The previous sections have discussed a number of possible CDA initiators. All of them have been shown to be most unlikely, and all but two may be ruled out as initiators. Attention would naturally be given to their absolute design prohibition. The two accidents that were not ruled out but further discussed were the local failure that might arise from an overenriched pin

or a blocked channel and the failure to scram in conjunction with another more likely event.

Analysis to date, combined with experiments on fuel-sodium interaction, transient destruction of fuel, and explosive testing of the fuel assembly wrappers, seems to indicate that propagation cannot occur following a local failure and therefore this case also should not be used to provide a CDA.

The scram failure case is analyzed as a direct result of licensing practice. It would be preferable to spend the technical effort in assessing reliability of the scram system, and this may well be done in the future. At that time a design basis for the containment may consist of a fuel handling mishap instead of a core disruptive accident. In that case the containment building will be reduced to the function of a roof for plant components.

A sodium fire is also used to evaluate containment design in many plants. Section 4.5 has shown how the sodium fire is analyzed and how its effect need not be restrictive to the design. Indeed the most sensible design solu­tion is to inert the sodium areas so as to rule out the sodium fire entirely.

In the future, the fast reactor may well consist of a covered rather than a contained plant. This will not be possible until a breakthrough comes in the analysis of initiating events or in the experimental program carried out in support of that analysis. Such a breakthrough will have to be accompanied by a breakthrough in the licensing attitude at the same time.