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Harada, Masahide; Sekijima, Mitsuaki*; Morikawa, Noriyuki*; Masuda, Shiho; Kinoshita, Hidetaka; Sakai, Kenji; Kai, Tetsuya; Kasugai, Yoshimi; Muto, Giichi*; Suzuki, Akio*; et al.
JPS Conference Proceedings (Internet), 33, p.011099_1 - 011099_6, 2021/03
In MLF at J-PARC, a unified mercury radioactivity monitor (UHAM) is installed to find an indication of failure of the mercury target and loop system by detecting radioactive materials leaked from the system with a 
-ray energy analysis with Germanium semi-conductor detectors (Ge detectors). It is composed of three units of sampling port and radiation monitors: (1) HAM for interstitial helium gas layer between the mercury vessel and surrounding water shroud of the mercury target, (2) CAM for atmosphere in the hot cell where the target loop is operated and (3) VAM for helium gas in the helium vessel where the target vessel is installed. Once any leakages of radioactive materials are detected, an alarm signal is issued immediately to the accelerator control system to stop beam operation. Software and hardware have been upgraded yearly. For example, two Ge detectors are used for HAM for redundancy, NaI Scintillation detectors are also used as supplemental for the Ge detector to keep availability of the system for high counting rate event. In April 2015, the UHAM activated when a small water coolant leakage from the water shroud of the mercury target occurred. VAM detected an abnormal increase of the counting rate in the helium vessel. It was also indicated that the measured radioactive nuclides were generated from the activation of the coolant (water) in the water shroud and not from the mercury.
Nemoto, Hideyuki; Wakai, Eiichi; Kinoshita, Hidetaka; Masuda, Shiho; Harada, Masahide; Takada, Hiroshi; Ishikawa, Koji*; Imanari, Kei*; Ito, Takeshi*
no journal, ,
no abstracts in English
Masuda, Shiho; Kai, Tetsuya; Harada, Masahide; Kinoshita, Hidetaka; Seki, Masakazu; Takagi, Motonori; Kasugai, Yoshimi; Haga, Katsuhiro
no journal, ,
Mercury is used as a target material for spallation neutron source at J-PARC. It is assumed that most of gaseous nuclides (tritium, noble gases and mercury vapor) among spallation products accumulate in the cover gas (helium) of the surge tank in the Mercury Circulation System (MCS). In the mercury target vessel replacement which is carried out every year, cover gas is transferred to the off-gas processing system before deinstallation of the vessel. It became clear from the previous operation that a certain amount of tritium and noble gases remain absorbed on the inner wall of the MCS. It is necessary to suppress release of these nuclides to the hot cell during vessel replacement. Therefore, the MCS was purged by helium several times to reduce the radioactivity concentration in the system. As a result, the purge was effective for the reduction of noble gas, but not for tritium. Therefore, at the time of replacement, air is drawn into the off-gas processing system via the MCS using a vacuum pump, thereby forming a air flow toward the inside (air-flow control) of the MCS at the opening to suppress the release of tritium out of the system. In this report, we will introduce the role of the off-gas processing system in mercury target vessel replacement and describe the efficacy to suppress the noble gas and tritium release, and future plan of system improvement.
Masuda, Shiho; Kai, Tetsuya; Harada, Masahide; Kinoshita, Hidetaka; Wakai, Eiichi; Nemoto, Hideyuki; Ikeda, Yujiro; Haga, Katsuhiro
no journal, ,
In the Materials and Life science experimental Facility at J-PARC, pulsed neutrons are provided by a mercury target via spallation reactions. During the target vessel replacement, gaseous spallation products are released from the mercury circulation system to outside. The release of radioactive gases needs to be reduced to a negligibly small level by a purging process in advance of replacement. The radioactivity of noble gases decreased by the purging process while that of tritium was almost unchanged. It is considered that most of tritium produced in mercury is accumulated in the vessel made of stainless-steel and is gradually desorbed during the purging and the vessel replacement. However, there have been no effective data associated with tritium behavior in an environment of mercury spallation target. Then, authors decided to develop an experimental system to understand these phenomena quantitatively and to discuss procedures to minimize tritium release during the vessel replacement. As a first step, we start experiments using deuterium before using tritium. Accumulation and release behaviors of deuterium to stainless-steel are examined under vacuum, controlled humidity and mercury coexistence conditions. Results are expected to be used to establish safer the target vessel replacement.
Masuda, Shiho; Kai, Tetsuya; Uehara, Toshiaki; Harada, Masahide; Kinoshita, Hidetaka; Sakai, Kenji; Haga, Katsuhiro
no journal, ,
no abstracts in English
