors: |
Singh; Krishna P.; (Jupiter,
FL) ; Anton; P. Stefan; (Wynnewood, PA) ;
Nadig; Ranga; (Cherry Hill, NJ) ; Rampall;
Indresh; (Cherry Hill, NJ) |
Family ID: |
44355832 |
Appl. No.: |
13/577163 |
Filed: |
February 7, 2011 |
PCT Filed: |
February 7, 2011 |
PCT NO: |
PCT/US11/23952 |
371 Date: |
August 3, 2012 |
Current U.S.
Class: |
376/298 |
Current CPC
Class: |
G21C 15/12 20130101;
G21C 15/26 20130101; Y02E 30/00 20130101; Y02E 30/30 20130101; G21C
7/32 20130101; G21C 13/04 20130101; G21D 1/006 20130101; G21C 1/086
20130101 |
Class at
Publication: |
376/298 |
International
Class: |
G21C 7/32 20060101
G21C007/32 |
Claims
1. A natural circulation nuclear reactor system comprising: a
reactor pressure vessel having an internal cavity; a reactor core
comprising nuclear fuel disposed within the internal cavity at a
bottom portion of the reactor pressure vessel; a heat exchange
sub-system located outside of the reactor pressure vessel; a
closed-loop primary coolant circuit that flows a primary coolant
through the reactor pressure vessel to cool the reactor core and
through the heat exchange sub-system to transfer heat to a
secondary coolant; and wherein operation of the reactor core causes
natural circulation of the primary coolant through the closed-loop
primary coolant circuit in a single phase.
2. The natural circulation nuclear reactor system according to
claim 1 further comprising: a partition dividing the internal
cavity of the reactor pressure vessel into a primary coolant riser
passageway and a primary coolant downcomer passageway, the reactor
core disposed within the primary coolant riser passageway, wherein
operation of the reactor core causes the primary coolant to rise
within the primary coolant riser passageway; the reactor pressure
vessel comprising a primary coolant outlet port located at a top
portion of the reactor pressure vessel in fluid Communication with
the primary coolant riser passageway; the reactor pressure vessel
comprising a primary coolant inlet port located at a top portion of
the reactor pressure vessel in fluid communication with the primary
coolant downcomer passageway; and a plenum at the bottom portion of
the reactor vessel that allows cross-flow of the primary coolant
from the primary coolant downcomer passageway to the primary
coolant riser passageway.
3. (canceled)
4. The natural circulation nuclear reactor system according to
claim 2 wherein the partition has an effective coefficient of
thermal conductivity measured from the primary coolant riser
passageway to the primary coolant downcomer passageway that is less
than an effective coefficient of thermal conductivity of the
primary coolant.
5. The natural circulation nuclear reactor system according to
claim 2 wherein the partition is a tubular structure having an
inner surface and an outer surface, the inner surface of the
tubular structure forming the primary coolant riser passageway, and
the primary coolant downcomer passageway being formed between the
outer surface of tubular structure and the inner surface of the
reactor pressure vessel, the primary coolant downcomer passageway
being an annular passageway that circumferentially surrounds the
primary coolant riser passageway.
6.-8. (canceled)
9. The natural circulation nuclear reactor system according to
claim 1 wherein the reactor pressure vessel extends along a
substantially vertical axis, a major portion of the axial length of
the reactor pressure vessel located below a ground level, and the
reactor core located below the ground level and the heat exchange
sub-system located above the ground level.
10. The natural circulation nuclear reactor system according to
claim 9 further comprising: a partition dividing the internal
cavity of the reactor pressure vessel into a primary coolant riser
passageway and a primary coolant downcomer passageway, the reactor
core disposed within the primary coolant riser passageway; the
reactor pressure vessel comprising a primary coolant outlet port
located at a top portion of the reactor pressure vessel above the
ground level and in fluid communication with the primary coolant
riser passageway, the primary coolant outlet port fluidly coupled
to the heat exchange sub-system to form an incoming hot leg of
primary coolant of the heat exchange sub-system; and the reactor
pressure vessel comprising a primary coolant inlet port located at
the top portion of the reactor pressure vessel above the ground
level and in fluid communication with the primary coolant downcomer
passageway, the primary coolant inlet port fluidly coupled to the
heat exchange sub-system to form an outgoing cool leg of primary
coolant of the heat exchange sub-system.
11. The natural circulation nuclear reactor system according to
claim 10 wherein the primary coolant has a first high temperature
in the incoming hot lee and a second low temperature in the
outgoing cool leg, the first high temperature being at least
220.degree. F. greater than the second low temperature.
12.-14. (canceled)
15. The natural circulation nuclear reactor system according to
claim 9 wherein the reactor pressure vessel comprises a flange
portion that supports the major portion of the reactor pressure
vessel below the ground level in a vertically-oriented cantilevered
manner within a reactor well.
16.-19. (canceled)
20. The natural circulation nuclear reactor system according to
claim 1 wherein the heat exchange sub-system comprises a first
horizontal steam generator and a second horizontal steam generator
operably coupled in series with one another other along the
closed-loop primary coolant circuit, the first and second steam
generators converting the secondary coolant from liquid-phase to
gas-phase via the heat transferred from the primary coolant.
21. The natural circulation nuclear reactor system according to
claim 20 wherein the first horizontal steam generator is a high
pressure steam generator and the second horizontal steam generator
is a low pressure steam generator, the high pressure steam
generator being upstream of the low pressure steam generator along
the closed-loop primary coolant circuit.
22. (canceled)
23. The natural circulation nuclear reactor system according to
claim 20 wherein the first and second horizontal steam generators
are single-pass heat exchangers, the primary coolant being a
tube-side fluid in both the first and second horizontal steam
generators, and wherein the first and second horizontal steam
generators do not cause any substantial pressure drop in the
closed-loop primary coolant circuit due to increase in
elevation.
24. (canceled)
25. The natural circulation nuclear reactor system according to
claim 20 wherein an inlet of the first horizontal steam generator
is coupled directly to a primary coolant outlet port of the reactor
pressure vessel, an outlet of the first horizontal steam generator
is coupled directly to an inlet of the second horizontal steam
generator, and an outlet of the second horizontal steam generator
is coupled directly to a primary coolant inlet port of the reactor
pressure vessel.
26. (canceled)
27. The natural circulation nuclear reactor system according to
claim 25 wherein the first and second horizontal steam generators
are integrally welded to the reactor vessel.
28. The natural circulation nuclear reactor system according to
claim 20 wherein the heat exchange sub-system comprises a first
superheater configured to heat the vapor-phase of the secondary
coolant exiting the first steam generator and a second superheater
configured to heat the vapor-phase of the secondary coolant exiting
the second steam generator, wherein the first and second
superheaters are operably coupled to one another in series along
the closed-loop primary coolant circuit and in parallel to the
first and second steam generators along the closed-loop primary
coolant circuit.
29. The natural circulation nuclear reactor system according to
claim 28 wherein between 10% to 15% of the flow of the primary
coolant through the heat exchange sub-system is directed through
the first and second superheaters, the remainder of the flow of the
primary coolant through the heat exchange sub-system being directed
through the first and second steam generators.
30. (canceled)
31. The natural circulation nuclear reactor system according to
claim 1 wherein operation of the reactor core causes natural
circulation of the primary coolant by creating a riser water column
and a downcomer water column within the internal cavity of the
reactor pressure vessel, the riser water column and the downcomer
water column having a vertical height in a range of 80 ft. to 120
ft.
32. The natural circulation nuclear reactor system according to
claim 1 wherein the primary coolant has a negative reactivity
coefficient.
33. (canceled)
34. (canceled)
35. The natural circulation nuclear reactor system according to
claim 1 wherein the internal cavity of the reactor pressure vessel
is maintained at a pressure in a range of 2000 psia to 2500
psia.
36. (canceled)
37. The natural circulation nuclear reactor system according to
claim 1 wherein the heat exchange sub-system is at an elevation
that is 80 ft. to 120 ft. greater than an elevation of the reactor
core.
38. (canceled)
39. A nuclear reactor system comprising: an elongated reactor
pressure vessel having an internal cavity containing a primary
coolant, the reactor pressure vessel extending along a
substantially vertical axis, a major portion of the axial length of
the reactor pressure vessel located below a ground level; a reactor
core comprising nuclear fuel disposed within the internal cavity at
a bottom portion of the reactor pressure vessel reactor and below
the ground level; the reactor pressure vessel comprising a primary
coolant outlet port located above the ground level; the reactor
pressure vessel comprising a primary coolant inlet port located
above the ground level; a heat exchange sub-system located outside
of the reactor pressure vessel and above the ground level, an
incoming hot leg of the heat exchange system fluidly coupled to the
primary coolant outlet port and an outgoing cold leg of the heat
exchange system fluidly coupled to the primary coolant inlet port;
and wherein the major portion of the reactor pressure vessel is
free of penetrations.
40. The nuclear reactor system according to claim 39 further
comprising: a partition dividing the internal cavity of the reactor
pressure vessel into a primary coolant riser passageway and a
primary coolant downcomer passageway, the reactor core disposed
within the primary coolant riser passageway; the primary coolant
outlet port in fluid communication with a top portion of the
primary coolant riser passageway ; and the primary coolant inlet
port in fluid communication with a top portion of the primary
coolant downcomer passageway.
41. The nuclear reactor system according to claim 40 wherein the
partition has an effective coefficient of thermal conductivity
measured from the primary coolant riser passageway to the primary
coolant downcomer passageway that is less than an effective
coefficient of thermal conductivity of the primary coolant.
42. The nuclear reactor system according to claim 40 wherein the
primary coolant has a first high temperature in the incoming hot
leg and a second low temperature in the outgoing cool leg, the
first high temperature being at least 220.degree. F. greater than
the second low temperature.
43. The nuclear reactor system according to claim 39 wherein the
major portion of the reactor pressure vessel is at least 75% of the
axial length of the reactor pressure vessel.
44. (canceled)
45. (canceled)
46. The nuclear reactor system according to claim 39 wherein the
heat exchange sub-system and the internal cavity of the reactor
pressure vessel collectively form a closed-loop primary coolant
circuit that flows the primary coolant through the reactor pressure
vessel to cool the reactor core and through the heat exchange
sub-system to transfer heat to a secondary coolant, wherein
operation of the reactor core causes natural circulation of the
primary coolant through the closed-loop primary coolant circuit in
a single phase, and wherein the secondary coolant is converted from
liquid-phase to gas-phase within the heat exchange sub-system by
the heat transferred from the primary coolant.
47. (canceled)
48. The nuclear reactor system according to claim 46 wherein the
heat exchange sub-system comprises a first horizontal steam
generator and a second horizontal steam generator operably coupled
in series with one another other along the closed-loop primary
coolant circuit, the first and second steam generators converting
the secondary coolant from liquid-phase to gas-phase via the heat
transferred from the primary coolant.
49. The nuclear reactor system according to claim 48 wherein the
first and second horizontal steam generators are single-pass heat
exchangers, the primary coolant being a tube-side fluid in both the
first and second horizontal steam generators, and wherein the first
and second horizontal steam generators do not cause any substantial
pressure drop in the closed-loop primary coolant circuit due to
increase in elevation.
50. The nuclear reactor system according to claim 48 wherein an
inlet of the first horizontal steam generator is coupled directly
to the primary coolant outlet port of the reactor pressure vessel,
an outlet of the first horizontal steam generator is coupled
directly to an inlet of the second horizontal steam generator, and
an outlet of the second horizontal steam generator is coupled
directly to the primary coolant inlet port of the reactor pressure
vessel.
51. (canceled)
52. (canceled)
53. The nuclear reactor system according to claim 46 wherein the
primary coolant has a negative reactivity coefficient.
54. A nuclear reactor system comprising: an elongated reactor
pressure vessel having an internal cavity containing a primary
coolant, the reactor pressure vessel extending along a
substantially vertical axis; a reactor core comprising nuclear fuel
disposed within the internal cavity at a bottom portion of the
reactor pressure vessel reactor; a partition dividing the internal
cavity of the reactor pressure vessel into a primary coolant riser
passageway and a primary coolant downcomer passageway, the reactor
core disposed within the primary coolant riser passageway; the
reactor pressure vessel comprising a primary coolant outlet port in
fluid communication with a top portion of the primary coolant riser
passageway; the reactor pressure vessel comprising a primary
coolant inlet port in fluid communication with a top portion of the
primary downcomer riser passageway; at least one steam generator
located outside of the reactor pressure vessel, an incoming hot leg
of the steam generator fluidly coupled to the primary coolant
outlet port and an outgoing cold leg of the steam generator fluidly
coupled to the primary coolant inlet port; and wherein the steam
generator does not cause any substantial pressure drop in a flow of
the primary coolant through the steam generator resulting from an
increase in elevation.
55. (canceled)
56. (canceled)
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 61/416,954, filed Nov. 24, 2010, U.S.
Provisional Patent Application No. 61/333,551, filed May 11, 2010,
and U.S. Provisional Patent Application No. 61/302,069, filed Feb.
5, 2010, the entireties of which are herein incorporated by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to nuclear reactor
systems, and specifically to nuclear reactor systems that utilize
natural circulation of the primary coolant in a single-phase, such
as pressurized water reactors ("PWRs").
BACKGROUND OF THE INVENTION
[0003] Over recent years, a substantial amount of interest has
grown in developing commercially viable PWRs that utilize the
phenomenon of natural circulation (also known as thermosiphon
effect) to circulate the primary coolant to both cool the nuclear
reactor and to vaporize a secondary coolant into motive vapor.
[0004] CAREM (Argentina) is a 100 MW(e) PWR reactor design with an
integrated self-pressurized primary system through which the
primary coolant circulation is achieved by natural circulation. The
CAREM design incorporates several passive safety systems. The
entire primary system including the core, steam generators, primary
coolant and steam dome are contained inside a single pressure
vessel. The strong negative temperature coefficient of reactivity
enhances the self-controlling features. The reactor is practically
self-controlled and need for control rod movement is minimized. In
order to keep a strong negative temperature coefficient of
reactivity during the whole operational cycle, it is not necessary
to utilize soluble boron for burn-up compensation. Reactivity
compensation for burn-up is obtained with burnable poisons, i.e.
gadolinium oxide dispersed in the uranium di-oxide fuel. Primary
coolant enters the core from the lower plenum. After being heated
the primary coolant exits the core and flows up through the riser
to the upper dome. In the upper part, the primary coolant leaves
the riser through lateral windows to the external region, then
flows down through modular steam generators, decreasing its
enthalpy by giving up heat to the secondary coolant in the steam
generator. Finally, the primary coolant exits the internal steam
generators and flows down through the down-comer to the lower
plenum, closing the circuit. CAREM uses once-through straight tube
steam generators. Twelve steam generators are arranged in an
annular array inside the pressure vessel above the core. The
primary coolant flows through the inside of the tubes, and the
secondary coolant flows across the outside of the tubes. A shell
and two tube plates form the barrier between primary and secondary
coolant flow circuits.
[0005] AST-500 (Russia) is a 500 MW(th) reactor design intended to
generate low temperature heat for district heating and hot water
supply to cities. AST-500 is a pressurized water reactor with
integral layout of the primary components and natural circulation
of the primary coolant. Features of the AST-500 reactor include
natural circulation of the primary coolant under reduced working
parameters and specific features of the integral reactor, such as a
built-in steam-gas pressurizer, in-reactor heat exchangers for
emergency heat removal, and an external guard vessel.
[0006] V-500 SKDI *(Russia) is a 500 MW(e) light water integral
reactor design with natural circulation of the primary coolant in a
vessel with a diameter less than 5 m. The reactor core and the
steam generators are contained within the steel pressure vessel
(i.e., the reactor pressure vessel). The core has 121 shroudless
fuel assemblies having 18 control rod clusters. Thirty six fuel
assemblies have burnable poison rods. The hot primary coolant moves
from the core through the riser and upper shroud windows into the
steam generators located in the downcomer. The coolant flows due to
the difference in coolant densities in the downcomer and riser. The
pressurizer is connected by two pipelines, to the reactor pressure
vessel and the water clean up system.
[0007] The NHR-200 (China) is a design for providing heat for
district heating, industrial processes and seawater desalination.
The reactor power is 200 MW(th). The reactor core is located at the
bottom of the reactor pressure vessel (RPV). The system pressure is
maintained by N2 and steam. The reactor vessel is cylindrical. The
RPV is 4.8 m in diameter, 14 m in height, and 197 tons in weight.
The guard vessel consists of a cylindrical portion with a diameter
of 5 m and an upper cone portion with maximum 7 m in diameter. The
guard vessel is 15.1 m in height and 233 tons in weight. The core
is cooled by natural circulation in the range from full power
operation to residual heat removal. There is a long riser on the
core outlet to enhance the natural circulation capacity. The height
of the riser is about 6 m. Even in case of interruption of natural
circulation in the primary circuit due to a LOCA the residual heat
of the core can be transmitted by steam condensed at the uncovered
tube surface of the primary heat exchanger.
[0008] While the aforementioned PWRs utilize natural circulation of
the primary coolant to both cool the reactor core and heat the
secondary coolant, all of these natural circulation PWRs suffer
from the drawback that the heat exchange equipment is integrated
with and located within the reactor pressure vessel. Such an
arrangement not only makes the heat exchange equipment difficult to
repair and/or service but also subjects the equipment to corrosive
conditions. Furthermore, locating the heat exchange equipment
within the reactor pressure vessel results in increased complexity
and a potential increase in the number of penetrations into the
reactor pressure vessel. However, prior to the present invention,
the location of the heat exchange equipment within the reactor
pressure vessel was likely deemed necessary to achieve the natural
circulation of the primary coolant in the PWR cycle.
[0009] A drawback of other PWRs that exist in the art is the fact
that the reactor pressure vessels have penetrations at both the top
portion of the reactor pressure vessel and at the bottom portion of
the reactor pressure vessel. Still another drawback of existing
PWRs is the fact that a substantial length of piping and a large
number of joints are used carry the primary coolant from the
reactor pressure vessel to the heat exchange equipment, thereby
increasing the danger of failure due to a pipe break scenario.
BRIEF SUMMARY OF THE INVENTION
[0010] These, and other drawbacks, are remedied by the present
invention. A nuclear reactor system is presented herein that, in
one embodiment, utilizes natural circulation (i.e., thermosiphon)
to circulate a primary coolant in a single-phase through a reactor
core and a heat exchange sub-system, wherein the heat exchange
sub-system is located outside of the nuclear reactor pressure
vessel. In some embodiments, the heat exchange sub-system is
designed so as to not cause any substantial pressure drop in the
flow of the primary coolant within the heat exchange sub-system
that is used to vaporize a secondary coolant. In another
embodiment, a nuclear reactor system is disclosed in which the
reactor core is located below ground and all penetrations into the
reactor pressure vessel are located above ground. In certain
embodiment, the inventive nuclear reactor system is a PWR
system.
[0011] In one embodiment, the invention can be a natural
circulation nuclear reactor system comprising: a reactor pressure
vessel having an internal cavity; a reactor core comprising nuclear
fuel disposed within the internal cavity at a bottom portion of the
reactor pressure vessel: a heat exchange sub-system located outside
of the reactor pressure vessel: a closed-loop primary coolant
circuit that flows a primary coolant through the reactor pressure
vessel to cool the reactor core and through the heat exchange
sub-system to transfer heat to a secondary coolant; and wherein
operation of the reactor core causes natural circulation of the
primary coolant through the closed-loop primary coolant circuit in
a single phase.
[0012] In another embodiment, the invention can be a nuclear
reactor system comprising: an elongated reactor pressure vessel
having an internal cavity containing a primary coolant, the reactor
pressure vessel extending along a substantially vertical axis, a
major portion of the axial length of the reactor pressure vessel
located below a ground level; a reactor core comprising nuclear
fuel disposed within the internal cavity at a bottom portion of the
reactor pressure vessel reactor and below the ground level; the
reactor pressure vessel comprising a primary coolant outlet port
located above the ground level; the reactor pressure vessel
comprising a primary coolant inlet port located above the ground
level; a heat exchange sub-system located outside of the reactor
pressure vessel and above the ground level, an incoming hot leg of
the heat exchange system fluidly coupled to the primary coolant
outlet port and an outgoing cold leg of the heat exchange system
fluidly coupled to the primary coolant inlet port: and wherein the
major portion of the reactor pressure vessel is free of
penetrations.
[0013] In yet another embodiment, the invention can be a nuclear
reactor system comprising: an elongated reactor pressure vessel
having an internal cavity containing a primary coolant, the reactor
pressure vessel extending along a substantially vertical axis; a
reactor core comprising nuclear fuel disposed within the internal
cavity at a bottom portion of the reactor pressure vessel reactor;
a partition dividing the internal cavity of the reactor pressure
vessel into a primary coolant riser passageway and a primary
coolant downcomer passageway, the reactor core disposed within the
primary coolant riser passageway; the reactor pressure vessel
comprising a primary coolant outlet port in fluid communication
with a top portion of the primary coolant riser passageway; the
reactor pressure vessel comprising a primary coolant inlet port in
fluid communication with a top portion of the primary downcomer
riser passageway: at least one steam generator located outside of
the reactor pressure vessel, an incoming hot leg of the steam
generator fluidly coupled to the primary coolant outlet port and an
outgoing cold leg of the steam generator fluidly coupled to the
primary coolant inlet port; and wherein the steam generator does
not cause any substantial pressure drop in a flow of the primary
coolant through the steam generator resulting from an increase in
elevation.
[0014] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating the preferred embodiment of the
invention, are intended for purposes of illustration only and are
not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The present invention will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0016] FIG. 1 is a schematic of a natural circulation nuclear
reactor system according to one embodiment of the present
invention.
[0017] FIG. 2 is a schematic of an embodiment of a heat exchange
sub-system that can be used in the natural circulation reactor
system of FIG. 1.
[0018] FIG. 3A is a schematic top view of a single-pass horizontal
steam generator in accordance with an embodiment of the present
invention.
[0019] FIG. 3B is a schematic side view of the single-pass
horizontal steam generator of FIG. 3A.
[0020] FIG. 4 is a side view of a portion of the natural
circulation nuclear reactor system of FIG. 1 according to one
structural embodiment:
[0021] FIG. 5 is an elevated isometric view of a portion of the
natural circulation nuclear reactor system of FIG. 1 according to
one structural embodiment.
DETAILED DESCRIPTION OF THE DRAWINGS
[0022] The following description of the preferred embodiment(s) is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses.
[0023] Prior to discussing FIGS. 1-5 in detail, an overview of one
specific embodiment of the inventive natural circulation reactor
system, and its operation, will be set forth. Those skilled in the
art will appreciate that the overview is directed to one very
specific embodiment and that the details thereof are not limiting
of the present invention in all embodiments. Furthermore, those
skilled in the art will appreciate how the overview applies to the
subsequent detailed discussion of FIGS. 1-5.
I. Overview of one Potential Commercial Embodiment
[0024] The inventive nuclear reactor system, in one potential
commercial embodiment, is a 145 MWe nuclear reactor designed to
provide an economical and safe source of clean energy from nuclear
fission. Strengths of the inventive nuclear reactor system include
its inherent safety and simplicity of operation. The operational
simplicity of the inventive nuclear reactor system and the modest
outlay required to establish and commission it will make it
possible to deliver the fruits of pollution-free nuclear energy to
the vast mass of humanity around the globe that does not presently
have access to a reliable source of power or to a robust electrical
energy delivery system. Competitive with large nuclear reactors on
a per-megawatt basis, the inventive nuclear reactor system is
tailored to add generation capacity to the installed base
incrementally with incremental capital outlays. Due to its inherent
operational simplicity, the inventive nuclear reactor system
requires a minimal cadre of trained personnel to run the plant.
Multiple units of the inventive nuclear reactor system can be
clustered at one location or geographically dispersed without a
significant increase in the per-megawatt construction cost.
Geographical dispersal and underground configuration serve as
natural antidotes to post-9/11 concerns. The modest power output of
the inventive nuclear reactor system makes it a viable candidate
source of reliable electrical energy or for providing heating steam
to a city or process steam as a cogeneration plant serving an
industrial plant.
[0025] As a passive small modular reactor of the PWR genre with
safety, ease of maintenance and superb security, the inventive
nuclear reactor system is ideally suited to serve as a reliable
power source to strategic national assets of any country. Design
features of the inventive nuclear reactor system that speak to its
inherent safety and reliability are:
[0026] 1. Reactor Core Deep Underground
[0027] The reactor core resides deep underground in a thick-walled
reactor pressure vessel (RPV) made of an ASME Code material that
has decades of proven efficacy in maintaining reactor integrity in
large PWR and BWR reactors. All surfaces wetted by the reactor
coolant are made of stainless steel or Inconel, which eliminates a
major source of crud accumulation in the reactor vessel.
[0028] 2. Natural Circulation of the Reactor Coolant
[0029] The inventive nuclear reactor system does not rely on any
active components, such as a reactor coolant pump, for circulating
the primary coolant through the closed-loop primary coolant
circuit, which includes flow through the reactor core and the heat
exchange sub-system. Instead, the flow of the primary coolant
through the reactor pressure vessel, the horizontal steam
generators, and other miscellaneous equipment occurs by the
pressure head created by density differences in the flowing water
in the hot and cold segments of the closed-loop primary coolant
circuit. The reliability of gravity as a motive force underpins
inherent safety of the inventive nuclear reactor system. The
movement of the primary coolant requires no pumps, valves, or
moving machinery of any kind, in certain embodiments.
[0030] 3. No Reliance on Off-Site Power
[0031] Offsite power is not essential for shutting down the
inventive nuclear reactor system. The rejection of reactor residual
heat during the shutdown also occurs by natural circulation. Thus,
the need for an emergency shutdown power supply at the site--a
major concern for nuclear plants--is eliminated.
[0032] 4. Assurance of a Large Inventory of Water Around and Over
the Reactor Core
[0033] The reactor pressure vessel of the inventive nuclear reactor
system has no penetrations in its below-ground portion, which can
be the bottom 100 feet, which means that the reactor core will
remain submerged in a large inventory of water. All penetrations in
the reactor pressure vessel are located in the above-ground
portion, or top portion, of the reactor pressure vessel and are
small in size. The absence of large piping in the closed-circuit
primary coolant circuit precludes the potential of a "large break"
LOCA event.
[0034] 5. All Critical Components Readily Accessible
[0035] Both the heat exchange sub-system, which includes the steam
generators, and the control rod drive system are located outside
the reactor pressure vessel at a level that facilitates easy
access, making their preventive maintenance and repair a
conveniently executed activity. Each of the steam generators is a
horizontal pressure vessel with built-in design features to
conveniently access and plug tubes.
[0036] 6. Demineralized Water
[0037] The primary coolant (which can also be referred to as the
reactor coolant) is demineralised water, which promotes criticality
safety because of its strong negative reactivity gradient with rise
in temperature. Elimination of borated water also simplifies the
nuclear steam supply system (NSSS) by eliminating the systems and
equipment needed to maintain and control boron levels in the
primary coolant. Pure water and corrosion resistant primary coolant
loop help minimize crud buildup in the reactor pressure vessel.
[0038] 7. Modularity
[0039] One can build only one of the inventive nuclear reactor
systems at a site, or a large number thereof. Clustering a number
of inventive nuclear reactor systems at one site will reduce the
overall O&M costs.
[0040] 8. Long Operating Cycle
[0041] The inventive nuclear reactor system will operate for
approximately 3.5 years before requiring refueling.
[0042] 9. Short Construction Life Cycle
[0043] Virtually all components of the inventive nuclear reactor
system are shop fabricated. Site work is limited to reinforced
concrete construction and a limited amount of welding to assemble
the shop-built equipment and parts. As a result, it is possible to
complete the construction of one of the inventive nuclear reactor
systems in 24 months from the first shovel in the ground.
[0044] 10. Efficient Steam Cycle
[0045] A pair of two horizontal steam generators are arranged in
series and integrally welded to the reactor pressure vessel. The
efficiency of the power cycle of the inventive nuclear reactor
system, and its compactness, is further enhanced by superheaters
that are integrally welded to the horizontal steam generators. The
superheaters, one attached to each steam generator, increases cycle
efficiency and also protect both the high pressure and low pressure
turbines from the deleterious effect of moist steam.
[0046] 11. Integral Pressurizer
[0047] The design of the reactor pressure vessel incorporates an
integral pressurizer that occupies the upper reaches of the reactor
pressure vessel. The pressurizer serves to control the pressure in
the reactor vessel.
[0048] 12. Suitable for Water-Challenged Sites
[0049] The inventive nuclear reactor system can be installed at
sites with limited water availability, such as creeks and small
rivers that are inadequate for large reactors. The inventive
nuclear reactor system can be operated equally well in a
water-challenged region by using air-cooled condenser technology to
reject the plant's waste heat. Using air in lieu of water, of
course, results in a moderate increase in the plant's cost.
[0050] 12. System Parameters in the Safe and Proven Range
[0051] The operating pressure and temperature within the reactor
pressure vessel is in the proven range for PWRs. Lower core power
density than that used in large PWRs for improved thermal-hydraulic
control (please see table below) and an improved margin to
departure-from-nucleate boiling in the reactor core.
TABLE-US-00001 Exemplary System Parameters Data Number of fuel
assemblies in the core 32 Nominal thermal power, MWt 446 Nominal
recirculation rate, MLb per hour 5.46 Reactor water outlet
temperature, deg. F. 580 Reactor water inlet temperature, deg. F.
333 Reactor pressure, pounds per sq. inch 2,250 Water in the RV
cavity, gallons 30.00
[0052] 13. Minimized Piping Runs and Minimum Use of Active
Components to Enhance Reliability and Cost Competitiveness
[0053] The amount of piping in the close-loop primary coolant
circuit and the secondary coolant circuit in the inventive nuclear
reactor system is the least of any nuclear plant design on the
market, as is the number of pumps and valves.
[0054] 14. In-Service Inspection
[0055] All weld seams in the primary system including those in the
reactor pressure vessel wall are available at all times for
inspection. In particular, the weld seams in the reactor pressure
vessel can be inspected by operating a manipulator equipped
in-service inspection device in the reactor well during power
generation. Thus, inventive nuclear reactor system exceeds the
in-service inspection capability expected of nuclear plants under
ASME Code Section XI.
[0056] 15. Earthquake Hardened Sesign
[0057] Virtually all major equipment in the inventive nuclear
reactor system are either underground or horizontally mounted to
withstand strong seismic motions. This includes the reactor
pressure vessel, the fuel pool, the reactor water storage tank (all
underground) and the horizontal steam generators, the horizontal
superheaters, and the horizontal kettle reboiler that are floor
mounted.
[0058] 16. Aircraft Impact Proof Containment
[0059] The containment structure of the inventive nuclear react
system is designed to withstand the impact of a crashing fighter
plane or a commercial liner without sustaining a thru-wall
breach.
II. Detail
[0060] Referring now to FIG. 1, a natural circulation nuclear
reactor system 1000 (hereinafter the "reactor system 1000") is
illustrated according to one embodiment of the present invention.
The reactor system 1000 generally comprises a reactor pressure
vessel 100 and a heat exchange sub-system 200. The reactor pressure
vessel 100 contains a primary coolant 101 that is used to cool the
rector core 102 and to heat a secondary coolant within the heat
exchange sub-system 200. The reactor pressure vessel 100 is fluidly
coupled to an incoming hot leg 201 of the heat exchange sub-system
200 via a primary coolant outlet port 103. Similarly, the reactor
pressure vessel 100 is also fluidly coupled to an outgoing cool leg
202 of the heat exchange sub-system 200 via a primary coolant inlet
port 104. As a result, a closed-loop primary coolant circuit 300 is
formed through which the primary coolant 101 flows in a
single-phase. As discussed in greater detail below, the flow of the
primary coolant 101 through the closed-loop primary coolant circuit
is a natural circulation flow induced by the heat given off by the
normal operation of the reactor core 102.
[0061] In certain embodiments, the internal cavity 105 of the
reactor pressure vessel 100 is maintained under sufficient pressure
to maintain the primary coolant 101 in a liquid-phase despite the
high temperature within the rector pressure vessel 100. In the
exemplified embodiment, a pressure control sub-system 50 (commonly
referred to in the art as a pressurizer) is located within a top
region of the reactor pressure vessel 100 and is configured to
control the pressure of the internal cavity 105 of the reactor
pressure vessel 100. The pressure control sub-system 50 is integral
with the removable head 106 of the reactor pressure vessel 100 to
prevent line break concerns and to provide a more compact reactor
system 1000. Pressurizers are well known in the art and any
standard pressurizer could be used as the pressure control
sub-system 50. In one embodiment, the internal cavity 105 of the
reactor pressure vessel 100 is maintained at a pressure in a range
of 2000 psia to 2500 psia. In one more specific embodiment, the
internal cavity 105 of the reactor pressure vessel 100 is
maintained at a pressure between 2200 psia to 2300 psia. Of course,
the exact pressure maintained in the internal cavity 105 of the
reactor pressure vessel 100 is not to be limiting of the invention
unless specifically claimed.
[0062] The reactor pressure vessel 100 is an elongated tubular
pressure vessel formed by a thick wall made of an acceptable ASME
material, such as stainless steel. The reactor pressure vessel 100
extends from a bottom end 107 to a top end 108 along a
substantially vertical axis A-A, thereby defining an axial length
of the reactor pressure vessel 100. In one embodiment, the reactor
pressure vessel 100 has an axial length of over 100 feet to
facilitate an adequate level of turbulence in the recirculating
primary coolant 101 from the natural circulation (also referred to
as thermosiphon action in the art). In certain other embodiments,
the reactor pressure vessel 100 has an axial length in a range
between 100 feet to 150 feet. Of course, the invention is not so
limited in certain alternate embodiments.
[0063] The reactor pressure vessel 100 generally comprises a domed
head 106 and a body 109. The domed head 106 is detachably coupled
to a top end of the body 109 so as to be removable therefrom for
refueling and maintenance. The domed head 106 can be coupled to the
body 109 through the use of any suitable fastener, including bolts,
clamps, or the like. In the exemplified embodiment, the body 109
comprises an upper flange 110 and the domed head 106 comprises a
lower flange 111 that provided mating structures through which
bolts 114 (FIG. 4) extend to couple the domed head 106 to the body
109. When the domed had 106 is coupled to the body 109, a hermetic
seal is formed therebetween via the use of a gasket or other
suitably contoured interface.
[0064] The body 109 of the reactor pressure vessel 100 comprises an
upstanding tubular wall 112 and a domed bottom 113 that
hermetically seals the bottom end 107 of the reactor pressure
vessel 100. The tubular wall 112 has a circular transverse
cross-sectional profile in the illustrated embodiment but can take
on other shapes as desired. In the exemplified embodiment, the
domed bottom 113 is integral and unitary with respect to the
tubular wall 112. Of course, in other embodiments, the domed bottom
113 may be a separate structure that is secured to the tubular wall
112 via a welding or other hermetic connection technique, such as
the flanged technique described above for the domed head 106 and
the body 109. Integral and unitary construct of the domed bottom
113 and the body 109 is, however, preferable in certain embodiments
as it eliminates seams and/or interfaces that could present rupture
potential.
[0065] The reactor pressure vessel 100 forms an internal cavity 105
in which a reactor core 102 is housed. The reactor core 102
comprises nuclear fuel, in the form of fuel assemblies, as is known
in the art. The details of the structure of the reactor core 102
are not limiting of the present invention in and the reactor system
1000 can utilize any type of reactor core or nuclear fuel. The
reactor core 102 is positioned in a bottom portion 115 of the
reactor pressure vessel 100. In one embodiment, the reactor core
102 has a core thermal power of 400 MWt to 600 MWt during the
operation thereof.
[0066] In one embodiment, the reactor core 102 is comprised of
vertically arrayed fuel assemblies. The spacing between the fuel
assemblies is governed by the design objective of keeping the
reactivity (neutron multiplication factor) at 1.0 at all locations
in the reactor pressure vessel 100. The criticality control in the
axial direction is provided by the built-in neutron poison in the
fuel rods (called IFBAs by Westinghouse) and possibly by control
rods.
[0067] A partition 120 is provided within the internal cavity 105
of the reactor pressure vessel 100 that divides the internal cavity
into a primary coolant riser passageway 105A and a primary coolant
downcomer passageway 105B. Both the passageways 105A, 105B are
axially extending vertical passageways that form part of the
closed-loop primary coolant circuit 300.
[0068] In the exemplified embodiment, the partition 120 comprises
an upstanding tubular wall portion 120A and a transverse wall
portion 120B. The tubular wall portion 120A is an annular tube that
is mounted within the internal cavity 105 of the reactor pressure
vessel 100 so as to be concentrically arranged with respect to the
upstanding wall 112 of the reactor pressure vessel 100. As a
result, the primary coolant downcomer passageway 105B is an annular
passageway that circumferentially surrounds the primary coolant
riser passageway 105A. The primary coolant downcomer passageway
105B is formed between an outer surface 121 of the upstanding
tubular wall portion 120A of the partition 120 and the inner
surface 116 of the upstanding wall 112 of the reactor pressure
vessel 100. The primary coolant riser passageway 105B is formed by
the inner surface 122 of the upstanding tubular wall portion 120A
of the partition 120.
[0069] The transverse wall portion 120B is annular ring-like plate
that is connected to a top end of the of the upstanding tubular
wall portion 120A of the partition 120 at one end and to the
upstanding wall 112 of the reactor pressure vessel 100 on the other
end. The transverse wall portion 120B acts a separator element that
prohibits cross-flow of the primary coolant 101 between the primary
coolant riser passageway 105A and the primary coolant downcomer
passageway 105B within the top portion 117 of the reactor pressure
vessel 100. In essence, the transverse wall portion 120B forms a
roof of the primary coolant downcomer passageway 105B that prevents
the heated primary coolant 101 that exits the reactor pressure
vessel 100 via the primary coolant outlet port 103 from mixing with
the cooled primary coolant 101 that enters the reactor pressure
vessel 100 via the primary coolant inlet port 104, and vice-versa.
Cross-flow of the primary coolant 101 between the primary coolant
riser passageway 105A and the primary coolant downcomer passageway
105B is prohibited by the upstanding tubular wall portion 120A of
the partition 120.
[0070] In addition to physically separating the flow of the heated
and cooled primary coolant 101 within the primary coolant downcomer
and riser passageways 105A, 105B as discussed above, the partition
120 also thermally insulates the cooled primary coolant 101 within
the primary coolant downcomer passageway 105B from the heated
primary coolant 101 within the primary coolant riser passageway
105A. Stated simply, one does not want heat to transfer freely
through the partition 120. Thus, it is preferred that the partition
120 be an insulating partition in the sense that its effective
coefficient of thermal conductivity (measured radially from the
primary coolant riser passageway 105A to the primary coolant
downcomer passageway 105B) is less than the coefficient of thermal
conductivity of the primary coolant 101.
[0071] Making the effective coefficient of thermal conductivity of
the partition 120 less than the coefficient of thermal conductivity
of the primary coolant 101 ensures that the primary coolant 101 in
the primary coolant downcomer passageway 105B remains cooler than
the primary coolant 101 in the primary riser passageway 105A,
thereby maximizing the natural circulation rate of the primary
coolant 101 through the closed-loop primary coolant circuit 300. In
a very simple construction, this can be achieved by creating the
partition 120 out of a single solid material that has a low
coefficient of thermal conductivity. However, it must be considered
that the material should neither degrade nor deform under the
operating temperatures and pressures of the reactor pressure vessel
100. In such an embodiment, the effective coefficient of thermal
conductivity is simply the coefficient of thermal conductivity of
the single solid material.
[0072] In the exemplified embodiment, the low coefficient of
thermal conductivity of the partition 120 is achieved by making the
partition 120 as a multi-layer construction. As exemplified, the
partition 120 comprises an insulating layer 124 that is sandwiched
between two outer layers 125A, 125B. In one embodiment, the
insulating layer 124 is a refractory material while the outer
layers 125A, 125B are stainless steel or another corrosion
resistant material. In certain embodiments, the insulating layer
124 is full encased in the outer layers 125A, 125B.
[0073] The internal cavity 115 of the reactor pressure vessel 100
also comprises a plenum 118 at the bottom portion 115 of the
reactor pressure vessel 100 that allows cross-flow of the primary
coolant 101 from the primary coolant downcomer passageway 105B to
the primary coolant riser passageway 105A. In the exemplified
embodiment, the plenum 118 is created by the fact that the bottom
end 123 of the upstanding tubular wall portion 120A of the
partition 120 is spaced from the inner surface 119 of the domed
bottom 113, thereby creating an open passageway. In alternate
embodiments, the partition 120 may extend all the way to the inner
surface 119 of the domed bottom 113. In such embodiments, the
plenum 118 will be formed by providing a plurality of
apertures/openings in the partition 120 so as to allow the desired
cross-flow.
[0074] The internal cavity 105 further comprises a plenum 126 at
the top portion 117 of the reactor pressure vessel 100. The plenum
126 allows the heated primary coolant 101 that is rising within the
primary coolant riser passageway 105A to gather in the top portion
117 of the reactor pressure vessel 100 and then flow transversely
outward from the vertical axis A-A and through the primary coolant
outlet port 103.
[0075] The reactor core 102 is located within the primary coolant
riser passageway 105A above the bottom plenum 118. During operation
of the reactor core 102, thermal energy produced by the reactor
core 102 is transferred into the primary coolant 101 in the primary
coolant riser passageway 105A adjacent the reactor core 102,
thereby becoming heated. This heated primary reactor coolant 101
rises upward within the primary coolant riser passageway 105A due
to its decreased density. This heated primary coolant 101 gather in
the top plenum 126 and exits the reactor pressure vessel 100 via
the primary coolant outlet port 103 where it enters the heat
exchange sub-system 200 as the incoming hot leg 201. In one
embodiment, the heated primary coolant 101 entering the hot leg 201
of the heat exchanger has a temperature of at least 570.degree. F.,
and in another embodiment a temperature in a range of 570.degree.
F. to 620.degree. F.
[0076] This heated primary coolant 101 passes through the heat
exchange sub-system 200 where its thermal energy is transferred to
a secondary coolant (described below in greater detail with respect
to FIG. 2), thereby becoming cooled and exiting the heat exchange
sub-system 200 via the cold leg 202. When exiting the cold leg 202
of the heat exchange sub-system, this cooled primary coolant 101
has a temperature in a range of 300.degree. F. to 400.degree. F. in
one embodiment. In another embodiment, the heat exchange sub-system
200 is designed so that the temperature differential between the
heated primary coolant in the hot leg 201 and the cooled primary
coolant in the cold leg is at least 220.degree. F.
[0077] The cooled primary coolant 101 exiting the cold leg of the
heat exchange sub-system 200 then enters the reactor pressure
vessel 100 via the primary coolant inlet port 104, thereby flowing
into a top portion 127 of the primary coolant downcomer passageway
105B. Once inside the primary coolant downcomer passageway 105B,
the cooled primary coolant 101 (which has a greater density than
the heated primary coolant 101 in the primary coolant riser
passageway 105A) flows downward through the primary coolant
downcomer passageway 105B into the bottom plenum 118 where it is
drawn back up into the primary coolant riser passageway 105A and
heated again by the reactor core 102, thereby completing a cycle
through the closed-loop primary circuit 300.
[0078] As discussed above, operation of the reactor core 102 causes
natural circulation of the primary coolant 101 through the
closed-circuit primary coolant circuit 300 by creating a riser
water column within the primary coolant riser passageway 105A and a
downcomer water column within the primary coolant downcomer
passageway 105B. In one embodiment, the riser water column and the
downcomer water column have a vertical height in a range of 80 ft.
to 150 ft., and more preferably from 80 ft. to 120 ft. The
vigorousness of the natural circulation (or termosiphon flow) is
determined by the height of the two water columns (fixed by the
reactor design), and the difference between the bulk temperature of
the two water columns (in water the SES and the downcomer space).
For example, water at 2200 psia and 580.degree. F. has density of
44.6 lb/cubic feet. This density increases to 60.5 lb/cubic feet if
the temperature reduces to 250.degree. F. The hot and cold water
colums 60 feet high will generate a pressure head of 6.6 psi which
is available to drive natural circulation of the primary coolant
101 through the closed-loop primary coolant circuit 300. A 90 feet
high column will generate 50% greater head (i.e., 9.9 psi).
[0079] As a result of the natural circulation of the primary
coolant 101 achieved by the water columns and gravity, the reactor
system 1000 is free of active equipment, such as pumps or fans, for
forcing circulation of the primary coolant through the closed-loop
primary coolant circuit.
[0080] In the embodiment illustrated in FIG. 1, the primary coolant
outlet port 103 is at a slightly lower elevation (1-3 ft.) than the
primary coolant inlet port 104. However, in other embodiments, the
primary coolant outlet port 103 and the primary coolant inlet port
104 will be at substantially the same elevation (see FIGS. 4 and
5). When the primary coolant outlet port 103 and the primary
coolant inlet port 104 are at substantially the same elevation the
partition 120 will be appropriately designed. Furthermore, as used
herein, the term port includes mere apertures or openings.
[0081] In one embodiment, the primary coolant 101 is a liquid that
has a negative reactivity coefficient. Thus, the chain reaction in
the reactor core 102 would stop automatically if the heat rejection
path to the heat exchange sub-system 200 is lost in a hypothetical
scenario. Thus, the reactor system 1000 is inherently safe. In one
specific embodiment, the primary coolant 101 is demineralized
water. All systems and controls used to maintain boron
concentration in the reactor vessel in a typical PWR are eliminated
from the reactor system 1000. Moreover, the use of demineralized
water as the primary coolant 101 and the existence of the corrosion
resistant surfaces of the reactor pressure vessel 100 help maintain
crud buildup to a minimum. The reactivity control in the reactor
core 102 is maintained by a set of control elements (burnable
poisons) that are suspended vertically and occupy strategic
locations in and around the fuel assemblies to homogenize and
control the neutron flux.
[0082] Referring now to FIGS. 1, 4 and 5 concurrently, it can be
seen that a major portion 130 of the axial length of the reactor
pressure vessel 100 located below a ground level 400 while a minor
portion 131 of the axial length of the reactor pressure vessel 100
extends above the ground level 400. As such, the reactor core 102
is located deep below the ground level 400 while the heat exchange
sub-system 200 is located above the ground level 400. In one
embodiment, the heat exchange sub-system 200 is at an elevation
that is 80 ft. to 150 ft, and preferably 80 ft. to 120 ft., greater
than the elevation of the reactor core 102.
[0083] The minor portion 131 of the reactor pressure vessel 100
includes a top portion 132 of the body 109 and the domed head 106.
The primary coolant outlet port 103 and the primary coolant inlet
port 104 are located on the minor portion 131 of the reactor
pressure vessel 100 that is above the ground level 400. More
specifically, the primary coolant outlet port 103 and the primary
coolant inlet port 104 are located on the top portion 132 of the
body 109 of the reactor pressure vessel 100 that is above the
ground level 400.
[0084] The major portion 130 includes a majority of the body 109
and the domed bottom 113. In certain embodiment, the major portion
130 of the reactor pressure vessel 130 is at least 75% of the axial
length of the reactor pressure vessel 100. In other embodiments,
the major portion 130 of the reactor pressure vessel 130 is between
60% to 95% of the axial length of the reactor pressure vessel 100.
In another embodiment, the major portion 130 of the reactor
pressure vessel 130 is between 75% to 95% of the axial length of
the reactor pressure vessel 100.
[0085] The reactor pressure vessel 100 comprises a reactor flange
150. The top portion 132 of the body 109 of the reactor pressure
vessel 100 is welded to the reactor flange 150, which is a massive
upper forging. The reactor flange 150 also provides the location
for the primary coolant inlet port 104 and the primary coolant
outlet port 103 (FIGS. 4 and 5), and the connections to the heat
exchange sub-system 200 (and for the engineered safety systems to
deal with various postulated accident scenarios). This reactor
flange 150 contains vertical welded lugs to support the weight of
the reactor pressure vessel 100 in the reactor well 410 in a
vertically oriented cantilevered manner (FIG. 1). As a result, the
reactor pressure vessel 100 is spaced from the wall surfaces 411
and floor surface 412 of the reactor well 410, thereby allowing the
reactor pressure vessel 100 to radially and axially expand as the
reactor core 102 heats up during operation and causes thermal
expansion of the reactor pressure vessel 100.
[0086] Furthermore, the major portion 130 of the reactor pressure
vessel 100 is free of penetrations. In other words, the major
portion 130 of the reactor pressure vessel 100 comprises no
apertures, holes, opening or other penetrations that are either
open or to which pipes or other conduits are attached. All
penetrations (such as the primary coolant inlet and outlet ports
103, 104) in the reactor pressure vessel 100 are located in the
above-ground minor portion 131, and more specifically in the top
portion 132 of the body 109 of the reactor pressure vessel 100. In
one embodiment, it is further preferred that the major portion 130
be a unitary construct with no connections, joints, or welds.
[0087] The bottom portion 115 of the reactor pressure vessel 100 is
laterally restrained by a lateral seismic restraint system 160 that
spans the space between the body 109 of the reactor pressure vessel
100 and the wall surfaces 411 of the reactor well 410 to withstand
seismic events. The seismic restraint system 160, which comprises a
plurality of resiliently compressible struts 161, allows for free
axial and diametral thermal expansion of the reactor vessel. The
bottom of the reactor well 410 contains engineered features to
flood it with water to provide defense-in-depth against a
(hypothetical, non-mechanistic) accident that produces a rapid rise
in the enthalpy of the reactor's contents. Because the reactor
system 1000 is designed to prevent loss of the primary coolant 101
by leaks or breaks and the reactor well 410 can be flooded at will,
burn-through of the reactor pressure vessel 100 by molten fuel
(corium) can be ruled out as a credible postulate. This inherently
safe aspect simplifies the design and analysis of the reactor
system 1000.
[0088] Referring now to FIGS. 2 and 4-5 concurrently, an embodiment
of the heat exchange sub-system 200 is illustrated. While a
specific embodiment of the heat exchange sub-system 200 will be
described herein, it is to be understood that, in alternate
embodiments, one or more of components can be omitted as desired.
For example, in certain embodiments, one or both of the horizontal
superheaters 205, 206 may be omitted. In certain other embodiments,
one of the horizontal steam generators 203, 204 may be omitted
and/or combined into the other one of the horizontal steam
generators 203,204. Moreover, additional equipment may be
incorporated as necessary so long as the natural circulation of the
primary coolant 101 through the closed-loop primary coolant circuit
300 is not prohibited through the introduction of substantial head
loss.
[0089] As mentioned above, the heat exchange subsystem 200
comprises an incoming hot leg 201 that introduces heated primary
coolant into the portion of the closed-loop primary coolant circuit
300 that passes through the heat exchange sub-system 200 and an
outgoing cold leg 202 that removes cooled primary coolant from the
portion of the closed-loop primary coolant circuit 300 that passes
through the heat exchange sub-system 200. In order to minimize (and
in some embodiments eliminate) pressure loss in the closed-loop
primary coolant circuit 300 caused by an increase in the elevation
of the primary coolant flow, the steam generators 203, 204 and the
superheaters 205, 206 are all of the horizontal genre (i.e., the
tubes which carry the primary coolant extend substantially
horizontal through the shell-side fluid) and are in horizontal
alignment with each other where possible.
[0090] Within the heat exchange sub-system 200, the primary coolant
flow of the closed-loop primary coolant circuit 300 is divided into
two paths 211, 212 at a flow divider 215. The flow divider 210 can
be a three-way valve, a three-way mass flow controller, or a simple
Y plumbing joint. The first path 211, which carries the majority of
the primary coolant flow, travels through the first horizontal
steam generator 203 and then through the second horizontal steam
generator 204. Meanwhile, the second path 212, which carries a
minority of the primary coolant flow, travels through the first
horizontal superheater 205 and then through the second horizontal
superheater 206. After passing through the first and second
horizontal steam generators 203, 204 and the first and second
horizontal superheaters 205, 206, the first and second paths 211,
212 converge in a flow converger 216, which combines the primary
coolant flows of the first and second paths 211, 212 and directs
the combined flow to the outgoing cold leg 202. As with the flow
divider 215, the flow converger 216 may be a three-way valve, a
three-way mass flow controller, or a simple Y plumbing joint.
[0091] In one embodiment, 10% to 15% of the incoming primary
coolant flow that enters the heat exchange sub-system 200 via the
hot leg 201 is directed into the second path 212 while the
remaining 85% to 90% of the incoming primary coolant is directed
into the first path 211. In one specific example, the incoming
primary coolant that enters the heat exchange sub-system 200 via
the hot leg 201 has a flow rate of 5 to 7 million lbs./hr. In this
example, 0.6 to 1 million lbs./hr. of the primary coolant is
directed into the second path 212 while the remainder of the
primary coolant flow is directed into the first path 211.
[0092] The first and second horizontal steam generators 203, 204
are operbaly coupled in series to one another along the first path
211 of the closed-loop primary coolant circuit 300. Both of the
horizontal steam generators 203, 204 are horizontally disposed
shell-and-tube heat exchangers. The first horizontal steam
generator 203 is a high pressure steam generator while the second
horizontal steam generator 204 is a low pressure steam generator
(in comparison to the high pressure steam generator). The high
first steam generator 203 is located upstream of the second
horizontal steam generator 204 along the closed-loop primary
coolant circuit 300. Similarly, the first and second horizontal
superheaters 205, 206 are operbaly coupled in series to one another
along the second path 212 of the closed-loop primary coolant
circuit 300. The first horizontal superheater 205 is a high
pressure superheater while the second horizontal superheater 206 is
a low pressure superheater (in comparison to the high pressure
superheater). The high first steam superheater 205 is located
upstream of the second horizontal superheater 206 along the
closed-loop primary coolant circuit 300. Furthermore, the first and
second superheaters 205, 206 are located in parallel to the first
and second horizontal steam generators 203, 204 along the
closed-loop primary coolant circuit 300.
[0093] Furthermore, the first and second horizontal steam
generators 203, 204 are interconnected by a return header so that
the hot primary coolant entering the first horizontal steam
generator 203 heats the secondary coolant to make steam for the
high-pressure turbine 220 and then proceeds to the second
horizontal steam generator 204 with minimal pressure loss to make
steam for the low-pressure turbine 221.
[0094] The flow of the primary coolant in the first path 211 is
used to convert a secondary coolant flowing through the shell-side
of the first and second horizontal steam generators 203, 204 from
liquid-phase to gas-phase through the transfer of heat form the
primary coolant to the secondary coolant within the first and
second horizontal steam generators 203, 204. Because the flow of
the primary coolant through the first and horizontal second steam
generators 203, 204 is substantially horizontal in nature, the flow
of the primary coolant through the first path 211 does not cause
any substantial pressure drop in the closed-loop primary coolant
circuit 300 resulting from an increase in elevation. Moreover,
because of the horizontal alignment of the first and second
horizontal steam generators 203, 204 with each other and the
primary coolant outlet and inlet ports 103, 104 of the reactor
pressure vessel 100 (FIG. 5), the primary coolant flow that travels
along the first path 211 from the primary coolant outlet port 103
of the reactor pressure vessel 100 to the primary coolant inlet
port 104 of the reactor pressure vessel 100 does not cause any
substantial pressure drop in the closed-loop primary coolant
circuit 300 resulting from an increase in elevation. While the
achievement of substantial zero pressure drop in the closed-loop
primary coolant circuit 300 resulting from an increase in elevation
is exemplified in terms of a horizontal flow, it is possible that
such substantial zero pressure drop can be achieved by a decline in
elevation as the primary coolant flows downstream in the
closed-loop primary coolant circuit 300.
[0095] The flow of the primary coolant in the second path 212 is
used to superheat the vapor-phase of the secondary coolant exiting
the first and second horizontal steam generators 203, 204 via the
first and second horizontal superheaters 205, 206 respectively,
thereby further drying the vapor-phase of the secondary coolant.
The use if the horizontal superheaters enhance the thermodynamic
efficiency of the turbine cycle, carried out on the high pressure
turbine 220 and the low pressure turbine 221.
[0096] The first and second horizontal superheaters 205, 206 are
horizontally disposed shell-and-tube heat exchanger positioned
directly above (and in series) with the first and second steam
generators 203, 204 (FIG. 5). However, due to the slight increase
in the elevation of the superheaters 205, 206 resulting from their
location above the first and second horizontal steam generators
203, 204, the flow of the primary coolant in the second path 212
does cause some pressure drop in the closed-loop primary coolant
circuit 300 resulting from an increase in elevation. However,
because only a small amount (10% to 15%) of the total primary
coolant that flows.through the heat exchange subsystem 200 is
directed into the second path 212 and through the horizontal
superheaters 205, 206, the pressure drop does not significantly
affect the desired natural circulation. Moreover, the increase in
elevation is negligible when compared to the height of the flow
driving water columns. In such an embodiment, at least 85% of the
flow of the primary coolant through the heat exchange sub-system
200 is still entirely horizontal from the primary coolant outlet
103 to the primary coolant inlet 104 and does not cause any
substantial pressure drop in the closed-loop primary coolant
circuit 300 due to increase in elevation. Further, in certain
alternate embodiments, the horizontal superheaters 205, 206 could
be eliminated and/or repositioned to be in horizontal alignment
with the horizontal steam generators 203, 204.
[0097] As shown in FIG. 5, the first and second horizontal steam
generators 203, 204 are coupled directly to the each other and to
the reactor pressure vessel 100. More specifically, the inlet of
the first horizontal steam generator 203 is coupled directly to the
primary coolant outlet port 103 of the reactor pressure vessel 100
while the outlet of the first horizontal steam generator 203 is
coupled directly to the inlet of the second horizontal steam
generator 204. The outlet of the second horizontal steam generator
204, is in turn, coupled directly to the primary coolant inlet port
104 of the reactor pressure vessel 100. The first and second
horizontal steam generators 203, 204 are arranged so as to extend
substantially parallel to one another, thereby collectively forming
a generally U-shaped structure. Thus, the first path 211 also takes
on a generally U-shape In certain embodiments, the first and second
horizontal steam generators 203, 204 are integrally welded to the
reactor vessel 100 and to each other.
[0098] Referring now to FIGS. 2 and 3A-B, each of the first and
second horizontal steam generators 203, 204 comprise a preheating
zone 208, 210 and a boiling zone 207, 209. Both of the first and
second horizontal steam generators 203, 204 are of the single-pass
type in which the primary coolant flow of the first path 211 is the
tube-side fluid. Each of the single-pass tubes 330 extend
substantially horizontally through the preheating zones 208, 210
and the boiling zones 207, 209. The secondary coolant circuit has a
main feedwater intake 501 and a return to condenser exit 502 into
and out of the heat exchange sub-system 200 respectively.
[0099] The secondary coolant, which is in the liquid-phase 505,
enters each of the first and second horizontal steam generators
203, 204 along line 503. The incoming liquid phase 505 of the
secondary coolant is preheated within the preheater zones 208, 210
of the first and second horizontal steam generators 203, 204. The
secondary coolant in liquid-phase 505 flows through a tortuous path
as shell-side fluid in the preheater zones 208, 210 and then enters
the boiling zones 207, 209, where it is further heated by the
primary coolant flow passing through the tubes 330. In the boiling
zones 207, 209, the liquid-phase secondary coolant 505 vaporizes
and exits the first and second horizontal steam generators 203, 204
as high pressure and low pressure steam 504 that is respectively
supplied to the high and low pressure turbines 220, 221.
[0100] The shells of the horizontal steam generators 203, 204 and
the horizontal superheaters 205, 206 provide additional barriers
against potential large-break LOCAs, as do the turning plenum and
the eccentric flanges that join the steam generators 203, 204 to
the reactor pressure vessel 100, as shown in FIGS. 4 and 5. All
systems connected to the reactor vessel 100 use a similar approach
to ensure that there is no potential for a large-break LOCA that
could rapidly drain the water from the reactor vessel 100 and
uncover the reactor core 102. As long as the reactor core 102 is
covered under all potential conditions of operation and
hypothetical accident, the release of radioactive material to the
public is minimal.
[0101] As explained in the foregoing, the reactor system 1000 is an
intrinsically safe reactor which, in the event of a problem
external to the reactor containment building or within containment,
is designed to automatically shut down in a safe mode with natural
circulation cooling. Nevertheless, to instill maximum confidence, a
number of redundant safety systems can be engineered to protect
public health and safety under hypothetical accident scenarios that
are unknown or unknowable, i.e., cannot be mechanistically
postulated. In the case of an abnormal condition when the normal
heat transport path through the steam generators are not available,
then the pressure in the reactor vessel 100 will begin to increase.
In such a case rupture discs will breach allowing the reactor
coolant to flow into a kettle reboiler located overhead. The kettle
will have a large inventory of water that will serve to extract the
heat from the reactor coolant until the system shuts down. Diverse
systems perform duplicate or overlapping functions using different
physical principles and equipment to ensure that a common-mode
failure is impossible.
[0102] As used throughout, ranges are used as shorthand for
describing each and every value that is within the range. Any value
within the range can be selected as the terminus of the range. In
addition, all references cited herein are hereby incorporated by
referenced in their entireties. In the event of a conflict in a
definition in the present disclosure and that of a cited reference,
the present disclosure controls.
[0103] While the invention has been described with respect to
specific examples including presently preferred modes of carrying
out the invention, those skilled in the art will appreciate that
there are numerous variations and permutations of the above
described systems and techniques. It is to be understood that other
embodiments may be utilized and structural and functional
modifications may be made without departing from the scope of the
present invention. Thus, the spirit and scope of the invention
should he construed broadly as set forth in the appended
claims.
* * * * *