FISSION-GAS RELEASE DETERMINATION USING AN ANTI-COMPTON SHIELD DETECTOR

Poolside measurements of fission gas release (FGR) in fuel pins have b een made using gamma-ray spectroscopy with a Ge detector measuring Kr- 85 activity in the fuel rod plenum. The gamma-ray energy spectra from irradiated nuclear fuel are characterized by prominent Compton distrib utions that can obscure the weak 514-keV Kr-85 peak. To improve the se nsitivity, the detector has been provided with an anti-Compton shield of six Bi3Ge4O12 detectors. Laboratory tests of the detector system sh owed that the maximum peak-to-Compton (p/c) ratio was improved by a fa ctor of similar to 6. The results of the poolside measurement p/c rati o showed a somewhat smaller improvement (a factor of similar to 4) bec ause of scattered gamma radiation from the surrounding material. Howev er the precision in the poolside FGR measurements was improved substan tially utilizing the Compton shield.