Gamma Radiolysis Research Articles

Melatonin related compounds inhibit lipid peroxidation during copper or free radical-induced LDL oxidation.

This study was designed to evaluate the protective effect of two melatonin related compounds towards low density lipoproteins (LDL) oxidation initiated in vitro either by defined free radicals [i.e. superoxide anion (O2*-) and ethanol-derived peroxyl radicals (RO(2)(*))] produced by gamma radiolysis or by copper ions. The compounds studied were N-[2-(5-methoxy-1H-indol-3-yl)ethyl]-3,5-di-tert-butyl-4-hydroxybenzamide (DTBHB) and (R,S)-1-(3-methoxyphenyl)-2-propyl-1,2,3,4-tetrahydro-beta-carboline (GWC20) which is a pinoline derivative. Their effects were compared with those of melatonin at the same concentration (100 micromol/L). None of the three tested compounds protected endogenous LDL alpha-tocopherol from oxidation by RO(2)(*)/O(2)(*)- free radicals. By contrast, they all protected beta-carotene from the attack of these free radicals with GWC20 being the strongest protector. Moreover, melatonin and DTBHB partially inhibited the formation of products derived from lipid peroxidation (conjugated dienes and thiobarbituric acid-reactive substances or TBARS) while GWC20 totally abolished this production. As previously shown, melatonin (at the concentration used) inhibited copper-induced LDL oxidation by increasing 1.60-fold the lag phase duration of conjugated diene formation over the 8 hr of the experimental procedure, however, DTBHB and GWC20 were much more effective, because they totally prevented the initiation of the propagation phase of LDL oxidation. It would be interesting to test in vivo if DTBHB and GWC20 which exhibit a strong capacity to inhibit in vitro LDL oxidation would reduce or not atherosclerosis in animals susceptible to this pathology.

One-electron reduction of 1,2-dihydroxy-9,10-anthraquinone and some of its transition metal complexes in aqueous solution and in aqueous isopropanol–acetone-mixed solvent: a steady-state and pulse radiolysis study

One-electron reduction of 1,2-dihydroxy-9,10-anthraquinone (DHA) and its complexes with Cu(II), Ni(II) and Fe(III), by acetone ketyl radical, (CH 3) 2C·OH, was carried out in aqueous solution and in aqueous isopropanol acetone mixed solvent using both steady-state gamma radiolysis and pulse radiolysis techniques. The rate constants for the reduction of DHA at different pH values by the ketyl radical are in the order of ∼10 9 dm 3 mol −1 s −1, whereas those for the metal complexes are comparatively less. These rate constants are, however, in conformity with the one-electron reduction potentials of the ligand in free DHA and in its metal complexes. Decay kinetics of the one-electron reduced semiquinones of the free ligand and its metal complexes suggest disproportionation of the semiquinone in the case of the free ligand and intermolecular electron transfer from the co-ordinated semiquinone radical to the metal centre in the case of the metal complexes.

EVALUATION OF DI(2-ETHYLHEXYL)ISOBUTYRAMIDE (D2EHIBA) AS A PROCESS EXTRACTANT FOR THE RECOVERY OF 233U FROM IRRADIATED Th

ABSTRACT Extraction behaviour of U(VI) and Th(IV) has been studied employing 0.5 M D2EHIBA (di(2-ethylhexyl)isobutyramide) in n-dodecane as a function of nitric acid concentration. An improved separation of U from Th could be achieved in the presence of fluoride ion. Use of 1 M Al(NO3)3 in 2 M HNO3 has been suggested as the scrubbing solution. Various physico-chemical properties like density, viscosity, interfacial tension (IFT) and limiting organic concentration (LOC) of Th/U have been measured to evaluate the use of D2EHIBA as a process solvent. Degradation behaviour (acid hydrolysis as well as gamma radiolysis) of D2EHIBA under process conditions has been investigated using potentiometry as well as distribution studies.

OH-Radical Induced Oxidation of Phenoxyacetic Acid and 2,4-Dichlorophenoxyacetic Acid. Primary Radical Steps and Products

The reactions of •OH radicals with 2,4-dichlorophenoxyacetic acid (2,4-D), k = (6.6 ± 0.5) × 109 M-1 s-1, phenoxyacetic acid (PAA), k = (10 ± 1) × 109 M-1 s-1, and 2,4-dichlorophenol (2,4-DCP), k = (7.1 ± 0.5) × 109 M-1 s-1, have been studied using pulse and gamma radiolysis. The •OH adducts produced by addition to the ring at positions not occupied by substituted groups were oxidized by K3[Fe(CN)6], with the corresponding hydroxylated species analyzed by HPLC. The distribution of •OH radical addition to the aromatic ring of 2,4-D is C1, 17%; C2/C4, 20%; C3/C5/C6, 47%; and for •OH reaction with PAA, it is C1, 5.5%; C2/C6, 45%; C3/C5, 11%; C4, 36%. Whereas the hydroxycyclohexadienyl radicals of 2,4-D have no observable reactivity toward oxygen, those of PAA and 2,4-DCP do react, with k(•OH adduct−PAA) + O2 = (5.1 ± 0.2) × 108 M-1 s-1 and k(•OH adduct−2,4-DCP) + O2 = (1.1 ± 0.1) × 108 M-1 s-1. The phenoxyl radicals formed by chloride elimination from the ipso-chloro-•OH adducts of 2,4-D rapidly oxidize TMPD to TMPD•+, k = (3.6 ± 0.5) × 109 M-1 s-1.

Stochastic simulation of gamma radiolysis of acidic ferrous sulfate solution at elevated temperatures.

The effect of temperature on the oxidation of Fe2+ in the gamma radiolysis of acidic ferrous sulfate solutions has been modelled using the stochastic IRT method, incorporating simulated electron track structures. There is an 11% increase in the Fe3+ yield in aerated 0.4 M H2SO4 solution on going from 298 to 573 K (25 to 300 degrees C). The H2 yield in aerated solution increases about 24% from 0.41 at 298 K to 0.51 at 573 K. In the absence of oxygen, the increase in the yields of both Fe3+ and H2 is about 12%. Calculated yields are consistent with available experimental data at room, and elevated temperatures. Simulations for heavy water (D2O) show similar temperature effects to those found for ferrous sulfate solutions in light water (H2O).

The Selective OH Radical Oxidation of Sorbitylfurfural: A Combined Experimental and Theoretical Study

Sorbitylfurfural (Furalglucitol), widely used in the cosmetic industry as antioxidant and antiinflammatory agent, reacts with hydroxyl radical in neutral aqueous solution with a rate constant almost at the diffusional limit, k1 = 7.3 × 109 M-1 s-1. Despite the unselective character of the OH radical, addition to the 5‘ position in the furanic ring seems to provide the dominant path. The consequent allylic radical undergoes the cleavage of the C−O bond (k2 = 1.7 × 106 s-1) in β position to form a pseudo-seven-atom ring via a hydrogen bond between the attacking OH group and the furanic oxygen. A 1,6 H-shift between the two oxygen atoms (k3 = 1.4 × 105 s-1) then precedes a disproportionation reaction which leads to the final products (k4 = 2.0 × 107 M-1 s-1). The proposed mechanism is based on the UV−vis spectra of intermediates and final products obtained after pulse and gamma radiolysis, on nonlinear kinetic fittings of absorbance versus time curves, on quantum-mechanical calculations of electronic transit...

Gamma radiolysis studies of uranyl fluoride

Summary The safe handling and storage of radioactive materials require an understanding of the effects of radiolysis on those materials. Radiolysis may result in the production of gases (e.g., corrosives) or pressures that are deleterious to storage containers. A study has been performed to address these concerns as they relate to the radiolysis of residual fluoride compounds in uranium oxides. Samples of UO2F2·xH2O and U3O8 (with ∼1.4 wt.% fluorine content) were irradiated in a 60Co source and in spent nuclear fuel (SNF) elements from the High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory. Container pressures were monitored throughout the irradiations, and gas and solid samples were analyzed after the irradiations. The irradiation of UO2F2·xH2O produced O2 – with G(O 2)-values ranging from 0.007 to 0.03 molecules of O2 produced per 100 eV. Neither F2 nor HF was produced by the irradiations. Chemical analyses of solid samples showed that some of the uranium was reduced from U(VI) to U(IV). A saturation damage limit for the UO2F2·xH2O was demonstrated by using the HFIR SNF elements, and the limit was found to be 7–9% at ∼108 rad/h). It is shown that the covalently bonded oxygen is more susceptible to radiation damage than is the ionically bonded fluorine. Irradiation of U3O8 (with ∼1.4 wt.% fluorine content) resulted in neither gas production nor a pressure increase. These experiments led to the conclusion that during long-term storage U3O8 is safe from overpressurization and the production of corrosives caused by gamma radiolysis of residual fluorides.

Micellar electrophoretic capillary chromatographic analysis of the products produced in the radiolytic oxidation of toluene and phenol

In this paper, we consider the effect of CH 3 and OH substitution on a benzene ring in directing the site of OH radical attack in oxidative processes initiated by the gamma radiolysis of aqueous solutions of phenol and toluene. The analytical method used was micellar electrophoretic capillary chromatography. This approach permits the resolution of the radiolytic products resulting from the oxidation of the hydroxycyclohexadienyl radicals initially produced by addition of OH to the aromatic compounds and allows one to obtain a complete mechanistic picture of the radiation chemical processes.

NMR study of the gamma radiolysis of poly(dimethyl siloxane) under vacuum at 303 K

The structural changes which occur on the γ-radiolysis of poly(dimethyl siloxane) (PDMS) under vacuum at 303K have been investigated using 29Si and 13C NMR. New structural units consistent with main chain scission and crosslinking through both H-linking and Y-linking reactions have been identified. The results obtained at various absorbed doses have been used to calculate the G-values for scission and crosslinking. G-values for scission of G(S)=1.3±0.2, for H-linking of G(DCH2–R)=0.34±0.02 and for Y-linking of G(Y)=1.70±0.09 were obtained for radiolysis under vacuum at 303K. Thus crosslinking predominates over scission for radiolysis of PDMS under these conditions, and, by contrast with previous studies, Y-links have been shown to be the predominant form of crosslinks.

STUDIES ON THE IDENTIFICATION OF HARMFUL RADIOLYTIC PRODUCTS OF 30% TBP-N-DODECANE-HNO3 BY GAS-LIQUID CHROMATOGRAPHY. II. FORMATION AND CHARACTERIZATION OF HIGH MOLECULAR WEIGHT ORGANOPHOSPHATES

Gamma radiolysis of Purex solvent, 30% tri-n-butylphosphate-n-dodecane-HNO3 is observed to yield many undesirable metal complexing species. A method for identifying the gas-liquid chromatographic (GLC) signatures of high molecular weight organophosphates (HMPs) through a nitrogen- and phosphorous-selective detector is described. Fractionation of the radiolyzed solvent by vacuum distillation resulted in the enrichment of HMP species in the high boiling, viscous residue in the last fraction. This residue showed intense infrared signals characteristic of the presence of nitro, carbonyl, and phosphoryl groups, which implies the presence of multifunctional species. The study revealed a strong association among the components of radiolyzed solvent, which inhibits clean fractionation. Gas chromatography–mass spectrometry assay of the sample indicated that these HMPs consist of(NO2─C4H8)(C4H9O)2PO, (OH─C4H8O)(C4H9O)2PO, and (CH3─C4H8)(C4H9O)2PO species. The HMP-rich fraction exhibited very high plutonium-retention behavior, which was substantially lowered by efficient uptake of HMPs upon alumina treatment. Thus, the present study correlates the GLC signatures of HMPs, especially those of nitrated species, formed by radiolysis of 30% tri-n-butylphosphate-n-dodecane-HNO3 and solvent quality deterioration with respect to Pu-retention behavior.

Pulse and gamma radiolysis studies of 3-sulfo propyl methacrylate in aqueous solutions

Radiation induced polymerization of 3-sulfo propyl methacrylate (SPMA) in aqueous solution (10wt%) has been studied by steady state and pulse radiolysis techniques. The effect of radiation characteristics such as irradiation dose, dose rate and the presence of crosslinking agent on the gel formation of SPMA monomer has been investigated. In N2 -saturated solution, the gel formation doses for SPMA were found to be 70 and 258Gy at dose rates of 1.2 and 5kGyh−1, respectively. The swelling ratio results showed that the gel obtained at a constant dose of 0.8kGy dose swells ∼630 times of its dry weight at a dose rate of 5kGyh−1 whereas it is 394 times of its dry weight for the dose rate 1.2kGyh−1. The reactions of the primary radicals of water radiolysis such as eaq−, H-atom, OH radical, O−, and some oxidizing radicals like N3,Cl2−,SO4− and reducing species like CO2− with SPMA have been studied using pulse radiolysis technique. The results show that the reaction of eaq−, H-atom and OH radicals with SPMA are in the diffusion controlled limit with their respective bimolecular rate constant values being 8.6×109, 2×109 and 1.5×1010dm3mol−1s−1. The radical anion, SPMA− , (λmax=280nm) is observed to undergo fast protonation forming H-adduct, SPMA—H, (λmax=310nm) with a pKa value of 9.1. Cl2− reacts with a bimolecular rate constant of 3.5×107dm3mol−1s−1 forming solute radical cation (λmax=265nm). One-electron oxidation and reduction potentials for SPMA/SPMA+ and SPMA/SPMA− couples are estimated to be more than +1.6 and less than −1.9V, respectively.

Comparison of the effects of O 2•−/HO • free radical- and copper ions-oxidized LDL or lipoprotein(a) on the endothelial cell releases of tissue Plasminogen Activator and Plasminogen Activator Inhibitor-1

We investigated the effects of low density-lipoproteins (LDL) and lipoprotein(a) [Lp(a)] oxidized by O 2 •−/HO • free radicals generated by gamma radiolysis of water, on the release of tissue Plasminogen Activator (tPA) and of its main inhibitor Plaminogen Activator Inhibitor-1 (PAI-1) by human umbilical vein endothelial cells (HUVEC). These effects were compared to those of lipoproteins issued from the same preparations but oxidized by the classical copper ions procedure. The results showed that O 2 •−/HO • free radical oxidized LDL and Lp(a) led to a dramatic decrease of PAI-1 release but did not affect tPA release, whereas copper oxidation of lipoproteins resulted in an increase in PAI-1 release and a decrease in tPA release. Chemical analysis revealed that O 2 •−/HO • free radical oxidized lipoproteins exhibited very much lower levels of phosphatidylcholine hydroperoxides, lysophosphatidylcholine and oxysterols (7-ketocholesterol, 7β-hydroxycholesterol, 5,6β-epoxycholesterol) than copper oxidized LDL. Thus, the discordant effects of O 2 •−/HO • oxidized and copper oxidized LDL and Lp(a) on the endothelial releases of PAI-1 and tPA appeared to be due to qualitatively and/or quantitatively different formation of oxidized components by the two oxidation processes.

Molecular weight changes and scission and crosslinking in poly(dimethyl siloxane) on gamma radiolysis

The molecular weight changes which occur on the γ-radiolysis of poly(dimethyl siloxane) under vacuum between 77 and 373 K and in air at 303 K have been investigated using triple detection GPC to obtain the complete molecular weight distributions for the irradiated samples and to determine the number and weight average molecular weights. The results have been interpreted in terms of the relative yields of scission and crosslinking. The total yields for crosslinking predominate over those for scission at all the temperatures investigated for radiolysis under vacuum. Based on a solid-state 29Si NMR analysis of PDMS irradiated under vacuum at 303 K, which yielded a value of G(Y) of 1.70, the values of G(S)=1.15±0.2 and G(H)=1.45±0.2 were obtained for radiolysis under vacuum at 303 K. For radiolysis in air at 303 K, crosslinking was also predominant, but the nett yield of crosslinking was much less than that observed for radiolysis under vacuum. Under the conditions of the radiolysis in air at 303 K, because of the low solubility of oxygen in PDMS, it is likely that the radiation chemistry is limited by oxygen diffusion.

An ESR study of the gamma radiolysis of aromatic polyesters containing isomeric naphthalene links

Six polyesters were synthesised from 4,4′-oxy-bis(benzoyl chloride) and 1,4-, 1,5-, 1,6-, 2,3-, 2,6-, and 2,7-naphthalenediol isomers. The structures of the polyesters were characterised by means of IR, inherent viscosities in tetrachloroethane (TCE), solutions at 303 K and thermal analysis. The glass transition temperatures were in the range of 425–494 K by DSC thermal analysis. All of the polyesters were irradiated in an AECL Gammacell 220 unit at a dose rate of approximately 6.7 kGy/h to doses in the range of 0–15 kGy at 77 and 300 K. ESR spectroscopy was used to examine the radicals formed during radiolysis and to measure their yields. The G-values for radical formation in the polyesters were found to be in the range 0.18–1.41 at 77 K and 0.19–0.78 at 300 K. At 77 K, up to 15% of the radicals formed on radiolysis were found to be photo-bleachable anion radicals. Annealing experiments were carried out in order to identify the neutral radicals, which were assigned to naphthyl- or phenyl- and phenoxyl-type radicals.

Effects of the degree of hydrolysis on radiation induced reactions in the poly(vinyl alcohol)–poly(vinyl acetate) system

In the early stages of radiolysis of 100% hydrolyzed poly(vinyl alcohol), PVA, ionizing radiation produces trapped electrons whose lifetimes depend on temperature and the water content. Pulse radiolysis of films containing pyrene show that the pyrene anion, Py −, in PVA is formed within the electron pulse, while in PVAC it takes 0.5 μs for the Py − to reach its maximum concentration. Similar observations of the pyrene cations show that the positive holes produced in the initial act of ionization in PVA do not oxidize Py, as shown in both low temperature steady state gamma radiolysis and pulse radiolysis experiments. This is rationalized as the effect of very fast deprotonation producing radicals with less oxidizing ability. Significant yields of P + are produced in PVAC, due to a more stable positive hole in this polymer. Decreasing the degree of hydrolysis of PVA affects the extent of the cation process. The G value for the Py + formation increases from 0 to 0.45 on decreasing the degree of hydrolysis to zero. Pulse radiolysis of PVAC/pyrene films gives rise to pyrene fluorescence. The decay of the fluorescence is not a single exponential as in photo-excitation, but exhibits an initial rapid decay. This is attributed to spur effects in the radiolysis. Following γ-irradiation at 77 K there is no thermally stimulated emission associated with the pyrene cation and anion decay process in PVAC due to the polarity of the polymer matrix. Py − in PVA undergoes protonation forming the 1-hydro-1-pyrenyl radical as shown in both pulse radiolysis and steady state gamma radiolysis experiments. This process does not depend on the degree of hydrolysis of the film. Contrary to the situation in fluids, the 1-hydro-1-pyrenyl radical is quite stable in PVA and PVAC as long as it is kept below the glass transition temperature(s) thus enabling a study of its physico-chemical properties.

Thiyl radical induced isomerization of unsaturated fatty acids: determination of equilibrium constants

Thiyl radical-induced isomerization of polyunsaturated fatty acids (PUFAs) have been studied in homogeneous solution and in liposomes. Four one-trans isomers of arachidonic acid have been assigned with the help of 13C NMR spectroscopy. At a dose of 132 Gy, the trans fraction amounts to 9.2 ± 1.2% in each of the four isomers. Therefore, all the four double bonds are equally susceptible to isomerization, which can be achieved by means of gamma radiolysis or chemolysis (AAPH) using both lipophilic and hydrophilic thiols. The equilibrium is characterised by a cis/trans ratio of 19 : 81, far away from the composition of the natural fatty acids (cis fraction 100%). However, compared to the linoleate isomerization in the homogeneous solution, we observed a preferential formation of trans-trans isomers if linoleate is incorporated in the bilayer of liposomes. This difference might be explained by the better fitting of the all-trans isomer into the parallel-aligned acyl chains. The isomerization step takes place within an adduct of the thiyl radical to an olefinic bond. Using a competition method, the numerical value of the equilibrium constant for the adduct formation was determined by pulse radiolysis to be (15 ± 5) dm3 mol-1. This value does not depend on the number of double bonds and holds for all fatty acids under investigation.

Interfacial Energy Transfer during Gamma Radiolysis of Water on the Surface of ZrO2 and Some Other Oxides

The effect of an oxide interface on 60Co gamma radiolysis of water molecules was studied. On the basis of the molecular hydrogen yield when compared with the radiolysis of the control ampules without oxides, all the tested materials can be generally classified into three groups: I. Oxides that lower the H2 yield (MnO2, Co3O4, CuO, and Fe2O3); II. Oxides with H2 yields that are close to G values obtained in control experiments (MgO, CaO, SrO, BaO, ZnO, CdO, Cu2O, NiO, Cr2O3, Al2O3, CeO2, SiO2, TiO2, Nb2O5 and WO3); and III. Oxides that can increase the H2 yield as compared with the radiolysis of water without oxides (Ga2O3, Y2O3, La2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Yb2O3, Er2O3, HfO2, and ZrO2). For the third group, the H2 yield can be much greater than for the homogeneous process due to effective energy transfer at the oxide/water interface. There are several parameters, such as the oxide band-gap, water adsorption form, and energy migration distance that can collectively contribute to “enhanced” radiolys...

Antioxidant effect of ethanol toward in vitro peroxidation of human low-density lipoproteins initiated by oxygen free radicals.

This study was designed to evaluate the effect of ethanol on the peroxidation of human low-density lipoprotein (LDL) initiated by oxygen free radicals (O(2)(.-) and (.)OH in the absence of ethanol; O(2)(.-) and ethanol-derived peroxyl radicals, RO(2)(.), in the presence of ethanol) generated by gamma radiolysis. Initial radiolytic yields as determined by several markers of lipid peroxidation [i.e. decrease in endogenous antioxidants alpha-tocopherol and beta-carotene, formation of conjugated dienes and of thiobarbituric acid-reactive substances (TBARS)] were determined in 3 g liter(-1) LDLs (expressed as total LDL concentration) in the absence of ethanol or its presence at six different concentrations (0.42-17 x 10(-2) mol liter(-1)). Ethanol acted as an antioxidant by decreasing the rate of consumption of LDL endogenous antioxidants and the yields of formation of lipid peroxidation products, and by delaying the onset of the propagation phase for conjugated dienes and TBARS. With regard to the different markers studied, except for alpha-tocopherol and beta-carotene consumption, the effect of ethanol did not appear to be dependent on its concentration. Indeed, (.)OH were scavenged by ethanol at the lowest ethanol concentration (0.42 x 10(-2) mol liter(-1)), leading to RO(2)(.). These RO(2)(.) resulted in lower radiation-induced yields related to endogenous antioxidant consumption or to formation of lipid peroxidation products (for example, approximately 10% of RO(2)(.) oxidized LDLs from TBARS). Thus, under our in vitro conditions, ethanol behaved as an antioxidant when added to the LDL solutions. This should be taken into account in the reported antioxidant activity of wine. This is also of interest when lipophilic compounds have to be added as ethanolic solutions to LDLs to evaluate in vitro their antioxidant activity toward LDL peroxidation.

Fast dimerisation of the triparaquat radical dication

The one-electron reduction of 2,4,6-tris(N-methylpyridinium-4-yl)pyridine trication, triparaquat, TPQ3+, synthesized in the form of the perchlorate salt, was studied by cyclic voltammetry on a platinum disc electrode. It was found that the reduction peak is centered at − 880 mV (s. SCE) at 500 mV s−1 scanning rate. The subsequent oxidation takes place at + 75 mV, indicating an irreversible process, but no changes in the solution content were found after the oxidation. The blue colored reduction product reacts anomalistically slowly with oxygen with a second-order rate constant of (0.65 ± 0.01) mol−1 dm3 s−1. EPR experiments showed that the reduction product in ethanol solution does not possess an unpaired electron. A low temperature gamma radiolysis experiment revealed that the spectral peak maximum of the reduction product of TPQ3+ solubilized in PVA film is shifted ∽200 nm with respect to that obtained in aqueous solution at room temperature. Pulse radiolysis experiments proved that this seemingly inconsistent set of data was a consequence of the very fast dimerisation process 2TPQ2+•(TPQ)24+ (kdim = 1.4 × 109 mol−1 dm3 s−1). Cyclic voltammetry experiments on a mercury electrode revealed that the second reduction step corresponds to the dimer reduction. The third and fourth reduction steps were irreversible and initiated further chemical reactions of triparaquat, which was consistent with the data obtained by the prolonged steady state gamma radiolysis.

Experimental determination and chemical modelling of radiolytic processes at the spent fuel/water interface

The spent fuel matrix constitutes a dynamic redox system, due to the time-dependent generation of oxidants and reductants at the spent fuel/water interface by alpha, beta and gamma radiolysis. In this context it is critical to understand the main processes and mechanisms that control the radiolytic production of redox components at this interface and their impact on the stability of the UO2 matrix and in radionuclide release. In order to achieve this, a series of carefully controlled experiments have been carried out in order to determine the time dependence of the radiolytic H2, O2 and H2O2 production and radionuclide release (U, Pu, Np, Tc, Mo, Sr and Cs). These tests have been performed by using PWR Ringhals spent fuel fragments in contact with 10 mM NaHCO3 solutions in an initially anoxic and closed system. The results of these experiments indicate quite a consistent and reproducible behaviour of the radiolytically generated reductants and oxidants. The results indicate that it is possible to define an equilibrium redox potential for the main redox pairs in the bulk system and that the experimentally determined radionuclide release can be rationalised in terms of the system redox potential.