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Maekawa, Fujio; Tamura, Masaya
Proceedings of ICANS-XVI, Volume 3, p.1051 - 1058, 2003/07
A three-dimensional (3-D) shielding calculation model for MCNPX was produced for shielding design of 1-MW JSNS. The model included simplified target-moderator-reflector assembly, helium-vessel and neutron beam extraction pipes, shutters, shield blocks, gaps and void spaces between these components, and so on, and could treat streaming effects precisely. The particle splitting and kill method with cell importance parameters was adopted as a variance reduction method. The cell importance parameters for such a large target station of about 15 m in diameter and 12 m in hight in which neutron fluxes attenuated more than 12 orders of magnitude could be determined appropriately by automated iteration calculations. This calculation procedure enabled detailed 3-D shielding design calculations for the whole target station in a short time, i.e., within 2 days, and contributed for progress of shielding designs of JSNS.
Maekawa, Fujio; Tamura, Masaya; Kawai, Masayoshi*; Furusaka, Michihiro*; Watanabe, Noboru
Proceedings of ICANS-XVI, Volume 3, p.1247 - 1255, 2003/07
A method for neutron-beam-line shielding calculation with a Monte Carlo code was newly developed. In the first step, components inside the biological shield such as a target-moderator-reflector-assembly and a neutron-beam-line were modeled, and a neutron current distribution along a duct of the neutron-beam-line was calculated. In the second step, decreases of neutron current along the beam-line were regarded as source terms for the beam-line shield, and required beam-line shield thickness was calculated. The most remarkable feature of this method was accurate treatment of the neutron source term distribution along the beam-line in the second step calculation. The followings were evaluated for JSNS by applying this method: (1) neutron-beam-line shield thickness with an empirical formula for estimating shield thickness conveniently, (2) beam stop sizes, (3) dose rates at a sample position when a shutter was closed, and (4) activation level of a To-chopper blade. These results gave conditions for determining the layout of 23 neutron-beam-lines in the experimental hall.
Takada, Hiroshi; Maekawa, Fujio; Honmura, Shiro*; Yoshida, Katsuhiko*; Teraoku, Takuji*; Meigo, Shinichiro; Sakai, Akio*; Kasugai, Yoshimi; Kanechika, Shuji*; Otake, Hidenori*; et al.
Proceedings of ICANS-XVI, Volume 3, p.1115 - 1125, 2003/07
no abstracts in English
Kogawa, Hiroyuki; Ishikura, Shuichi*; Haga, Katsuhiro; Kinoshita, Hidetaka; Kaminaga, Masanori; Hino, Ryutaro
Proceedings of ICANS-XVI, Volume 3, p.1295 - 1304, 2003/07
no abstracts in English
Kai, Tetsuya; Harada, Masahide; Teshigawara, Makoto; Watanabe, Noboru; Ikeda, Yujiro
Proceedings of ICANS-XVI, Volume 3, p.657 - 666, 2003/07
Neutronic design studies were carried out on the J-PARC coupled H
moderator. The highest time- and energy- integrated intensity below 15 meV, pulse peak intensity at 2 meV and 10 meV, were given by 100% para-H moderators, but the optimal moderator thickness was different for each: more than 220 mm, about 120 mm and 80 mm, respectively. Finally, we concluded 140 mm was the optimal thickness for the 100% para-H coupled moderator. Cold neutron distributions on the moderator viewed surface were found to exhibit an intensity-enhanced region at a picture frame part near premoderator. This rather peculiar distribution suggested that the moderator and the viewed surface must be designed so as to take the brighter region near premoderator in use. The intensity decreases along with beam-extraction angle to the normal direction down to about 70% at 25.4
. Then, we propose a cylindrical shape coupled moderator which brings about a slight intensity decrease for 0 but a increase in the averaged intensity over the angles of interest.
Kawai, Masayoshi*; Furusaka, Michihiro; Li, J.-F.*; Kawasaki, Akira*; Yamamura, Tsutomu*; Mehmood, M.*; Kurishita, Hiroaki*; Kikuchi, Kenji; Takenaka, Nobuyuki*; Kiyanagi, Yoshiaki*; et al.
Proceedings of ICANS-XVI, Volume 3, p.1087 - 1096, 2003/07
In order to establish the technique fabricating a thin target slab with a real size, thin tantalum-clad tungsten slab with a hole for a thermocouple was fabricated with the high-precision machinery techniques and the HIP'ing method. The ultrasonic diagnostic showed that tantalum and tungsten bond was perfect. The HIP optimum condition was certified by means of the small punch test as already reported. The electrolytic coating technique in a molten salt was developed to make a thinner tantalum cladding on a tungsten target with a complicated shape, in order to reduce radioactivity from tantalum in an irradiated target.
Kinoshita, Hidetaka; Haga, Katsuhiro; Kogawa, Hiroyuki; Kaminaga, Masanori; Hino, Ryutaro
Proceedings of ICANS-XVI, Volume 3, p.1305 - 1314, 2003/07
The JAERI and the KEK are promoting a plan to construct the spallation neutron source at the Tokai Research Establishment, JAERI, under J-PARC project. A mercury circulation system has been designed so as to supply mercury to the target stably. Conceptual design is almost finished. But, it was necessary to confirm a mercury pump performance, and more, to investigate erosion rate under the mercury flow as well as an amount of mercury remained on the surface after drain. The mercury pump performance was tested under the mercury flow conditions by using an experimental gear pump, which had almost the same structure as a practical mercury pump to be expected, and the erosion rates in a mercury pipeline as were investigated. The discharged flow rates of the gear pump increased linearly with the rotation speed. Erosion rates obtained under the mercury velocity less than 1.6 m/s was found to be so small. For the amount of remaining mercury on the pipeline, radioactivity of this remaining mercury volume was found to be three-order lower than that of the target casing.
Kai, Tetsuya; Maekawa, Fujio; Kasugai, Yoshimi; Niita, Koji*; Takada, Hiroshi; Meigo, Shinichiro; Ikeda, Yujiro
Proceedings of ICANS-XVI, Volume 3, p.1041 - 1049, 2003/07
A radioactivity calculation code system DCHAIN-SP was validated in view of the following points: (1) Activation cross section data library for the energy region below 20 MeV. (2) NMTC/JAM code for calculation of the nuclide yield induced by the high energy particles above 20 MeV. (3) DCHAIN-SP code system which treats overall nuclide yield by the high energy particles. 42 of activation cross sections and 22 tritium production cross sections were revised so that the DCHAIN-SP calculation could improve its accuracy within 30% for typical materials irradiated by 14-MeV neutrons. The NMTC/JAM code was improved to implement the GEM model for better estimation of light fragment production. Accuracy of the nuclide yield for proton induced reactions in 10 MeV - 10 GeV still remains in the level of a factor of 2 to 3. The DCHAIN-SP code system was employed for the analysis of time evolution of the radioactivity produced in the samples on a thick mercury target bombarded with 2.83 and 24 GeV protons. It is found that the code system agrees with the measured data by a factor of 2 to 3.
Meigo, Shinichiro; Harada, Masahide; Takada, Hiroshi
Proceedings of ICANS-XVI, Volume 3, p.1059 - 1067, 2003/07
In the neutronics design for the J-PARC facilities, transport codes of NMTC/JAM, MCNPX and MARS are used. In order to confirm the predict ability for these codes, it is important to compare with the experiment result. For the validation of the source term of neutron, the calculations are compared with the experimental spectrum of neutrons produced from thick target. Although slightly disagreement exists, NMTC/JAM, MCNPX and MARS are in good agreement with the experiment within by a factor of 2.
Meigo, Shinichiro; Harada, Masahide; Teraoku, Takuji*; Maekawa, Fujio
Proceedings of ICANS-XVI, Volume 3, p.1175 - 1180, 2003/07
It is important to monitor the proton beam for the high intensity pulse spallation target. Especially for the beam halo, which may irradiate the bulk surrounding the target, it is important to be observed to prevent causing heat spot in the shielding bulk. At JSNS, a proton beam monitors are located at front of the target. These monitors are assembled with the proton beam window. Since this scheme increases the radiation on the monitor due to the beam loss at the windows, it may arise heat deposition on the monitor. Therefore, heat deposition is calculated with NMTC/JAM. It is found that the heat deposition for normal operation is less than 0.1 W/cc.
Meigo, Shinichiro; Noda, Fumiaki*; Fujimori, Hiroshi*; Ikeda, Yujiro
Proceedings of ICANS-XVI, Volume 3, p.967 - 976, 2003/07
In J-PARC project, spallation target is irradiated by 3 GeV proton beam of 1 MW. Due to hands on maintenance for the proton beam lines, loss of proton beam is limited less than 1 W/m. Since it is difficult to predict the phase space distribution of the proton beam, we decided that the beam line have to be larger acceptance for 324 
mrad, which is determined by the collimator located in the synchrotron. Distortion of proton beam is caused by the by the instability of angle at the extraction of 3-GeV synchrotron, miss alignment of the magnet, and un-uniformity of the magnet field. In this study, the distortion is calculated. In order to fit the conditions, the stability of extraction angles should be kept smaller than 0.2 mrad. As for the magnetic field, it is found that the uniformity should be kept better 5x10
and 2x10
for bending and quadruple magnets, respectively. It is also found the error of alignments should be limited smaller than 1.0 mm and 1.0 mrad.