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Protecting Against Earthquakes

12 May 05
DFR Seismic Modification Milestone
During the construction of the renowned Dounreay dome back in the 1950's, there was no requirement to make the giant sphere capable of withstanding an earthquake. But fifty years later, this unusual necessity has earned the Dounreay Fast Reactor (DFR) facility its first key milestone under the Nuclear Decommissioning Authority.

Modern standards for nuclear establishments now require ‘quake-proofing’ for all new and existing safety-related equipment and plant. This is tricky for facilities such as the DFR Nak Disposal Plant, which is a mixture of both old and new plant and is also contained inside the DFR sphere. The sphere itself has been computer modelled and proven to withstand the once-in-ten-thousand years chance of an earthquake. However, the plant contained within it needed a more detailed assessment.

A specialist firm, who also designed the required modifications, carried out these assessments. The older items of plant were considered unable to cope with the side to side shaking which occurs in earthquakes, even though they were designed to support their own weight, plus that of their contents i.e. to take vertical loadings. To ensure the plant was safe and met the required standards of today, additional bracing was added so that in the unlikely event of an earthquake in Caithness, the plant containment would not be breached. As well as the supports, 800+ lead blocks were also secured in place with straps and clamps to prevent them shaking loose.

Jim Sudd, Project Manager, said ‘Everyone involved in this project worked extremely hard to ensure the milestone targets were delivered on time. Luckily the probability of the work actually being necessary is remote, but it proves how different the thinking is nowadays and the safety constraints we face fifty years on.’