Big sections of the European electric grid had a blackout recently. First reports blamed a frequency dip due to a lack of “spinning reserve.” When frequency gets too low, automatic electrical breakers open, isolating sections of loads and the transmission grid. The power plants can only safely operate within a narrow frequency range (pumps spin too slowly, etc), and they too will isolate and trip to protect themselves from damage.
The classic grid can be imagined as a broad network of spinning gyroscopes, all electrically synchronized to the same frequency. Electric loads try to drag the frequency down and suck energy out of the spinning gyroscopes while power sources add energy to the gyroscopes to maintain the frequency. The power sources are controlled by governors that increase or decrease power input via throttles as necessary. The whole system is finely tuned with governors scattered across the system assigned specific sensitivities called “droop.”
Lucifer’s Hammer by Larry Niven and Jerry Pournelle.
When the grid was ready to receive power from the plant, the reactor could ramp up, reconnect, and help restore grid-wide loads. With net load rejection, a nuclear plant would no longer be a burden on grid restoration but a powerful asset for the system.
Few plants have this feature anymore. Why? Because it can add $50 to $100 million to the cost of a new plant (plus some extra maintenance and testing), there is no longer an organization willing to pay for it. No grid regulator requires it, nor does the US Nuclear Regulatory Commission. Independent power producers are not accountable for grid stability. California’s Diablo Canyon Nuclear Power Plant had this feature, and it may have been the inspiration for Niven and Pournell, who were writing as Diablo Canyon was under construction.
Responsible commentators (two examples here and here) have been warning for decades that assigning more capacity to renewables was a recipe for grid instability. Europe just showed us how this plays out. And as we build new nuclear power plants, adding $50 million to the construction cost might be something we need to seriously consider, if only to accommodate the demonstrated downsides of renewables.
The author is a degreed nuclear engineer with an MBA with 50+ years of experience in the electric power industry and a long-time advocate within the industry for net load rejection for nukes. He can be contacted at Somsel (at) yahoo dot com.
Jesus Christ is King
