Study on the impact of transition from 3‐batch to 4‐batch loading at Loviisa NPP on the long‐term decay heat and activity inventory
26th Symposium of AER on VVER Reactor Physics and Reactor Safety (2016, Helsinki, Finland)
Intermediate storage of spent fuel decommissioning and radwaste / Spent fuel disposal and actinide transmutation
Abstract
STUDY ON THE IMPACT OF TRANSITION FROM 3-BATCH TO 4-BATCH LOADING AT LOVIISA NPP ON THE LONG-TERM DECAY HEAT AND ACTIVITY INVENTORYTuukka LahtinenFortum Power and Heat Ltd, Espoo, Finland tuukka.lahtinen@fortum.comABSTRACTThe fuel economy of Loviisa NPP was improved by implementing a transition from 3-batch to 4-batch loading scheme between 2009 and 2013. Equilibrium cycle length, as well as all process parameters, were retained unchanged while the increase of fuel enrichment enabled to reduce the annual reload batch size from 102 to 84 assemblies.The transition had an impact on decay heat and activity inventory. This effect has not earlier been studied properly, i.e. by applying consistent calculation models and detailed description of assembly-wise irradiation histories. In this paper, the effect is analyzed with the emphasis on decay heat, produced by annual discharge batch, on the time scale which is relevant in final disposal studies.The transition involved a few changes having opposite consequences and, therefore, the net effect on decay heat is not self-evident. These changes include: modification of fuel assembly design decrease of uranium mass of reload batch (-13 %) increase of average burnup of discharge batch (+15 %) changes in assembly-wise end-of-life fission ratesThe paper documents the decay heat calculation results for both loading schemes. Based on the results, it is concluded that for the cooling time, foreseen typical prior to encapsulation of assemblies, the decay heat of discharge batch increases by 2…4 %. The net effect is dominated by increase of Pu-238 and Cm-244 activities. Furthermore, considering assembly-wise average decay heat, it turns out that prolongation of cooling time by about 10…15 years is needed when unchanged decay heat load is desired.26th Symposium of AER on VVER Reactor Physics and Reactor Safety 61 10 – 14 October 2016, Helsinki, Finland