New Nukes and Grid Recovery

The recent NERC report on grid reliability should focus our attention on one of the advantages of the next generation of nuclear build – “net load rejection.”

While only a very few nuclear units today can withstand a grid blackout without scramming, the newly designed plants will all be able to. Net load rejection allows a nuclear unit to automatically disconnect from a dead transmission grid, decrease reactor power to only internal demand, and keep running. Those “hotel” loads are typically 5% of maximum power and include pumps, fans, control rod drive mechanisms, etc – everything to keep the plant running. The generator keeps spinning at rated voltage but only energizing plant loads.

Once the grid is stabilized, the system dispatchers then will have the option of using the large nuclear units to help bootstrap the grid (and the tripped generating units) back up to normalcy. Restoring a dead grid from a system’s large nuclear units is much easier than doing the same from the typically very small units equipped with “blackstart” capability or outside transmission links. (Hydro plants can be an exception in being very large.) During the great blackout of 2003, all the nuclear units in the affected region tripped. It took a minimum of 24 hours to restart them after transmission power was locally available and then bring them back on line. At least one required special NRC dispensation.

The as yet unbuilt new designs (EPR, AP1000, and ESBWR) all have this feature as part of their licensing basis. New European and Asian nukes will often have it too at grid operator insistence. Some Gen III+ units offer it as an option too.

One issue is the institutional arrangements for incentizing reactor owners to invest in this feature and to use it. A nuclear reactor owned and operated as a merchant plant could save a few million in construction costs and minimize risk of plant damage by just tripping off an unstable grid. They would only lose a day or three of lost revenue otherwise. Merchant plants in general have been criticized for not being good "grid citizens." Maybe the new nukes can avoid that PR trap.

This is an issue that NERC, FERC, and NRC need to address at the regulator level. Nukes with net load rejection should be justly compensated for that service.

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