Production and Verification of Materials Measurement Data for Near Real Time Accountancy (NRTMA) in THORP

The safeguards strategy developed for THORP and the corresponding design features have recently been described in a paper to the ANS 3rd International Conference Because of the large in-process plutonium inventory, BNFL decided to adopt NRTMA for its own purposes as a materials accountancy and control tool, with the expectation that it would serve to provide the safeguards inspectorates with short term assurance against diversion. The essential extra step in adapting NRTMA to safeguards is to provide the inspectorates with the means of verifying the accountancy data. Whilst the development of statistical techniques has produced a powerful method of analyzing and interpreting the data, the important question of verification has received less attention. This paper describes the techniques that will be available to safeguards inspectors in THORP. It is important to appreciate that the designer can do no more than provide the physical means of verification; the degree of assurance gained will depend on the design of inspection strategies, which is the business of the inspectorate.