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小宮山 大輔
no journal, ,
To understand the behaviors of leaker fuels under LOCA condition, the difference in fracture boundaries between normal and leaker fuels was investigated by semi-integral LOCA tests for the test rods with/without a pinhole. The fracture boundary of test rods with a pinhole was similar to that of reference test rods below 1200 
C, but a little bit lower above 1200 C under fully restrained condition; while under 540 N partially restrained condition, it was a little higher in the case of test rods with a pinhole.
Li, F.
no journal, ,
Mechanical response of pre-cracked zircaloy-4 tubes under biaxial EDC conditions had been studied. Typical strain ratios under RIA conditions, which varies from 0 to 1, was considered as a key parameter of the experiments. Tubes of three different heat treatment conditions: stress relieved, cold worked and recrystallized, had been used in this research. The results showed that larger strain ratio and larger pre-crack depth lead to lower circumferential strain at failure. Metallographic structure and texture seem to have influence to crack propagation under biaxial EDC conditions.
成川 隆文
no journal, ,
JAEA has conducted studies on fuel behaviors under loss-of-coolant-accident (LOCA) conditions with both unirradiated and high-burnup advanced fuel cladding tubes. As a result, various kinds of information have been obtained on behaviors of these cladding tubes under LOCA conditions: oxidation, ballooning and rupture, thermal shock resistance (fracture/non-fracture conditions), post-LOCA mechanical strength, etc. In addition, new LOCA tests are planned at JAEA for the purpose of investigating effects of phenomena of fuel fragmentation, relocation and dispersal (FFRD) on fuel behaviors and coolability of reactor core during LOCA. It is expected that these results including those obtained by the future study provide necessary information for future regulation on high-burnup fuels with advanced cladding alloys.
宇田川 豊
no journal, ,
JAEA launched ALPS-II program in 2010 in order to obtain regulatory data for advanced fuels. Five new reactivity-initiated accident (RIA) simulated tests on the advanced fuels have been performed. The first two fuels tested, VA-5 and VA-6, were 17
17-PWR-type with stress-relieved and recrystallized M-MDA cladding tube, and irradiated to ~80 GWd/tU. The cladding failed due to the pellet-cladding mechanical interaction. The following two tests, VA-7 and VA-8, with sibling test rods and high temperature coolant condition showed temperature effect; the VA-7 test rod survived and the VA-8 test rod failed at higher fuel enthalpy level than VA-6. Also the GR-1 test, with M5 cladding and irradiated to 84 GWd/tU, was performed at room temperature condition and the fuel did not fail.
天谷 政樹
no journal, ,
原子力機構における燃料安全研究の目的は、軽水炉燃料に関して現在の規制基準や安全裕度の妥当性を評価すること、新材料からなる被覆管やペレットを使用した改良型燃料に係る規制のためのデータを提供すること、及び規制に活用可能な計算コードを提供することである。本発表では、最近の反応度事故(RIA)模擬試験、冷却材喪失事故(LOCA)模擬試験の進捗に加え、原子力機構における燃料安全研究の概況を報告する。
Negyesi, M.
no journal, ,
The presentation deals with oxidation behavior of Zry-4 alloy during severe accidents of LWR. Zry-4 fuel cladding was exposed in steam-air mixtures at temperatures of 1000-1200 C. Specimen weight gain was measured, metallographic observations were carried out, hydrogen uptake was determined and ring compression tests were conducted. The oxidation kinetics of Zry-4 was significantly affected by the air fraction in steam at 1000 C in the post-transient regime and at 1200 C. The effect of air fraction was diminished at 1000 C in the pre-transient regime. Metallographic examination revealed severe oxide layer cracking and nitride formation. Substantial hydrogen pick-ups were measured, especially at 1000 C after 60 min, strongly depending on the air fraction. They probably led to the significant decrease in plastic strain at 1000 C after 60 min. The effect of air fraction on plastic strain has been hardly observed at 1200 C.
三原 武
no journal, ,
燃焼の進んだ燃料の反応度事故模擬実験でみられているペレット被覆管相互作用(PCMI)破損に関し、被覆管に生じる多軸応力がその変形及び破損挙動に及ぼす影響を調べた。応力除去焼鈍及び再結晶焼鈍処理を行った未照射被覆管を対象に、室温で二軸荷重負荷試験を実施した。試験で取得した軸・周ひずみから応力ひずみ曲線を求めた。これらの曲線から、試験を行った応力比において同じ塑性仕事を行った場合の軸・周応力の値を読み取った点の集合である等塑性仕事面を得た。これらの形状が等方性材料の理論的な降伏曲面を表すミーゼス降伏条件と異なっていたことから、試験に供した被覆管の多軸応力条件における変形挙動には異方性があることが分かった。また、反応度事故時に発生しうる応力比条件下における破損時ひずみの応力比依存性によると、破損時ひずみが最小となる応力比は、応力除去焼鈍材と再結晶焼鈍材とで異なることが分かった。
湯村 尚典
no journal, ,
Fuel safety during long-term cooling following a LOCA sequence has been a key issue since the accident at the Fukushima Daiichi Nuclear Power Plant. In order to investigate effects of ballooning and rupture on the fracture resistance of cladding tube, the relationship between the fracture resistance and the cladding deformation due to ballooning and rupture is investigated by performing four-point-bend test on non-irradiated Zircaloy-4 cladding tube specimen. As a result, the maximum bending moment at fracture decreased with increasing the maximum circumferential strain. However, the correlation between the maximum bending moment and the size of rupture opening was not clear. The oxidation and stress concentration in the region around rupture opening seemed to be more effective on the fracture position than those of the secondary hydriding within the examined conditions.
谷口 良徳
no journal, ,
In the current Japanese regulation concerning fuel safety, a part of Japanese PCMI failure criteria was determined based on the result of SPERT-CDC test 859 (SPERT859). In this study, the corrosion formed on the cladding outer surface of SPERT859 test rod and the fuel enthalpy increase at PCMI failure of the test rod under the corrosion condition were estimated by using fuel performance codes FEMAXI-7 and RANNS. The result of FEMAXI-7 indicated that the cladding of the test rod had probably excessive corrosion in consideration of the effect of pellet swelling. The result of RANNS suggested that the fuel enthalpy at failure of SPERT859 was affected by the excessive corrosion on the cladding of the test rod.