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Report No.
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Experimental evaluation of transmutation behaviour for americium under fast and thermal neutron spectra

Koyama, Shinichi  ; Mitsugashira, Toshiaki

In order to evaluate the transmutation behavior of americium under fast and thermal neutron spectra, two kinds of irradiated $$^{241}$$Am oxide samples were analyzed by radiochemical methods in Japan Atomic Energy Agency. One is $$^{241}$$Am encapsulated in a vanadium capsule which was irradiated in the experimental fast reactor JOYO for 275 effective full power days (EFPD) under the fast neutron flux of 3$$times$$10$$^{15}$$ c/cm$$^{2}$$s. The other is $$^{241}$$Am oxide pelletized with MgO which was irradiated in Japan Material Testing Reactor for 207 EFPD under the thermal neutron flux of 2$$times$$10$$^{14}$$ c/cm$$^{2}$$s. After dissolution of these samples, americium, curium and plutonium were chemically separated and their isotope compositions were analyzed by alpha and $$gamma$$-ray spectrometry and mass spectroscopy. $$^{137}$$Cs and $$^{148}$$Nd were measured by $$gamma$$-ray spectrometry and mass spectroscopy, respectively, to determine the total fission events and burnup. $$^{242m}$$Am, $$^{243}$$Am, $$^{238-242}$$Pu and $$^{242-248}$$Cm were clearly observed. The total transmutation ratios of americium under the fast and thermal neutron spectra were about 10% and 80% in the irradiation conditions, respectively. The fission to capture cross-section ratios were evaluated in order to compare the transmutation behavior of americium. As the result, it is proved that the accumulation of even-even nuclei, such as $$^{244}$$Cm and $$^{246}$$Cm, in the thermal neutron spectrum was remarkable than that under the fast neutron spectrum. It is expected that these results show the important aspect to discuss the transmutation concept by using several neutron reaction in the reactor. In this study, the fundamental analytical data could be obtained.

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