JP2011226783A - Nuclear power plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the rise width of the reactor pressure in case of occurrence of a load loss event.SOLUTION: In an atomic power plant which is provided with a containment vessel containing a nuclear reactor, a main steam piping connecting the nuclear reactor to a turbine, a condenser which condenses steam emitted from the turbine, a feedwater pump which drives cooling water supplied by the condenser to the nuclear reactor, separation valves placed before and after a penetration part of the main steam piping which penetrates the containment vessel, a relief safety valve placed on the main steam piping between the separation valves and the nuclear reactor, a steam adjustment valve placed on the main steam piping between the separation valves and the turbine, a turbine bypass piping that connects the main steam piping between the steam adjustment valve and the separation valves to the condenser, and a turbine bypass valve placed on the turbine bypass piping, a turbine bypass safety valve which is opened by pressure difference between the upstream and the downstream is provided on the main steam piping between the steam adjustment valve and the separation valves, and emits steam into the condenser.

Description

  The present invention relates to a boiling water nuclear power plant.

  In boiling water nuclear power plants, steam generated in a nuclear reactor is supplied to a high-pressure turbine and a low-pressure turbine through main steam piping, and these turbines are rotated to generate electricity. The steam exhausted from the low-pressure turbine is condensed into water by the condenser.

  In such a boiling water nuclear power plant, when the reactor pressure rises, the steam in the core portion is compressed, the steam volume ratio becomes smaller, the neutron deceleration is promoted, and the core output may increase.

  A typical abnormal transient that can cause such a phenomenon is a load loss event (also called a load shedding event). The load loss event is an event in which the load on the generator is lost due to disconnection of the transmission line.

  When a load loss event occurs, the rotational speed of the turbine is increased because the rotational resistance of the turbine due to the generator decreases. In order to avoid damage to the turbine due to an increase in the rotational speed of the turbine, the steam control valve provided at the turbine inlet is closed rapidly to protect the turbine. When the supply of steam to the turbine is stopped, an increase in the rotational speed of the turbine is avoided, but the destination of the steam generated in the reactor is eliminated, and the reactor pressure increases.

  In response to this increase in reactor pressure, during a load loss event, the turbine bypass valve that normally directs steam generated in the reactor to the condenser without passing through the turbine is opened. Thereby, the pressure rise of a nuclear reactor is suppressed.

  On the other hand, the reactor safety measures also assume that the turbine bypass valve will fail to open, and in this case, the safety valve function of the relief safety valve will eventually operate to increase the reactor pressure. Suppress.

  However, the relief safety valve is a valve installed in the reactor containment vessel, and when it is opened, radioactive material is released into the containment vessel. As a post-measure, it may be necessary to perform cleaning for maintenance work.To prevent the relief safety valve from opening due to small pressure fluctuations, the set value of the release pressure for the safety valve function of the relief safety valve is It is set to a high value within a range that can sufficiently secure the property. In the event of a load loss event, it is essential that the safety of the reactor can be ensured even if the turbine bypass valve is inoperative.

  For the purpose of making the reactor pressure rise at the time of a load loss event smaller than that of the current system, it is proposed in Patent Document 1 to install a steam escape control valve inside the containment vessel.

  Further, Patent Document 2 proposes to install a new turbine bypass pipe connected from the low-pressure turbine inlet to the condenser for the purpose of ensuring turbine protection when a load loss event occurs.

JP-A-60-36987 JP-A-5-65805

  The techniques described in Patent Documents 1 and 2 are effective when the turbine bypass valve is opened, but the reactor pressure increases when the load loss event occurs when the turbine bypass valve fails to open. In this case, it does not contribute to the suppression of the reactor pressure rise.

  On the other hand, it is indispensable to assume that the turbine bypass valve does not operate in terms of reactor safety measures. If the increase in reactor pressure in the event of failure to open the turbine bypass valve can be suppressed, the increase in reactor power at the time of a load loss event and the associated decrease in thermal margin can be suppressed, and further increase in reactor heat output can be achieved. It becomes.

  In view of the above, an object of the present invention is to provide means capable of suppressing the increase in the reactor pressure even when the opening of the turbine bypass valve fails when a load loss event occurs.

  In order to achieve the above object, the present invention includes a containment vessel including a nuclear reactor, a main steam pipe connecting the nuclear reactor and the turbine, a condenser for condensing the steam discharged from the turbine, and an atom from the condenser. A feed water pump for driving the cooling water supplied to the reactor, an isolation valve installed before and after the main vessel piping containment, and a relief safety valve installed on the main steam piping between the isolation valve and the reactor A steam control valve installed on the main steam pipe between the isolation valve and the turbine, a turbine bypass pipe for connecting from the main steam pipe between the steam control valve and the isolation valve to the condenser, and a turbine bypass pipe In a nuclear power plant having a turbine bypass valve installed above, a turbine bypass safety valve is provided on the main steam pipe between the steam control valve and the isolation valve, and is opened by a pressure difference between the upstream side and the downstream side. The vapor emission destination Zenben to the condenser side.

  Moreover, it is good to connect the downstream side of a turbine bypass safety valve to turbine bypass piping.

  Further, it is preferable that the opening set pressure of the turbine bypass safety valve is smaller than the minimum value of the opening set pressure of the safety valve function of the relief safety valve.

  The turbine bypass safety valve is preferably a valve that opens without an external driving force or an open signal due to a pressure difference between the upstream side and the downstream side of the valve.

  In order to achieve the above object, the present invention includes a containment vessel including a nuclear reactor, a main steam pipe connecting the nuclear reactor and the turbine, a condenser for condensing the steam discharged from the turbine, and an atom from the condenser. A feed water pump for driving the cooling water supplied to the reactor, an isolation valve installed before and after the main vessel piping containment, and a relief safety valve installed on the main steam piping between the isolation valve and the reactor In a nuclear power plant having a steam control valve installed on the main steam pipe between the isolation valve and the turbine, a turbine bypass connecting the main steam pipe between the steam control valve and the isolation valve to the condenser A turbine bypass valve, which is a control valve, and a turbine bypass safety valve, which is a non-control valve, are juxtaposed on the pipe due to a pressure difference between the upstream side and the downstream side.

  According to the present invention, the safety margin of the nuclear power plant when a load loss event occurs is increased, and the increased safety margin can be utilized to improve the heat output.

It is a block diagram of the boiling water nuclear power plant of this invention. It is a block diagram of the boiling water nuclear power plant of this invention.

  The present inventors examined means that can suppress the increase in the reactor pressure even when the opening of the turbine bypass valve fails when a load loss event occurs.

  As a result, we focused on the turbine bypass valve that guides steam from the reactor to the condenser without going through the turbine. However, since this turbine bypass valve is used when the nuclear reactor is started, it is necessary to use a control valve that can be opened and closed by external power. For this reason, in order to use as a means capable of suppressing the increase in the reactor pressure, it is essential to consider the loss of external power and the failure of the control system from the viewpoint of ensuring the safety of the reactor. That is, a countermeasure against the malfunction is also required for the turbine bypass valve.

  On the other hand, the relief safety valve installed upstream (reactor side) from the isolation valve can be reliably operated when the pressure rises. However, it is necessary to set the open pressure to a pressure that is higher than the pressure loss of the main steam pipe from the turbine to the reactor, and there is a problem that radioactive material is released into the containment vessel at the time of release.

  The present inventors have studied a reactor overpressure prevention valve that can operate reliably when the pressure rises and can set the open pressure low, and as a result, a turbine is installed on the main steam pipe between the isolation valve and the main steam control valve. A new finding was found that a bypass safety valve should be installed.

  Thereby, even if it is a case where opening of a turbine bypass valve fails at the time of load loss event occurrence, the rise of a reactor pressure can be controlled more effectively than the case where only the relief safety valve installed in the conventional containment vessel is used. .

  Examples of the present invention reflecting the above examination results will be described below.

  A boiling water nuclear power plant that is a preferred embodiment of the present invention will be described with reference to FIG.

  A boiling water nuclear power plant is roughly divided into a reactor-side facility and a turbine-side facility, and a steam system and a water supply system are installed between them. The reactor side equipment accommodates the reactor 2 which is a steam generator in the containment vessel 3, and the turbine side equipment includes a high pressure turbine 5, a low pressure turbine 6, a condenser 7, and the like.

  The feed water system supplies the condensate from the condenser 7 as feed water to the nuclear reactor through the feed water heater 8 and the feed water pump 9.

  On the other hand, the steam system includes a main steam pipe 4, a turbine bypass pipe 13, and the like, and valve devices having various functions that influence the reactor pressure are installed on these pipes. The locations and functions of these valves are as follows.

  Steam control valve 12: It is installed at the inlet of the high-pressure turbine 5 and adjusts the amount of steam supplied to the high-pressure turbine 5.

  Isolation valve 10: A main steam pipe 4 connected from the nuclear reactor 2 to the high-pressure turbine 5 is installed before and after a portion penetrating the containment vessel 3. When the main steam pipe 4 outside the reactor containment vessel 3 is broken, the isolation valve 10 is closed to prevent the radioactive material inside the reactor from being continuously released from the break opening outside the containment vessel.

  Relief safety valve 11: installed between the reactor 2 and the isolation valve 10. When the pressure of the nuclear reactor 2 rises excessively, the relief safety valve 11 is opened to release the steam inside the nuclear reactor 2 into the containment vessel 3 to suppress the pressure rise of the nuclear reactor 2. Since the vapor | steam discharge | released through the relief safety valve 11 is confined in the storage container 3, it is not discharge | released outside. The safety valve 11 is located upstream of the isolation valve 10 so that the steam discharge destination from the safety valve 11 is inside the containment vessel 3 and the relief safety valve 11 operates even when the isolation valve 10 is closed. 3 must be installed inside. The relief valve 11 is a relief valve that detects an increase in the pressure of the nuclear reactor 2 and receives an opening signal transmitted from the control system and opens by electric drive or high-pressure gas drive, and the relief valve does not operate. This is a valve that combines a safety valve that opens without a driving force or an open signal from the outside due to the differential pressure between the upstream side and downstream side of the valve when the reactor pressure becomes higher.

  Turbine bypass valve 14: installed on a turbine bypass pipe 13 that extracts steam from the main steam pipe 4 between the isolation valve 10 and the steam control valve 12 and sends the steam to the condenser 7. Although the turbine bypass valve 14 is normally closed, when the steam control valve 4 is closed, the turbine bypass valve 14 is opened, and the steam in the main steam pipe 4 is released to the condenser 7. When the isolation valve 10 is open, the pressure increase in the reactor can also be suppressed by opening the turbine bypass valve 14.

  The apparatus configuration described above is provided in a conventional boiling water nuclear power plant. In the boiling water power plant of this embodiment, the main steam pipe 4 between the steam control valve 12 and the isolation valve 10 is further provided. A turbine bypass safety valve 15 is installed above the steam discharge destination of the turbine bypass safety valve 15 as the condenser 7.

  The installation position of the turbine bypass safety valve 15 on the main steam pipe 4 may be upstream or downstream of the installation position of the turbine bypass pipe 13 on the main steam pipe 4. Further, since the turbine bypass safety valve 15 is a valve that plays an auxiliary role of the relief safety valve 11, the capacity of the turbine bypass safety valve 15 (the cross-sectional area of the flow path per valve, the number of valves, or both) is The capacity of the relief safety valve 11 may be smaller.

  Furthermore, if the opening setting pressure of the turbine bypass safety valve 15 is set smaller than the opening pressure of the safety valve function of the relief safety valve 11, the effect of suppressing the pressure rise can be improved.

  Further, when the turbine bypass safety valve 15 is a valve having a static mechanism that opens without a driving force or an open signal from the outside due to a pressure difference between the upstream side and the downstream side of the valve, such as a spring type valve, the turbine bypass safety valve 15 The operation probability of can be improved.

  The turbine bypass safety valve 15 added according to the present invention is as described above, but this is also related to the turbine bypass valve 14 installed in the turbine bypass system from the main steam pipe 4 to the condenser 7. In comparison and verification, there are the following functional differences.

  When confirming safety when a load loss event occurs, it is necessary to assume that the operation of the turbine bypass valve 14, which is a control valve driven by external power, is inoperative from the viewpoint of ensuring the safety of the reactor. There is. That is, it is necessary to assume that the system becomes inoperative due to an abnormality in the system that drives the control valve. In this respect, the turbine bypass safety valve 15 of the present invention is, for example, a spring-type valve as described above, and is a valve having a mechanism that is opened by a pressure difference between the upstream side and the downstream side of the valve. It can be improved.

  Moreover, it is as follows when it arranges in relation with the relief safety valve 11 which was the last conventional safety function valve. If the turbine bypass valve 14 is not opened after the load loss event occurs and the steam control valve 12 is closed, in the conventional boiling water power plant, in the worst case, up to the opening set pressure of the safety valve function of the relief safety valve 11 Reactor pressure increases.

  However, since it is necessary to prevent the relief safety valve 11 from opening during normal operation, the release pressure is at least higher than the normal turbine inlet pressure plus the main steam pipe pressure loss from the turbine inlet to the relief safety valve. It needs to be set high. However, since the relief safety valve 11 needs to be installed on the upstream side (reactor side) from the isolation valve 10, the main steam pipe pressure loss to be taken into consideration is considerably large, and the open pressure that can be set must be increased.

  With respect to this open set pressure, the turbine bypass safety valve 15 of the present invention is installed on the downstream side (turbine side) of the isolation valve, so that the main steam pipe pressure loss to be considered may be small and can be set considerably lower than the relief safety valve 11. .

  As a result, in the boiling water power plant of the present invention, the reactor pressure only rises up to the set opening pressure of the turbine bypass safety valve 15, and the pressure increase width can be reduced.

  Another embodiment of the present invention will be described with reference to FIG. In the case of FIG. 2, the steam discharge destination of the turbine bypass safety valve 15 is changed from the condenser 7 to the downstream side (condenser side) from the turbine bypass valve 14 on the turbine bypass pipe 13.

  By taking such a connection method, an increase in the amount of piping due to the installation of the turbine bypass safety valve 15 can be suppressed.

  Further, the turbine bypass valve 14 and the turbine bypass safety valve 15 may be manufactured integrally.

  The turbine bypass safety valve 15 is opened by a pressure difference between the upstream side and the downstream side, and should be a non-control valve rather than a so-called control valve. On the other hand, the turbine bypass valve is a control valve, and in the present invention, it can be said that the control valve and the non-control valve are juxtaposed in the turbine bypass system 13.

  1 and 2, the steam discharge destination of the turbine bypass valve 14 may be on the condenser side. The difference is whether two bypass pipes are completely provided or a part of the bypass pipe is used.

  The present invention can be applied to a nuclear power plant such as a boiling water nuclear power plant.

DESCRIPTION OF SYMBOLS 1 ... Boiling water nuclear power plant 2 ... Reactor 3 ... Containment vessel 4 ... Main steam piping 5 ... High pressure turbine 6 ... Low pressure turbine 7 ... Condenser 8 ... Feed water heater 9 ... Feed water pump 10 ... Isolation valve 11 ... Relief Safety valve 12 ... Steam control valve 13 ... Turbine bypass piping 14 ... Turbine bypass valve 15 ... Turbine bypass safety valve

Claims (5)

A containment vessel including a nuclear reactor, a main steam pipe connecting the nuclear reactor and the turbine, a condenser for condensing steam discharged from the turbine, and cooling supplied from the condenser to the nuclear reactor A water supply pump for driving water, an isolation valve installed before and after the containment vessel penetration of the main steam pipe, a relief safety valve installed on the main steam pipe between the isolation valve and the reactor, A steam control valve installed on a main steam pipe between the isolation valve and the turbine; a turbine bypass pipe connecting the main steam pipe between the steam control valve and the isolation valve to the condenser; In a nuclear power plant including a turbine bypass valve installed on the turbine bypass pipe,
A turbine bypass safety valve that opens due to a pressure difference between the upstream side and the downstream side is provided on the main steam pipe between the steam control valve and the isolation valve, and the steam discharge destination of the turbine bypass safety valve is on the condenser side A nuclear power plant characterized by The nuclear power plant of claim 1,
A nuclear power plant, wherein a downstream side of the turbine bypass safety valve is connected to the turbine bypass pipe. In the nuclear power plant according to claim 1 or 2,
The nuclear power plant, wherein an opening set pressure of the turbine bypass safety valve is smaller than a minimum opening setting pressure of the relief valve function of the relief valve. In the nuclear power plant according to claim 1 or 2,
The nuclear power plant according to claim 1, wherein the turbine bypass safety valve is a valve that opens without an external driving force or an open signal due to a pressure difference between the upstream side and the downstream side of the valve. A containment vessel including a nuclear reactor, a main steam pipe connecting the nuclear reactor and the turbine, a condenser for condensing steam discharged from the turbine, and cooling supplied from the condenser to the nuclear reactor A water supply pump for driving water, an isolation valve installed before and after the containment vessel penetration of the main steam pipe, a relief safety valve installed on the main steam pipe between the isolation valve and the reactor, In a nuclear power plant comprising a steam control valve installed on a main steam pipe between an isolation valve and the turbine,
A turbine bypass valve that is a control valve and a pressure difference between the upstream side and the downstream side are opened on the turbine bypass pipe that connects the main steam pipe between the steam control valve and the isolation valve to the condenser. A nuclear power plant characterized by juxtaposing turbine bypass safety valves that are non-control valves.

Images