12.203. Should an accident occur, what is to be done? Strategies need to be considered carefully since some adverse effects may accompany the apparent advantages of a given strategy. For example, should the core slump to the bottom of a PWR pressure vessel, a logical strategy is to flood the surrounding reactor cavity, which will submerge the lower vessel head. Hopefully, this would prevent vessel failure and help cool the contained debris. However, should the vessel breach, a steam explosion is now a possibility as a result of the reaction between the molten fuel and the water that has been introduced.

12.204. Assessment of severe accident management strategies by var­ious means is therefore a necessary feature of planning. Procedures based on decision trees (§12.212), an operations research method, can be used to evaluate systematically all of the options and to develop choices. Sen­sitivity analysis may also be included [38]. Then guidelines in a form useful for operators can be prepared.