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新型燃料高速炉の炉心核特性評価

Physics parameter evaluation of advanced fuel FBR cores

三田 敏男*; 白方 敬章*; 金城 勝哉他*

Sanda, Toshio*; not registered; not registered

金属、炭化物、窒化物などいわゆる新型燃料の高速炉燃料としての実用化の可能性を評価する一環として、新型燃料高速炉の炉心核特性を酸化物燃料炉心との比較において評価した。昭和63年度作業として以下のような結果を得た。新型燃料の臨界実験及び炉心設計例を調査した。新型燃料の臨界実験例は少なく、今後設計が進むにつれてその精度をつめる上でさらに詳細な実験が必要になる。一方、炉新設計は最近各国で精力的に実施されており、その設計上の特徴と問題点をまとめた。また、新型燃料炉心の核計算で必要となる断面積のうち、ZR,NはJENDL-2に収納されていないので、JENDL-3のものを用いる必要がある。新型燃料炉心と酸化物燃料炉心の核特性の差及びその要因を検討した。設定炉心は、2領域均質炉心で、炉心形状や出力密度を一定とする条件で検討した。主な成果は以下の通りである。新型燃料炉心では、大幅な増殖性向上が得られ、燃焼反応度をほぼ0とすることができる。また増殖比は、新型燃料炉心では酸化物燃料炉心に比べ0,2程度向上できる。金属燃料炉心では、スペクトル硬化と実効核分裂断面積の減少等の要因のため、高速フルエンスは酸化物燃料炉心に比べて30%程度増大する。金属燃料炉心では、ドップラー係数の絶対値が減少し、ナトリウムボイド係数が増大し、炉心安全解析の観点からは悪くなる方向である。一方、膨張による温度係数は金属燃料でより負側となる(燃料膨脹、炉心支持板膨脹)。

Physics parameters were evaluated for FBR Cores with new fuels, i.e., metal, carbide and nitride fuels in comparison with the oxide fuel cores. The main results in FY'88 are as follows. (1)Some critical experiments and FBR core designs with new fuels were investigated and reviewed from the view point of nuclear characteristics of the core, For Zr and N cross sections, which are needed for new fuel cores, JENDL-3 library data must be used because these cross sections are not included in JENDL-2 library. (2)Physics parameters were compared between new fuels and oxide fuel cores. The conventional two-zone homogeneous core was selected for the calculation. The four cores were designed to be equal to another in dimension, core configuration, specific power density and peak linear heat rate, Comparisions are summarized as follows. (i)The burn-up reactivity loss is decreased to be nearly zero for the new fuel cores, and the breeding ratio is raiseed by about 0.2 for the new fuel cores compared with the oxide core. (ii)The maximum fast neutron fluence of the metal fuel core is about 30% larger than the oxide core due to harder spectrum and decreased effective fission cross section. (iii)The Na void reactivity and the Doppler coefficient for the metal fuel core are worse than those for the oxide core from the safety point of view, but reactivity coefficients due to fuel axial and radial expansion becomes more negative, (3)Cross section sensitivity analyses were conducted and uncertainties of core parameters due to cross section uncertainties were evaluated using cross section sensitivities and covariances. It was made clear that their total sensitivities to individual cross sections, except oxygan, were not very much different between the metal and oxide fuel core, though 100KeV$$sim$$1MeV sensitivities for the metal are larger than those for the oxide fuel core. The uncertainties of core parameters due to cross section uncertainties are almost equal for the ...

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