U.S. patent application number 15/584659 was filed with the patent office on 2017-11-02 for molten fuel reactor thermal management configurations.
This patent application is currently assigned to TerraPower, LLC. The applicant listed for this patent is TerraPower, LLC. Invention is credited to Ryan Abbott, Anselmo T. Cisneros, JR., Daniel Flowers, Charles Gregory Freeman, Mark A. Havstad, Christopher J. Johns, Brian C. Kelleher, Kevin Kramer, Jeffery F. Latkowski, Jon D. McWhirter.
Application Number | 20170316840 15/584659 |
Document ID | / |
Family ID | 58708039 |
Filed Date | 2017-11-02 |
United States Patent
Application |
20170316840 |
Kind Code |
A1 |
Abbott; Ryan ; et
al. |
November 2, 2017 |
MOLTEN FUEL REACTOR THERMAL MANAGEMENT CONFIGURATIONS
Abstract
Configurations of molten fuel salt reactors are described that
allow for active cooling of the containment vessel of the reactor
by the primary coolant. Furthermore, naturally circulating reactor
configurations are described in which the reactor cores are
substantially frustum-shaped so that the thermal center of the
reactor core is below the outlet of the primary heat exchangers.
Heat exchanger configurations are described in which welded
components are distanced from the reactor core to reduce the damage
caused by neutron flux from the reactor. Radial loop reactor
configurations are also described.
Inventors: |
Abbott; Ryan; (Mountain
View, CA) ; Cisneros, JR.; Anselmo T.; (Seattle,
WA) ; Flowers; Daniel; (Bellevue, WA) ;
Freeman; Charles Gregory; (Kirkland, WA) ; Havstad;
Mark A.; (Esparto, CA) ; Johns; Christopher J.;
(Tacoma, WA) ; Kelleher; Brian C.; (Seattle,
WA) ; Kramer; Kevin; (Redmond, WA) ;
Latkowski; Jeffery F.; (Mercer Island, WA) ;
McWhirter; Jon D.; (Kirkland, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TerraPower, LLC |
Bellevue |
WA |
US |
|
|
Assignee: |
TerraPower, LLC
Bellevue
WA
|
Family ID: |
58708039 |
Appl. No.: |
15/584659 |
Filed: |
May 2, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62330726 |
May 2, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G21C 1/03 20130101; G21C
5/14 20130101; G21C 15/26 20130101; G21C 1/22 20130101; G21C 11/06
20130101; G21C 3/24 20130101; G21C 15/243 20130101; G21C 1/326
20130101; Y02E 30/30 20130101; G21C 15/02 20130101; G21C 3/54
20130101; G21C 15/12 20130101; G21C 1/14 20130101; G21C 15/28
20130101 |
International
Class: |
G21C 15/02 20060101
G21C015/02; G21C 3/54 20060101 G21C003/54; G21C 1/32 20060101
G21C001/32; G21C 1/32 20060101 G21C001/32; G21C 15/28 20060101
G21C015/28; G21C 15/25 20060101 G21C015/25 |
Claims
1. A method for actively cooling a containment vessel and fuel salt
in a molten fuel salt nuclear reactor comprising: flowing primary
coolant into the containment vessel adjacent to a first portion of
the containment vessel, thereby cooling the first portion; flowing
primary coolant into a heat exchanger within and spaced apart from
the containment vessel, the heat exchanger discharging cooled fuel
salt; routing discharged cooled fuel salt through a channel
adjacent to a second portion of the containment vessel, thereby
cooling the second portion; routing cooled fuel salt through the
channel adjacent to a neutron reflector, thereby cooling the
neutron reflector; and wherein the cooled neutron reflector is
adjacent to a third portion of the containment vessel such that
cooling the neutron reflector indirectly cools the third
portion.
2. The method of claim 1 wherein the flowing the primary coolant
into the containment vessel further comprises: flowing the coolant
through a coolant inlet duct inside the containment vessel
thermally connected to the first portion of the containment
vessel.
3. The method of claims 1 wherein the flowing the primary coolant
into the containment vessel further comprises: flowing the coolant
through a coolant inlet duct inside the containment vessel to a
heat exchanger coolant inlet adjacent a heat exchanger cooled fuel
salt outlet.
4. The method of claim 1 wherein the flowing the primary coolant
into the containment vessel further comprises: flowing the coolant
through a coolant inlet duct inside the containment vessel
thermally connected to the first portion of the containment
vessel.
5. The method of claim 1 wherein the fuel salt is a mixture of at
least one fissile salt and at least one non-fissile salt.
6. The method of claim 1 wherein the fuel salt includes one or more
of the following fissile salts: UF.sub.6, UF.sub.4, UF.sub.3,
ThCl.sub.4, UBr.sub.3, UBr.sub.4, PuCl.sub.3, UCl.sub.4, UCl.sub.3,
UCl.sub.3F, and UCl.sub.2F.sub.2.
7. The method of claim 1 wherein the fuel salt includes one or more
of the following non-fissile salts: NaCl, MgCl.sub.2, CaCl.sub.2,
BaCl.sub.2, KCl , SrCl.sub.2, VCl.sub.3, CrCl.sub.3, TiCl.sub.4,
ZrCl.sub.4, ThCl.sub.4, AcCl.sub.3, NpCl.sub.4, AmCl.sub.3,
LaCl.sub.3, CeCl.sub.3, PrCl.sub.3 and/or NdCl.sub.3.
8. The method of claim 1 wherein the fuel salt is a mixture of
UCl.sub.4, UCl.sub.3, and one or both of NaCl and MgCl.sub.2.
9. A molten fuel nuclear reactor comprising: an upper neutron
reflector defining a top of a reactor core; a lower neutron
reflector defining a bottom of the reactor core; at least one inner
neutron reflector defining sides of the reactor core; at least one
heat exchanger that receives heated fuel salt at a heat exchanger
fuel salt inlet below a reactor core heated fuel salt outlet,
transfers heat from the fuel salt to a coolant, and discharges the
cooled fuel salt at a heat exchanger fuel salt outlet fluidly
connected to a reactor core cooled fuel salt inlet; the at least
one heat exchanger including a welded component separated from the
fuel salt by one of the upper neutron reflector, the lower neutron
reflector, the inner neutron reflector or a neutron moderator.
10. The molten fuel nuclear reactor of claim 9 wherein the welded
component is a tube sheet.
11. The molten fuel nuclear reactor of claim 10 wherein the welded
component is a tube sheet through which the coolant exits the at
least one heat exchanger and the tube sheet is separated from the
fuel salt by the upper neutron reflector.
12. The molten fuel nuclear reactor of claim 10 wherein the welded
component is a tube sheet through which the coolant enters the at
least one heat exchanger and the tube sheet is separated from the
fuel salt by the lower neutron reflector.
13. The molten fuel nuclear reactor of claim 10 wherein the welded
component is a tube sheet through which the coolant both enters and
exits the at least one heat exchanger.
14. The molten fuel nuclear reactor of claim 13 wherein the tube
sheet through which the coolant both enters and exits the at least
one heat exchanger is located above the reactor core.
15. The molten fuel nuclear reactor of claim 13 wherein the tube
sheet through which the coolant both enters and exits the at least
one heat exchanger is separated from the fuel salt by the upper
neutron reflector.
16. The molten fuel nuclear reactor of claim 13 wherein the tube
sheet through which the coolant both enters and exits the at least
one heat exchanger is separated from the fuel salt by a neutron
absorber.
17. A radial loop molten salt reactor comprising: a reactor core
containment vessel; one or more reflectors in the reactor core
containment vessels, the one or more reflectors defining a reactor
core volume within the reactor core containment vessel; and a
plurality of heat exchanger legs spaced apart outside of the
reactor core containment vessel, each heat exchanger leg having a
reactor outlet pipe configured to receive heated fuel salt from the
reactor core volume, a heat exchanger that transfers heat from the
heated fuel salt to a primary coolant thereby creating a cooled
fuel salt, and a reactor inlet pipe configured to return the cooled
fuel salt into the reactor core volume.
18. The radial loop molten salt reactor of claim 17 further
comprising: a secondary containment vessel containing the reactor
core containment vessel and the plurality of heat exchanger legs,
the secondary containment vessel defining a volume sufficient to
hold at least all of the fuel salt contained in reactor core
containment vessel and in the plurality of heat exchanger legs.
19. A molten salt nuclear reactor comprising: a substantially
frustum-shaped reactor core containing a fissionable fuel salt, the
reactor core having a heated fuel salt outlet, a cooled fuel salt
inlet, and a thermal center above the cooled fuel salt inlet; at
least one heat exchanger that receives heated fuel salt at a heat
exchanger fuel salt inlet below the reactor core's heated fuel salt
outlet, transfers heat from the fuel salt to a coolant, and
discharges the cooled fuel salt at a heat exchanger fuel salt
outlet fluidly connected to the reactor core's cooled fuel salt
inlet; and wherein the thermal center of the reactor core is at a
level below the heat exchanger fuel salt outlet; and wherein the
location of the thermal center causes natural circulation in the
case of a loss of forced flow while the reactor is in a state of
criticality.
20. The molten salt nuclear reactor of claim 19 wherein the reactor
core has a depth that is the distance between the top level of the
fuel salt in the reactor core and the bottom of the fuel salt in
the reactor core, the reactor further comprising: wherein a ratio
of a distance below the heat exchanger fuel salt outlet of the
thermal center to the depth of the reactor core of the thermal
center is between 0.1 and 0.45; and wherein the shape of the
reactor core is selected from a frustum of a cone, a frustum of a
pyramid, a trapezoidal prism or a hyperboloid.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/330,726, filed May 2, 2016, which application is
hereby incorporated by reference.
INTRODUCTION
[0002] The utilization of molten fuels in a nuclear reactor to
produce power provides significant advantages as compared to solid
fuels. For instance, molten fuel reactors generally provide higher
power densities compared to solid fuel reactors, while at the same
time having reduced fuel costs due to the relatively high cost of
solid fuel fabrication.
[0003] Molten fluoride fuel salts suitable for use in nuclear
reactors have been developed using uranium tetrafluoride (UF.sub.4)
mixed with other fluoride salts such as UF.sub.6, and UF.sub.3.
Molten fluoride salt reactors have been operated at average
temperatures between 600.degree. C. and 860.degree. C. Binary,
ternary, and quaternary chloride fuel salts of uranium, as well as
other fissionable elements, have been described in co-assigned U.S.
patent application Ser. No. 14/981,512, titled MOLTEN NUCLEAR FUEL
SALTS AND RELATED SYSTEMS AND METHODS which application is hereby
incorporated herein by reference. In addition to chloride fuel
salts containing one or more of PuCl.sub.3, UCl.sub.4, UCl.sub.3F,
UCl.sub.3, UCl.sub.2F.sub.2, and UClF.sub.3, the application
further discloses fuel salts with modified amounts of .sup.37Cl,
bromide fuel salts such as UBr.sub.3 or UBr.sub.4, thorium chloride
(e.g., ThCl.sub.4) fuel salts, and methods and systems for using
the fuel salts in a molten fuel reactor. Average operating
temperatures of chloride salt reactors are anticipated between
300.degree. C. and 600.degree. C., but could be even higher, e.g.,
>1000.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The following drawing figures, which form a part of this
application, are illustrative of described technology and are not
meant to limit the scope of the invention as claimed in any manner,
which scope shall be based on the claims appended hereto. The
patent or application file contains at least one drawing executed
in color. Copies of this patent or patent application publication
with color drawing(s) will be provided by the Office upon request
and payment of the necessary fee.
[0005] FIG. 1 illustrates, in a block diagram form, some of the
basic components of a molten fuel reactor.
[0006] FIGS. 2A-2C illustrate different views of an embodiment of a
reactor that uses only natural circulation to circulate fuel salt
around the fuel loop.
[0007] FIG. 3 illustrates an embodiment of an improved
configuration for a naturally circulating fission reactor core in
which the reactor core is larger at the bottom than at the top.
[0008] FIG. 4 illustrates another embodiment of a frustoconical
reactor core design.
[0009] FIG. 5 illustrates a frustum of a decagonal pyramid
(10-sided pyramid) reactor core suitable for a naturally
circulating reactor core.
[0010] FIGS. 6A-6C illustrate an embodiment of a reactor design
that integrates active cooling of the containment vessel into the
primary coolant loop.
[0011] FIG. 7 is a flow diagram of an embodiment of a method for
active vessel cooling.
[0012] FIG. 8 illustrates an embodiment of a reactor with a
shell-side fuel heat exchanger configuration.
[0013] FIG. 9 illustrates an alternative embodiment of the reactor
of FIG. 8.
[0014] FIG. 10 illustrates an embodiment of a reactor with a
shell-side fuel, U-tube heat exchanger configuration in which the
single tube sheet is located above the reactor core.
[0015] FIG. 11 illustrates an embodiment of a reactor with a
shell-side fuel, U-tube heat exchanger configuration in which the
single tube sheet is within the reactor but laterally mounted in a
location away from the reactor core.
[0016] FIGS. 12A and 12B illustrate an alternative reactor design
referred to as a radial loop reactor.
DETAILED DESCRIPTION
[0017] This disclosure describes various configurations and
components of a molten fuel nuclear reactor. For the purposes of
this application, embodiments of a molten fuel reactor that use a
chloride fuel, such as a mixture of one or more fuel salts such as
PuCl.sub.3, UCl3, and/or UCl.sub.4 and one or non-fissile salts
such as NaCl and/or MgCl.sub.2, will be described. However, it will
be understood that any type of fuel salt, now known or later
developed, may be used and that the technologies described herein
may be equally applicable regardless of the type of fuel used. For
example, a fuel salt may include one or more non-fissile salts such
as, but not limited to, NaCl, MgCl.sub.2, CaCl.sub.2, BaCl.sub.2,
KCl , SrCl.sub.2, VCl.sub.3, CrCl.sub.3, TiCl.sub.4, ZrCl.sub.4,
ThCl.sub.4, AcCl.sub.3, NpCl.sub.4, AmCl.sub.3, LaCl.sub.3,
CeCl.sub.3, PrCl.sub.3 and/or NdCl.sub.3. Note that the minimum and
maximum operational temperatures of fuel within a reactor may vary
depending on the fuel salt used in order to maintain the salt
within the liquid phase throughout the reactor. Minimum
temperatures may be as low as 300-350.degree. C. and maximum
temperatures may be as high as 1400.degree. C. or higher.
Similarly, except were explicitly discussed otherwise, heat
exchangers will be generally presented in this disclosure in terms
of simple, single pass, shell-and-tube heat exchangers having a set
of tubes and with tube sheets at either end. However, it will be
understood that, in general, any design of heat exchanger may be
used, although some designs may be more suitable than others. For
example, in addition to shell and tube heat exchangers, plate,
plate and shell, printed circuit, and plate fin heat exchangers may
be suitable.
[0018] FIG. 1 illustrates, in a block diagram form, some of the
basic components of a molten fuel reactor. In general, a molten
fuel reactor 100 includes a reactor core 104 containing a
fissionable fuel salt 106 that is liquid at the operating
temperature. Fissionable fuel salts include salts of any nuclide
capable of undergoing fission when exposed to low-energy thermal
neutrons or high-energy neutrons. Furthermore, for the purposes of
this disclosure, fissionable material includes any fissile
material, any fertile material or combination of fissile and
fertile materials. The fuel salt 106 may or may not completely fill
the core 104, and the embodiment shown is illustrated with an
optional headspace 102 above the level of the fuel salt 106 in the
core 104. The size of the reactor core 104 may be selected based on
the characteristics and type of the particular fuel salt 106 being
used in order to achieve and maintain the fuel in an ongoing state
of criticality, during which the heat generated by the ongoing
production of neutrons in the fuel causes the temperature of the
molten fuel to rise when it is in the reactor core. Criticality
refers to a state in which loss rate of neutrons is equal to or
less than the production rate of neutrons in the reactor core. The
performance of the reactor 100 is improved by providing one or more
reflectors 108A, 108B, 108C around the core 104 to reflect neutrons
back into the core. Reflectors may be made of any neutron
reflecting material, now known or later developed, such as
graphite, beryllium, steel, tungsten carbide. The molten fuel salt
106 is circulated between the reactor core 104 and one or more
primary heat exchangers 110 located outside of the core 104. The
circulation may be driven using one or more pumps 112.
[0019] The primary heat exchangers 110 transfer heat from the
molten fuel salt 106 to a primary coolant 114 that is circulated
through a primary coolant loop 115. In an embodiment the primary
coolant may be another salt, such as NaCl-MgCl.sub.2, or lead.
Other coolants are also possible including Na, NaK, supercritical
CO.sub.2 and lead bismuth eutectic. In an embodiment, a reflector
108 is between each primary heat exchanger 110 and the reactor core
104 as shown in FIG. 1. For example, in an embodiment a cylindrical
reactor core 104, having a diameter of 2 meters (m) and a height of
3 m, is oriented vertically so that the flat ends of the cylinder
are on the top and bottom respectively. The entire reactor core 104
is completely encased in reflectors 108 between which are provided
channels for the flow of fuel salt 106 into and out of the reactor
core 104.
[0020] Although FIG. 1 illustrates one heat exchanger 110,
depending on the embodiment any number of heat exchangers 110 may
be used, the heat exchangers 110 being spaced around the exterior
of the core 104. For example, embodiments having two, four, six,
eight, ten, twelve and sixteen primary heat exchangers are
contemplated.
[0021] As discussed above, any design of heat exchanger may be used
but, generally, the heat exchangers 110 will be discussed in terms
of a shell and tube heat exchanger. In shell and tube heat
exchanger embodiments, the fuel salt may flow through the tubes
which are contained within a shell filled with the primary coolant.
The fuel salt enters the tubes via one or more tube sheets in the
shell to prevent the fuel salt from mixing with the primary
coolant. This is referred to as either a tube-side fuel or a
shell-side coolant configuration. Alternatively, the fuel salt may
flow through the shell and the primary coolant may flow through the
tubes, which is referred to either as a tube-side coolant or
shell-side fuel configuration.
[0022] Salt contacting surfaces of heat exchanger components may be
clad to protect against corrosion. Other protection options include
protective coatings, loose fitting liners or press-fit liners. In
an embodiment, cladding on the internal surface of the tubes is
molybdenum that is co-extruded with the base heat exchanger tube
material. For other fuel salt contacting surfaces (exterior
surfaces of the tube sheets and exterior surface of the shell), the
cladding material is molybdenum alloy. Nickel and nickel alloys are
other possible cladding materials. Molybdenum-rhenium alloys may be
used where welding is required. Components in contact with primary
cooling salt may be clad with Alloy 200 or any other compatible
metals, such as materials meeting the American Society of
Mechanical Engineers' pressure vessel code. The tube primary
material may be 316 stainless steel or any other compatible metals.
For example, in an embodiment alloy 617 is the shell and tube sheet
material.
[0023] In a tube-side fuel embodiment the fuel salt flows through
the tubes of the heat exchanger 110 and exits into the fuel salt
outlet channel. The primary coolant within the shell of the heat
exchanger 110 removes heat from the fuel salt traveling through the
tubes and heated coolant is then passed to the power generation
system 120.
[0024] As shown in FIG. 1, heated primary coolant 114 from the
primary heat exchangers 110 is passed to a power generation system
120 for the generation of some form of power, e.g., thermal,
electrical, or mechanical. The reactor core 104, primary heat
exchangers 110, pumps 112, molten fuel circulation piping
(including other ancillary components that are not shown such as
check valves, shutoff valves, flanges, drain tanks, etc.) and any
other components through which the molten fuel circulates or
contacts during operation can be referred to as the fuel loop 116.
Likewise, the primary coolant loop 115 includes those components
through which primary coolant circulates, including the primary
heat exchangers 110, primary coolant circulation piping (including
other ancillary components that are not shown such as coolant pumps
113, check valves, shutoff valves, flanges, drain tanks, etc.).
[0025] The molten fuel reactor 100 further includes at least one
containment vessel 118 that contains the fuel loop 116 to prevent a
release of molten fuel salt 106 in case there is a leak from one of
the fuel loop components. Note that not all of the primary coolant
loop 115 is within the containment vessel 118.
[0026] In an embodiment fuel salt flow is driven by a pump 112 so
that the fuel salt circulates through the fuel loop 116. In the
embodiment shown, there is one pump 112 for each primary heat
exchanger 110. Fewer or more pumps may be used. For example, in
alternative embodiments multiple, smaller pumps may be used for
each heat exchanger 110. In an embodiment, a pump 112 may include
an impeller at some location within the fuel loop 116 that when
rotated drives the flow of fuel salt around the fuel loop. The
impeller may be attached to a rotating shaft that connects the
impeller to a motor which may be located outside of the containment
vessel. An example of this embodiment can be found in FIGS. 6A-6C,
discussed below. Other pump configurations are also possible.
[0027] Broadly speaking, this disclosure describes multiple
alterations and component configurations that improve the
performance of the reactor 100 described with reference to FIG.
1.
Frustoconical Reactor Core Configuration
[0028] In typical fuel salts, higher temperature molten salt is
less dense than lower temperature salt. For example, in one fuel
salt (71 mol % UCl.sub.4-17 mol % UCl.sub.3-12 mol % NaCl) for a
300.degree. C. temperature rise (e.g., 627.degree. C. to
927.degree. C.), the fuel salt density was calculated to fall by
18%, from 3660 to 3010 kg/m.sup.3. In an embodiment, it is
desirable that the reactor core and primary heat exchanger be
configured such that fuel circulation through the fuel loop can be
driven by the density differential created by the temperature
difference between the higher temperature salt in the core and the
lower temperature salt elsewhere in the fuel loop 116. This
circulation may be referred to as natural circulation as the
circulation flow occurs naturally as a result of the density
differences in the fuel salt during steady state operation.
[0029] FIGS. 2A-2C illustrate an embodiment of a reactor that uses
only natural circulation to circulate fuel salt around the fuel
loop. This configuration can obviate the need for fuel salt pumps
and no pumps are shown. This reduces the complexity of the reactor
200, however, relying solely on natural circulation may limit the
amount of heat that can be removed and, thus, limit the total power
output of the reactor 200.
[0030] FIG. 2A illustrates a reactor 200 that includes a roughly
cylindrical reactor core 204, which is a volume defined by, a upper
reflector 208A at the top, a lower reflector 208B at the bottom,
and a lateral or inner reflector 208C that rings the circumference
of the core. As with FIG. 1, flow paths are provided at the top and
the bottom of the reactor core 204 to allow the fuel salt to flow
around the lateral reflector 208C. In this natural circulation
embodiment, heated fuel salt flows over the top the lateral
reflector 208C to the heat exchanger(s) 210 during steady state
fission. The fuel salt then circulates downward through the heat
exchanger(s) 210 and cooled fuel salt returns to the reactor core
204 via one or more flow paths between the bottom reflector 208B
and the lateral reflector 208C. In the embodiment shown, the
lateral reflector 208B is provided with a flow guide shaped as a
bulge below the heat exchanger 210 that constricts the cooled fuel
salt flow path back into the reactor core 204. Any type of flow
guide shape may be used.
[0031] FIG. 2B is a cross-sectional view of half of the reactor of
FIG. 2A showing the flow paths for the fuel salt. In the embodiment
shown, for modeling purposes the reactor core 204 is 1 meter (m) in
radius with a height of 3 m. Solid upper and lower bottom
reflectors 208A, 208B define the upper and lower extents of the
fuel salt. The spaces between the reflectors create flow paths,
which may alternately be referred to as channels or ducts, allowing
the circulation of fuel salt from the reactor core over the inner
reflector, through the primary heat exchanger, under the inner
reflector, and back into the bottom of the reactor core. One or
more flow directing baffles or guide vanes may be provided in the
fuel salt ducts of the fuel loop in order to obtain a more uniform
flow and equally distribute the flow of fuel salt through the fuel
loop and to reduce stagnant zones in the fuel loop.
[0032] Fuel salt heated in the core will buoyantly rise and flow
around the inner reflector 208C, through the heat exchanger 210,
then through the return channel defined by the bulging shape of the
inner reflector 208C and the lower reflector 208B. In an
embodiment, the reflectors may be lead filled vessels and the guide
structures (e.g., vanes 212) are solids with thermal properties of
stainless steel. The contouring and guide structures illustrated
are provided to promote good flow at the inlet of the heat
exchanger and reduce the occurrence and impact of recirculation
cells within the fuel loop.
[0033] FIG. 2C illustrates temperature and flow modelling results
for the embodiment shown in FIG. 2B under a set of representative
operating conditions for a representative fuel salt (71 mol %
UCl.sub.4-17 mol % UCl.sub.3-12 mol % NaCl). From the modeling, it
was found that the highest temperature was approximately
1150.degree. C. at the top of the center of the core 204 and the
lowest temperature was about 720.degree. C. at the outlet of the
heat exchanger 210. The temperature results indicate that, under
the conditions of the model, a natural circulation cell is created
in which the dense, cool fuel salt flows into the bottom of the
reactor core 204 thereby displacing the lighter, hot fuel salt into
the heat exchanger 210. The ongoing fission in the center of the
core 204 reheats the cooled fuel salt and drives the circulation
cell until the fission is interrupted, for example by the
introduction of a moderator or degradation of the fuel salt.
[0034] In an alternative embodiment a reactor may use both pumps
and natural circulation to move the fuel salt through the fuel loop
during normal power-generating operation. Natural circulation is
still beneficial, in such an embodiment, both in reducing the size
of the pumps needed to achieve a target flow rate and in the event
of a loss of power to the pump or pumps because the circulation,
and thus the cooling, will continue even without the active pumping
fuel salt through the fuel loop.
[0035] One method of increasing the strength of natural circulation
is through selectively locating the high temperature reactor core
204 below the primary heat exchanger 210. This enhances the effect
of the density differential on the circulation by locating the
densest salt, e.g., the cooled salt output by the primary heat
exchanger, at a location in the fuel loop 116 physically above the
highest temperature (thus least dense) salt, which can be found at
the "thermal center" of the reactor core.
[0036] For the purposes of this disclosure, the "thermal center"
refers to that location within the reactor core, based on the shape
and size of the core, where the most heat is generated by the
ongoing nuclear fission reactions in the reactor core, in the
absence of flow through the reactor. This point is identified in
FIG. 2B, located at the center of the cylindrical reactor core,
both vertically and horizontally. In a subcritical homogenous fuel
salt, the location of the thermal center due to decay heat can be
approximated by using the center of mass of the fuel salt volume
defined by the reactor core 204. This is just an approximation,
however, as the configuration and shape of the reflectors 208 and
other components will have some impact on the fission reaction
within the reactor core 204, and thus the location of the thermal
center.
[0037] In its most simple embodiment (not shown), a reactor
designed to use natural circulation can locate the primary heat
exchanger completely above the reactor core. However, this
vertically stacked design is complicated by the generation of gases
in the fuel salt during nuclear fission as well as potentially
requiring a larger containment vessel. The evolution of gases into
the heat exchanger increases the chance of vapor lock of the
exchanger and generally increases the complexity and reduces the
efficiency of the heat exchanger. For that reason, reactors with
heat exchangers at or below the typical working surface level of
the salt in the reactor core have certain benefits.
[0038] FIG. 3 illustrates an embodiment of an improved
configuration for a naturally circulating fission reactor core in
which the reactor core is larger at the bottom than at the top. In
the embodiment shown, the reactor core 304 has a roughly
frustoconical shape. Frustoconical refers to the shape of a cone
with the tip truncated by a plane parallel to the cone's base. FIG.
3 is a cross sectional view of half of the reactor core 300 similar
to that of FIGS. 2A-2C. The reactor core 304 is surrounded by an
upper reflector 308A, a lower reflector 308B and an inner reflector
308C that separates the reactor core from the primary heat
exchanger 310. As with the reactor in FIG. 2B, there is no
headspace and the entire reactor, i.e., reactor core 304, channels,
and primary heat exchanger 310 is filled with fuel salt. The spaces
between the reflectors 308A, 308B, 308C create channels allowing
the circulation of fuel salt from the reactor core 304 over the
inner reflector 308C, through the primary heat exchanger 310, under
the inner reflector 308C, and back into the bottom of the reactor
core 304. The frustoconical shape has the effect of moving the
center of mass and, thus, the thermal center 324 of the fuel salt
lower in the reactor core 304 and requires that the thermal center
be below midpoint between the top and the bottom of the reactor
core. Given a fixed location of the primary heat exchangers
relative to the reactor core, this change to a shape in which the
bottom of the reactor core is larger than the top, as occurs in a
frustum of a cone or pyramid, will improve the natural circulation
of the fuel salt in the fuel loop.
[0039] FIG. 4 illustrates another embodiment of a frustoconical
reactor core design. FIG. 4 is a cross sectional view of half of
the reactor core 400 similar to that of FIGS. 2A-2C and 3. The
reactor core 404 is surrounded by an upper reflector 408A, a lower
reflector 408B and an inner reflector 408C that separate the
reactor core from a vertically-oriented primary heat exchanger 410.
The spaces between the reflectors 408A, 408B, 408C create channels
allowing the circulation of fuel salt from the reactor core 404
over the inner reflector 408C, through the primary heat exchanger
410, under the inner reflector 408C, and back into the bottom of
the reactor core 404. Again, the frustoconical shape has the effect
of moving the center of mass and the thermal center 424 of the fuel
salt lower in the reactor core.
[0040] FIGS. 2A-2C, 3 and 4 are drawn roughly to the same scale and
a comparison of the three illustrates the difference in approximate
locations of their respective thermal centers. In FIG. 2B, the
thermal center is approximately at the center of the reactor core
which is almost level to the bottom of the primary heat exchanger.
In FIGS. 3 and 4, the thermal centers are located significantly
lower in the reactor core and clearly below the bottom of the
primary heat exchanger. By bottom of the heat exchanger, it is
meant the location where the coldest molten salt will be in the
system, which is the outlet of the heat exchanger. For example, in
a shell-and-tube heat exchanger, the bottom of the heat exchanger
will be at the lower tube sheet.
[0041] By using a reactor core that is larger at the bottom than at
the top as shown in FIGS. 3 and 4, for any given heat exchanger
configuration in which the top of the heat exchanger is level with
or below the fuel salt level in the reactor core, the location of
the thermal center relative to the location of the coldest fuel
salt in the circulation loop can be altered. This further allows
the amount of natural circulation to be controlled. In an
embodiment, one performance factor that determines the strength of
the natural circulation in a reactor is the ratio of the vertical
distance, A, between the top and bottom of the reactor core, that
is the depth of salt in the reactor core, (identified as distance A
in FIGS. 3 and 4) and the distance below the bottom of the heat
exchanger of the thermal center of the reactor core (identified as
distance B in FIGS. 3 and 4). In an embodiment, the ratio of B/A is
positive, that is the thermal center is below the bottom of the
heat exchanger. The larger the ratio of B/A is, the stronger the
natural circulation cell will be. In an embodiment, the ratio of
B/A is between 0.01 and 0.45. In yet another embodiment, the ratio
is between 0.1 and 0.4.
[0042] Reactor cores shaped as the frustum of a cone are but one
example of a reactor core shape that is larger at the bottom than
the top and that, therefore, enhances the natural circulation
through a primary heat exchanger. Other shapes are possible,
especially since the shape of the reactor core is essentially
defined by the upper, lower and internal reflectors. For example,
the frustum need not be exactly conical, but could be a frustum of
a pyramid having any number of planar or curved sides, e.g., a
3-sided pyramid, a 4-sided (or square) pyramid, a 5-sided (or
pentagonal) pyramid, a 6-sided (or hexagonal) pyramid, and so on up
to any number sides of a pyramid, each having a truncated tip.
[0043] FIG. 5, for example, illustrates a frustum of a decagonal
pyramid (10-sided pyramid), which would be a suitable shape for a
naturally circulating reactor core. In addition, the shape need not
be axially symmetrical. That is, a reactor core could be shaped as
a trapezoidal prism having a base, a top, one set of parallel
vertical sides and an opposing set of sloping planar sides. In yet
another alternative some of the prism's sides could be curved
instead of planar. The reactor core also could be shaped as a
hyperboloid, as with the commonly observed cooling towers at some
nuclear facilities, or irregularly shaped. Any such frustum shape
is suitable as long as the area of the base of the reactor core is
larger than the area of the top or the majority of the mass of the
fuel salt is below the midpoint between the top and bottom of the
reactor core so that the thermal center is lower than the midpoint
between the level of fuel salt in the reactor core and the bottom
of the reactor core. In combination with a heat exchanger having an
inlet at or below the level of fuel salt in the reactor core and an
outlet above the thermal center, the frustum-shaped reactor core
significantly improves the natural circulation of the fuel salt
during power-generating operation over a cylinder-shaped core of
the same height.
Integrated Active Vessel Cooling
[0044] FIGS. 6A-6C illustrate an embodiment of a reactor design
that integrates active cooling of the containment vessel into the
primary coolant loop. FIG. 6A illustrates a perspective view of an
eight-exchanger configuration of a molten salt reactor 600
partially cutaway to show different internal components. FIG. 6B is
a cross-sectional view through the center of the reactor and two
opposing heat exchangers. FIG. 6C is a cross-sectional view in
perspective showing more detail about the heat exchanger design and
the routing of the primary coolant. In the FIGS. 6B and 6C,
brackets are provided to show the sections of the containment
vessel 618 that are subjected to active cooling due to coolant or
fuel salt flow.
[0045] In the embodiment shown, the reactor core 604 and heat
exchangers 610 are within a containment vessel 618. The primary
containment vessel 618 is defined by a liner or set of liners that
create an open-topped vessel. The cooled primary coolant enters and
exits the vessel 618 from the top, which allows the containment
vessel to be unitary and have no penetrations. The primary coolant
loop is integrated into the reactor 600 so that the entering
primary coolant first cools at least a portion of the containment
vessel 618. After being routed next to an interior surface of the
containment vessel 618 for some distance in a primary coolant inlet
channel 630, in the embodiment shown the coolant is then routed
into the bottom of the primary heat exchanger 610. The coolant
exits the top of the primary heat exchanger 610 and is then routed
out of the containment vessel 618 and to a power generation system
(not shown).
[0046] In the embodiment shown fuel salt is driven through the fuel
loop eight separate impellers 612A located above the heat
exchangers 610. Each impeller 612A is connected by a rotating shaft
612B to a motor (not shown) located above the reactor 600. The flow
of the salt through the fuel loop is shown by dashed line 606 while
flow of the primary coolant is shown by dotted line 614.
[0047] Another aspect of the illustrated design is that the cooled
fuel salt exiting the heat exchangers 610 is routed along a portion
of the containment vessel prior to entering the reactor core 604.
This integrates additional active cooling into the containment
vessel. As the embodiment illustrates, the containment vessel is
not immediately adjacent to the reactor core at any point. In fact,
the containment vessel 618 of FIGS. 6A-6C is immediately adjacent
to only three components: the inlet channel 630 for cooled primary
coolant, the cooled fuel salt channel 632 that returns cooled salt
to the reactor core 604, and the lower reflector 608B. Note also
that the lower reflector 608B itself is cooled by the flow of
cooled fuel salt entering the reactor core 604, which then
indirectly cools the portion of the containment vessel 618 adjacent
to the lower reflector. Thus, the containment vessel 618 is only
adjacent to components that have been actively cooled by contact
with either the cooled primary coolant or the cooled fuel salt.
[0048] In operation, the primary coolant loop not only serves to
remove heat from the molten fuel salt, but also directly removes
heat from, and maintains the temperature of, the containment
vessel. Note that the system as illustrated allows for independent
control of both the fuel temperature and containment vessel
temperature through the independent control of the flow of fuel
salt and of the primary coolant. By modulating the two flows, the
operator may be able to selectively maintain both the core
temperature and the containment vessel temperature at independent
levels. In addition, by routing the flows and providing insulation
at various locations, the heat transfer characteristics between
different components may be tailored to provide more or less
cooling as needed.
[0049] FIG. 7 is a flow diagram of an embodiment of a method for
active vessel cooling. In the embodiment shown, integrated active
cooling may be considered as a method 700 for actively cooling a
containment vessel in a molten fuel salt nuclear reactor by
removing heat directly from both the molten salt and at least a
portion of the containment vessel via a primary coolant loop. In a
first direct containment vessel cooling operation 702, at least a
first portion of the containment vessel is cooled by the primary
coolant, before the coolant enters the fuel salt heat exchanger
proper. This is achieved by routing cooled primary coolant adjacent
to an inside surface of at least a portion of the containment
vessel prior to routing it into a primary heat exchanger. This
serves to actively cool that portion of the containment vessel. In
an embodiment, the coolant inlet channel and its thermal contact to
the containment vessel in this portion may be designed to enhance
the heat transfer between the coolant and the vessel.
[0050] The first direct containment vessel cooling operation 702
may also include cooling the reactor head by routing the primary
coolant through the reactor head. In an embodiment, this routing
may be used to specifically cool the upper reflector of the
reactor. This may be done using the same coolant that then flows to
the heat exchanger, a side stream of coolant that is then combined
with the main coolant stream, or using a completely separate
coolant stream.
[0051] In the embodiment shown, in a second direct containment
vessel cooling operation 704 at least a second portion of the
containment vessel is cooled by the cooled fuel salt exiting the
primary heat exchanger before the cooled fuel salt enters the
reactor core. This may be achieved by routing the cooled fuel salt
adjacent to an interior surface of the second portion of the
containment vessel as shown in FIGS. 6A-6C. Similar to the coolant
inlet channel, the cooled fuel salt channel and its thermal contact
to the containment vessel in this portion may be designed to
enhance the heat transfer between the cooled fuel salt and the
vessel.
[0052] A third indirect cooling operation 706 may be performed, as
well. In the third operation the cooled fuel salt may be routed
adjacent to a surface of a neutron reflector that is in contact
with some third portion of the containment vessel, thereby cooling
the neutron reflector and, indirectly, the third portion of the
containment vessel in contact with the neutron reflector. In this
operation 706, depending on the embodiment, the reflector may be a
lower reflector such as reflector 608B as shown in FIGS. 6A-6C, or
a lateral reflector that is adjacent to a portion of the
containment vessel.
Shell-Side Fuel Configuration of Primary Heat Exchanger
[0053] Where described in any detail above, primary heat exchangers
have been discussed in terms of shell and tube heat exchangers with
the fuel salt flowing through the tubes and primary coolant flowing
through the shell and around the tubes. As mentioned, this may be
referred to as a "tube-side fuel" or "shell-side coolant"
configuration, alternatively. However, an improvement in the
overall operation of the reactor may be obtained by moving to a
shell-side fuel configuration.
[0054] It has been determined that in an environment where metal
components are exposed to high doses of radiation over long periods
of time, it is more difficult to predict the degradation of welded
components than of the unwelded material. Welds are weak and
potentially subject to radiation damage and degradation over time
at high doses. Thus, to reduce risk and increase the level of
predictability inherent in a particular design, it is helpful to
move welded components as far away as possible from the high
neutron flux regions or eliminate welded components from the design
altogether.
[0055] One welded component that is difficult to eliminate are tube
sheets in shell and tube heat exchangers. As the welds in the tube
sheets prevent the mixing of the fuel salt with the primary
coolant, the reduction of degradation of the welds over time is a
design factor.
[0056] An improvement in the reactor design is to switch the heat
exchanger design to a shell-side fuel design and move the opposing
tube sheets as far from the center of the reactor core as possible
while remaining within the containment vessel. This reduces the
relative dose received by the tube sheets in comparison to the
designs in FIGS. 2A-2C, 3, 4, and 6A-6C.
[0057] FIG. 8 illustrates an embodiment of a reactor with a
shell-side fuel heat exchanger configuration. In the embodiment,
half of the reactor 800 is illustrated as in FIGS. 4A-6. The
reactor core 804 is surrounded by an upper reflector 808A, a lower
reflector 808B and an inner reflector 808C that separates the
reactor core from the primary heat exchanger 810. The spaces
between the reflectors 808A, 808B, 808C create channels allowing
the circulation of fuel salt (illustrated by a dashed line 806)
from the reactor core 804 over the inner reflector 808C, through
the shell side of the primary heat exchanger 810, under the inner
reflector 808C, and back into the bottom of the reactor core 804.
Baffles 812 are provided in the shell to force the fuel salt to
follow a circuitous path around the tubes of the heat
exchanger.
[0058] Coolant flows through the tube-side of the heat exchanger
810, but before entering the bottom of the heat exchanger first
flows down the length of a coolant inlet channel 830 adjacent to
the side wall and a portion of the bottom of the containment vessel
818. Thus, the reactor 800 shown uses an embodiment of the active
cooling method 700 described above with reference to FIG. 7 in
which a portion of the reactor vessel 818 is directly cooled by the
cool primary coolant and the lower reflector 808B is directly
cooled by the cool fuel salt returning to the reactor core 804.
[0059] The primary coolant enters the tubes of the heat exchanger
810 by flowing through the lower tube sheet 831, which is
illustrated as being level with the bottom of the reactor core. The
lower tube sheet 831 may be at or below the level of the lower
reflector 808B depending on the embodiment. The coolant exits the
tubes of the heat exchanger at the upper tube sheet 832, which is
located in FIG. 8 some distance above the reactor core 804 and
containment vessel 818. The flow of the coolant is also illustrated
by a dashed line 814.
[0060] FIG. 8 illustrates a region 834 within the shell of the heat
exchanger that is above the level of salt in the reactor core 804.
This region may either be solid, except for the penetrating tubes,
or may be a headspace filled with inert gas.
[0061] One or more pumps (not shown) may be provided to assist in
the fuel salt circulation, the primary coolant circulation or both.
For example, an impeller may be provided in one or both of the
heated fuel salt inlet channel at the top of the reactor core 804
or (as discussed in greater detail below) the cooled fuel outlet
channels at the bottom of the reactor core 804. Likewise, an
impeller may be provided in the coolant inlet channel 830 to assist
in control of the primary coolant flow.
[0062] FIG. 9 illustrates an alternative embodiment of the reactor
of FIG. 8. In the embodiment shown, the reference numbers
correspond to those of FIG. 8 for the same elements. FIG. 9
illustrates an alternative configuration for the tube sheets 931,
932 that reduces, even further, the exposure of the welded tube
sheets to neutron flux from the fuel salt. In the embodiment shown,
at the tubes of the tube set at least partially penetrate the upper
and lower reflectors 908A and 908B at either end of the heat
exchanger 910. In yet another embodiment, the tube sheet is
eliminated in favor of the reflectors 908A, 908B which then
performs the tube sheet's role of preventing fuel salt from shell
side leaking into the coolant on the tube side.
[0063] Note also that FIG. 9 illustrates a second lateral reflector
908D between the heat exchanger 910 and the coolant inlet channel
930. This can provide additional reflection or can simply be a
moderator or other protection to reduce neutron flux outside of the
core 904.
U-Tube Configurations of Primary Heat Exchanger
[0064] Another improvement in the reactor design is to switch the
heat exchanger design to a shell-side fuel design and utilize a
U-tube heat exchanger. In this design, the single tube sheet of the
U-tube exchanger is located above the reactor core and outside of
the containment vessel, and thus in a relatively reduced dose
environment in comparison to the designs in FIGS. 2A-2C, 3, 4, and
6A-6C.
[0065] FIG. 10 illustrates an embodiment of a reactor with a
shell-side fuel, U-tube heat exchanger configuration in which the
single tube sheet is located above the reactor core. In the
embodiment, half of the reactor 1000 is illustrated as in FIGS. 8
and 9. The reactor core 1004 is surrounded by an upper reflector
1008A, a lower reflector 1008B, and an inner reflector 1008C that
define the reactor core and separate it from the primary heat
exchanger 1010. The spaces between the reflectors 1008A, 1008B,
1008C create channels allowing the circulation of fuel salt
(illustrated by a dashed line 1006) from the reactor core 1004 over
the inner reflector 1008C, through the shell side of the primary
heat exchanger 1010, under the inner reflector 1008C, and back into
the bottom of the reactor core 1004. Baffles 1012 are provided in
the shell to force the fuel salt to follow a circuitous path around
the tubes of the heat exchanger. Coolant flows through the U-shaped
tubes of the heat exchanger 1010, so that the coolant both enters
the tubes and exits the tubes from the top, through the single tube
sheet 1032. The upper tube sheet 1032 is located in FIG. 10 some
distance above the reactor core 1004 and containment vessel 1018,
and thus its exposure to radiation is reduced relative to the other
designs as discussed above. The flow of the coolant is also
illustrated by a dashed line 1014.
[0066] FIG. 10 illustrates a region 1034 within the shell of the
heat exchanger that is above the level of salt in the reactor core
1004. Again, this region may either be solid, except for the
penetrating tubes, or may be a headspace filled with inert gas. If
solid, it may be filled with a reflector material through which the
tube set penetrates.
[0067] Again, one or more pumps, or at least their impellers, (not
shown) may be provided to assist in fuel salt and/or coolant
circulation. For example, an impeller may be provided in one or
both of the heated fuel salt inlet channel at the top of the
reactor core 1004 or the cooled fuel outlet channel at the bottom
of the reactor core 1004.
[0068] In yet another embodiment, welded components such as tube
sheets 1032 may be shielded from neutrons with a sheet of
neutron-absorbing material. The neutron-absorbing material may be
placed adjacent to the tube sheet on the side facing the reactor
core 1004. Such a tube sheet, neutron-absorbing material
combination may be used in any embodiment discussed above. The
neutron-absorbing material may be a coating, an additional layer,
or an independent structural component adjacent to or spaced apart
from the tube sheet.
[0069] Yet another embodiment of a U-tube heat exchanger design
rotates the heat exchanger 90 degrees so that the coolant enters
and exits the heat exchanger laterally with reference to the
containment vessel.
[0070] FIG. 11 illustrates an embodiment of a reactor with a
shell-side fuel, U-tube heat exchanger configuration in which the
single tube sheet is within the reactor but laterally mounted in a
location away from the reactor core. In the embodiment, half of the
reactor 1100 is illustrated as in FIGS. 4A-6. The reactor core 1104
is surrounded by an upper reflector 1108A, a lower reflector 1108B
and an inner reflector 1108C that separates the reactor core from
the primary heat exchanger 1110. The spaces between the reflectors
1108A, 1108B, 1108C create channels allowing the circulation of
fuel salt (illustrated by a dashed line 1106) from the reactor core
1104 over the inner reflector 1108C, through the shell side of the
primary heat exchanger 1110, under the inner reflector 1108C, and
back into the bottom of the reactor core 1104. Baffles 1112 are
provided in the shell to force the fuel salt to follow a circuitous
path around the tubes of the heat exchanger. Coolant flows through
the U-shaped tubes of the heat exchanger 1110, so that the coolant
both enters the tubes and exits the tubes from the top of the
reactor 1000. In the embodiment shown, coolant enters the reactor
in a channel next to the containment vessel 1118 and flows downward
and then laterally through the lower portion of the tube sheet 1132
and into the heat exchanger 1110. The coolant then exits from the
upper portion of the tube sheet 1132 and out of the top of the
containment vessel 1118. The flow of the coolant is illustrated by
a dashed line 1114. Because the tube sheet 1132 is farther from the
reactor core, relative to the designs discussed above, exposure to
radiation is reduced. Note that this design is also another
embodiment of an actively cooled containment vessel as described
above.
[0071] In yet another embodiment, the U-tubes may be
horizontally-oriented (not shown) as opposed to the
vertically-oriented U-tubes illustrated in FIG. 11. This
orientation may provide benefits in terms of heat transfer while
still locating the tube sheets away from the high flux
environment.
[0072] In an embodiment, the tube sheet 1132 is further protected
from neutron damage by providing a second inner neutron reflector
(not shown) between the tube sheet and the fuel salt. In this
embodiment, the tubes penetrate the second inner neutron reflector
before coming into contact with the fuel salt. This serves to
further distance the tube sheet from neutrons emitted by the fuel
salt. In an alternative embodiment, the tube sheet 1132 is
separated from the fuel salt by a neutron moderator made of some
amount of material having a relatively large neutron absorption
cross-section such as steel alloys or other materials that include
Ag, In, Cd, Bo, Co, Hf, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. For
example, high boron steel, Ag-In-Cd alloys, boron carbide, Titanium
diboride, Hafnium diboride, gadolinium nitrate, or any other
material used as a control rod or neutron absorber, now known or
later developed may be used. In an embodiment, the reflector or
absorber may simply be a coating of the appropriate material on the
salt contacting side of the tube sheet 1132.
Radial Loop Reactor
[0073] FIGS. 12A and 12B illustrate an alternative reactor design
referred to as a radial loop reactor. FIG. 12A is a plan view of
the reactor 1200 and FIG. 12B is a cross section along the line A-A
indicated on FIG. 12A. In the embodiment of the radial loop reactor
1200 illustrated, a reactor core 1204 is defined by an upper
reflector 1208A, a lower reflector 1208B and a lateral or inner
reflector 1208C in the shape of a tube. The reflectors 1208 are
within a core containment vessel 1218A that is penetrated by eight
heated fuel salt outlet pipes 1209 located at the top of the
containment vessel 1218A and eight cooled fuel salt return pipes
1211 that penetrate the containment vessel at a level of the bottom
of the reactor core 1204. Each set of outlet pipe 1209, heat
exchanger 1210 and return pipe 1211 may be referred to as a heat
exchanger leg.
[0074] Eight primary heat exchangers 1210 are shown in a diagonal
configuration around the core containment vessel 1218A, although
more or fewer primary heat exchangers 1210 may be used depending on
the embodiment. It should also be noted that the heat exchanger
legs may be vertical or may be more or less diagonal than
shown.
[0075] In the embodiment shown, heated fuel salt circulates from
the reactor core 1204 through the outlet pipes 1209 and through the
heat exchangers 1210. The heat exchangers cool the fuel salt which
then returns to the bottom of the reactor core 1204 via the return
pipes 1211.
[0076] In the embodiment shown the reactor core 2204 is cylindrical
in shape but this shape could be modified into a substantially
frustoconically-shaped reactor core or substantially frustum-shaped
reactor core as described above to improve natural circulation of
the fuel salt during operation. The word "substantially" is used
here to convey that the reactor core shape may not be a perfect
frustum having perfectly flat surfaces for the bottom and top and
perfectly flat or conical sides. For example, FIGS. 3 and 4
illustrate substantially frustum-shaped reactor cores even though
flow directing bulges or other shapes are provided in the center of
the top and bottom and on the sides of the reactor core.
[0077] In an embodiment (not shown), one or more pumps (or at least
the impeller components of such pumps) are provided in one or both
of the return and outlet pipes 1211, 1209. In yet another
embodiment (not shown), shutoff valves may also be provided in one
or both of the return and outlet pipes 1211, 1209, as well as drain
taps to allow any one of the eight heat exchanger legs to be
independently shut off from the reactor core 1204 and drained of
fuel salt for ease of maintenance. In an embodiment (not shown) one
or more drain tanks may be provided below the level of the heat
exchangers, the core containment vessel 1218A, or the heat
exchanger legs for receiving drained fuel salt. In an alternative
embodiment, each heat exchanger leg may include a pump in the inlet
pipe that evacuates the heat exchanger of fuel salt when it is
drained; returning the fuel salt to the reactor core 1204 instead
of to a drain tank. One benefit of this layout is that the loop
legs and the angles of the heat exchangers can be adjusted to
provide additional flexibility for fuel pump location (pumps not
shown) to be located at the bottom of the heat exchanger.
Furthermore, pump shafts through/beside the heat exchangers or
vessel penetrations from below are not required in this
embodiment.
[0078] As shown in FIG. 12D, a secondary containment vessel 1218B
may be provided around the entire reactor core assembly, that is,
around all the components in the fuel loop of the reactor 1200. In
an embodiment, the secondary containment vessel has a volume
sufficient to hold at least all of the fuel salt contained in the
reactor. The size may be further increased to provide a safety
margin and sized sufficiently large to hold both a volume of
coolant and the entire volume of fuel salt in the reactor. The
containment vessel may completely surround the radial loop reactor
1200 as shown, may partially surround the reactor, or may simply be
a large vessel below the reactor 1200 of sufficient size. In the
embodiment, primary coolant is circulated through the primary heat
exchangers 1210 from above the secondary containment vessel
1218B.
[0079] Radial loop reactors 1200 allow for the size of the primary
heat exchangers 1210 to not be limited by the height of the reactor
core 1204. Furthermore, as the heat exchangers are outside of the
core containment vessel 1218A, they may be more easily serviced and
controlled, as well as being farther away from the reactor core and
therefore receiving a reduced dose of radiation.
[0080] It will be clear that the systems and methods described
herein are well adapted to attain the ends and advantages mentioned
as well as those inherent therein. Those skilled in the art will
recognize that the methods and systems within this specification
may be implemented in many manners and as such is not to be limited
by the foregoing exemplified embodiments and examples. In this
regard, any number of the features of the different embodiments
described herein may be combined into one single embodiment and
alternate embodiments having fewer than or more than all of the
features herein described are possible.
[0081] While various embodiments have been described for purposes
of this disclosure, various changes and modifications may be made
which are well within the scope contemplated by the present
disclosure.
[0082] Numerous other changes may be made which will readily
suggest themselves to those skilled in the art and which are
encompassed in the spirit of the disclosure.
* * * * *