Theoretical study on new bias factor methods to effectively use critical experiments for improvement of prediction accuracy of neutronic characteristics

Kugo, Teruhiko ; Mori, Takamasa; Takeda, Toshikazu*

The extended methods with two concepts, the LC and the PE methods, are proposed to enhance the bias factor method for improvement of the prediction accuracy of neutronic characteristics. The two methods utilize a number of critical experimental results and produce a semi-fictitious experimental value with them. The LC method defines a bias factor by a ratio of a linear combination of experimental values to that of calculation values for the experiments. The PE method defines it by a ratio of a product of exponentiated experimental values to that of exponentiated calculation values. We formulate how to determine weights for the LC method and exponents for the PE method in order to minimize the variance of the design prediction value. From a theoretical comparison among the two methods, the conventional method and the previously proposed method called the generalized bias factor method, it is concluded that the PE method is the most useful method in order to improve the prediction accuracy. Main advantages of the PE method are summarized as follows. The prediction accuracy is necessarily improved compared with the design calculation value and is the most improved by utilizing all the experimental results. From these facts, it can be said that the PE method effectively utilizes all the experimental results and has a possibility to make a full scale mockup experiment unnecessary with use of existing and future benchmark experiments.