Objective

The project objective was to provide technical support and assistance to the Russian regulatory authority GAN and related technical safety organizations to review and evaluate the industrial projects for reactor vessel embrittlement with regard to nuclear safety (Tacis 1991, 1.1 and 1.2). The completeness of all the measures taken also has been reviewed.

The detailed tasks to be performed were as follows:

Task 1:
Review of the industrial project regarding the latest basic information on material properties and accompanying surveillance data. Plant specific data as well as generic knowledge has to be examined. Surveillance data available had to be collected and reviewed thoroughly to infer the current and projected transition temperatures of RPV materials.

Task 2:
The effectiveness of the annealing process was to be assessed. Also, the post-annealing surveillance issue was to be covered. Emphasis will be given to repeated annealing treatment.

Task 3:
The design transients had to be reviewed in order to select the main contributors to the PTS event. PTS analyses (Fracture mechanical analyses) of RPV were to be examined in detail to assess the margin against the RPV embrittlement.

Task 4:
Review of the In-Service Inspection (ISI) programme as regards locations inspected, frequency of examinations, acceptance criteria and NDE methods. Qualification of technical equipment and personnel for ISI. Review of previous records of ISI.

Task 5:
Review of stress report of boot sampling impact on RPV structural integrity.

Task 6:
Development of technical recommendations for the resolution of VVER 440/230 RPV safety issues.

Result

The project results were in line with the objectives.