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Content archived on 2024-04-15

RADIONUCLIDE RELEASE FROM SOLIDIFIED HIGH LEVEL WASTE

Objective

THE AIM OF THE RESEARCH IS TO ENSURE THAT VITRIFIED WASTE FORMS IN GENERAL AND THE UK'S REFERENCE GLASS MW IN PARTICULAR ARE SUITABLE FOR EVENTUAL DISPOSAL IN EITHER HARD-ROCK OR CLAY.

STUDIES ARE IN PROGRESS OF THE LEACHING BEHAVIOUR OF MW GLASSES WHICH HAD BEEN DOPED WITH SELECTED RADIOISOTOPES. IN PARTICULAR, MEASUREMENTS HAVE BEEN MADE OF THE CONCENTRATIONS, UNDER A RANGE OF CONDITIONS THAT COULD OCCUR AFTER DISPOSAL, OF THE RADIOLOGICALLY IMPORTANT ELEMENTS TC, NP, PU AND AM. IT IS ASSUMED THAT THE RELEASE OF THESE ELEMENTS FROM THE REPOSITORY MUST BE LESS THAN THIS CONCENTRATION MULTIPLIED BY THE WATER FLOW-RATE THROUGH THE REPOSITORY. SIMILAR MEASUREMENTS HAVE ALSO BEEN MADE ON FULLY ACTIVE WASTE GLASSES.

STUDIES ARE ALSO IN PROGRESS OF THE GLASSES RADIATION STABILITY TO ENSURE THAT THIS WILL NOT CAUSE PROBLEMS.
Samples of glass were made up containing a full inactive simulation of high level waste. They were doped with isotopes of the 4 radioelements americium, plutonium, neptunium and technetium. After crushing they were mixed with possible components of the repository and water, and loaded into capsules. The capsules were held in an oven at 60 C, normally, for periods of up to a year before they were opened and the water overlying the solids sampled and analysed.
After a series of such experiments, the following conclusions were obtained:
the steady state concentrations of technetium and the actinides neptunium and americium could be up to 5 times the limiting concentration;
the steady state concentration of plutonium could be increased from 0.03 times to 15 times the limiting concentration;
bentonite did not sorb neptunium and americium as efficiently as the cements;
under oxidising conditions technetium was quite soluble.

Further results concerning steady state concentrations of americium, plutonium, neptunium and technetium, under varying conditions as well as with various barrier materials and leachants, are also reported.
1. LEACHING BEHAVIOUR OF REFERENCE MATERIALS AND SOLUBILITY OF SELECTED RADIOISOTOPES.
2. EFFECT OF RADIATION AND RADIOLYSIS
3. EFFECT OF PRODUCT QUALITY ON THE RELEASE RATE.

Topic(s)

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Coordinator

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