Implementation of a Mini-slab-based neutron detector system to increase the efficiency of safeguards verification of hold-up at MOX fuel fabrication facilities in Japan

In collaboration with the Japan Safeguards Office, the Nuclear Material Control Centre, and the Japan Atomic Energy Agency, the IAEA Department of Safeguards is implementing a new neutron detector system for the verification of plutonium hold-up in process gloveboxes at MOX fuel fabrication facilities in Japan. This nuclear material is subject to monthly inspection verification for the timely detection of diversion. The previous verification technique utilised the so-called Super Glove Box Assay System (SBAS), which, while capable of detecting partial defects, is a heavy and bulky detector system that requires both significant operator support for safe assembly and positioning, and long measurement times.  The recent development of a detector system based on two Plutonium Neutron Coincidence Collar (PNCL) miniature neutron slabs, known as the Mini-slab detector system, provides the capability of detecting gross defects with semi-quantitative plutonium mass measurement, and is sufficient in respect to inspections for timeliness purposes. For regular use, the Mini-slab detector offers several advantages, including improved safety, reduced operator support requirements and shorter measurement times. The Mini-slab detector satisfies the required verification role with a quarter of the inspector-days compared to SBAS. Furthermore, it has the capability to measure in tighter spaces, with the need for such use expected to grow as parts of these facilities begin decommissioning. The development and implementation of the Mini-slab detector system relied on cooperation with Japanese State representatives and operators to provide facility glove box design details, characterisation of hold-up material, ongoing engagement on operational plans, assistance with trial measurements and operator training to support inspection activities. Within the IAEA Department of Safeguards, the Division of Operations A and the Division of Technical and Scientific Services worked closely to define the verification needs, technical capabilities of the detector concept, data analysis methodologies and operational procedures. The experience gained using the new detector system will be reviewed to further optimise the efficiency of inspections, and potentially to utilise the system at other facilities that incorporate glove boxes on a routine or ad-hoc basis, such as during decommissioning.