SAFETY OF THE SUPER LWR

Ishiwatari, Yuki,Oka, Yoshiaki,Koshizuka, Seiichi Korean Nuclear Society 2007 Nuclear Engineering and Technology Vol.39 No.4

Supercritical water-cooled reactors (SCWRs) are recognized as a Generation IV reactor concept. The Super LWR is a pressure-vessel type thermal spectrum SCWR with downward-flow water rods and is currently under study at the University of Tokyo. This paper reviews Super LWR safety. The fundamental requirement for the Super LWR, which has a once-through coolant cycle, is the core coolant flow rate rather than the coolant inventory. Key safety characteristics of the Super LWR inhere in the design features and have been identified through a series of safety analyses. Although loss-of-flow is the most important abnormality, fuel rod heat-up is mitigated by the "heat sink" and "water source" effects of the water rods. Response of the reactor power against pressurization events is mild due to a small change in the average coolant density and flow stagnation of the once-through coolant cycle. These mild responses against transients and also reactivity feedbacks provide good inherent safety against anticipated-transient-without-scram (ATWS) events without alternative actions. Initiation of an automatic depressurization system provides effective heat removal from the fuel rods. An "in-vessel accumulator" effect of the reactor vessel top dome enhances the fuel rod cooling. This effect enlarges the safety margin for large LOCA.

Ophiolite belts in Northeast Asia: Importance of the Plume-type

Akira Ishiwatari,Ganbat Erdenesaihan,Yuji Ichiyama 대한지질학회 2013 대한지질학회 학술대회 Vol.2013 No.10

SAFETY OF THE SUPER LWR

YUKI ISHIWATARI 한국원자력학회 2007 Nuclear Engineering and Technology Vol.39 No.4

Supercritical water-cooled reactors (SCWRs) are recognized as a Generation IV reactor concept. The Super LWR is a pressure-vessel type thermal spectrum SCWR with downward-flow water rods and is currently under study at the University of Tokyo. This paper reviews Super LWR safety. The fundamental requirement for the Super LWR, which has a oncethrough coolant cycle, is the core coolant flow rate rather than the coolant inventory. Key safety characteristics of the Super LWR inhere in the design features and have been identified through a series of safety analyses. Although loss-of-flow is the most important abnormality, fuel rod heat-up is mitigated by the “heat sink” and “water source” effects of the water rods. Response of the reactor power against pressurization events is mild due to a small change in the average coolant density and flow stagnation of the once-through coolant cycle. These mild responses against transients and also reactivity feedbacks provide good inherent safety against anticipated-transient-without-scram (ATWS) events without alternative actions. Initiation of an automatic depressurization system provides effective heat removal from the fuel rods. An “in-vessel accumulator” effect of the reactor vessel top dome enhances the fuel rod cooling. This effect enlarges the safety margin for large LOCA.

외국인 유학생의 한국어능력에 영향을 미치는 고등교육기관의 교육환경 요소 분석

이정현,안병훈,Ishiwatari Atsuki,Kawanami Reina 사단법인 한국융합기술연구학회 2024 아시아태평양융합연구교류논문지 Vol.10 No.2

본 연구는 외국인 유학생의 한국어 능력에 영향을 미치는 대학의 교육환경요소들을 분석하는데 목적이 있다. 외국인 유학생 중 TOPIK(Test of Proficiency in Korean) 4급 이상 획득한 학생비율을 종속변수로 하여 대학환경의 네 가지 요소인 학교 고정적 특성, 국제적 요소, 경제적 요소, 교육시설 등 각 요소들이 어떠한 영향을 주는지 살펴보았다. 분석에는 에듀데이터서비스(EDSS: EduData Service System)에서 제공하는 8년간의 자료(2014~2021년)를 활용하여 연도별 200개 내외 대학을 분석하였다. 기간동안 6년 이상 통계적으로 유의미한 영향을 나타내는 요소는 수도권 소재지인 경우, 대규모인 경우, 사립의 경우, 분교의 형태인 것으로 나타났다. 국제적 요소에서 외국인 유학생 비율이 부적인 영향을 미치고 있는 것으로 나타났다. 경제적 요소와 시설에 관한 변수의 경우 이번 분석 결과에서 유의한 결과가 나타나지 않았다. 연구결과에 따라, 외국인 유학생의 대학 내 교육환경 개선방안의 기초자료, 각 대학의 외국인 유학생을 대상으로 하는 재정지원 방안의 기초자료, 각 대학의 외국인 유학생을 대상으로 한 학습지원 프로그램 설계에 활용될 수 있다고 보았다. 마지막으로 외국인 유학생의 비율 증가에 따라 한국인 학생과 교류할 수 있는 프로그램의 확대와 지원을 제언하였다. This study aims to analyze the factors of the university's educational environment that affect the Korean language ability of international students. Using the proportion of international students. who obtained TOPIK level 4 or higher as a dependent variable, this study examined how each factor affects four areas of the university environment: school fixed characteristics, international factors, economic factors, and educational facilities. Eight years of data (2014-2021) provided by EduData Service (EDSS) were used for the analysis. As a result of the study, it was slightly different from year to year, but in the location of the metropolitan area, large-scale, private, and branch schools showed a significant effect. Regarding international factors, it was found that the proportion of international students had a negative impact. In the case of variables related to economic factors and facilities, no significant results were found in the results of this analysis. According to the research results, it can be used to design basic data on how to improve the educational environment of international students in universities, basic data on financial support plans for international students at each university, and learning support programs for international students at each university. Finally, as the proportion of international students increased, it was suggested that programs to interact with Korean students be expanded and supported. Accordingly, as the proportion of international students increases, developing and supporting programs that can interact with Korean students is suggested.

Detecting Early Pancreatic Cancer: Current Problems and Future Prospects

Hiroyuki Matsubayashi,Hirotoshi Ishiwatari,Keiko Sasaki,Katsuhiko Uesaka,Hiroyuki Ono 거트앤리버 소화기연관학회협의회 2020 Gut and Liver Vol.14 No.1

The number of patients with pancreatic cancer (PC) is currently increasing in both Korea and Japan. The 5-year survival rate of patients with PC 13.0%; however, resection with minimal invasion (tumor size: ≤10 mm) increases the 5-year survival rate to 80%. For this reason, early detection is essential, but most patients with early-stage PC are asymptomatic. Early detection of PC has been reported to require screening of high-risk individuals (HRIs), such as those with a family history of PC, inherited cancer syndromes, intraductal papillary mucinous neoplasm, or chronic pancreatitis. Studies on screening of these HRIs have confirmed a significantly better prognosis among patients with PC who were screened than for patients with PC who were not screened. However, to date in Japan, most patients with early-stage PC diagnosed in routine clinics were not diagnosed during annual health checks or by surveillance; rather, PC was detected in these patients by incidental findings during examinations for other diseases. We need to increase the precision of the PC screening and diagnostic processes by introducing new technologies, and we need to pay greater attention to incidental clinical findings.

THREE-DIMENSIONAL CORE DESIGN OF A SUPER FAST REACTOR WITH A HIGH POWER DENSITY

Cao, Liangzhi,Oka, Yoshiaki,Ishiwatari, Yuki,Ikejiri, Satoshi,Ju, Haitao Korean Nuclear Society 2010 Nuclear Engineering and Technology Vol.42 No.1

The SuperCritical Water-cooled Reactor (SCWR) pursues high power density to reduce its capital cost. The fast spectrum SCWR, called a super fast reactor, can be designed with a higher power density than thermal spectrum SCWR. The mechanism of increasing the average power density of the super fast reactor is studied theoretically and numerically. Some key parameters affecting the average power density, including fuel pin outer diameter, fuel pitch, power peaking factor, and the fraction of seed assemblies, are analyzed and optimized to achieve a more compact core. Based on those sensitivity analyses, a compact super fast reactor is successfully designed with an average power density of 294.8 W/$cm^3$. The core characteristics are analyzed by using three-dimensional neutronics/thermal-hydraulics coupling method. Numerical results show that all of the design criteria and goals are satisfied.

Comparison of the Diagnostic Yield of the Standard 22-Gauge Needle and the New 20-Gauge Forward-Bevel Core Biopsy Needle for Endoscopic Ultrasound-Guided Tissue Acquisition from Pancreatic Lesions

( Shinya Fujie ),( Hirotoshi Ishiwatari ),( Keiko Sasaki Junya Sato ),( Hiroyuki Matsubayashi ),( Masao Yoshida ),( Sayo Ito ),( Noboru Kawata ),( Kenichiro Imai ),( Naomi Kakushima ),( Kohei Takizawa 대한간학회 2019 Gut and Liver Vol.13 No.3

Background/Aims: To compare the diagnostic yield of 20-gauge forward-bevel core biopsy needle (CBN) and 22-gauge needle for endoscopic ultrasound (EUS)-guided fine needle aspiration (FNA) of solid pancreatic masses. Methods: The use of 20-gauge CBN was prospectively evaluated for 50 patients who underwent EUS-FNA from June 2016 to December 2016. Data were compared with those obtained by a retrospective study of 50 consecutive patients who underwent EUS-FNA using standard 22-gauge needles between December 2016 and April 2017. At least two punctures were performed for each patient; the sample from the first pass was used for cytology with or without histology and that from the second pass was used for histology. Sample quantity was evaluated using the sample obtained from the second pass. Results: There was no significant difference in the diagnostic accuracy rate between the first and second passes (20-gauge CBN: 96% [48/50]; standard 22-gauge needle: 88% [44/50]). Samples >10× power fields in length were obtained from 90% (43/48) and 60% (30/50) of patients using the 20-gauge CBN and standard 22-gauge needle, respectively (p=0.01). Technical failure occurred for two patients with the 20-gauge CBN. Conclusions: Diagnostic accuracy of the 20-gauge CBN was comparable to that of the 22-gauge needle. However, two passes with the 20-gauge CBN yielded a correct diagnosis for 100% of patients when technically feasible. Moreover, the 20-gauge CBN yielded core tissue for 90% patients, which was a performance superior to that of the 22-gauge needle. (Gut Liver 2019;13:349-355)

Subchannel analysis of supercritical light water-cooled fast reactor assembly

Yoo, J.,Oka, Y.,Ishiwatari, Y.,Yang, J.,Liu, J. North-Holland Pub. Co 2007 Nuclear engineering and design Vol.237 No.10

Subchannel analyses have been carried out for supercritical water-cooled fast reactor fuel assembly. Peak cladding surface temperature difference arising from subchannel heterogeneities have been calculated by using the improved subchannel analysis code STARS and was evaluated to be about 18.5<SUP>o</SUP>C. Several suggestions have been also made for reducing the PCST difference arising from channel heterogeneity. Influences of local power peaking on deflection of cladding surface temperature are explained with pin power distribution taken from core depletion calculation in this paper. Maximum cladding surface temperature at nominal condition is evaluated to be 645.3<SUP>o</SUP>C over the cycle. Statistical thermal design uncertainty associated with PCST calculation is evaluated by Monte-Carlo sampling technique combined with subchannel analysis code. Maximum statistical design uncertainty of PCST is calculated to be 31<SUP>o</SUP>C and is in a good agreement with that from RTDP method. Influence of downward flow in seed region on system sensitivity is investigated by improved Monte-Carlo thermal design procedure. Limiting thermal condition of MCST is 681<SUP>o</SUP>C (650<SUP>o</SUP>C of nominal+31<SUP>o</SUP>C) within 95/95 limit for SWFR.

A Prospective Multicenter Study Evaluating Bleeding Risk after Endoscopic Ultrasound-Guided Fine Needle Aspiration in Patients Prescribed Antithrombotic Agents

( Kazumichi Kawakubo ),( Kei Yane ),( Kazunori Eto ),( Hirotoshi Ishiwatari ),( Nobuyuki Ehira ),( Shin Haba ),( Ryusuke Matsumoto ),( Keisuke Shinada ),( Hiroaki Yamato ),( Taiki Kudo ),( Manabu Onod 대한소화기학회 2018 Gut and Liver Vol.12 No.3

Background/Aims: Although the risk of bleeding after endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) is low, the safety of EUS-FNA in patients prescribed antithrombotic agents is unclear. Therefore, this study evaluated the incidence of bleeding after EUS-FNA in those patients. Methods: Between September 2012 and September 2015, patients who were prescribed antithrombotic agents underwent EUS-FNA at 13 institutions in Japan were prospectively enrolled in the study. The antithrombotic agents were managed according to the guidelines of the Japanese Gastrointestinal Endoscopy Society. The rate of bleeding events, thromboembolic events and other complications within 2 weeks after EUS-FNA were analyzed. Results: Of the 2,629 patients who underwent EUS-FNA during the study period, 85 (62 males; median age, 74 years) patients were included in this stduy. Two patients (2.4%; 95% confidence interval [CI], 0.6% to 8.3%) experienced bleeding events. One patient required surgical intervention for hemothorax 5 hours after EUS-FNA, and the other experienced melena 8 days after EUS-FNA and required red blood cell transfusions. No thromboembolic events occurred (0%; 95% CI, 0.0% to 4.4%). Three patients (3.5%; 95% CI, 1.2% to 10.0%) experienced peri-puncture abscess formation. Conclusions: The rate of bleeding after EUS-FNA in patients prescribed antithrombotic agents might be considerable. (Gut Liver 2018;12:353-359)

Three-dimensional Core Design of a Super Fast Reactor with a High Power Density

LIANGZHI CAO,YOSHIAKI OKA,YUKI ISHIWATARI,SATOSHI IKEJIRI,HAITAO JU 한국원자력학회 2010 Nuclear Engineering and Technology Vol.42 No.1

The SuperCritical Water-cooled Reactor (SCWR) pursues high power density to reduce its capital cost. The fast spectrum SCWR, called a super fast reactor, can be designed with a higher power density than thermal spectrum SCWR. The mechanism of increasing the average power density of the super fast reactor is studied theoretically and numerically. Some key parameters affecting the average power density, including fuel pin outer diameter, fuel pitch, power peaking factor, and the fraction of seed assemblies, are analyzed and optimized to achieve a more compact core. Based on those sensitivity analyses, a compact super fast reactor is successfully designed with an average power density of 294.8 W/cm3. The core characteristics are analyzed by using three-dimensional neutronics/thermal-hydraulics coupling method. Numerical results show that all of the design criteria and goals are satisfied.