Research on the behavior of polonium produced in lead-bismuth eutectic irradiated with neutrons. JAERI's nuclear research promotion program, H10-026. Contract research

Lead-Bismuth Eutectic (LBE) is proposed by several research institutes as a coolant of liquid metal cooled fast reactors, instead of sodium, and a target of accelerator driven subcritical nuclear reactor systems (ADS). LBE has some advantages that it is chemically inert compared to sodium and that its melting point is low like sodium. A problem might be that bismuth produces polonium, which is an alpha emitter, by irradiation of neutrons. The purpose of the study is to get information for quantitative estimations of the release of polonium on LBE cooled fast reactors and on ADSs by making it clear about production rate of polonium (information about cross section) by neutron irradiation of LBE, release rate of the produced polonium from LBE, and adsorption rate of the polonium on various materials. To get the information about production rate of polonium, neutron cross sections of bismuth were measured in keV energy region, which was important in fast reactors, by using the Pelletron accelerator in Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology. The obtained neutron capture cross sections were from 1/2 to 1/3 of the evaluated values in JENDL and the obtained polonium production cross sections were almost 1/3 of it. At the same time, an experimental device was designed for heating and adsorption experiments and the performance was tested. The performance of alpha spectrometer was tested also. By those the method was established for the measurement of polonium released from melted LBE after neutron irradiation. (author)