Modeling the Radiolytic Corrosion of Fractured Nuclear Fuel under Permanent Disposal Conditions

Abstract

A two-dimensional model has been developed to simulate the corrosion of nuclear fuel pellets under permanent waste disposal conditions in a steel vessel with a corrosion-resistant copper shell. The primary emphasis was on the corrosion behavior within cracks with various dimensions. It was shown that a simplified α-radiolysis model which only accounts for the radiolytic production of H 2 O 2 and H 2 provides a reasonably accurate simulation and is a time-efficient alternative to the use of a model including a full α-radiolysis reaction set. Both radiolytic H 2 O 2 and H 2 can accumulate inside the cracks. However, the [H 2 O 2 ] is regulated by its reaction with UO 2 to cause corrosion and especially its decomposition to O 2 and H 2 O. This leads to [H 2 ] much greater than [H 2 O 2 ] within the cracks. The critical [H 2 ], [H 2 ] crit , required to completely suppress corrosion has been calculated for various crack widths and depths. The maximum [H 2 ] crit is only ∼ 12 times that required on a planar surface irrespective of the dimensions of the crack. The build up of H 2 within cracks is effectively a shift to more reducing conditions. As a consequence, the redox conditions within cracks begin to decouple from the external redox conditions. This makes the fuel corrosion process at these locations less sensitive than might be expected to the influences of the H 2 and Fe 2+ produced by corrosion of the steel vessel.

Extraction of Lanthanide and Actinide Ions from Aqueous Mixtures Using a Carboxylic Acid-Functionalized Porous Aromatic Framework

“…This solidification process is particularly important for fuel storage, as the long-term stability of a stored fuel is heavily dependent upon the nature of the solid, preventing leaching of contaminants over time, as well as reducing the potential for highly penetrating radiation to escape the containment vessel into the environment. 66 Industrial, large-scale processes are conducted as a covitrification with silica, which may cause separation of radionuclides and metallic phases, and poor solid phase stability. 67 However, the process described in our study allows for separation of nuclides prior to vitrification, with the added benefit of minimal contamination by the adsorbent, which can readily be discarded as volatile combustion products.…”

“…Thus, this material has potential not only to separate particular components of a nuclear fuel but also to preserve them in a stable, solid, insoluble form. This solidification process is particularly important for fuel storage, as the long-term stability of a stored fuel is heavily dependent upon the nature of the solid, preventing leaching of contaminants over time, as well as reducing the potential for highly penetrating radiation to escape the containment vessel into the environment . Industrial, large-scale processes are conducted as a covitrification with silica, which may cause separation of radionuclides and metallic phases, and poor solid phase stability .…”

The influence of hydrogen peroxide and hydrogen on the corrosion of simulated spent nuclear fuel

“…To determine the overall inuence of these many reactions we have developed a model to determine the inuence of steel corrosion products on the alpha (a) radiolytic corrosion of spent nuclear fuel within a failed waste container. [28][29][30] The key reactions incorporated in this model are illustrated in Fig. 2 and include: (1) a complete reaction set for the a-radiolysis Fig.…”

Roles of Radiolytic and Externally Generated H2 in the Corrosion of Fractured Spent Nuclear Fuel

“…This approach considers only the radiolytic production of these two molecular species as opposed to a full radiolysis model that would include the radical species as well (e.g., OH, H, etc.). Our previous comparison of this simplified model to the full model showed the simplified model overestimates the steady-state [UO 2 2+ ] by ∼20% at the bottom of a fracture (width = 0.1 mm, depth =1 mm); i.e., it overestimates the oxidizing effect of H 2 O 2 compared to the reducing effect of H 2 , making our calculations in this paper conservative …”

“…Using this database generated by Jonsson et al, Wu et al developed a 1-D model for fuel corrosion that includes a full α-radiolytic reaction set. This model was subsequently expanded to account for the complex geometry of spent fuel, particularly the fracturing of the fuel pellets due to the thermal stress during the in-reactor irradiation and the cooling process on discharge from reactor . This 2-D model showed that both radiolytically produced H 2 ((H 2 ) int ) and H 2 from steel corrosion ((H 2 ) ext ) can inhibit fuel corrosion, although (H 2 ) ext would be expected to be the primary redox scavenger.…”