Power change operating method of a boiling water reactor

A method for changing thermal power of a nuclear reactor by controlling the speed of a recirculation pump of the reactor comprising the steps of:

• (a) calculating the current thermal power in accordance with heat balance signals derived from the reactor and generating electrical signals of the thermal power;
• (b) calculating xenon and iodine concentrations in accordance with the electrical signals of the thermal power and generating electrical signals of the xenon and iodine concentrations;
• (c) calculating upper and lower limits of xenon concentration for different final power values in accordance with the relation between the thermal power and core flow in the current control rod pattern and generating electrical signals of the upper and lower limits;
• (d) calculating transitional changes in the xenon and iodine concentrations after a power change for different initial values in accordance with the following equations, ##EQU2## wherein:
• Xe and I:
• Mean concentrations of Xe.sup.135 and I.sup.135 at
• .SIGMA..sub.f :
• Means macroscopic fission cross section at core,
• P:
• Mean thermal power at core,
• .lambda..sub.X and .lambda..sub.I :
• Decay constants of Xe.sup.135 and I.sup.135, and
• .gamma..sub.X and .gamma..sub.I :
• Numbers of Xe.sup.135 and I.sup.135 generated at each fission,
• and generating electrical signals of the transitional changes;
• (e) determining operating allowable ranges for the different initial values in accordance with the electrical signals generated in steps (c) and (d);
• and
• (f) controlling the speed of the recirculating pump to maintain the current xenon and iodine concentrations within the operating allowable range.