Thermal-hydraulic design calculations for JRR-3 cold neutron source with the new moderator cell

Tokunaga, Sho; Horiguchi, Hironori; Nakamura, Takemi

JAEA-Technology 2023-001, 37 Pages, 2023/05

JAEA-Technology-2023-001.pdf:1.39MB

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.

Neutron spectrum change with thermal moderator temperature in a compact electron accelerator-driven neutron source and its effects on spectroscopic neutron transmission imaging

Ishikawa, Hirotaku*; Kai, Tetsuya; Sato, Hirotaka*; Kamiyama, Takashi*

Journal of Nuclear Science and Technology, 56(2), p.221 - 227, 2019/02

https://doi.org/10.1080/00223131.2018.1561339

Fundamental aspects of neutron moderators and neutron beam optics for designing high intensity laser-driven neutron source

Ikeda, Yujiro; Shimizu, Hirohiko*

Reza Kenkyu, 46(11), p.641 - 646, 2018/11

https://doi.org/10.2184/lsj.46.11_641

In viewing significant progresses in technical achievement toward a high-intensity neutron source driven by a high-power laser came up with the high power laser development, we have reviewed the currently most advanced moderator system and neutron optics, which are the key elements for the neutron beam applications. Regarding the moderators, concepts adopted in J-PARC pulsed neutron source, which is one of most advanced system, were described to give a baseline design. Also a new direction of moderator concept is shown, which could be a high brightness candidate for the high-intensity laser driven system. On the neutron optics, the most fundamental consideration is primarily reviewed along with recent progress in new devises for enrichment of neutron-beam characteristics.

Present fabrication status of spare moderators and reflector in J-PARC spallation neutron source

Teshigawara, Makoto; Harada, Masahide; Oi, Motoki; Takada, Hiroshi

Journal of Physics; Conference Series, 1021(1), p.012061_1 - 012061_4, 2018/06

https://doi.org/10.1088/1742-6596/1021/1/012061

At the spallation neutron source of J-PARC, the structural material of moderators and reflector, such as an aluminum alloy, is going to reach to the design value (20 DPA) around 2020 by an accumulation of irradiation-damage. We started the fabrication of the spare moderators and reflector in 2013 with following design of two improvements. The invar joints, such as invar-A6061 and invar- SS316L joints were newly developed to utilize them in the cryogenic multi-layered pipe with 5th annular geometry, improving the fabrication procedure much simple. The Gold-Indium-Cadmium (Au-In-Cd) as a decoupler material is also developed to reduce residual radioactivity of the used components significantly for the decoupled moderator. In this presentation, we will report these results and progress of fabrication.

Implementation of a low-activation Au-In-Cd decoupler into the J-PARC 1 MW short pulsed spallation neutron source

Teshigawara, Makoto; Ikeda, Yujiro; Oi, Motoki; Harada, Masahide; Takada, Hiroshi; Kakishiro, Masanori*; Noguchi, Gaku*; Shimada, Tsubasa*; Seita, Kyoichi*; Murashima, Daisuke*; et al.

Nuclear Materials and Energy (Internet), 14, p.14 - 21, 2018/01

https://doi.org/10.1016/j.nme.2018.02.001

We developed an Au-In-Cd (AuIC) decoupler material to reduce induced radioactivity instead of Ag-In-Cd one, which has a cut off energy of 1eV. In order to implement it into an actual moderator-reflector assembly, a number of critical engineering issues need to be resolved with regard to large-sized bonding between AuIC and A5083 alloys by the hot isostatic pressing process. We investigated this process in terms of the surface conditions, sizes, and heat capacities of large AuIC alloys. We also show a successful implementation of an AuIC decoupler into a reflector assembly, resulting in a remarkable reduction of radioactivity by AuIC compared to AIC without sacrificing neutronic performance.

Developments of high-performance moderator vessel for JRR-3 cold neutron source

Arai, Masaji; Tamura, Itaru; Hazawa, Tomoya

JAEA-Technology 2015-010, 52 Pages, 2015/05

JAEA-Technology-2015-010.pdf:7.11MB

In the Department of Research Reactor and Tandem Accelerator, developments of high-performance CNS moderator vessel that can produce cold neutron intensity about two times higher compared to the existing vessel have been performed in the second medium term plans. We compiled this report about the technological development to solve several problems with the design and manufacture of new vessel. In the present study, design strength evaluation, mockup test, simulation for thermo-fluid dynamics of the liquid hydrogen and strength evaluation of the different-material-bonding were studied. By these evaluation results, we verified that the developed new vessel can be applied to CNS moderator vessel of JRR-3.

Deterioration of pulse characteristics and burn-up effects with an engineering model in Japanese spallation neutron source

Harada, Masahide; Watanabe, Noboru; Teshigawara, Makoto; Kai, Tetsuya; Maekawa, Fujio; Kato, Takashi; Ikeda, Yujiro

LA-UR-06-3904, Vol.2, p.700 - 709, 2006/06

Pulse characteristics data for every neutron beam line are indispensable in designing devices for neutron scattering experiments of JSNS. A detailed model was built and pulse characteristics of each beam line were estimated using the PHITS code and the MCNP-4C code. These results have been disclosed on the J-PARC homepage since September 2004. Due to changes of moderator shapes in a progress of manufacture design, we observed from the calculation that pulse structures of decoupled moderators were deteriorated, especially, those of pulse tail. We found that this deterioration was caused by leakage neutron from gaps between decouplers and absorbing liners of the reflector. For a final stage of the manufacture design, we carefully tried to find other factors which deteriorated the pulse characteristics. Furthermore, pulse structures of poisoned and unpoisoned decoupled moderators were evaluated with the consideration of heterogeneous burn-up and leakage neutron spectra including high-energy region up to GeV were estimated for each neutron beam hole.

Neutronic performance of rectangular and cylindrical coupled hydrogen moderators in wide-angle beam extraction of low-energy neutrons

Kai, Tetsuya; Harada, Masahide; Teshigawara, Makoto; Watanabe, Noboru; Kiyanagi, Yoshiaki*; Ikeda, Yujiro

Nuclear Instruments and Methods in Physics Research A, 550(1-2), p.329 - 342, 2005/09

https://doi.org/10.1016/j.nima.2005.04.082

Neutronic study was performed on coupled hydrogen moderators to maximize time-integrated and pulse-peak intensities of slow neutrons when a large number of beams was required. The total increased with the number of beams, although the average decreased due to a reflector-missing by the beam extraction holes in the reflector. At a large beam extraction angle (25 degree), the spatial distribution of the vector-flux of neutrons was undesirable for a rectangular shape moderator. As an alternative we proposed a cylindrical shape one, resulting in a much improved spatial distribution. In addition, neutronic performance was calculated as a function of the diameter, indicating the optimal diameter was about 140 mm. The cylindrical one gave higher pulse-peak intensities with narrower pulse widths without penalty in time-integrated intensities and pulse decay characteristics, providing a more uniform angle-dependence. Some explanations are given for the difference in the pulse characteristics between the two. We decided to adopt the cylindrical one for the Japanese spallation neutron source.

Design of a single moderator-type neutron spectrometer with enhanced energy resolution in energy range from a few to 100 keV

Tanimura, Yoshihiko; Saegusa, Jun; Yoshizawa, Michio; Yoshida, Makoto

Nuclear Instruments and Methods in Physics Research A, 547(2-3), p.592 - 600, 2005/08

https://doi.org/10.1016/j.nima.2005.03.162

The moderator structure of a neutron spectrometer was optimized with a Monte Carlo code of MCNP-4B. The spectrometer consists of a cylindrical moderator and a position-sensitive thermal neutron detector. It can obtain an energy spectrum from thermal neutron distribution along the cylindrical axis of the moderator. The structure of the moderator was improved by putting a low hydrogen density material in the front of a high hydrogen density one and inserting a neutron absorber which eliminated thermal neutrons diffusing in the moderator. These improvements make energy resolution of the spectrometer better especially for the low energy neutrons from a few tens to 100 keV. The designed spectrometer can be applied to the measurement of energy spectrum over a neutron energy range from a few keV to 20 MeV.

Neutronic studies on decoupled hydrogen moderator for a short-pulse spallation source

Harada, Masahide; Watanabe, Noboru; Teshigawara, Makoto; Kai, Tetsuya; Ikeda, Yujiro

Nuclear Instruments and Methods in Physics Research A, 539(1-2), p.345 - 362, 2005/02

https://doi.org/10.1016/j.nima.2004.10.013

Neutronic studies of decoupled hydrogen moderators were performed by calculations taking into account para hydrogen content, decoupling energy, moderator dimensions/shapes and reflector material. Low-energy parts of calculated spectral intensities with different para hydrogen contents were analyzed by a modified Maxwell function to characterize neutron spectra. The result shows that a 100% para hydrogen moderator gives the highest pulse peak intensity together with the narrowest pulse width and the shortest decay times. Pulse broadening with a reflector was explained by time distributions of source neutrons entering into the moderator through a decoupler. Material dependence of time distribution was studied. A decoupling energy higher than 1 eV does not bring about a large improvement in pulse widths and decay times, even at a large penalty in the peak intensity. The optimal moderator thickness was also discussed for a rectangular parallelepiped shape and a canteen shape moderators.