Radiolytic Compounds Formed by Dissolution of Irradiated NaCl and MgCl₂ · 6H₂O in Water

Abstract

High level waste disposed in rock salt irradiates its surrounding. Penetrating water produces radiolytic compounds which can undergo redox and complexation reactions with dissolved radionuclides, thus changing their mobility. To investigate such radiolytic effects, samples of solid NaCl and MgCl 2 • 6H 2 0 were irradiated with a M Co source with doses between 0.1 and 7 MGy and dose rates between 0.1 and 7 kGy/h and then dissolved in water. After the dissolution of irradiated NaCl, only CIO" was formed as a water soluble product with G = 0.0006. The respective results for MgCl 2 · 6H 2 0 were G = 0.012 for CIO" and G = 0.0012 for C10 2 ". In both cases, the pH of nearly saturated solutions was shifted towards the alkaline region and reached maximum values of about 9 and 7.8 respectively. The solutions prepared from irradiated salts were strongly oxidizing and showed redox potentials of 850 mV and 1100 mV.

Gamma radiolysis of NaCl brine: Effect of dissolved radiolysis gases on the radiolytic yield of long-lived products

“…The gas composition is determined by mass spectroscopy. The solution is analyzed for HClO, ClO À 2 , ClO À 3 as described elsewhere and by ICP-MS for corrosion products from the autoclave [10].…”

Radiation chemical effects on radiochemistry: A review of examples important to nuclear power

“…Long-term exposure of transuranic nuclides to repository matrices, such as rock salt and salt brines following inundation of a repository, would also result in radiolytic production of oxidative species. For example, when Kelm and Bohnert [89] made a 6 M-solution from NaCl that had been irradiated with 60 Co γ -rays, the redox potential was 850 mV, as opposed to 450 mV for unirradiated salt. The result was even more dramatic for 5 M MgCl 2 ·H 2 O, which increased from 430 to 1100 mV.…”

Contrary effects of the water radiolysis product H2O2upon th dissolution of nuclear fuel in natural ground water and deionized water

“…These results indicate that a) different radicals are responsible for the promotion of the dissolution of UO 2 in aerated and in radiolysed solutions, and b) explain why reaction (2) is inhibited in the case of the groundwater samples, since Fe(II) can be expected to be oxidized to Fe(III), which was found to catalytically decompose H 2 O 2 [26]. Cl − should not be converted into an oxidized Cl anion species (as ClO − ) [21], and SO 4 2− is expected to remain unchanged in solution (Ag, Mn and Co were present in insignificant amounts in the groundwater used here). Carbonate, which is one of the major ions present in groundwaters, was found to form carbonate radicals in irradiated solutions [11].…”