EFFECTS OF IMPACT ACCIDENTS ON TRANSPORT CRITICALITY SAFETY CASES FOR LWR PACKAGES – A NEW APPROACH

Transport criticality safety cases for packages containing Light Water Reactor (LWR) fuel assemblies assess reactivity under normal and accident conditions. Depending upon the particular packaging design it may be necessary to consider the fuel assemblies in a variety of states. This approach can result in a combination of pessimisms that are in extreme cases unrealistic, thereby resulting in design limits that are unnecessarily restrictive. Furthermore, due to the international nature of transporting such fuel assemblies, there are variations in the assumptions made in safety cases, which are country dependent. These variations reflect the domestic experience of the country and development of their analytical techniques. This situation can result in additional analysis and assessment time by Competent Authorities when considering international transports. To rationalise this aspect of the package safety case, a two–year Fuel Integrity Project (FIP) has been initiated between BNFL and Transnucleaire Paris (TN) which is scheduled for completion in 2002. This paper explains the project structure adopted and the scope of the work undertaken together with information relating to the intended deliverables from the project. The objective of the FIP is to develop a common method to assess the nature of impact response of a LWR fuel assembly when subjected to the decelerations associated with the BNFL and TN fleet of transport packages. A variety of structural analysis routes will be identified together with confidence levels to enable the package designer to demonstrate the appropriateness of the assertions and assumptions used in a package criticality safety case. The FIP is being undertaken in consultation with the Competent Authorities of France (DSIN, IPSN) and the UK (DTLR) and their support is being sought at key stages throughout the project programme. The French and UK Competent Authorities are therefore being given the opportunity to peer review the scope, content and direction of the FIP to provide assurance that the developed method can be adopted into transport safety cases in the future. A programme of mechanical testing will begin in 2001 and include unirradiated and irradiated fuel assembly components. This will provide a basis for extending the method developed thus far for unirradiated fuel, to cover additional fresh fuel applications and also spent fuel.