Influence of distant scatterer on air kerma measurement in the evaluation of diagnostic X-rays using Monte Carlo simulation

Tominaga, Masahide*; Nagayasu, Yukari*; Sasaki, Motoharu*; Furuta, Takuya; Hayashi, Hiroaki*; Oita, Masataka*; Nishiyama, Yuichi*; Haga, Akihiro*

Radiological Physics and Technology, 14(4), p.381 - 389, 2021/12

https://doi.org/10.1007/s12194-021-00641-3

Due to recent advance of diagnostic radiology, the increase of diagnostic radiation exposure to patient becomes problem. Diagnostic Reference Levels has been released to optimized the radiation exposure to patients in Japan recently. The evaluation of entrance surface dose (ESD) is recommended to assess the dose level for general X-ray examination. The ESD can be easily evaluated by multiplying the backscatter factor of the patient body on the free-in-air air kerma. The air kerma free-in-air value used to estimate ESD may contain X-rays scattered from obstacles located at the time of measurement, which may induce non-minor error in assessments. We therefore studied the influence of scattered X-rays on air kerma measurement under various environments (distances, field sizes, and materials). It was found that the dependence on the X-ray energy and field size was different for different materials. The X-ray contamination can be ignored for all the materials when the distance to the scatterer exceeds 35 cm.

Effect of neutron irradiation on the microstructure of the stainless steel electroslag weld overlay cladding of nuclear reactor pressure vessels

Takeuchi, Tomoaki; Kakubo, Yuta*; Matsukawa, Yoshitaka*; Nozawa, Yasuko*; Nagai, Yasuyoshi*; Nishiyama, Yutaka; Katsuyama, Jinya; Onizawa, Kunio; Suzuki, Masahide

Journal of Nuclear Materials, 443(1-3), p.266 - 273, 2013/11

https://doi.org/10.1016/j.jnucmat.2013.07.035

Investigation on irradiation effects of weld-overlay claddings is necessary for safety assessment of reactor pressure vessels. We investigated microstructural changes in the cladding, which was composed of about 90% austenite and 10% -ferrite phases, subjected to the neutron irradiation to 7.210 n/cm at 290C, by 3D atom probe tomography technique. In the ferrite phase, the amplitude of the Cr and Si concentration fluctuation was increased by the irradiation and Ni and Mn concentration fluctuations were newly occurred. In the austenite phase, '(NiSi) -like clusters were formed. In contrast, the results of our previous work on the cladding subjected to thermal aging showed the amplitude of the Cr fluctuation was significantly increased and G (Ni-Si-Mn) phase was formed in the ferrite phase. Moreover, no changes were observed in the austenite by the aging.

New JMTR irradiation test plan on fuels and materials

Nakamura, Takehiko; Nishiyama, Yutaka; Chimi, Yasuhiro; Sasajima, Hideo; Ogiyanagi, Jin; Nakamura, Jinichi; Suzuki, Masahide; Kawamura, Hiroshi

Proceedings of 16th Pacific Basin Nuclear Conference (PBNC-16) (CD-ROM), 6 Pages, 2008/10

In order to maintain and enhance safety of light water reactors in long-term and up-graded operations, proper understanding of irradiation behavior of fuels and materials is essentially important. Japanese government and the Japan Atomic Energy Agency have decided to refurbish the JMTR and to install new tests rigs, in order to play an active role for solving irradiation related issues on plant aging and high-duty uses of the current LWRs and on development of next-generation reactors. New tests on fuel integrity under simulated abnormal transients and high-duty irradiation conditions are planned in the JMTR. Power ramp tests of new design fuel rods will also be performed in the first stage of the program, which is expected to start in year 2011 after refurbishment of the JMTR. Combination of the JMTR tests with simulated reactivity initiated accident tests in the NSRR and loss of coolant accident tests in hot laboratories would serve as the integrated fuel safety research on the high performance fuels at extended burnups, covering from the normal to the accident conditions, including abnormal transients. For the materials irradiation, fracture toughness of reactor vessel steels and stress corrosion cracking behavior of stainless steels are being studied in addition to basic irradiation behavior of nuclear materials such as hafnium. The irradiation studies would contribute not only to solve the current problems but also to identify possible seeds of troubles and to make proactive responses.

Phosphorus segregation and intergranular embrittlement in thermally aged and neutron irradiated reactor pressure vessel steels

Nishiyama, Yutaka; Onizawa, Kunio; Suzuki, Masahide

Journal of ASTM International (Internet), 4(8), 12 Pages, 2007/09

no abstracts in English

Report of Examination of the Sample from Core Shroud (2F2-H3) at Fukushima Dai-ni Power Station Unit-2 (Contract research)

The Working Team for Examination of the Sample from Core Shrouds and Primary Loop Recirculation Pipi; Nakajima, Hajime*; Shibata, Katsuyuki; Tsukada, Takashi; Suzuki, Masahide; Kiuchi, Kiyoshi; Kaji, Yoshiyuki; Kikuchi, Masahiko; Ueno, Fumiyoshi; Nakano, Junichi; et al.

JAERI-Tech 2004-015, 114 Pages, 2004/03

JAERI-Tech-2004-015.pdf:38.06MB

The Tokyo Electric Power Company (TEPCO) visually inspected the weld joint of core shroud at Fukushima Dai-ni Nuclear Power Station Unit-2 by a direction of the Nuclear and Industrial Agency, cracks were observed at outer side of the ring weld joint (H3) between a core shroud middle trunk and a middle ring. TEPCO has conducted a material examination with Nippon Nuclear Fuel Development Co. Ltd. (NFD) on the specimen including cracks sampled from the core shroud. The present examination has been performed with the objective to independently investigate and evaluate the materials by jointly attending the examination with NFD from the planning stage. Based on results of the present examination, the probable presence of tensile residual stress by welding process and dissolved oxygen contents in the cooling water, it was shown that the cracks were considered to be stress corrosion cracking (SCC). However, the cause of the cracks needs more consideration on the way of shroud construction.

Magnetic ordering and spin dynamics in potassium jarosite; A Heisenberg kagom lattice antiferromagnet

Nishiyama, Masahide*; Maegawa, Satoru*; Inami, Toshiya; Oka, Yoshio*

Physical Review B, 67(22), p.224435_1 - 224435_11, 2003/06

https://doi.org/10.1103/PhysRevB.67.224435

The spin dynamics of the Heisenberg kagom lattice antiferromagnet, potassium jarosite KFe(OH)(SO), have been investigated by means of NMR. The spin-lattice relaxation rate, 1/, in the ordered phase decreases sharply with lowering temperature. The experimental rate is well explained by the two-magnon process of the spin waves having an energy gap of 15 K. The temperature dependence of the sublattice magnetization also supports the existence of the spin wave. These are the first experimental evidence that the low-energy excitation in the frustrated classical kagom lattice antiferromagnet is described by the spin wave. We calculate the spin wave in the q = 0 type 120 spin structure with weak single-ion-type anisotropy, and discuss the characteristics of the spin fluctuations in the Heisenberg kagom lattice antiferromagnet.

Magnetic ordering in the kagom lattice antiferromagnet KCr(OD)(SO)

Inami, Toshiya; Morimoto, T.*; Nishiyama, Masahide*; Maegawa, Satoru*; Oka, Yoshio*; Okumura, H.*

Physical Review B, 64(5), p.054421_1 - 054421_6, 2001/08

https://doi.org/10.1103/PhysRevB.64.054421

no abstracts in English

Residual stresses and aging degradation of stainless steel weld overlay clading for nuclear reactor pressure vessel (Contract research)

Nishiyama, Yutaka; Onizawa, Kunio; Idei, Yoshio; Suzuki, Masahide

JAERI-Research 2000-047, 32 Pages, 2000/10

JAERI-Research-2000-047.pdf:1.69MB

no abstracts in English

Development of reconstitution technique of irradiated speciments, 3; Report for FY 1995 and FY 1996 on JAERI-IHI cooperated research program (Joint research)

Nishiyama, Yutaka; Fukaya, Kiyoshi; Onizawa, Kunio; Suzuki, Masahide; *; *; *; *

JAERI-Tech 98-041, 30 Pages, 1998/10

JAERI-Tech-98-041.pdf:2.0MB

no abstracts in English

Irradiation embrittlement of 2.25Cr-1Mo steel at 400C and its electrochemical evaluation

Nishiyama, Yutaka; Fukaya, Kiyoshi; Suzuki, Masahide; Eto, Motokuni

Journal of Nuclear Materials, 258-263, p.1187 - 1192, 1998/00

https://doi.org/10.1016/S0022-3115(98)00184-6

no abstracts in English