JPS59151098A - Transporting container for radioactive material - 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 is a method for transporting radioactive materials such as irradiation tube nuclear fuel material and irradiated metal materials between a nuclear power plant, a post-irradiation test facility, and a reprocessing plant. This invention relates to a container for transporting radioactive materials that has an improved structure to prevent the radiation of radioactive materials.

[Prior art]

As shown in the vertical cross-sectional view in Fig. 1, a conventional transport container for radioactive materials has a main body 1, a main body lid 2, a drain valve part 6, and a vent valve part 7. The interior 5 is surrounded by a layer 3 and a water layer 4 for shielding neutron beams.

After the irradiation tube nuclear fuel material and the like are stored in the interior 5 of the main body 1, the main body lid 2 is attached to shut off the main body 1 from the outside. The boundary between the inside 5 and the outside of the transport container, that is, the sealing boundary is defined by the O-ring 8 attached to the main body lid 2, the drain valve part 6, and the vent valve part 7. Details of the sealing structure of the vent valve section 7 are shown in FIGS. 2 and 3. The O-ring 8 has a double seal structure using rubber or the like with good radiation resistance, and a pore 9 is arranged between the two O-ring positions.
A plug 10 with an O-ring is provided at the outlet of the pore 9, that is, at the outer periphery of the main body lid 2, to maintain airtightness from the outside during transportation. Incidentally, the pore 9 and the plug 10 are used during an airtight leakage test to be described later. On the other hand, the drain valve part 6
Similarly, the vent valve part 7 is made up of a stop pulp 11 and a flange 12 as shown in FIG. ing. Also, a plug 13 is attached to the flange 12.
It has an fc and is designed to be used during airtight leakage tests.

On the other hand, gaseous radioactive substances such as rare gas and iodine are likely to leak from a container containing irradiated nuclear fuel materials, and the leakage occurs at the sealed boundary portion described above. Therefore, in order to confirm the sealability of the container before transportation, it is necessary to carry out an actual airtight leakage test to confirm that the amount of leakage from the container is minute. However, all currently used leakage testing methods employ a gas pressurization method. this is,
Gas (nitrogen gas or dry air) at a pressure equivalent to the internal pressure of the container during transportation is applied to the sealed boundary through the plug IO, 13, left for a long time, and the pressure drop is measured with an external manometer, and the pressure drop is measured as a unit. This is done by converting the amount of leakage of indoor gas and dry air per hour and correlating that value with the leakage of radioactive materials. The leakage device used in this case is shown in FIG. A leak test device 14 is connected to the container via three lateral pressure hoses 17, and the leak test device It14 is composed of a manometer 15, a pressure gauge 16, etc.

By the way, the above-mentioned gas pressurization method has a drawback in that it is greatly influenced by the ambient temperature during the milliliter determination.

Ru. In other words, accurate measurements can only be achieved by keeping the temperature around the armhole container, especially the temperature at the sealed boundary, and the temperature around the leak test device 14 the same, and also by suppressing temperature changes during measurement as small as possible. is difficult to implement. As a rule of thumb, the temperature change should be within 1-2 c. Due to the decay heat of the contained nuclear fuel material, the ambient temperature of the container after reaching thermal equilibrium is higher than the ambient temperature of the leak test device 14.

Therefore, the transportation container is placed inside the vinyl house 19, for example, and the leakage test device t14 is also installed inside the vinyl house 18. A heat generating element such as a light source is placed inside and blinked at appropriate times to optimize the ambient temperature of the leak test device 14.

@Although it depends on the size of the shipping container, in the case of a small container that can accommodate one or two irradiated fuel assemblies, if the calorific value is several kilowatts, the temperature of one set of container surfaces will be the same. As a result, it is not uncommon for the ambient temperature of the container to rise to 5C or more, even around the leak test device 14. Therefore, the gas pressurization method requires a complicated procedure for adjusting the ambient temperature, and also requires a long time to reach a measurable state. Furthermore, installation of the vinyl sheet requires labor, and a large amount of flame-retardant waste called vinyl sheet is produced. These drawbacks are exactly the same in the hermetic leakage test for large 1@ shipping containers.

[Purpose of the invention]

The present invention was made in view of the above situation, and an object of the present invention is to provide a container for transporting radioactive materials that completely eliminates the leakage of radioactive materials from inside the container, eliminates the need for airtight leakage tests, and can be transported safely. It is.

[Summary of the invention]

The transport container for radioactive materials of the present invention is suitable for transporting irradiated nuclear fuel,
The irradiation tube is formed so that a radioactive substance such as a metal material is stored and transported inside the main body, and a space is provided at the border that seals the inside, and the radioactive substance is stored inside the main body for transportation. During this period, high-pressure gas is sealed in the above-mentioned space (C) to prevent the radioactive substance from dispersing to the outside. Therefore, by leaking the high-pressure gas from within the sealed boundary into the transport vessel, leakage of radioactive materials from inside the container to outside the container can be prevented.

[Embodiments of the invention]

Hereinafter, the transport container for radioactive VJ material of the present invention will be described with reference to Examples and FIGS. 5 and 6, using the same reference numerals for the same parts as in the prior art and omitting the explanation of the structure of the same parts.

Figure 5 is a vertical cross-sectional view of the main body lid attachment part of the container, and Figure 6 is the 5th section.
It is a detailed view of part C in the figure. The location of the leak is as mentioned above.
The seal part of the main body lid 2, the drain valve part 6 and the vent valve part 7
However, the drain valve part 6 and vent valve part 7 have sealing performance themselves, and an O-ring is also placed on the flange that covers the valve part to provide a sealing function. It is important to take measures to prevent leakage from the two parts of the main body lid. For this reason, as shown in FIGS. 5 and 6, cutout spaces 20 and 21 are provided between the double O-rings 8 and 8 of the main body lid 2 in both directions of the main body lid 2 and the main body 1, respectively. Space 20 is pore 9
and is connected to the outside via a glove 10 with an O-ring. Further, the space 21 is also connected to the outside via a pore 22, a high pressure-resistant stop pulp 23, and a lid 24 with an O-ring. It should be noted that a small-sized stop pulp 23 with high pressure resistance is used to reduce the volume of the pulp installation space and to reduce shielding defects in the container.

Irradiated nuclear fuel, etc. is stored in the transport container in the fuel storage pool, so pool water remains in the space 20.21, so after opening the lid 10.24 and drawing out the residual water. Then, the lid 10 is closed again and nitrogen or dry air is sent through the valve 23. After reaching a predetermined high pressure, the pulp 23 is closed and the lid 24 is attached. After the transportation is completed, the lid 24 is removed and the valve 23 is gradually opened to release the gas in the space 20.21. As shown in FIG. 6, the structure of the cutout spaces 20 and 21 is such that the side walls are inclined to facilitate decontamination work after use of the transport container.

Next, a case will be described in which a small container is used to transport one or two irradiated fuel assemblies as radioactive materials into the transport container. The diameter of the intermediate position between the two 0-rings 8°8 in Figure 5 is 500 rtan, the distance between the top surface of the main body lid 2 and the 0' J song, that is, the thickness of the lid plate, is 60 m +, and the width of the 0-ring is 500 rtan. 5wn, and further set the distance between the two O-ring grooves to 15
Let it be mm. In addition, the volume of the notch space is 20.2
1f: 300 crn3 each, total 600 cm3
Let us assume that the width of the space 20.21 is 10 depressions.

As is clear from FIG. 6, the leak passage for the high-pressure gas sealed in the two notch spaces 20.21 is one that exits into the interior 5 of the container or the outside of the container through two O-rings 8.8. Those that exit the container from the O-ring part of the lid 10 through the pores 9,
There are four holes, one exiting from the O-ring part of the lid 24 to the outside of the container via the pore 22 and the stop valve 23. However, since the probability that the injection gas leaks through the stop valve 23 and further through the O-ring seal portion of the lid 24 is small, there are actually three leakage paths.

The sealed gas leaks due to viscous flow considering the pressure conditions, but
At that time, the gas is formed between the contact surface of the O-ring and the normally finished O-ring, for example, the diameter (a circle is used because it is easy to calculate and will be expressed as the diameter from now on) is several μ''%0! J groove width. It is thought that it passes through a minute gap with a length of 5 Wm and exits the container.Use an O-ring with no scratches on the surface, make sure that the surface that contacts the surface of the transportation container, that is, the sealing surface, is well finished, and then close the lid. By equalizing the tightening force of the bolts, it was easy to reduce the diameter of the minute gap to 1 to 2 μm or less.

Here, the pressure of the gas sealed in the space 20.21 is set to 20.
In terms of atmospheric pressure, the time required for all the sealed gas to leak out of the container due to leakage is given by the diameter of the minute gap being 3 μm.
If it is 2 μm, it will take about 10 days, if it is 2 μm, it will take about 40 days, and if it is 1 μm, it will take several hundred days or more. Therefore, there is a space of 20.
The gas in 21 only moves into the interior 5 of the radioactive material storage in the container, and the radioactive material does not leak out of the container.If the transportation work is completed during this time, the leakage of radioactive material can be completely ignored. . Note that the amount of leakage can also be determined by mixing several inches of helium into the sealed gas and using a helium suction probe and a V6 leak detector. and,
If it is determined by measurements during transportation that the amount of leakage from the temporary container is larger than expected, it is possible to perform the gas filling operation again.

In addition, the volume of the notch space 20.21 and the pressure of the sealed gas may be determined by taking into account the structure and dimensions of the transport container, the number of days required for transportation, etc. The sealed gas need not be limited to nitrogen gas, etc., and may be a rare gas. But that's fine. Generally, the amount of gas leaked under viscous flow conditions is inversely proportional to the viscosity coefficient, so if the gas has a large viscosity coefficient and is safe, there will be no problem. The depth of the notch space 20.21 in this embodiment is 20 mm, which is sufficiently small compared to the thickness of the main body lid 2, which is 60 ron, so that even if the transport container is dropped onto a rigid surface, Even if impact stress is concentrated in the space 20 of the main body lid 2 under such accident conditions, the main body lid 2 will not be damaged and the radioactive materials inside the container will not be scattered into the atmosphere.

If the transport container becomes larger, the diameter of the main body lid 2 will also become larger, and therefore the diameter of the notch space can be made larger, so as long as the space volume remains the same, the depth of the notch space will be shallower. It's over. In cases where it is difficult to provide a space 20 in the main body lid 2.
In this case, it may be possible to form the space 21 only on the container body l side as shown in FIG. 7 of another embodiment. In addition, even if a transport container were to catch fire and the surface temperature of the tea utensil rose to several hundred degrees Celsius, the airtightness of the container could be maintained by selecting O-rings and valves that could withstand the temperature. can be maintained.

In this way, the transport container for radioactive materials of this embodiment has high-pressure gas sealed in the space provided at the boundary that seals the interior containing the radioactive materials so as to leak to the inside.
There is no leakage of radioactive materials from the inside, so the airtight leakage test can be omitted, significantly reducing the number of work steps and improving safety compared to the conventional method.

FIG. 8 shows another embodiment, and the difference from the above embodiment is that the above embodiment has a single annular notch space, whereas this embodiment has a double annular notch space, and the outer annular cutout space is double. The point is that the pressure in the space is higher than that in the inner space. Three O-rings 25 are arranged on the main body lid 2, and cutout spaces 20° 21, 26, 30 are provided between each O-ring 25, and the outer annular spaces 20, 21 are provided with pores 9, 26, 30, respectively. M via 22
lo.

It is connected to the stop pulp attachment part 29. The inner spaces 26 and 30 are connected to the lid 28 through the pores 27 and 31, respectively.
It is connected to the stop valve attachment part 32. and,
The space 20.21 and the space 26.30 are independent of each other, and the pressure of the sealed gas in the space 26.30 is also the same as the outside space 20.
．． No. 21 has a higher sealing pressure. Therefore,
The gas in the space 26.30 never leaves the container and enters the interior 5.Also, the same amount of gas as the gas that entered the container from the space 26.30 always flows into the space 20.21. In the above embodiments, even more reliable sealing effects can be expected. Further, as shown in FIG. 7, a double annular space may be provided with an annular space provided only on the main body side.

〔Effect of the invention〕

As described above, the radioactive material transport container of the present invention has the effect of eliminating any leakage of radioactive material from inside the container, eliminating the need for airtight leakage tests, significantly reducing the number of work steps, and improving safety. .

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view of a conventional transport container for radioactive materials;
Figure 3 is a detailed view of part A in Figure 1, Figure 3 is a detailed view of part B in Figure 1, Figure 4 is an explanatory diagram of the airtight leakage test state of the transport container in Figure 1, and Figure 5 is a detailed view of part B in Figure 1. FIG. 6 is a detailed view of the section C in FIG. 5, and FIGS. 7 and 8 are a longitudinal cross-sectional view of the main body lid attachment part of the embodiment of the radioactive material transport container, and FIG. 7 and FIG. 7 is a detailed view of the same portion as FIG. 6, and FIG. 8 is a longitudinal sectional view of the same portion as FIG. 5. l...Body, 2...Body lid, 5...Inside, 20,
21゜Figure 1 Figure 21 Figure 4 19

Claims (1)

[Claims] 1. Irradiation cylinder In a transportation container that stores and transports radioactive materials such as nuclear fuel materials and irradiated metal materials inside the main body, a space is provided at the border that seals the interior, and the radioactive materials are stored inside the container for transportation. A container for transporting radioactive substances, characterized in that a high-pressure gas is sealed in the space to prevent the radioactive substances from dispersing to the outside while the radioactive substances are contained therein.