Presentation Evaluation of neutron capture cross section on Pb-205 with photonuclear data

岩本, 信之  ,  静間, 俊行

Transmutation and reduction of high level radioactive wastes (e.g. minor actinides) produced in nuclear reactors are expected by an accelerator driven system (ADS). Japan Atomic Energy Agency proposed that Pb and Bi are used as a spallation target and coolant. The neutronics design was performed without including 205Pb, which is a long-lived radioactive nuclide with half-life of 1.7×107 years and thus has long-lasting radiotoxicity. 205Pb is produced by the neutron capture reaction on 204Pb. In order to evaluate the accumulated amount of 205Pb, the neutron capture cross section of 205Pb is needed. However, it has not been measured in the keV to MeV neutron energy region. In the present work the calculations of cross sections were performed by the nuclear reaction calculation code, CCONE. Measured photonuclear data of (γ,γ) reaction and photoneutron cross sections were used to evaluate photon strength function of 206Pb. The (γ,γ) reaction data used were newly obtained by an experiment at HZDR. The fixed photon strength function was applied to calculate the neutron capture cross sections of 205Pb. The resulting cross section is smaller than the data of 204Pb in the relevant energy region. As a result, it is predicted that the accumulation of 205Pb is negligible unless the Pb-Bi target is used under the conditions of high neutron flux (>5×1016 n/cm2/s) and long-term use (>5 years).
16th International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics

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