VVER-440 Fuel Cycles Possibilities Using Modified FA Design

P. Mikoláš, ŠKODA JS a.s., Czech Republic

20th Symposium of AER on VVER Reactor Physics and Reactor Safety (2010, Hanasaari, Espoo, Finland)
Core Design and Operation


A nearly equilibrium five-year cycle has been achieved at Dukovany NPP in the last years.
This means that working fuel assemblies (WFA) with an average enrichment of 4.25 w% of 235U
(control assemblies (CA) with an average enrichment of 3.82 w% of 235U) are normally loaded
and reloaded for five years. Operation at uprated thermal power (105% of the original one,
increase from 1375 MWth to 1444 MWth) started by use of WFA with an average enrichment of
4.38 w% of 235U (CA with an average enrichment of 4.25 w% of 235U) in 2009.
With the aim of fuel cycle economy improvement, the fuel residence time in the core has to be
prolonged up to six years with one cycle duration time and preserving loadings with very low
leakage. In order to achieve this goal, at least neutron-physical characteristics of FA must be
improved and such changes should be evaluated from other viewpoints. Some particular changes
have already been analyzed earlier.
Designs of new fuel assemblies with higher (and in the central part of a FA the highest
possible, i.e. 4.95 w% of 235U) enrichment with preserving low pin power non-uniformity are
described in the presented paper. An FA with an average enrichment of 4.76 w% of 235U (lower
than originally evaluated) containing six fuel pins with 3.35 w% of Gd2O3 content was selected
in the end. Fuel pins have bigger pellet diameter, but preserved central hole.
A newly designed FA?s were evaluated at first from the viewpoint of physics (pin power nonuniformity, cycle length etc.).
Possibilities of fuel cycles are evaluated on model loadings with the newly designed FA,
where the base are loadings for 27th ? 34th cycles of the third unit of Dukovany NPP for uprated
power. These cycles were prolonged (from approx 330 FPD to 370 FPD) using FA with higher
Also, a preliminary evaluation of FA with a quite new design is presented.

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