JP5687440B2 - Reactor containment heat removal apparatus and heat removal method - Google Patents

Description

  The present invention relates to a reactor containment heat removal apparatus and a heat removal method for a nuclear power plant.

  In a nuclear power plant, when the main steam pipe connected to the reactor pressure vessel breaks, a reactor coolant loss accident (hereinafter referred to as `` high temperature / high pressure '' reactor primary coolant is released into the reactor containment vessel) , "LOCA") may occur. In addition, when LOCA occurs, there is a possibility that a severe accident (SA) may occur where the coolant is lost, the reactor water level is lowered, the core is exposed, cooling becomes insufficient, and the core may melt. is there.

  For example, when LOCA occurs in a boiling water nuclear power plant, when high-temperature and high-pressure reactor primary coolant is discharged to the dry well in the reactor containment vessel, the temperature and pressure in the dry well rapidly increase. To do. In order to prevent radioactive materials from being released outside the containment vessel during LOCA, the nuclear power plant uses high-temperature and high-pressure coolant released into the dry well before the design temperature and design pressure of the containment vessel. It is structured to reduce the temperature and pressure in the reactor containment vessel by discharging into the suppression chamber through the vent pipe and absorbing it into pool water in the suppression chamber.

  In addition, if the coolant is not returned to the reactor pressure vessel due to the coolant piping breakage, the reactor water level may be lowered and the core may be exposed, resulting in insufficient cooling, but as an emergency core cooling system An emergency core cooling device (hereinafter referred to as “ECCS”) using suppression pool water as a water source is provided, and when ECCS is activated, cooling water is injected into the reactor pressure vessel to flood the core. This prevents core melting.

  On the other hand, even if ECCS does not start for some reason and water injection fails, using the residual heat removal system (RHR) water injection equipment that sprays into the reactor containment vessel by manual operation of the central control room worker, It is structured to reduce the temperature and pressure in the reactor containment by condensing water vapor generated during cooling of the reactor pressure vessel by spraying.

  In the unlikely event that a severe accident occurs due to the temperature rise of the reactor pressure vessel and the reactor pressure vessel is damaged, the core melt falls to the bottom of the dry well and exits from the reactor pressure vessel. In direct contact with pool water, a large amount of water vapor is generated. Although pressure rise and steam explosion may occur with the generation of hydrogen, pressure rise and steam explosion are prevented by removing heat from the reactor containment vessel with heat removal equipment.

  In this way, when a LOCA or severe accident occurs, the core is cooled by the ECCS being activated, but by direct water injection into the core melt, water vapor is decomposed by radiation due to the reaction between the water and the core melt. Hydrogen gas and oxygen gas are generated. Further, when the temperature of the fuel cladding tube rises, a reaction occurs between the water vapor generated during cooling and the zirconium of the fuel cladding tube material, and hydrogen gas is generated. The hydrogen gas generated in this way is released into the reactor containment vessel through the broken port of the broken pipe, and the hydrogen gas concentration gradually increases. Since hydrogen gas is non-condensable, the pressure in the reactor containment vessel increases. In order to suppress such a pressure increase, it is necessary to remove hydrogen generated in the reactor containment vessel or remove heat in the reactor containment vessel to reduce the hydrogen partial pressure. Therefore, as means for removing hydrogen gas in the reactor containment vessel, means for removing hydrogen by synthesizing hydrogen and nitrogen into ammonia using an ammonia synthesis means or the like has been proposed (Patent Document 1).

  Also, as a countermeasure against severe accidents such as melting of the core due to a drop in the water level inside the reactor, a cooling water tank is installed at the top of the reactor containment vessel, and the water source in the tank depends on power. There is proposed a static cooling means that sprays into the reactor containment vessel without gravity, and a means for suppressing the pressure by removing and condensing the water vapor released into the reactor containment vessel with a heat exchanger. (Patent Documents 2 and 3).

  In addition, as a facility for cooling the drywell atmosphere to a specified temperature during normal operation, multiple drywell cooling units with cooling coils are installed in the drywell, and the drywell atmosphere is circulated by a blower and cooled by the cooling coil. The cooled air is blown to various places in the dry well through a duct to remove heat (Patent Document 4).

JP 2006-322768 A JP-A-7-128482 Japanese Patent No. 3666836 Japanese Patent No. 4180783

  In the above-described conventional heat removal means, for example, the cooling facility by the cooling water tank at the upper part of the containment vessel is designed assuming an operating period (grace period) of up to 3 days, so long-term heat removal is not considered. In addition, in order to remove heat for a long period of time, an extremely large cooling tank is required to secure cooling water, but there are significant restrictions in terms of earthquake resistance, layout design, cost, etc. of nuclear power plants. There was a problem of giving.

  In addition, ECCS, residual heat removal system, etc. are dynamic equipment, so it is necessary to perform functional tests and maintenance inspections regularly, and ECCS, residual heat removal system is activated in the event of an accident, and power, water source, etc. When exhausted, there was a problem that the subsequent heat removal could not be performed. Further, the dry well cooling unit has problems of improving the cooling capacity of the heat transfer tube and reducing the pressure loss of the coolant.

  The present invention has been made to solve the above-described problems, and it is possible to remove the atmosphere in the reactor containment vessel for a long period of time without using a cooling water tank or dynamic equipment at the time of LOCA or a severe accident. An object of the present invention is to provide a static reactor containment heat removal apparatus and heat removal method that can be performed.

In order to solve the above problems, a reactor containment vessel heat removal apparatus according to the present invention includes at least one duct provided outside a reactor containment vessel, a heat exchanger disposed inside the duct, and the containment. At least one drywell cooling unit having a cooling coil disposed inside the vessel, a cooling water circulation system connected to the drywell cooling unit, a heat exchanger in the duct outside the reactor containment vessel, and the And a heat pipe for connecting the cooling coil .

  The reactor containment vessel heat removal method of the present invention is characterized in that the atmosphere in the reactor containment vessel is cooled using the reactor containment vessel heat removal apparatus according to the present invention.

  According to the present invention, the atmosphere in the reactor containment vessel can be removed for a long period of time without using a cooling water tank or dynamic equipment at the time of LOCA or a severe accident.

1 is an overall configuration diagram of a reactor containment heat removal apparatus according to a first embodiment. FIG. The modification of the reactor containment vessel heat removal apparatus which concerns on 1st Embodiment. The block diagram of the heat exchanger tube of the nuclear reactor heat exchanger which concerns on 1st Embodiment. The whole block diagram of the reactor containment vessel heat removal apparatus which concerns on 2nd Embodiment.

Hereinafter, embodiments of a reactor containment heat removal apparatus and a heat removal method according to the present invention will be described with reference to the drawings.
(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the reactor containment vessel heat removal apparatus according to the first embodiment includes a reactor containment vessel 1 that houses a reactor pressure vessel 2, and a heat exchange installed in the reactor containment vessel 1. The heat exchanger 3a, the duct 5 installed outside the reactor containment vessel 1, the heat exchanger 3b installed in the duct 5, and the heat pipe 4 connecting the heat exchangers 3a and 3b are configured. .

  The fluid sealed in the heat pipe 4 is preferably a fluid whose boiling point is close to the temperature in the containment vessel at the time of the accident, for example, water, in order to promote natural circulation in the heat pipe 4. Moreover, as shown in FIG. 3, you may provide the fin 6 in the heat exchanger tube 10 in the heat exchanger 3a, 3b, and it can improve heat-transfer performance by this.

  In the containment vessel heat removal apparatus configured as described above, the air in the duct 5 installed outside the reactor containment vessel 1 is heated by the heat exchanger 3b to generate an upward flow. This upward flow promotes heat transfer in the heat exchanger 3b, and the heat exchanger 3a in the containment vessel removes heat from the atmosphere in the containment vessel 1 by the heat exchange function of the heat pipe 6.

For example, in the case of a nuclear reactor having a thermal output of 480 MW class, the decay heat one day after a severe accident is about 29 MW. Under these conditions, three exhaust ducts 5 having a diameter of 6 m are installed, the flow velocity of the upward flow in the exhaust duct 5 is 5 m / s, the air temperature at the inlet of the exhaust duct 5 is 30 ° C., and the temperature on the high temperature side of the heat pipe 6 Is 153 ° C., and the heat transfer area of the heat exchanger 3b outside the containment vessel at which the temperature on the low temperature side of the heat pipe is 100 ° C. or less is calculated using a general heat transfer characteristic equation, it becomes 28000 m ² . Further, the heat transfer area of the heat exchanger 3a inside the containment vessel is 3000 m ² . In this calculation example, as shown in FIG. 2, three ducts are arranged outside the containment vessel 1, and three heat exchangers 3a and 3b are arranged in each duct 5 and in the containment vessel 1, respectively.
Of course, the number and size of the ducts and the number of heat exchangers are not limited to the above-described embodiment, and can be appropriately changed according to various conditions.

  According to the first embodiment, without using a cooling water tank or dynamic equipment, the reactor containment vessel at the time of LOCA or severe accident by the heat exchange function by natural circulation in the heat pipe and natural ventilation in the duct. The atmosphere inside can be removed for a long time.

(Second Embodiment)
A second embodiment will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the structure similar to 1st Embodiment, and the overlapping description is abbreviate | omitted.

  In the second embodiment, instead of the heat exchanger 3a in the reactor containment vessel 1 in FIG. 1, the existing dry well cooling arranged for cooling the inside of the reactor containment vessel during normal operation of the reactor is performed. A cooling coil (not shown) of the unit 7 is used. The heat exchanger 3 b in the duct 5 is connected to the cooling water circulation system 8 of the dry well cooling unit 7 by the heat pipe 4.

Thus, by using the cooling coil of the existing dry well cooling unit 7, it is possible to remove heat from the atmosphere in the reactor containment vessel at low cost.
During normal operation of the nuclear power plant, the heat pipe 4 connected to the heat exchanger 3b of the duct 5 is closed by the on-off valve 9, so that the cooling function of the normal drywell cooling unit 7 is not impaired and an accident occurs. It is possible to remove heat from the containment vessel.

  According to the second embodiment, by using the existing dry well cooling unit, the atmosphere in the reactor containment vessel can be removed for a long period of time at the time of LOCA or severe accident with a simple facility.

DESCRIPTION OF SYMBOLS 1 ... Reactor containment vessel, 2 ... Reactor pressure vessel, 3a, 3b ... Heat exchanger, 4 ... Heat pipe, 5 ... Duct, 6 ... Fin, 7 ... Drywell cooling unit, 8 ... Cooling water circulation system, 9 ... Opening and closing Valve, 10 ... Heat transfer tube.

Claims (3)

At least one duct provided outside the reactor containment vessel, a heat exchanger arranged inside the duct, and at least one drywell cooling unit having a cooling coil arranged inside the containment vessel; A reactor containment vessel comprising: a cooling water circulation system connected to the dry well cooling unit; and a heat pipe that connects the heat exchanger in the duct and the cooling coil outside the reactor containment vessel. Heat removal device. The reactor containment vessel heat removal apparatus according to claim 1, wherein an opening / closing valve is provided on the heat pipe. A reactor containment vessel heat removal method, wherein the reactor containment vessel heat removal apparatus according to claim 1 or 2 is used to cool an atmosphere in the reactor containment vessel.

Images