British Nuclear Fuels plc (BNFL) Defuelling Machine Refurbishment and Verification System Installation – Bradwell Power Station
The decommissioning of a nuclear power station takes many years to complete. The first stage is the removal of the spent fuel from the reactor and the shipment to BNFL Sellafield where it will be re-processed. The second stage involves removal of the non-radioactive plant from the site (i.e. the turbines, ancillary plant equipment).
Then the remaining active plant will be decommissioned in later years. The final stage is the clearance of the site, removal of any residual contamination and final de-licensing to make it available for re-use.
At the end of March 2002, Bradwell Power Station located in Essex, reached the end of its design life and ceased generation. Fuel is currently being removed from both reactors and then packaged for shipment from site to Sellafield, a routine process that was completed in 2005.
There are approximately 20,000 fuel elements per reactor and each one has to be removed individually. This represents a huge number of operations. It is essential that every one is removed from the reactor and the details of each carefully recorded.
The existing equipment was not designed for a full defuelling process and the procedures currently used at Bradwell for tracking fuel elements is essentially a manual paperwork system which relies heavily on human intervention.
Magnox Electric relies on the defuelling equipment and associated processes in order to commit to a programme of safely removing, tracking and shipping the fuel off site.
Therefore, BNFL Magnox decided to invest in a complete refurbishment of the defuelling machine plant control system at Bradwell (both electrical, instrumentation, and mechanical) to provide a modern and reliable system, and to install a computer based Verification System to monitor and record all defuelling operations.
The key aims of the project are:
- To modernise the current control system and improve its reliability
- To enable fuel elements to be removed with an overall potential for error of 10 -4 or less
- To modernise the operator interface and control room environment
- To assist BNFL Magnox to meet their commitments for delivery of fuel to Sellafield
- To enable accurate logging of all defuelling actions
How we helped
As one would expect on a nuclear site, there are very stringent design standards in place on the project. We are obliged to support BNFL Magnox in demonstrating to the Independent Nuclear Safety Assessor (INSA), that the Safety Case can be made for the work. The company’s PES guidelines for the design of programmable systems in safety related applications were used in the design.
The scope included:
- A Control, Tracking and Verification solution based on Mitsubishi Q series hot standby PLC system with variable speed drive and remote I/O sub-systems, with a MX2000 based SCADA system, and a Microsoft SQL Server based relational database system running on an industrial computer with RAID disks
- A complete refurbishment of the control room including heating, ventilation and lighting
- Designing and supplying a new operator desk, along with PLC cubicles, drive cubicles and various panels
- Extensive field work. New resolvers and optical encoders for accurate measurement of machine positions, 9 new motors and a variable speed drive to give better speed control of the fuel element hoist were all installed
- A number of fixed and flexible (umbilical) electrical cables were replaced. A number of manual control panels located out on the reactor pile cap area were installed
- Mechanical refurbishment of a number of parts of the defuelling machinery, i.e. to replace seals, fit transducers, overall moving parts etc.
All site work was carried out in a radiation controlled area and co-ordinated by our site manager in conjunction with Magnox staff. The resultant system provides increased automation of the process, gives better indication of the plant state and logs all events to a database system for historical storage.
The Verification system for Reactor 1 and 2 was successfully delivered to specification and on cost, whilst meeting all the design and safety criteria mandated on a project of this nature.