Validation of Coupled Neutronics / Thermal Hydraulics Codes for VVER Reactors (VALCO)

The VALCO project aims at the improvement of the validation of coupled neutron-kinetics / thermal-hydraulics codes for VVER reactors. VALCO was started on January 1, 2002 and will be completed December 31, 2003. The project is split into three Work Packages.

In Work Package 1, lead by VTT, the existing data base, containing measured VVER transient data from the former EU Phare project SRR1/95, has been extended by five new transients. Two of these transients were used for the validation of different coupled codes suitable for VVER. The comparison between the codes and the validation against the measurements was successful. The obtained deviations from the experimental data are well understood and mostly caused by missing information about the operational regime during the transient.

A comprehensive uncertainty analysis for the two SRR1/95 transients, one for each a VVER-440 and a VVER-1000, has been carried out in Work Package 2 under the leadership of GRS. An essential result of the analysis is the identification of the input parameters, such as the secondary-circuit pressure, the control-assembly position (as a function of time), and the control-assembly efficiency, that most sensitively affect the safety-relevant output parameters.

In Work Package 3, lead by FZR, stand-alone three-dimensional neutronics codes have been validated against measurements in the Russian V-1000 zero power test facility. After correcting the geometrical input data, a good agreement between calculated and measured steady-state power distributions could be achieved, both for assembly-averaged powers and pin powers. The real time behavior of local power measured during transients is well modeled by the reactor-dynamic codes.