JP3156982B2 - Reactor containment venting equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor containment vent device for improving the safety of a boiling water reactor.

[0002]

2. Description of the Related Art At the time of a nuclear reactor accident, if it is assumed that the removal of residual decay heat of a core by engineering safety equipment fails,
Radioactive materials are released into the containment vessel,
It is possible that the pressure inside the containment vessel increases. In such a case, a method of venting (evacuating) the containment container has been considered in order to prevent overpressure damage due to an increase in the internal pressure of the containment container. In this case, a containment filter vent system that reduces the radioactivity released into the environment by inserting a device for removing radioactive materials in the middle of the containment vessel vent piping is being studied.

[0003] Looking at an installation example in Europe, a particularly large radioactive substance removing apparatus has a diameter of about 20 m and a height of about 40 m, and a relatively small apparatus has a diameter of about 4 m and a height of about 12 m. Furthermore, it has a building for storing this device, and it is a very large system as a whole.

[0004]

However, in the above-mentioned containment filter vent system, since it is necessary to collect radioactive substances from a large amount of discharged gas, it is necessary to install a very large radioactive substance removing device. . In addition, a large heat tank such as a water pool is required to remove the decay heat of the collected radioactive materials. When this radioactive material removing device is installed, it is very large, so that a large installation place is required and a large amount of manufacturing and installation costs are required. In addition, although the radioactive substance is expected to adhere to the mere containment vent pipe, the particles once adhered re-scatter due to the high flow velocity. The present invention has been made in consideration of the above points, and has as its object to provide a reactor containment venting device that does not require a large-sized radioactive material removing device.

[0005]

In order to achieve the above object, according to the present invention, a reactor containment vessel, a stack installed outside the reactor containment vessel, the reactor containment vessel and the stack are communicated. Vent pipe, an isolation valve interposed in the middle of the vent pipe, radioactive material removing means installed on the inner wall of the vent pipe, and radioactive material collected on the outer wall of the vent pipe and collected by the radioactive material removing means And a decay heat radiating means for radiating decay heat of the reactor vessel.

[0006]

With this configuration, a large amount of gas containing a radioactive substance flows through the vent pipe when the containment vessel is evacuated. The radioactive material contained in this large flow rate gas is deviated from the streamline at the center of the vent pipe by the driving force of diffusion, gravity, inertia, etc., and the radioactive substance removing means arranged along the inner wall of the vent pipe Passed and collected. Since most of the released gas flows through the central part in the vent pipe, the flow velocity of the gas flowing through the radioactive substance removing means becomes small. For this reason, the re-scattering of the radioactive material once collected by the radioactive material removing means is small. In addition, since the radioactive substance is dispersed and attached over the entire length of the vent pipe, the decay heat of the radioactive substance can be radiated into the atmosphere by decay heat radiation means provided outside the vent pipe. Therefore, the reactor containment vessel can be evacuated without installing a large-sized radioactive substance removing device.

[0007]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a configuration diagram showing a schematic configuration of a reactor containment venting device according to the present invention. The vent pipe assembly 2 connected to the reactor containment vessel 1 is connected to a stack 4 installed outside the reactor containment vessel 1 via an isolation valve 3 interposed between the vent pipe assembly 2. Along the inner wall of this vent pipe assembly 2, radioactive substance removing means 5
Is installed. On the outer wall of the vent pipe assembly 2, a decay heat radiating means 6 for radiating decay heat of the radioactive material collected by the radioactive material removing means 5 is provided.
The section from isolation valve 3 to stack 4 is about 200m,
The vent pipe assembly 2 is constructed by assembling a large number of vent pipes 7.

FIG. 1A is a longitudinal sectional view of a vent pipe showing one embodiment of the present invention, and FIG. 1B is a sectional view taken along the line AA of FIG. Vent pipe 7 is 50cm long and 35cm in diameter
Of the pipe 8. Inside the pipe 8, a radioactive substance removing means 5 is incorporated. The radioactive substance removing means 5 comprises a concentric stainless steel mesh inner cylinder 9 having a diameter of 30 cm installed inside the pipe 8, and further, a diameter of 4 μm filled between the pipe 8 and the stainless steel mesh cylinder 9. And stainless steel fiber 10.
The stainless steel fiber 10 is effective as a filter material because the material is hardly deteriorated by radiation, has high heat resistance, and has good heat conductivity. Cooling fins 11 serving as decay heat radiating means 6 are provided on the outer periphery of the pipe 8 along the longitudinal direction of the pipe. The cooling fins 11 promote the effect of dissipating the decay heat of the radioactive substance attached to the stainless steel fiber 10 from the surface of the pipe 8 to the atmosphere by natural convection. Piping 8
Are provided with flanges 12 at both ends. This flange
With 12, both ends of the pipe 8 and the stainless steel mesh cylinder 9 are fixed. Also, a large number of vent pipes 7 can be connected by the flange 8. The design pressure of the pipe 8 and the flange 12 should be equal to or higher than the design pressure of the containment vessel 1.

Next, the operation of this embodiment having the above configuration will be described. Since the vent pipe assembly 2 is installed over a section of about 200 m from the isolation valve 3 to the stack 4, the inside of each vent pipe 7 is distributed so as to uniformly disperse the decay heat of the radioactive material throughout the vent pipe assembly 2. In order to uniformly disperse the decay heat of the radioactive substance of the radioactive substance removing means 5 formed, the radioactive substance collection efficiency is designed to be smaller toward the upstream side and to be gradually increased toward the downstream side. Have been. As a result, the amount of collected radioactive material per unit length in the entire vent pipe assembly 2 becomes substantially uniform, and the generated decay heat is also uniformly dispersed. The outer surface of each vent pipe 7 is in contact with the atmosphere, and the decay heat of the radioactive substance attached to the stainless steel fiber 10 is transmitted from the stainless steel fiber 10 to the pipe 8, and the outer surface of the pipe 8 and the cooling fin 11 Dissipates heat into the atmosphere.
The amount of radioactive material adhering to the entirety of the vent pipe 7 is at most about 1/100 of the total core abundance. In other words, about 1/100 of the total decay heat source adheres to the PCV vent pipe. Now, assuming a reactor with a heat output of 3 million KW class, the decay heat is about 0.7% of the heat output, that is, about 20,000 KW. Therefore, the decay heat attached to the vent pipe 7 is about 1/100, that is, 200 kW.

[0013] 0.35 m in diameter and 2 length without cooling fins 11
In the case of the vent pipe 7 of 00 m, heat can be removed by natural convection when the temperature difference from the atmosphere is 180 °. By providing the cooling fins 11, heat can be radiated at a lower temperature by natural convection. 2 shows a radioactive particle collection mechanism in a reactor containment venting device.

FIG. 3 shows a particle collecting mechanism in the vent pipe 7 in a laminar flow state. Gas stream flowing through pipe 8
Considering the state in which the particles pass along 13, the particles on the streamlines adhere to the stainless steel fiber 10 by the following mechanism. (1) With the gas flow 14, the particles 14a pass through the stainless steel mesh cylinder 9, enter the stainless steel fiber 10, and adhere on the stainless steel fiber 10. (2) The particles 15a on the streamline 15 pass through the stainless steel mesh cylinder 9 by diffusion motion, enter the stainless steel fiber 10, and adhere to the stainless steel fiber 10. (3) The particles 16a pass through the stainless steel mesh cylinder 9 by gravity sedimentation on the stream line 16, enter the stainless steel fiber 10, and adhere to the stainless steel fiber 10.

The heat of decay of the radioactive substance attached to the stainless steel fiber 10 is transmitted from the stainless steel fiber 10 to the pipe 8, and is radiated from the surface of the pipe 8 and the cooling fins 11 to the atmosphere by natural convection.

FIG. 4 shows a particle collecting mechanism in the vent pipe 7 in a turbulent state. Gas stream flowing through pipe 8
17 is often bent, so that the particles flowing into the pipe 7 together with the gas flow behave in a complicated manner. Particles passing through the pipe 8 adhere to the stainless steel fiber 10 by the following mechanism. (1) With the gas flow 18, the particles 18a pass through the stainless steel mesh cylinder 9 and enter the stainless steel fiber 10,
It adheres on this stainless steel fiber 10. (2) The particles 19a on the stream line 19 pass through the stainless steel mesh cylinder 9 by diffusion motion, enter the stainless steel fiber 10, and adhere to the stainless steel fiber 10. (3) The particles 20a on the stream line 20 pass through the stainless steel mesh cylinder 9 by gravity sedimentation, enter the stainless steel fiber 10, and adhere to the stainless steel fiber 10.

(4) The particles 21a cannot ride on the streamline 21 bent inside the stainless steel mesh cylinder 9 and pass through the stainless steel mesh cylinder 9 due to the inertia of its own weight.
The stainless steel fiber 10
Adheres to

The heat of decay of the radioactive substance attached to the stainless steel fiber 10 is transmitted from the stainless steel fiber 10 to the pipe 8 and is radiated from the surface of the pipe 8 and the cooling fins 11 to the atmosphere by natural convection.

Since the stainless steel fiber 10 having a diameter of 4 μm has a very high particle collection efficiency, almost all of the particles contained in the stainless steel fiber 10 adhere to the fiber 10.
Since most of the gas passing through the pipe 8 flows through the stainless steel mesh cylinder 9, the flow velocity in the stainless steel fiber 10 is small, and particles that once adhere to the stainless steel fiber 10 are unlikely to re-scatter.

An example of the particle removal effect of the above-described reactor containment vent device will be described. Figure 5 shows the length in the turbulent state.
The measurement result of the particle size dependence of the decontamination coefficient (hereinafter referred to as DF) with a 0.5 m vent pipe is shown. Particle size 0.2 ~
At 1.4 μm, the DF ranges from 1.3 to 3.6. Here, DF is the ratio of the number concentration of the inlet to the number concentration of the particles at the outlet of the vent pipe 7, and the larger the value of DF, the greater the effect of removing particles. No re-scattering of the particles once attached was observed.

When a 200 m long vent pipe 7 is assumed, 400 0.5 m long vent pipes are connected, and the total DF of the 200 m long vent pipe is 400 times the DF of the 0.5 m long pipe filter. Becomes Now, if it is attempted to secure a DF of about 100 to 10,000 in the entire vent pipe having a length of 200 m, the DF per 0.5 m length will be 1.012 to 1.024. The measurement result of DF shown in FIG.
It can be seen that F is secured.

In the embodiment described above, stainless steel fiber having high heat conductivity is used as the filter material, but the present invention is not limited to this. For example, it is possible to use a filter material having high heat resistance such as ceramic fibers.

Although the above embodiment shows that the decay heat attached to the vent pipe 7 can be removed by natural convection, other heat removal effects can be used. For example, it is possible to effectively remove decay heat by immersing a part or the whole of the vent pipe 7 in water. In this case, the evaporation amount of water is about 320 kg / hr.

Further, as described above, when the heat removal effect is large, it is not necessary to uniformly adhere the particulate radioactive substance in the pipe. Therefore, the filter material is not limited to the fibrous filter material as long as the particulate radioactive substance once adhered is not easily scattered again. For example, by installing the collision plate 21 inside the pipe 8 as shown in FIG.
Since 22 is deposited 23, it is possible to suppress re-scattering to be small.

By using activated carbon or the like as a filter material, gaseous radioactive iodine can be removed. In this case, gas molecules of radioactive iodine enter the filter material mainly by diffusion and are adsorbed on activated carbon or the like.

[0024]

As described above, according to the reactor containment vent apparatus of the present invention, radioactive substances are collected in the vent pipe and decay heat is reduced without installing a large-sized radioactive substance removing device. It is possible to remove it.

[Brief description of the drawings]

FIG. 1A is a longitudinal sectional view of a vent pipe of a reactor containment vent device according to one embodiment of the present invention, and FIG.
FIG. 3A is a cross-sectional view taken along the line AA.

FIG. 2 is a configuration diagram showing a schematic configuration of a reactor containment venting device of the present invention.

FIG. 3 is an operation diagram showing a particle collecting mechanism in a vent pipe in a laminar flow state.

FIG. 4 is an operation view showing a particle collection mechanism in a vent pipe in a turbulent state.

FIG. 5 is a characteristic diagram showing a measurement result of a particle diameter dependence of a decontamination coefficient by a vent pipe in a turbulent state.

FIG. 6 is a vertical sectional view of a vent pipe showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reactor containment vessel 3 ... Isolation valve 4 ... Stack 5 ... Radioactive substance removal means 6 ... Decay heat radiation means 7 ... Vent piping

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G21F 9/02 G21C 9/004 G21C 13/00 G21D 3/00

Claims (2)

(57) [Claims] 1. A reactor containment vessel of a boiling water reactor, a stack installed outside the reactor containment vessel, a vent pipe communicating the reactor containment vessel and the stack, and an intermediate part of the vent pipe. , A radioactive substance removing means provided on the inner wall of the vent pipe, and a collapse which is provided on the outer wall of the vent pipe and dissipates decay heat of the radioactive substance collected by the radioactive substance removing means. PCV vent apparatus according to claim Rukoto to have a heat radiating means. 2. The radioactive substance removing means is a mesh cylinder.
The reactor containment vessel according to claim 1, wherein
Equipment.