Role of ( n ,2 n ) reactions in transmutation of long-lived fission products
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SSION PHYSICS
Role of (n,2n) Reactions in Transmutation of Long-Lived Fission Products V. A. Apse, G. G. Kulikov*, and E. G. Kulikov National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoe sh. 31, Moscow, 115409 Russia *e-mail: [email protected] Received March 28, 2016
Abstract—The conditions under which (n,γ) and (n,2n) reactions can help or hinder each other in neutron transmutation of long-lived fission products (LLFPs) are considered. Isotopic and elemental transmutation for the main long-lived fission products, 79Se, 93Zr, 99Tc, 107Pd, 126Sn, 129I, and 135Cs, are considered. The effect of (n,2n) reactions on the equilibrium amount of nuclei of the transmuted isotope and the neutron consumption required for the isotope processing is estimated. The aim of the study is to estimate the influence of (n,2n) reactions on efficiency of neutron LLFP transmutation. The code TIME26 and the libraries of evaluated nuclear data ABBN-93, JEF-PC, and JANIS system are applied. The following results are obtained: (1) The effect of (n,2n) reactions on the minimum number of neutrons required for transmutation and the equilibrium amount of LLFP nuclei is estimated. (2) It is demonstrated that, for three LLFP isotopes (126Sn, 129I, and 135Cs), (n,γ) and (n,2n) reactions are partners facilitating neutron transmutation. The strongest effect of (n,2n) reaction is found for 126Sn transmutation (reduction of the neutron consumption by 49% and the equilibrium amount of nuclei by 19%). Keywords: long-lived fission products, neutron transmutation, neutron consumption, equilibrium amount of nuclei DOI: 10.1134/S1063778816130019
1. INTRODUCTION Operation of a nuclear power system is accompanied by radioactive waste production. Existing technologies of handling radioactive waste assume their immobilization in materials stable to the impact of the ambient medium and final burial in geological formations [1]. A passive strategy of protection of the population and environment via development of engineering barriers against penetration of radioactive waste from the burial grounds into the biosphere is implemented. There exists an alternative approach to handling radioactive waste based on the strategy of waste processing by transforming it into short-lived or stable isotopes [2–7]. This transformation is called transmutation. Transmutation can be performed by irradiating radioactive waste with fluxes of elementary particles in specialized nuclear installations (transmuters) or power reactors, as a by-process. At present, the most efficient is transmutation under neutron irradiation (neutron transmutation). The main long-lived fission products (LLFPs) are the following seven isotopes with half-lives from several tens of thousands to millions of years: 79Se, 93Zr, 99Tc, 107Pd, 126Sn, 129I, 135Cs.
One of the variants of neutron transmutation is the transformation of long-lived fission products into short-lived isotopes via neutron capture chains. By successively capturing several neutrons, an LLFP can be tran
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