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「常陽」照射試験における照射条件評価精度の向上

Improvement of evaluation of irradiation test condition in JOYO

関根 隆; 北村 了一; 青山 卓史

not registered; Kitamura, Ryoichi; Aoyama, Takafumi

「常陽」の照射試験における照射条件評価精度の向上を目的として、連続エネルギーモンテカルロコード"MCNP"を導入し、炉心燃料集合体と反射体の境界における148Nd生成量を評価し、照射後試験による実測値と比較した。"MCNP"による計算では、「常陽」炉心管理コードシステム"MAGI"から求めた炉内の中性子源分布を用いて、評価対象としたINTA-2集合体内部の中性子束及びスペクトルを計算し、JNDC-V2の核分裂収率データを用いて148Nd生成量を評価した。これを同位体希釈質量分析法により測定した結果と比較した。その結果、"MCNP"は炉心中心方向から反射体に向かうにつれて軟らかくなる中性子スペクトルの変化を詳細に計算でき、"MCNP"による148Nd生成量計算値と実測値の比(C/E)は0.99$$sim$$1.00となり、両者は誤差範囲内で一致した。これにより、従来のHex-Z 7群拡散計算に基づく評価方法では十分な精度が得られなかった炉心燃料集合体と反射体の境界での照射試験における照射条件を"MCNP"により精度良く評価できることを確認した。

In order to improve the calculation accuracy of the irradiation test conditions in the experimental fast reactor JOYO, a three dimensional, continuous energy Monte Carlo code "MCNP" was employed. The fission product yields (148Nd) in the instrumented test assembly (INTA-2) which was loaded between the driver fuel subassemblies and reflectors were evaluated in this study. The results from the "MCNP" code were compared with the experimental values. In the calculation of the "MCNP" code, the neutron source distribution data which was calculated with the JOYO core management code system "MAGI" was used to evaluate the neutron flux and spectrum inside the INTA-2 subassembly. The $$^{148}$$Nd yields were evaluated with the calculated fission reactions and the fission yield data from JNDC-V2. The calculated $$^{148}$$Nd yields werc compared with the experimental values which were obtained from post irradiation examination results. The ratios of the "MCNP" values to experimental values of $$^{148}$$Nd yields are about 0.99$$sim$$1.00 of all pins. The "MCNP" code calculation values were within the range of the experimental error. These results indicate that the irradiation condition of the subassembly which was loaded next to the reflector can be evaluated accurately with the "MCNP" code.

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