Closure of San Onofre Nuclear Power Plant Increased Emissions in California by 37 Million Metric Tons of CO2e

Closing nuclear power plants consistently increase emissions. As momentum is building for California to reconsider the planned closure of Diablo Canyon Nuclear Power Plant, it’s instructive to look back at the impact of closing another Californian nuclear power plant.

San Onofre Nuclear Generating Station (SONGS) shut down in 2012 and retired in 2013. SONGS Unit 2 was shut down in early January 2012 for routine maintenance, and Unit 3 was shut down in late January 2012 for a radioactive leak. The units never ran again. The formal retirement was announced in June 2013 by Southern California Edison after protracted opposition to restarting the plants from anti-nuclear environmental groups, led most prominently by Friends of the Earth.

What was the impact on emissions?

California’s total statewide emissions have declined since the early 2000s. Notably, however, the only year between 2007 and 2017 that saw an increase in total emissions was 2012, the year that SONGS closed.

The impact of the closure is particularly apparent in the electric sector emissions and generation mix data.

Figure 1: The annual emissions of the electricity sector in California

California in-state electric sector emissions increased by 11 MMT CO2 equivalent (+25%) in the year following the SONGS closure (2012) relative to the year prior (2011). It took four more years to reduce emissions back down to the same level and an additional, unnecessary 37 MMT CO2e was emitted in that period due to the closure of SONGS.

What was the impact on the generation mix?

Figure 2: Annual electricity generation in California by source

The SONGS closure caused a 33% drop in clean generation in California in 2012 relative to 2011. As Figure 2 shows, the drop in clean generation was almost exactly mirrored by a 35% increase in natural gas generation. This increase in natural gas generation persisted for several years and, just like the increased emissions, did not return back down to 2011 levels for several years.

Figure 3: Annual electricity generation imports to California by source

Electricity imports, on the other hand, were not drastically impacted by the sudden closure of SONGS. Imported renewables continued their long-term upward trend, and coal and diesel continued their long-term downward trend. The lack of impact on imported electricity is due to two factors. First, imported electricity from outside CAISO is often contracted far ahead of time and cannot be changed quickly. California is experiencing a similar problem increasing imports this year in response to an emergency procurement order. Second, many of the gas plants that filled the gap in California were previously running at low capacity factors, ramping up and down to meet peaks in demand. The simplest way to fill the electricity shortfall caused by the closure of SONGS was to run California’s gas plants more.

Will it happen again?

The shutdown of the Diablo Canyon nuclear power plant reactors is scheduled for 2024 and 2025. Despite a law requiring that the shutdown will not increase emissions, a lengthy California Public Utility Commission (CPUC) planning process, and a very large renewables procurement order, it is likely that the closure will result in increased emissions. The CPUC has already added more gas capacity in the face of ongoing emergency procurement orders, asked the Department of Energy for waivers for emissions limits, and is now considering adding even more gas capacity in the longer-term planning process to bolster reliability.

Additionally, the resources ordered to replace Diablo Canyon are scheduled to come online in 2028 — four years after the first reactor shuts down. This is almost exactly the same timeframe it took for the state to recover from the emissions impact of the SONGS closure. Now, however, the CPUC is also considering further limiting annual electricity sector emissions from 48 MMT to 30 MMT. Considering gas generators in California already produce five times as much electricity as Diablo Canyon, it is quite possible that the emissions increase after SONGS shutdown will be repeated. Instead of adding clean energy in an attempt to replace Diablo Canyon, the same additions would be more productively used to meet the 30 MMT emissions reductions target by reducing gas generation.