Both units are capable of islanding mode, which means that the reactor can self-sustain its own power production when cut off from the offsite power. In islanding mode, both main buses (and their pumps) are powered directly from the turbine generator, while it is not synchronized with the outside network. Turbine speed can vary between 3400-3800 RPM, which provides a stable enough current for the buses. Site load induces a certain drag on the turbine depending on the load.
In order to enter islanding mode, generator load has to be reduced to below 100 MW and ideally matched equally with site power needs (so that power sent to the network equals zero). Now, the turbine can be desynchronized. If the load matches site power usage, the turbine will more or less stay around 3600 RPM and requires just a little supervision with the turbine precision valve. If desynchronization is done at higher loads, the turbine would spin up, requiring an immediate reduction in the turbine valve to maintain the required RPM. Similarly, if desynchronization is done at lower loads, the turbine would spin down, requiring additional steam to be provided.
Islanding mode can be prepared if offsite power cutoff is announced in advance. In that case, reactor power should be reduced to around 10%, generator load matched with site demand, and the turbine desynchronized. Points will be earned exactly as in the demand until the event ends when the turbine can be synced back to the offsite. If during the event the turbine trips, the reactor will have to be cooled down as in a classical offsite event scenario. In that case, 650 points will be awarded minus what has already been earned during islanding.
In Unit 2, a Chernobyl-like test can also be performed. To maintain the main bus breakers closed during the test, protection has to be disabled. The turbine would trip at that point, but it will provide power until it spins down to around 300 RPM. Please refer to the safety test checklist. In order to successfully complete the test, neither the startup transformer nor RCIC can be used. Feedwater should be provided thanks to power from the running-down turbine, and once generator power is lost, diesels should already be up for further offline cooling and the use of LPCI if needed.