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Terada, Atsuhiko; Hino, Ryutaro
no journal, ,
In JAEA, a simulation code system has been developed to analyze hydrogen behaviors including diffusion, combustion, explosion and structural integrity evaluation. As one of validation test of a numerical simulation system for leaked hydrogen gas behavior, we compared calculated results and time histories of helium gas concentration etc in large scale container which NUPEC executed. The calculated results using some concentration models show stratification phenomena with experimental results.
Sugawara, Takanori; Eguchi, Yuta; Obayashi, Hironari; Iwamoto, Hiroki; Tsujimoto, Kazufumi
no journal, ,
A new beam window concept for accelerator-driven system (ADS) is investigated by changing the design condition. New proton beam current, which is an important factor for the beam window design was derived by the neutronics calculation. Based on the new proton beam current, the investigation of the beam window was performed by the couple analyses of the particle transport, the thermal hydraulics and the structural analysis. Through these coupled analyses, it was found that hemispherical shapes with the outer radius = 180-235 mm and the thickness at the top = 1.5-3.5 mm were acceptable for the beam window.
Yamano, Hidemasa; Naruto, Kenichi*; Kurisaka, Kenichi; Nishino, Hiroyuki
no journal, ,
Spent fuels are transferred from a reactor core to a spent fuel pool through an external vessel storage tank (EVST) filled with sodium in sodium-cooled fast reactors in Japan. This paper describes identification of dominant accident sequences leading to fuel failure, which was achieved through probabilistic risk assessment for the EVST designed for a next sodium-cooled fast reactor plant system in Japan to improve the EVST design. The safety strategy for the EVST involves whole core refueling-early transfer of all core fuel assemblies into the EVST-assuming a severe situation that results in sodium level reduction leading finally to the top of the reactor core fuel assemblies in a long time. This study introduces the success criteria mitigation along the decay heat decrease over time. Based on the design information, this study has carried out identification of initiating events, event and fault tree analyses, a probability analysis for human error, and quantification of accident sequences. The fuel damage frequency of the EVST was evaluated to be approx. 10
/year. This study also quantitatively showed the effectiveness of design improvement.
Iioka, Tomoya*; Uyama, Masao*; Iyatomi, Yosuke; Mori, Kanta*; Saito, Hiroyuki*
no journal, ,
no abstracts in English
Nishimura, Satoshi*; Satake, Masaaki*; Nishi, Yoshihisa*; Kaji, Yoshiyuki; Nemoto, Yoshiyuki
no journal, ,
After the accident in Fukushima-Daiichi Nuclear Power Plants in 2011, deployment of spray and substitutional water inlet systems for cooling the spent fuels are recommended as safety measures against spent fuel pool (SFP) accident. In this work, analyses on an hypothetical accident which occurred by simultaneous lost of cooling ability and leaking of cooling water in SFP were conducted by using the severe accident code MAAP. For the counter measure optimization, water inlet condition to avoid cladding rupture was investigated.
Sato, Yuji; Shirahama, Takuma*; Ishibashi, Junichi*; Muramatsu, Toshiharu
no journal, ,
no abstracts in English
Kobayashi, Jun; Aizawa, Kosuke; Ezure, Toshiki; Kurihara, Akikazu; Tanaka, Masaaki
no journal, ,
The hot sodium from the fuel subassembly can mix with the cold sodium from the control rod channel and the blanket assemblies at the bottom of Upper Internal Structure (UIS) in an advanced-sodium cooled fast reactor (A-SFR). Temperature fluctuation due to mixing of the fluids at different temperature between the core outlet and the bottom of the UIS may cause high cycle thermal fatigue on the structure around the bottom of the UIS. A water experiment using a 1/3 scale 60 degree sector model simulating the upper plenum of the A-SFR has been conducted to examine countermeasures for the significant temperature fluctuation generated around the bottom of UIS. As a result of temperature distribution measurement around the radial blanket fuel subassemblies, a large temperature fluctuation was observed. In order to reduce this temperature fluctuation, the shape of Core Instrumentation Support Plate edge was improved. The countermeasure to mitigate the temperature fluctuation intensity was applied and its effectiveness was confirmed.
Suzuki, Minoru*; Sakai, Takaaki*; Takata, Takashi; Doda, Norihiro
no journal, ,
With an aim to establish a quantitative risk assessment of accident managements (AMs) for various external hazards, the plant dynamics analyses with Continuous Markov Chain Monte Carlo (CMMC) method were carried out to assess repeatedly occurred multi-failures by volcano ash in volcanic eruption event. AM repetition of the filter exchange to recover the cooling function of the air coolers (ACs) of auxiliary cooling system (ACS) were considered. The uncertainty of AM measure was set as a parameter. The results showed that extending the endurance time of ACS-AC filter was effective as AM measure against volcanic ash hazard.