Safeguards Concept for the High Temperature Engineering Test Reactor Using Unattended Fuel Flow Monitor System

The High Temperature Engineering Test Reactor (HTTR) is an HTGR-type research reactor — direct access to the core for inspection is difficult because of strong radiation from the burned fuels and the long fuel reloading time. Opening the upper-hemisphere of the reactor vessel is not possible, unlike other water-cooled research reactors. It takes about 200 days to carry out item counting by reloading the fuel blocks from the core. Furthermore, it takes about 30 days to reload the fuel blocks in the spent fuel storage. The inspection efforts are very extensive when the inspection is carried out by discharging the fuel blocks from the core and spent fuel storage. These areas are defined as "difficult to access." Therefore, an adequate safeguards approach for the HTTR cannot be found among the established techniques for research reactor and critical assemblies (RRCAs). A new specific safeguards approach that is appropriate for the HTTR is needed. The difficulty in inventory verification of the core and spent fuel storage is overcome by introducing an unattended fuel flow monitor system (UFFM). Safeguards efforts are reduced from 230 man-days per year to several mandays per year by the UFFM and application of the dual C/S for the spent fuel storage.