The following differences exist which make some of the AEC general criteria inapplicable to the liquid-metal-cooled fast reactor systems.

(a) The LMFBR is a low-pressure system whereas the LWRs are high- pressure systems.

(b) LMFBR fuel is generally enriched with plutonium, which presents a different radiological hazard from that of iodine and krypton fission products.

(c) The LMFBR plant is cooled with sodium, therefore water systems cannot be used for pressure reduction or for emergency cooling.

(d) A soluble reactivity poison for control purposes is impracticable in a liquid metal system, since no suitable injection systems exist at the present time.

(e) The LMFBR has a different set of reactivity coefficients from a LWR, and therefore the criteria dealing with coefficients deserve different treat­ment.

(f) The LMFBR has a different range of accidents and the design basis accidents are very different ones from those in the LWRs. The AEC criteria refer specifically to the loss-of-coolant (as opposed to loss-of-cooling) acci­dent, which is so critical in the LWR systems.

To clear the charge of inapplicability, a set of fast reactor criteria will necessarily be produced within a few years. At that time there are some omissions that could be rectified; the most outstanding being some classi­fication of accidents, their probability ranges and their allowable conse­quences. This classification could be stated in general terms, whereas at present a classification is only implied in terms of the redundancy required, the emphasis placed on certain accidents, and the definition of an antici­pated operational occurrence (an unlikely fault as defined in Section 3.1.3.2).