Radiation Induced Spent Nuclear Fuel Dissolution under Deep Repository Conditions

Abstract

The dynamics of spent nuclear fuel dissolution in groundwater is an important part of the safety assessment of a deep geological repository for high level nuclear waste. In this paperwe discussthe most important elementary processes and parameters involved in radiation induced oxidative dissolution of spent nuclear fuel. Based on these processes, we also present a new approach for simulation of spent nuclear fuel dissolution under deep repository conditions. This approach accounts for the effects of fuel age, burn up, noble metal nanoparticle contents, aqueous H2 and HCO3- concentration, water chemistry, and combinations thereof. The results clearly indicate that solutes consuming H202 and combined effects of noble metal nanoparticles and H2 have significant impact on the rate of spent nuclear fuel dissolution. Using data from the two possible repository sites in Sweden, we have employed the new approach to estimate the maximum rate of spent nuclear fuel dissolution. This estimate indicates that H2 produced from radiolysis of groundwater alone will be sufficient to inhibit the dissolution completely for spent nuclear fuel older than 100 years.

Radiation Effects on Materials Used in Geological Repositories for Spent Nuclear Fuel

“…The only question is how long it takes before a steady-state concentration of H 2 O 2 , is reached. This problem has been addressed in some previous papers where the system was simulated taking the geometrical dose distribution, the radiolytic production of H 2 O 2 , the surface reaction consuming H 2 O 2 and diffusion of H 2 O 2 into account [65,73,74]. Interestingly, the results of the simulations showed that the surface concentration of H 2 O 2 approaches the steady-state level within a matter of seconds to minutes, even though the bulk concentration is much lower.…”

“…There are numerous other constituents that could also influence the process of radiation-induced oxidative dissolution [65][66][67]. A few of these constituents will be discussed here.…”

“…Iron (Fe(II)) will also be able to scavenge radiolytic oxidants, and since Fe(II) is more reactive towards H 2 O 2 , the impact of iron is expected to be larger. Simulations have shown that 10 μM Fe 2+ in the groundwater will reduce the rate of matrix dissolution by at least one order of magnitude [65]. The presence of various organic substances (e.g., humic substances) will also reduce the rate of oxidation, mainly by scavenging the oxidizing radical species formed upon radiolysis of water.…”

“…Solution reactions consuming radiolytic oxidants are more difficult to account for using this simple approach. However, simple methods accounting for solution reactions have also been proposed [65].…”

Factors influencing the rate of radiation-induced dissolution of spent nuclear fuel

“…where _ DðxÞ is the dose rate at distance x from the fuel surface, q is the density of water and GðH 2 O 2 Þ is the radiation chemical yield for H 2 O 2 [31]. The maximum rate of the reaction between H 2 O 2 and the UO 2 surface corresponds to the steadystate.…”