Comparison of calculated and measured radionuclide inventory of a Zircaloy-4 cladding tube plenum section
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.274
Comparison of calculated and measured radionuclide inventory of a Zircaloy-4 cladding tube plenum section Michel Herm1, Ron Dagan2, Ernesto González-Robles1, Nikolaus Müller1 and Volker Metz1 1
Karlsruhe Institute of Technology (KIT), Institute for Nuclear Waste Disposal, P.O. Box 3640, 76021 Karlsruhe, Germany
2
KIT, Institute for Neutron Physics and Reactor Technology, P.O. Box 3640, 76021 Karlsruhe, Germany
ABSTRACT
Cladding tubes of water-cooled nuclear reactors are usually made of Zircaloy and are an important retaining element for radionuclides present in the fuel both during predisposal activities such as reloading of fuel assemblies from interim storage casks to final disposal casks and during final disposal in the case of canister breaching. However, cladding integrity is affected by various processes during reactor operation and beyond, e.g. fuel cladding chemical interaction and fission product precipitation onto the inner cladding surface. Using experimental and modelling methods, the radionuclide inventory of an irradiated Zircaloy-4 plenum section is analyzed. Quantities of 235/238U, 237Np, 238/239/240/241/242Pu, 241/243Am, 243/244Cm besides 14C, 55Fe, 125Sb, 154Eu, and 134/137Cs were (radio-)chemically determined in digested Zircaloy-4 subsamples. Measured inventories of activation products in the Zr-alloy are in good agreement with calculated values. However, amounts of actinides and fission products exceed the calculated inventory by factor ~57 (minor actinides and non-volatile fission products) and ~114 (137Cs). Excess of minor actinides and part of enhanced Cs inventory originate from fuel residues deposited on the inner cladding surface during fuel rod fabrication, whereas vast amount of cesium is volatilized from subjacent fuel pellets and transported to the plenum.
INTRODUCTION In Germany as well as many other countries, spent nuclear fuel (SNF) assemblies, after being discharged from a nuclear power reactor, are cooled in spent fuel pools for several years, and eventually sent for dry cask storage. Dual-purpose casks
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(CASTOR®, GNS) are used for transport and dry interim storage of SNF assemblies in facilities in Gorleben, Ahaus, and Nord, as well as on site of the nuclear power plants. In the German waste management concept, SNF is designated for direct disposal in a deep geological repository available by 2050 at the best [1]. However, considering the delay in the site selection process so far as well as the time needed for exploration, construction, and commissioning of a repository for high-level waste, start of waste emplacement is expected by the end of this century/beginning of next century [1]. Thus, a prolonged dry interim storage of SNF assemblies is inevitable. M
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