Customer Organisation, name and address
Dounreay Site Restoration Ltd, Dounreay, Thurso, Caithness, KW14 7TZ.
Contract Start Date:
26/01/12
Contract Completion Date:
02/04/15 – all components delivered and installed in the DFR Hot Trap system and linked to the sodium/potassium processing and treatment system.
Description of contract, including full scope details
This project was developed as part of a series of complex activities in order to decommission the Dounreay Fast Reactor (DFR). The reactor coolant was a combination of sodium and potassium designed to create a eutectic alloy (i.e. NaK) that was essentially liquid at reactor shut down temperatures. Decommissioning of DFR, and removal of some 50 tonnes of NaK has presented many technical challenges and especially the recovery of the coolant from discrete pockets within the reactor vessel. Such a challenge was the recovery of NaK from the 7 Hot Trap loops in the vessel, which were particularly difficult to access and in which to insert an engineered system for the safe effective removal and treatment of NaK which was contaminated with traces of fission products from reactor operation between 1959 and 1978. Gow’s Lybster and DRSL designed a system whereby a series of 7 Dip legs were to be inserted into the Hot Traps, fastened in position, and then linked to a shielded liquid metal transportation system which would feed the NaK to the disposal unit for treatment and waste disposal. A large, and complex Glove Box system, was also built to drill into the Hot Traps to allow the Dip Legs to be inserted and this was engineered through the glove box system. The transfer system was heavily shielded and contained trace heating to ensure that the NaK was sufficiently mobile to reach the treatment plant.
Gows Lybster was responsible for the following activities:
- Dip Legs: Fabrication and testing of 7 Dip legs of varying design – each unit was approximately 6.5m long and fabricated in stainless steel.
- Dip Legs: Fitting and testing of solenoid valves to the Dip Legs
- Dip Legs: Completion of trials with a Hot Trap mock up to test the arrangements for fitting the Dip Legs and development of safe systems of work in the reactor environment.
- Drilling and Dip leg Installation: Glove Box: Manufacture, testing and installation of the Glove Box unit which included the installation of valves, electrical installation and a control system.
- NaK Transfer System: Fabrication of the inner transfer line (i.e. connected to the Dip Legs and treatment unit), outer secondary containment shells, insulation, trace heating, actuated valve control systems and conrol panels.
- Nak Transfer System Support Units: Detailed design, build and installation of stools and brackets to support the transfer lines from the Dip Legs to the treatment plant.
- Piping Systems: The company manufactured and installed a comprehensive suite of piping for the Nitrogen gas inert atmosphere to the Drilling Glove Box and associated systems.
- Installation: Gow’s Lybster Ltd installed all of the components described above in association with the DSRL project team.
The scope of works is given below:
- Machined parts were fabricated in stainless steel for in-reactor systems and in mild steel for the structural support systems.
- Provision of all documentation in support of the project including, Management, Procurement and Fabrication Procedures, Training Records, Weld Procedures, Welder Qualifications, NDT Procedures for Radiographic Inspection, MPI, DPI, Inspector Qualifications, Quality Control Plan, Progress Reports and Life Time Quality Records.
- Draughting service, as specified by the project manager for the design of bespoke components to support the on going fabrication works as part of the development and commissioning elements of the machine design and operation.
- Machining of all component parts which included, milling, drilling, bending and lathe turning work.
- Fabrication, welding and assembly of machined parts
- Inspection and Non-Destructive Inspection of parts and welded components (i.e. Radiography, MPI and DPI)
- On going cleaning, identification to maintain traceability and storage of all stainless steel components.
- Trial fit of Dip Legs in Test Rig and development of installation procedure in the reactor environment.
- Installation of electrical and pneumatic systems.
- Installation and commissioning of the Blove Box unit.
- Drilling into the Hot Traps, insertion of the Dip Legs and sealing of the units until the transfer sytem had been installed.
- Installation of the transfer system supports.
- Installation of the primary transfer line, fitting of trace heating, insulation, the secondary containment system and the fitting of lead shielding to the whole system.
- Installation of the electrical and instrumentation systems and control units.
- Supporting commissioning trials and maintenance of commissioning schedule record.
- Continuous records management in support of the Life Time Quality Records information for the client.
- Continuous management and updating of the Quality Control Plan
- Pre-delivery testing and inspection of by the customer respresentatives
- Submission of a delivery plan to DSRL.
- Delivery of all components to the Dounreay site.
- Completion of the Quality Control Plan.
- Completion of the Life Time Quality Records Information and handover to the client.
- Receipt of a completion certificate from the client.
- Contract review with the client
Location of the Contract/Project
All mechanical components were manufactured, tested, and inspected, and modified as necessary, at the Gow’s Lybster Ltd Facility, Lybster, Caithness, Scotland KW3 6AS. Sub-contractors were engaged to design, install and commission the electrical
