JPS59201000A - Method of storing radioactive solid waste - 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] [Original field of application of emitting ψ] The present invention is a method for storing highly radioactive FM bodies and other cold materials that must be strictly isolated from the environment and flavored in a safe and green manner. Regarding how to.

[Background of the invention]

When storing highly radioactive solid ash vehicles, such as used 61 nuclear fuel, in containers and storing them, consideration must be given to the following points.

B. Shield from radiation.

Do not leak radioactive materials outside the container.

..., the ability to safely remove decay heat.

2. Under no circumstances should a criticality accident (nuclear runaway accident) occur.

E. Reducing the volume of a certain amount of radioactive solid waste and the volume of its storage container, and reducing the volume of waste.
11. What is economically desirable.

Regarding radiation-induced erosion, the waste storage and supply container should be stored separately in a container made of relatively short and strong elements such as iron or lead, or it should be stored underwater or in a concrete container or underground. However, these are not directly related to the present invention. Hon Umoaki is directly related to the above statement.
Ha, that's two.

A typical example of this type of prior art is the storage of high-level waste generated during the reprocessing of used fuels in glass assimilates. A concrete example of the glass assimilation storage method is the French AVM method (Techniques for the
5olidification of High −
Level Wastes+IAEA, Vienna
a, 1977, STI/DOC/10/176
) i There are two. The approximate process is shown in Fig. 1f. In the figure, the part surrounded by the dashed line is the part directly related to the storage method based on the glass assimilation method.

As shown in FIG. 1, the spent fuel is sheared and dissolved in nitric acid so that the nuclear fuel material inside the temporary casing is easily dissolved into nitric acid. The uranium and plutonium are then extracted using an organic solvent in a bath. The remaining high-level liquid contains most of the fission products that were present in the liquid as nitrate. High-level waste liquid is condensed and temporarily stored. The streaked waste liquid is fed at a constant rate to the kiln, where the moisture first evaporates and
Subsequently, the nitrate is thermally decomposed to form a solid infusion. This liquefied material contains norconium, molybdenum, cesium, strontium, ruthenium, cerium, neotum and other elements.
2 radioactive thread force ≦ included.

Next, as a special step of the glass assimilation method, the above-mentioned liquefaction product is mixed with boride glass powder, heated to 1150°C by induction heating in an Inconel glass melting furnace, and melted to form boride glass and various melts. The glass melt is poured into a heat-resistant and corrosion-resistant container into a bale of uniform glass melt by allowing the vitrification reaction to proceed between the objects, and is then cooled and solidified. After that, a lid is welded to the container, the outer surface is decontaminated, and the container is stored in a concrete storage container.

In this glass assimilation method, the leakage of radioactivity is firstly prevented by using a heat-resistant and corrosion-resistant sealed container, but secondarily, radioactive elements are added to the glass in a vitrified material that is difficult to dissolve in water. It is given by incorporating it as a constituent element of the crystal.

Normally, a fuel assembly for a light water reactor (Shikacho Suiou) contains about 200 parts of uranium, but the container ♦ calculated from its external shape is about 90 A, and 9 parts per ton of uranium is 360 A'. In the glass assimilation method, when light water reactor fuel consisting of 1 ton of uranium is reprocessed, a vitrified material with a volume of 150 t is produced.

The glass assimilate material is exposed to the central 161S due to the decay heat of the radioactive material.
During storage, the temperature should be cooled (by ensuring air flow, etc.) to maintain the vitrification reaction temperature.
It must be ensured that the temperature does not exceed 00℃. Since the amount of fissile material trapped in the vitrified material is small, there is no risk of criticality failure occurring.

The force solidification method described above is currently considered to be one of the safest and most reliable methods for storing highly radioactive materials, but problems include the sloppyness of the process and the highly radioactive glass bath melt. ``Old technology due to the play of equipment etc.'': 1 is point and economy. The handling of commercial radiation injection materials must be carried out completely remotely, but in this respect as well, the core miscellaneousness of the glass assimilation method, coupled with the difficulty of equipment maintenance, poses a great deal of problems.
This is a burden on the neighbors.

[Purpose of the invention]

The purpose of the present invention is to reduce the volume of densified 7 pieces of waste + radioactive 1 piece of waste into a container and reduce the volume by 1 to 1. The purpose is to provide a new and easy method.

[Summary of the invention]

The method of the present invention does not use a chemical process that is complicated and difficult to remotely control as seen in the above-mentioned prior art, and is characterized by heat resistance, which exceeds the plasticity of pressurization 1, and which can be used at around room temperature. After filling a container made of an edible metal material with a solid radioactive substance, welding blood to the container and sealing it with little coexisting gas, the container is placed together with the contents in a moss mold at a high temperature. The container is then compressed and placed in such a way that the outer shape of the pressed container has a substantially uniform shape determined by the mold. This reduced volume sealed container can be easily stored in a secondary oven.

[Embodiment of the invention: f:j>] FIG. 2 shows a process flow diagram of an instant embodiment of the method of the present invention. The commercially resistant solid waste targeted for this disaster relief project was spent fuel from Keisui reactors (boiling water type), which was burned down in 1 tank and 9
An assembly of fuel rods in which a pellet of uranium dioxide is enclosed in a zirconium alloy tube: 4') rJ
y, -J is written.

゛First, after removing the upper and lower stainless steel members of the fuel assembly, the fuel pruning that is not used in normal spent fuel reprocessing 1
Using the device e, Somura (, i) was sheared into a length of approximately 4 m.

The container made of gold H1 that serves as the collection container is made by bath-welding austenitic stainless steel ↓ Oka plate with a thickness of 5111 m.
Outer diameter is 30 cm and height is 35 cm -CG A”A
Vmar,”b) 20t.

The sheared pieces with a small amount of fuel were charged into this vessel. At this time, by applying vibration over time, the final porosity (porosity W /
The ratio of lji to the total ratio of 1) was 0.4. The force of each discharged fuel rod fragment is 100 kg,
Of these, uranium dioxide is 81, g, '&4'i'
The weight of metal members such as "m" material was 19 kg.

Next, a metal tray was fitted into the filled container.

The lid of the container is machined to fit into the opening of the container.

After the container was filled with fuel rod sheared pieces and fitted with a lid, the container and the lid were welded using a 111 twin beam welding device. Since the electron beam bath welding rod performs welding by irradiating the entire electronic assembly in a vacuum-kept container and concentrating the electron beam on the welding area, the inside of the device must be in a vacuum state before welding. Therefore, the gas inside the container was also removed.

As a result, the fuel rod sheared pieces are exposed to light and sealed in a state where there is little gas coexisting in the welded container.

The integrity of the welded part is determined by first transferring the sealed container after welding is completed into a vacuum container, evacuating the vacuum container, filling it with helium, and then evacuating it again to remove any residual gas in the vacuum container. The fuel rods were tested by mass spectrometry to confirm that there was no leakage of helium from the sealed container.

The outer surface of the sealed container is polished and smoothed in advance to prevent contamination from nuclear fuel materials from adhering to it; however, any contamination along the surface after the above inspection can be removed by wiping it with a damp cloth. The removed O is then smeared (wiping method) on the surface of the bud-sealed container.
Measure the contamination density by k J
IJ came. By this operation, there is no need to worry about secondary surface contamination of the equipment when handling the storage container from this point on.

Next, the sealed container was heated to 1200°C, which is the solution treatment temperature for austenitic stainless steel, in an inert gas-filled furnace, and the contents were brought to a uniform temperature before being compressed. carried out the work.

Two examples adopted for this compression process will be described below.

In one example, a sealed container heated to 7 il at 1200° C. is transferred to a 40 cnr (D) mold with an inner diameter of 31, and immediately IB
Compressed. Pressure was applied until the total pressure reached 2000 m. The compressed primary M-body (symbol of the above-mentioned sealed container at this stage) was extruded from the mold with a punch at the bottom.

After this secondary storage body is completely cooled, the outer diameter is 3 I CIn5 ? m is 21 saw and 7 Hi.

The total weight, including the container weight, is 124 kg, the volume is approximately 16 tons, and the volume reduction of the container is 20%, which is very low. The solution treatment temperature is 40%, which prevents the precipitation of carbide between crystal grains by heating to this temperature and then rapidly cooling it by pressure wire processing.
The i+1l property was chosen as the temperature at which it was impossible to reduce the temperature by 1. In addition, the yield point of austenitic stainless steel heated to 1000°C is low enough to be deformed by pressurization, whereas the yield point of austenitic stainless steel heated to 1000°C is sufficiently thick to cause extreme thinning phenomenon when deformed by pressurization. It was something. Fuel rod sheared pieces 'ff filled in container (c): The IQ drop point of the composing zolconium alloy is lowered by heating it to 1200°C for 8 hours, and it is easily deformed by pressurization, forming a sintered pellet of uranium dioxide. It acted to fill the void f in the crushed grains. Although the beam point of uranium dioxide is as high as 2740'C, it does not cause plastic deformation when heated to a temperature exceeding 1000°C, and when pressurized, it cooperates with the deformation of the zirconium alloy to deform the body of the sealed container. Contributed to 1 decrease.

The heating temperature needs to be higher than 1200°C, which is the solution treatment temperature for austenitic stainless steel, but it needs to be kept lower than 1600°C, which generates a bath melt phase at grain boundaries. For Mihara, it is recommended that the temperature be set to 1,300°C for the design, operation, and maintenance of the equipment.

A second embodiment of compression processing is fully described below.

It started heating to 1200℃! Inside the sealed container -31αn
The mixture was transferred to a mold with a depth of 40 cm, and immediately compressed by impact using a pair of upper and lower punches that fit the inner diameter of the mold. Opposite I
The compression was carried out by instantaneously introducing the barge gas pressurized to about 2,000 atmospheres into the gas chamber connected to the piston of the pressure rope to reduce the amount of coexisting gas in the gap where the radioactive solid was sealed in the 7Co container. Therefore, when the gas inside the container is compressed and compressed during compression processing, the internal pressure of the container is not hindered.

The compressed primary storage body was ejected from the mold using the lower punch (LC). The dimensions of the secondary storage body were measured after being air-cooled, and the outer diameter was 31C + z + v and the quotient was 20.771. Container The total weight including weight is i 24 + < y,
The volume was about 15 tons, and the reduction in weight per 1'4 of the container was 25 so. In this way, compared to the case of the above-mentioned frP compaction, the volume reduction of the sealed container was improved by 5 cm in the case of price compaction, although the pressure per unit area was 9 cm lower. This is thought to be due to the extremely one-shot compression process promoting plastic deformation of uranium dioxide. It was also observed that the plastic rhombus shape of the Norcaloy alloy tube material was -4.

-The shape of the storage body is similar to the shape of the mold, but in the example, the shape was cylindrical with the side wall of the container bent, as shown in Figure 3, which will be described later. .

Even if the sealed container is deformed due to compression processing, the sealing performance of the container must be maintained soundly. For this purpose, it is necessary to adjust the initial porosity of the optical layer of the radioactive solid waste so that the volume reduction rate due to compression processing does not exceed 50%.

Although the primary container thus neglected may be suitable for storage as is, it is desirable to store it in a secondary container for safe storage. If a plurality of primary containers are stored in a secondary container using bamboo, storage and handling operations become easier.

Next, we will explain the process of storage in a secondary container.

In Fig. 3, 1 is the hermetic awn (4, sheared piece), 2 is the sealed container filled with the compressed awn (Ia primary container),
3 is the lid, 4 is the secondary container, 5 is the tray of the secondary container, 6 is the welded part, 7 is the helium that has been stored in the secondary container, 8 is the helium filling hole, and 9 is the handle. The secondary container is made of austenitic stainless steel with an inner diameter of 330 ns and an outer diameter of 35 cm.
0 tnr.

In this secondary container, the above-mentioned primary storage bodies are stored in eight stacked stages. The lid 5 is manufactured to fit into the opening of the secondary container 4. Book 5 describes the inside of the secondary container (r) after welding.
(It has a filling hole 8 for filling and sealing with helium and a handle 9 for handling the secondary storage body.

For the fitting part between the secondary container 4 and the lid 5, maintain argon gas.
As J gas, the sword 11 is made in advance: yi: TIG using the bath knife mouth (〉;, which is made of the same material as the container 4) for the tip.
Bathing was performed entirely remotely. Fill the inside of the secondary container with helium through the filling hole 8 provided in the hole 5, and then roughly blow argon into the filling hole 8.
It was sealed by G welding. Large 4i like secondary container
TIG to weld part of i'j lumber with full remote control
Excellent welding operability.

As a result, 650 kg of uranium dioxide and 150 kg of ridge material were simultaneously stored in the secondary container.

As for the secondary container, it is sealed inside and it is confirmed that no hyhelium is leaking from the sealed welded part by chain weight analysis.
The contamination level on the surface of the secondary container was measured using the smear method (wiping method) for 2 years to confirm that there was no contamination, and the container was completed.

Due to its high heat content 4t4, the helium filled and sealed in the secondary container promotes the transfer of decay heat from the surface of the primary container to the outside, reducing the effect of preventing the surface temperature from rising. Filling with helium has the effect of making it easier to perform a leak test on the trench/ζ cold welding part and making it easier to check the health of the bath welding part.

Compared to a primary storage body processed by static pressure processing, one processed by shock pressure and compression processing has a higher rate of decrease in body mass, so by carefully determining the dimensions of the secondary container, the same Next, I will store a large number of them in a container.

When the sheared pieces of spent fuel are put into the primary (outer container) and sealed, the height of the secondary container (-J, 35/17++) is stored in the secondary container as it is. Then, although only 5 primary storage objects can be stored in the secondary valley, by allowing compression, 8 primary storage objects can be stored in 41 meters, increasing the storage capacity by 60%.

In the above-mentioned embodiment, spent light water reactor fuel is used as a radioactive solid substance.
(including powder) - can also be used for shrimp radiation 1 biological liability. In other words, the sludge diagram shown in Figure 2 can also be applied to powdered garbage and ceramic powder.

The radioactive substance to be stored is a substance that does not emit gas when heated, and may be a single substance or a compound (the present invention can be applied even to a mixture thereof. When it comes to substances that generate gas due to pK, there is a limit to the pressure I processing of the Fujisashi container, and depending on the case, it may become repeated.

Even in the case of these general applications, the mechanical features regarding volume reduction, high intelligence, sealing performance, isolation performance, operability, etc. are the same.

〔Effect of the invention〕

According to the method of the present invention, the storage operation of a single radioactive solid waste can be performed by a combination of relatively simple operating means established in the prior art. (・Prevents the scattering and dispersion of radioactive materials and the generation of secondary waste.

The various pumping equipment necessary for carrying out the present invention are less likely to be contaminated with radioactive materials during normal operation, so maintenance of the equipment is easy, and process reliability and operation rate are high. , it is possible to keep the radiation exposure of nine workers during operation to a low level.

According to the method of the present invention, a volume-reduced/ζ-order storage body in which radioactive solid waste is densely filled in a sealed container is obtained. For example, as in the embodiment described above, the outer diameter is 35 cTn%.
Ti7j All eight primary storage bodies are stored in a secondary container with a length of 180 cm and an internal volume of 150 tons, which is equivalent to approximately 57 uranium.
To 0! It can store as many as 9 fuels. According to conventional vitrification methods, approximately 1000
Reprocessing high-level waste from spent fuel equivalent to 1,000 y of uranium can be made into 150 tons of glass assimilate, so compare this point! i
It seems that the reduction ratio is low for 7. However, in contrast to the rice promotion method, which produces glass assimilates and medium- to low-level solid materials with a volume of about 10 times or more depending on the reprocessing, the wide-aggregation method of the present invention produces liquid assimilates. Since it does not use a medium-to-low level) vehicle generation-il, it has the advantage of requiring fewer employees.

According to the present invention, by increasing the density of the radioactive solid inside the secondary storage body, the thermal conductivity is high even in the case of low-density powder packing, and even if disintegration heat is generated, the radioactive solid is not radioactive. This has the effect of preventing the temperature of the solid from becoming too cold.

In addition, by making the radiation pressure solids the same density inside the container, even if water should enter the container, the reaction between water and radioactive solids will be prevented, and even if there is nuclear fuel material, water will not react with the radioactive solids. This prevents the uniform dispersion and mixing of the substances, which has the effect of completely preventing criticality accidents from occurring.

In addition, by storing it in the secondary container, a double V unit ± 1 kilometer can be constructed.
9. Reliability is increased and at the same time, the storage unit becomes easier to operate.

[Brief explanation of the drawing]

Figure 1 shows the conventional method of storing radioactive solid waste using the glass solidification method, step 0;
Figure 33 is a process flow diagram showing an embodiment of the method of the present invention, and Figure 33 is a cross-sectional view showing the yield + body obtained by carrying out the present invention. DESCRIPTION OF SYMBOLS 1... Spent fuel rod sheared pieces, 2... Reduced primary container, 3... Lid of secondary container, 4... Secondary container, 5...
...Secondary container tray, 6...Bath contact, 7...Helium, 8...1 hole filled with helium, 9...
handle. Figure 1 'J': 'S Figure 2 Figure 3

Claims (5)

[Claims] (1) A container made of heat-resistant metal material that is plastic under heating and corrosion-resistant at room temperature, is filled with radioactive facepiece waste with a small porosity, and a lid is welded to the container in a state with little coexisting gas. Then, the container is heated to a solution treatment temperature corresponding to the properties of the metal material, placed in a mold, and compressed with a punch to a constant outer diameter 'ff determined by the inner diameter of the mold. : A method for storing a radioactive solid bεε animal, characterized in that the volume of the container is reduced so as to have the following properties: (2) In the storage method described in the preceding paragraph, special measures are now being taken to ensure that the radioactive solid waste is not compressed in the mold of the completely sealed container. How to store Hobetsu Sen solid 1-yuan pear food described in Section 1 of the Men's Koumi episode. (3) Confirmation of the seal of the container in which the radioactive IL-・i body j; C vehicle was stored in a state with a small amount of coexisting gas.
3. A method for storing radioactive face piece waste according to claim 1 or 2, wherein the heating and compressing portions described above are carried out by hoeing. (4) Sealing the radioactive solid waste whose volume has been reduced by the compression in a completely sealed container or nuclear ridges in another container. 1st
Section 2, Section 2 or Section 3, "Coffin's Hougetsu 1sha" storage method for physical belongings. (5) A straw material having a thermal conductivity is sealed between the walls of the completely sealed radioactive solid waste container whose volume has been reduced by compression and which are present in the separate container. A method for storing radioactive facepiece waste as set forth in claim 4.