Siemens Aktiengesellschaft

Godehard Rauch

Joachim Schulze

Dieter Kreuter

A transiently unstable state of a boiling-water reactor is damped by measuring the oscillating neutron flux and, after a first threshold value is exceeded over a plurality of oscillation periods, the rate of increase of the oscillation is determined. Depending on the slope of the increase, and after a further threshold value (in particular one dependent on the rate of increase) for the oscillating flux is exceeded, a selection is made which one of various stabilization strategies for damping the oscillation should be triggered before a SCRAM becomes necessary. A hierarchy of stabilization strategies is available: blocking a power increase, for instance, in the control system, controlled slow reduction of the power, or rapid power reduction by a 'partial SCRAM'. The monitoring of the unstable state is effected with a system of sensors strategically distributed throughout the core and which redundantly measure the flux in one region of the core. The sensors act on a plurality of redundantly operating systems, and the signal from each sensor is effective in only one of the redundant systems.

Method and device for operating a reactor in an unstable state

A system for controlling control rods which can be moved into and out of a reactor core of a nuclear power plant, includes a selector device, a monitor device and a rod control device. The selector device contains travel sequences which are selectable and defined for regulating the nuclear power plant, i.e. allocation and movement sequences of the control rods, and it transmits the selector signals allocated to each travel sequence to the rod control device. The monitor device checks the selector signals for acceptability while taking into account the structural features of the reactor core and the control rods, which are allocated to the respective travel sequence, in particular proximity relationships of the control rods. If the selector signals are acceptable, an enable signal is transmitted to the rod control device and the rod control device induces a displacement of the control rods according to the selector signals. From the point of view of process control, the selector device and the monitor device are separate from each other so that the system and method have a high degree of reliability which corresponds to safety regulations for nuclear power plants.

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Rodgau, Germany

Godehard Rauch