JP4448159B2 - Radioactive waste treatment method - Google Patents

Description

The present invention, radioactive waste discharged from nuclear power plants (metals, inorganic substances, etc.) are those concerning the volume reduction processing for volume reduction and specifically in the high-frequency heating in the volume reduction treatment When the canister (crucible) is damaged, the molten material (molten metal) is surely prevented from flowing out of the crucible and contaminating the work chamber (so-called cell). it is to shall so can be done.

A high-frequency heating and melting furnace loads a radioactive waste (conductive metal) w that is subject to volume reduction into a ceramic crucible called a canister, and heats and melts the waste w to reduce the volume. It is. By reducing the volume of radioactive waste, the storage cost of the waste is greatly reduced.
The conductive metal in the canister is heated and melted by high-frequency heating, and the non-conductive substance (inorganic material) put together in the canister is also melted.

The canister used in this high-frequency heating and melting furnace is designed so as not to be damaged in the heating and melting process, but may be damaged. Canister damage includes internal / external temperature differences during temperature rise or cracks due to thermal shock, damage due to physical shock, and erosion of the inner wall due to boiling convection of the melt.
If the canister is damaged during the heating and melting operation, the melt (radioactive material) will flow out and contaminate the surrounding area. It is necessary to perform work to restore the work environment such as necessary gradual contamination. Further, in order to suppress the spread of contamination as much as possible, gradual dyeing work and the like are urgently performed, but this post-processing work is performed by remote operation in a sealed space called a cell. Therefore, workability is poor and work efficiency is poor.
Various devices have been made to speed up post-processing operations such as minimizing the outflow of contaminated melt when the canister is damaged. One of them is described in Japanese Patent Application Laid-Open No. 2004-77218 (Patent Document 1) (hereinafter referred to as “prior art”).

  By installing the canister in an insulated container, even if the canister is damaged, the leaked material is received by the insulated container, thereby preventing the melt from flowing out and polluting the work environment. This is described in Japanese Patent Laid-Open No. 1-181088 (Patent Document 2).

[Conventional technology]
3 and 4 show an outline of the prior art of the above-mentioned Patent Document 1, in which a receiving tray 6 is provided below the pedestal 3, and the receiving tray 6 and the pedestal 3 are moved up and down by the elevator 5. .
The cylindrical body (sleeve) 4a of the high-frequency heating furnace 4 has a larger diameter than the canister 2, and when the canister 2 is pushed up and attached to the high-frequency heating furnace 4, a relatively large gap 7 is formed between the cylindrical body 4a. Is formed. Then, high-frequency heating is performed in a state where the gap 7 is filled with the sand-like material 8. The original function of the cylindrical body 4a is a protective sleeve for protecting the inner surface of the heating furnace from the scattered matter when the melt in the canister boils.

If the canister is damaged in the heating and melting step and the melt flows out, the melt is received by the sandy object 8. When the canister 2 is lowered together with the pedestal 3, the sandy object 8 falls and is accommodated in the tray 6.
The sand-like material 8 has heat resistance and fluidity, and has heat insulation properties for the canister 2, thereby greatly reducing the temperature difference between the inner surface and the outer surface of the canister 2, and thermally protecting the canister 2. Has the function of
Moreover, since the layer of the sandy object 8 supports the canister 2 from the outside, it also functions to reinforce the canister 2.

Further, in Patent Document 1, a canister 21 is built in an outer container 22 to form a heavy duty composite container, and a sand-like object 23 is filled in a gap between the inner and outer containers, and the sand-like object 23 is the bottom of the outer container 22. There is also described an example in which it is excluded from the discharge hole 24 and collected by the receiving tray 25. In this example, if there is a molten material leak, it is received by the sandy material 8, which acts to harden and reinforce the damaged part, and removes the sandy material to be post-processed. The outer container is often fixed to the canister due to the curing of the object, and there is a problem that the removal is extremely difficult (this removal operation is performed by remote control in the cell), and the sandy object There are many problems that need to be solved for practical use, such as the filling and removing operation, and the control thereof being difficult, and the possibility that the sandy material becomes a new radioactive material.
In short, the thing of patent document 1 supports the outside of a canister with a sandy material layer, receives a molten leak with a sandy material layer, and prevents this from leaking into a work environment and being polluted, Its practical use is difficult and expensive.

[Problems of the prior art]
By the way, in this device that handles high-level radioactive waste, it is necessary to operate the device remotely (because humans cannot enter the cell), and the molten leaked material that has entered the pan is solidified here. Removing the saucer 6 and installing a new saucer is a difficult task. Moreover, since the used tray is also radioactive waste, it is not easy to treat it.
As described above, by installing the canister in the outer container (ceramic container with excellent heat resistance), even if there is a melt leak from the canister, it can be received by the outer container and prevented from flowing out to the tray. can do.

However, in the prior art, it is necessary to remove and clean (decontaminate) the sand-like material contaminated with the melt, and post-processing work for resuming operation is not easy. And since a post-processing work is done by remote control, it is troublesome and inefficient, and it is inevitable that the operation stop time becomes long.
It is necessary to construct a system that does not allow a melt leak from the canister to flow out of the outer container, and to allow easy and easy post-processing work by remote control.
JP 2004-77218 A Japanese Patent Laid-Open No. 1-181088

Therefore, the present invention has the following problems.
In other words, there is a leakage of molten material from a canister in a case where a double composite container is configured by combining a canister that is loaded with radioactive waste and is heated and melted with a high-frequency heating device to reduce the volume, and an outer container. However, it is intended to prevent it from flowing out of the outer container and to easily and easily perform post-processing work when there is a melt leakage by remote control.

Means for solving the above-mentioned problem is a radioactive waste treatment using a radioactive waste volume reduction container which is loaded with radioactive waste to be reduced in volume and heated and melted with a high-frequency heating device to reduce the volume. About a method, it is based on following (a)-(f).
(B) The radioactive waste volume reduction container is a double composite container with a canister fitted to the outer container.
(B) The outer container is a heat-resistant ceramic container, and there is a gap between the canister and
(C) The gap between the canister and the outer container should be large enough to hold the canister by inserting the remote control jig.

(D) The outer container is made of silica-based ceramic, mullite-based ceramic, or alumina-based ceramic.
And (e) an infrared temperature sensor for measuring the temperature of the outer surface of the outer container.
And (f) when the waste is leaked from the canister when the waste is heated and melted by a high-frequency heating device, the double composite container of the canister and the outer container is placed outside the high-frequency heating device. In the next step, post-processing is performed on the entire double composite container,
If the previous SL molten product was not leaked from the canister, insert the remote control jig to hold the canister in a gap between the outer container and the canister is taken out from the outer container, that In the next step, subsequent processing is performed on the canister alone.

[Action]
A double composite container composed of a canister and an outer container is mounted on a high-frequency heating device, and the radioactive waste in the canister is heated and melted. Then, after being taken out from the high-frequency heating furnace and cooled, a remote control jig is inserted into the gap between the canister and the outer container, and the canister is taken out from the outer container and stored in a storage container such as a drum can. On the other hand, the outer container is reused.
Since there is a gap between the canister and the outer container, the canister can be easily removed from the outer container by remote control by inserting a remote control jig into this, and a new canister can be removed from the remote control jig. It can be fitted into the outer container while being held on.

Even if the canister is damaged during heating and melting, and the molten material leaks, the leaked material is received by the outer container and does not flow out to the outside. Therefore, the outflow of radioactive melt does not contaminate the canister base (cradle), the melt pan, the cell inner floor, and the like.
When leakage is detected, the high frequency heating is immediately stopped, and the double composite container with the canister and the outer container is moved out of the high frequency heating apparatus, and in the next step, the entire composite container is subjected to post-processing. Is made. That is, when the molten material leaks from the canister, the leaked material is held in the outer container, and the canister and the outer container are integrated by hardening of the leaked material. Double composite containers are relatively easy to handle. In the meantime, molten contaminants do not contaminate the pedestal, etc. Therefore, it is not necessary to remove, properly process, or decontaminate the contaminated items, so no special post-treatment work is required. Post processing for the leakage of the melt out of the canister is simple and easy.
Further, since the gap between the canister and the outer container functions as a heat insulating layer, the canister has high thermal efficiency.

  In addition, since the outer container is made of silica-based ceramic, mullite-based ceramic or alumina-based ceramic, it has excellent heat resistance, thermal shock resistance and mechanical strength. Therefore, even if impact force acts on the double composite container. The canister is protected by the outer container, and even if the canister is severely damaged by a thermal shock or the like, the outer container is not damaged, so there is no risk of the melt leaking out of the container.

  Further, since the molten leakage from the canister directly touches the inner surface of the outer container, the outer container is immediately heated and the temperature of the outer surface rapidly increases. By measuring the outer surface of the outer container with an infrared temperature sensor and detecting this sudden increase in the outer surface temperature, the presence of the leak can be detected quickly and reliably, even if the leak is gradual. However, since this can be detected quickly and with high accuracy, it can be dealt with quickly and accurately.

  The gap between the canister and the outer container must be large enough to insert the remote control jig and take out the canister from the outer container.

  By placing the canister in an outer container made of ceramic (for example, silica-based ceramic) with excellent heat resistance and mechanical strength and making it double, even if there is leakage of the molten material from the canister, The molten leaked material is not discharged to the outside, and the outflow of the melted leakage is stopped by the outer container. Therefore, even if the molten material leaks from the canister, it is possible to construct a system on the premise that it can be handled by remote control together with the outer container. It becomes simple.

In the double composite container according to the present invention, since there is a gap between the canister and the outer container, this forms a heat insulating layer for the canister, and a thermal load on the canister (heat due to a temperature difference between the inner surface and the outer surface). (Load due to stress) can be reduced and the thermal efficiency of the canister can be improved.
In addition, the high-frequency heating furnace cannot apply electrical leakage detection means due to the influence of high-frequency noise, but in the double composite container of the present invention, the molten leaked material directly touches the inner surface of the outer container. Since the temperature of the side also rises rapidly, the outer surface temperature of the outer container is measured with an infrared temperature sensor, and by detecting the abnormal temperature rise, the leakage of the melt from the canister can be detected with high accuracy. The detection accuracy is high. Therefore, according to the present invention, the leakage of the melt from the canister can be detected quickly and reliably by the remote monitoring device.

Next, embodiments will be described with reference to the drawings.
FIG. 1 conceptually shows the gist of this embodiment. A canister 32 is placed on a pedestal 33 in a state of being fitted in an outer container 31 and mounted in an induction heating furnace in that state. There is a gap 37 having a width of 10 mm between the canister 32 and the outer container 31 at this time. There is a tray 36 under the pedestal 33.

  The radioactive waste in the canister 32 is heated and melted in the high-frequency heating furnace 40. If there is no leakage of the melt, heating and melting are completed according to a predetermined work program, the pedestal 33 is lowered, the double composite container 30 is moved out of the high-frequency heating furnace 40, and the floor of the cell (sealed work room) It moves on the installation conveyor f and is moved to a predetermined position. During heating and melting, the temperature change is constantly monitored by the infrared temperature sensors 50a and 50b, whereby the presence or absence of leakage is confirmed with high accuracy and quickly.

Note that the infrared temperature sensors 50a and 50b are provided on the two circumferences of the lower part and the upper part at approximately equal intervals, respectively, so that the temperature of almost the entire outer peripheral surface can be monitored. The measurement accuracy by this infrared temperature sensor is very high.
The outer surface temperature of the outer container is measured at any time by the infrared temperature sensors 50a and 50b, the temperature change in a predetermined time (for example, 3 minutes) is detected, and this is compared with a reference value (in this example, 100 ° C.). When the change is greater than or equal to the reference value, it is determined that there is a leak, and a leak detection signal is transmitted.
Since the reference value is about twice the maximum temperature rise rate on the outer periphery of the outer container in a normal state, it is possible to accurately detect melting leakage.

  If there is no leakage of the molten material into the outer container 31, after moving it to a predetermined position, the canister 32 is taken out from the outer container 31 with a remote control jig, a new one is attached, and the double composite container 30 is again mounted. This is moved under the heating furnace, the pedestal 33 is raised, and the double composite container 30 is inserted into the heating furnace. Thereafter, waste is loaded into the canister 32 from above using a remote control jig, high-frequency heating is started, and the waste is melted.

  When the canister 32 is damaged, the waste w in the canister 32 flows out from the damaged portion c into the gap 37 between the outer container 31 and is captured in the gap. When leakage of the melt is detected by the monitoring system using the infrared temperature sensors 50a and 50b, the high-frequency heating is stopped, and the waste w in the canister 32 is cooled and solidified. At this time, the melt trapped in the gap 37 is also solidified and held in the gap 37.

Next, the structure of a specific embodiment will be described with reference to FIG.
A sleeve 41 is provided inside the cylindrical body of the high-frequency heating furnace 40, and a lower end thereof is detachably fitted to a lower portion of the pedestal 33. The sleeve 41 is a protective sleeve for protecting the inner surface of the high-frequency heating furnace from scattered matter caused by boiling of the melt in the canister 32.
And the outer container 31 is a product made from a silica type ceramic, and the compressive strength of this is about 60 Mpa (normal temperature). The canister 32 is made of an aluminum-based ceramic, and its compressive strength is about 20 MPa (normal temperature). Since this material has high mechanical strength and heat resistance strength, it is not easily damaged to cause leakage, but it is not possible to damage it, so it must be prepared for any possible leakage.

In this embodiment, the pedestal 33 moves up and down, and travels on the floor f of the conveyor installed on the cell. The pedestal 33 moves to the lower part of the heating furnace and moves up and down to move the double composite container 30 to the heating furnace. A withdrawal operation is performed.
Infrared temperature sensors 50a and 50b are attached to the cylindrical body F of the heating furnace, and these infrared temperature sensors are provided at the lower and upper portions of the double composite container 30 at approximately equal intervals on the circumference. Yes. Thus, the temperature of almost the entire outer peripheral surface of the canister can be monitored.

The temperature of the outer peripheral surface of the outer container 31 is measured at any time by the infrared temperature sensors 50a and 50b, and the temperature difference measured before and after is compared with a reference value (for example, 100 ° C.) at intervals of 3 minutes. When a leak detection signal is transmitted.
Since the temperature rise of the outer container during normal melting and heating is in the range of approximately 0 to 20 ° C./min, the presence or absence of melting leakage is accurately detected by determining the abnormal temperature rise based on the reference value.

(A), (b) is explanatory drawing which shows an Example notionally Is a sectional view of the embodiment (A), (b), (c) is explanatory drawing of an example of a prior art (A), (b) is explanatory drawing of the other example of a prior art.

Explanation of symbols

30: double composite container 31: outer container 32: canister 33: pedestal 36: tray 37: gap 40: high-frequency heating furnace 41: sleeve 50a, 50b: infrared temperature sensor f: conveyor on the floor of the cell w: waste

Claims (2)

In the radioactive waste processing method in which the radioactive waste to be reduced in volume is loaded into a volume reduction container for radioactive waste processing, and the waste is heated and melted with a high-frequency heating device, the volume reduction container is connected to the canister. is configured as a double composite container is fitted to the container,
The outer container is a heat-resistant ceramic container, and there is a gap between the canister and
The gap between the canister and the outer container is a size that can hold the canister by inserting a remote control jig,
When the waste is leaked from the canister when the waste is heated and melted by a high-frequency heating device, the double composite container of the canister and the outer container is moved out of the high-frequency heating device, and the next In the process, post-processing is performed on the entire double composite container ,
If the heated melt does not leak from the canister, a remote operation jig is inserted into the gap between the canister and the outer container, and the canister is held and taken out from the outer container. A radioactive waste treatment method, wherein post-treatment is performed on the canister alone in the step. The radioactive waste processing method according to claim 1, wherein leakage of heated melt from the canister to the outer container is detected by measuring an outer surface temperature of the outer container with an infrared temperature sensor . Waste disposal method.

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