Here the system is not at significant temperature and so a rise in power produces no significant Doppler feedback to help to cut back the transient. Thus the power rise might progress through several decades in flux before significant feedback is induced. During this stage of the calculation only the neutron kinetics equations are needed.

The following trip signals are available: (a) control rod drive sensors;

(b) period meters if they are included; (c) low flux; (d) intermediate flux;

(e) high flux; and (f) high coolant temperatures eventually. Again, it is possible to define highest acceptable rates of reactivity addition if the pro­tective system is well defined.

Figures 2.14-2.16 show power, fuel temperatures, and reactivity feed-

backs involved following a continuous rod withdrawal initiated at low power. Two rod withdrawal rates are shown for a typical LMFBR. In both cases even the fourth of the above sequence of trip signals will maintain acceptable conditions within the fuel. Figure 2.16 very clearly shows how important in each case the Doppler reactivity feedback is in reducing the reactivity addition and curtailing the power rise. In the 50/sec addition case, no feedback occurs for 15 sec, but when it does occur, the power is almost immediately curtailed.