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Tokunaga, Sho; Horiguchi, Hironori; Nakamura, Takemi
JAEA-Technology 2023-001, 37 Pages, 2023/05
The cold neutron source (CNS) of the research reactor JRR-3 converts thermal neutrons generated in the reactor into low-energy cold neutrons by moderating them with liquid hydrogen stored in the moderator cell. Cold neutrons generated by the CNS are transported to experimental instruments using neutron conduits, and are used for many studies of physical properties, mainly in life science, polymer science, environmental science, etc. Improvement of cold neutron intensity is essential to maintain competitiveness with the world's research reactors in neutron science, and we are developing a new CNS that incorporates new knowledge. The current moderator cell for the CNS of JRR-3 is a stainless-steel container which is a canteen bottle type, and the cold neutron intensity can be improved by changing the material and shape. Therefore, the basic specifications of the new moderator cell were changed to aluminum alloy which has a smaller neutron absorption cross section, and the shape was optimized using a Monte Carlo code MCNP. Since these changes in specifications will result in changes in heat generation and heat transfer conditions, the CNS of JRR-3 was re-evaluated in terms of self-regulating characteristic, heat transport limits, heat resistance and pressure resistance, etc., to confirm its feasibility in thermal-hydraulic design. This report summarizes the results of the thermal-hydraulic design evaluation of the new moderator cell.
Fukaya, Yuji; Goto, Minoru; Nakagawa, Shigeaki; Nakajima, Kunihiro*; Takahashi, Kazuki*; Sakon, Atsushi*; Sano, Tadafumi*; Hashimoto, Kengo*
EPJ Web of Conferences, 247, p.09017_1 - 09017_8, 2021/02
The Japan Atomic Energy Agency (JAEA) started the Research and Development (R&D) to improve nuclear prediction techniques for High Temperature Gas-cooled Reactors (HTGRs). The objectives are to introduce a generalized bias factor method to avoid full mock-up experiment for the first commercial HTGR and to introduce reactor noise analysis to High Temperature Engineering Test Reactor (HTTR) experiment to observe subcriticality. To achieve the objectives, the reactor core of graphite-moderation system named B7/4"G2/8"p8EUNU+3/8"p38EU(1) was newly composed in the B-rack of Kyoto University Critical Assembly (KUCA). The core is composed of the fuel assembly, driver fuel assembly, graphite reflector, and polyethylene reflector. The fuel assembly is composed of enriched uranium plate, natural uranium plate and graphite plates to realize the average fuel enrichment of HTTR and it's spectrum. However, driver fuel assembly is necessary to achieve the criticality with the small-sized core. The core plays a role of the reference core of the bias factor method, and the reactor noise was measured to develop the noise analysis scheme. In this study, the overview of the criticality experiments is reported. The reactor configuration with graphite moderation system is rare case in the KUCA experiments, and this experiment is expected to contribute not only for an HTGR development but also for other types of a reactor in the graphite moderation system such as a molten salt reactor development.
Sakon, Atsushi*; Nakajima, Kunihiro*; Takahashi, Kazuki*; Hohara, Shinya*; Sano, Tadafumi*; Fukaya, Yuji; Hashimoto, Kengo*
EPJ Web of Conferences, 247, p.09009_1 - 09009_8, 2021/02
In graphite-reflected thermal reactors, even a detector placed far from fuel region may detect a certain degree of the correlation amplitude. This is because mean free path of neutrons in graphite is longer than that in water or polyethylene. The objective of this study is experimentally to confirm a high flexibility of neutron detector placement in graphite reflector for reactor noise analysis. The present reactor noise analysis was carried out in a graphite-moderated and -reflected thermal core in Kyoto University Critical Assembly (KUCA). BF proportional neutron counters (1" dia.) were placed in graphite reflector region, where the counters were separated by about 35cm and 30cm -thick graphite from the core, respectively. At a critical state and subcritical states, time-sequence signal data from these counters were acquired and analyzed by a fast Fourier transform (FFT) analyzer, to obtain power spectral density in frequency domain. The auto-power spectral density obtained from the counters far from the core contained a significant degree of correlated component. A least-squares fit of a familiar formula to the auto-power spectral density data was made to determine the prompt-neutron decay constant. The decay constant was 63.314.5 [1/s] in critical state. The decay constant determined from the cross-power spectral density and coherence function data between the two counters also had a consistent value. It is confirmed that reactor noise analysis is possible using a detector placed at about 35cm far from the core, as we expected.
Oi, Motoki; Teshigawara, Makoto; Harada, Masahide; Ikeda, Yujiro
Journal of Nuclear Science and Technology, 56(7), p.573 - 579, 2019/07
Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)In pulsed neutron sources, a neutron absorber called decoupler is attached to the moderator to sharpen the neutron pulses for achieving good neutron energy resolutions. Cadmium and boron carbide (BC) are widely used as the decoupler materials. However, it is difficult to use BC in MW-class spallation neutron sources owing to high burn-up, which decreases cut-off energy and increase of helium gas swelling. To solve these issues, we introduce the concept of pre-decoupler to reduce neutron absorption in the BC decoupler, which is sandwiched by appropriate neutron absorption materials. Then, we study impacts of the pre-decouplers on BC decoupler in terms of burn-up by performing simplified model calculations. It is shown that neutron absorption in BC is reduced by 60% by using a Cd pre-decoupler without neutron intensity penalty. Moreover, helium gas swelling in BC is restrained to be one-third of the value when not using the pre-decoupler.
Oi, Motoki
Shiki, 43, P. 3, 2019/06
At the J-PARC Materials and Life Science Facility (MLF), we developed an Au-In-Cd alloy as a low activation neutron absorber for reducing the activity of moderator assembly, and put it to practical use in the reflector and moderator. As a method to confirm the distribution of indium in the alloy, pulse neutron imaging method is adopted, and the individual element distribution is measured by focusing on the resonance peak of indium, and the uniformity of the alloy is confirmed.
Takada, Hiroshi
Kasokuki Handobukku, p.330 - 333, 2018/04
Spallation neutron source provides thermal and cold neutrons for materials researches. Those neutrons are obtained by slowing down the neutrons generated in a neutron production target by injecting high energy protons in surrounding reflector and moderators. This article introduces basic characteristics of the neutron production target at first, and then explains the characteristics of moderator, especially the design to generate high intensity and high quality neutron pulses with narrow width in the moderators used in the 1-MW spallation neutron source at J-PARC. Furthermore, the design procedure of the spallation neutron source is described.
Takada, Hiroshi
JAEA-Conf 2017-001, p.51 - 56, 2018/01
A pulsed spallation neutron source of Japan Proton Accelerator Research Complex (J-PARC) is aimed at promoting a variety of cutting-edge materials researches at state-of-the-art neutron instruments with neutrons generated by a 3-GeV proton beam with a power of 1-MW at a repetition rate of 25 Hz. In 2015, for the first time it received 1-MW equivalent proton beam pulse, and the beam power for user program was ramped up to 500 kW. The moderator system of the neutron source was optimized to use (1) 100% para-hydrogen for increasing pulse peak intensity with decreasing pulse tail, (2) cylindrical shape with 14 cm diam. 12 cm long for providing high intensity neutrons to wide neutron extraction angles of 50.8 degrees, (3) neutron absorber made from Ag-In-Cd alloy to make pulse widths narrower and pulse tails lower. As a result, it gives highest intensity pulsed neutrons per incident proton in the world. Towards the goal to achieve the target operation at 1-MW for 5000 h in a year, efforts to mitigate cavitation damages at the target vessel front with injecting gas micro-bubbles into the mercury target are under way. Also, improvement of structural target vessel design is an urgent issue since there was failure twice at the water shroud of the mercury target due to the thermal stress during operating periods at 500 kW in 2015.
Kai, Takeshi; Yokoya, Akinari*; Fujii, Kentaro*; Watanabe, Ritsuko*
Yodenshi Kagaku, (8), p.11 - 17, 2017/03
It is thought to that the biological effects such as cell death or mutation are induced by complex DNA damage which are formed by several damage sites within a few nm. We calculated dynamic behavior of secondary electrons produced by primary electron and positon of high energy in water whose composition ratio is similar to biological context. The secondary electrons induce the ionization or electronic excitation near the parent cations. The decelerated electrons about 10% are distributed to their parent cations by the attractive Coulombic force. From the results, we predicted the following formation mechanism for the complex DNA damage. The electrons ejected from DNA could induce the ionization or the electronic excitation within the DNA. The electrons attracted by the Coulombic force are pre-hydrated in water layer of the DNA. The pre-hydrated electrons could induce to the DNA damage by dissociative electron transfer. As the results, the complex DNA damage with 1 nm could be formed by the interaction of not only the primary electron or positon but also the secondary electrons.
Takahashi, Satoshi*; Okuno, Hiroshi; Miyoshi, Yoshinori
JAERI-Tech 2005-056, 51 Pages, 2005/09
In the heterogeneous system of the mixed oxide fuel of uranium and plutonium, hereafter, MOX fuel, it was investigated whether the system could be modeled as a homogeneous system on the conditions which dealt with the MOX fuel of particle diameter 0.02mm or less in MOX fuel fabrication facilities in Japan. The infinite multiplication factor of the homogeneous system of the MOX fuel was first calculated, and the optimum moderation condition over the each ratio of PuO was determined. It was verified that carried out critical calculation for the heterogeneous system of the MOX fuel in which the spherical fuel diameter in a cube unit cell increased, and an atomic number ratio of hydrogen to heavy metal fixed conditions, and the probability for neutrons to escape resonance by a spherical fuel diameter no less than 0.1mm, and analyzed critical conditions etc. using a contiguous energy Monte Carlo code MVPII and JENDL3.3. The details of these calculations are reported. These results are expected to be quoted in a revised edition of "Nuclear Criticality Safety Handbook."
Yamazaki, Atsushi; Kotaki, Hideyuki; Daito, Izuru; Kando, Masaki; Bulanov, S. V.; Esirkepov, T. Z.; Kondo, Shuji; Kanazawa, Shuhei; Homma, Takayuki*; Nakajima, Kazuhisa; et al.
Physics of Plasmas, 12(9), p.093101_1 - 093101_5, 2005/09
Times Cited Count:70 Percentile:88.77(Physics, Fluids & Plasmas)no abstracts in English
Akie, Hiroshi; Nabeshima, Kunihiko; Uchikawa, Sadao
JAERI-Conf 2005-009, 153 Pages, 2005/08
As a research on the future innovative water reactor, the development of Reduced-Moderation Water Reactors (RMWRs) has been performed in JAERI. The workshop on RMWRs is aiming at information exchange between JAERI and other organizations, and has been held every year since 1998. The program of the 7th workshop was composed of 5 lectures and an overall discussion time. This report includes the original papers presented at the workshop and summaries of the questions and answers for each lecture as well as of the discussion time. In addition in Appendix, there are included presentation handouts of each lecture.
Yoshida, Hiroyuki; Ose, Yasuo*; Kureta, Masatoshi*; Nagayoshi, Takuji*; Takase, Kazuyuki; Akimoto, Hajime
Nihon Genshiryoku Gakkai Wabun Rombunshi, 4(2), p.106 - 114, 2005/06
no abstracts in English
Yoshida, Hiroyuki; Nagayoshi, Takuji*; Ose, Yasuo*; Takase, Kazuyuki; Akimoto, Hajime
Nihon Genshiryoku Gakkai Wabun Rombunshi, 4(1), p.25 - 31, 2005/03
no abstracts in English
Kureta, Masatoshi
Kashika Joho Gakkai-Shi, 24(Suppl.1), p.265 - 268, 2004/07
Visualization of 3D and instantaneous void fraction distribution of boiling flow in a tight-lattice 14-rod bundle is conducted by using neutron tomography and high-frame- rate neutron radiography void fraction measurement techniques. The purpose of the experiment is to understand vapor bubbles/water behavior ranging from the onset of boiling to the high void fraction region based on ("3D" + "2D+Time") void fraction data, and to obtain the fine-mesh database for verification of advanced analysis codes. Following phenomena are made clear from the present experiment: Vapor accumulates in the channel center; High void fraction spots appear between adjacent heater rods, that is, in narrow space at the inlet; Void fraction in the triangular space among three rods becomes high by void drift phenomenon, and "vapor chimney" is formed; Flow is intermittent, and vapor bubble clusters are formed periodically; Onset points of net vapor generation are scattered not only in the center but in the peripheral.
Kureta, Masatoshi; Tamai, Hidesada
Proceedings of 5th International Conference on Multiphase Flow (ICMF 2004) (CD-ROM), 10 Pages, 2004/06
3D void fraction distribution of boiling flow in a tight-lattice 7-rod bundle was measured by neutron radiography 3D computed tomography (neutron tomography) to investigate the flow characteristics in tight-lattice rod bundles and to verify the numerical analysis codes. The test section simulates the fuel rod bundle of the RMWR and consists of 7 heater rods with gap of 1.0mm and with diameter of 12.0mm. In this paper, the neutron tomography system, experiments and comparison of the measured data with a subchannel analysis code, COBRA-TF, are reported. It was found from this experiment that water layer which surrounds the heater rod becomes thick between rods, narrow region, and steam accumulates at the center region among three rods. COBRA-TF code overestimates the void fraction in a tight-lattice bundle compared with the present data.
Ose, Yasuo*; Takase, Kazuyuki; Yoshida, Hiroyuki; Kano, Takuma; Kureta, Masatoshi; Akimoto, Hajime
Dai-41-Kai Nihon Dennetsu Shimpojiumu Koen Rombunshu, 2 Pages, 2004/05
no abstracts in English
Sato, Hiroshi; Aso, Tomokazu; Kogawa, Hiroyuki; Teshigawara, Makoto; Hino, Ryutaro
JAERI-Tech 2004-018, 23 Pages, 2004/03
The Japan Atomic Energy Research Institute is constructing a mega-watt class spallation neutron source in cooperation with the High Energy Accelerator Research Organization. A cold moderator using liquid hydrogen is one of the key components in the system, which directly affects the neutronic performance both in intensity and pulse time structure. Since a hydrogen temperature rise in the moderator vessel affects the neutronic performance, it is necessary to suppress the recirculation and stagnant regions which would cause hot spots. A cold moderator with a poison plate (poisoned decoupled moderator) has a high possibility to generate the stagnant region on and near the poison plate. Thermal-hydraulic analyses were carried out with proposed inner structure of the poisoned cold moderator. The stagnant and recirculation regions could be reduced by making a gap between the poison plate end and the vessel bottom surface, and the local temperature rise also could be kept under the required design value.
Kureta, Masatoshi; Hoshi, Yoshiyuki; Yamada, Kazuyuki*; Sakamoto, Kiyotaka*
Nikkei Saiensu, 111 Pages, 2004/01
no abstracts in English
Takase, Kazuyuki; Yoshida, Hiroyuki; Ose, Yasuo*; Tamai, Hidesada; Akimoto, Hajime
Transactions of the American Nuclear Society, 89, p.88 - 89, 2003/11
no abstracts in English
Aso, Tomokazu; Sato, Hiroshi; Kaminaga, Masanori; Hino, Ryutaro; Monde, Masanori*
Kashika Joho Gakkai-Shi, 23(Suppl.2), p.13 - 16, 2003/10
no abstracts in English