One-quarter to two-thirds of all U.S. nuclear plant reactors are at-risk of being closed prematurely, according to a new analysis by Environmental Progress. If half are closed and replaced with natural gas, the additional carbon emissions would be the equivalent of adding roughly 50 million cars to the road.

But 20 percent fewer nuclear reactors are at risk of closure now than at the beginning of 2016 thanks to policies implemented by New York and Illinois governments to recognize the environmental value of nuclear energy.

In 2016, there were three major published calculations of U.S. nuclear plants at-risk closure:

Environmental Progress (EP) estimated in March 2016 that 54 gigawatts (GW) of operating nuclear capacity were at-risk of closure before 2030. That number now declines to 44 GW thanks to actions by Illinois and New York state governments.
Bloomberg New Energy Finance (BNEF) estimated in June 2016 that 50.39 GW of operating nuclear capacity was at-risk of closure before 2030. With the saved plants that number now declines to 40 GW.
Rhodium Group in November 2016 estimated that 24 gigawatts of of operating nuclear capacity are at-risk of closure before 2030. Because it did not specify which reactors were at-risk, we cannot calculate if or how much that number changes with the saved plants.

We count 35 GW of nuclear energy in the "Triple Risk" because they are in de-regulated markets, uneconomical (according to BNEF) and up for relicensing before the end of 2030.

The total amount of at-risk nuclear capacity climbs to 65 GW when all the plants identified by EP and BNEF are combined. We label that number "EP Bloom."

This higher number is due to the fact that while EP and BNEF plants at-risk estimates are similar at 44 gigawatts and 40 gigawatts respectively, nuclear plants on each of our lists did not overlap perfectly, resulting in a longer list of plants at-risk. While this high number is an outlier, at least four plants on that larger list — DC Cook, Seabrook, Millstone, and Davis Besse — are considered at high risk of closing early.

EP's estimate came from counting all 34 gigawatts in de-regulated markets plus 19 gigawatts in regulated markets that are up for re-licensing before 2030. The assumption undergirding EP's analysis was that cheap natural gas, heavily-subsidized solar and wind, and flattening electricity demand, make nuclear plants less economical everywhere, not just in deregulated markets.

BNEF used publicly available data on plant costs in regulated markets, and estimated plant costs (2013 - 2019) using marginal electricity price data and capacity payment data in de-regulated markets. EP staff interviewed several nuclear industry executives from de-regulated markets with direct knowledge of their cost information, and other industry experts, about BNEF's analysis. They told us that while some of the specific plant cost predictions are inaccurate, the national picture and aggregate amounts estimated by BNEF are accurate.

Rhodium's number is comprised of half of all plants in de-regulated markets (17 gigawatts) and an additional 7 gigawatts from regulated markets. Rhodium lists threatened total capacity by geographic region, but not how it made its calculations. Some numbers Where both BNEF and EP find 9.3 gigawatts of nuclear threatened in Illinois, Rhodium finds 7.4 gigawatts for the whole East North Central region, which includes Illinois and Michigan, whose Palisades nuclear plant was announced for closure in December.

We are making our calculations publicly available as a Google Sheet here.

Despite actions by New York and Illinois, one-quarter to two-thirds of U.S. nuclear reactors still at-risk of closure