The NOx composition and iodine species in the dissolution of spent fuels are discussed on the basis of thermochemical calculations and experimental results. The influence of NOx sparging on the expulsion of iodine is also discussed. The dissolution of a spent PWR-fuel specimen ( ~3 g) in 30 ml of 3. 5 ~~ HNO, at lOOoC is calculated to yield a concentration of 7 x I0-2 atm of N02 , which is 80~,; of the total NOx in the dissolver. This NO, fraction is much higher than experimental values of 15q,; or less that were reported for dissolver off-gas cooled near to room temperature. The high N02 fraction suppresses the formation of iodate (10,-) m the dissolution. The calculations predict that 10"-is not formed in 3. 5 :VI HN0 8 at lOOoC at an NO, pressure ~3x10-2 atm (3 kPa). Attempts to expel iodine from the fuel solution indicated that the main iodine species in the solution was colloidal iodine and not iodate (10 3 -) which earlier workers postulated. The obtained experimental results are consistent with the thermochemical predictions. For the decomposition of the colloidal iodine in the expulsion process, NO, sparging has a negative effect. This is because an increase in N0 2 pressure promotes the formation of colloidal Agl.
Precise measurements of burnup and accumulated transuranium elements were carried out on specimens which were taken out from spent fuel of Japan Power Demonstration Reactor (JPDR) -I, by means of chemical analysis and r-ray spectrometry. Results of the measurements are summarized numerically. Core configuration and operational history of the reactor are also described.
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