A Study on Embrittlement of Fast Neutron-irradiated Nuclear Reactor Pressure Vessel Steels at Room- and Liquid Nitrogen-temperature

The embrittlement of fast neutron-irradiated reactor pressure vessel (RPV) steels was investigated by X-ray diffraction patterns at room temperature and Mdssbauer spectroscopy at room-and liquid nitrogen-temperature. Neutron fluence on the samples were 10(12), 10(13), 10(14), 10(15), 10(16), 1017, 10(18) n/cm(2). The X-ray diffraction patterns showed that the structure of the neutron unirradiated sample was bcc type, where as but the neutron irradiated samples with the fluence higher than 10(17) n/cm(2) were so severely damaged, that bcc type structure disappeared. The Mdssbauer spectra of all samples showed superposition of two or more sextets. In this paper all Mossbauer spectra were fitted by three set of sextet. The isomer shift and quadrupole splitting values were found around zero. At liquid nitrogen temperature, magnetic hyperfine field and absorption area increase rapidly S1 sextet in the samples of 10(17)similar to 10(18) n/cm(2) neutron fluences. And at room temperature, magnetic hyperfine field and absorption increased rapidly at SI sextet in the samples of 10(17)similar to 10(18) n/cm(2) neutron fluences. This rapid increase of magnetic hyperfine field and absorption area were inferred to be caused by the change of Fe-56, Mn-55 into Fe-57 due to by neutron irradiation.