JPH0631782B2 - Light water reactor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light water reactor for ensuring the safety of a nuclear reactor in the event of a loss of coolant, and particularly to a core even if the coolant is discharged by reduced pressure boiling. It is intended to obtain a core submergence-maintaining reactor in which the coolant amount is secured above the upper end of the fuel heating portion of the core so as not to be exposed.

[Background of the Invention]

Regarding the conventional boiling water reactor (hereinafter referred to as BWR),
This will be described with reference to FIG.

FIG. 2 shows a reactor pressure vessel 5 for storing the core 1, a recirculation system located below the core 1 and having a function of removing heat generated in the core 1 and controlling the reactor heat output, and reactor water. A water supply system 6 for keeping the water level constant, and a high pressure core spray system 7 (hereinafter referred to as HPCS) and a low pressure core spray system (hereinafter referred to as LPCS) as an emergency core cooling system (hereinafter referred to as ECCS). And a low pressure water injection system 9 (LPCI), a coolant loss accident (hereinafter referred to as LOCA)
This is the change in the reactor water level and reactor pressure.

The most severe accident in cooling the core 1 due to the BWR LOCA event is the suction pipe 1 of the recirculation system located below the core 1.
No. 5 fracture. Recirculation pump 13 and downcomer 14
In the recirculation system having the suction pipe 15 located at the lower part of the pipe and the discharge pipe 17 for boosting the coolant taken out from the downcomer 14 and supplying the driving water to the jet pump 16, when the suction pipe 15 is broken, the downcomer 1
The water level of No. 4 and the pressure in the reactor vessel 5 are suddenly lowered (decompressed) (see the part (a) of FIG. 2), and the water level in the core shell is also drastically lowered. As shown in the figure, L
Approximately 50 seconds after OCA, the core 1 is exposed, and the temperature of the fuel cladding tube rises (see (B) in FIG. 2).
On the other hand, when the reactor pressure drops, ECCS is injected, so that the water level inside the shell is restored, and the reactor core 1 is re-submerged (after about 150 seconds) and cooled (see (c) in Fig. 2). . As described above, in the BWR, the large-diameter pipe is located below the core 1, so that when LOCA occurs, the core 1 is completely exposed, and core cooling is performed by the ECCS system.

Next, a new boiling water reactor (hereinafter referred to as ABWR) will be described with reference to FIG.

FIG. 3 shows a reactor pressure vessel 5 that stores the core 1, an internal pump 10 that has functions of removing heat generated in the core 1 and controlling the reactor heat output, and water supply for keeping the reactor water level constant. HPCS as ECCS system
Fig. 7 is a diagram showing an analysis result in the case where the severest HPCS fracture in core cooling is assumed in an ABWR having a reactor isolation cooling facility 11 (hereinafter referred to as RCIC) and a low pressure water injection system 12 (hereinafter referred to as LPFL). is there. H
When the PCS piping 7 is broken, the HPCS super jar 18
The coolant is discharged to the outside of the reactor pressure vessel 5 from the portion.
However, when the water level in the downcomer 14 drops, the RCIC 11 operates in about 55 seconds (see (d) in FIG. 3), and the automatic depressurization system (ADS) operates in about 150 seconds ((in FIG. 3). E) See). Reactor pressure is LPFL
When the pressure drops to the operating pressure of 12 (at this time, depressurization boiling occurs and the reactor core level rises), the LPFL 12 starts water injection (see (f) in FIG. 3) in about 33 seconds, so that the reactor water level rises again. Therefore, the reactor core 1 will be flooded during the entire period of the accident. In this way, RCIC11 is for cooling the core flood from the start of LOCA until LPFL12 is activated. It is provided to supplement. On the other hand, the change in the temperature of the fuel rod cladding tube occurs after the occurrence of LOCA, the transition boiling occurs due to the rapid decrease in the core flow rate due to the stop of the internal pump 10, and the thermal conductivity decreases, so the temperature of the fuel rod cladding tube rises ( (See (g) of FIG. 3). However, the rise in the temperature of the fuel rod cladding tube is suppressed in a short period due to the decrease in output due to the scrum. As described above, in ABWR, RCIC is generated at the initial stage of LOCA occurrence.
After the reactor pressure dropped due to 11, LPFL1
Since the coolant is injected into the reactor by No. 2, it is possible to maintain the flooding for the entire period after the accident and obtain sufficient core cooling.

FIG. 4 shows the rate at which the reactor pressure is released to the outside of the reactor pressure vessel 5 by the reduced pressure boiling from 70 ATA, and about 38% of the total amount of the coolant possessed is released. I am aware of this.

FIG. 5 shows the residual water amount with respect to the water level in the reactor pressure vessel 5 at the time of LOCA. From the figure, in the BWR, the large-diameter pipe is located below the core, so a large amount of coolant flows out when the pipe breaks, and the reactor water level drops to the point in Fig. 5, but the ABW
In R, the primary system piping is located above the core 1 and the operation of the RCIC 11 causes the amount of residual water in the reactor pressure vessel 5 to be larger than that in BWR, and to the point in FIG. descend. However, the coolant was released by the reduced pressure boiling (38% of the total coolant), and RCIC11
The reactor water level without is shown in Fig. 5 and is below the upper end of the fuel heat generation part.

Figure 6 shows the safety peculiar to each reactor. The core 1, the cooling system circulation pump 2, and the cooling system intermediate heat exchanger 3 are connected by a pipe, the heat generated in the core 1 is transferred to water by sodium, which is a coolant, and steam is generated to rotate a turbine to generate electricity. Fast amplification reactor (FBR) is LOC at the reactor coolant boundary
Even if A occurs, the core 1 can be cooled safely without hindering the circulation of the primary coolant.
The piping and equipment of the primary main cooling system are located in high places.
Also, the guard bezel cell 4 is arranged in the piping and equipment which are unavoidably arranged at a low position, and the design is such that the liquid level in the reactor vessel can be maintained above an allowable level. Yotsutte, EC
Since the core can be sufficiently cooled without the CS system, the safety peculiar to the reactor is very high. In addition, guard bet cell 4
Is the reactor pressure vessel 5, the primary main cooling system intermediate heat exchanger 3,
Each is installed in the primary main cooling system circulation pump 2.
However, in BWR, when LOCA occurs due to complete rupture of the piping connected to the reactor pressure vessel such as the primary reactor cooling system, the coolant flow from the breakage port and the coolant flow due to reduced pressure boiling cause the reactor core 1 Since the core is exposed, the core cooling is largely responsible for ECCS. Therefore, it can be said that the inherent safety of the reactor is low.

On the other hand, in the ABWR, the breakage hole that should be assumed in design is extremely small, and the breakage position is also located above the core 1. For this reason, the amount of coolant flowing out of the reactor during LOCA is small and the core is difficult to be exposed, so the safety peculiar to the plant is higher than that of the BWR.

From the above, in particular in ABWR, even if LOCA occurs, the coolant (38
%) Can be secured in the upper part of the core 1, the safety inherent to the plant can be enhanced.

FIG. 7 shows the ABWR ECCS system.

The ECCS system has an independent structure so that the safety function of the device can be achieved even if a single failure is assumed. As shown in the figure, the ECCS system is divided into three categories, Category I, Category II, and Category III. An emergency diesel generator 19 is installed as a power source for each category. For example, considering breakage of HPLS7, which is the most severe for core cooling, assuming that the HPCS7 function of Category II shown in the figure stops and a single failure is assumed,
This is a very severe accident in which the functions of the ECCS system of Category III are also stopped at the same time. However, the remaining RCIs of Category I
With C11, LPFL12 and LPFL12 of section II, it has the capacity to cool the core sufficiently.
The capacity of each system is 180T / H for one system of RCIC11.
r and HPCS7 are 730 T / Hr in 2 lines, and LPFL12 is 950 T / Hr in 3 lines.

In addition, as a conventional publicly known example, Hitachi review Vo1.66, No.
4 (April 1984 issue), pages 59 to 64, there is a technology entitled "ABWR (New Boiling Water Atomic Plant)".

[Object of the Invention]

An object of the present invention is to obtain a highly reliable light water reactor in which the reactor core is not exposed and flooding is maintained even during the LOCA of the reactor primary system piping.

[Outline of Invention]

The present invention relates to a reactor pressure vessel that stores a reactor core and an upper plenum installed above the reactor core, a water injection pipe connected to the reactor pressure vessel as a water injection system, and the reactor pressure vessel. In a light water reactor having a main steam pipe connected to it, when the pressure inside the reactor pressure vessel is suddenly reduced from the pressure during normal operation to atmospheric pressure, the coolant is released to the outside of the reactor pressure vessel by depressurization boiling. In this case, the position of the opening of each pipe in the reactor pressure vessel is set above the upper end of the fuel heat generating part so that the coolant can be secured above the upper end of the fuel heat generating part of the core. A light water reactor characterized by improving the safety and reliability of the reactor by maintaining the core flooded even during depressurization boiling in the reactor pressure vessel at the time of an accident.

Example of Invention

A specific embodiment of the present invention is a light water reactor in which LO
Even if CA occurs, a structure that can secure 38% or more of the total retained water below the break port between the break port and the upper end of the fuel heat generation part can sufficiently cool the core with only a small volume of low pressure ECCS. The feature is that you can do it.

An embodiment of the present invention will be specifically described below with reference to FIGS. 1 and 8.

FIG. 1 is an example in which the present invention is applied to an ABWR. In the figure, 5 is a reactor pressure vessel for storing the core 1, 10 is an interface having functions of removing heat generated in the core 1 and controlling the reactor heat output. Null pump 6 is a water supply system for keeping the reactor water level constant. ECCS systems include HPCS7, RCI
C11 and LPFL12 are installed. Upper plenum 2
1 is about 40 cm higher, and the upper plenum 21
The structure including the upper reactor pressure vessel 5 is elevated. The total amount of water held at the normal water level of the 1350 MWe class ABWR plant is about 30 m ³ , and the rate of release to the outside of the reactor pressure vessel 5 by depressurization boiling is 38% of the total amount of water held, so the cooling released. The material amount is about 11.5 m ³ . In order to secure this discharge amount between the HPCS nozzle 18 and the upper end of the fuel rod heat generating portion, the HPCS nozzle 18 may be positioned higher by about 40 cm.

In the present invention, the upper plenum 21 is raised by about 40 cm, and the HPCS nozzle 18 is positioned higher by that amount, so that even if LOCA occurs due to the HPCS rupture that is the most severe for core cooling, the automatic depressurization system operates for about 150 seconds. RCIC
Even if water is not injected into the reactor 11, a large amount of coolant can be secured above the upper end of the heat generating portion, so the core is not exposed. Moreover, even if 38% of the total amount of water held is released to the outside of the reactor pressure vessel 5 by the reduced pressure boiling, the core is not exposed.
The core remains submerged for about 330 seconds until L is activated. Therefore, according to the present invention, sufficient core cooling can be obtained only by the LPFL 12 without the RCIC 11. Further, the capacity of the LPFL 12 does not need to consider the amount of the coolant released by the reduced pressure boiling, so that only the amount of the coolant released by the decay heat is sufficient.

As described above, even in the case of LOCA due to HPCS fracture, which is the most severe for core cooling, the core is flooded,
RCIC11, LPF connected to another reactor pressure vessel
L12, Even if breakage occurs in 6 pipes of the water supply system (installed above the HPCS pipe 7), if 38% of the total retained water amount released by reduced pressure boiling can be secured between the breakage port and the upper end of the fuel heat generating part, the core Is flooded, ECC
The S system can be simplified.

FIG. 8 shows a new configuration of the ECCS system according to the present invention. As mentioned above, at the time of LOCA, the RCI
Although it is not necessary to operate C12, RCIC12 cannot be reduced because it must be installed for the purpose of cooling the core during reactor isolation during a transient event. However, the HPCS 7 shown in FIG. 7, which is conventionally required, is not necessary because the core is flooded without the high pressure ECCS. Therefore, assuming the LOCA and the single failure, the ECCS system shown in FIG. 8 can be obtained. For ECCS capacity, conventional ABWR is RCIC11: 180T
/ Hr (1 line), HPCS7: 730T / Hr (2 lines), LPFL12: 950T / Hr (3 lines), according to the ABWR of the present invention, RCIC11:
180T / Hr (1 system), LPFL12: about 230T
/ Hr (3 systems) ECCS system sufficiently cools the core 1. The basis of 230 T / Hr is a value including some margin in the amount of loss of coolant due to decay heat (2% or less of total output) about 3 minutes after LOCA.

〔The invention's effect〕

According to the present invention, even if LOCA occurs, the core is not exposed and flooding is maintained, so that it is possible to obtain plant-specific safety, and at the same time, the ECCS system can be simplified and its capacity can be made conventional. On the other hand, it can be 1/5 or less. Thus, according to the present invention, the reliability is high,
Moreover, it is possible to obtain a light water reactor capable of significantly reducing the product price.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing an embodiment of a light water reactor of the present invention, FIG. 2 is a diagram showing a conventional BWR structure and its accident analysis results, and FIG. 3 is a conventional ABWR structure. And a diagram showing the accident analysis result, FIG. 4 is a diagram showing the reduced pressure boiling rate, FIG. 5 is a diagram showing the relationship between the reactor water level and the volume in the Bethel, and FIG. FIG. 7 is a diagram showing the comparison between the safety of the present invention and the inherent safety of the ABWR as one embodiment of the present invention, FIG. 7 is a diagram for explaining the ECCS system of the conventional ABWR, and FIG. 8 is one of the present invention. E in the example
It is a figure explaining a CCS system. 1 ... Reactor core, 2 ... Cooling system circulation pump, 3 ... Cooling system intermediate heat exchanger, 4 ... Guard vessel, 5 ... Reactor pressure vessel, 6 ...
Water supply system, 7 ... High pressure core spray system (HPCS), 9 ... Low pressure water injection system (LPCI), 10 ... Internal pump, 1
1 ... Reactor isolation cooling facility (RCIC), 12 low pressure injection system (LPFL), 13 ... recirculation pump, 14 ... downcomer,
15 ... Recirculation system suction pipe, 16 ... Jet pump, 1
7 ... Recirculation system discharge piping, 18 ... High pressure core sparger, 19 ... Emergency diesel generator, 20 ... Main steam system, 21 ... Upper plenum.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuaki Uezuma 3-2-1, Sachimachi, Hitachi, Ibaraki Prefecture Hitachi Engineering Co., Ltd. (72) Inventor Toshihiko Sugisaki 3-chome, Hitachi, Hitachi, Ibaraki No. 1 Hitachi Ltd., Hitachi Works (56) References JP 59-231484 (JP, A) JP 60-202390 (JP, A)

Claims (4)

[Claims] 1. A reactor pressure vessel for storing a reactor core and an upper plenum installed above the core, a water injection pipe connected to the reactor pressure vessel as a water injection system, and the same reactor pressure vessel. In a light water reactor that has a main steam pipe connected to, when the pressure inside the reactor pressure vessel is suddenly reduced from the pressure during normal operation to atmospheric pressure, the coolant is released to the outside of the reactor pressure vessel by reduced pressure boiling. The height of the coolant above the upper end of the fuel heating part of the core, the position of the opening of each pipe in the reactor pressure vessel is set above the upper end of the fuel heating part. Is a light water reactor. 2. The amount of coolant that can be ensured between the opening position of the pipe connected to the reactor pressure vessel and the upper end of the fuel heat generating portion is set below the opening position of the pipe according to claim 1. A light water reactor characterized by containing 38% or more of the total amount of coolant that can be secured in the reactor pressure vessel. 3. The position of the opening in the reactor pressure vessel of the water injection pipe connected to the reactor pressure vessel by raising the upper plenum according to claim 2, the position of the opening from the upper end of the fuel heating portion A light water reactor characterized by having a height that can secure a coolant of approximately 11.5 m ³ or more between and. 4. The water injection system according to claim 2, wherein the water injection system is composed of a cooling system for reactor isolation cooling and a low pressure water injection system, and the capacity of the low pressure water injection system is about 230.
A light water reactor characterized by having T / Hr or less.