Chapter 2: Introduction to Nuclear Safety

Practical elimination of sequences leading to large or early radioactive releases

Requirement 20 of SSR-2/1 (Rev. 1) requires that “the plant shall be designed so that it can be brought into a controlled state and the containment function can be maintained, with the result that the possibility of plant states arising that could lead to an early radioactive release or a large radioactive release is ‘practically eliminated’ ”.

An ‘early radioactive release’ in this context is a radioactive release for which off-site protective actions would be necessary but would be unlikely to be fully effective in due time. A ‘large radioactive release’ is a radioactive release for which off-site protective actions that are limited in terms of lengths of time and areas of application would be insufficient for the protection of people and of the environment.

The possibility of certain conditions arising may be considered to have been ‘practically eliminated’ if it would be physically impossible for the conditions to arise or if these conditions could be considered with a high level of confidence to be extremely unlikely to arise.

The requirement on ‘practical elimination’ is among those which bring the highest level of novelty of  SSR-2/1 (Rev. 1) with respect to previous standards.

Read more: SSR-2/1 (Rev. 1), TECDOC-1791