Plutonium Determination in Compacted Bentonite by Using PERALS

Abstract

The determination of plutonium activities at low levels was occurred during study on diffusion of plutonium onto compacted bentonite, a candidate buffer material of multi-barrier system suggested for high-level radioactive waste disposal in Japan. It was performed by using photo/electron-rejecting alpha liquid scintillation (PERALS) spectrometry, model 8100AB (ORDELA INC.), followed by plutonium extraction from slices of the bentonite by hydrochloric acid (HC1). Pulse shape spectrum was chosen because of a high counting efficiency and only one alpha emitter existing. For an accurate determination, the optimum pulse shaped discrimination (PSD) setting was obtained. Effects resulted from HC1 concentration used for plutonium extraction and sample-loading (SL) were also investigated by PERALS spectrometry from the view of its application. The results showed that peak region in pulse shape spectrum shifted with changes of the HC1 concentrations and sample-loading. Pulse shape spectrum of background blank (liquid scintillator, Ultima Gold AB) showed an obvious peak located on the left side of alpha region. This peak influenced seriously plutonium counting by means of peak overlap when total plutonium activity in sample was less than several Bq. The low limit of detective concentration was estimated to be 0.79 Bq/g-bentonite.