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.

not registered; Fukumura, Nobuo*; not registered

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.