Abstract: Usually, concentration of fission product monitors ~(137)Cs and ~(148)Nd are measured experimentally, from which burnup of irradiation fuel element can be derived. The method needs several parameters, such as average fission yields of fission products, correction for reaction (n, γ), decay correction for radlioactive fission products in reactor, average fission energies of fissionable nuclides and so on. These parameters are strongly effected by irradiation history. The brief description of calculation method of above parameters and the results obtained are given. Main features of the method are follows: 1. Real parameters on fuel element as input data; 2. Calculation according to practical operation history of the reactor; 3. Besides atomic concentrations and radioactivities of desired heavy nuclides and fission products, calculations of neutron capture reaction of (n—1) decay chain of ~(137)Cs, ~(148)Nd are performed.