Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
Introduction
Following the nuclear accident at “Fukushima” nuclear power plant on March 11, 2011, it
became paramount for the Bulgarian Government to take urgent measures to reassess the
preparedness of Kozloduy nuclear power plant to respond to emergency situations.
On March 24 the Nuclear Regulatory Agency (NRA) made the Government initiative more
specific and placed to Kozloduy NPP their requirements to review and verify the technical status of
the systems, structures and components (SSCs), operating environment and operability of SSCs
involved in severe accident management as well as relevance and applicability of procedures and
instructions These requirements are aimed at taking preliminary and short term actions for plant
safety reassessment prior to adoption of unique uniform requirements for all nuclear power plants
that later became known as “stress tests”. Kozloduy NPP fulfilled the measures specified on June
10, 2011, submitted the report with the results of the review to NRA.
On May 31, 2011, NRA required to carry out an in-depth safety assessment of KNPP in the
light of Fukushima events (stress-tests)[1]. As a result on June 01, 2011, Kozloduy NPP PLC
initiated “Conduct of stress-tests as a targeted assessment of safety margins of facilities within
“Kozloduy NPP PLC at disastrous natural events that lead to severe accidents” [2], [3]. The
reassessment covers all nuclear facilities of the site: units 5 and 6, fuel storage pools of units 3 and
4, spent fuel storage (SFS) and dry spent fuel storage (DSFS).
The stress test requires summarising the plant response and preventive measures
effectiveness in extreme situations [1], [4], [5], [6] in order to identify any potential weakness and
cliff-edge effects. This is required in order to evaluate robustness of the defence in-depth approach,
adequacy of existing accident management measures and to identify potential technical and
organizational (procedures, human resources, organization of emergency response or use of external
resources) improvements to enhance Kozloduy NPP nuclear safety. According to references [1], [4]
and [5], the objectives of the stress test can be summarized as follows:
· Defining measures provided in the plant design and plant compliance with the design
requirements with regard to external events;
· Defining the plant capabilities to respond to beyond design basis events, namely
assessing plant robustness and identifying potential weak points;
· Defining measures to improve the existing level of robustness of components and
SSCs in order to improve general plant robustness against extreme natural phenomena.
This report is aimed at summarizing the safety margins reassessment conducted at Kozloduy
NPP and provides the main results and recommendations of conduct of stress tests with its format
and content strictly following the NRA requirements and recommendations [5].
The first part of the report provides the main data for the site and the nuclear facilities
located in it with special emphasis made on the site and their characteristics. The design bases of the
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