Since deregulation of the European energy market, demands that nuclear power plants should meet uniform safety standards are growing louder and louder. Over the years, one of the aims of the Bulgarian VVER plant, Kozloduy, has been not only to upgrade individual features of the plant pertinent to safety (based on IAEA recommendations) but also to generally bring all plant components, systems and structures in line with internationally recognized safety standards, essentially creating a new VVER 440 reactor design. Because this approach involved various exemplary and innovative efforts, it serves as a model for pioneering a new safety philosophy.

Developing an Aging-Management Program

A custom-tailored aging management program is an extremely interesting option in this context as it contributes towards maintaining plant safety at a high level over the plant's entire design service life and beyond. At the same time, it also is reasonable to expect economic advantages resulting from higher reliability and availability.

With this in mind, a special program was jointly developed by experts from Kozloduy and Framatome ANP and is being implemented by a consortium formed of Framatome ANP and the Russian company, Atomstroyexport. The primary goals of the program are to:
• perform an independent assessment of the remaining service life of plant components, systems and structures that conforms to international experts' acceptance criteria,
• identify the need for further investigations or analyses in certain cases,
• find solutions for improving safety that are economical at the time.

Part of a Comprehensive Backfitting Program

The aging-management program is part of a comprehensive backfitting project for Units 3 and 4 of the Kozloduy plant and comprises three phases:
• In the first phase, the remaining service life of representative components, systems and structures (relevant to safety and availability) is determined at both plant units, using state-of-the-art techniques.
• In the second phase, a computerized system is developed to handle all relevant component and system data - both original construction data and data recorded during plant operation (e.g. loads and environmental conditions) - as well as information obtained from in-service inspections and replacement activities.
• In the final phase, an aging-management program is generated to detect, evaluate and mitigate relevant aging degradation mechanisms and to identify locations in the plant where they are likely to occur.

The 18-month project is scheduled for completion in June 2002. So far, the customer is very satisfied with the way the project is progressing and with the promising results obtained to date.

Example:
Assessing the Remaining Service Life
of the Reactor Pressure Vessel
and its Supports

RPV Analysis
• Bolting joint: fatigue
• TC-Nozzles: fatigue
• TC flange connection: leak tightness
• Sampling study: necessity/possibility
• Testing of templates from Unit 1

RPV Support Structure Analysis
• Fluence measurement at Unit 4