Determination of 129I in cement-solidified radwastes using neutron activation

The purpose of this study is to develop a neutron activation method to determine trace amounts of I-129 in cement-solidified radwastes. The radwaste samples were alkaline fused using KOH and then I-129 and iodine carrier were chemically separated by solvent extraction before and after neutron irradiation. Both stable iodine (I-127) and I-129 can be activated by neutrons through I-127 (n, 2n) I-126 and I-129 (n, gamma) I-130 reactions; their activated radionuclides were counted together with a high-purity germanium detector. The chemical recovery yields ranged from 30 to 60 %, and it was found that more than 99.9 % of interfering radionuclides can be removed using solvent extraction after neutron irradiation. The minimum detectable amounts can be lowered to less than 1 mBq g(-1), which is superior to low energy gamma-ray spectrometry by a factor of > 10(2), on average. The established technique can be applied to re-evaluation of I-129 content in radwastes that can be re-classified to lower classes, and the cost for designing a final disposal facility can be significantly reduced.