ESTIMATING PLUTONIUM BUILDUP FROM THE CS-137 U-238 RATIO FOR SLIGHTLYIRRADIATED LOW ENRICHED URANIUM/

A nondestructive gamma spectrometric method has been developed to get a quantitative estimate for the neutron fluence obtained by slightly i rradiated low-enriched uranium. The approach is based on intrinsic cal ibration method and applicable whenever Pa-234m gamma-lines can be see n and secular equilibrium between U-238 and (234)Tn (T-1/2 = 24.1 d) i s attained. The obtained fluence and the plutonium buildup is estimate d directly from the measured Cs-137/U-238 activity ratio, providing a high level of independence from the irradiation history data. Although enrichment is an input datum, under favourable conditions it can be d etermined from the same gamma-spectrum as well. The method and its sen sitivity was demonstrated fro the case of slightly irradiated fuel rod s.