UKAEA ^{A World Leader in Decommissioning & Waste Management.}

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Project background

The Steam Generating Heavy Water Reactor in Winfrith was a100 MW (electrical) reactor. It ceased operation in October 1990, and was defuelled over the next three years. One of the major tasks during the first stage of decommissioning was the preparation of the fuel ponds for long-term care and maintenance.

Key challenges

During the initial planning, we identified four major areas to work on: the pond furniture; the sludge and debris which had accumulated on the pond floors; the installed fuel handling plant and associated systems; and the concrete structure of the ponds themselves.

Our approach

We began by decontaminating the walls and floors of the ponds to similar levels as those in the primary containment. A roof was then installed over the fuel pond, grouping together all of the ponds as part of the primary containment. Although the work largely involved conventional dismantling techniques, at one stage we used divers to cut steelwork approximately 8m under water.

The pond bridges and a number of other items were removed as they were in poor condition. In total, we removed approximately 40 tonnes of solid LLW. However, most of the stainless steel pipe work and plant was left in position.

We used water jetting equipment and decontamination agents to decontaminate the pond walls. We worked off pontoons installed in each of the ponds, and narrow bands of the pond walls were decontaminated as the pond water was removed. This was an extremely cost-effective technique that required minimal use of scaffolding. It also allowed us carry out most of the decontamination underwater, and avoid airborne contamination. We then painted the walls with a water- based paint to tie down the remaining small amounts of loose contamination.

The results

The final cost of the decommissioning the pond was around 50% of our initial estimates. The dose uptake was approximately 100 man mSv (25% less than the original estimate), with some 24,000 man hours of work being recorded.

Thanks to strategic planning and the use of simple, well-proven techniques, we completed the pond decommissioning successfully. By placing three contracts for option studies, we were able to consider a wide range of decommissioning methods before we made our final choice. We also ensured that our pond decommissioning solution was fully integrated with the overall strategy for the rest of the reactor decommissioning.