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Advanced management of radioactive wastes : comparative evaluation of processes for enhanced separation of very long-lived radioactive species

Objective

For the evaluation of advanced HLW management, it is convenient to categorize the nuclear waste constituents into two parts: short-lived radioisotopes, mainly fission products, comprised of hundred of various isotopes, and long-lived radioisotopes, mainly actinides, comprised of uranium and transuranic elements (neptunium, plutonium, americium, curium). Most of fission products decay in relatively short periods. After a few centuries, the fission products decay to a level giving radiological risk factor below the risk level due to their original uranium ore. Actinides, as well as some long lived fission products such as Tc-99, I-129, have longer half-lives and their radiological risk factor remains to be orders of magnitude higher than that due to fission products for million of years. The main objective of this research programme is to test and demonstrate the feasibility of the enhanced separation of the long-lived radioisotopes (mainly actinides) from high level liquid radioactive wastes, in order to obtain a residual HLW stream practically alpha-free (less than 370-3,700 Bq/g of long-lived alpha emitters). The feasibility study will be based on the application of known technologies or on minor extrapolations from them.
For evaluation of advanced high level radioactive waste (HLW) management, it is convenient to categorize the nuclear waste constituents into 2 parts: short lived radioisotopes, mainly fission products, comprised of hundreds of various isotopes, and long lived radioisotopes, mainly actinides, comprised of uranium and transuranic elements. Most of the fission products decay in relatively much shorter periods than actinides. In the order of a few centuries, the fission products decay to a level low enough that their radiological risk factor drops below the risk level due to their original uranium ore. Actinides, as well as some long lived fission products such as technetium-99, iodine-129, on the other hand, have longer half lives and their radiological risk factor remains to be orders of magnitude higher than that due to fission products for millions of years. The main objective of this research programme is to test and demonstrate the feasibility of the enhanced separation of the long lived radioisotopes (mainly actinides) from high activity liquid radioactive wastes, in order to obtain a residual HLW stream practically alpha free (less than 10-100 nanocuries/g of long lived alpha emitters). The feasibility study will be basedon the application of known technologies or on minor extrapolations from them.

A thorough examination of the current available literature has been performed with the purpose of collecting all the data useful to perform the selection of the most promising processes. The long lived radionuclides under consideration were mainly the transuranic elements but attention was also given to some long lived fission products such as technetium-99, stontium-90 and caesium-137. Concerning the separation agents, the following classes of reagents were reviewed:
organophosphorous compounds;
organonitrogen compounds;
organophosphorus nitrogen compounds;
macrocyclic derivatives;
soft donor ligands.
Work programme:

The research programme will be developed according to the following main phases:

- criterial review of the present state of the art on separation processes for actinides and long-lived fission products;
- comparative evaluation (lab scale) of the selected separation agents computer modelling, and definition of an optimized flowsheet.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Ente per le Nuove Tecnologie l'Energia e l'Ambiente (ENEA)
Address
Via Anguillarese 301
00060 Santa Maria Di Galeria Roma
Italy