Emergency Instrumentation Systems for Nuclear Power Plants

Accident Monitoring Equipment

The function of the Accident Monitoring Equipment is to provide accurate indication for the operator following design basis events. The NRC has identified the parameters for which indication must be operable in Regulatory Guide 1.97, Instrumentation for Light-Water-Cooled Nuclear Power Plants to Assess Plant and Environs Conditions During and Following an Accident. This equipment must be capable of functioning after exposure to high temperature, high pressure, and high radiation conditions. The equipment must also be capable of withstanding seismic conditions appropriate to the area the plant is located in.

The steam generator tube rupture event at the Ginna plant in 1980 showed several weaknesses in the accident monitoring equipment required at the time. According to an NRC report issued after the event, these weaknesses were (1) non-redundant monitoring of RCS pressure; (2) failure of the position indication for the steam generator relief and safety valves; and (3) the limited range of the charging pump flow indicator for monitoring charging flow during accidents.

Today, typical parameters expected to be functional following an accident are:

Reactor (BWR) or pressurizer (PWR) level
Reactor Coolant System pressure
Steam generator level and pressure (PWR)
Position indication for pressurizer and steam generator safety and relief valves
Containment hydrogen
Containment pressure
High level radiation monitors

The NRC has recently proposed Rev. 4 to Regulatory Guide 1.97 which references IEEE Standard 497-2002, IEEE Standard Criteria for Accident Monitoring Instrumentation for Nuclear Power Generating Stations.

The IAEA has published Technical Report 387, Modern Instrumentation and Control for Nuclear Power Plants: A Guidebook, a 648 page reference providing considerable detail about instrumentation, including accident instrumentation.