JPS61160086A - Nuclear reactor container neutron shielding system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a reactor containment vessel and biological shielding device for a boiling water reactor, which has an effective cooling function in a dry well during an accident and under normal conditions. In particular, the present invention relates to a neutron shielding system that prevents activation of concrete on the inner surface of a biological shielding device due to neutrons generated in a nuclear reactor and is suitable for a rational biological shielding device structure.

[Background of the invention]

Figure 2 shows the reactor and concrete containment vessel of the current 11 million KWe class boiling water reactor facility.

The neutron beams generated in the reactor core inside the reactor pressure vessel 1 and leaked out of the reactor core were transported to a reinforced concrete 17-wall approximately 600 m thick.
Although the neutron beams are partially attenuated by the reactor shielding wall 2 of the reactor shielding wall 2, the neutron beams that have passed through the reactor shielding wall 2 or passed through the approximately 40 piping penetrations 3 in the reactor shielding wall 2 are transferred to the reactor containment vessel. It is shielded by the reactor containment vessel 4, which is made of reinforced concrete and has a thickness of about 2000 mm and also serves as a biological shielding device, located on the outside of the reactor building, and has a structure that prevents neutron beams from leaking into the reactor building. For this reason, the reinforced concrete on the core side of the reactor containment vessel 4 is irradiated with neutron beams, and iron, which is a constituent element of the reinforcing bars and concrete, is irradiated with neutron beams.

Nickel, manganese, potassium, calcium, aluminum, etc. are activated, so when a nuclear reactor reaches the end of its useful life and is dismantled, a large amount of concrete and reinforcing steel will be removed from the reactor containment vessel at a low level or Generated as extremely low-level radioactive waste.

Next, FIG. 3 shows an example of the neutron shielding structure of the piping penetration portion 3 that penetrates the reactor containment vessel 4 used in current boiling water reactor facilities.

An iron sleeve 5 is installed in the piping penetration portion of the reactor containment vessel 4, and an iron sleeve 6 and piping 7 pass through it. The sleeve 6 is connected to the reactor containment vessel liner 8 by welding.

The space between the sleeve 5 and the sleeve 60 is absolutely necessary to release deformation of the piping due to thermal stress, and in order to shield neutron beams leaking through the space, a reactor containment vessel is provided inside the reactor containment vessel 4. A disc-shaped neutron shielding material 9 having a diameter larger than the diameter of the vessel through-hole is installed around the outer periphery of the sleeve 6, and a neutron shielding material 10 is placed between the pipe 7 and the sleeve 6.
is filled. Further, a neutron shielding material 11 is installed on the reactor building side of the reactor containment vessel 4 in order to shield neutrons that have passed through the pipe penetration part 3. Furthermore, a gamma ray shielding device 12 made of iron is installed on the outside.

Generally, the reactor containment vessel 4 of a 1100 MWe class nuclear reactor has about 200 penetrations for piping, etc., of which 40 to 50 require a neutron shielding structure and about 70 require a gamma ray shielding structure. Individuals exist. Therefore, it is important to devise an effective neutron shielding structure that requires minimal installation space.

Next, the cooling function of the reactor containment vessel 4 of a light water reactor during normal operation and during an accident will be described below.

During normal operation, the dry well 13 portion of the reactor containment vessel 4 is maintained at 57° C. or lower by a fan and a cooler. In the event of a loss of coolant accident such as a rupture in the coolant recirculation piping, the energy of the coolant leakage, decay heat, and heat generated by the reaction between the fuel cladding and water due to overheating of the fuel are removed, and the inside of the reactor containment vessel 4 is To prevent the pressure and temperature from exceeding the design pressure and temperature of the reactor containment vessel 4, the pool water in the suppression chamber 14 is sprayed into the dry fel 13 and the suppression chamber 14 by the containment vessel spray system. After the water level sprayed into the dry fell reaches the vent pipe 150, the water returns to the suppression chamber 14 through the vent pipe 15.
After being cooled in the heat exchanger of the residual heat removal system, it is sprayed again.

Figure 4 shows an example of the seal structure of the reactor containment vessel piping penetration part of the current power plant.

The iron sleeve 5 is connected to the lining cylinder 8 of the reactor containment vessel 4 by welding so as to keep the containment vessel airtight, and the iron sleeve 6 and piping 7 inside the iron sleeve 5
They are also connected by welding to maintain airtightness.

Further, the iron sleeve 5 and the iron sleeve 6 are metal bellows 2.
5 and are connected to each other by welding so as to maintain airtightness.

Therefore, expansion and contraction of the piping due to thermal stress can be absorbed by the bellows 25, and the structure is such that the inside and outside of the reactor containment vessel 4 are kept airtight by welding.

[Purpose of the invention]

The purpose of the present invention is to provide a function to effectively cool the surrounding air inside the dryfell both during normal operation of a nuclear reactor and in the event of an accident, and in particular to prevent leakage of neutrons generated in the core during normal operation of a nuclear reactor. This prevents the activation of the concrete on the inside of the biological shielding device or the inside of the reinforced concrete reactor containment vessel, and prevents the generation of large amounts of concrete as low-level or extremely low-level waste during reactor dismantling. It is an object of the present invention to provide a neutron shielding system that is effective in rounding and achieves an effective and rational neutron shielding structure for a large number of piping through holes penetrating a containment vessel or a biological shielding device.

[Summary of the invention]

The present invention attenuates neutrons generated in the reactor core with a water layer provided on the inner surface of the biological shielding device or the inner surface of the reinforced concrete reactor containment vessel. This will prevent low-level or extremely low-level radioactive waste from concrete, which is generated in large quantities during nuclear reactor dismantling.

Furthermore, the atmosphere inside the containment vessel during normal operation and during accidents is effectively cooled by the water layer, and the piping penetrations that pass through biological shielding devices are integrated with the water layer described above. The objective is to provide a system that can perform effective and rational neutron shielding.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1, 5, and 6.

FIG. 1 shows a nuclear reactor facility consisting of a reactor containment vessel 4 made of reinforced concrete that has both the functions of a reactor containment vessel and a biological shielding device.

A liner 16 is installed on the pressure vessel side of the liner 8 of the concrete reactor containment vessel 4 by a support 17. The upper and lower ends of the steel liner 8 and the steel liner 16 are connected by welding, and a bag-like sealed container structure is formed between the liners. In the upper part of the liner-surrounded vessel, a pump 18. A piping system consisting of a check valve 19 and piping 20 is connected.

Furthermore, an air vent pipe consisting of a pipe 21 and a control valve 22 is installed at the top of the container. A suppression pool return line consisting of a control valve 23 and piping 24 is provided at the bottom of the container.

A column 17 that maintains a constant distance between the liner 16 and the liner 8 and fixes the nine vessels surrounded by the liner to the inner surface of the reactor containment vessel 4.
is based on a concrete IJ-containment reactor containment vessel 4,
Fixed. Moreover, this support column 17 has a spiral guide vane structure between the liners.

In this system, first, the control valve 22 is opened, and the control valve 23 is opened.
It is completely closed, and the suppression pool water is injected into the container surrounded by the liner by the pump 18. When the inside of the container is filled with water, the control valve 22 is closed and the control valve 23 is opened, and the suppression pool water is sent into the container by the pump 18 and circulated via the return piping 24.

During reactor operation, the water layer between the liners absorbs 31 neutrons leaking from the core! ! : This prevents activation of the concrete containment vessel walls by neutrons and greatly reduces the generation of low-level or extremely low-level concrete waste during reactor dismantling. Also, water has a higher neutron shielding ability than concrete, reducing the contribution of neutrons to the dose rate by 1.
To make it extremely low, approximately 14 cm of water is required, but for concrete 17-cm, approximately 25 cm is required. Therefore, by providing a water layer, the thickness of concrete related to neutron shielding can be reduced, resulting in a reduction in the amount of concrete.

Furthermore, during reactor operation, the water layer between the liners has the effect of cooling the inside of the dry fell. The cooling capacity inside the dry well is controlled by controlling the flow rate of the pump 18, and the guide vane-shaped support that goes around the container surrounded by the liner in a spiral shape prevents local accumulation of water in the container. Prevent and promote the cooling effect of dry fell. Therefore, the capacity of the dry well cooling system for maintaining the temperature inside the dry well at 57° C. or lower during normal operation can be reduced.

In addition, in the event of a loss of coolant accident, steam in the dryfell can be effectively condensed on the wall surface, reducing the design pressure of the reactor containment vessel or reducing the space volume of the reactor containment pressure suppression chamber. becomes possible.

Furthermore, during normal operation and in the event of an accident, the inner surface of the containment vessel is cooled by the sublet pool water, so the temperature difference between the inner and outer surfaces of the containment concrete, which is approximately 30°C even during normal operation, is reduced to 10°C or less. This makes it possible to reduce the thermal stress to a certain degree, and improves the reliability of concrete by reducing thermal stress.

Next, the sealing structure of the reactor containment vessel piping penetration portion in this embodiment will be described with reference to FIGS. 5 and 6. FIG. 5 is an example of a large-diameter high-temperature pipe.

The iron sleeve 5 is connected to the reactor containment vessel liner 8 and liner 1.
6, and the iron sleeve 6 is connected to the iron sleeve 5 via a bellows 25. Furthermore, the iron sleeve 6 and the piping 7 are connected, and 26 tons of heat insulating material is filled around the piping 7 inside the iron sleeve 6 to prevent the temperature of the high-temperature piping from dropping.

Since the spaces between the liners 8 and 16 and between the iron sleeves 5 and 6 are filled with suppression pool water, a sufficient water-shielding effect can be expected.

Further, deformation of the piping due to thermal stress can be absorbed by the bellows 25 and the water layer between the iron sleeves 5 and 6.

FIG. 6 shows the case of a small diameter pipe, in which the iron sleeve 5 and the pipe 7 are connected via bellows 25 by welding.

In this case as well, as in FIG. 5, the deformation of the piping due to thermal stress can be absorbed by the bellows 25, the steel tube 17, and the water layer of the piping 7, and the water layer between the piping 7 and the sleeve 5 provides sufficient shielding. You can expect good results.

Therefore, by adopting the structure shown in this embodiment, the elaborate neutron shielding structure that has been conventionally applied to the penetration portion becomes unnecessary, the amount of neutron shielding material can be reduced, and the dead space can be significantly reduced. As plant rationalization progresses in the future, the containment vessels will become smaller and more holes will be placed near the reactor core than at present, which will increase the advantages of this neutron shielding structure. .

Furthermore, by covering the piping penetrations with water, the airtightness of the reactor containment vessel is improved, and the reliability of the reactor containment vessel's original function of confining radioactive materials is improved.

〔Effect of the invention〕

Implementation of the present invention has the following effects.

(a) It is possible to effectively attenuate leaked neutron beams from a nuclear reactor and prevent activation of bioshielding devices or the concrete and reinforcing bars of the reinforced concrete reactor containment vessel, so that low-level or The generation of extremely low-level radioactive waste can be prevented.

(Reducing the amount of radioactive solid waste generated) (b) Reducing the amount of concrete and reinforcing bars in the current 2m reinforced concrete biological shielding device or the reinforced concrete reactor containment vessel.

(Regarding neutron beams, 67 cm of water is 11 cm of concrete.
It has a shielding effect of 00C. ) (C) It is possible to reduce the amount of neutron shielding material in the through-holes of biological shielding devices or reinforced concrete containment vessels.

(d) Since the containment vessel can be cooled during normal operation, the capacity of the dry well cooling system can be reduced.

(e) Since the biological shielding wall or the reinforced concrete reactor containment vessel wall does not come into direct contact with the atmosphere inside the containment vessel, the temperature difference between the inside and outside of the concrete wall can be reduced during normal operation and during an accident. For,
Thermal stress can be reduced and the reliability of concrete can be improved.

(f) By covering the biological shielding wall and the inner surface of the concrete containment vessel with a water layer, the airtightness of the containment vessel is improved, and the reliability of the containment vessel's original function of confining radioactive materials is improved.

(g) Steam in the reactor containment vessel can be effectively condensed on the walls of the reactor containment vessel in the event of a loss of coolant accident. As a result, (1) the design pressure of the reactor containment vessel can be reduced; Alternatively, (II) the space volume of the reactor containment pressure suppression chamber can be reduced. There are effects such as

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of an embodiment of the present invention, Fig. 2 is an explanatory diagram of a conventional example, Fig. 3 is a structural diagram showing a conventional example of a through-hole shielding structure, and Fig. 4 is a conventional seal of a penetrating part. Fig. 5 is a structural diagram of a sealing structure of a large-diameter pipe penetration part in the present invention, and Fig. 6 is a diagram of a sealing structure of a small-diameter pipe penetration part in the present invention. 1... Reactor pressure vessel, 2... Reactor shielding wall, 3...
...Pipe penetration, 4...Reactor containment vessel, 12...
Gamma ray shielding device, 13...Dreiwael, 18...
・Pump, 25...Bellows, 26...Heat insulation material. v-,,1 story 1 melody 0

Claims (1)

[Claims] 1. Neutron shielding for a reactor containment vessel, characterized in that a reactor containment facility consisting of a reactor containment vessel and a concrete bioshielding device has a structure in which a water layer is provided between the containment vessel and the bioshielding device. system.