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Journal Articles

Activation, Radiation shielding materials

Sukegawa, Atsuhiko; Iida, Hiromasa*; Itoga, Toshio*; Okumura, Keisuke; Kai, Tetsuya; Konno, Chikara; Nakashima, Hiroshi; Nakamura, Takashi*; Ban, Shuichi*; Yashima, Hiroshi*; et al.

Hoshasen Shahei Handobukku; Kisohen, p.299 - 356, 2015/03

no abstracts in English

Journal Articles

Development of in-vessel components of the microfission chamber for ITER

Ishikawa, Masao; Kondoh, Takashi; Okawa, Kiyofumi*; Fujita, Kyoichi*; Yamauchi, Michinori*; Hayakawa, Atsuro*; Nishitani, Takeo; Kusama, Yoshinori

Review of Scientific Instruments, 81(10), p.10D308_1 - 10D308_3, 2010/10

 Times Cited Count:2 Percentile:83.65(Instruments & Instrumentation)

Microfission chambers (MFCs) will provide total neutron source strength in ITER. The MFC is a pencil-sized gas counter containing the fissile material, $$^{235}$$U. The MFCs will be installed behind blanket modules in the vacuum vessel (VV). Double coaxial mineral insulated (MI) cables will carry signals from the MFCs to the upper port. Though the MI cables will be installed at a factory of the vacuum vessel or ITER assembly hall, detectors with $$^{235}$$U will be installed to the vacuum vessel at the tokamak pit. Then, the MI cable should be connected in the vacuum vessel. In this work, the connection of the MI cable with the MFC was conceptually designed. The MI cable should be also installed with small curvature radius (R) of 100 $$sim$$ 200 mm to avoid the VV structure and other diagnostics. So, the vending test of the MI cable was conducted. As a result, damages leak, electrical disconnection and the change in insulation resistance have not been observed at R = 100 mm.

Journal Articles

Multi-scattering time-of-flight neutron spectrometer for deuterium to tritium fuel ratio measurement in fusion experimental reactors

Asai, Keisuke*; Yukawa, Kyohei*; Iguchi, Tetsuo*; Naoi, Norihiro*; Watanabe, Kenichi*; Kawarabayashi, Jun*; Yamauchi, Michinori*; Konno, Chikara

Fusion Engineering and Design, 83(10-12), p.1818 - 1821, 2008/12

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

The fuel ratio in a DT burning plasma can be derived from the intensity ratio of DD/DT neutrons, and detecting a trace of DD neutrons in the DT burning plasma is a key issue. A new type of neutron spectrometer is proposed to monitor the fuel ratio in the core of the ITER plasma. The system based on a conventional time-of-flight method consists of a water cell as a neutron scattering material and tens of scintillator pairs arranged around the first scintillator in a corn shape. We call it a multi-scattering time-of-flight neutron spectrometer (MS-TOF). A trial experiment was conducted for the prototype MS-TOF system with a DT neutron beam (20-mm diameter) at the Fusion Neutronics Source (FNS), Japan Atomic Energy Agency. The experimental results show that the DD and DT neutron peaks are clearly observed, and the experiment has successfully demonstrated the feasibility of the MS-TOF concept for detecting trace-DD neutrons within a DT neutron beam extracted from a DT burn plasma.

Journal Articles

Problem on unresolved resonance data in recent nuclear data libraries

Konno, Chikara; Nakagawa, Tsuneo; Ochiai, Kentaro; Sato, Satoshi; Yamauchi, Michinori

Proceedings of International Conference on Nuclear Data for Science and Technology (ND 2007), Vol.1, p.713 - 716, 2008/05

A leakage neutron spectrum from a niobium sphere of 0.5 m in radius with a 20 MeV neutron in the center, which was calculated with ANISN, MCNP and JENDL-3.3, had a large strange bump around 100 keV, which originated from the unresolved resonance data. We checked cross section data of (n,$$gamma$$) reaction and elastic scattering in $$^{93}$$Nb with and without self-shielding correction by using a multigroup library of JENDL-3.3. The self-shielding correction of the unresolved resonances seems to be too large even around the upper energy of the unresolved resonance region. It is considered that the average reduced neutron widths or the upper energy of the unresolved resonance region in $$^{93}$$Nb have any problems. It is found out that many nuclei with unresolved resonance data in JENDL-3.3 and ENDF/B-VI have the similar problem. The unresolved resonance data in JENDL-3.3 and ENDF/B-VI should be revised by considering self-shielding correction in the next version.

Journal Articles

Activation analysis for sequential reactions of a fusion Demo-reactor

Yamauchi, Michinori; Nishitani, Takeo; Nishio, Satoshi; Hori, Junichi*; Kawasaki, Hiromitsu*

Fusion Science and Technology, 52(4), p.781 - 785, 2007/11

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

Low activation material is one of the important factors for constructing high power fusion reactors in future. Unexpected activation, however, may be produced through sequential reactions due to charged particles created by primary neutron reactions. In the present work, the effect of the sequential activation reaction was studied for candidate low activation materials of a fusion demo-reactor. The calculations were conducted by the ACT4 code developed in JAEA for the activation analysis of fusion reactor designs and revised for dealing with the sequential activation reactions. The results say that the real dose rate around vanadium alloy which may be used as structural material becomes larger after the cooling for 3 years by considering the reaction. Although metal hydrate is regarded as an excellent low activation shield material, the reactions due to recoil protons are influential and the dose rate around vanadium hydrate is several orders of magnitude larger than the value calculated without the sequential process after 2 weeks cooling. In case of liquid breeders, the effect of sequential reactions is popularly observed and it affects the shield design of circulation loop.

Journal Articles

Thin slit streaming experiment for ITER by using D-T neutron source

Ochiai, Kentaro; Sato, Satoshi; Wada, Masayuki*; Kubota, Naoyoshi; Kondo, Keitaro; Yamauchi, Michinori; Abe, Yuichi; Nishitani, Takeo; Konno, Chikara

Fusion Engineering and Design, 82(15-24), p.2794 - 2798, 2007/10

 Times Cited Count:4 Percentile:63.84(Nuclear Science & Technology)

Neutron streaming experiments have been conducted by using the FNS D-T neutron source at Japan Atomic Energy Agency under the ITER/ITA Task 73-10 in order to evaluate effects of the slit on nuclear properties and validate prediction accuracies on numerical simulations. The experimental assembly with a slit of 2 cm in width and 55 cm in depth was prepared with two iron blocks of 30 cm in height, 100 cm in width and 55cm in thickness as first campaign. The slit was located in the 12-cm upper part from the D-T neutron source point. In order to evaluate distributions of the neutron fluxes along the slit as a function of the depth from the assembly surface, fission reaction rates were measured by U-238 and U-235 micro-fission chambers. The experimental accuracies of these fission reaction rates are within 5%. Monte-Carlo calculation code, MCNP-4c, was used to calculate the U-238 and U-235 reaction rates and neutron energy spectra due to each measured position. From our first experiment, the following facts were found: (1) At d = 20 and 40 cm, reaction rates on U-238, which represent fast neutron flux, decreased by about three orders of magnitude along slits with 50 cm in depth. Monte Carlo calculation results agree well with measured values within 6 %. (2) Reaction rates on U-235, which represent thermal neutron flux, decrease by about one order of magnitude along slits with 50 cm in depth. Values of C/E of U-238 and U-235 reaction rates were 1.10-1.22 and 1.10-1.23 respectively and the calculated values overestimated slightly.

Journal Articles

Engineering design of the ITER invessel neutron monitor using micro-fission chambers

Nishitani, Takeo; Yamauchi, Michinori; Izumi, Mikio*; Hayakawa, Atsuro*; Ebisawa, Katsuyuki*; Kondoh, Takashi; Kusama, Yoshinori

Fusion Engineering and Design, 82(5-14), p.1192 - 1197, 2007/10

 Times Cited Count:4 Percentile:70.71(Nuclear Science & Technology)

no abstracts in English

JAEA Reports

ACT-XN; Revised version of an activation calculation code for fusion reactor analysis; Supplement of the function for the sequential reaction activation by charged particles

Yamauchi, Michinori; Hori, Junichi*; Sato, Satoshi; Nishitani, Takeo; Konno, Chikara; Kawasaki, Hiromitsu*

JAEA-Data/Code 2007-016, 58 Pages, 2007/09

JAEA-Data-Code-2007-016.pdf:7.33MB

The ACT-XN is a revised version of the ACT4 code, which was developed in the Japan Atomic Energy Agency (JAEA) to calculate the transmutation, induced activity, decay heat, delayed $$gamma$$-ray source etc. for fusion devices. The ACT4 code has not dealt with the sequential reactions of charged particles generated by primary neutron reactions. However, the reactions cannot be disregarded in the design employing low activation material, and the code was newly supplemented with the function to calculate the activation for sequential reactions and renamed the ACT-XN. The FISPACT data were adopted for (x,n) reaction cross sections, charged particles emission spectra and stopping powers. An application of the code to the analysis of FNS experiment for LiF activation confirmed that the function is enough reliable, and a notice was presented through the design calculation of the Demo-reactor with FLiBe that the dose rate may be enhanced by sequential reactions.

Journal Articles

Search for luminescent materials under 14 MeV neutron irradiation

To, Kentaro*; Shikama, Tatsuo*; Nagata, Shinji*; Tsuchiya, Bun*; Yamauchi, Michinori; Nishitani, Takeo

Journal of Nuclear Materials, 367-370(2), p.1128 - 1132, 2007/08

 Times Cited Count:6 Percentile:51.27(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Measurement of tritium production rate in water cooled pebble bed multi-layered blanket mockup by DT neutron irradiation experiment

Sato, Satoshi; Ochiai, Kentaro; Verzilov, Y.*; Wada, Masayuki*; Kubota, Naoyoshi; Kondo, Keitaro; Yamauchi, Michinori; Nishitani, Takeo; Konno, Chikara

Nuclear Fusion, 47(7), p.517 - 521, 2007/07

 Times Cited Count:13 Percentile:49.81(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Surface analysis for the TFTR Armor tile exposed to D-T plasmas using nuclear technique

Kubota, Naoyoshi; Ochiai, Kentaro; Kutsukake, Chuzo; Hayashi, Takao; Shu, Wataru; Kondo, Keitaro; Verzilov, Y.*; Sato, Satoshi; Yamauchi, Michinori; Nishi, Masataka; et al.

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 7 Pages, 2007/03

Fuel and impurity particles show complicated behavior on the surface of plasma facing components (PFC) in fusion devices. The study is important for the design of the fuel recycling, safety management of the tritium inventory, etc. Quantitative measurements of hydrogen and lithium isotopes together with other impurities on the PFC surface exposed to D-T plasmas in TFTR were performed using the deuteron-induced nuclear reaction analysis, imaging plate method, full combustion method and activation analysis. The tritium depth profile was different from deuterium one. The surface tritium largely contributed to the whole tritium in the sample. On the other hand, the retained amount of lithium-6 was lager than that of lithium-7. This relates to the injection of enriched lithium-6 pellets in some campaigns. No other impurities were detected. So the large amount of tritium remained near the surface and did not diffuse more deeply, which gives a bright prospect for tritium safety.

Journal Articles

Experimental study on nuclear properties of water cooled pebble bed blanket

Sato, Satoshi; Verzilov, Y.*; Ochiai, Kentaro; Wada, Masayuki*; Kubota, Naoyoshi; Kondo, Keitaro; Yamauchi, Michinori; Nishitani, Takeo; Konno, Chikara

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03

no abstracts in English

JAEA Reports

Evaluation of deuteron-induced activation for IFMIF accelerator structural materials

Nakao, Makoto*; Hori, Junichi*; Ochiai, Kentaro; Kubota, Naoyoshi; Sato, Satoshi; Yamauchi, Michinori; Ishioka, Noriko; Suto, Hiroyuki*; Nishitani, Takeo

JAEA-Research 2006-071, 37 Pages, 2006/11

JAEA-Research-2006-071.pdf:6.72MB

In the design of IFMIF, long-term operation with total facility availability of at least 70 % is required. However, activation of structural materials by deuteron beam limits maintenance, which causes lower facility availability. Thus it is essential to prepare deuteron-induced activation cross section database and to select low activation materials based on it. In this work, we measured deuteron-induced activation cross sections of aluminum, vanadium, chromium, manganese, iron, nickel, copper, tantalum, tungsten and gold. The measured cross sections were compared with other experimental data and calculations. Deuteron-induced activities of nuclides produced in SS316 and F82H alloys used as the accelerator structural material were also measured to validate the measured cross sections comprehensively. It demonstrated that the measured activities of almost all the nuclides were in agreement with evaluated ones based on the measured cross sections within error.

Journal Articles

Possibility of tritium self-sufficiency in low aspect ratio tokamak reactor with the outboard blanket only

Hayashi, Takao; Tobita, Kenji; Nishio, Satoshi; Sato, Satoshi; Nishitani, Takeo; Yamauchi, Michinori

Fusion Engineering and Design, 81(23-24), p.2779 - 2784, 2006/11

 Times Cited Count:2 Percentile:79.89(Nuclear Science & Technology)

We have studied the possibility of tritium self-sufficiency with the outboard blanket only in low aspect ratio tokamak reactor to simplify the inboard structure in high magnetic field. The tritium breeding ratio (TBR) of the outboard blanket increases by applying the inboard reflector working as a neutron multiplier such as lead and beryllium. Assuming that the coverage of the breeder zone to plasma facing components is 0.78, the requirement of local TBR is above 1.35. The local TBR calculated with both the inboard reflector of lead and the outboard blanket using beryllium multiplier and Li$$_{2}$$O breeder is larger than 1.35 for aspect ratios smaller than 2.9. These results indicate there is a solution for tritium self-sufficiency using the outboard breeding blanket only in low-A tokamak reactor when the appropriate inboard reflector and outboard blanket are adopted. In case both inboard and outboard blankets are applied, the total TBR with the combination of Li$$_{2}$$O and Be is more than 1.5. However, Be$$_{12}$$Ti and Li$$_{2}$$TiO$$_{3}$$ are recommended from the viewpoint of safety, and the TBR with the combination is slightly larger than 1.35 for aspect ratios from 2 to 4.

Journal Articles

Measurements of deuteron-induced activation cross-sections for IFMIF accelerator structural materials

Nakao, Makoto*; Hori, Junichi*; Ochiai, Kentaro; Kubota, Naoyoshi; Sato, Satoshi; Yamauchi, Michinori*; Ishioka, Noriko; Nishitani, Takeo

Nuclear Instruments and Methods in Physics Research A, 562(2), p.785 - 788, 2006/06

 Times Cited Count:20 Percentile:15.77(Instruments & Instrumentation)

Activation cross sections for deuteron-induced reactions on aluminum, iron, copper, tantalum and tungsten were measured by using stacked-foil method. The stacked-foils were irradiated with deuteron beam at the AVF cyclotron in TIARA facility, JAERI. We obtained the activation cross-sections for $$^{27}$$Al(d,x)$$^{22,24}$$Na, $$^{nat}$$Fe(d,x)$$^{55,56}$$Co, $$^{nat}$$Cu(d,x)$$^{61}$$Cu, $$^{nat}$$Cu(d,x)$$^{62}$$Zn, $$^{nat}$$Ta(d,x)$$^{178,180}$$Ta and $$^{nat}$$W(d,x)$$^{181,183}$$Re in 20-40MeV region. These cross-sections were compared with other experimental ones and the data in the ACSELAM library calculated by the ALICE-F code.

Journal Articles

Effect of photobleaching on radiation-induced transmission loss of fused-silica-core optical fibres under $$gamma$$-ray and 14 MeV neutron irradiation

To, Kentaro*; Shikama, Tatsuo*; Nagata, Shinji*; Tsuchiya, Bun*; Yamauchi, Michinori; Nishitani, Takeo

Measurement Science and Technology, 17(5), p.955 - 959, 2006/05

 Times Cited Count:6 Percentile:50.98(Engineering, Multidisciplinary)

The effect of photobleaching on radiation-induced transmission loss of fused-silica-core optical fibres was examined under $$^{60}$$Co $$gamma$$-ray and 14 MeV neutron irradiation. In the visible wavelength range, the radiation-induced transmission loss could be reduced by photobleaching under both types of irradiation. It is considered that the number of radiation-induced defects such as E' centre and NBOHC that cause optical absorption was reduced by photobleaching. For using optical fibres in the visible wavelength range as light guides or image guides, photobleaching is an effective technique to improve their radiation resistance. However, a so-called microbending loss is induced by radiation in the entire wavelength range. The loss response to photobleaching was different under $$gamma$$-ray and fast-neutron irradiation. The loss under the $$gamma$$-ray irradiation increased due to photobleaching, while that under the fast-neutron irradiation decreased. It is considered that there are multiple reasons for the radiation-enhanced microbending loss. In general, it is concluded that the photobleaching technique is effective in improving the radiation resistance of fused-silica-core optical fibres under neutron and moderate flux radiation environments.

JAEA Reports

Analyses of heat load in ITER NBI duct and neutron streaming through pressure relief line

Sato, Satoshi; Yamauchi, Michinori; Nishitani, Takeo; Ioki, Kimihiro; Iida, Hiromasa; Kataoka, Yoshiyuki

JAEA-Technology 2006-032, 91 Pages, 2006/03

JAEA-Technology-2006-032.pdf:12.8MB

no abstracts in English

Journal Articles

Measurements of deuteron-induced activation cross sections for IFMIF accelerator structural materials

Nakao, Makoto; Hori, Junichi*; Ochiai, Kentaro; Kubota, Naoyoshi; Sato, Satoshi; Yamauchi, Michinori; Ishioka, Noriko; Nishitani, Takeo

FAPIG, (172), p.3 - 7, 2006/03

The IFMIF (International Fusion Materials Irradiation Facility) is in the design planning stage as neutron source to test fusion reactor materials for high fluence neutron. In the design of it long-term operation that total facility is 70 % at least is required. However, deuteron beam activates the structural materials and these activation limits maintenance and makes long-term operation difficult. Thus the accurate estimation of deuteron-induced activity and the selection of structural materials are important. In this work, measurements of deuteron-induced activation cross sections for aluminum, iron, copper, tantalum, and tungsten were performed.

Journal Articles

Neutronics design of the low aspect ratio tokamak reactor, VECTOR

Nishitani, Takeo; Yamauchi, Michinori*; Nishio, Satoshi; Wada, Masayuki*

Fusion Engineering and Design, 81(8-14), p.1245 - 1249, 2006/02

 Times Cited Count:13 Percentile:27.36(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Analysis of sequential charged particle reaction experiments for fusion reactors

Yamauchi, Michinori*; Hori, Junichi*; Ochiai, Kentaro; Sato, Satoshi; Nishitani, Takeo; Kawasaki, Hiromitsu*

Fusion Engineering and Design, 81(8-14), p.1577 - 1582, 2006/02

 Times Cited Count:1 Percentile:88.32(Nuclear Science & Technology)

no abstracts in English

72 (Records 1-20 displayed on this page)