An Assaying System for HTGR Fuel Compacts

An automatic gamma scanning apparatus to determine U-235 content in fuel compacts is described. Two automatic scanners, controlled by a logic unit, drive each compact past a NaI(Tl) scintillation detector. Pulse-height selection permits counting only the emitted 184 KEV gamma-rays. After each scan, a scaler containing the total count is gated off and a readout cycle initiated. Comparison logic analyzes the count in terms of 4 values set into the system by selector switches. The interrogation circuits then decide the percentage of fuel loading relative to a standard element and indicate this to the operator. Simultaneously, the scaler count is printed on paper tape. Possible errors are considered and these are correlated with test results.