Challenging cycles of Dukovany NPP with highly enriched fuel optimized by the Athena code

K. Katovsky, SKODA JS, a.s.; F. Fej & J. Prehradny, Czech Technical University; R. Čada, University of West Bohemia, Czech Republic

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


The Dukovany NPP has operated four VVER-440 reactor units. Starting 2009 power of 3rd unit has been uprated, so
reactor is operated at power level of 1444 MWt instead of 1375 MWt used up to now. Innovation of secondary circuit
and electrical equipment leads to electrical output of 500 MWe. During four years all four units will be uprated this
way. Power uprates together with outage shortages are challenges for fuel cycles optimization. Reactors of Dukovany
NPP have already operated in incomplete five-year fuel cycles based on modified Gd-2+ fuel design called Gd-2M
with 4.38 % average enrichment now. New fuel types with high enrichment were proposed by fuel manufacture
(4.87 % avg. enrich.) and by SKODA JS Company (4.76 % avg. enrich.). These fuels should allow complete fiveyear fuel cycle with higher power and has also ability to allow incomplete six-year fuel cycle. Fuels should
economize fuel assemblies and operational costs.
The SKODA JS Company together with the University of West Bohemia has developed new optimizing code
called Athena. The code has been used to optimize fuel cycles from 25th cycle of 3rd unit of Dukovany NPP up to 34th
cycle with new fuel types presented above. Comparison between fuel cycles with Gd-2M fuel and with mixed
loading patterns (Gd-2M mixed with new types) has been calculated. Positives and negatives are discussed from
physical, safety, operational, and economical points of view. New fuels allow 330 to 340 FPD long cycles with
uprated power, but are very challenging to radial power distribution parameter (FdH). Results show, that operational
parameter limit of FdH used until now should be increased from 1.54 to 1.58. Couple of fuel assemblies is
economized. Results are a part of study of applicability and feasibility of new fuels and might be important for
additional development of fuel design. Results will also be used as a comparison of presently used optimization code
Optimal and new Athena code.

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