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Evaluation of Neutron Emission from Vitrified HLW Compositions

by A. A. Rimski-Korsakov, V.G. Khlopin Radium Inst, St. Petersburg, Russia,
A. S. Aloy, V.G. Khlopin Radium Inst, St. Petersburg, Russia,
V. N. Dushin, V.G. Khlopin Radium Inst, St. Petersburg, Russia,



Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1993

Abstract:

Neutron radiological hazards from vitrified HLW are important for handling and transportation - especially if the concept of separate storage of concentrated transuranics is adopted, as in some projects developed in Russia. In such cases gamma radiation hazards are small and the dose rates depend on neutron emission (due to (?,n) and fission reactions) and neutron absorption in waste block composition. Both processes should be taken into account to develop methods of evaluation/optimizing of different glass compositions from this point of view. Combined processes of neutron production, moderation and absorption in complex matrixes were calculated by Monte-Carlo techniques, by special computer codes developed for this purpose. It has been shown that simplified neutron propagation codes can be used to evaluate the expected neutron fluxes, spectra and dose, and that special additives can be recommended to decrease neutron emission from HLW compositions. This paper describes the methods and results of neutron production and transport calculations developed for evaluation of neutron doses encountered in handling of vitrified HLW compositions. The aim of this project was to provide the HLW technologists with some simple and reliable computer tool predicting the HLW glass blocks neutron fields and doses depending on their size, composition and shielding. Well-established high-precision reactor neutron transport codes (such as ANISN [] ) could solve this problem easily if they were readily applicable and if their input data could be generated fast and simple. But for many reasons generating the input data for such codes is a separate scientific job by itself and is out of proportion to the final task, pursued in the HLW radiological hazard evaluation. On the other hand some oversimplified approaches, where evaluation of neutron emission does not take into account the neutron transport at all and concentrates only on the expected neutron emission from (?,n) and fission sources, neglects to use certain neutron moderating and absorbing properties of the HLW block and so limits the technologist in his effort to minimize radiological hazard by simple 'chemical means' as we purport to show.

Subject Headings: Emissions | Chemical wastes | Waste disposal | Recycling | Radioactive wastes | Standards and codes | Radiation | Russia | Europe

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