Gamma Measurements on MTR Fuel Assemblies

Fuel for Material Test Reactors (MTRs) presents an interesting and challenging problem for International Atomic Energy Agency (IAEA) inspectors. Most such reactors use fuel which was made from high enriched uranium (^-^U ^ 20%) . The fuel is in the form of an uraniumaluminium alloy and is considered direct use material. This type fuel is found in two types of facilities, fuel fabrication plants and at the reactors themselves. While the fabrication plants normally have large inventories of MTR assemblies, individual reactor sites have small but often significant quantities of fuel material. The gamma ray measurement of fuel assemblies for safeguards purposes is the topic of this paper. The methods described use computer codes to calculate predicted count rates considering detector—assembly coupling including assembly self-absorption and buildup. Results of actual measurements and estimates of measurement uncertainties are given for both rectangular and cylindrical MTR fuel elements.