The use of real-time plant simulators running in parallel with a nuclear plant to predict the control system
behaviour and highlighting unexpected plant behaviour is presented. The study is performed on a
910 MW Generation II Framatome Pressurised Water Reactor model and simulator. By simulating the
plant behaviour in real-time whilst comparing it with the real-time transient the plant is following, a
complete second set of expected control operations and simulated plant measurements is generated. This
enables the calculation of the unknown set of variables introduced into the plant as a fault condition. The
benefit of such a system is that plant faults that are too small to detect (especially during transients when
the plant operating point is moving around) can be identified as unexpected or faulty plant behaviour.
The behaviour of the control system is also continually predicted so the effect of the control system compensating
for fault symptoms (which in most cases hides the fault condition) is used to characterise the
fault as a control variable acting on the plant. The approach is illustrated by simulating a specific fault,
small enough to go undetected for an extended period of time, during a typical transient. This is continually
compared with a plant simulation, simulating the same transient without the fault. Using the
described methodology, the fault is detected and characterised long before the plant safety is jeopardised
or the fault is detected by the conventional protection system.