SAFETY REVIEW OF RBMK REACTORS

The objective of the work was to review the safety of the RBMK reactors in nine technical areas:

System Engineering and Accident Progression;
Protection Systems;
Core Physics;
External Events;
Engineering Quality;
Operating Experience;
Human Factors;
Regulatory Interface;
Probabilistic Safety Assessment.
The review should be focused on the Smolensk-3 and Ignalina-2 reactors and extensions should be made to other reactors whenever this was possible.
A key feature of the project was the expected close collaboration between the Eastern and Western technical experts.

The following results were obtained:

The first generation units in their original or partially modified form are of special concern to both Eastern and Western members and should be the prime focus of safety improvements;
The particular situation of the Chernobyl reactors needed immediate clarification;
The review has highlighted the importance of improving management systems and practices at the plant and throughout the Eastern Nuclear Industry. This is seen as a cost-effective route to safety improvement;
A large number of (more than 300) recommendations for safety improvement have been made. Many of these recommendations had been recognised by the Eastern side and for some others actions are already initiated. Still others are recognised by the Western side as important new recommendations;
It was imperative that work proceeds as quickly as possible on the implementation of the recommendations in Appendix 9.
Concern was exacerbated by the current economic situation of Russia, Lithuania and Ukraine; Safety enhancement programmes became in jeopardy. The availability of early international funding support for these programmes was considered of the greatest importance.

There are considerable differences between the different generations of RBMK reactors and even significant differences among reactors within the same generation. Therefore, it was essential that plant-specific safety studies, including a PSA, be performed for each station using modern state-of the-art methodologies and computer codes (modified and verified for the RBMK case) in order to get an accurate assessment of the safety level and also the effectiveness of modifications.

The situation surrounding the Russian, Lithuanian and Ukrainian regulators, gave cause for two concerns:

The lack of a nuclear law and derived regulating philosophy specific to RBMK conditions;
A serious lack of resources at a critical time.
Changes in the implementation of regulatory regimes, which the regulatory authorities themselves would like to make, were considerably impeded by lack of financial and technical support.

Over 300 recommendations for safety improvement have been made and priorities have been assigned.