New engineering safety factors for Loviisa NPP core calculations

J. Kuopanportti (Mr), Fortum

26th Symposium of AER on VVER Reactor Physics and Reactor Safety (2016, Helsinki, Finland)
Fuel management issues

Abstract

NEW ENGINEERING SAFETY FACTORS FOR LOVIISA NPP CORE CALCULATIONSKuopanportti, J., Saarinen, S., Lahtinen, T. and Ekström, K. Fortum Power and Heat Ltd, Espoo, Finland jaakko.kuopanportti@fortum.comABSTRACTIn Loviisa NPP, there are two limiting thermal margins called the enthalpy rise margin and the linear heat rate margin that are monitored during normal operation. The purpose of the first margin is to prevent bulk boiling and the second is meant to prevent fuel failures. Both of these margins are calculated with engineering safety factors. The factors take into account the effect of various manufacturing tolerances, impact of the irradiation and simulation uncertainties on the local heat rate and on the enthalpy of the coolant.The engineering factors were re-evaluated during 2015 and the factors were approved by the safety authority in 2016. The re-evaluation was performed by considering all of the identified phenomena that affect the local heat rate or the enthalpy of the coolant. These phenomena include: the calculation accuracy of the theoretical assembly power distribution and rod power distribution, the effect of various manufacturing tolerances of the assembly, the bowing of the assembly and the rods, the uncertainty of the coolant mixing within the assembly, the uncertainty of the coolant mass flow through an assembly, the uncertainties caused by the transformations of the fuel during irradiation, the uncertainty of the thermal power of the reactor.This paper summarizes the work that was performed during the re-evaluation of the engineering safety factors and presents the results for each uncertainty component. The new engineering safety factor of the linear heat rate is 1.115 when the old factor was 1.12. Whereas, the new engineering safety factor of the enthalpy rise margin is 1.100 when the old one was 1.16. The significant reduction of the engineering safety factor of the enthalpy rise margin will increase the fuel economy by about 1 %. 26th Symposium of AER on VVER Reactor Physics and Reactor Safety 21 10 – 14 October 2016, Helsinki, Finland

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