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RADIOLYTIC OXIDATION

Objective

PRELIMINARY STUDIES IN THE UK AND USA HAVE SUGGESTED THAT ALPHA AND GAMMA RADIATION FIELDS CAN INCREASE THE OXIDATION STATE OF SOME ELEMENTS IMPORTANT TO RADIOACTIVE WASTE MANAGEMENT. THIS PROGRAMME WILL ESTABLISH THE SIGNIFIANCE OF THESE EFFECTS AS A MECHANISM FOR CAUSING ENHANCED FLUX OF RADIATION NECESSARY TO CAUSE THESE OXIDATION STATE CHANGES, THE PROGRAMME THEREFORE ADDRESSES ONLY THESE WASTE FORMS.

THE EXPERIMENTAL RESULTS OF THIS PROGRAMME WILL BE USED IN THE CONSTRUCTION OF A MODEL COMPATIBLE WITH THE GEOCHEMICAL CODES THAT ARE USED FOR MODELLING REPOSITORY BEHAVIOUR.
The effects of alpha and gamma irradiation on the chemistries of plutonium, neptunium and technetium under conditions representative of the near fields of intermediate and high level waste repositories were investigated. Gamma radiolysis of neptunium(IV) results in oxidation in solutions below pH 12. Solutions of technetium(VII) are reduced to technetium(IV) by gamma irradiation in contact with blast furnace slag and ordinary Portland cement under an inert atmosphere, but not when in contact with pulverised fuel ash and ordinary Portland cement. Technetium(IV) is shown to be susceptible to oxidation by the products of the alpha radiolysis of water. Mathematical models of the behaviour of plutonium and neptunium during gamma radiolysis have been developed and indicate that oxidation to plutonium(VI) is possible at dose rates typical of those expected for high level waste (HLW). Simulations at intermediate level waste (ILW) dose rates have indicated some effect upon the speciation of neptunium. Laboratory studies of the gamma irradiation of neptunium(IV) in bentonite equilibrated water have also been modelled.

The effects of alpha and gamma irradiation on the chemistries of plutonium, neptunium and technetium, under conditions representative of the near fields of intermediate and high level waste repositories, were investigated.

Gamma radiolysis of neptunium(IV) results in oxidation in solutions below pH 12. Solutions of technetium(VII) are reduced to technetium(IV) by gamma irradiation in contact with blast furnace slag/ ordinary Portland cement under an inert atmosphere, but not when in contact with pulverised fuel ash/ordinary Portland cement. Technetium(IV) is shown to be susceptible to oxidation by the products of the alpha radiolysis of water.

Mathematical models of the behaviour of plutonium and neptunium during gamma radiolysis indicate that oxidation to plutonium(VI) is possible at dose rates typical of those expected for high level waste. Simulations at intermediate level waste dose rates indicate some effect upon the speciation of neptunium. Laboratory studies of the gamma irradiation of neptunium(IV) in bentonite equilibrated water have also been modelled.
B1. EFFECTS OF GAMMA IRRADIATION ON NEPTUNIUM AND URANIUM SOLUBILITY LIMITS.
B2. ELECTROCHEMICAL STUDY OF THE DISSOLUTION OF OXIDES OF TC, NP, PU AND AM.
B3. EFFECT ON ENHANCED ALPHA RADIATION ON THE SOLUBILITY OF ELEMENTS SELECTED BY STUDIES UNDER B.2.
B4. EFFECT OF RADIOLYSIS ON SORPTION OF TC, NP AND PU.
B5. STUDY OF OVERALL EFFECTS OF RADIATION, WASTE, MATRIX AND BACKFILL.
B6. EFFECT OF COLLOIDS.
B7. MODELLING STUDIES.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

United Kingdom Atomic Energy Authority
Address
353,Harwell
OX11 0RA Didcot - Oxfordshire
United Kingdom