Risks of adaptive control of NPP electrical systems and stability of the grid

Flexible operation research has gained more traction in recent years and some countries have long experience from actual operation. Countries like France, Russia and Germany have operated NPPs to balance power system. Flexible operation of NPPs in power systems with diverse options for balancing has been seen as not profitable. Claims from literature have been presented that operation cost per MWh produced increases about 4% to some claiming that costs will be lower than regular operation for modern plants. Study on Swedish power system found that flexible operation up to 20 TWh of wind power is theoretically possible without noticeable impact to yearly capacity factor of the NPPs if all unit took part in the flexible operation.
Balancing possibilities in FCR-N market was estimated with assumption of 4.6% additional cost of flexible operations. Using market data from 2016, there were 1144 hours when flexible operation could have been profitable. In this case 4.6% increase was calculated respect to Nordpool SPOT price but in reality there is plant specific operation cost. Also a rough estimation of system where all power plants would take part in automatic frequency regulation was done. With that , the capacity factor decrease per plant was estimated to be only 0.5% with two months of measured frequency data with 1 s interval.
Interview of Fingrid was organized for the project. Fingrid sees that 2020 onwards rotating generation will be more limited in the power system and there also will be less controllable power plants. This means that price variations might be large. There has been some talks with flexible nuclear power with energy producers but all of them currently have better resources than NPP’s for balancing purposes. There has not been instances that Fingrid had to demand nuclear power plant to reduce power or demand disconnection. Market based solutions have been enough for now. For voltage control however there has been more requests to change reactive power injection / voltage setpoint. Call to change output power would go from Fingrid operations center straight operator of the nuclear power plant. When grid frequency is outside normal operation region, the grid code demands power plant to be controlled lower or higher output linearly respect to deviations in frequency.
Instead of bidirectional balancing, nuclear power plants could serve better in down regulation reserve in cases for system over-frequency and normally leave bids to down regulation balancing market. This practice would guarantee down regulation capacity even if NPPs would never win the bids to actually activate. It should be noted that FCR-D for disaster situations is only defined for situations when there is lack of power in the system(and not for over -frequency). For system stability respect, there are no large risks in NPP participating to balancing. The most obvious risk to system stability is that if large nuclear plant is taking major role in system balancing and plant disconnects from grid when there is low inertia in the grid(summer time). For risk analysis perspective, role of single plant in balancing should be limited. It is likely that pressures on all generation to participate more actively on system balancing will increase and it is very likely that new NPPs will be required to take part at some point of their long operation life cycle.