An estimation of the release of radioactive iodine from the waste package solidified by the copper matrix. Research document

Radioactive Iodine in the spent nuclear fuel is trapped by Iodine-adsorber in the off-gas process of reprocessing plant. The radioactive iodine includes very long half-lived nuclide (I-129; Half life=1.57 x 107y). The I-129 cannot be expected to decay due to containment by the barrier system because of its long half life. The Iodine have soluble and poorly sorbing nature in the geological disposal condition, because the element can take the chemical form of I in the reducing condition such as the condition of deep underground. Therefore Iodine can migrate in barrier system easily and strongly contribute to the peak of dose in the performance assessment of TRU waste disposal. An effective measure for reducing the dose peak is the controlled release of Iodine from the waste package in the low flux. The solidification by the copper matrix was proposed as one of the previous controlled release technology by JNC. The release rate of I-129 from the waste package solidified by the copper matrix was estimated. The corrosion rate of copper matrix was estimated as the sum of those both in the oxidizing and reducing conditions. The rates and periods of I-129 release were estimated under the assumption of congruent release of I-129 with corrosion of the copper matrix. The total release rate and period in the FRHP groundwater case were 3.11 x 106 Bq y-1 and 1.64 x 107y (Initiated at 103y and finalized at 1.64 x 107y) respectively. The total release rate and period in the SRHP groundwater case were 9.03 x 108 Bq y-1 and 5.66 x 104y(Initiated at 103y and finalized at 5.76 x 104y). (author)