A neutron balance approach in flux shape control

Among the procedures built to verify the reactor power capability there is the determination of the value of parameters constrained to the control of the neutron flux shape. The most common of this kind of problem is the search of the axial position of a control bank leading the axial offset of the power distribution to a target value. The most used procedures to solve this kind of problem are based on the iterative Newton-Raphson method. We present here another way to solve these problems where an equation, derived from the neutron balance, is set and the parameter controlling the shape is the unknown. This method has the advantage to reduce considerably the computation time in situations where changes on the control parameter induce a high distortion on the flux distribution, as is the case of the control rods. CPU time gains of a factor 3 are attained. As an example the case of control of the axial offset of the power distribution is presented, showing its performance and the gain in stability.