JUSTIFICATION OF PROPER DEGREE OF CONSERVATISM IN CALCULATION OF ENGINEERING MARGIN FACTORS FOR DNBR AS APPLIED TO VVER-1000 CORES CONTAINING FUEL ASSEMBLIES OF VARIOUS TYPES
24th Symposium of AER on VVER Reactor Physics and Reactor Safety (2014, Sochi, Russia)
Advances in spectral and core calculation methods
Abstract
JUSTIFICATION OF PROPER DEGREE OF CONSERVATISM IN CALCULATION OF ENGINEERING MARGIN FACTORS FOR DNBR AS APPLIED TO VVER-1000 CORES CONTAINING FUEL ASSEMBLIES OF VARIOUS TYPES
Oleksyuk D.A., Pinegin A.A., Ryzhov A.A. NRC “Kurchatov Institute” Moscow, Russia
ABSTRACT
In the paper is represented the procedures of determining the engineering safety factors for DNBR, for the linear thermal load from the surface of the fuel element and for coolant heating based on complex statistical model neutron-physical and thermal-hydraulic processes in FA and thermomechanical deformation of FA. The proposed statistical model allows to eliminate a number of conservative assumptions that used in obtaining of engineering safety factors according to traditional methods and taking into account the correlations between the specified processes.
On the basis of the statistical model FA using FORTRAN-90 it was created STAT-TVS code, which includes SC-1 code as a block of thermal-hydraulic calculations. Statistical analysis of STAT-TVS code is performed by GRS method, which allows to refuse from hypothesis about normal distribution of the random parameters, which is important when taking into account the thermomechanical deformations of FA and test the robustness of results to the choice of statistical hypotheses.
Obtained by STAT-TVS code statistical estimates for DNBR, as a rule, is 15 % higher than the corresponding values obtained by traditional techniques.
In the paper is represented the results of sensitivity analysis of engineering safety factors for DNBR to change of power distribution in FA and used statistical hypotheses.
We consider the features of using engineering safety factors applied to non-stationary processes associated with the decrease of the power in FA and the reduction of coolant flow rate through the fuel assemblies. It is presented the first results of numerical researching.