An assessment of the FORK detector as a partial defect tester

A Coordinated Technical Meeting on Spent Fuel Verification Methods held in Vienna in March 2003 stressed the need for partial defect testers for spent fuel in both wet and dry storage. One of the candidates for partial defect testing is the FORK detector. The performance of the FORK detector as a partial defect tester was investigated experimentally in the framework of a Joint Task for the IAEA by the Finnish, Swedish and Belgian Support Programmes. This was done by replacing fission chambers in the FORK detector by He-3 tubes and simulating spent fuel with fresh MOX-fuel. It was concluded that the FORK detector was not suitable as a partial defect tester, since fuel pin removal could be not be detected in an unambiguous way for all possible scenarios. However, later analysis of the results revealed that a possibility exist to interpret the measurement results unambiguously, provided that some additional measurements are performed. It was decided to perform simulation calculations for some of the configurations that were investigated during the Joint Task for validation of the correctness of the simulation methodology and to investigate the applicability of the proposed additional measurements for an unambiguous partial defect test. This paper describes the comparison of the simulation calculations with the FORK detector measurements.