Recent improvements and operating experiences of Loviisa NPP fuel loadings
26th Symposium of AER on VVER Reactor Physics and Reactor Safety (2016, Helsinki, Finland)
Fuel management issues
Abstract
RECENT IMPROVEMENTS AND OPERATING EXPERIENCES OF LOVIISA NPP FUEL MANAGEMENTS. Saarinen, J. Kuopanportti, T. Lahtinen, J. Arjoranta Fortum Power & Heat Ltd, Espoo, Finland simo.saarinen@fortum.comABSTRACTLoviisa NPP has two VVER-440 reactors with the thermal power of 1500 MW. There have been several changes impacting the fuel economy of Loviisa reloads during the past 10 years. Ten years ago, the plant was operated with 3 year loading scheme with fuel assembly average enrichment between 3.7 % and 4.0 %. In 2009 first Gd fuel assemblies with higher enrichment, namely 4.37 %, were loaded into Loviisa. The enrichment increase enabled to move to a 4 year loading scheme. In connection with the transition to the 4 year loading scheme, the assembly burnup limit was increased from 45 MWd/kgU to 57 MWd/kgU.The fuel economy in the 4 year loading scheme has been further improved by introducing mixing vanes to the spacer grids. The mixing vanes improve the internal coolant mixing inside the fuel assembly. Thus the with same pin powers, the maximum subchannel outlet temperature remains lower with the mixing vanes than without them.The engineering safety factors for Loviisa were reassessed. The reassessment lead to a significant reduction of the subchannel enthalpy engineering safety factor from 1.16 to 1.10. With this change, a fully low leaking loading pattern was possible to be implemented to Loviisa compared to the previously utilized partially low leaking one.In this paper, the changes in the reactor physical properties of the above mentioned different reloads are discussed. In the end, also an outlook to the possible future improvements to the fuel economy are given.26th Symposium of AER on VVER Reactor Physics and Reactor Safety 20 10 – 14 October 2016, Helsinki, Finland