2領域炉心臨界実験によるテスト領域未臨界度測定のための実験式の立式とその検証計算

Formulation of a new emprical formula for estimating the subcriticality of test-region from the critical experimental data on two-region coupled core system and verification calculations for the proposed formula.

古橋 晃*; 福村 信男*; 相原 永史*

not registered; Fukumura, Nobuo*; not registered

R.Averyの結炉理論を発展させ,DCA2領域炉心の臨界実験を行い,その情報からテスト領域単独の実効増倍率を導入するための式を考案・立式し,反応度摂動の種類別効果,実験上適当な摂動量の大きさおよび誤差等の評価を行い,式の妥当性と実験の成立性を考察した。これらの結果から,反応度摂動に伴う結合指数の変化を取り入れる必要があること,通常臨界実験装置の実験に用いられる反応度添加法即ち吸収摂動と水位摂動では結合指数の変化率が異なるとともに,かつその符号も条件により異なり得ることを明らかにするとともに,結合指数の変化率を一次式でとり入れた改良式により許容できる程度の誤差内でかなりの範囲の体系に適用できることを示した。実験上適当とされる反応度摂動量の大きさについても考察し,吸収法摂動では,0.2%K,水位摂動では0.01K程度を最大とすることを提案した。この摂動は小さいが,10B濃度の測定やドライバー領域水位の測定を高精度で行えば実施可能な範囲である。

A new empilical fomula which serves for estimating the unknown subcriticality or test region in the two-region coupled reactor system has been formulated as an extention of the coupled reactor theory by R.Avery. This formula will be available for the two-region coupled reactor critical experiment with some reactivity perturbation to the driver region. The validity of this formula has been studied from the view points of reactivity perturbation means, suitable amount of reactivity perturbation, probable error due to the structure of the formula and so on through the computer simulation calculations. From the results it has been found that the treatment of the change of the coupling index is indispensable but the linear change model of the coupling index adopted in our formula is simple and effective. The rate of the change of the coupling index will be fairly different between the case of absorption perturbation and the case of water level perturbation, but it has been found that our formulas will be applicable to both cases within the allowable error by properly estimating the coefficient of the linear change of coupling index and by choosing the details of the reactivity perturbation to be suited to the cases. The maximum amount of reactivity perturbation suitable for the present method has been found to be 0.2 % K in the absorption perturbation method or 0.01 % K in the water level perturbation method. These values require fairly high precision measurement of boron concentration or of the level of moderator in the driver region, but we expect the experiments will be possible under careful execution of the measurement and suitable application of our formurlas.