Long-term radiotoxicity of high level wastes and spent fuels produced by light water reactors: impact of burn-up extension and of the use of mixed oxide fuels

The time evolution of radiotoxicities of spent fuels and high-level wastes have been calculated up to 107 years, in the framework of the I.C.R.P.-30 guideline, except for neptunium and plutonium. For those elements, one has taken into account two recent modifications adopted in March 1986 by the International Commission on Radiological Protection, concerning a reduction by a factor 10 of the ratio dose/ingested activity for neptunium and an increase by the same factor for plutonium. In the case of burn-up extension of the standard 33,000 MWd/Mt enriched uranium fuel, and in the case of plutonium recycle in light-water reactors, one shows that the spent fuel radiotoxicity is now dominated by its plutonium content, up to about 105 years. Possible incineration effects are discussed within these two fuel cycle options