GB2537957A - Emergency core cooling system of nuclear power plant - Google Patents

Abstract

An Emergency Core Cooling System (ECCS) in a nuclear power plant is split into at least three sections, first section 1A including a reactor core isolation cooling system RCIC having a high-pressure injection pump 7 driven by a turbine 9, and a low-pressure flooder system LPFL(A) having a low-pressure injection pump 5A driven an emergency diesel generator 8A. In the event of a loss of coolant accident (LOCA), water may initially be supplied into a reactor pressure vessel 2 through a first pipe and a first feedwater pipe 12B by the RCIC. Once the pressure in the pressure vessel 2 has been reduced by an automatic depressurisation system ADS, water is supplied into the reactor through a second pipe and a second feedwater pipe 12A by the LPFL(A). However, if a fracture is detected in the second feedwater pipe 12A by a fracture detection system 22 & 29, valves 23 & 24 are actuated so as to redirect water from the LPFL(A) to the reactor pressure vessel via the first feedwater pipe 12B and a tie-in line 21 connecting the first and second pipes.

Description

DESCRIPTION

Title of Invention: EMERGENCY CORE COOLING SYSTEM OF NUCLEAR POWER PLANT

Technical Field [0001]

The present invention relates to an Emergency Core Cooling System (ECCS) of a nuclear power plant including redundant injection systems for injecting a reactor coolant into a Reactor Pressure Vessel (RPV) to achieve cold shutdown. Background Art [0002] In the nuclear power plant, events which should be assumed on evaluation of validity in design are defined with the objective of safety, and a Loss of Coolant Accident (LOCA) is one of the events.

[0003] The LOCA is an event in which the reactor coolant flows out and the cooling ability in a reactor core is reduced during power operation of the reactor due to damage, failure and so on in pipes forming a reactor coolant pressure boundary or incidental instruments. Here, the reactor coolant pressure boundary corresponds to a facility having the same pressure condition as the reactor by enclosing the reactor coolant at normal operation of the reactor and forming a pressure barrier under severe conditions at the time of abnormal transient during operation or at the time of accidents, and if the facility is broken, the ',GOA may occur.

[0004] In order to secure the safety in reactor facilities, the reactor is safely shut down, the reactor core is cooled by injecting the reactor coolant into the RPV to confine radioactive substances inside a Primary Containment Vessel (PCV).

[0005] In the above processes, the cooling of the reactor core is achieved by an ECCS. The ECCS is designed to prevent damage in a fuel cladding tube, to keep the integrity of the PCV and to remove the reactor decay heat over a long period of time by cooling the reactor core at the LOCA. Additionally, in the design of the ECCS, a safety function under a single failure of an active component is guaranteed, and installation of an Emergency Diesel Generator (EDG) on the assumption of the loss of an on-site power source and an off-site power source as well as the securement of redundancy/independence of functions/systems are considered. Here, the single failure means that single component loses a given safety function by a single factor, including multiple failures based on dependent factors.

[0006] In an Advanced Boiling Water Reactor (ABWR), the ECCS includes a High Pressure Core Flooder system (HPCF) and a Reactor Core Isolation Cooling system (RCIC) capable of injecting the reactor coolant even when the RPV is in a high pressure state, a Low Pressure Flooder system (LPFL) injecting the reactor coolant when the inside of the RPV is in a low pressure state and an Automatic Depressurization System (ADS) which depressurizes the RPV automatically.

[0007] Fig. 2 is a system schematic diagram of the ECCS 1 in the existing ABWR. In the drawing, the ABWR has the following configuration.

[0008] In Fig. 2, "3" denotes a PCV, and a RPV 2 storing a reactor core 4 is installed thereinside. In a Suppression Chamber (S/C) 19 on the bottom of the PCV 3, a Suppression Pool (S/P) 11 is formed to store cooling water. "20" denotes a dry well corresponding to portions other than the S/C 19 inside the PCV 3. "12" denote a feedwater pipe, which guides supply water to the RPV 2 by a not-shown reactor water supply pump. The feedwater pipe includes two systems of 12A, 12B. Steam generated inside the RPV 2 is fed to a not-shown steam turbine through a main steam pipe 18.

[0009] An ECCS 1 shown in Fig. 2 is sectioned into a section 1A, a section 1B and a section 1C, supplying cooling water stored in the S/P 11 to the RPV 2 by cooling pumps 5, 6 and 7 provided in these sections, thereby cooling the reactor core 4.

[0010] The ECCS 1 of the existing ABWR includes three systems of LPFLs (LPFL (A), LPFL (B) and LPFL (C)) having LPFL pumps 5 (5A, 5B and.5C) driven by motors 8, two systems of HPCFs (HPCF (B), HPCF (C)) having HPCF pumps 6 (6B, 6C) driven by motors 8, one system of RCIC having a RCIC pump 7 driven by a steam turbine 9 and an ADS.

[0011] These cooling systems are separately arranged so as to correspond to the section 1A, the section 1B and the section 1C. The LPFL (A) and the RCIC are arranged in the section 1A, the LPFL (B) and the HPCF (B) are arranged in the section (B) and the LPFL (C) and the HPCF (C) are arranged in the section (C).

[0012] The ECCS 1 receives power supply from three systems of EDGs 8 (8A, 8B and 8C) as emergency power sources so as to achieve the safety function of the system even in the loss of off-site power source and in case of the single failure of a component included in the system is assumed. Accordingly, the system are configured by three sections which are the section lA including one system of LPFL (A), one system of RCIC and one system of EDG 8A, the section B including one system of LPFL (B), one system of HPCF (B) and one system of EDG 8E, and the section 1C including one system of LPFL (C), one system of HPCF (C) and one system of EDG 8C.

[0013] The LPFL in the configurations of injection systems is one of operation modes in a residual heat removal system (RHR), which is a system absorbing pool water inside the S/P 11 and injecting the water to the outside of a core shroud of the RPV 2, including independent three systems (LPFL (A), LPFL (B) and LPFL (C). In the LPFLs in the three sections, the LPFL (A) in the section 1A uses the feedwater pipe 12A as an injection route through a controllable valve 24, and LPFL injection pipes 13, 14 are used as injection pipes in remaining sections 1B and 10.

[0014] The HPCF is a system absorbing water from a condensate storage tank (CST) 15 as a first water source first, and from the S/P 11 as a second water source finally, injecting the water to the inside of the core shroud of the REV 2, including independent two systems. HPCF injection pipes 16, 17 are used as injection routes in the sections 1B and 10 of the system. [0015] The RCIC absorbs water from the CST 15 first, and from the S/P 11 finally, injecting the water to the outside of the core shroud. In the system, the feedwater pipe 12B is used as an injection route.

[0016] The ADS is a system relieving the steam inside the RPV 2 to the S/C 19, reducing the pressure inside the RPV 2 to a pressure in which injection can be performed by the LPFL to promote cooling of the reactor core. The steam is relieved to the S/C 19 through a Safety Relief Valve (SRV) 27 provided at, for example, part of the main steam pipe 18.

[0017] As the severest assumption of the EGGS 1 in the existing ABWR, the loss of the on-site power source and the off-site power source are assumed as well as under a condition that the EGOS in the section 1B or 10 is unavailable due to some reason, a further damage in any of remaining injection pipes 16 or 17 in the HPCFs is considered. At this time, the RCIC pump 7 is activated, and the reactor coolant is injected into the RPV 2 in the high pressure state to thereby mitigate the lowering of a reactor water level. Subsequently, the ADS is operated and the SRV 27 is opened, which reduces the pressure inside the RPV 2 and the injection is performed by the LPFL.

[0018] In addition to the severest assumption in the EGOS 1 of the existing ABWR, a state where further one section is unavailable due to some reason is assumed. In this case, as the new severest assumption, the loss of the on-site power source and the off-site power source are assumed as well as under the condition that the FCCSs in the sections 1B, 1C are unavailable due to some reason, a further damage of the injection pipe 12A of the LPFL (A) in the section 1A is considered.

[0019] That is, the state shown in Figs. 3, 4 is assumed. Among them, Fig. 3 shows functions of system components of the ECCS 1 by sorting out the functions in respective sections. The RCICpump(7) and the LPFL pump (5A) and the EDG (8A) are provided in the section 1A, the HPCF pump (63), the LPFL pump (53) and the EDG (813) are provided in the section 13, and the HPCF pump (60), the LPFL pump (50) and the EDG (80) are provided in the section 10. The drawing shows that the ADS which depressurizes the RPV automatically is provided regardless of these sections. [0020] In the assumed state, functions of the core cooling systems shown in Fig. 3 with marks "X" are unavailable. Fig. 4 shows a configuration diagram of the FCCS under the severer condition than a condition assumed in the existing ABWR, in which marks "X" are added to places where functional disorders occur. Only the RCIC pump 7 and the EDG 8A in the section 1A and the SRV 27 of the ADS which depressurizes the RPV automatically function in a sound state. Although the EDG 8A can operate, cooling water supplied by the LPFL pump 5A does not contribute to cooling of the reactor core due to the damage of the injection pipe 12A (feedwater pipe).

[0021] The cooling function by the sound functions in this state is considered to be as follows. In this case, the pump 7 of the RCIC is activated by the steam turbine, which injects the reactor coolant into the RPV 2 in the high pressure state to mitigate the lowering of the reactor water level. Subsequently, the ADS is operated (the SAV 27 is opened) to thereby reduce the pressure inside the RPV 2, however, the RCIC is unavailable under a condition that the RPV 2 is in the low pressure state, and other cooling systems belonging to the ECCS 1 are also unavailable, therefore, cold shutdown of the reactor core is hardly achieved.

[0022] Concerning the above problems, a design in which the RCIC in the section lA is replaced with the HPCF which is available under the low pressure condition is disclosed in Patent Literature 1.

Citation List Patent Literature [0023] [Patent Literature 1] JP-A-2009-31079

Summary of Invention

Technical Problem [0024] According to the solution proposed in Patent Literature 1, cold shutdown of the reactor core can be achieved, however, any cooling systems are available to achieve injection of cooling water to the reactor core under the condition of station blackout (SBO). Moreover, it is necessary to perform large-scaled removing and installation works in the case of existing facilities. Accordingly, it is desirable to achieve cold shutdown of the reactor core by a method available to inject cool ing water into the reactor core even in the condition of SBO and by a simpler method.

[0025] In view of the above, the present invention provides a reactor available to achieve cold shutdown of a reactor core in each single system in a configuration of an ECCS including a RCIC.

Solution to Problem [0026] According to an embodiment of the present invention, in order to solve the problem there is provided an ECCS of a nuclear power plant including ECCSs sectioned into at least three sections in which a first section in the ECCSs has a RCIC having a high-pressure injection pump driven by a turbine, a LPFL having a low-pressure injection pump driven by a motor and an emergency power source, water is supplied into a RPV through a first pipe and a first feedwater pipe by the RCIC, and water is supplied into the RPV through a second pipe and a second feedwater pipe by the LPFL, and an ADS which is used in common by the ECCSs sectioned into three sections, which includes a fracture detector detecting a fracture in the first feedwater pipe or the second feedwater pipe and a first valve provided in the second pipe of the LPFL and a tie-line connecting the first pipe and the second pipe through a second valve in an upstream side of the first valve, in which the fracture detector detects a fracture of the second feedwater pipe and operates the first valve and the second valve to supply water into the RPV from the LPFL through the tie line and the first feedwater pipe.

Advantageous Effects of Invention [0027] According to the present invention, it is possible to provide the ECCS which allows the injection systems to have redundancy so as to inject the reactor coolant into the RPV and achieve cold shutdown of the reactor core under a condition where the emergency cooling systems in two sections in the ECCSs having three sections are unavailable due to some reason as well as when a fraction is further assumed to occur in an injection pipe included in any of injection systems of the ECCS in one section which can be used.

Brief Description of Drawings

[0028] [Fig. 1] Fig. 1 is a diagram showing a system outline of an ABWR including an ECCS according to an embodiment of the present invention.

[Fig. 2] Fig. 2 is a diagram showing a system outline of an ECCS in the existing ABWR.

[Fig. 3] Fig. 3 is a view showing functions of system components of an ECCS 1 by sorting out the functions in respective sections.

[Fig. 4] Fig. 4 is a diagram showing a configuration of the ECCS in the ABWR under a severest condition.

[Fig. 5] Fig. 5 is a diagram mainly showing additional components of the present invention.

[Fig. 6] Fig. 6 is a view showing a specific measuring instrument setting position of an instrument 22 (differential pressure gauge) for detecting a fracture in a feedwater pipe 12A.

[Fig. 7] Fig. 7 is a view showing that a fracture F in the feedwater pipe 12A occurs in the configuration of Fig. 6. [Fig. 8] Fig. 8 is a diagram showing a configuration example of 2-out-of-4 logic adopted for a differential pressure gauge for measuring a differential pressure between feedwater pipes. Description of Embodiments [0029] Hereinafter, an embodiment of the present invention will be explained in detail with reference to the drawings. [Embodiment] [0030] Fig. 1 is a system schematic diagram of an ABWR including an ECCS according to an embodiment of the present invention. [0031] In Fig. 1, portions surrounded by dotted lines indicate functional configuration portions added by the present invention. In short, a tie line 21 including a controllable valve 23 connects between a pipe of a RCIC and a pipe of a LPFL (A) in a section 1A, and the controllable valve 23 is controlled to be opened when a fracture in a feedwater pipe 12A is detected (for example, a differential pressure of a set value or more occurs between pipes).

[0032] According to the above configuration, a pump 7 of the RCIC is activated by a steam turbine 9, which injects a reactor coolant into a RPV 2 in the high pressure state to mitigate the lowering of the reactor water level. Subsequently, an ADS is operated (a SRV 27 is opened) to thereby reduce the pressure inside the RPV 2. Moreover, when a fracture in the feedwater pipe 12A is detected (for example, a differential pressure of the set value or more occurs between pipes), the controllable valve 23 is opened and the LPFL pump SA is driven by a EDG 8A which can be activated to thereby inject water into the reactor core through the LPFL (A), the tie line 21 and the feedwater pipe 12B can be achieved.

[0033] Embodiment 1 according to the present invention having the above configuration and used as described above will be explained in detail as follows.

[0034] First, main components of the ECCS in the ABIgR according to the embodiment are the same as the components shown in Fig. 2. An ECCS 1 includes three systems of LPFLs (LPFL (A), LPFL (B) and LPFL (C)) having LPFL pumps 5 (5A, 5B and 50) driven by EDGs 8, two systems of HPCEs (HPCF (B), HPCF (C)) having HPCF pumps 6 (6B, 60) driven by EDGs 8, one system of RCIC having the RCI0 pump 7 driven by the steam turbine 9 and the ADS. [0035] These cooling systems are separately arranged so as to correspond to the section 1A, the section 1B and the section 10. The LPFL (A) and the RCIC are arranged in the section 1A, the LPFL (B) and the HPCF (B) are arranged in the section (B) and the LPFL (C) and the HPCF (C) are arranged in the section (0).

[0036] The ECCS 1 receives power supply from three systems of EDGs 8 (8A, 8B and 80) as emergency power sources so as to achieve the safety function of the system even when an off-site power source is unavailable and in case of a single failure of a component included in the system is assumed. Accordingly, the system are configured by three sections which are the section lA including one system of LPFL (A), one system of ROTC and one system of EDG BA, the section B including one system of LPFL (B), one system of HPCF (B) and one system of EDG BB, and the section 10 including one system of LPFL (C), one system of HPCF (C) and one system of EDG BC.

[0037] The LPFL in the configurations of injection systems is one of operation modes in a RHR, which is a mode absorbing pool water inside a S/P 11 and injecting the water to the outside of a core shroud of the RPV 2, including independent three systems (LPFL (A), LPFL (B) and LPFL (C). In the LPFLs in the three sections, the LPFL (A) in the section 1A uses the feedwater pipe 12Aas an injection route through a controllable valve 24, and LPFL pipes 13, 14 are used as injection routes in remaining sections 1B and 1C.

[0038] The HPCF is a system absorbing water from a CST 15 as a first water source first, and from the S/P 11 as a second water source finally, injecting the water to the inside of the core shroud of the RPV 2, including independent two systems. FPCF pipes 16, 17 are used as injection routes in the sections 1B and 10 of the system.

[0039] The ROTC absorbs water from the CST 15 first, and from the S/P 11 finally, injecting the water to the outside of the core shroud. In the system, a feedwater pipe 12B is used as an injection route.

[0040] The ADS is a system relieving the steam inside the RPV 2 to a S/C 19, reducing the pressure inside the RPV 2 to a pressure in which injection can be performed by the LPFL to promote cooling of the reactor core. The steam is relieved to the S/C 19 through a SRV 27 provided at, for example, part of a main steam pipe 18.

[0041] As the severest assumption of the ECCS 1 in the existing ABWR, the loss of an on-site power source and the off-site power source are assumed as well as under a condition that the ECCS in the section 1B or 10 is unavailable due to some reason, a further damage in any of remaining injection pipes 16 or 17 in the HPCFs is considered. At this time, the RCIC pump 7 is activated, and the reactor coolant is injected into the RPV 2 in the high pressure state to thereby mitigate the lowering of a reactor water level. Subsequently, the ADS is operated and the SRV 27 is opened, which reduces the pressure inside the RPV 2 and the injection is performed by the LPFL.

[0042] In addition to the severest assumption in the ECCS 1 in the existing ABWR, a state where further one section is unavailable due to some reason is assumed. In this case, as the new severest assumption, the loss of the on-site power source and the off-site power source are assumed as well as under the condition that the ECCSs in the sections 1B, 1C are unavailable due to some reason, a further damage of the injection pipe 12A of the LPFL (A) in the section lA is considered.

[0043] In this case, only one system of the ROTC can inject the reactor coolant into the RPV 2 as shown in Fig. 3.

[0044] In the embodiment of the present invention, the following additional components are included in addition to the above existing components. The portions surrounded by circles in Fig. 1 are the additional portions, and Fig. 5 mainly shows components in the additional portions by sorting out the components. The explanation of the additional portions will be made with reference to Fig. 5.

[0045] The section 1A is mainly explained in Fig. 5. In this case, a connecting pipe 31 to the injection pipe (feedwater pipe) 12A of the LPFL (A) and a connecting pipe 32 to the injection pipe (feedwater pipe 123) of the AMC are connected by the tie line 21. The controllable valve 23 is provided on the tie line 21 (a motor driven valve MO is tentatively shown in Fig. 1). Additionally, the controllable valve 24 is provided also on the connecting pipe 31 of the LPFL (A). An existing valve can be used as the valve 24.

[0046] An instrument 22 measuring state quantities (a differential pressure gauge is tentatively shown in Fig. 1) is connected to both supply pipes 12A, 12B, and a fracture detector 29 for specifying a fractured pipe based on the state quantities of both supply pipes 12A, 12B is connected to the instrument 22. In the example of Fig. 5, a differential pressure detector is provided in the feedwater pipes 12A, 123 for detecting a fractured pipe by the fracture detector 29. [0047] The fracture detector 29 detects a fracture F in the feedwater pipe 12A from an output of the instrument 22, operating the valve 23 on the tie line 21 and the valve 24 on the connecting pipe 31. Accordingly, the LPFL (A) can inject water from two pipes of the feedwater pipe 12A and the feedwater pipe 123 selectively.

[0048] For example, when a fracture is detected in the feedwater pipe 12A, the fracture detector 29 performs operation so that the valve 24 on the connecting pipe 31 to the pipe 12A is closed and the valve 23 on the tie line 21 is opened, thereby enabling water injection to the reactor core also from the LPFL (A). In this case, the LPFL pump 5A is activated by the EDG 8A which can be activated, and water injection to the reactor core is performed from the pipe 31 of the LPFL through the valve 23 on the tie line 21, the pipe 32 of the ROTC and the injection pipe (feedwater pipe) 12B thereof.

[0049] Accordingly, in the case where the two ECCS sections of the three ECCS sections are unavailable due to some reason and only the ECCS in one section is available, even when a fraction is further assumed to occur in the injection pipe in any of injection systems included in the FCCS in one section which can be used, a stable flow rate of reactor coolant can be injected into the RPV 2 by switching the injection route of the LPFL in the section lA by operating the valve 23 of the tie line 21 and the valve 24 on the connecting pipe if necessary in the ECCS according to the embodiment.

[0050] That is, cold shutdown of the reactor core can be achieved by allowing the injection systems to have redundancy even in a severer assumed state than the above existing ABWR. [0051] Although the embodiment has been explained by citing the ABWR as an example, the present invention can be applied all reactors.

[0052] In the above explained embodiment, further modifications and alternatives maybe further adopted. First, in embodiment 1, as the controllable valve 24 on the tie line 21 between the LPFL and the ROTC in the section 1A, valves such as a motor driven valve, a compressed air driven valve, a nitrogen driven valve and a manual valve may be adopted regardless of types. [0053] As the instrument 22 measuring state quantities of both feedwater pipes 12A, 12B to detect a fracture in the feedwater pipes 12A, 12B, instruments such as a differential pressure gauge, a differential flowmeter, a thermometer and a radiation densitometer may be adopted regardless of types.

[0054] When the differential pressure gauge configured by setting a RCIC side as a high-pressure side and setting a LPFL side as a low-pressure side is used as the instrument 22 measuring state quantities of both feedwater pipes 12A, 123 to detect a fracture of the feedwater pipe 12A, it is possible to prevent undesirable switching of the injection route LPFL (A) of the LPFL by downscaling in the case where the feedwater pipe 123 is fractured.

[0055] Fig. 6 is a view showing a specific measuring instrument setting position of the instrument 22 (differential pressure gauge) for detecting a fracture in the feedwater pipe 12A. In this case, when the measuring instrument setting position is set closer to the PCV 3 side than rising parts 33 of both feedwater pipes 12A, 123 in the RPV 2, a larger differential pressure can be obtained from a viewpoint of the static head. [0056] Fig. 7 is a view showing that a fracture F in the feedwater pipe 12A occurs in the configuration of Fig. 6. In Fig. 7, pressures at pressure measuring points by the instrument 22 (differential pressure gauge) are PA, PB, and a pressure inside the reactor core is PO. In this case, a differential pressure to be set for switching the injection route in the section 1A is set to a value higher than a differential pressure AP1 between both feedwater pipes 12A and 123 in the normal state as well as lower than a differential pressure AP2 between both feedwater pipes 12A and 12B obtained when the pipe fracture F occurs in the vicinity of the RPV 2 in the feedwater pipe 12A as well as in a position closer to the RPV 2 side than a rising part 33A of the feedwater pipe 12A. Accordingly, the undesirable switching of the injection route in the normal state is prevented and the differential pressure can be detected as well as the injection route can be switched even in the case where the fracture is assumed to occur in most of positions on the feedwater pipe 12A in the assumed states in the present invention.

[0057] In the configuration shown in Fig. 6 and Fig. 7, a shock wave may occur just after the fracture occurs in any fracture occurring in both feedwater pipes 12A, 12B. In this case, it becomes difficult to measure a differential pressure between both feedwater pipes 12A and 12B accurately due to effects of the shock wave. In response to the event, a timer is set in the fracture detector 29 so as to operate, for example, after several ten seconds pass from the occurrence of the fracture, thereby preventing the undesirable switching of the injection route due to inaccurate measurement of the differential pressure.

[0058] Furthermore, in the configuration shown in Fig. 6 and Fig. 7, it is effective to allowing measuring instruments and so on to have redundancy for improving the reliability in measurement, and a positional configuration example in this case is shown in Fig. 8. In Fig. 8, four differential pressure gauges 22 (22a, 22b, 22c and 22d) are installed, and 2-out-of-4 logic is adopted for signals of the four differential gauges in the fracture detector 29, thereby improving the probability of preventing erroneous measurement by the differential pressure gauges.

Reference Signs List [0059] 1: Emergency Core Cooling System (ECCS) 2: Reactor Pressure Vessel (RPV) 3: Primary Containment Vessel (PCV) 4: reactor core 5: Low Pressure Flooder system (LPFL) pump 6: High Pressure Core Flooder system (HPCF) pump 7: Reactor Core Isolation Cooling system (RCIC) pump 8A, 8B, 8C: Emergency Diesel Generators (FDGs) 9: steam turbine for driving RCTC pump 11: Suppression Pool (S/P) 12A, 12B: feedwater pipes LPFL (A), LPFL (B), LPFL (C): low pressure flooder systems HPCF (B), HPCF (C): high pressure core flooder systems RCIC: reactor core isolation cooling system 13, 14: LPFL injection pipes 15: Condensate Storage Tank (CST) 18: main steam pipe 19: Suppression Chamber (S/C) 20: dry well 21: tie line between LPFL (A) and ROTC 22: instrument for detecting fracture 23: valve for switching injection route of LPFL (A) 24: controllable valve on connecting pipe to feedwater pipe 12A of LPFL (A) 33A, 333: rising parts of feedwater pipe 27: Safety Relief Valve (SRV) 29: fracture detector 31: connecting pipe to injection pipe (feedwater pipe) 12A of LPFL (A) 32: connecting pipe to injection pipe (feedwater pipe) 12B of RCIC