Year
2011
Abstract
The large flux of antineutrinos that leaves a reactor carries information about two quantities of interest for safeguards: the reactor power and fissile inventory. Our SNL/LLNL collaboration has demonstrated that antineutrino based monitoring is feasible using a relatively small cubic meter scale liquid scintillator detector at tens of meters standoff from a commercial Pressurized Water Reactor (PWR). This detector was deployed in an underground gallery that lies directly under the containment dome of an operating PWR, and provides a muon-screening effect of some 20-30 mwe earth and concrete overburden. However, many PWR facilities do not have an available underground gallery to provide the screening of muon-induced backgrounds. To address this issue, we have recently developed and fielded two new detectors: a water based design and a segmented design based upon scintillation technology. In both cases, the detectors are surrounded by about 50 cm of passive and active shielding, and the whole assembly is enclosed in a transportable 6-meter ISO container. The container has been deployed aboveground next to Reactor Unit 3 at the San Onofre Nuclear Generating Station (SONGS) in southern California. The water detector, doped with gadolinium to increase the neutron detection, is based on the observation of the same inverse beta-decay process used in the liquid scintillator detectors. However, by using the Cerenkov radiation signature, it has the advantage that it is insensitive to one of the major aboveground backgrounds arising from fast neutron induced proton recoils. The second detector comprises individual segments of liquid or plastic scintillator, with screens of a lithium-doped inorganic scintillator: ZnS:Ag/ 6 LiF. The inclusion of the ZnS:Ag/ 6 LiF allows the unique identification of neutron capture events with no contamination from normal electromagnetic interactions. The final target design is a 64-cell array of 80cm long modules. We chose to first construct a smaller 4-cell prototype that allows us to better understand the improved background rejections that we may achieve through the use of event topology. We will describe the construction and deployment of each of these technologies, and present preliminary data evaluating their performance as a possible aboveground antineutrino detection system