UK/TS/02 Co operation of Riskaudit Science

RISKAUDIT was contracted by the European Commission for advising the Commission and other co-lenders during the loan approval procedures for the completion of the K2R4 project.

In fact EBRD, one of the EC co-lenders, needed to obtain within its “Due Diligence policy“ a second, independent technical advice on the loan procedure and contracted Scientech NUS to that purpose.
In a meeting held on Nov. 12, 1997 at the EBRD offices, the EC representatives agreed to fund the cooperation between RISKAUDIT and Scientech NUS in the review of the R4/K2 modernisation programme.

The objective of this project was to provide a technical support to NRA and Scientech NUS in their review of selected safety issues on the R4K2 modernisation programme. Therefore, the specific objectives were defined as follows:

• provide R4/K2 modernisation programme evaluation report to Scientech, in particular transferring the lesson learnt from the Safety Audit and safety review of the PSA of Temelin VVER-1000/320
• review the technical areas and specific questions of Scientech and develop a technical discussion
• participate to technical meetings between Riskaudit and Scientech for the resolution of the identified safety issues
• issue comments on the report of Scientech

The selected review process was organised in the following steps:

Riskaudit provided the R4/K2 Modernization Program Evaluation Report to Scientech-NUS
Scientech-NUS studied the evaluation report and identified a number of technical areas for discussion. These technical areas were related to specific measures proposed under the programme itself and included also additional areas of safety improvement that resulted from the lessons learned at Temelin. To guide this discussion, Scientech-NUS developed several questions within each discussion area.

• Riskaudit reviewed the technical areas and the specific questions.
• Riskaudit identified and allocate appropriate technical resources to review the questions and to support the technical discussion
• Scientech-NUS and Riskaudit conduct a 2 day technical discussion in Berlin
• Scientech-NUS developed and issued a report for comment to Riskaudit
• Riskaudit issued comments on the report and participated to the comment resolution via telephone, fax and e-mail.

The project output included the following:
Transfer of the following reports from Riskaudit to Scientech for information and review

• Assessment Report for the loan Approval Procedure, Evaluation of the Modernization Programmes
• Safety Evaluation, Rovno 4 -Khmelnitsky 2 Upgrades, General Safety Objectives
• Evaluation of the Modernization Program
• Safety Evaluation of VVER-440/213 and VVER-1000/320 Reactors in Rovno NPP Units 1,2 and 3
• Safety Assessment of the Nuclear Power Plant Stendal, UnitA
• Approach to Review of the Upgrading Programs of Rovno 4 and Khmelnitsky 2
• Generic Databank, by Science and Technology Center
• Plant Quality Status of Rovno 4 and Khmelnitsky 2 Units
• Transfer of questions and areas of safety concern from Scientech to Riskaudit

Technical report developed by Scientech (Draft-Review of methodology for development of Rovno 4 and Khmelnitsky 2 project safety, prepared for EBRD by Scientech-NUS, February 4,1998) and commented by Riskaudit

The main areas of review were identified in the following:

• Development and application of safety objectives specific to the R4K2 project.
• Development of a safety case for the delay of the implementation of the modernisation measures after the start-up.
• Use of probabilistic arguments in the selection and implementation of the safety measures and of the improvement measures
• More specifically, the following items were discussed and the relevant safety issues resolved during the project:

Pressurized Components

• RPV embrittlement and its monitoring: analytical, experimental or other basis for the relevant upgrading measure
• Leak Before Break (LBB): justification for the implementation of the LBB for the primary piping and relationship between LBB and design basis (double-end guillotine rupture)
• Primary to Secondary leakage (SG Integrity): Probabilistic significance of SG header cover end tube integrity failures –Relevant sequences of initiators

Electrical systems

• Diesel unit: Justification for delay in implementation of additional diesel generators, concerns with: lack of diversity in the safety systems and service water availability

Instrumentation and Control

• Obsolete medium and lower level control facilities: Safety significance of UCTF, safety basis for the upgrade and reliability data analysis
• Turbine Regulating System: safety classification
• SG level measuring system: Selection of the upgrading measures, sensor performance, qualification of the SG relief valves.

Containment

• Design in relation to the aircraft crash scenario

Systems Analysis

• Control of water Inventory: RCP seal requirements in relation to injection capability, battery life and electrical supplies, use of test of the sump filter performance
• Design of the Service Water system
• Main steam system: relationship with the upgrade measures relating to primary-to-secondary leakage
• Primary Pressure Control/Operation during transients: Safety Valve performance and BDBA capability (total loss of secondary heat sink).

Cooling of the spent fuel pool: fire hazards at shutdown

Accident analysis: SAR requirements

Comments

(Quality of the results, Lesson learnt, Recommendations for follow-up)

The project met the objectives stated in the TORs: full support was provided to the licensing process of R4K2, resolving all the safety issues identified in the modernization program and therefore endorsing the proposal for the course of actions at the site.