Fast critical assembly safeguards. Summary report, October 1978-September 1979

Nuclear material inventory verification techniques for large split-table type fast critical assemblies are being studied under this program. Emphasis has been given to techniques that minimize fuel handling in order to reduce facility down time and radiation exposure to the inventory team. The techniques studied include autoradiography, reactivity, and spectral index measurements. Autoradiographic techniques capable of verifying the core loading diagram for a uranium or plutonium core have been demonstrated and examples of results are given. Results of reactivity and spectral index measurements for detection of simulated diversion of fuel from a large plutonium core are presented. These measurements indicate that the sensitivity of reactivity measurements to fuel removal is sufficient to detect a removal of 2 kg in a 2600 kg core. Reactivity compensation by the addition of polyethylene was readily detected by spectral index measurements using indium foils, if the foils were located within 10 cm of the moderator. The measurements made in this study were relative to a known reactor configuration and were made using facility equipment. Independent verification of reactivity and spectral index measurements by a safeguards inspector may be difficult. 27 figures, 5 tables