Safeguarding the Pebble Bed Modular Reactor: A new challenge for the IAEA

The Pebble Bed Modular Reactor (PBMR) is a 400MWth, 160MWe helium-cooled, graphite moderated high temperature reactor (HTR). The fuel consists of silicon carbide and pyrolytic carbon coated particles of enriched uranium oxide encased in graphite to form fuel pebbles with a diameter of 60mm. Each fuel pebble nominally contains 9g of uranium enriched to 9,6% U235. During equilibrium core operation, a total of about 452,000 fuel pebbles will constitute the core of the reactor. During operation, a fuel sphere will circulate, on average, six times through the core and the target burn up is nominally 90,800 Mwd/tonne U. The reactor is an on-load reactor and therefore is not shut down at the time of the physical inventory. The core fuel and the spent fuel (SF) will therefore not be directly accessible. The Agency has designed a generic safeguards approach for the South African PBMR based on the diversion strategies identified, and taking into account the Agency detection goals applicable to such a reactor. The paper describes the safeguards inspection goals and procedures to be implemented.