July 2000 Highlight

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Key members of the EOI team for Kozloduy NPP include (from top) Emo Popov, Energoproekt; Stoyan Kalchev and Peter Demerdjiev, Kozloduy NPP; and Pavlin Groudev, Institute of Nuclear Reactors and Nuclear Energy.

Kozloduy completes thermal-hydraulic analysis for EOI validation

Kozloduy nuclear power plant (NPP) and its analytical support organizations Energoproekt and the Institute of Nuclear Reactors and Nuclear Energy (INRNE) have completed the thermal-hydraulic validation of the symptom-based emergency operating instructions (EOIs) for Kozloduy’s VVER-1000 reactor units. On July 4, the EOI team from Kozloduy NPP reported that plant management had given approval to the final report that summarizes the results obtained from more than 18 months of analytical work. All work was done with Bulgarian resources using site-specific Kozloduy VVER-1000 RELAP5 computer codes. Specialists from Data Systems & Solutions (DS&S) and Pacific Northwest National Laboratory served as mentors for the Bulgarian analysts. The EOI team now will incorporate the results of the analysis into the EOIs and prepare a submittal to the Bulgarian regulatory agency. Having completed this significant analytical obstacle, the remaining activities required to support implementation are final verification and simulator validation of the EOIs and operator training. Final implementation of EOIs for Kozloduy Units 5 and 6 is expected in early 2001.

The purpose of the thermal-hydraulic analysis is to prove, or validate, the adequacy and effectiveness of the mitigating strategies contained in the approximately 50 symptom-based Kozloduy EOIs under all transient conditions. By following a best-estimate bounding analytical methodology devised by Pacific Northwest National Laboratory and its contractor DS&S, Kozloduy NPP reduced the original estimated level of effort for the EOI analysis by approximately 75 percent. This new reduced and highly efficient scope was both manageable and cost effective.

By consolidating their analytical scope into 13 "bounding modes" (e.g., large-break loss-of-coolant accident, total loss of electrical power, steam generator tube rupture, total loss of feedwater) that summarized the most severe challenges to the critical safety functions (i.e., subcriticality, core cooling, heat sink, containment, integrity, and inventory), the team reduced the number of scenarios that needed to be analyzed from the originally estimated 450 to 475 scenarios to 125 to 150 scenarios. These scenarios described bounding plant conditions, transient sequences, and operator actions that occur during these 13 bounding mode initiating events. By analyzing plant responses with and without operator actions during the sequence of events that lead to the most severe challenges to the six critical safety functions, mitigating strategies in the approximately 50 EOIs could be validated, thus validating the same strategies used for less significant transients.

The team now turns its attention to the thermal-hydraulic analysis to validate the EOIs for Kozloduy’s VVER-440/230 reactors. Now approximately 25 percent complete, the VVER-440/230 work should be finished later this year.

Members of the Kozloduy EOI team pause on their way to a meeting at the plant-owned hotel in Pomparova, Bulgaria; (back row, left to right) Alexander Krastev, Uli Hristov, Pavlin Groudev, Stoyan Kalchev, Kent Faris, Pacific Northwest National Laboratory; and Ron Beelman, Science Applications International Corporation; (front row) Krassimer Avdjiev, Diana, Vladimir Uruchev, and Elizabet Tcvetanova.

(Dennis Meyers, DOE, 301-903-1418; Kent Faris, PNNL, 509-372-4068)