Linear free energy correlations for fission product release from the Fukushima-Daiichi nuclear accident

This paper extends the preliminary linear free energy correlations for radionuclide release performed by Schwantes et al., following the Fukushima-Daiichi Nuclear Power Plant accident. Through evaluations of the molar fractionations of radionuclides deposited in the soil relative to modeled radionuclide inventories, we confirm the initial source of the radionuclides to the environment to be from active reactors rather than the spent fuel pool. Linear correlations of the form In π = -α ((ΔGrxn°(T_C))/(RT_C)) + β were obtained between the deposited concentrations, and the reduction potentials of the fission product oxide species using multiple reduction schemes to calculate ΔG°_rxn (T_C). These models allowed an estimate of the upper bound for the reactor temperatures of T_C between 2015 and 2060 K, providing insight into the limiting factors to vaporization and release of fission products during the reactor accident. Estimates of the release of medium-lived fission products ⁹⁰Sr, ^121mSn, ¹⁴⁷Pm, ¹⁴⁴Ce, ¹⁵²Eu, ¹⁵⁴Eu, ¹⁵⁵Eu, and ¹⁵¹Sm through atmospheric venting during the first month following the accident were obtained, indicating that large quantities of ⁹⁰Sr and radioactive lanthanides were likely to remain in the damaged reactor cores.