Halcrow provided multidisciplinary engineering services as the design partner in the DFR-PCD Alliance between 2001 and 2003 for UKAEA Dounreay.
This project entailed planning and design for removal of some 6km of coolant filled pipework from within the reactor vault. The project was unique due to the hazardous and radioactively contaminated sodium-potassium alloy (NaK) coolant that is present within the reactor and primary coolant pipework system, together with the radioactive contamination in the reactor and pipework itself.
Halcrow’s integrated services involved considerable mechanical handling and civil, mechanical and electrical engineering including vault freezing, HVAC, electrical supply, control and instrumentation and building services, as well as major civil/structural design for penetration of the DFR vault and design of a proposed new waste processing building and freeze plant.
In order to make a penetration of the reactor vault, it was necessary to undertake extensive surveys of existing services (electrical, liquids, HOAC and C&I), validate their safety functional requirements (since DFR is still under operational safety concerns) and to design services and C&I diversions. The project also had to divert old mains supplies to the facility and, since some buildings were to be demolished, to terminate some existing services and strip out the disconnected parts.
Several buildings associated with DFR were cleared and demolished under the DFR-PCD contract including the former turbine buildings. This made way for the recently completed DFR-BFR building. Halcrow were designers for these demolitions which included planned deconstruction with all associated safety cases, waste route planning and approvals. Many of the new services to be provided were safety critical and included air handling and filtration systems, back-up generators, electrical controls, electronic interlocks, radiation detection equipment, fire suppression equipment and a range of process plant for NaK passivation, neutralisation of liquors, ion exchange and waste packaging.
The original DFR-PCD concept developed by UKAEA was to first remove bulk NaK from the DFR and remove the remaining breeder fuel, leaving residual NaK within the primary circuit and in various vessels and traps. DFR-PCD was to involve freezing of the vault to inert any residual NaK, then removal of the pipework and traps using remote operated vehicles into a new process building where NaK would be reacted and wastes collected for disposal.
Halcrow led that design up to development of an outline scheme and cost estimate, which at c£120m exceeded the available budget. Consequently, Halcrow went on to lead a small team (challenge team) to re-evaluate the PCD decommissioning process resulting in an alternative lower cost option using in situ passivation in preference to the freezing option. This was subsequently adopted by UKAEA and the PCD Alliance was disbanded as implementation would not take place for some years after that time.
Halcrow received a commendation from UKAEA for its work on that project.