Isotope Dilution Alpha Spectrometry for the Determination of Plutonium Concentration in Irradiated Fuel Dissolver Solution: IDAS and R-IDAS

Isotope Dilution Alpha Spectrometry (IDAS) and Reverse Isotope Dilution Alpha Spectrometry (RIDAS) have been developed for determining the concentration of plutonium in the irradiated fuel dissolver solution. The method exploits ²³⁸Pu in IDAS and ²³⁹Pu in R-IDAS as a spike and provides an alternative method in the event of nonavailability of ²⁴²Pu, which is required in Isotope Dilution Mass Spectrometry (IDMS). Depending upon the burnup of the fuel, ²³⁸Pu or ²³⁹Pu is used as a spike to change the ²³⁸Pu/(²³⁹Pu + ²⁴⁰Pu) alpha activity ratio in the sample by a factor of 10. This change is determined by alpha spectrometry on electro-deposited sources using a solid-state silicon surface barrier detector coupled to a multichannel analyzer. The validity of a simple method based on the geometric progression decrease for the far tail of the spectrum to correct for the tail contribution of ²³⁸Pu (5.50-MeV) peak to the low energy ²³⁹Pu + ²⁴⁰Pu (5.17-MeV) peak is established. Results for the plutonium concentration on different irradiated fuel dissolver solutions with burnup ranging from 1000 to 100 000 MWd/tU are presented and compared with those obtained by IDMS. The values obtained by IDAS or R-IDAS and IDMS agree to within 0.5%.