Monitoring control rod element assembly position

In a pressurized water nuclear power plant having a nuclear reactor core and a multiplicity of control rods arranged for movement through the core for controlling the reactor power by absorbing nuclear particles while exposed to the nuclear reactions in the core, wherein a subset of said multiplicity of control rods is designated for controlling reactor power during normal power production in the plant, said subset including a plurality of groups of control rods, the groups being under the control of a reactor operator who can move each group through the core in staggered sequence, and wherein each said group has imposed thereon an administrative limit of cumulative exposure in the core while each group is situated within a preestablished position range in the core, a method for the operator to monitor compliance with said administrative limit, comprising:

• continually measuring the core power and generating a power signal commensurate therewith;
• continually measuring the position of each group in the core;
• establishing an incremental time base common to measuring the core power and measuring the position of each group;
• from said measuring of position, continually determining when on said time base, each group is within said prestablished position range;
• from said measuring of core power, determining the core power when each group is in said prestablished position range;
• computing an incremental effective exposure for each group, commensurate with core power, for each time increment at which each group is within said prestablished position range;
• accumulating said incremental effective exposures for each group;
• comparing the accumulated effective exposure for each group with the administrative limit for each group;
• and
• displaying said comparison to the reactor operator.