Plant full scope replica simulators are commonly used for conducting emergency planning exercises. In order to reach the General Emergency level, an offsite release must be imminent or ongoing. This requires fuel damage and failure of multiple fission barriers. However, this is beyond the scope of current training simulators.
A common practice is to run the simulator to the extent of its limit and override plant instruments to provide the indications of fuel damage and significant offsite release. The overridden values are obtained from calculations performed using in-house developed methods or commercially acquired spreadsheet type of programs. In general this follows NUREG 1228 “Source Term Estimation of Severe Accidents”. Its output data is then used as input for an offsite dispersion model such as RASCAL or a plant-specific offsite dose model. The projected area dose map is finally used for event classifications, protective action recommendations and as a guide for directing the offsite field teams.
During an exercise, “batch files” are often used to override the simulator’s radiation monitors (and other) indications so that they match the scenario’s data book and can be displayed remotely at the TSC or EOF. The “batch file’ driven parameters are simply running in a playback mode and are decoupled from the other simulator models. In many situations, actions taken by the operating crew can significantly alter the timing of events; so it not unusual for radiation monitors to provide indications of fuel damage before the core is uncovered or to indicate offsite releases persist after the operators have isolated the leak, etc. Drill controllers often use multiple event-based batch files as a work-around, but this is still very awkward.
Our PC-based severe accident simulator, PCTRAN, is designed to overcome these handicaps. PCTRAN has the ability to model the event, fuel damage, radiation monitors and radionuclide dispersion as a function of changing weather conditions, all in one simulation. PCTRAN will not replace the simulator for most EP exercises, as the simulator is needed to drive the plant computer that supplies data the TSC and EOF. The plant simulator and site-specific offsite dose projection software will still be used, but by tuning their inputs so that the results match those of PCTRAN, we can ensure that all of these tools are providing consistent data.
During an exercise, both the plant simulator and a plant specific model of PCTRAN can be run simultaneously. When the limits of simulation for the plant simulator are reached, continue to run PCTRAN as far as the scenario demands. PCTRAN output, in the form of a custom-designed Excel or script file can be provided to controllers for use in overriding simulator instrumentation and as input for the plant specific offsite dose prediction program. As a result your familiar transcripts and display are preserved and all existing procedures and resource are fully utilized to its optimum capacity. In the meantime the missing gap is seamlessly connected by the latest technology of PCTRAN.