Nuclear Decommissioning
JAMES FISHER RUMIC LTD (JFRL)
Background:
Built between 1956 and 1971, the UK’s fleet of Magnox power stations was the country’s first generation of civil nuclear reactor. The operational lifespan of a Magnox station was originally conceived to be around 20 – 25 years, but all have exceeded this by some 20 years or more. Today, on behalf of the NDA, British Nuclear Group is managing the fleet through a progressive programme of winding down operations, shutdown and decommissioning.
Decommissioning:
James Fisher Rumic Ltd (JFRL) has worked within the nuclear industry since 1990. They have added extensive experience of decommissioning operations to their existing wealth of expertise of operations in Offshore environments.
Rumic’s Nuclear Services Division works with the licensed site holders (or main contractors) providing surveys, methodology studies and reviews of equipment and technology to supply information that will assist in decommissioning projects. Rumic provide On-Site Operations Services in both active and non active areas, backed up by Design services providing an integrated service from design through build, operation, maintenance to survey information presentation.
Engineering Analysis:
JFRL commissioned FEA Online to perform an engineering analysis of transferring the self-weight of the Windscale Advanced Gas-Cooled Reactor (WAGR) pressure vessel assembly from the upper strakes to the lower vessel support structures under a variety of load cases, each of which considers “off-centre” loading that may be present due to previous construction tolerances.
In addition, several dropped-object load cases were considered to determine the effect on RPV stability and lower vessel support structures in the event of dropping an object during various stages of the decommissioning process.
The results from this study were used to underpin the Safety Case submitted to BNFL as part of the justification of adopting the “top-down” decommissioning strategy.
This investigation was undertaken in collaboration with James Fisher RUMIC Ltd who were responsible for the design of tooling and methodology specification.
Objective:
The scope of the FE analysis considered removal of plate from the main cylindrical section of the pressure vessel and the attached outer membrane of insulation down to the upper edge of the hemispherical section. Therefore, support of the Reactor Pressure Vessel will be transferred from the corbel level to the lower vessel support structures. It was important to ensure the support structures maintain their integrity during this process, i.e. they don’t become over stressed or deform into potential buckling modes, which could lead to premature collapse.
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Steve Lainson, Senior Design Engineer, James Fisher Rumic Ltd, UK:
" I would like to thank FEA Online for your professionalism during the project and in particular the times of close scrutiny we had to endure during the peer review stages. The work you have presented has been fundamental to the acceptance of the dismantling methodology for something that has never before been attempted on such a scale".
