Year
2012
Abstract
The Improved Plutonium Canister Assay System 2 (IPCA 2) is a nondestructive assay system designed to measure incoming canisters of bulk mixed uranium-plutonium oxide (MOX) powders at the proposed Japan Nuclear Fuel Limited mixed-oxide fuel fabrication plant. The system consists of a 3He-based passive neutron well counter with an integrated high-purity germanium gamma system comprised of three individual detectors, a load cell, and a camera. Each MOX canister holds three individual cans of MOX powder stacked on top of each other. The IPCA 2 is calibrated with a representative MOX canister, so much of the positioning uncertainty for the neutron measurements is removed in calibration; however, every effort is made prior to calibration to limit the efficiency variation across the active region of the measurement cavity. This is particularly important in the axial direction so that small changes in the fill height of each can are insignificant in the total measurement uncertainty. We used cadmium tailoring on the 3He tubes to flatten the efficiency profile in the axial direction. The target was to limit the change in efficiency in the Singles count rate across the active material zones in the three cans to 5%. Prior to physically applying cadmium to the 3He tubes, we performed Monte Carlo calculations to estimate the optimal cadmium configuration, which allowed us to meet the flatness target on the first iteration of applying cadmium to the tubes. In this paper, we provide a summary of the Monte Carlo calculations, a description of the cadmium tailoring activity, and results of the efficiency profile measurements before and after the cadmium tailoring.