Possible Relief for Nuclear?

Applied Energy:

Highlights


– Nuclear power plants are subject to different operational constraints than other power plants.

– We provide a mathematical representation of these distinct constraints on nuclear flexibility.

– Benefits of nuclear flexibility are significant in a power system with high shares of renewables.

– Benefits include lower power system operating costs and increased revenue for nuclear plants.

Abstract
Nuclear power plants are commonly operated in a “baseload” mode at maximum rated capacity whenever online. However, nuclear power plants are technically capable of flexible operation, including changing power output over time (ramping or load following) and providing frequency regulation and operating reserves. At the same time, flexibility is becoming more valuable as many regions transition to low-carbon power systems with higher shares of variable renewable energy sources such as wind or solar power. We present a novel mixed integer linear programming formulation to more accurately represent the distinct technical operating constraints of nuclear power stations, including impacts of xenon transients in the reactor core and changing core reactivity over the fuel irradiation cycle. This novel representation of nuclear flexibility is integrated into a unit commitment and economic dispatch model for the power system. In a case study using representative utility data from the Southwest United States, we investigate the potential impacts of flexible nuclear operations in a power system with significant solar and wind energy penetration. We find that flexible nuclear operation lowers power system operating costs, increases reactor owner revenues, and substantially reduces curtailment of renewables.

CleanTechnica:

But as the headline says, there’s hope for the 98 US reactors in operation today. When the various countries of the world were selecting their preferred technology for nuclear generation, the US swung to light-water pressurized water reactors (PWRs). They were deeply familiar with them as they were the same technology used on nuclear powered submarines and aircraft carriers, something the USA had which most other countries didn’t.
And PWRs can be used to follow load. It’s a much slower response rate than peaker gas or using SCADA controls to curtail or spin up wind and solar, but it’s viable. They can drop or increase generation by 25% per hour, although when production is dropped they have to remain at the lower level for typically hours to allow xenon to dissipate before they can be increased again.
But unlike France, reactors are treated by grid operators as fixed, baseload generation, either on or off. There’s some limited seasonal load following related to hydro’s spring peak, but that’s about it. Part of that is purely economic. Load following with a nuclear reactor reduces the total GWh that are generated annually, and the only contracts they have are for committed baseload. If they were operated to follow load, they would lose money. Instead, renewables end up being curtailed when surplus baseload generation occurs. This is a somewhat reasonable approach, but it comes with an interesting wrinkle. Gas and coal reserve power is maintained for the nuclear plant and burn fossil fuels while wind and solar are curtailed.
So we have a technology that could load follow but isn’t allowed to by regulatory and contractual structures without economic penalty, and as a result lower-carbon forms of generation are curtailed while more gas and coal are burned. That’s an odd systemic choice in 2019.

Enter Jesse D. Jenkins of MIT and Zhi Zhou of Argonne National Laboratory, who led a team to model a Southwest alternative system management regimen, one which used real-world data from Arizona and New Mexico to project what would happen if Arizona’s PWRs were able to exploit their inherent technical abilities. They published their results in mid-2018 in the Applied Energy journal report The benefits of nuclear flexibility in power system operations with renewable energy. This peer-reviewed research paper crossed my screen this week and I dug into it deeply. It’s a solid paper in a rock-solid journal, not a think tank puff piece. Their conclusions are very worth assessing.
The big one is that if the PWRs were allowed to load-follow and bid on day-ahead reserve markets, the following would occur:

– A lowering of wind and solar curtailment
– A reduction of coal and gas being burned
– Overall electricity costs drop due to not burning coal and gas
– And a net revenue increase for the nuclear plants

This is a very good news story for the US PWR fleet and their owners. If they could convince regulators to allow this change in grid management and draw up new contracts to support it, they could keep more reactors running producing low-carbon electricity longer in the face of competition from cheap gas, wind, and solar. And the US overall would reduce its very high carbon pollution rate.
This would be a much better path forward than giving more public money in the form of subsidies or tax breaks to keep the nuclear reactors going. It’s non-trivial, as all things related to grid management and nuclear power are, but it’s viable. It would require regulatory changes, contractual changes, grid operation procedural changes and plant operation procedure changes, but that’s business as usual.
There are some wrinkles, both good and bad. As with many studies in this area, it assumes that there are no transmission constraints, which isn’t true in reality but is becoming more true. It also assumes a smaller regional grid without additional load balancing across a broader geographic region, something which is becoming less true with each passing decade. The load following ability for PWRs only applies for roughly the first year of their 18-month fuel cycle as in the last third they have to operate at or above 86% of capacity for technical reasons that are immutable. Only 20% combined wind and solar are assumed, so this is a next decade model, not a 2050 model. And for some reason they model in the PTC for wind energy despite that going away in 2020 and there being no possibility of this model being applied for any US region before then. This is very much a point-in-time approach and the basis for further studies specific to different plants in different regions as part of the assessment of viability and results, and the authors fully acknowledge this.
This doesn’t provide a path forward for new nuclear of course. That’s still too expensive and too slow to build. But it gives a path to a more leisurely retirement for the existing plants and lower overall CO2e emissions for the USA.