報告書番号

T97004

タイトル（和文）

金属燃料要素における燃料－被覆管機械的相互作用の解析的評価

タイトル（英文）

ANALYTICAL EVALUATION OF FUEL -CLADDING MECHANICAL INTERACTION IN METALLIC FUEL PINS

概要 （図表や脚注は「報告書全文」に掲載しております）

金属燃料挙動解析コードＡＬＦＵＳにおいて，大クラックによる燃料スラグ径増加を模擬するモデルの導入，固体ＦＰスエリング速度の設定，等を行うことにより，Ｕ－Ｐｕ－Ｚｒ合金燃料の高燃焼度までのＦＣＭＩ挙動を定量的に解析することができるようになった。ＡＬＦＵＳの妥当性は，ＥＢＲ－ＩＩ試験燃料の照射データによって確認した。ＬＦＵＳを緩和するオープンポアの量が欠乏する高燃焼度では，固体ＦＰの蓄積によって高いＦＣＭＩが発生すること，高スメア密度燃料では，オープンポアが欠乏する時期が早まるため早期に高いＦＣＭＩが発生すること，などの結論が得られた。さらに，約７５％以上のスメア密度であっても，目標燃焼度に応じて，プレナム長さやスメア密度などを調整すれば，最適な燃料要素設計が可能であるとの見通しが得られた。

概要 （英文）

THE IRRADIATION BEHAVIOR ANALYSIS CODE, ALFUS, FOR METALLIC FUEL PINS HAS BEEN IMPROVED TO QUANTIFY THE FUEL-CLADDING MECHANICAL INTERACTION (FCMI) OF U-PU-ZR FUEL PINS AT HIGHER BURNUP.THE EFFECT OF LARGE RADIAL CRACKS OCCURRING DURING THE EARLY IRRADIATION STAGE HAS BEEN INCORPORATED INTO THE BOUNDARY CONDITION FOR THE FUEL-CLADDING CONTACT STATE. THE VOLUME INCREASE IN THE FUEL SLUG DUE TO SOLID-STATE FISSION PRODUCT ACCUMULATION (SOLID FP SWELLING) WAS DETERMINED BASED ON THE BURNUP CALCULATION. THE IMPROVED ALFUS CODE REASONABLY SIMULATES THE FCMI BEHAVIOR OF THE U-PU-ZR FUEL PINS UP TO HIGHER BURNUP. ANALYSES OF EBR-II IRRADIATION TEST PINS AND LARGER PROTOTYPE FUEL PINS LEAD TO THE FOLLOWING CONCLUSIONS ON FCMI BEHAVIOR; (1)FCMI STRESS IS SIGNIFICANT AT THE LOWER PART OF THE PIN WHERE THE VOLUME DECREASE OF OPEN PORES IS SMALLER DUE TO THE LOWER FUEL TEMPERATURE. (2)FISSION GAS BUBBLES AND SOLID FP SWELLING ARE ACCOMMODATED BY THE VOLUME DECREASE OF OPEN PORES. HOWEVER, AT HIGHER BURNUP, THE VOLUME OF THE OPEN PORES BECOMES INSUFFICIENT AND HIGHER FCMI OCCURS DUE TO ACCUMULATION OF SOLID FISSION PRODUCTS. RAISING THE FUEL SMEAR DENSITY ADVANCES THE OPEN PORE SHORTAGE, LEADING TO EARLIER OCCURRENCE OF HIGHER FCMI. WHILE APPROXIMATELY 75% SMEAR DENSITY FUELS HAVE BEEN DESIGNED AND TESTED AS DRIVER FUELS, A HIGHER SMEAR DENSITY FUEL CAN BE DESIGNED BY ADJUSTING THE PIN SPECIFICATION, WHICH INCLUDES THE PLENUM LENGTH AND THE SMEAR DENSITY, ACCORDING TO THE TARGET BURNUP.

報告者

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