Year
2013
Abstract
Several mixed oxide (MOX) fuel facilities are now under development including J-MOX in Japan and the Mixed Oxide Fuel Fabrication Facility (MFFF) in the USA. J-MOX will have MOX fuel rods and other material under IAEA safeguards. The IAEA might also be involved in verifying MOX related to the Plutonium Management and Disposition Agreement (PMDA) at the MFFF in the USA and at a MOX facility in the Russian Federation once PMDA becomes operational. This paper describes a method to estimate Pu content in fuel rods using a medium energy resolution Lanthanum Bromide (LaBr3) detector. Traditionally, neutron coincidence collars are used for Pu mass estimation. However, due to 3He shortage and space limitations in some installations, there is a need for compact non 3He based detectors for such measurements. The IAEA is exploring alternatives. For a thin sample such as a fuel rod, the source-detector geometry is known and constant. The measurement time and branching ratio are also well known. It is therefore possible to use the 413 keV gamma line from the 239Pu decay to estimate Pu content. While high purity germanium detectors could be used for this, safeguards and verification applications sometimes require continuous and unattended operation. Medium energy resolution detectors, such as LaBr3, provide good detection efficiency and reasonable energy resolution. They are also less expensive, smaller and more reliable than germanium detectors for un-attended operation. We have explored monitoring of the important 239Pu gamma ray line using a LaBr3 detector. Measurements were conducted using a LaBr3 detector and MOX fuel rods. These measurements will be presented in this paper. Our results suggest a LaBr3 detector could work reasonably well to monitor Pu content in MOX fuel rods. LaBr3 could be an alternative to 3He neutron coincidence collars, neutron slabs or high purity germanium detectors in some applications.