Integrity evaluation for welding of irradiated and un-irradiated type 316 stainless steels

Shibata, Akira; Nakamura, Natsuki; Futakawa, Masatoshi; Maekawa, Katsuhiro*

Zairyo Shiken Gijutsu, 62(1), p.35 - 40, 2017/01

Welding between irradiated and un-irradiated type 316 stainless steel is demanded for in-pile IASCC tests in Japan Materials Testing Reactor. Specimens were made from type 316 stainless steel which was irradiated up to 610 n/m( 1 MeV) in Reactor and welding tests of irradiated and un-irradiated type 316 stainless steels were performed to confirm integrity of the welding. Relationship between heat input and amount of Helium bubbles in welding bead was evaluated and hardness test was performed. It appeared that there is threshold value of heat input for welding without problem.

Corrosion properties of Zircaloy-4 and M5 under simulated PWR water conditions

Shibata, Akira; Kato, Yoshiaki; Taguchi, Taketoshi; Futakawa, Masatoshi; Maekawa, Katsuhiro*

Nuclear Technology, 196(1), p.89 - 99, 2016/10

https://doi.org/10.13182/NT16-54

Cladding material Zircaloy-4 is gradually replaced by M5 (Zr-Nb alloy) and other new Nb added Zirconium alloys which are expected to have long operating life. Corrosion tests on Zircaloy-4 and M5 were performed in various hydrogen concentrations in water to research corrosion properties of those alloys. Specimens were exposed under PWR conditions. Increase of oxide layer was analysed by weight gain and observation. Electro chemical impedance spectroscopy was performed to compare corrosion properties. And effect of dissolved hydrogen concentration on increase of oxide layer of M5 is smaller than that of Zircaloy-4. M5 is less affected by local uniformity of dissolved hydrogen concentration and is more suitable as PWR fuel cladding. Results of Electro chemical spectroscopy shows that structural significant difference existed in oxidizing reaction of Zircaloy-4 and M5.

Damage evaluation by impulsive response in structure filled with liquid

Wan, T.; Naoe, Takashi; Wakui, Takashi; Futakawa, Masatoshi; Maekawa, Katsuhiro*

Applied Mechanics and Materials, 566, p.629 - 636, 2014/06

https://doi.org/10.4028/www.scientific.net/AMM.566.629

A double-walled liquid mercury target vessel, which consists of outer and inner walls, is being globally developed for MW-class spallation neutron sources. When proton beams bombard a mercury target, pressure waves are generated due to the rapid thermal heat deposition. These pressure waves trigger impulsive vibrations in the mercury vessel, and cause cavitation damage to the inner wall of the vessel. In this study, the dependency of the vibration behavior of the mercury vessel on the damage is systematically investigated through numerical simulations and experiments, for inner wall damage characterized by hole diameters of 1, 5, 10, 20, and 40 mm. A method referred to as wavelet differential analysis is developed, and a parameter referred to as average intensity is derived for a quantitative damage evaluation. Both the numerical simulation and experimental results show that the average intensity is damage-sensitive and depends on the damage feature size. The critical damage hole diameter is estimated to be 10 mm during damage evaluation.

A Novel ultrasonic evaluation process for cavitation damage by combination of attenuation and higher harmonics

Wan, T.; Wakui, Takashi; Naoe, Takashi; Futakawa, Masatoshi; Maekawa, Katsuhiro*; Wan, T.*

Jikken Rikigaku, 13(4), p.387 - 394, 2013/12

http://ci.nii.ac.jp/naid/40019937781

The mercury target system is used for MW-scale neutron sources in the Japan Spallation Neutron Source. During this operation, cavitation damage is imposed on the mercury target vessel. It is very important to nondestructively evaluate the cavitation damage from the viewpoints of the structural integrity evaluation and lifetime estimation of the mercury target vessel. In this study, the cavitation damage was evaluated using a nonlinear ultrasonic method. First, the cavitation damage was imposed on plate specimens using an electro-Magnetic IMpact Testing Machine with 108 impact cycles. Nonlinear ultrasonic imaging was used to evaluate the damage. We found that the damping factor and higher harmonics of reflected waveforms from the damaged area can be used to evaluate the damage. An effective cavitation damage evaluation process has been developed based on our results. The evaluation process successfully detected minimal cavitation damage with peak-to-peak roughness of about 25 m.

Influence of Great East Japan Earthquake on neutron source station in J-PARC

Sakai, Kenji; Sakamoto, Shinichi; Kinoshita, Hidetaka; Seki, Masakazu; Haga, Katsuhiro; Kogawa, Hiroyuki; Wakui, Takashi; Naoe, Takashi; Kasugai, Yoshimi; Tatsumoto, Hideki; et al.

JAEA-Technology 2011-039, 121 Pages, 2012/03

JAEA-Technology-2011-039.pdf:10.87MB

This report investigates the behavior, damage and restoration of a neutron source station of the MLF at the Great East Japan Earthquake and verified the safety design for emergency accidents in the neutron source station. In the MLF, after an occurrence of the Earthquake, strong quakes were detected at the instruments, the external power supply was lost, all of the circulators shut down automatically, and the hydrogen gas was released. The leakages of mercury, hydrogen and radio-activation gases did not occur. While, the quakes made gaps between the shield blocks and ruptured external pipe lines by subsidence around the building. But significant damages to the components were not found though the pressure drop of compressed air lines influenced on a target trolley lock system and so on. These results substantiated the validity of the safety design for emergency accidents in the source station, and suggested several points of improvement.

Horonobe Underground Research Laboratory Project; Synthesis of phase I investigation 2001 - 2005, Volume "Geological disposal research"

Fujita, Tomoo; Taniguchi, Naoki; Matsui, Hiroya; Tanai, Kenji; Maekawa, Keisuke; Sawada, Atsushi; Makino, Hitoshi; Sasamoto, Hiroshi; Yoshikawa, Hideki; Shibata, Masahiro; et al.

JAEA-Research 2011-001, 193 Pages, 2011/03

JAEA-Research-2011-001.pdf:5.23MB

This report summarizes the progress of research and development on geological disposal during the surface-based investigation phase (2001-2005) in the Horonobe Underground Research Laboratory project, of which aims are to apply the design methods of geological disposal and mass transport analysis to actual geological conditions obtained from the surface-based investigations in the Horonobe Underground Research Laboratory project as an example of actual geological environment.

Microbubble formation at a nozzle in liquid mercury

Bucheeri, A.; Kogawa, Hiroyuki; Naoe, Takashi; Futakawa, Masatoshi; Haga, Katsuhiro; Maekawa, Katsuhiro*

Journal of Nuclear Science and Technology, 45(6), p.525 - 531, 2008/06

https://doi.org/10.3327/jnst.45.525

A mercury target for pulsed neutron sources is being developed in JAEA. Cavitation will be induced by pressure waves which are caused by high intense proton beam injection into the target. Microbubbles with 50 to 200 m in diameter injected in mercury are plausibly effective to mitigate cavitation. The mitigation is dependent on the conditions of bubble size and population. It is important to understand bubble formation behavior in mercury to develop microbubble injection method. CFD simulations were carried out to investigate the bubble formation behavior in mercury. Bubbles in stagnant mercury were visualized with X-ray to observe the formation behavior of bubbles at a micro-gas-nozzle and compared with the simulation results. It was found that high surface tension makes the bubble to grow around the outer surface of the nozzle in stagnant and makes it larger until its effect becomes small in the flow. The bubble diameter in stagnant increases with increasing the contact angle.

Basic approach to solute transport analysis utilizing information from surface-based investigations at two generic underground research laboratories

Maekawa, Keisuke; Sawada, Atsushi; Ota, Kunio; Kurikami, Hiroshi; Kunimaru, Takanori; Funaki, Hironori; Hama, Katsuhiro; Takeuchi, Shinji; Amano, Kenji; Saegusa, Hiromitsu; et al.

JAEA-Review 2007-011, 8 Pages, 2007/03

JAEA-Review-2007-011.pdf:0.66MB

In the current programme for research and development on the technical aspects of geological disposal, it is of significance to establish techniques for evaluating solute transport with a direct link to surface-based investigations through the processes of data interpretation, modelling and parameter designation within the immediate five years following the H17 Project. This report presents a basic approach to promoting multidisciplinary research activities involving field investigations and relevant solute transport analysis.

Laser surface alloying of SUS316 stainless steel with Al-Si; Effect of substrate temperature on structure and properties of modified layer

Zherebtsov, S.*; Maekawa, Katsuhiro*; Hayashi, Terutake*; Futakawa, Masatoshi

JSME International Journal, Series A, 48(4), p.292 - 298, 2005/10

The effect of temperature on the structure and properties of the type 316 stainless steel alloyed with Al-Si has been reported in the present paper. It has been found that four different types of structure are formed in the alloyed zone depending on the temperature of the substrate. These structures differ from each other in phase composition, microhardness and relation to cracking. Hard, crack-free microstructures are formed at temperatures of about 350 and 750 C. Maintaining the temperature of the sample at 350 C a uniform, crack-free layer with a high hardness is produced by laser alloying with an energy density of 0.76 W/mm.

Effect of proton beam profile on stress in JSNS target vessel

Kogawa, Hiroyuki; Ishikura, Shuichi*; Sato, Hiroshi; Harada, Masahide; Takatama, Shunichi*; Futakawa, Masatoshi; Haga, Katsuhiro; Hino, Ryutaro; Meigo, Shinichiro; Maekawa, Fujio; et al.

Journal of Nuclear Materials, 343(1-3), p.178 - 183, 2005/08

https://doi.org/10.1016/j.jnucmat.2004.08.032

A cross-flow type (CFT) mercury target with flow guide blades, which has been developed for JSNS, can suppress the generation of stagnant flow region especially near the beam window where the peak heat density is generated due to spallation reaction. Then, a flat type beam window has been applied to the CFT target from the viewpoint of suppressing dynamic stress caused by a pressure wave, which has been estimated with a mercury model of the linear equation of state. The recent experimental results obtained by using a proton beam incidents to mercury led that a cutoff pressure model in the equation of state of mercury caused a suitable dynamic stress with experimental results. Dynamic stress analyses were carried out with the cutoff pressure model, in which the negative pressure less than 0.15 MPa was not generated. The generated dynamic stress in the flat beam window became much larger than that in a semi-cylindrical type window. However, the generated stress in the semi-cylindrical type beam window was over the allowable stress of SS316L under the peak heat density of 668 W/cc. In order to decrease the dynamic stress in the semi-cylindrical beam window, the incident proton beam was defocused to decrease the peak heat density down to 218 W/cm. As a result, the dynamic stress could be suppressed less than the allowable stress. On the other hand, due to defocus of the proton beam, high heat density was generated on the end of the flow guide blades, which caused high thermal stress exceeding the allowable stress. To decrease the thermal stress, several shapes of the blade ends were studied analytically, which were selected so as not to affect the mercury flow distribution. A simple thin-end blade showed low thermal stress below the allowable stress.