Method for starting up and monitoring an apparatus for controlling a boiling water nuclear reactor

A method of monitoring an operation of a boiling water reactor with a reactor core, the reactor core having control rods distributed about a cross section thereof in a pattern corresponding to a two-color checkerboard with squares of different color each assigned a control rod, the checkerboard representing a regular grid with square meshes, each of the control rods being movable via a respective control rod drive from an initial position, in which the control rod is moved completely in the reactor core, into a final position, in which the control rod is moved completely out of the reactor core, and the method comprises:

• during a start-up, activating at most some control rod drives and interlocking other control rod drives and using a monitoring device for the interlocking of the control rod drives permitting one of a first configuration, in which simultaneously moved control rods are assigned to squares of different color in the checkerboard pattern, and a second configuration, in which substantially half the control rods are moved at least partially out of the reactor core and fully moved-in control rods are assigned to squares of different color, and preventing violation of the following rules:
• a) the control rod drives of the control rods which are directly adjacent one another and the control rod drives of the control rods which are diagonally adjacent one another must not be activated simultaneously;
• and
• b) for each control rod no longer in the initial position, the drives of the directly adjacent control rods must not be activated before a predetermined minimum number of control rods are in the final position or the reactor power output reaches an upper limit predetermined for the start-up.