GB2181883A

GB2181883A - Radioactive waste disposal

Info

Publication number: GB2181883A
Application number: GB08618902A
Authority: GB
Inventors: William Robert Burton
Original assignee: NUCLEAR TECHNOLOGY
Current assignee: NUCLEAR TECHNOLOGY
Priority date: 1985-08-05
Filing date: 1986-08-01
Publication date: 1987-04-29
Also published as: GB2181883B; GB8618902D0; GB8519645D0

Abstract

Intermediate level radioactive waste and plutonium contaminated material are disposed in waste packages 11, 14 in a repository and voids between packages and repository are filled with a combination of removable blocks 15 and "weak filler" 17 between the blocks, between blocks and packages, and between packages and repository wall 16. A "weak filler" is capable of inhibiting the movement of water whilst at the same time being removable e.g. by scraping or water jetting. An access tunnel has lengthwise partitions provided on each side with weak back-fill and shaped blocks. Monitoring probes may be in the tunnel connected to an alarm. The material in the emplacement is readily removable. <IMAGE>

Description

SPECIFICATION Radioactive waste disposal This invention relates to the disposal of radioactive waste.

Two aspects of emplacement of radioactive waste packages are shown in Fig. 7 and 11 of a publication entitled "An Engineering Design Study for Storage and Disposal of Intermediate Level Waste" by J R Griffin et al, ND-R-777(R) November 1982 available from Her Majesty's Stationery Office. Fig. 7 shows intermediate level waste (abbreviated to "ILW" and typically with significant betagamma content such that shielding is required) in the bottom section of a tunnel and plutonium contaminated material (abbreviated "PCM" and which implies significant level of alpha activity but low enough beta-gamma content such that heavy shielding is unnecessary) in the top section of the tunnel. Fig. 11 shows a respository layout for ILW or PCM.

The above-mentioned publication shows the tunnel back-filled with concrete thus creating a situation where package recovery is not reasonably possible. This is the commonly accepted position for ILW and PCM.

According to one aspect of the invention there is provided a method of forming a respository for radioactive waste in which waste packages in a respository have the voids between packages and repository filled with a combination of removable blocks and "weak filler" between the blocks, between blocks and packages, and between packages and repository wall.

The "weak filler" is defined as being capable of inhibiting the movement of water whilst at the same time being removable e.g.

by scraping or water jetting.

The machine operator would be protected against radiation and/or contamination for example from the PCM.

With this, special stand-by machinery does not have to be provided which will represent tied-up capital serving no function other than that of safeguarding against the unexpected.

According to another aspect of the invention there is provided a repository for radioactive waste in which waste packages in the respository have the voids between packages and repository filled with a combination of removable blocks and "weak filler" between the blocks, between blocks and packages, and between packages and respository wall.

Preferably, the void fillers are such that they can be placed and retrieved by a simple form of mobile or movable machine.

The repository may comprise a tunnel having partitions therein at space locations, with, on each side of at least some of the partitions a layer of weak back-fill plus shaped blocks.

There may be probes in said tunnel responsive to radioactivity, and alarm means responsive to said probes.

There may be back fill in the tunnel, the back fill comprising bentonite.

The invention may be performed in various ways and some specific embodiments with possible modifications will now be described further by way of example with reference to the accompanying drawings in which: Figure 1 and 2 are cross-sections of a tunnel repository and respectively show waste package emplacement similar to that of Fig. 7 and 11 of the above mentioned publication but modified in accordance with the invention.

In Fig. 1: Numeral 10 denotes a preformed base for stacking ILW packages, Numeral 11 denotes ILW packages, Numeral 12 denotes a loading base e.g.

concrete slabs on weak backfill, Numeral 13 denotes a large container for redundant contaminated plant items, Numeral 14 denotes PCM packages, Numeral 15 denotes space filler block e.g.

concrete, Numeral 16 denotes a construction lining for the tunnel, Numeral 17 denotes spaces to be occupied by weak backfill.

Weak backfill is backfill of weak filler.

Similarly in Fig. 2 20 denotes waste packages, 21 denotes the construction liner of the tunnel, 22 denotes spaces to be occupied by weak backfill, 23 denotes the preformed space filler block e.g. concrete, 24 denotes the thick liner e.g. of concrete, to inhibit water movement.

Tunnels may be divided lengthwise with strong partitions if deemed necessary e.g. one metre of concrete. However, it would be recommended that at each side of at least some of the strong partitions there would be (say) one metre of weak backfill plus shaped blocks. This would enable conventional drilling methods to be used to break down the strong partition at a safe distance from the wastes.

Monitoring connections (say) by metallic tube could be arranged to leave probes, responsive to radioactivity, in advantageous position, perhaps recoverable and/or replaceable down the tube. Given an alarm from monitors, a tunnel would then be excavated in the controlled manner necessary in the event of radioactive contamination in part of the tunnel.

Bentonite which increases its volume on reaction with water could be useful here as part of backfill with sand as the other part. Sufficient of such a material could be used to fill all voids (including internals of monitor tubes) to inhibit water movement in either the retrievable period or after this time (when eventually monitor tubes fail e.g. by cracking or corrosion).

With the described arrangements ILW and PCM is retrievable so that it can be re-located or other remediable action taken in event of unexpected events occuring.

The arrangement provides easy removal of fill, with the operator suitably protected by for example distance, shielding and/or protective clothing, and the blocks are readily removable so that the whole emplacement is readily removable. The arrangement avoids the necessity for the operator to have close contact with the waste e.g. to use drill or thermic lances.

Claims

1. A method of forming a repository for radioactive waste in which waste packages in a repository have the voids between packages and repository filled with a combination of removable blocks and "weak filler" between the blocks, between blocks and packages, and between packages and repository wall.

2. A method as claimed in claim 1, in which the void fillers are such that they can be placed and retrieved by a simple form of mobile or movable machine.

3. A method of forming a repository for radioactive waste as claimed in claim 1 and substantially as hereinbefore described.

4. A repository for radioactive waste in which waste packages in the respository have the voids between packages and repository filled with a combination of removable blocks and "weak filler" between the blocks, between blocks and packages, and between packages and repository wall.

5. A repository as claimed in claim 4, in which the void fillers are such that they can be placed and retrieved by a simple form of mobile or movable machine.

6. A repository as claimed in claim 4 or claim 5, comprising a tunnel having partitions therein at spaced locations, with, on each side of at least some of the partitions a layer of weak back-fill plus shaped blocks.

7. A repository as claimed in claim 6, including probes in said tunnel responsive to radioactivity, and alarm means responsive to said probes.

8. A repository as claimed in claim 6 or claim 7, comprising backfill in the tunnel, said backfill comprising bentonite.

9. A repository for radioactive waste material as claimed in claim 4 and substantially as hereinbefore described with reference to, and as illustrated in, Fig. 1, or Fig. 2, of the accompanying drawings.