Alexander Duchac

There are four units of WWER 440 in operation in the Slovak Republic. Two units belong to the first WWER 440 generation equipped with 230 reactor type and two units belong to the second WWER 440 generation equipped with 213 reactors. All four units are located at Bohunice site. Four units with WWER 440-213 reactors are under the construction at Mochovce site.

Safety review of the operating units started relatively soon. This proces was accelerated after the year 1986. Safety issues of 230 reactors were addressed by former Czechoslovak Atomic Energy Commission in its Decision No.5/91. The decision comprised a set of safety upgrading measures to be implemented at Unit 1 and Unit 2 of Bohunice NPP. The upgrading process was known as the Small reconstruction. At the same time, the original operating license for Unit 1 and Unit 2 of Bohunice NPP has been changed and licensee has to apply for permission to operate these units for every single fuel cycle.

Having completed Small reconstruction the licensee commenced works on further upgrading process which was based on decision No. 1/94 of Slovak Nuclear Regulatory Authority (UJD SR). The decision No.1 set up safety measures which would substantially increase the safety level of 230 reactors at Bohunice NPP when implemented. Due to the complexity and technical difficulties of such reconstruction process it has been decided to implement these measures gradually in four years.

Bohunice Unit 3 and Unit 4 are equipped with 213 reactors. Although 213 reactors have numerous safety features incorporated in their design the licensee implemented number of modifications since the beginning of operation. Significant step towards the safety was development a new Safety Analysis Report (SAR) which has been elaborated after ten years of operation. Regulatory body made an assessment of SAR and recommended their further upgrading.

In the IAEA document “Safety Issues for WWER 440/213 reactors and their ranking” there is a summary of generic safety issues for 213 reactors. Framework for safety upgrading of units with 213 reactors has been based on generic findings in the IAEA document as well as on safety assessment carried out by the licensee, Slovak technical support organizations and regulatory body.

Commencement of the first unit of Mochovce NPP (WWER 440/213) is expected in second half of 1998. Experience gained from the safety review and safety upgrading at Bohunice NPP is being used during a licensing process for Mochovce NPP. Therefore, setting the priority and time schedule for implementation of generic safety measures for 213 reactors becomes a key issue of the licensing process.