NDE of Copper Canisters for Long Term Storage of Spent Nuclear Fuel from the Swedish Nuclear Power Plants

Tadeusz Stepinski

28th Polish Conference on NDT, Zakopane, Poland, October 1999

Abstract:

Sweden has been intensively developing methods for long term storage of spent fuel from nuclear power plants for almost twenty years. A dedicated research program has been initiated and realised by the Swedish company SKB (Swedish Nuclear Fuels and Waste Management Co.) in collaboration with many research groups in different countries. After the interim storage SKB plans to encapsulate the spent nuclear fuel in copper canisters with inner containers made of steel. The canisters will then be transported to a deep repository located at a depth of 500 m in the bedrock. The canisters after filling with fuel rods will be sealed by a weld made using electron beam technology. This paper discusses NDE techniques uses for assessing the weld in copper canisters. Three different complementary NDE techniques are briefly presented, radiography, ultrasound, and eddy current. A powerful source and a digital detector connected to a PC is used for radiography. An ultrasonic array system consisting of a linear ultrasonic array made of piezoelectric composite material and a digitally controlled multi-channel electronics is used for the ultrasonic examination. The array system enables electronic focusing and rapid electronic scanning eliminating the use of complicated mechanical scanner. A specially designed coil generating electromagnetic field with high penetration depth in copper is used for the eddy current inspection. Presently, all the NDE techniques are verified in SKB's Canister Laboratory where full scale canisters are welded and examined.