Efficiency Calibration and Testing of a Commercial Active Well Coincidence Neutron Counter to Inventory U-Al Reactor Fuel and Target Elements at the Savannah River Site

In this paper we describe testing, efficiency calibration and use of the Aquila active well neutron coincidence counter for nuclear material assays of U-235 in Savannah River Site (SRS) U-Al fuel. All of the SRS production reactors have been in standby mode since 1993. However the Department of Energy still requires material control and accountability of the fuel and target material stored in the reactor assembly areas. Because the SRS fuel is pure of plutonium, it has a very low passive neutron emission rate and is very well suited for assay of the U-235 content by active well induced fission neutron counting. These U-Al active well assays for inventory verification are compared to the fuel element assays attained from the SRS fuel production facility Californium shuffler. In addition we describe experiments performed at Argonne West National Laboratory with the Aquila active well counter. In these experiments we tested the capability of the instrument to determine U-235 content in metallic uranium chunks of nonuniform shape.