Post-inerting of a large dry containment in beyond-design-basis accidents in PWR plants. A survey of existing studies with an initial assessment

The objective of this report is to present a summary of basic thoughts and concepts as described in various publications on the subject of ''Post-inerting of large dry containments''. The report furthermore points out the obvious advantages and disadvantages of individual strategies as well as the requirements derived from the knowledge of possible accident sequences for such a concept. Scoping calculations on the injection of inert-gas into the containment during the progress of accidents revealed additional indications as regards e.g. the required amount of inert-gas, the injection rate, and the resulting pressure behaviour in the containment. Thereby an assessment of the effectiveness as well as of the feasibility of such measures has become possible. From the large number of different initial conclusions, two major ones are singled out and presented here: 1) In principle, the technical realisation of post-inerting is possible. Thus a deflagration of hydrogen in the containment can be prevented. 2) Post-inerting cannot be realised independent of the accident progress. Specific criteria for carrying out such measures will require extensive examinations. (orig./HP)