Justification of the radiation load calculation procedure for VVER reactor vessels
20th Symposium of AER on VVER Reactor Physics and Reactor Safety (2010, Hanasaari, Espoo, Finland)
Reactor physics experiment and code validation
Abstract
The reactor plant service life is governed, to a high extent, by radiation life of the
reactor vessel that, in its turn, depends on maximum value of the fast neutron fluence (E>0.5
MeV) to the reactor vessel inner surface. Therefore the calculation of fast neutron fluence to
the reactor vessel, as well as determination of calculation error, is an important task in
justification of the reactor vessel service life.
Result of neutron fluence calculation and its error depend substantially on the
accuracy of assigning the source of fission neutrons in the core, and especially in the
peripheral fuel assemblies. The given paper deals with consideration of two main approaches
to assigning the source of fission neutrons ? rod-by-rod and assembly-by-assembly. The main
objective of this paper is to determine the difference in results of calculation of neutron
fluence to the reactor vessel using different methods of description of the fission neutron
source, and to determine which of these methods is the most preferable for justification of the
reactor vessel service life from the viewpoint of maintaining the reasonable conservatism.
Error of calculation of fast neutron fluence to the reactor vessel of VVER-440 and
VVER-1000 was estimated by a comparison of calculated and experimental values of activity
of templets taken from the inner surface of reactor vessels of VVER-440 (V-230) and activity
of neutron activation detectors on the outer surface of reactor vessels of VVER-440 and
VVER-1000. On the basis of the analysis of calculated and experimental data a conclusion
was made on the error of calculation results obtained with the use of assembly-by-assembly
and rod-by-rod distribution of fission neutron source.