The Effects of Simulated Fission Products in the Reduction of Hydrogen Peroxide on Simulated Nuclear Fuel Electrodes

Abstract

The electrochemical reduction of hydrogen peroxide ͑H 2 O 2 ͒ has been studied on a series of simulated nuclear fuel ͑SIMFUEL͒ materials with different amounts of simulated fission products. Steady-state polarization measurements under diffusioncompensated conditions show that the reaction proceeds with a weak dependence on applied potential and fractional reaction orders with respect to H 2 O 2 . A mechanism for H 2 O 2 reduction on SIMFUEL materials is proposed to explain these features. It is found that the activity of the material for the H 2 O 2 reduction reaction increases with the doping level. This increase can be attributed to noble metal particles present in the SIMFUEL. This enhanced reactivity is most apparent at low overpotentials, where H 2 O 2 reduction proceeds significantly faster on the noble metal particles than on the UO 2+x lattice.

The electrochemical reduction of hydrogen peroxide on uranium dioxide under intermediate pH to acidic conditions

“…Although not shown in Table 1, similar slopes have been observed up to pH 12 [21]. These values are consistent with the mechanism proposed previously [21,23] involving reaction steps (1) and (2), and confirm that, provided the UO 2+x layer is stable on the electrode surface, the mechanism of H 2 O 2 reduction is the same and independent of pH. This is confirmed by the comparison of the forward scans for peroxide reduction over the pH range 4-9 (Fig.…”

“…Previous work has shown that H 2 O 2 reduction can be catalyzed on the noble metal () particles in SIMFUEL, particularly at low potentials (≤−300 mV) [23]. As the enhanced current for H 2 O 2 reduction at low pH occurs in this range, a similar experiment to that in Fig.…”

“…A problem with the use of this equation is its insensitivity to the choice of reaction order [48] and our previous evidence that demonstrates that reaction orders can be fractional [21] and change with potential and [H 2 O 2 ] [23]. Taking m = 1, the measured currents at various pH values over the range 3-9 have been corrected for diffusion using Eq.…”

“…The influence of H 2 O 2 on fuel corrosion has been extensively studied [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] and much of the early literature has been reviewed [5,24]. The cathodic reduction of H 2 O 2 on UO 2 surfaces was found to proceed via a coupled chemical-electrochemical process in which H 2 O 2 chemically creates U IV -U V donor-acceptor sites on the UO 2 surface…”

The Role of Dissolved Hydrogen on the Corrosion/Dissolution of Spent Nuclear Fuel

“…Good electrochemical evidence exists to show that the first electron transfer to H 2 O 2 involves the creation of an OH • radical (116,117). The results in Figure 20 show that, for this scavenging process to occur, the concentration ratio [H 2 ]/[H 2 O 2 ] needs to be >10 5 .…”