U.S. patent application number 13/204000 was filed with the patent office on 2011-12-29 for reactor containment vessel cooling system, reactor containment vessel, and reactor containment vessel cooling method.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Ryoichi Hamazaki, Akira Murase, Mikihide Nakamaru, Mika Tahara.
Application Number | 20110314858 13/204000 |
Document ID | / |
Family ID | 42709669 |
Filed Date | 2011-12-29 |
![](/patent/app/20110314858/US20110314858A1-20111229-D00000.png)
![](/patent/app/20110314858/US20110314858A1-20111229-D00001.png)
![](/patent/app/20110314858/US20110314858A1-20111229-D00002.png)
![](/patent/app/20110314858/US20110314858A1-20111229-D00003.png)
![](/patent/app/20110314858/US20110314858A1-20111229-D00004.png)
![](/patent/app/20110314858/US20110314858A1-20111229-D00005.png)
United States Patent
Application |
20110314858 |
Kind Code |
A1 |
Tahara; Mika ; et
al. |
December 29, 2011 |
REACTOR CONTAINMENT VESSEL COOLING SYSTEM, REACTOR CONTAINMENT
VESSEL, AND REACTOR CONTAINMENT VESSEL COOLING METHOD
Abstract
A reactor containment vessel cooling technology for preventing
the cooling capability and structural integrity of a reactor
containment vessel cooling system from decreasing by lowering the
temperature of water vapor and gases acquired by the reactor
containment vessel cooling system is provided. Based on the
technology, the present invention provides a reactor containment
vessel cooling system that acquires water vapor in a reactor
containment vessel by using water vapor pressure in the vessel as a
drive force, condenses the acquired water vapor into condensate,
and cools the reactor containment vessel with the condensate. The
reactor containment vessel cooling system includes a heat exchange
pool 21 that is arranged apart from a dry well 15 and a suppression
chamber 16 in the reactor containment vessel 10 and stores a medium
for cooling water vapor, a heat exchanger 22 that is immersed in
the heat exchange pool 21, acquires water vapor from the dry well
15 in the reactor containment vessel 10, and performs heat exchange
between the eater vapor and the cooling medium in the heat exchange
pool 21 to generate condensate, and a condensate drain pipe 25 that
extracts the condensate from the heat exchanger 22 and guides and
discharges the condensate toward a reactor pressure vessel 12.
Inventors: |
Tahara; Mika; (Yokohama-shi,
JP) ; Nakamaru; Mikihide; (Fujisawa-Shi, JP) ;
Murase; Akira; (Yokohama-Shi, JP) ; Hamazaki;
Ryoichi; (Yokohama-Shi, JP) |
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
42709669 |
Appl. No.: |
13/204000 |
Filed: |
March 1, 2010 |
PCT Filed: |
March 1, 2010 |
PCT NO: |
PCT/JP10/53243 |
371 Date: |
August 31, 2011 |
Current U.S.
Class: |
62/259.1 |
Current CPC
Class: |
G21C 15/18 20130101;
G21C 9/004 20130101; Y02E 30/30 20130101; Y02E 30/40 20130101 |
Class at
Publication: |
62/259.1 |
International
Class: |
F25D 31/00 20060101
F25D031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 2, 2009 |
JP |
2009-048348 |
Claims
1. A reactor containment vessel cooling system for cooling a
reactor containment vessel by acquiring the water vapor in the
reactor containment vessel and by using water vapor pressure in the
vessel as a drive force to thereby condense the acquired water
vapor into condensate and cool the reactor containment vessel with
the condensate, the cooling system comprising; a heat exchange pool
that is arranged apart from a dry well and a suppression chamber in
the reactor containment vessel and stores a medium for cooling
acquired water vapor; a heat exchanger that is immersed in the heat
exchange pool, acquires water vapor from the dry well in the
reactor containment vessel, and performs heat exchange between the
water vapor and the cooling medium in the heat exchange pool so as
to convert the water vapor into condensate; and a condensate drain
pipe that extracts the condensate from the heat exchanger and
guides and discharges the condensate toward a reactor pressure
vessel.
2. The reactor containment vessel cooling system according to claim
1, wherein the condensate drain pipe is configured to discharge the
condensate in a way that the condensate flows down along a side
surface of a thermally insulating member that surrounds the reactor
pressure vessel.
3. The reactor containment vessel cooling system according to claim
2, wherein the condensate drain pipe id configured to discharge the
condensate from a position above a reactor shielding wall provided
outside the thermally insulating member at a side surface of the
thermally insulating member.
4. The reactor containment vessel cooling system according to claim
3, wherein the condensate drain pipe includes a ring-shaped header
tube which circumferentially surrounds the thermally insulating
member and through which the condensate flows and a plurality of
condensate discharge ports provided at intervals along the header
tube in a circumferential direction thereof.
5. The reactor containment vessel cooling system according to claim
1, wherein the condensate drain pipe id configured to discharge the
condensate in a way that the condensate flows down along a side
surface of the reactor pressure vessel.
6. The reactor containment vessel cooling system according to claim
5, wherein the condensate drain pipe is configured to discharge the
condensate from a position above a reactor shielding wall at a side
surface of the reactor pressure vessel.
7. The reactor containment vessel cooling system according to claim
6, wherein the condensate drain pipe includes a ring-shaped header
tube which circumferentially surrounds the reactor pressure vessel
and through which the condensate flows and a plurality of discharge
ports which are provided at intervals along the header tube in a
circumferential direction thereof and through which the condensate
is discharged.
8. The reactor containment vessel cooling system according to claim
7, wherein each of the discharge ports is formed of a nozzle
penetrating a thermally insulating member that surrounds the
reactor pressure vessel from outside to inside.
9. The reactor containment vessel cooling system according to claim
7, wherein the header tube is embedded in the thermally insulating
member.
10. The reactor containment vessel cooling system according to
claim 1, wherein a part of the condensate drain pipe is replaced
with curved tube having a downwardly convex shape.
11. A reactor containment vessel comprising: a reactor pressure
vessel that accommodates a core; a reactor shielding wall provided
to surround an outer circumferential surface of the reactor
pressure vessel; a dry well that forms a space that accommodates
the reactor pressure vessel; a suppression chamber for controlling
an internal pressure in the reactor containment vessel; and a
reactor containment vessel cooling system that acquires water vapor
in the reactor containment vessel by using water vapor pressure in
the vessel as a drive force to thereby condense the acquired water
vapor into condensate and cool the reactor containment vessel with
the condensate, wherein the reactor containment vessel cooling
system includes: a heat exchange pool that is arranged apart from
the dry well and the suppression chamber in the reactor containment
vessel and stores a medium for cooling acquired water vapor; a heat
exchanger that is immersed in the heat exchange pool, acquires
water vapor from the dry well in the reactor containment vessel,
and performs heat exchange between the water vapor and the cooling
medium in the heat exchange pool so as to convert the water vapor
into condensate; and a condensate drain pipe that extracts the
condensate from the heat exchanger and guides and discharges the
condensate at the reactor pressure vessel.
12. A reactor containment vessel cooling method for cooling an
interior of the reactor containment vessel by acquiring water vapor
in a reactor containment vessel and by using water vapor pressure
in the vessel to thereby condense the acquired water vapor into
condensate and cool an internal space of the reactor containment
vessel with the condensate, the cooling method comprising: storing
a water vapor cooling medium in a position set apart from a dry
well and a suppression chamber in the reactor containment vessel;
and acquiring water vapor from the dry well in the reactor
containment vessel, performing heat exchange between the water
vapor and the cooling medium so as to convert the water vapor into
condensate, and guiding and discharging the condensate at a reactor
pressure vessel.
Description
TECHNICAL FIELD
[0001] The present invention relates to a reactor containment
vessel cooling technology for maintaining safety of the environment
around a reactor by removing decay heat generated when reactor
water is accidentally lost, and particularly, to a reactor
containment vessel cooling technology for producing emergency
cooling water by using water vapor pressure in a reactor
containment vessel as a drive force, and the present invention
includes a reactor containment vessel cooling system, a reactor
containment vessel, and a reactor containment vessel cooling
method.
BACKGROUND ART
[0002] A nuclear reactor includes an emergency core cooling system
and a decay heat removing system for maintaining safety of the
environment around the reactor by cooling the inside of a reactor
containment vessel with water to remove decay heat in case reactor
water is accidentally lost. In addition, in consideration of a case
where the emergency core cooling system or the decay heat removing
system is not activated, a full accident countermeasure guideline
has been provided by introducing cooling water from an external
water source to the reactor containment vessel to reliably cool the
reactor containment vessel.
[0003] In a cooling method using an external water source, water
vapor and gases are appropriately released into the atmosphere so
that the cooling water supplied into the reactor containment vessel
does not cause the water vapor pressure in the reactor containment
vessel to rise excessively. In the cooling method, fission products
and other radioactive nuclides contained in the water vapor and
gases to be released into the atmosphere are basically separated in
advance, but it is difficult to completely eliminate the
possibility of releasing part of the radioactive materials into the
atmosphere along with the water vapor and other gases. Therefore,
there is an opinion that such a cooling method is not acceptable by
the society.
[0004] In view of the background described above, there is a
reactor containment vessel cooling technology proposed for
acquiring water vapor in a reactor pressure vessel by using the
water vapor pressure in the reactor containment vessel as a drive
force, converting the acquired water vapor into condensate, and
cooling the react or containment vessel with the condensate (see
Patent Document 1).
[0005] In the reactor containment vessel cooling technology
described in Patent Document 1, the following cooling cycle is
repeated in a closed area in the reactor containment vessel:
acquisition of water vapor, condensation of water vapor, cooling
with condensate, and acquisition of water vapor originating from
condensate.
[0006] Requiring no external water source, the technology will be
accepted by the society unlike the method using external water
source.
[0007] Furthermore, since the reactor containment vessel cooling
technology described above requires no pump or other electric drive
sources to cool the inside of the reactor containment vessel, the
reactor containment vessel can be cooled even in a case where the
power supply responsible for the entire nuclear facility is
accidentally lost.
PRIOR ART DOCUMENT
Patent Document
[0008] Patent Document 1: Japanese Patent Laid-Open No.
2003-240888
Non-Patent Document
[0008] [0009] Non-Patent Document 1: ICONE-6426, M. Akinaga et al.,
"EVALUATION OF PASSIVE CONTAINMENT COOLING SYSTEM PERFORMANCE
DURING SEVERE ACCIDENTS," APPENDIX A, 1998.
DESCRIPTION OF THE INVENTION
Problems to be Solved by the Invention
[0010] When reactor water is accidentally lost, since a large
amount of fission products, fuel nuclides, and other radioactive
nuclides have been attached to a reactor pressure vessel, decay
heat generated by the radioactive nuclides continues to heat the
reactor pressure vessel. The reactor pressure vessel, which works
as a heat source, therefore increases the temperature of the
atmosphere in a reactor containment vessel.
[0011] When the temperature in the reactor containment vessel
increases, the temperature of water vapor and gases introduced into
a react or containment vessel cooling system increases, resulting
in decrease in capability of cooling the reactor containment vessel
and faster degradation of the structure of the reactor containment
vessel cooling system due to the heat.
[0012] The present invention has been made in view of the
circumstances of the prior art described above, and an object of
the present invention is to provide a reactor containment vessel
cooling system, a reactor containment vessel, and a reactor
containment vessel cooling method that prevent cooling capability
and structural integrity of the reactor containment vessel cooling
system from being decreased by lowering or raising the temperature
of water vapor and gases acquired by the reactor containment vessel
cooling system.
Means for Solving the Problems
[0013] To achieve the object described above, the present invention
provides a reactor containment vessel cooling system that cools the
reactor containment vessel by acquiring water vapor in a reactor
containment vessel and using water vapor pressure in the vessel as
a drive force to thereby condense the acquired water vapor into
condensate and cool the reactor containment vessel with the
condensate, the reactor containment vessel cooling system
comprising a heat exchange pool that is arranged apart from a dry
well and a suppression chamber in the reactor containment vessel
and stores a medium for cooling acquired water vapor, a heat
exchanger that is immersed in the heat exchange pool, acquires
water vapor from the dry well in the reactor containment vessel,
and perform heat exchange between the water vapor and the cooling
medium in the heat exchange pool so as to generate condensate, and
a condensate drain pipe that extracts the condensate from the heat
exchanger and guides and discharges the condensate toward a reactor
pressure vessel.
[0014] The reactor containment vessel cooling system having the
features described above may employ the following preferred
aspects.
[0015] The condensate drain pipe may discharge the condensate in
such a way that the condensate flows down along a side surface of a
thermally insulating member that surrounds the reactor pressure
vessel.
[0016] The condensate drain pipe may discharge the condensate from
a position above a reactor shielding wall provided outside the
thermally insulating member at a side surface of the thermally
insulating member.
[0017] The condensate drain pipe may include a ring-shaped header
tube which circumferentially surrounds the thermally insulating
member and through which the condensate flows and a plurality of
condensate discharge ports provided at intervals along the header
tube in a circumferential direction thereof.
[0018] The condensate drain pipe may discharge the condensate in
such a way that the condensate flows down along a side surface of
the reactor pressure vessel.
[0019] The condensate drain pipe may discharge the condensate from
a position above a reactor shielding wall at a side surface of the
reactor pressure vessel.
[0020] The condensate drain pipe may include a ring-shaped header
tube which circumferentially surrounds the reactor pressure vessel
and through which the condensate flows and a plurality of discharge
ports which are provided at intervals along the header tube in a
circumferential direction thereof and through which the condensate
is discharged.
[0021] Each of the discharge ports may be formed of a nozzle
penetrating a thermally insulating member that surrounds the
reactor pressure vessel from outside to inside.
[0022] The header tube may be embedded in the thermally insulating
member.
[0023] A part of the condensate drain pipe may be replaced with a
curved tube having a downwardly convex shape.
[0024] To achieve the object described above, the present invention
provides a reactor containment vessel including: a reactor pressure
vessel that accommodates a core; a reactor shielding wall provided
to surround an outer circumferential surface of the reactor
pressure vessel; a dry well that forms a space that accommodates
the reactor pressure vessel; a suppression chamber for controlling
internal pressure in the reactor containment vessel: and a reactor
containment vessel cooling system that acquires water vapor in the
reactor containment vessel by using water vapor pressure in the
vessel as a drive force, condenses the acquired water vapor into
condensate, and cools the reactor containment vessel with the
condensate. The reactor containment, vessel cooling system has the
structural features described above.
[0025] To achieve the object described above, the present invention
provides a reactor containment vessel cooling method for cooling
the reactor containment vessel by acquiring water vapor in a
reactor containment vessel, using water vapor pressure in the
vessel, condensing the acquired water vapor into condensate, and
cooling an internal space of the reactor containment vessel with
the condensate, the reactor containment vessel cooling method
including: storing a water vapor cooling medium in a position
arranged apart from a dry well and a suppression chamber in the
reactor containment vessel, and acquiring water vapor from the dry
well in the reactor containment vessel, performing heat exchange
between the water vapor and the cooling medium so as to convert the
water vapor into condensate, and guiding and discharging the
condensate toward a reactor pressure vessel.
Effect of the Invention
[0026] The present invention can prevent the cooling capability and
structural integrity of a reactor containment vessel cooling system
from decreasing by lowering the temperature of water vapor and
gases acquired by the reactor containment vessel cooling
system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a front sectional view showing a first embodiment
of a reactor containment vessel cooling system according to the
present invention.
[0028] FIG. 2 is an enlarged sectional view of an essential portion
of the react or containment vessel cooling system shown in FIG. 1,
including FIG. 2A showing a layout of a condensate drain pipe and
FIG. 2B being an enlarged view of an encircled portion P shown in
FIG. 2A.
[0029] FIG. 3 is a perspective view of the condensate drain pipe
shown in FIG. 2A.
[0030] FIG. 4 is a graph explaining function of the reactor
containment vessel cooling system shown in FIG. 1.
[0031] FIG. 5 is a sectional view showing a second embodiment of
the reactor containment vessel cooling system according to the
present invention.
[0032] FIG. 6 is an enlarged sectional view of an essential portion
showing a third embodiment of the reactor containment vessel
cooling system according to the present invention.
MODES FOR EMBODYING THE INVENTION
[0033] Embodiments of a reactor containment vessel cooling system,
a reactor containment vessel, and a reactor containment vessel
cooling method according to the present invention will be described
hereunder with reference to the accompanying drawings. In the
following description, it should be understood that the terms
"upper," "lower," "right," "left," and other like terms concerning
directions are used only based on the illustration on the
accompanying drawings or actual installation.
First Embodiment
[0034] FIG. 1 is a front sectional view showing a first embodiment
of a reactor containment vessel cooling system according to the
present invention.
[0035] A reactor containment vessel cooling system 20 according to
the first embodiment is provided inside or outside a reactor
containment vessel 10.
[0036] The reactor containment vessel 10 is provided so as to
surround reactor pressure vessel 12 that accommodates a core 11, a
react or shielding wall 13 and other reactor structures or
components. The reactor containment vessel 10 has a structure
capable of preventing fission products from being released into the
atmosphere even in a case where a primary steam tube 14 or any of
her component is broken and hence reactor water in the reactor
pressure vessel 12 is lost and a fuel is melt or damaged.
[0037] The reactor containment vessel 10 includes a dry well 15
(upper dry well 15a and lower dry well 15b) that forms a space for
accommodating the reactor pressure vessel 12 and a suppression
chamber (wet well) 16 that is responsible for controlling the
internal pressure in the reactor containment vessel 10. The dry
well 15 and the suppression chamber 16 communicate with each other
via vent tube 18. The suppression chamber 16 includes a suppression
pool 17 that stores emergency cooling water and surrounds the
reactor pressure vessel 12.
[0038] The reactor containment vessel 10 is provided with an
emergency core cooling system and a decay heat removing system
(both systems are omitted in FIG. 1), which are activated to remove
decay heat generated around the core 11 when the primary steam tube
14 is accidentally broken and hence reactor water is lost. When the
emergency core cooling system and a decay heat removing system are
activated, the dry well 15 is filled with water vapor originating
from the reactor water having leaked out of the reactor pressure
vessel 12 through the broken portion of the tube and water vapor
originating from the water acquired from the suppression pool 17 by
the emergency core cooling system. The water vapor with which the
dry well 15 is filled passes through the vent tube 18 and travels
into the suppression pool 17, where the water vapor is absorbed and
condensed. The increase in internal pressure in the reactor
containment vessel 10 is thus reduced.
[0039] At this instance, the reactor containment vessel cooling
system 20 condenses the water vapor, with which the reactor
pressure vessel 12 is filled, into condensate and cools the reactor
containment vessel 10 with the condensate in order to reinforce the
cooling capability of the emergency core cooling system and a decay
heat removing system. The reactor containment vessel cooling system
20 includes, as shown in FIG. 1, a heat exchange pool 21, a heat
exchanger 22, a water vapor sucking tube 23, a noncondensable gas
vent pipe 24, and a condensate drain pipe 25.
[0040] The heat exchange pool 21, which is so provided that it is
thermally and spatially set apart from the dry well 15 and the
suppression chamber 16 in the reactor containment vessel 10, stores
a medium for cooling water vapor with which an upper portion of the
upper dry well 15a in the reactor containment vessel 10 is filled.
The cooling medium is, for example, light water.
[0041] The heat exchanger 22, which includes a heat transfer tube
22a made of a material having excellent heat conductivity, is
immersed in the heat exchange pool 21. The heat exchanger 22 allows
water vapor introduced into the heat transfer tube 22a to exchange
heat with the cooling medium in the heat exchange pool 21 so that
the water vapor becomes condensate.
[0042] The water vapor sucking tube 23 has a sucking port
positioned in the upper dry well 15a, sucks the water vapor with
which the upper dry well 15a is filled, and delivers the water
vapor into the heat transfer tube 22a. The operation of sucking the
water vapor into the water vapor sucking tube 23 is driven by the
water vapor pressure in the reactor containment vessel 10.
[0043] The noncondensable gas vent pipe 24 extracts a
noncondensable gas delivered along with the water vapor into the
heat transfer tube 22a out of the heat transfer tube 22a to
maintain the heat exchanging capability between the water vapor in
the heat transfer tube 22a and the cooling medium in the heat
exchange pool 21.
[0044] The noncondensable gas vent pipe 24, for example, extends
from the exit port of the heat transfer tube 22a, which forms the
heat exchanger 22, toward the suppression chamber 16, and the
distal end of the noncondensable gas vent pipe 24 is immersed in
the suppression pool 17.
[0045] The condensate drain pipe 25 extracts the condensate from
the heat exchanger 22 and guides and discharges the condensate
toward the reactor pressure vessel 12. The operation of extracting
and guiding the condensate is driven by the water vapor pressure in
the reactor containment vessel 10 and the gravity.
[0046] FIG. 2 is an enlarged sectional view of an essential portion
of the reactor containment vessel cooling system 20 shown in FIG.
1. FIG. 2A is a cross-sectional view showing the layout of the
condensate drain pipe 25. FIG. 2B is an enlarged sectional view of
the portion "P" shown in FIG. 2A. FIG. 3 is a perspective view of
the condensate drain pipe 25 shown in FIG. 2A.
[0047] As shown in FIGS. 2A and 3, the distal end of the condensate
drain pipe 25 is formed of a ring-shaped header tube 26 which
circumferentially surrounds a thermally insulating member 19 that
circumferentially covers the reactor pressure vessel 12 and through
which the condensate extracted from the heat exchanger 22 flows
around the thermally insulating member 19. The thermally insulating
member 19, which is made of a metallic material, suppresses heat
dissipation from the reactor pressure vessel 12 during normal
operation of the reactor.
[0048] The header tube 26 has a plurality of discharge ports 27
provided at intervals along the circumferential direction of the
header tube 26. The angle and layout of the discharge ports 27 are
set so as to face the gap formed between the reactor shielding wall
13 and the thermally insulating member 19 and to discharge the
condensate flowing through the header tube 26 at the side surface
of the thermally insulating member 19, as shown in FIG. 2B. The
symbol D in FIG. 2B represents the direction in which the
condensate is discharged from the header tube 26.
[0049] The reactor containment vessel cooling system 20 of the
structure mentioned above will attain the following functions and
effects.
[0050] Supposing that a possible severe accident in which the
primary steam tube 14 (see FIG. 1) connected to the reactor
pressure vessel 12 is broken and a coolant is lost. In this case,
the emergency core cooling system and a decay heat removing system
are activated, and water vapor originating from the reactor water
having leaked from the broken portion of the tube connected to the
reactor pressure vessel 12 and water vapor originating from the
pooled water discharged from the emergency core cooling system
travel to an upper portion of the dry well 15 and fill the upper
dry well 15a.
[0051] The thus configured reactor containment vessel cooling
system 20 according to the present embodiment provides the
following advantageous effects:
[0052] (1) The reactor containment vessel cooling system 20
includes: the heat exchange pool 21, which is installed apart from
the dry well 15 and the suppression chamber 16 in the reactor
containment vessel 10 and stores a medium for cooling water vapor;
the heat exchanger 22, which is immersed in the heat exchange pool
21, extracts water vapor from the dry well 15 in the reactor
containment vessel 10, and allows the water vapor to exchange heat
with the cooling medium in the heat exchange pool 21 so as to
convert the water vapor into condensate; and the condensate drain
pipe 25, which extracts the condensate from the heat exchanger 22
and guides and discharges the condensate at the reactor pressure
vessel 12. Accordingly, the water vapor produced in the dry well 15
as described above undergoes a heat exchange process and becomes
condensate, and the condensate is discharged around the reactor
pressure vessel 12. The discharged condensate efficiently removes
decay heat generated by radioactive nuclides attached to the
reactor pressure vessel 12, thus suppressing increase in the
temperature of the atmosphere in the dry well 15 due to the decay
heat. As a result, the temperature of the water vapor and gases
introduced into the reactor containment vessel cooling system 20
can be lowered, and degradation in cooling capability and
structural integrity of the reactor containment, vessel cooling
system 20 can be suppressed.
[0053] (2) Since the condensate drain pipe 25 discharges condensate
from a position above the reactor shielding wall 13 at the side
surface of the thermally insulating member 19, the condensate flows
down along the side surface of the thermally insulating member 19.
As a result, the condensate can indirectly absorb the heat
accumulated in the thermally insulating member 19, that is, decay
heat generated by radioactive nuclides attached to the reactor
pressure vessel 12 over a wide area of the thermally insulating
member 19.
[0054] The condensate that has not evaporated but has been left in
the process, in which the condensate flows down the thermally
insulating member, 19 is accumulated between the reactor shielding
wall 13 and the thermally insulating member 19 and overflows
through an opening 13a for inter-pipe communication, such as a
recirculation nozzle provided through the reactor shielding wall
13. The overflow condensate absorbs the decay heat and becomes
water vapor, which passes through the vent tube 18, eventually
flows into the suppression pool 17, at which a part of the water
vapor is cooled and condensed, and the rest of the water vapor
travels to the upper dry well 15a and enters the heat exchanger
22.
[0055] It has been known that the concentration of the ratio of the
volume (ratio of partial pressure) of a noncondensable gas
introduced into the heat exchanger 22 to the volume of the
atmosphere correlates with the heat exchanging capability of the
heat exchanger 22, and that the heat exchanging capability of the
heat exchanger 22 decreases as the proportion of the partial
pressure of the noncondensable gas increases. FIG. 4 shows a graph
illustrating the relationship between the proportion of the partial
pressure of a noncondensable gas (ratio of noncondensable gas
partial pressure to atmospheric pressure) and a degradation factor
(index representing relative performance) of a heat exchange-type
reactor containment vessel cooling system shown in Non-Patent
Document 1.
[0056] In the reactor containment vessel cooling system 20, since
the decay heat generated by radioactive nuclides attached to the
reactor pressure vessel 12 efficiently evaporates condensate, the
proportion of water vapor in the upper dry well 15a is greater than
that in the lower dry well 15b. Therefore, the proportion of the
partial pressure of a noncondensable gas in the upper dry well 15a
is lower than that in the lower dry well 15b. The reactor
containment vessel cooling system 20 primarily extracts water vapor
from the upper dry well 15a, where the proportion of the partial
pressure of the noncondensable gas is relatively small, thus
suppressing the decreasing in heat exchange capability of the heat
exchanger 22, that is, decreasing in cooling capability of the
reactor containment vessel cooling system 20.
[0057] (3) The condensate drain pipe 25 includes the ring-shaped
header tube 26, which circumferentially surrounds the thermally
insulating member 19 and through which condensate flows, and the
plurality of condensate discharge ports 27 provided at intervals
along the header tube 26 in the circumferential direction thereof.
As a result, the advantageous effect (2) described above is
provided without any change in the structure of the thermally
insulating member 19 or without degradation of the thermally
insulating performance of the thermally insulating member 19
required during normal operation of the reactor.
Second Embodiment
[0058] FIG. 5 is an enlarged sectional view of a key portion
showing a second embodiment of the reactor containment vessel
cooling system according to the present invention. The present
embodiment is an example in which the condensate drain pipe 25 in
the reactor containment vessel cooling system 20 in the first
embodiment is configured differently. In the following
descriptions, components or members similar to those in the first
embodiment are added with the same reference numerals, and
components different from those in the first embodiment or added
thereto are labeled with "A" in the following description.
[0059] A condensate drain pipe 25A in the present embodiment
includes a header tube 26A.
[0060] The header tube 26A is formed of a ring-shaped pipe through
which condensate extracted from the heat exchanger 22 (see FIG. 1)
flows, as in the first embodiment, but is embedded in the thermally
insulating member 19 and circumferentially surrounds the reactor
pressure vessel 12.
[0061] The header tube 26A has a plurality of discharge ports 27A
provided at intervals along the circumferential direction of the
header tube 26A. The angle and layout of the discharge ports 27A
are arranged so as to face the gap formed between the reactor
pressure vessel 12 and the thermally insulating member 19 and to
discharge the condensate flowing through the header tube 26A at the
side surface of the reactor pressure vessel 12.
[0062] The condensate drain pipe 25A further includes a folded
portion (bent portion) 28A, as shown in FIG. 5. The folded portion
28A is a downwardly convex curved tube that replaces a portion of
the condensate drain pipe 25A and holds water therein during the
normal operation of the reactor. The curved tube is formed of a
U-shaped or V-shaped tube. The symbol W in FIG. 5 represents a
water surface.
[0063] The reactor containment vessel cooling system 20A can
provide not only the advantageous effect (1) provided in the first
embodiment but also the following advantageous effects (4) to
(6).
[0064] (1) Since the condensate drain pipe 25A discharges
condensate at the side surface of the reactor pressure vessel 12
instead of the thermally insulating member 19, the condensate flows
down along the side surface of the reactor pressure vessel 12. As a
result, the condensate directly absorbs the decay heat generated by
the radioactive nuclides attached to the reactor pressure vessel
12, whereby the advantageous effect (1) provided in the first
embodiment is enhanced. The condensate flowing down along the
reactor pressure vessel 12 travels, for example, through the gap
between guide tubes (not shown) of a control rod drive mechanism
into the lower dry well 15b (see FIG. 1), where the condensate
becomes water vapor. The water vapor originating from the
condensate passes through the vent tube 18 and eventually flows
into the suppression pool 17, where a part of the water vapor is
cooled and condensed, and the rest of the water vapor travels to
the upper dry well 15a and enters into the heat exchanger 22.
[0065] (5) Since the header tube of the condensate drain pipe 25A
is embedded in the thermally insulating member 19, any structural
gap between the condensate drain pipe 25A and the thermally
insulating member 19 is unlikely created. As a result, the
condensate can be directly discharged at the reactor pressure
vessel 12 without degradation of the capability of thermally
insulating the reactor pressure vessel 12 during the normal
operation of the reactor.
[0066] (6) A part of the condensate drain pipe 25A is replaced with
the U-shaped tube having a convexly downward shape, and water is
held in the U-shaped tube. The water held in the U-shaped tube
works as a barrier, which substantially prevents the atmosphere gas
with which the structural space between the reactor pressure vessel
12 and the thermally insulating member 19 from traveling toward the
upstream side of the condensate drain pipe 25A. That is, the heat
accumulated between the reactor pressure vessel 12 and the
thermally insulating member 19 unlikely leaks through the
condensate drain pipe 25A. As a result, condensate can be directly
discharged at the reactor pressure vessel 12 without degradation of
the capability of thermally insulating the reactor pressure vessel
12 during the normal operation of the reactor.
Third Embodiment
[0067] FIG. 6 is an enlarged sectional view of an essential portion
representing a third embodiment of the reactor containment vessel
cooling system 20B according to the present invention. The present
embodiment is an example in which the condensate discharge parts
27A in the reactor containment vessel cooling system 20A in the
second embodiment are configured differently. In the following
descriptions, components or members similar to those in the second
embodiment are added with the same reference numerals, and
components different from those in the second embodiment or added
thereto are labeled with "B" in the following description.
[0068] The reactor containment vessel cooling system 20B includes
nozzles 29B, as shown in FIG. 6. Each of the nozzles 29B extends
from the edge of the corresponding discharge port 27A (see FIG. 5)
in the second embodiment and forms a discharge portion through
which the condensate extracted from the heat exchanger 22 (see FIG.
1) is discharged.
[0069] The nozzles 29 are so provided that they penetrate through
the thermally insulating member 19 from outside to inside, and the
angle of the nozzles 29 are arranged so as to discharge the
condensate at the side surface of a reactor pressure vessel 12. The
tube wall of each of the nozzles 29B is in close contact with the
thermally insulating member 19.
[0070] The reactor containment vessel cooling system 20B can
provide not only the advantageous effect (1) provided in the first
embodiment and the advantageous effects (4) to (6) provided in the
second embodiment but also the following advantageous effect
(7).
[0071] (7) The discharge ports of the condensate drain pipe 25B are
formed of the nozzles 29B, which penetrate through the thermally
insulating member that surrounds the reactor pressure vessel 12
from outside to inside. That is, in the configuration in which the
condensate is directly discharged at the reactor pressure vessel
12, the atmosphere gas with which the structural space between the
reactor pressure vessel 12 and the thermally insulating member 19
is filled unlikely leaks out of the thermally insulating member 19.
As a result, the condensate can be directly discharged at the
reactor pressure vessel 12 without degradation of the capability of
thermally insulating the reactor pressure vessel 12 during the
normal operation of the reactor.
[0072] The reactor containment vessels, the reactor containment
vessel cooling system, and the reactor containment vessel cooling
methods according to the present invention have been described
above with reference to the three embodiments. Specific
configurations are, however, not limited to those in the
embodiments, but changes, additions, and other modifications in
design may be made to the extent as far as departing from the
subjects of the present invention set forth in the claims.
[0073] For example, although the first embodiment has been
described with reference to the case where the condensate drain
pipe is used to discharge condensate at the side surface of the
thermally insulating member, the condensate may alternatively be
discharged at the top surface of the thermally insulating member.
Furthermore, although the second and third embodiments have been
described with reference to the case where the condensate drain
pipe is used to discharge condensate at the side surface of the
reactor pressure vessel, the condensate may alternatively be
discharged at the top of the reactor pressure vessel. In this
configuration, the condensate flows over a wider area of the
reactor pressure vessel, whereby decay heat held by the reactor
pressure vessel can be more effectively removed.
[0074] Moreover, although the second embodiment has been described
with reference to the case where water is held in the curved tube
(such as U-shaped tube) during normal operation of the reactor,
water is not necessarily held in the U-shaped tube because the
thermal stratification that occurs in the U-shaped tube prevents
the atmosphere gas between the reactor pressure vessel and the
thermally insulating member from traveling to the upstream side of
the U-shaped tube.
* * * * *