Fission Product Yields
Experimental Mapping of Fission Product Yields in the Fast and Intermediate Energy Neutron-Induced Fission of 232Th, 235U, 238U and 237Np
Tech Area / Field
- PHY-ANU/Atomic and Nuclear Physics/Physics
- FIR-NOT/Nuclear and Other Technical Data/Fission Reactors
3 Approved without Funding
Khlopin Radium Institute, Russia, St Petersburg
- University of Uppsala / Department of Physics and Astronomy, Sweden, Uppsala\nEuropean Commission / Joint Research Center / Institute for Reference Materials and Measurements, Belgium, Geel\nUniversity of Jyväskylä, Finland, Jyväskylä
Project summaryA sustainable development of nuclear energy is impossible without a permanent and safe solution for radioactive waste management. In this context, innovative fuel cycles making use of technologies for partitioning and transmutation of minor actinides (Np, Am and Cm isotopes) are expected to strongly minimize the nuclear waste legacy for final disposal . It is generally acknowledged that fast spectrum irradiations in critical reactors, fusion-fission hybrids or accelerator-driven systems provide an efficient method for transmutation of minor actinides, because the fission-to-capture cross section ratio in fast spectrum is larger as compared to a thermal spectrum. Research and development (R&D) efforts on the “fast” transmutation systems require nuclear data on neutron-induced fission of actinides at energies up to several hundreds MeV. Over the past years, significant efforts have been devoted to measurements of these data. Neutron-induced fission cross sections, fragment mass distributions, multiplicities and spectra of prompt fission neutrons have been measured at energies far above the upper limits of conventional evaluated nuclear data files. At the same time, there is an evident lack of experimental data on fission product yields at neutron energies above 1 MeV. In this energy domain, the current experimental database for fission yields suffers from significant data gaps and uncertainties, so the corresponding nuclear data libraries are generated with the use of extrapolation and modeling methods, which cannot guarantee the data accuracy in the domain where experimental data are not available. At the same time, these data are of particular importance for both nuclear reactor operation and back-end of nuclear fuel cycle. In particular, independent fission product yields enter calculations of nuclear reactor reactivity, criticality and safety. They are also necessary for calculations of such physical parameters of spent nuclear fuel as decay heat, radiation dose and neutron multiplication which are most important prerequisites for the spent fuel handling, transport and storage.
The present project is aimed at measurement of fission product yields from neutron-induced fission of 232Th, 235U, 238U and 237Np in the energy range 1-60 MeV. The experimental part of the project will consist of two measurement campaigns. The first one will be carried out at the University of Jyväskylä (Finland), where a novel method for measuring independent fission yields has recently been developed and proved . In this method, the Ion Guide Isotope Separator On-Line technique  is used in a combination with a Penning trap which operates as a precision mass separator with the mass resolving power of about 105. The method is fast enough to measure independent yields of fission products with half-lives as short as several hundred milliseconds. Moreover, the measurements can be done for any element including the stable and refractory ones. The measurements will be performed in a simulated fast reactor neutron field. Neutrons with the reactor-like energy spectrum will be produced by protons impinging on a full-stop tungsten target surrounded by a moderator. The neutron source will be developed making use of a long-standing experience of Uppsala University (Sweden) in this area [4,5].
The other experiments will be performed at the neutron time-of-flight (TOF) spectrometer GNEIS based on the 1 GeV proton cyclotron of Petersburg Nuclear Physics Institute. The chain yields will be measured in the neutron energy range from 1 to 60 MeV using a multi-section Frisch-gridded ionization chamber (MCFGIC) . The detector is a stack of seven twin Frisch-gridded ionization chambers, so simultaneous measurements for seven fissile targets can be done. Each section allows neutron TOF measurements with a time resolution of about 2 ns and has almost 100% efficiency for fission fragment detection. This experimental technique has been developed by Khlopin Radium Institute in the frame of the ISTC project #3192. Its application to measurement of fragment mass yields in neutron-induced fission at intermediate energies has recently been demonstrated in experiments with quasi-monoenergetic neutron beams .
We will make use of the long standing experience of the JRC-IRMM in the field of fission yield measurements and compare the measured data with those of JRC-IRMM as a reference in the energy region of overlap. The data are important input to modeling of neutron induced reaction cross sections conducted by a JRC-IRMM in close collaboration with theoreticians from Bucharest University and CEA/DAM, Bruyeres-le-Chatel.
Thus the project deliverables will comprise the independent fission product yields measured in a simulated fast reactor neutron field and the chain yields measured at “white” neutron spectrum in the energy range 1-60 MeV. In addition to the experimental data, the project deliverables will comprise ENDF-formatted data file for the independent fission product yields. The experimental data to be obtained in the course of the project will find a wide application to elaboration of nuclear data libraries needed for safe nuclear waste management as well as for R&D of fast nuclear reactors, fusion-fission hybrids and accelerator-driven systems.
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