Cavitation damage prediction for the JSNS mercury target vessel

Naoe, Takashi; Kogawa, Hiroyuki; Wakui, Takashi; Haga, Katsuhiro; Teshigawara, Makoto; Kinoshita, Hidetaka; Takada, Hiroshi; Futakawa, Masatoshi

Journal of Nuclear Materials, 468, p.313 - 320, 2016/01

BB2014-2665.pdf:3.4MB

https://doi.org/10.1016/j.jnucmat.2015.08.035

Mercury target vessel in the JSNS, which is made of 316L SS, is damaged owing to the pressure wave-induced cavitation resulting from the proton beam bombardment. The cavitation damage decreases the structural integrity of the target vessel and is currently a dominant factor to decide the service life in compared with the radiation damage. Injecting microbubbles into mercury is one of the prospective techniques to mitigate the pressure waves and cavitation damage. In the JSNS, a microbubble generator with a gas circulation system was installed and has been operated since October 2012. The effects of microbubble injection into mercury on pressure wave mitigation were studied using a laser Doppler vibrometer. The result showed that the vibrational velocity of the target vessel is clearly reduced according to the increase of void fraction. An average peak vibrational velocity under 340 kW operation with the void fraction of 0.1% was reduced to 1/4 of that without injecting microbubbles.

Small gas bubble experiment for mitigation of cavitation damage and pressure waves in short-pulse mercury spallation targets

Riemer, B. W.*; Wendel, M. W.*; Felde, D. K.*; Sangrey, R. L.*; Abdou, A.*; West, D. L.*; Shea, T. J.*; Hasegawa, Shoichi; Kogawa, Hiroyuki; Naoe, Takashi; et al.

Journal of Nuclear Materials, 450(1-3), p.192 - 203, 2014/07

https://doi.org/10.1016/j.jnucmat.2013.10.011

Populations of small helium gas bubbles were introduced into a flowing mercury experiment test loop to evaluate mitigation of beam-pulse induced cavitation damage and pressure waves. The test loop was developed and thoroughly tested at the Spallation Neutron Source (SNS) prior to irradiations at the Los Alamos Neutron Science Center - Weapons Neutron Research Center (LANSCE-WNR) facility. Twelve candidate bubblers were evaluated over a range of mercury flow and gas injection rates by use of a novel optical measurement technique that accurately assessed the generated bubble size distributions. Final selection for irradiation testing included two variations of a swirl bubbler provided by Japan Proton Accelerator Research Complex (J-PARC) collaborators and one orifice bubbler developed at SNS. Bubble populations of interest consisted of sizes up to 150 m in radius with achieved gas void fractions in the 10 to 10 range. The nominal WNR beam pulse used for the experiment created energy deposition in the mercury comparable to SNS pulses operating at 2.5 MW. Nineteen test conditions were completed each with 100 pulses, including variations on mercury flow, gas injection and protons per pulse. The principal measure of cavitation damage mitigation was surface damage assessment on test specimens that were manually replaced for each test condition. Damage assessment was done after radiation decay and decontamination by optical and laser profiling microscopy with damaged area fraction and maximum pit depth being the more valued results. Damage was reduced by flow alone; the best mitigation from bubble injection was between half and a quarter that of flow alone. Other data collected included surface motion tracking by three laser Doppler vibrometers (LDV), loop wall dynamic strain, beam diagnostics for charge and beam profile assessment, embedded hydrophones and pressure sensors, and sound measurement by a suite of conventional and contact microphones.

Neutron Facility Group Center for Neutron Facility Japan Atomic Energy Research Institute

Kogawa, Hiroyuki

Jikken Rikigaku, 5(1), P. 64, 2005/03

no abstracts in English

Hardening effect on impact erosion in interface between liquid and solid metals

Futakawa, Masatoshi; Naoe, Takashi*; Kogawa, Hiroyuki; Ishikura, Shuichi*; Date, Hidefumi*

Zairyo, 53(3), p.283 - 288, 2004/03

https://doi.org/10.2472/jsms.53.283

no abstracts in English

R&D on mercury target pitting issue

Kikuchi, Kenji; Kogawa, Hiroyuki; Futakawa, Masatoshi; Ishikura, Shuichi*; Kaminaga, Masanori; Hino, Ryutaro

Journal of Nuclear Materials, 318(1-3), p.84 - 91, 2003/05

https://doi.org/10.1016/S0022-3115(03)00016-3

In mercury spallation target development pitting is a technical issue, which is appeared on the target vessel in conjunction with the pressure wave. Pitting is found in the off-beam line test by Split Hopkinson Pressure Bar (SHPB) test and then found in the on-beam test of mercury target at WNR of LANSCE. In SHPB tests pressure in mercury was reduced from 80, 40, 20 and 10MPa. And type 316 stainless steel was inspected before and after the impacting test at x450 magnification. Results show that over 20MPa pitting was generated. But at the lowest pressure in mercury, the number of pitting was very limited and substantial damage was small. Substantial damage by pitting is characterized by holes because mass will be removed from the wall. Depression itself may not be a substantial damage as long as it is not accompanied with holes.

Coupled behavior between structural body and liquid under impact loading

Kogawa, Hiroyuki; Ishikura, Shuichi*; Futakawa, Masatoshi; Hino, Ryutaro

Jikken Rikigaku, 2(2), p.122 - 127, 2002/06

https://doi.org/10.11395/jjsem2001.2.122

no abstracts in English

Structural integrity of heavy liqudi-metal target installed in spallation neutron facility, 2; Dynamic stress analysis of target container

Ishikura, Shuichi*; Kogawa, Hiroyuki; Teshigawara, Makoto; Kikuchi, Kenji; Futakawa, Masatoshi; Kaminaga, Masanori; Hino, Ryutaro

JAERI-Tech 2000-008, p.80 - 0, 2000/02

JAERI-Tech-2000-008.pdf:3.19MB

no abstracts in English

Structural integrity of heavy liquid-metal target instabled in neutron spallation facility, Part 1; Preliminary study on stress wave generated by irradiating pulsed-proton beam

Ishikura, Shuichi*; Kikuchi, Kenji; Futakawa, Masatoshi; Hino, Ryutaro

JAERI-Tech 97-037, 36 Pages, 1997/08

JAERI-Tech-97-037.pdf:0.92MB

no abstracts in English

Evaluatin of large leak sodium-water reaction events for the cover-gas type and non-cover-gas type steal generators (II); Large leak sodium-water reaction analysis (Report No.16)

*; *; *

PNC TN9410 88-068, 114 Pages, 1988/06

PNC-TN9410-88-068.pdf:7.15MB

Pressure behaviors in a large scale sodium-water reaction event were analyzed to clarify the effect of the location of a cover gas region and to reflect on the design study of the Large LMFBR plant of Japan. In the present study, initial spike pressures and quasi-static pressures were calculated by the SWACS code in the case that the pressure relief line was installed at the upper plenum of the non-cover gas type steam generator. The calculated results revealed as follows: The attachment of two 16 inch or one 24 inch diameter pipe on the upper plenum is more advisable than that of two 16 pipes on the lower and upper plenum, respectively, from the viewpoint of initial spike pressure depression and hydrogen gas expulsion. The shortening of the crossover-leg piping also has an initial spike pressure depression effect because the sodium free surface approaches the reaction zone.

Development of the techniques to mitigate the cavitation damages in the J-PARC mercury target

Haga, Katsuhiro; Kogawa, Hiroyuki; Naoe, Takashi; Wakui, Takashi; Futakawa, Masatoshi; Takada, Hiroshi

no journal, , 

For the mercury target of a pulsed spallation neutron source of J-PARC, cavitation damage of the target vessel wall which is caused by the pressure wave in mercury induced by high power pulsed proton beam of 1 MW is the crucial issue. In order to mitigate the cavitation damage, a microbubble injection technique has been developed. A microbubble generator to generate bubbles with a diameter less than 100m in mercury was developed and has been used in the mercury target system of J-PARC since October 2012. The effect of microbubble injection into mercury was verified by using a laser Doppler vibrometer (LDV). The measured data showed that the displacement velocity of the target vessel was reduced to 1/3 in average by injecting microbubbles. For further development of the high power target, we focused on the mercury flow effect to mitigate the cavitation damage. In order to realize this effect into the target design of J-PARC, we adopted doubled-walled structure to the beam window of the target vessel. The mercury flow channel with a narrow gap of 2 mm was made by adding an inner wall to just inside of the beam window. Numerical simulations were carried out using the conventional code, ANSYS FLUENT. While the mercury velocity outside of the narrow channel was 1.2 m/s, the mercury velocity in the narrow channel increased to almost 4 m/s, which was promising to suppress the cavitation damages.