Method for calculating the isotope content change

A brief review of the methods used for calculating changes in nuclear reactor fuel isotope ratio is given. On the base of the analysis of the common solution of the first order differential equation system and the methods based on the Taylor series expansion for the exponential function describing isotope ratio change the method of recurrent relations is suggested. The method Under consideration provides calculating the concentration of any n-th isotope in a decay chain as a function of integrated flux and time for different amount of initial isotopes. Two ways for realization of the method of recurrent relations based on the chain and reaction type catcutations as well are considered. The method is realized as a program for the BESM-6 computer. On the base of the test calculation result analysis the conclusion is made that the suggested method does not give additional error in the data obtained