Design of an on-line, multi-spectrometer fission product monitoring system (FPMS) to support advanced gas reactor (AGR) fuel testing and qualification in the advanced test reactor

The US Department of Energy (DOE) is embarking on a series of tests of tristructural isotropic (TRISO) coated-particle reactor fuel for the advanced gas reactor (AGR). As one part of this fuel development program, a series of eight fuel irradiation tests are planned for the Idaho National Laboratory\´s (INL\´s) advanced test reactor (ATR). The first test in this series (AGR-1) will incorporate six separate capsules irradiated simultaneously, each containing about 51,000 TRISO-coated fuel particles supported in a graphite matrix and continuously swept with inert gas during irradiation. The effluent gas from each of the six capsules must be independently monitored in near real time and the activity of various fission gas nuclides determined and reported. A set of seven heavily-shielded, high-purity germanium (HPGe) gamma-ray spectrometers and sodium iodide [NaI(Tl)] scintillation detector-based total radiation detectors have been designed and are being configured and tested for use during the AGR-1 experiment. The AGR-1 test specification requires that the fission product monitoring system (FPMS) have sufficient sensitivity to detect the failure of a single coated fuel particle and sufficient range to allow it to "count" multiple (up to 250) successive particle failures. This paper describes the design and expected performance of the AGR-1 FPMS.