Development and application of a remotely deployed radiography technique for restrictive access and difficult geometry

摘要

The Boiler Closure Units (BCU) at Heysham 1 and Hartlepool Nuclear Power Stations form the reactor pressure boundary at the penetrations for the 8 boiler units at the top of the reactor. Each BCU consists of a set of boiler pipework and inspection penetrations contained in a cylindrical can filled with concrete. The concrete is held in compression by pre-stressed wires wrapped around the outer circumference of the can. The wires are locked at anchor points on the top and bottom edges of the can. This assembly is in turn contained within a protective outer can. The discovery of cooling water ingress to a number of the BCUs, due to leakage, raised concerns about the potential for corrosion and consequently failure of the pre-stressing wire system. This resulted in British Energy initiating an extensive inspection programme aimed at determining the condition and integrity of the important components, especially the pre-stressing wires and anchor points. The highly restrictive geometry and access presented a demanding challenge for any NDT technique which would have to be both non-invasive and capable of remote deployment. This paper describes the NDT techniques considered and how an Ir192 radiography technique was selected despite being ruled out initially by the restrictive geometry. Technique development, site application and results will be presented.