Delays in refuelling reflect on the performance of the reactor and the effect is dependent on the mag­nitude of the delay. Referring again to the channel reactivity curve, any fuel not discharged at its due irradiation will become even less reactive and will de­press the overall reactor reactivity. If the delay is continued for any length of time, it may become necessary to discharge absorber to support the falling reactivity, which will be reflected in lower than nor­mal operating temperatures. Whilst some overrun of channel irradiation is acceptable in the flattened zone, there will be a limit which cannot be exceeded. Simi­larly, inner regions of the unflattened zone may be irradiation-limited whilst the outer regions will be dwell-limited.

In either case, the imposed loss of reactivity tends to reduce power output. The resumption of refuelling at too high a rate, in an attempt to redress the imbal­ance of refuelling, results in the insertion of a block of low reactivity fuel. This may require the removal of absorber even if this has not already taken place due to the loss of reactivity by the more highly irra­diated fuel removed. At a later stage, this block of new fuel will become more reactive as the fuel rises to іь peak of reactivity and may require the re-insertion of absorber. This enforced changing pattern of reactivi­ty will be reflected in changes of control rod positions of both coarse rods and regulating rods and will be re Пес ted in the temperature distribution across the core, i. e., low reactivity zones will tend to have lower than normal temperatures and high reactivity zones to have higher than normal temperatures.

Anv significant asymmetry of the delayed fuel load­ing will serve to enhance the resultant effects and in the extreme could limit the reactor output due to an asymmetric temperature distribution depressing the overall bulk gas outlet temperature.