Application of indentation technique to material degradation evaluation in the mercury target vessel for spallation neutron sources

Wakui, Takashi; Saito, Shigeru; Futakawa, Masatoshi

Jikken Rikigaku, 24(4), p.212 - 218, 2024/12

Irradiation damage is one of the main factors determining the lifetime of the mercury target vessel for spallation neutron source in J-PARC. To understand material degradation of the used vessels, it is planned to conduct an evaluation using inverse analyses with indentation tests on the structural materials of the used vessels and numerical experiments. This evaluation technique was applied to two kinds of ion-irradiated materials with different displacement damage doses, in which the irradiation condition was simulated. It could be confirmed that the ultimate strength increased, and the total elongation decreased with increasing irradiation. These trends are like the material degradation behaviors which have been reported by using small specimen's tensile tests.

Development of nanosized graphene material for neutron intensity enhancement below cold neutron energy

Teshigawara, Makoto; Ikeda, Yujiro*; Muramatsu, Kazuo*; Sutani, Koichi*; Fukuzumi, Masafumi*; Noda, Yohei*; Koizumi, Satoshi*; Saruta, Koichi; Otake, Yoshie*

Journal of Neutron Research, 26(2-3), p.69 - 74, 2024/09

https://doi.org/10.3233/JNR-240002

Slow neutrons, such as cold neutrons, are important non-destructive probes not only for basic physics but also for the structural genomics advancements in the life sciences and the battery technology advancements needed for the transition to a hydrogen society. Neutron-based science is also known as high-neutron-intensity-dependent science. A new unique method focusing on nanosized particle aggregation has been proposed to increase neutron intensity in that energy region. The method is based on intensity enhancement by multiple coherent scatterings with nanosized particle aggregation. The aggregation of nanosized particles matches the wavelength of below cold neutrons, causing a similar effect to coherent scattering, so-called Bragg scattering, leading to neutron intensity enhancement by several orders of magnitude. Nanodiamonds and magnesium hydride have recently been studied numerically and experimentally. The major challenge with nanodiamonds in practical applications is the molding method. Another carbon structure, graphene is focused on to find a solution to this problem. It is hypothesized that nanosized graphene could aid coherent neutron scattering under particle size conditions similar to nanodiamonds. We report the potential of nanosized graphene as a reflector material below cold neutrons, together with experimental results.

Single-shot laser-driven neutron resonance spectroscopy for temperature profiling

Lan, Z.*; Arikawa, Yasunobu*; Mirfayzi, S. R.*; Morace, A.*; Hayakawa, Takehito*; Sato, Hirotaka*; Kamiyama, Takashi*; Wei, T.*; Tatsumi, Yuta*; Koizumi, Mitsuo; et al.

Nature Communications (Internet), 15, p.5365_1 - 5365_7, 2024/07

https://doi.org/10.1038/s41467-024-49142-y

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.

Development of a miniature electromagnet probe for the measurement of local velocity in heavy liquid metals

Ariyoshi, Gen; Obayashi, Hironari; Sasa, Toshinobu

Journal of Nuclear Science and Technology, 59(9), p.1071 - 1088, 2022/09

https://doi.org/10.1080/00223131.2022.2030824

Electromagnetic induction method is one of the effective techniques for local velocity measurement in heavy liquid metals. Ricou and Vives' probe and Von Weissenfluh's probe are famous instrumentations using a permanent magnet. However, sensitivity and measurement volume of the probes show unexpected variation since demagnetization of the magnet is occurred by temperature increase up to the Curie temperature. In this study, electromagnetic probe incorporating a miniature electromagnet was newly developed to overcome such unexpected variation. The diameter and the length of the sensor was 6 mm and 155 mm, respectively. The sensitivity and the measurement volume of the probe were assessed by measurement of local velocity of flowing mercury in a square channel. To clarify the validity for the measured velocity profiles, numerical velocity profiles were calculated and compared with experiment. And the validity for the measured velocity profiles were confirmed by calculated result.

Integral experiment of I(n, ) using fast neutron source in the "YAYOI" reactor

Nakamura, Shoji; Toh, Yosuke; Kimura, Atsushi; Hatsukawa, Yuichi*; Harada, Hideo

Journal of Nuclear Science and Technology, 59(7), p.851 - 865, 2022/07

https://doi.org/10.1080/00223131.2021.2011794

The present study performed integral experiments of I using a fast-neutron source reactor "YAYOI" of the University of Tokyo to validate evaluated nuclear data libraries. The iodine-129 sample and flux monitors were irradiated by fast neutrons in the Glory hole of the YAYOI reactor. Reaction rates of I were obtained by measurement of decay gamma-rays emitted from I. The validity of the fast-neutron flux spectrum in the Glory hole was confirmed by the ratios of the reaction rates of flux monitors. The experimental reaction rate of I was compared with that calculated with both the fast-neutron flux spectrum and evaluated nuclear data libraries. The present study revealed that the evaluated nuclear data of I cited in JENDL-4.0 should be reduced as much as 18% in neutron energies ranging from 10 keV to 3 MeV, and supported the reported data by Noguere below 100 keV.

Current status and upgrading strategies of J-PARC Materials and Life Science Experimental Facility (MLF) and related components

Teshigawara, Makoto; Nakamura, Mitsutaka; Kinsho, Michikazu; Soyama, Kazuhiko

JAEA-Technology 2021-022, 208 Pages, 2022/02

JAEA-Technology-2021-022.pdf:14.28MB

The Materials and Life science experimental Facility (MLF) is an accelerator driven pulsed spallation neutron and muon source with a 1 MW proton beam. The construction began in 2004, and we started beam operation in 2008. Although problems such as exudation of cooling water from the target container have occurred, as of April 2021, the proton beam power has reached up to 700 kW gradually, and stable operation is being performed. In recent years, the operation experience of the rated 1 MW has been steadily accumulated. Several issues such as the durability of the target container have been revealed according to the increase in the operation time. Aiming at making a further improvement of MLF, we summarized the current status of achievements for the design values, such as accelerator technology (LINAC and RCS), neutron and muon source technology, beam transportation of these particles, detection technology, and neutron and muon instruments. Based on the analysis of the current status, we tried to extract improvement points for upgrade of MLF. Through these works, we will raise new proposals that promote the upgrade of MLF, attracting young people. We would like to lead to the further success of researchers and engineers who will lead the next generation.

Optimization of a slab geometry type cold neutron moderator for RIKEN accelerator-driven compact neutron source

Ma, B.*; Teshigawara, Makoto; Wakabayashi, Yasuo*; Yan, M.*; Hashiguchi, Takao*; Yamagata, Yutaka*; Wang, S.*; Ikeda, Yujiro*; Otake, Yoshie*

Nuclear Instruments and Methods in Physics Research A, 995, p.165079_1 - 165079_7, 2021/04

https://doi.org/10.1016/j.nima.2021.165079

We have optimized a cold neutron moderator to be operated at the RIKEN accelerator-driven compact neutron source. We selected a safe and easy to manage material, mesitylene, as the RANS cold moderator. An efficient moderator system was designed by studying and optimizing a coupled cold neutron moderator of mesitylene at 20 K with a polyethylene (PE) pre-moderator at room temperature in the slab geometry with Particle and Heavy Ion Transport code System (PHITS) simulations. The parameters of mesitylene and PE thickness, the reflector, and the shielding configuration were studied to increase cold neutron intensities. Consequently, an integrated cold neutron intensity of 1.1510n/cm/A at 2 m from the neutron-producing target was finally achieved, which was 12 times higher than that of the current PE moderator. The results showed attractive application prospect of mesitylene as cold neutron moderator material.

New design of high power mercury target vessel of J-PARC

Wakui, Takashi; Wakai, Eiichi; Kogawa, Hiroyuki; Naoe, Takashi; Hanano, Kohei*; Haga, Katsuhiro; Shimada, Tsubasa*; Kanomata, Kenichi*

Materials Science Forum, 1024, p.145 - 150, 2021/03

https://doi.org/10.4028/www.scientific.net/MSF.1024.145

To realize a high beam power operation at the J-PARC, a mercury target vessel covered with water shroud was developed. In the first step, to realize an operation at 500 kW, the basic structure of the initial design was followed and the connection method between the mercury vessel and the water shroud was changed. Additionally, the operation at a beam power of 500 kW was realized in approximately eight months. In the second step, to realize the operation at 1 MW, the new structure in which only rear ends of vessels were connected was investigated. Cooling of the mercury vessel is used to reduce thermal stress and thick vessels of the water shroud are used to increase stiffness for the internal pressure; therefore, it was adopted. The stress in each vessel was lower than the allowable stress based on the pressure vessel code criteria prescribed in the Japan Industrial Standard, and confirmation was obtained that the operation with a beam power of 1 MW could be conducted.

Recent status of the pulsed spallation neutron source at J-PARC

Takada, Hiroshi; Haga, Katsuhiro

JPS Conference Proceedings (Internet), 28, p.081003_1 - 081003_7, 2020/02

https://doi.org/10.7566/JPSCP.28.081003

At the Japan Proton Accelerator Research Complex (J-PARC), the pulsed spallation neutron source has been in operation with a redesigned mercury target vessel from October 2017 to July 2018, during which the operational beam power was restored to 500 kW and the operation with a 1-MW equivalent beam was demonstrated for one hour. The target vessel includes a gas-micro-bubbles injector and a 2-mm-wide narrow mercury flow channel at the front end as measures to suppress the cavitation damage. After the operating period, it was observed that the cavitation damage at the 3-mm-thick front end of the target vessel could be suppressed less than 17.5 m.