JP2020165660A - Atws countermeasure facility and natural circulation type boiling water reactor including the same - Google Patents

Abstract

To provide a countermeasure facility of anticipated transient without scram (ATWS) and a natural circulation type boiling water reactor including the facility, which improve safety of a plant by efficiently reducing output of all fuel assemblies when ATWS occurs and which do not require reinforcement of a cooling system and high pressure resistance of a reactor pressure vessel and a reactor containment vessel.SOLUTION: An ATWS countermeasure facility includes: communication flow channels 6 which are partially provided outside a reactor pressure vessel 1 and which allow the inside of a chimney 7 and the outside of a shroud wall 4 to communicate with each other; and bypass valves 24 which are provided at the communication flow channels 6 outside the reactor pressure vessel 1 and which control flow of cooling water in the communication flow channels 6.SELECTED DRAWING: Figure 1

Description

The present invention relates to ATWS countermeasure equipment and a natural circulation type boiling water reactor equipped with the same.

As an example of a compact and economical nuclear power plant, Patent Document 1 provides a core composed of a core support plate, an upper lattice plate, and a fuel assembly supported by these at the inner bottom of the reactor pressure vessel, and provides an upper portion. By arranging the control rod guide cylinder and core shroud on the lattice plate and further providing the control rod drive mechanism above it, the control rod can be inserted from the upper part of the core, and the cooling water is cooled by the chimni effect of the control rod guide cylinder. It is stated that it enables natural circulation in the reactor.

JP-A-2002-122686

In a boiling water reactor, steam is generated by boiling cooling water due to the heat generated by the core, and the steam is sent to a turbine to generate electricity.

In a general boiling water reactor, a recirculation pump that circulates water in the reactor pressure vessel and supplies it to the core is provided, and the recirculation pump is operated by electric power to supply cooling water to the core.

On the other hand, in the natural circulation type boiling water reactor, water mixed with steam generated by the heat generated by the core inside the reactor pressure vessel and non-boiling water in the down-kama region outside the shroud wall inside the reactor pressure vessel ( It is a nuclear reactor in which cooling water circulates due to the difference in density (natural circulation force) from water without steam), and has the advantage of not requiring a recirculation pump. Therefore, the cost can be reduced as compared with a general boiling water reactor.

In such a natural circulation type boiling water reactor, for the purpose of increasing the natural circulation force, an area is provided in the upper part of the core and inside the shroud wall described above in which a large number of tubular structures called chimni are lined up. .. By installing the chimni, the area where there is a difference in density inside and outside the shroud wall is expanded by the height of this chimni, and the cooling water flow rate increases.

Boiling water reactors generally have the characteristic that the output increases as the cooling water flow rate increases, and the output decreases as the cooling water flow rate decreases. Therefore, increasing the cooling water flow rate increases the output during operation. Can be increased.

In a nuclear power plant, when it becomes necessary to stop the plant, such as when a part of the plant malfunctions, the fission reaction is stopped by inserting control rods into the core.

In addition, although it is a very low probability, boric acid is introduced into the reactor by a boric acid water injection system as a reactivity control system for the preparation when the control rod insertion fails (hereinafter referred to as ATWS: Anticipated Transient Without Sclam). Inject water to stop the core reaction.

It takes time to complete the injection of boric acid water by the boric acid water injection system as compared with the insertion of the control rods. Therefore, in a conventional boiling water reactor equipped with a recirculation pump, it is necessary to stop the pump and reduce the flow rate of the cooling water flowing through the core. When the flow rate of the cooling water is reduced, the boiling of the cooling water in the core is promoted, and the negative reactivity is applied to the core to reduce the output and alleviate the phenomenon.

On the other hand, since the natural circulation type boiling water reactor does not have a recirculation pump, the cooling water flow rate cannot be controlled to reduce the output. Therefore, in order to prepare for such an event, it is necessary to strengthen the boric acid water injection system, strengthen the cooling system, and increase the pressure resistance of the reactor pressure vessel and the reactor containment vessel. Is costly.

Therefore, in order to eliminate the need for these measures and reduce costs, there is a mechanism as described in Patent Document 1 as a mechanism for reducing the cooling water flow rate and the output when ATWS occurs.

In Patent Document 1, a control rod guide cylinder is provided in the upper part of the core, and this cylinder is used as a chimni. When ATWS occurs, the cooling water is bypassed from the inside of the chimni to the down-kama region to reduce the cooling water flow rate when ATWS occurs. The output is decreasing.

In a naturally circulating boiling water reactor, in order to reduce the cooling water flow rate and reduce the output when ATWS occurs, in Patent Document 1, the cooling water bypasses the chimni that also serves as the control rod guide tube. This reduces the cooling water flow rate.

Therefore, Patent Document 1 describes that a flow path such as a pipe penetrating from the inside to the outside of the shroud head portion is provided, and a valve with a built-in reactor pressure vessel that can be arbitrarily opened is attached to the downside of this flow path. Has been done.

However, in Patent Document 1, a valve with a built-in reactor pressure vessel that determines the flow rate of cooling water flowing through the bypass flow path is installed in the reactor pressure vessel. However, since high-temperature and high-pressure cooling water is flowing in the reactor pressure vessel, it is necessary to protect the valve from this cooling water. However, in order to maintain the reliability of the valve, a large-scale protective device or the like is required, and it is very difficult to protect the valve. In addition, there is a problem that some separate measures must be taken so that the presence of the reactor pressure vessel built-in valve arranged in the pressure vessel does not obstruct the flow of cooling water.

Therefore, in the present invention, the output of the entire fuel assembly is efficiently reduced when ATWS occurs to improve the safety of the plant, the cooling system is strengthened, and the pressure resistance of the reactor pressure vessel and the reactor containment vessel is increased. It is an object of the present invention to provide an ATWS countermeasure facility that does not require the above and a natural circulation type boiling water reactor equipped with the same.

The present invention includes a plurality of means for solving the above problems, for example, a core loaded with a fuel assembly and an upper portion of the core that generates heat due to a nuclear split reaction in the fuel assembly. A shroud wall in which the cooling water flows vertically upward and the cooling water flows downward in the vertical direction inside the shroud wall, a chimni formed in the upper region of the core, and the core are included. It is an ATWS countermeasure facility in a natural circulation type boiling water type reactor equipped with a reactor pressure vessel, and a part thereof is arranged outside the reactor pressure vessel, and inside the chimni and the shroud wall. It is provided with a communication flow path that communicates with the outside and a bypass valve that is arranged in the outer portion of the communication flow path and controls the flow of cooling water flowing through the communication flow path. It is characterized by.

According to the present invention, the output of the entire fuel assembly is efficiently reduced when ATWS occurs, the safety of the plant is improved, the cooling system is strengthened, and the pressure resistance of the reactor pressure vessel and the reactor containment vessel is increased. Can be eliminated, so the cost can be reduced. Issues, configurations and effects other than those mentioned above will be clarified by the description of the following examples.

It is a figure which shows the outline of the main system of the natural circulation type boiling water reactor which concerns on Example 1 of this invention. FIG. 1 is a cross-sectional view taken along the line AA'in FIG. It is a schematic diagram which shows the state of the opening / closing mechanism of the bypass valve which concerns on Example 1 of this invention in a normal state. It is a schematic diagram which shows the state at the time of ATWS of the opening / closing mechanism of the bypass valve which concerns on Example 1 of this invention. It is a cross-sectional view of AA' of the part shown in FIG. 1 in the natural circulation type nuclear reactor which concerns on Example 2 of this invention. It is a cross-sectional view of AA' of the part shown in FIG. 1 in the natural circulation type nuclear reactor which concerns on Example 3 of this invention. It is a cross-sectional view of AA' of the part shown in FIG. 1 in the natural circulation type nuclear reactor which concerns on Example 4 of this invention. It is a cross-sectional view of AA' of the part shown in FIG. 1 in the natural circulation type nuclear reactor which concerns on Example 5 of this invention.

Hereinafter, an example of the ATWS countermeasure equipment of the present invention and a naturally circulating boiling water reactor equipped with the same will be described with reference to the drawings.

<Example 1>
The ATWS countermeasure equipment of the present invention and the first embodiment of the natural circulation type boiling water reactor equipped with the same will be described with reference to FIGS. 1 to 4. FIG. 1 is a main system diagram of a naturally circulating boiling water reactor according to the first embodiment. FIG. 2 is a cross-sectional view of the naturally circulating boiling water reactor according to the first embodiment. 3 and 4 are schematic views showing an opening / closing mechanism of the bypass valve according to the first embodiment.

In the natural circulation type boiling water reactor 100 shown in FIG. 1, a core 2 in which a plurality of fuel assemblies (omitted for convenience of illustration) are loaded in a grid pattern is contained in the reactor pressure vessel 1. A main steam pipe 15 and a water supply pipe (not shown) are connected to the reactor pressure vessel 1.

In the reactor pressure vessel 1 of this embodiment, steam is generated by boiling the cooling water that has flowed into the core 2 by the heat generated by the nuclear fission generated in the fuel assembly in the core 2.

The generated steam becomes a two-phase flow mixed with water and flows into the separator 17 through the chimni 7 and the stand pipe 16 formed in the upper region of the core 2. In the separator 17, water and steam are separated (gas-liquid separation) by centrifugal force. Depending on the design, there is a furnace type without this separator, but the present invention can be applied to such a furnace type.

The water separated by the separator 17 flows downward through the gap (downside region) between the shroud wall 4 and the reactor pressure vessel 1, and is supplied from outside the reactor pressure vessel 1 via a water supply pipe (not shown) on the way. Mixed with water supply. After that, it flows into the core 2 again from below via the lower plenum 10.

As described above, in this embodiment, the waste water flows upward in the vertical direction inside the shroud wall 4, and the cooling water flows downward in the vertical direction outside the shroud wall 4.

On the other hand, the steam accompanied by the fine droplets separated by the separator 17 is guided to a turbine (not shown) via the main steam pipe 15 after removing almost all the droplets with the dryer 9, and power is generated. Will be.

Here, in the natural circulation type boiling water reactor 100 shown in FIG. 1, unlike a general boiling water reactor, there are a jet pump and an internal pump (also referred to as RIP) that supply cooling water to the core 2. do not do.

Boiling water reactors have the advantage that the core is easier to cool by natural circulation than pressurized water reactors because the average density of cooling water changes significantly due to boiling. The average water density of the gas-liquid two-phase flow in which steam and water are mixed in the region inside the shroud wall 4 is smaller than the water density of the single-phase water in the down-kama region outside the shroud wall 4. Therefore, the cooling water can be supplied to the core 2 without using a pump by using the head difference between the inside and outside of the shroud wall 4 as a driving force.

In this way, the cooling water can be supplied to the core 2 by the natural circulation force, but the flow rate of the cooling water needs to be a flow rate capable of sufficiently removing the heat generated in the core 2.

Here, a pressure loss occurs when the cooling water flows through the core 2, but the natural circulation flow rate, which is the flow rate of the cooling water flowing through the core, is the driving force due to the head difference caused by the density difference between the inside and outside of the shroud wall 4 and the above. It is determined by the balance of pressure loss. In general, it is known that it is difficult to secure a sufficient cooling water flow rate only by the driving force caused by the head difference corresponding to the core height.

Therefore, in the natural circulation type boiling water reactor 100, in general, in order to secure the flow rate required for removing heat from the core 2, the chimni 7 is installed above the core 2 and the shroud wall 4. ing.

By installing such a chimni 7, in addition to the density difference between the inside and outside of the shroud wall 4 for the height of the core, the cooling water density between the inside of the chimni 7 and the down-kama area outside the chimni 7 by the height of the chimni 7. The difference can also be used as a natural circulation force. Therefore, the flow rate of the cooling water is increased, and the core 2 can be sufficiently cooled.

By utilizing such natural circulation power, it is possible to eliminate the need for a recirculation pump for supplying cooling water, reduce costs, and eliminate the possibility that a failure of the recirculation pump will adversely affect the plant. ..

The output of the core 2 in the naturally circulating boiling water reactor 100 having the above structure is adjusted by inserting and pulling out the control rods 5 from below the reactor pressure vessel 1.

In addition, in the natural circulation type boiling water reactor 100, in the case of a strong earthquake, for example, the power supply supplied from the outside is lost, the piping is broken, the turbine has a problem, etc. Even if a problem occurs, the reactor is stopped by rapidly inserting the control rod 5. When such a situation occurs, the main steam isolation valve 8 is closed to avoid the risk of radioactive material leaking to the outside, and the steam containing radioactive material is prevented from leaking to the outside of the reactor containment vessel 12. To do.

However, even when the control rod 5 is inserted and the reactor is shut down, steam is generated in the core 2 due to the decay heat of the fuel. Further, since the main steam isolation valve 8 is closed, the pressure in the reactor pressure vessel 1 rises.

In such a case, the pressure rise of the reactor pressure vessel 1 is detected, the emergency condenser start valve 20 is opened, and the steam of the reactor pressure vessel 1 flows into the emergency condenser 18. The steam is cooled by the emergency condenser pool water 19 and returned to water. After returning to water, it returns to the inside of the reactor pressure vessel 1 by gravity, contributes to the cooling of the core 2 again, and the pressure of the reactor pressure vessel 1 decreases.

Since the temperature of the emergency condenser pool water 19 is low at the initial stage of starting the emergency condenser 18, the cooling capacity is limited until the emergency condenser pool water 19 starts boiling. .. In such a case, if the pressure of the reactor pressure vessel 1 rises further, the main steam relief safety valve 21 opens to guide the steam of the reactor pressure vessel 1 to the pressure suppression chamber 23. As a result, steam is released through the quencher 22 into the pressure suppression pool water 13 in the pressure suppression chamber 23 and condensed to suppress the pressure rise in the reactor pressure vessel 1.

In a general design, when a failure occurs in the plant, the control rods 5 are rapidly inserted by water pressure. However, although the probability of occurrence is very low, it is necessary to prepare for an event (ATWS) in which the insertion of the control rod 5 fails due to a malfunction of the detector or a trouble of the drive mechanism due to water pressure.

Therefore, in preparation for such an event, the control rod 5 is electrically inserted, or boric acid water is injected into the core to stop the reaction (boric acid water injection system, SLC: Standby Liquid Control System, etc.). There are preparations such as).

However, since these operations take longer than the insertion of control rods by water pressure, the high output continues for a while, and the pressure of the reactor pressure vessel 1 is also compared with the case where the control rods are successfully inserted. It stays high for a while.

In a boiling water reactor equipped with a recirculation pump as in the past, the recirculation pump is stopped in parallel with the insertion of electric control rods and the injection of boric acid water to reduce the flow rate of cooling water flowing through the core. , The output can be reduced.

However, since the natural circulation type boiling water reactor 100 is not equipped with a recirculation pump, it is equipped with ATWS countermeasure equipment in order to prevent damage to the plant due to the continuous high output for a while. The conventional ATWS countermeasure equipment for naturally circulating boiling water reactors has taken measures to increase the capacity of the above-mentioned emergency condenser and increase the pressure resistance of the reactor pressure vessel and reactor containment vessel. There was a problem that these measures were costly.

On the other hand, in this embodiment, as shown in FIGS. 1 and 2, as ATWS countermeasure equipment, the inside of the chimni 7 and the outside of the chimni 7 located above the inner peripheral side of the shroud wall 4 (outside of the shroud wall 4). A communication flow path 6 for communicating with the down-commercial region of As shown in FIG. 2, it is assumed that a part of the communication flow path 6 is arranged outside the reactor pressure vessel 1.

Further, a bypass valve 24 that controls the flow of cooling water flowing through the communication flow path 6 is arranged in the outer portion of the communication flow path 6 of the reactor pressure vessel 1.

By arranging a plurality of communication flow paths 6 when the reactor pressure vessels 1 are viewed from the cross-sectional direction as shown in FIG. 2, the diameter of each communication flow path 6 can be reduced and the cooling water can be prevented from being biased. You can also. It is sufficient that at least one communication flow path 6 is provided.

The bypass valve 24 has a structure in which the naturally circulating boiling water reactor 100 is closed during normal operation and opened in the unlikely event that ATWS occurs.

When the bypass valve 24 is opened, the pressure inside and outside the chimni 7 is equalized through the communication flow path 6, and the head difference between the inside and outside of the chimni 7 disappears, so that the effect of increasing the cooling water flow rate by the chimni 7 disappears. As a result, the flow rate of the cooling water flowing through the core 2 is reduced, and the output can be reduced.

Details of the structure of the bypass valve 24 will be described with reference to FIGS. 3 and 4.

As shown in FIG. 3, the valve body 26 of the bypass valve 24 is pressed against the valve seat 33 by the valve spring 27 to close the communication flow path 6. Further, the valve body 26 is connected to the piston 28, and a pressure transmission pipe 25 communicating with the reactor pressure vessel 1 is connected to one side of the piston 28 so that the pressure of the reactor pressure vessel 1 is applied to the piston 28. It is desirable that the piston 28 of the bypass valve 24 be opened so that the pressure outside the reactor pressure vessel 1 is applied to the side opposite to the side where the pressure of the reactor pressure vessel 1 is applied.

As a result, if ATWS occurs with a probability and the pressure inside the reactor pressure vessel 1 rises and exceeds the pressing force by the valve spring 27, the piston 28 moves and the bypass valve 24 moves as shown in FIG. The valve body 26 is separated from the valve seat 33 and can be opened.

The pipe penetrating the reactor pressure vessel 1 needs to be provided with an isolation valve in order to prevent the cooling water from flowing out of the system from the reactor pressure vessel 1 when the pipe breaks.

Therefore, isolation valves 35 are installed at all points in the communication flow path 6 near the reactor pressure vessel 1. The isolation valve 35 needs to be prepared with a highly reliable valve so that it can operate in the unlikely event of a pipe breakage, and it is also necessary to perform sufficient maintenance and the like.

Next, the effect of this embodiment will be described.

The above-mentioned natural circulation type boiling water reactor 100 of the first embodiment of the present invention is arranged above the core 2 loaded with the fuel assembly and the core 2 generating heat due to the nuclear split reaction in the fuel assembly. A shroud wall 4 in which cooling water flows upward in the vertical direction and downward in the vertical direction on the outside, a chimni 7 formed in the upper region of the core 2, and a reactor pressure containing the core 2. It is equipped with a container 1 and ATWS countermeasure equipment. Of these, the ATWS countermeasure equipment is partly arranged outside the reactor pressure vessel 1, and of the communication flow path 6 communicating between the inside of the chimni 7 and the outside of the shroud wall 4, and the communication flow path 6. It is provided with a bypass valve 24 which is arranged in an outer portion of the reactor pressure vessel 1 and controls the flow of cooling water flowing through the communication flow path 6.

By adopting the above structure, the bypass valve 24 is opened and passive as the phenomenon occurs, even in the natural circulation type boiling water reactor and in the case of ATWS where the control rod insertion fails. The cooling water flow rate can be reduced. Therefore, the output of the entire fuel assembly can be automatically reduced, and the safety can be improved. In addition to this, it is not necessary to strengthen the safety system for preparing for ATWS and to increase the pressure resistance of the reactor pressure vessel and the reactor containment vessel, and it is possible to reduce the cost.

Further, in Patent Document 1 described above, the valve with a built-in reactor pressure vessel is installed inside the reactor pressure vessel, but as in the present invention, the bypass valve 24 is outside the reactor pressure vessel 1 in the communication flow path 6. Many measures to improve reliability because it is not necessary to protect the valve from the cooling water and it is not necessary to take any separate measures so as not to obstruct the flow of the cooling water because it is placed in the part of. The effect is that there is no need to apply.

Further, since the bypass valve 24 is closed during normal operation and is configured to be opened in response to an increase in pressure inside the reactor pressure vessel 1, it is passively operated without any operator operation. The valve opens during ATWS, and the flow rate can be reduced to reduce the output, which can further improve safety.

<Example 2>
The ATWS countermeasure equipment of Example 2 of the present invention, which is one of the preferred examples for achieving the above-mentioned object, and the naturally circulating boiling water reactor equipped with the equipment will be described with reference to FIG. FIG. 5 is a cross-sectional view of the naturally circulating boiling water reactor according to the second embodiment.

Also in the second embodiment, the configuration of the entire plant, the opening / closing mechanism of the bypass valve 24, and the like are the same as those in the first embodiment, and only the differences from the first embodiment will be described here. The same shall apply in the following examples.

As shown in FIG. 5, in the natural circulation type boiling water reactor of this embodiment, the chimni side header 29 is provided at the inner end of the chimni 7 and the outer end of the shroud wall 4 in the communication flow path 6A. A down-kama side header 30 is provided inside the down-kama area 14.

Further, a bypass valve 24 is provided in the communication flow path 6A connecting both headers.

The headers 29 and 30 are not limited to the cases where the headers 29 and 30 are provided on both sides of the end of the communication flow path 6A on the chimni 7 side and the outer end of the communication flow path 6A on the shroud wall 4, but on the chimni 7 side of the communication flow path 6A. It can be provided at either the end portion or the outer end portion of the shroud wall 4 of the communication flow path 6A.

Other configurations and operations are substantially the same as those of the ATWS countermeasure equipment of Example 1 described above and the naturally circulating boiling water reactor equipped with the equipment, and details thereof will be omitted.

The ATWS countermeasure equipment of Example 2 of the present invention and the naturally circulating boiling water reactor provided with the same are almost the same as the ATWS countermeasure equipment of Example 1 and the naturally circulating boiling water reactor provided with the same. A similar effect can be obtained.

Further, the headers 29 and 30 are further provided on at least one of the end of the communication flow path 6A on the chimni 7 side and the outer end of the shroud wall 4 of the communication flow path 6A, so that the cooling water flow rate can be increased. While preventing bias, the communication flow path 6A penetrating the wall surface of the reactor pressure vessel 1 can be minimized as compared with the first embodiment. Therefore, the number of isolation valves 35 can be reduced to further reduce costs, and the number of through pipes themselves can be reduced to further reduce the possibility of breakage.

<Example 3>
The ATWS countermeasure equipment of Example 3 of the present invention, which is one of the preferred examples for achieving the above-mentioned object, and the naturally circulating boiling water reactor equipped with the equipment will be described with reference to FIG. FIG. 6 is a cross-sectional view of the naturally circulating boiling water reactor according to the third embodiment.

As shown in FIG. 6, in the natural circulation type boiling water reactor of this embodiment, the wall surface of the chimni 7 in the first embodiment is omitted, and the shroud wall 4B itself is extended above the core 2 to form the chimni 7B. The structure will be used.

Other configurations and operations are substantially the same as those of the ATWS countermeasure equipment of Example 1 described above and the naturally circulating boiling water reactor equipped with the equipment, and details thereof will be omitted.

The ATWS countermeasure equipment of Example 3 of the present invention and the naturally circulating boiling water reactor provided with the same are almost the same as the ATWS countermeasure equipment of Example 1 and the naturally circulating boiling water reactor provided with the same. A similar effect can be obtained.

Further, since the shroud wall 4B extends to the upper side of the core 2 and forms the chimni 7B, the number of structures arranged in the reactor pressure vessel 1 can be reduced, further cost reduction. Can be planned.

In this embodiment as well, a structure having a header can be used as in the second embodiment described above.

<Example 4>
The ATWS countermeasure equipment of Example 4 of the present invention, which is one of the preferred examples for achieving the above-mentioned object, and the naturally circulating boiling water reactor equipped with the equipment will be described with reference to FIG. FIG. 7 is a cross-sectional view of the naturally circulating boiling water reactor according to the fourth embodiment.

As shown in FIG. 7, in the natural circulation type boiling water reactor of this embodiment, the chimni dividing plate 31 is arranged inside the chimni 7C, so that the reactor is divided into a plurality of sections. Further, the chimuni 7C of any of the divided sections is communicated to the outside of the shroud wall 4 by the communication flow path 6C.

Further, in the method of dividing the chimni 7C, as shown in FIG. 7, a part of the outer peripheral wall of the divided area is formed by the shroud wall 4, that is, the divided area is formed of the shroud wall 4 via the shroud wall 4. It is divided so that there are no sections that are not adjacent to the outer circumference.

Other configurations and operations are substantially the same as those of the ATWS countermeasure equipment of Example 1 described above and the naturally circulating boiling water reactor equipped with the equipment, and details thereof will be omitted.

The ATWS countermeasure equipment of Example 4 of the present invention and the naturally circulating boiling water reactor provided with the same are almost the same as the ATWS countermeasure equipment of Example 1 and the naturally circulating boiling water reactor provided with the same. A similar effect can be obtained.

Further, the chimni 7C is divided into a plurality of sections, and the chimni 7C in any of the divided sections is communicated to the outside of the shroud wall 4 by the communication flow path 6C, so that the inside of the chimni 7C during normal operation is used. The volume ratio of bubbles (called the void ratio) can be increased. Therefore, when the void ratio inside the chimni 7C increases, the density difference between the inside and outside of the chimni 7C becomes large, and the flow rate of the cooling water increases, so that the output can be effectively reduced.

That is, since the increase in the cooling water flow rate per the length of the chimni 7C is large, the length of the chimni 7C can be reduced, and the height of the reactor pressure vessel 1 containing the chimni 7C can also be reduced. As a result, further cost reduction can be achieved.

In Patent Document 1 described above, since the chimni also serves as a control rod guide tube, almost the same number of chimni as the fuel assembly loaded in the core is required, and the control rods need to pass between the chimni 7. was there. Therefore, only the chimni installed on the outermost circumference can bypass the cooling water in the chimni and flow to the down-kama area outside the chimni installation space, and this effect can be obtained for other chimni. There was a problem that the effect of reducing the cooling water flow rate was limited.

Further, in Patent Document 1, when the chimni and the fuel assembly have a one-to-one correspondence, the output of only the fuel assembly corresponding to the bypassed chimni is reduced, and the output reduction of the other fuel assemblies is sufficient. There was a possibility that it would not be done.

On the other hand, as in the present embodiment, the chimni 7C of each of the divided sections is communicated from any of the sections because a part of the outer peripheral wall of the divided sections is formed by the shroud wall 4. A structure can be adopted in which the flow path 6 can be pulled out and the flow rate of the cooling water can be stably reduced when ATWS occurs.

In this embodiment, the chimni dividing plate 31 can be directly connected to the inner wall of the shroud wall 4. Further, the chimni 7C of any of the divided sections is not limited to the case where all of the divided sections are connected to the outer peripheral side by the dedicated communication flow path 6, and each section is connected with a header as in the second embodiment. It can be connected to form one communication flow path. Further, as in the third embodiment, the shroud wall 4 can be extended to the upper side and used as the wall surface of the chimni 7.

<Example 5>
The ATWS countermeasure equipment of Example 5 of the present invention, which is one of the preferred examples for achieving the above-mentioned object, and the naturally circulating boiling water reactor equipped with the equipment will be described with reference to FIG. FIG. 8 is a cross-sectional view of the naturally circulating boiling water reactor according to the fifth embodiment.

As shown in FIG. 8, in the natural circulation type boiling water reactor of this embodiment, the flow rate of the cooling water flowing through the communication flow path 6D is set at a position parallel to the bypass valve 24 in the communication flow path 6D. A flow control valve 32 for controlling is installed.

The flow rate control valve 32 has a structure that can be opened by an operator's operation when the occurrence of ATWS is detected by electric drive or the like. Further, even during normal operation, the operator can freely control the flow rate of the cooling water by opening and closing the flow rate control valve 32.

Other configurations and operations are substantially the same as those of the ATWS countermeasure equipment of Example 1 described above and the naturally circulating boiling water reactor equipped with the equipment, and details thereof will be omitted.

The ATWS countermeasure equipment of Example 5 of the present invention and the naturally circulating boiling water reactor provided with the same are almost the same as the ATWS countermeasure equipment of Example 1 and the naturally circulating boiling water reactor provided with the same. A similar effect can be obtained.

Generally, in a boiling water reactor, the output can be adjusted by controlling the flow rate of cooling water. As a result, the amount of power supplied can be controlled according to changes in power demand.

On the other hand, in a naturally circulating boiling water reactor, the flow rate of cooling water cannot be controlled, so it is difficult to adjust the output using the flow rate.

However, as in this embodiment, the flow control valve 32 which is arranged in parallel with the bypass valve 24 in the communication flow path 6D and controls the flow rate of the cooling water flowing through the communication flow path 6D is further provided. , The output can be adjusted even during normal operation. Further, by providing the bypass valve 24, even if the operator does not operate the flow rate control valve 32 when ATWS occurs, the bypass valve 24 passively opens, so that the cooling water flow rate is reduced and the output is reduced. The effect that it can be made is obtained.

The mode in which the flow rate control valve 32 is provided as in this embodiment can also be adopted in any one of the natural circulation type boiling water reactors of Examples 2 to 4.

<Others>
The present invention is not limited to the above examples, and includes various modifications. The above-mentioned examples have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the described configurations.

1: Reactor pressure vessel 2: Core 4, 4B: Shroud wall 5: Control rods 6, 6A, 6C, 6D: Communication flow paths 7, 7B, 7C: Chimni 8: Main steam isolation valve 9: Dryer 10: Lower plenum 12: Reactor vessel 13: Pressure suppression pool water 14: Downside area 15: Main steam pipe 16: Stand pipe 17: Separator 18: Emergency condenser 19: Emergency condenser Pool water 20: Emergency condenser Condenser start valve 21: Main steam relief safety valve 22: Quencher 23: Pressure suppression chamber 24: Bypass valve 25: Pressure transmission pipe 26: Valve body 27: Valve spring 28: Piston 29: Chimuni side header 30: Down cami side header 31: Chimuni Dividing plate 32: Flow control valve 33: Valve seat 35: Isolation valve 100: Natural circulation type boiling water reactor

Claims (8)

The core loaded with the fuel assembly and
A shroud wall located above the core that is generating heat due to the fission reaction in the fuel assembly, and inside which the cooling water flows upward in the vertical direction and outside the shroud wall in which the cooling water flows downward in the vertical direction.
Chimuni formed in the upper region of the core and
It is an ATWS countermeasure facility in a natural circulation type boiling water reactor equipped with a reactor pressure vessel containing the core.
A communication flow path that is partially arranged outside the reactor pressure vessel and communicates between the inside of the chimni and the outside of the shroud wall.
A naturally circulating boiling water reactor, which is arranged in an outer portion of the communication flow path and controls the flow of cooling water flowing through the communication flow path, and is provided with a bypass valve. ATWS countermeasure equipment in a nuclear reactor. In the ATWS countermeasure equipment according to claim 1,
The ATWS countermeasure facility is characterized in that the bypass valve is closed during normal operation and is configured to be opened in response to an increase in pressure inside the reactor pressure vessel. In the ATWS countermeasure equipment according to claim 1,
An ATWS countermeasure facility characterized in that a header is further provided at at least one of the inner end of the chimni of the communication flow path and the outer end of the shroud wall of the communication flow path. In the ATWS countermeasure equipment according to claim 1,
An ATWS countermeasure facility characterized in that the shroud wall extends above the core and forms the chimni. In the ATWS countermeasure equipment according to claim 1,
The chimni is divided into a plurality of sections.
ATWS countermeasure equipment characterized in that the inside of the chimni of any of the divided sections is communicated to the outside of the shroud wall by the communication flow path. In the ATWS countermeasure equipment according to claim 5,
The ATWS countermeasure facility for each of the divided compartments is characterized in that a part of the outer peripheral wall of the divided compartment is formed by the shroud wall. In the ATWS countermeasure equipment according to claim 1,
An ATWS countermeasure facility comprising a flow rate control valve which is arranged in parallel with the bypass valve in the communication flow path and controls the flow rate of cooling water flowing through the communication flow path. A naturally circulating boiling water reactor provided with the ATWS countermeasure equipment according to any one of claims 1 to 7.

Images