Shallow and Deep Repositories
Assessment of radiological and conventional safety in construction and operation
Client
UK Nirex Ltd
Project
To provide the safety input to the design studies for deep and shallow radioactive waste repositories.
Services Provided
See below
Execution Period
1986-1989
Project Description
The Pöyry Energy business group(UK) formed a consortium with Costain and Ove Arup to undertake repository designs for shallow and deep disposal. The Pöyry Energy business group(UK) provided the safety input.
Particular Services
The Pöyry Energy business group (UK) interacted with the engineering team from the outset of the design project for deep and shallow waste burial. A strong interaction resulted, which led to optimum designs. An example of this was the influence of possible accidents on the design of the deep emplacement vaults.
A problem arose when considering cavern vaults since, in order to take advantage of the economy of large excavations, the overhead crane would be between 10m and 30m above the floor depending on the host rock conditions. Partitions within the vaults were considered desirable to limit the volume of backfill to be poured at any time, suggesting the waste packages would be carried at high level before placement.
The probability of an in-vault dropped load is not high, but it is not negligible either. Particularly in the case of operational ILW of which over 200,000 crane loads are to be handled an appreciable release could result in the case of severe, if improbable, impact.
A range of design solutions were proposed, such as:
- reverting to fork-life handling on the stacked waste and delivering the packages to a moving platform at stack level;
- using a long crane cable to move the waste at just above stack level;
- using a long crane cable to move the waste over a ramp down to stack level;
- building cells in the vaults and lowering waste loads under a hood completing local containment;
- reverting to tunnels and fork lift handling;
- overpacking all wastes sufficiently to provide impact protection;
- providing ventilation and access control, with facilities to recover from an in-vault release.
Each solution had to be judged on its merits as a way of improving safety to a degree which justified the cost. The handling system design would be based on high integrity equipment, interlocked lifting features, and rigorous monitoring. The vault itself would be a contained environment without anyone working in it.
The design solution which most effectively eliminated the hazard, at a level appropriate to its assessed severity, was to adopt the cavern vault design with ventilation and access control. |
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