JP2012230030A - Static water supply device for spent fuel pool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a static water supply device for a spent fuel pool, which suppresses decrease in water volume of the spent fuel pool even when an external power source for cooling the spent fuel pool is lost over a long period.SOLUTION: Heat exchangers which exchange heat inside and outside a reactor building are installed above a spent fuel pool. The heat exchanger inside the reactor building is used for condensing vapor in the reactor building, and heat removed by vapor condensation is released from the heat exchanger outside the reactor building to the outside. Water which is formed by condensing the vapor with use of the heat exchanger inside the reactor building is collected by a condensed water recovery unit installed below the heat exchanger, and is returned to the spent fuel pool through a condensed water return pipe connecting a bottom of the condensed water recovery unit to the spent fuel pool.

Description

  The present invention relates to a static water supply device for a spent fuel pool used in a nuclear power plant.

  Nuclear power generation systems, such as boiling water light water reactors (hereinafter referred to as BWRs), are used fuels that have already been operated for several cycles in the reactor building, and fuels that have been removed from the reactors during periodic inspections (hereinafter collectively referred to as these). There is a spent fuel pool (hereinafter abbreviated as SFP) that temporarily stores spent fuel). Spent fuel is installed at the bottom of the pool and stored with the fuel completely flooded. Since spent fuel generates heat due to decay heat, the pool water is circulated and cooled to control the temperature of the pool water at about 40 ° C.

  On the other hand, as a natural circulation type cooling method that does not use power such as a pump, there is an air cooling system using a heat pipe. The thermal characteristics of general heat pipes are described in technical data such as heat transfer engineering data. The first idea has been used for cooling and heat removal of equipment in the state of weightlessness in outer space in order to increase heat transport capacity without using power. On the other hand, as a heat pipe for consumer use, it has a track record of being applied to several products for cooling electronic devices and industrial machines. Compared to natural heat circulation of liquid single-phase flow in the working fluid, the heat pipe uses a phase change phenomenon such as boiling and condensation of the working medium. It is known that the heat transfer capability is extremely large compared to the heat transfer by heat conduction of the structural member.

Heat transfer engineering data (4th revised edition), Japan Society of Mechanical Engineers

  The SFP pool water cooling system used in the current BWR generally circulates cooling water using an electric pump. When the power source necessary for circulating the cooling water is lost, the pool water in the SFP is gradually heated by decay heat generated from the spent fuel. Since there is a sufficient amount of water in the SFP, the temperature rise of the SFP pool water is very gradual, but if the power loss is prolonged, a part of the SFP pool water evaporates. May be lost.

  The objective of this invention is providing the static water supply apparatus of the spent fuel pool which can suppress the reduction | decrease of the pool water of a spent fuel pool, even when the loss of a power supply is prolonged.

  In order to achieve the above object, the present invention installs a heat exchanger for exchanging heat inside and outside the reactor building above the spent fuel pool. The heat exchanger on the reactor building side is for condensing the steam inside the reactor building, and the heat taken away by the steam condensation is released to the outside from the heat exchanger on the reactor building outdoor side. The water generated by condensing steam in the heat exchanger inside the reactor building is collected by the condensate recovery unit installed at the bottom of the heat exchanger, and the condensed water connected from the lower part of the condenser recovery unit to the spent fuel pool It is set as the structure returned to SFP through a return pipe.

  According to the present invention, it is possible to suppress a decrease in pool water of the spent fuel pool even when power is lost for a long time.

It is a block diagram of the static water supply apparatus of the spent fuel pool which is one suitable Example of this invention. It is a figure showing the heat transfer promotion fin. It is a figure showing the inclination of an outer side heat exchanger.

  In order to suppress the decrease of pool water in the SFP when power is lost for a long time, the inventors installed a heat exchanger for exchanging heat outside and inside the reactor building above the SFP, and steam inside the reactor building. It was concluded that it is sufficient to condense and return to SFP.

  Thereby, since the decrease in SFP pool water can be suppressed even when power is lost for a long time, the safety of the nuclear reactor can be further improved.

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

  A spent water pool static water supply apparatus according to embodiment 1, which is a preferred embodiment of the present invention, will be described with reference to FIG. Although the present embodiment shows an example of a boiling water light water reactor (BWR), the present invention can be applied to a pressurized water light water reactor, for example, whose basic structure is close.

  The spent water pool static water supply device of the present invention is installed below the outer heat exchanger 2 installed outside the reactor building 1, the inner heat exchanger 3 installed inside, and the inner heat exchanger. The condensed water recovery device 4 and the condensed water return pipe 5 connected to the lower portion of the condensed water recovery device are provided. The outer heat exchanger and the inner heat exchanger are connected by a high temperature side connecting pipe 6 and a low temperature side connecting pipe 7.

  Below the condensate recovery unit is a spent fuel pool (SFP) 8 for storing spent fuel, in which spent fuel 9 is stored. The normal SFP water level is above the upper end of the spent fuel and below the upper end 10 of the SFP.

  The pool water in the SFP is usually cooled by a decay heat removal system driven by an external power source. When the external power source is lost, the pool water temperature gradually rises due to the decay heat of the spent fuel. In SFP, a sufficiently large amount of water is secured against decay heat, and when the external power supply is lost for a short time, the rise in pool water temperature is small and does not cause a problem. When the loss of the external power supply is long, the pool water evaporates due to the rise in pool water temperature, and the pool water volume decreases. Pool water evaporated from the SFP is discharged into the reactor building in the form of steam.

  In this example, an outer heat exchanger and an inner heat exchanger are installed on the outer and inner sides of the reactor building, and the outer heat exchanger and the inner heat exchanger are connected by a high-temperature side connection pipe and a low-temperature side connection pipe. Constitutes a closed loop of heat pipes. Inside this closed loop, a fluid boiling between 35 ° C. and 99 ° C. (hereinafter referred to as a low boiling point fluid) is enclosed as a working fluid of the heat pipe. In the situation where pool water evaporates from SFP, the inside of the inner heat exchanger is in a state close to the saturation temperature of 100 ° C of atmospheric water, and the low boiling point fluid inside the inner heat exchanger absorbs the surrounding heat. Evaporate. Conversely, the steam outside the inner heat exchanger is deprived of heat and cooled and condensed. The low boiling point fluid evaporated inside the inner heat exchanger flows into the outer heat exchanger through the high temperature side connecting pipe connected to the upper part of the inner heat exchanger. Since the outside heat exchanger has an outside air temperature (about 35 ° C. in Japan), the low boiling point fluid condenses by releasing heat to the outside. The condensed low boiling point fluid flows again into the inner heat exchanger through the low temperature side connecting pipe.

  In order to improve the heat exchange performance, it is effective to add fins for promoting cooling to the outer heat exchanger and the inner heat exchanger. The heat exchanger is composed of several hundred heat transfer tubes 12 (FIG. 2). In FIG. 2, with respect to the heat transfer tube 12 provided in the vertical direction, a plurality of heat transfer promotion fins 11 are provided to be inclined by an angle α with respect to the horizontal plane. About an inner side heat exchanger, it is good to attach the inclination of (alpha) = 10 degrees or more to the installation angle of a fin with respect to a horizontal surface. Preferably, fins with α = 90 ° (vertical direction) with respect to the horizontal plane are used. By providing an angle to the heat transfer-promoting fin, the water condensed on the inner heat exchanger surface can efficiently flow down to the condensate recovery unit.

  Furthermore, in order to prevent the low boiling point fluid from staying in part, the high temperature side connecting pipe is the upper end of the outer heat exchanger and the inner heat exchanger, and the low temperature side connecting pipe is the outer heat exchanger and the inner heat exchanger. It is good to arrange | position so that it may install in a lower end part and the upper end height and lower end height of an outer side heat exchanger may become higher than the upper end height and lower end height of an inner side heat exchanger.

  It is further preferable that the outer heat exchanger has a structure that can be cooled from the outdoor part of the reactor building by water discharge from a fire engine. In order to efficiently apply water discharge to the outer heat exchanger, the outer heat exchanger may be installed at an angle in the range of β = 30 ° to 180 ° with respect to the horizontal plane (FIG. 3).

  Since the object of the present invention is to release heat from the inside of the reactor building to the outside, there is no problem even if the inner heat exchanger and the outer heat exchanger are connected by a heat exchange method other than a heat pipe.

  As described above, the vapor evaporated from the SFP is cooled and condensed around the inner heat exchanger. The water produced by condensation will flow down along the inner heat exchanger surface. In order to collect the water condensed around the inner heat exchanger, a dish-shaped condensate collector is installed below the inner heat exchanger. The condensed water collected in the condensed water collector is discharged from a condensed water return pipe connected to the lower part of the condensed water collector.

The condensed water return pipe is connected to the SFP, and its outlet height is lower than the upper end of the SFP in order to prevent scattering of condensed water, but preferably lower than the normal SFP water level.
By adopting the above configuration, even when the external power source is lost for a long time, the vapor evaporated from the SFP can be condensed and returned to the SFP again, so that the decrease of the pool water of the SFP can be suppressed.

  DESCRIPTION OF SYMBOLS 1 ... Reactor building, 2 ... Outer heat exchanger, 3 ... Inner heat exchanger, 4 ... Condensate recovery unit, 5 ... Condensate return pipe, 6 ... High temperature side connection pipe, 7 ... Low temperature side connection pipe, 8 ... Spent fuel pool, 9 ... spent fuel, 10 ... upper end of spent fuel pool, 11 ... heat transfer promotion fin, 12 ... heat transfer tube.

Claims (10)

In a nuclear power plant having a nuclear reactor building and a spent fuel pool installed inside the reactor building,
A static water supply device for a spent fuel pool is installed in the reactor building, and the static water supply device for the spent fuel pool is installed inside an outer heat exchanger installed outside the reactor building. The outer heat exchanger is connected to the inner heat exchanger, and the heat absorbed by the inner heat exchanger can be discharged from the outer heat exchanger. A condensed water recovery unit is installed below, a condensed water return pipe is connected to the lower part of the condensed water recovery unit, and the outlet of the condensed water return pipe is the spent fuel pool. Static water supply device for fuel pool.   The static water supply apparatus for a spent fuel pool according to claim 1, wherein the outer heat exchanger and the inner heat exchanger are a high temperature side connecting pipe and a low temperature side connecting pipe at a position lower than the high temperature side connecting pipe. A static water supply device for a spent fuel pool, which is a heat pipe heat exchanger connected and filled with a working fluid.   The static water supply device for a spent fuel pool according to claim 2, wherein the working fluid inside the heat pipe is a fluid having a boiling point between 35 and 99 ° C. apparatus.   The static water supply device for a spent fuel pool according to claim 2, wherein the upper end height of the outer heat exchanger is higher than the upper end height of the inner heat exchanger. Water supply device.   The static water supply device for a spent fuel pool according to claim 2, wherein a lower end height of the outer heat exchanger is higher than a lower end height of the inner heat exchanger. Water supply device.   2. The spent water pool static water supply device according to claim 1, wherein the outer heat exchanger has an angle of 30 to 180 [deg.] With respect to a horizontal plane. Feeding device.   2. The spent fuel pool static water supply device according to claim 1, wherein at least one of the outer heat exchanger and the inner heat exchanger has fins for promoting heat transfer. 3. Static water supply device.   The static water supply device for a spent fuel pool according to claim 6, wherein the heat transfer promoting fins installed in the inner heat exchanger have an angle of 10 ° or more with respect to a horizontal plane. Static water supply device for spent fuel pool.   The static water supply apparatus for a spent fuel pool according to any one of claims 1 to 7, wherein the static water supply apparatus for a spent fuel pool is installed in a boiling water light water reactor plant.   The spent water pool static water supply apparatus according to any one of claims 1 to 7, wherein the spent water pool static water supply apparatus is installed in a pressurized water light water reactor plant.

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