The present role and the future of small and medium sized reactors in the Bulgarian electricity generation industry

At the moment, six PWR units WWER type are in operation in the Bulgarian electric grid, located in Kozloduy NPP. All of these units operate in the basic load diagram. There are four reactors of 440 MWel and 2 reactors of 1000 MWel. During the last ten years the total demand of power in the national grid varies between 3500 MW during the summer and 7500 MW in the winter. For certain periods the capacity even of a single reactor WWER-440 has exceeded more than 10% the total system demand. This fact has imposed some restrictions on reactor operation, but the reactors nevertheless operate in the load diagram basis. More often these restrictions are in form of operation at reduced power. For WWER-440 reactors this means operation at 50-55% (with one turbine). This fact leads to some negative consequences as for example unbalanced fuel burning and increased core peaking factors. Another sensitive problem for the plant is the case when due to technical specification operational limits and conditions violation one unit has to be shutdown and put in a cooldown condition for a period of time for different reasons (forced outage, maintenance,etc.). In some cases, this is not desirable for the grid dispatchers due to lack of redundant generating capacities. As far as Kozloduy NPP is concerned, since April 2000 it has been separated from the National Electric Company (NEC) as a stand-alone electricity generating company, it suffers some penalties applied by NEC, based on the contract for purchase of the electricity between NEC and the plant. The scheduled modernizations of the units will lead to some extensions of the outages, which will force NEC to put into operation less profitable power plants in the country. In order to cope with the problems of the grid frequency regulations and the backup of the power generation capacity of the biggest unit in the national grid, which is WWER-1000 MW, a pumping accumulation hydrostation with capacity 840 MW in turbine mode was constructed and put in operation in Bulgaria in 1998. In spite of above-mentioned, Kozloduy NPP staff operate the plant units with definitive priority of safety. This year 2001, the State Agency for Energy and Energy Resources of Bulgaria together with National Electric Company elaborated an update of the National plan for development of electricity generation capacities in the grid. According to this Plan, a new nuclear generation capacity with 2 units has to be constructed and put in operation on the site of Belene between 2008-2015. The preliminary feasibility study of this project, performed by the national architect-engineering company Energoproekt shows that the optimal unit capacity for this project is between 600-900 MWel. The preliminary engineering activity of the project is expected to start effectively by the end of 2001. (author)