Spent Fuel Monitoring for International Inspection at the High-Temperature Engineering Test Reactor*

This paper describes the detector design features, performance, and operating characteristics of the high-temperature engineering test reactor (HTTR) door valve monitor system spent-fuel monitor. The HTTR door valve monitor system (HDVM) is installed in the HTTR door valve to provide unattended monitoring data for the transfer of spent fuel through the door valve on the top of the reactor. The system includes a pair of detectors to provide direction of travel and redundancy. The fission product gamma rays are measured using ion chambers (ICs) and the curium neutrons are measured using shielded 3He detectors. There are two ICs and one 3He tube inside each detector package. Gammaray and neutron detector (GRAND) electronics supply power to the ICs and 3He tubes, and the data are collected in the GRAND and the field works computer. The system is designed to operate unattended with data pickup by the inspectors on a 90-day period.