INVESTIGATION INTO THE USE OF DUCTILE CAST IRON AND CAST STEEL FOR TRANSPORT CONTAINERS WITH PLASTIC FLOW SHOCK ABSORBERS

UK Nirex Ltd is responsible for the development of facilities for the disposal of low and intermediate level radioactive waste in the United Kingdom, including the development of the transport facilities for this waste. Intermediate Level Waste (ILW) will be packaged in 500 litre drums or 3m3 boxes or drums, and transported to the repository in reusable shielded transport containers (Smith et al. 1989, Sievwright et al. 1991). The transport containers and their contents will form Type B packages and the containers will thus be required to survive impacts up to the equivalent of a 9 metre drop onto an unyielding surface without loss of integrity. The container design concepts rely on absorption of the energy of an accident impact by means of plastic flow of the transport container material, in the form of integral \"plastic flow shock absorbers\" (Figure 1). Such design features are common practice in the UK nuclear industry, being used for example in transport flasks for irradiated nuclear fuel. As part of the development programme, Nirex is examining the feasibility of manufacturing these ILW transport containers by means of casting instead of the more usual forging process, as this would bring advantages of lower cost and shorter manufacturing time. Cast materials, however, are perceived to be less tough and less ductile than forged materials. To demonstrate the feasibility of using cast materials for this application it is necessary to show that sufficient fracture toughness can be obtained to preclude low-energy brittle failure modes at low temperatures, and to show that there is sufficient ductility in the plastic flow shock absorbers to absorb the energy of an impact equivalent to a 9 metre drop test. This paper describes the results of a programme of work carried out by Ove Arup & Partners on behalf of UK Nirex Ltd, in which castings were produced in both Ductile Cast Iron (DCI) and Cast Steel, and subjected to various tests including: Non-destructive testing (NDT) to locate and characterise flaws Mechanical property tests, including dynamic fracture toughness tests Welding and cladding tests Drop testing. -The paper concludes with an evaluation of both materials for use as the main material of construction of the Nirex transport containers.