JPH02147899A - Treatment for volume reduction of radioactive waste by hip - Google Patents

Abstract

PURPOSE:To treat the radioactive waste consisting of zircaloy to reduce its volume by a hot isostatic pressurization (HIP) method of a relatively low pressure by using a metal having the high eutectic m.p. with the zircaloy as the material of a capsule. CONSTITUTION:The material for constituting the capsule 16 is selected from titanium, titanium alloy, zirconium, and zirconium alloy as the metal having the high eutectic m. p. with the zircaloy. Used fuel cladding pipes consisting of the zircaloy are packed as the radioactive waste 18 into the capsule 16 to form an object 14 to be treated. The object 14 is installed into an HIP pressure vessel 10 and a pressure medium is introduced therein and is heated by a heater 12. The object is thus solidified and treated by the HIP at a high temp. under a uniform pressure and is thereby reduced in volume. The sufficient solidification performance is obtainable even if the pressure is kept under <10kgf/cm<2> if the treating temp. is set at about 1,400 deg.C which is below the eutectic m. p. of the capsule material with the zircaloy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for HIPg treatment of radioactive metal waste mainly composed of Zircaloy, such as spent fuel cladding tubes.

[Prior art] Radioactive waste such as spent fuel cladding tubes generated in the reprocessing process of spent twisted t-1 is produced by H! Volume reduction and solidification treatment is carried out by the P (hot isostatic pressing) method.
As shown in Fig. 1, in the HIP method, a pressure medium (inert gas) is introduced into a pressure vessel 10, and at the same time the internal heat tank 10 is
This is a method of compressing the object to be processed 14 at high temperature and uniform pressure by heating at step 2, and is widely used in various fields.

In the volume reduction treatment of spent fuel cladding using this HIP method, a stainless steel capsule 16 is used, and the capsule is filled with radioactive waste 18 such as spent fuel cladding made of Zircaloy. It is referred to as a processing body 14. Here, the processing temperature is limited to 1100°C or less, and usually 1
It is necessary to maintain a pressure of 50 kgf/cm" or more at a temperature of 1,000°C for several hours.

[Problem to be solved by the invention] In the conventional technology, high pressure Ar gas as described above is used as a pressure medium in HIP processing, so it is necessary to conduct periodic safety inspections under the High Pressure Gas Control Law. .

Since the object to be treated here is radioactive waste, the inside of the facility must be completely decontaminated so that inspectors can enter the controlled area during inspections. Therefore, it becomes necessary to close the facility for a long period of time, during which time the HIP processing operation must also be stopped, which significantly reduces the operating efficiency of the facility.

The purpose of the present invention is to eliminate the drawbacks of the prior art as described above, and to meet the conditions where the High Pressure Gas Control Law is not applicable, that is, 10 k
The object of the present invention is to provide a HIP volume reduction treatment method for radioactive waste that can obtain sufficient assimilation performance even at a pressurizing pressure of less than "gf/cm" and that allows easy installation and management of the device.

[Means for Solving the Problems] The present invention, which can solve the above technical problems, uses a capsule made of titanium, titanium alloy, zirconium, or zirconium alloy, and contains radioactive waste mainly made of zircaloy. and the capsule material 4
and at a temperature below the eutectic melting point of Zircaloy and]
This is a $1 volume IIIP treatment method for radioactive waste in which the IIP treatment is carried out at a pressurizing pressure of less than f/cm''.

Preferred conditions for actually carrying out this process are that the HIP treatment temperature is approximately 1400° C. and the pressurization pressure is approximately 9 kgf/cm”.

[Function] In the conventional technology, the pressurizing pressure is at least 50 kgf/cm'
The above reason is necessary because the heating temperature is limited to 1100° C. or lower. This is because the eutectic melting point of stainless steel, which is the capsule component material, and Zircaloy, which is radioactive waste, is 1100°C, so when heated to that temperature, the stainless steel capsule melts and the pressure medium enters the capsule. This is because it cannot be compressed. Therefore, in practice, II IP treatment was performed at about 1000° C., allowing for a margin for temperature control.

Since the present invention uses capsules made of titanium, titanium alloy, zirconium, or zirconium alloy, the eutectic melting point of titanium and zircaloy is high; for example, titanium has a high eutectic melting point of 1537°C, which is much higher than that of the conventional technology!
, i It can be processed at about 00°C.

On the other hand, as shown in FIG. 2, the strength of Zircaloy decreases as the temperature increases, and if the heating temperature is set to about 1400°C, sufficient assimilation performance can be obtained with an applied pressure of less than 10 kgf/cm'.

[Example] The first feature of the present invention is that a metal material having a high eutectic melting point with Zircaloy is used as the constituent material of the capsule, instead of stainless steel as in the prior art. This type of material is selected from titanium, titanium alloys, zirconium, and zirconium alloys. A spent nuclear fuel cladding tube made of Zircaloy, a radioactive waste, is then filled into a capsule made of that material.

The object to be treated thus obtained is placed in a HIP pressure vessel, heated by an internal heater, and a pressure medium is introduced to perform IIIFσ solidification treatment at high temperature and uniform pressure.

The second feature of the present invention is its I (I P treatment conditions. This treatment is carried out at a temperature below the eutectic melting point of the encapsulant and Zircaloy and at an applied pressure of less than lOkgf/c, m2. More preferably, it is carried out at a temperature of about 1,400°C and a pressure of about 9 kgf/cm.In the present invention, the capsule is made of a metal with a high melting point of eutectic T8 with Zircaloy instead of stainless steel. Strength is maintained up to high temperatures.For example, when titanium is used as the capsule material, its eutectic melting point with Zircaloy is 1537°C.
Therefore, even if allowances are made for temperature control costs, etc., it is 14
The treatment can be carried out sufficiently at 00°C.

On the other hand, the high temperature strength of Zircaloy is 1 as shown in Figure 2.
When it exceeds 000°C, it gradually decreases.

Apply pressure for compression of less than 10 kgf/cm" (actually, if the design pressure is 9.9 kgf/cm", set the normal pressure to 9.0 kgf/cm") to reduce the volume. A temperature of about 1400°C is sufficient for solidification. Also, the pressurization time can be determined appropriately depending on the size of the object to be treated. Therefore, if capsules made of the above materials are used, the temperature will be relatively low. It becomes possible to exhibit sufficient solidification performance with force n pressure.

[Effects of the Invention] As described above, the present invention uses a metal material with a high Af4 point of eutectic melting with Zircaloy instead of stainless steel as the capsule material of the object to be processed, so that it can withstand high l crystals at about 1400°C. ,
This has the effect of making it possible to perform II + P volume reduction treatment of radioactive waste made of Zircaloy at a relatively low pressure of less than 10 kgf/cm''.

For this reason, the application of the High Pressure Gas Control Law will be exempted, and there will be no need to stop IIIP treatment work for a long period of time due to decontamination work by inspectors for safety inspections or preparation of the Yl. Of course, regular self-inspections using gastric sweat must be carried out, but in that case, inspectors can provide the necessary shielding protection, greatly shortening decontamination work. In this way, the installation and management of the device is facilitated, and the operating efficiency of the device is increased.

4. fiii A'- explanation of U21 side Figure 1 is HI
An explanatory diagram showing an example of the P method, and FIG. 2 is an explanatory diagram showing the high temperature strength characteristics of Zircaloy.

DESCRIPTION OF SYMBOLS 10... Pressure vessel, 12... Heater, 14... Treated object, 16... Capsule, [8... Radioactive waste.

Special contract applicant: Power reactor/nuclear fuel development +1 industrial group representative: Osamu Man Shigeru Mi Selection

Claims (1)

[Claims] 1. A capsule made of titanium, titanium alloy, zirconium, or zirconium alloy is used, and radioactive waste mainly made of zircaloy is filled inside the capsule, and the eutectic melting point of the capsule material and zircaloy is 1. A HIP volume reduction treatment method for radioactive waste, characterized in that HIP treatment is performed at a temperature below 10 kgf/cm^2 and at a pressure below 10 kgf/cm^2. 2.HIP treatment at a temperature of approximately 1400℃ and a pressure of approximately 9kg.
The HIP volume reduction treatment method according to claim 1, which is carried out at f/cm^2.