Journal of Critical Infrastructure Policy
Nuclear Power ’ s Current Grid Roles
Only 96 of the 7,700 electricity generating stations in the U . S . are commercial nuclear power reactors . However , these 96 reactors , located at 58 nuclear power plant ( NPP ) sites , are responsible for approximately 20 % of all U . S . electricity generation , and over 50 % of the U . S . carbon-free electricity generation ( EIA 2020b ). Nuclear power stations have extremely high unit availability , typically operating over 93 % of the time , compared with wind (~ 35 % availability ) and solar energy systems (~ 25 % availability ). Unlike wind and solar energy , nuclear energy is directly “ dispatchable ”— Grid operators can call on NPPs to generate electricity day or night and regardless of weather . Nuclear power plants add diversity and fuel security to the mix of fuels utilized by U . S . electricity generating plants . These NPPs have repeatedly demonstrated their value during extreme weather events that forced the shutdown of fossil and renewable energy generators across wide geographic regions of the U . S . ( Greene 2017 ).
Despite these benefits , the current generation of commercial NPPs are not significant Grid resilience assets . The operational characteristics of these plants do not enhance the ability of the Grid to absorb , adapt to , or recover from major Grid anomalies . Today ’ s NPPs do not have very robust real and reactive power load following capabilities , and have little inherent island mode operational capability . Indeed , there are a number of scenarios in which current NPPs are actually Grid resilience liabilities ( Greene 2017 , Greene 2018b ). Today ’ s NPPs tend to have brittle interfaces with the surrounding Grid . They are intolerant of Grid disruptions and external events ( such as Grid voltage anomalies , seismic events , etc .), frequently responding by isolating from the Grid , tripping off-line , and shutting down . Once shutdown , these large NPPs become priority loads Grid operators must supply with electric power for safe shutdown cooling before other loads are served . Assurance of safe shutdown cooling is distinct from being an asset restoration priority . Today ’ s NPPs require as much as a few tens of MWe of cranking power from the Grid in order to restart . Since such large cranking loads cannot be met by traditional onsite diesel generators , the value of the NPPs as Grid restart / recovery assets is minimal . As a result of NPP unit size and cranking power requirements , current generation NPPs would often be the first plants to drop offline and the last plants to return to service in the event of major Grid disruptions .
While future large LWRs could incorporate technologies to address many resilience short-comings , the unavoidable need for large cranking power supplies for large reactor prevents them from being black start-capable with current technologies . Additionally , because the safety case for existing large LWRs depends on the availability of electric power , traditional NPPs are required by the U . S . Nuclear Regulatory Agency to have independent onsite and offsite power sources available to them at all times . This regulatory requirement effectively prevents today ’ s NPPs
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