Control rod operation system

This invention concerns a system for restricting the withdrawing amount of control rods from increasing than that required relative to the status of the plant, thereby preventing abrupt increase in neutron fluxes. That is, there are provided first means for calculating the control rod withdrawal amount based on a previously planned value and second means for on-line calculation of the withdrawal amount based on the status amount of the plant. The value obtained from the first means is compared with the value obtained from the second means and the smaller value is used as the actual withdrawal amount for the control rod. The reason is that the range of increasing the neutron flux is less as the withdrawal amount corresponding to the amount of reactivity applied to the reactor core is smaller. Further, the status amount of the nuclear reactor upon approaching the criticality used for the on-line calculation of the second means includes the withdrawal amount estimated to be necessary at least from the present point to the criticality, the withdrawal amount of the former operation and the reactor period at this instance. Accordingly, abrupt increase in the neutron fluxes can surely be prevented. (K.M.)