Monday, March 26
1045 Engineering Centers Building
Speaker: Jianwei Hu, Nuclear Nonproliferation Division, Los Alamos National Laboratory
Collaborators: Stephen J. Tobin and Howard O. Menlove, Nuclear Nonproliferation Division, Los Alamos National Laboratory
"Developing the Californium Interrogation with Prompt Neutron Technique to Measure Fissile Content and to Detect Diversion in Spent Nuclear Fuel Assemblies"
Abstract: This talk mainly focuses on development of nondestructive assays (NDA) for spent fuel measurement. In the end, I would like to briefly discuss my PhD thesis work and my experience with a few nuclear codes, including MCNP5/X, MONTEBURNS, CINDER90, and NJOY.
The majority of plutonium is stored in spent nuclear fuel assemblies. Presently, there is no means for directly measuring the mass of the plutonium in these assemblies by NDA. Since 2009 researchers at Los Alamos National Laboratory have been coordinating a multi-laboratory effort to develop new NDA techniques to quantify Pu in, and to detect diversion of fuel pins from, spent fuel assemblies. Over a dozen NDA techniques have been researched, and efforts have now turned to the construction of three or more integrated systems comprised of the most promising and complementary techniques. This talk will firstly discuss the needs for advanced NDA techniques for international safeguards and overview of the overall project. Then the focus will be moved onto a specific NDA technique that we developed during this process -- Californium Interrogation with Prompt Neutron (CIPN) technique.
CIPN is a relatively low-cost and lightweight instrument, and it looks like a modified fork detector combined with an active interrogation source (252 Cf). Fission chambers were chosen as the neutron detectors because of their insensitivity to photon radiation. The design has been optimized so CIPN has almost uniform sensitivity to diversions at different locations across the assembly. A 100 µg 252 Cf source was proven strong enough to provide sufficiently high signal above background. The capability of CIPN was quantified against a virtual library of 64 spent fuel assemblies using MCNPX simulations. The CIPN assay comprises two measurements, a background count and an active count, without and with the presence of the Cf source respectively. The net signal is mainly due to multiplication of the Cf source neutrons; this multiplication is dependent on both the fissile content and the neutron absorbers present in the assembly. Two novel corrections have been introduced to account for the absorption caused by neutron absorbers. With the help of empirical fitting, the fissile content in a target spent fuel assembly can be determined from the CIPN signal. CIPN is also tested in a series of hypothesized diversion cases. Preliminary results show that CIPN can detect diversion of 8 or more fuel pins (3% of total mass) provided the count rate of baseline case was previously measured. Engineering design and conceptual experiment setup of CIPN is also discussed.
In the end, a few minutes will be spent to briefly discuss my PhD thesis on fuel performance modeling of TRISO fuel, as well as several other projects to show my involvements with a few nuclear codes.