Nuclear load following

Nuclear generation is sometimes misunderstood as “only baseload capable” and therefore incompatible with wind and solar because of their erratic generation profiles. This is not true. It is true that if there is a large baseload demand, then the economics favor nuclear plants that are optimized to run 24/7/365. Like any productive asset with high capital cost, the owner prefers high utilization to earn the highest return on that investment. This is one of the essential reasons that wind and solar will always be expensive – every hour they are not generating at rated capacity their high capital investment is not earning a return.

The engineering design of nuclear plants covers a range of load-response capabilities: from very fast response (think nuclear submarines and warships) to pure-baseload. The electric power market has mostly been characterized by baseload customers so traditional plant designs have been optimized for those economics. That said, even old 1960s designs like the French and German fleets are operated in load following mode. Here’s the power output time series of Golftech 2, one of the load following French nuclear plants.

The French electrical grid is sometimes 90%+ nuclear, so obviously nuclear generation has to maneuver to match the real-world demand (there is no magical “demand management” which makes the problem of the intermittency of wind/solar go away, this is the real-world of near zero carbon electricity in 2015). More references on nuclear load-following:

IAEA Technical Meeting – Load Following Sept 4-6 2013, Paris (source of the Golfech 2 chart, considerable details on how EDF plants are operated for load following)

Load-following capabilities of NPPs

So far we’ve only discussed the 1970s technology – designed and built when the primary market was for pure baseload generation. Tomorrow’s generation market will need to incorporate “renewables” which generate if the sun and weather dictate. For the zero carbon carbon future we can balance the intermittent renewables with storage or nuclear. If everyone is as wealthy as Bill Gates we could use storage. Otherwise we need dispatchable nuclear plants that can respond with high ramp-rates to VRE (variable renewable energy). Many of the advanced Gen IV reactors have economic load-following capability inherent in their designs.

The first to be deployed SMR load-follower is likely to be NuScale’s design, a creative way to achieve variable output with tried and true LWR technology:

10. Can NuScale’s SMR technology be complementary to Renewables?

Yes. NuScale’s SMR technology includes unique capabilities for following electric load requirements as they vary with customer demand and rapid changes experienced with renewable generation sources.
There are three means to change power output from a NuScale facility:
Dispatchable modules – taking one or more reactors offline over a period of days
Power Maneuverability – adjusting reactor power over a period of minutes/hours
Turbine Bypass – bypassing turbine steam to the condenser over a period of seconds/minutes/hours

NuScale power is working with industry leaders and potential customers to ensure that these capabilities provide the flexibility required by the evolving electric grid. This capability, called NuFollowTM, is unique to NuScale and holds the promise of expanding the deployment of renewables without backup from fossil-fired generating sources, such as natural gas-fired, combined cycle gas turbines (CCGTs)

6 thoughts on “Nuclear load following

  1. Of course the anti-nuclear people who claim that nuclear plants are incapable of load following are wrong. They can load follow just as well as coal-fired plants can. However, load following, even for nuclear and coal plants which are designed for load following, does increase costs.

    The varying temperatures of turbines, generators, and transformers required for load following shortens their lives because of thermal stress. When nuclear plants are used for load following, the nuclear fuel is fissioned less evenly thereby somewhat increasing the amount of nuclear waste. And, as has been pointed out, when plants are operating at less than 100% of load, the return on the investment is reduced.

    Having solar and wind power systems on the grid increases the load following requirements for both coal and nuclear plants thereby increasing costs thereby reducing the economic attractiveness of solar and wind systems, an unpleasant fact that is ignored by the purveyors of solar and wind systems.

    The available methods to keep demand for power as steady as possible have not been implemented to the extent possible. Some very large users have a demand charge which increases the KWH rate they pay for using power during periods of high demand thereby motivating them to modify operations to level their demand to the extent possible. In some places, the KWH charge for electric water heaters depends on the time of day. If all users of electricity were charged on the basis of when they use power, surely loads would vary less than they do now. It is unclear why that approach is not more widely used.

  2. Would it not be a good idea to build a suite of nuclear reactors which are capable of producing electricity, but spend most of their time generating Hydrogen? When demand is high, or it’s not windy, they can generate electricity, when that isn’t necessary, they’re returned to Hydrogen generation.

    • The concept of “variable demand” such as producing synfuel may prove to be economic, especially with high temperature reactors. Whether the economics are competitive is complicated, and above my pay grade. That said I’m pretty confident that we need to replace fossil transport fuels with some variety of synfuel. I think nuclear synfuel is a “least worst choice” compared to “biofuel”.

    • Graeme,

      It is unclear that producing large amounts of H2 could be justified. Storing and transporting H2 is difficult. For vehicle fuel, there are more attractive possibilities, such as ammonia, dimethyl ether, or artificially produced hydrocarbons. At this time, we cannot know for certain what the optimal way will be to power vehicles. It could be batteries or an artificial fuel, or perhaps both depending on circumstances, but it is unlikely to be H2.

      • My reading on current synfuel options brought me to the same conclusion. H2 may be a useful precursor but unlikely to be distributed for end use combustion. DME and ammonia seem to be the best of breed.

      • Steve,

        Before I got my degree, I worked as an electrical technician for a manufacturer of engines and generators. From reading about the characteristics of NH3 which make it difficult to use in an engine designed for gasoline, it seems clear that an engine designed specifically for NH3 could work very well.

        NH3 is harder to ignite than gasoline and burns much more slowly, but it has much higher resistance to knocking than gasoline. The fact that it is harder to ignite could most likely be overcome by designing spark plugs with a much larger gap and designing an ignition system to have a much higher voltage and produce a longer spark duration. The fact that it burns more slowly could be overcome by having a long stroke engine which would have a more compact combustion chamber and running the engine more slowly. That would result in lower power but because of the high knock resistance of NH3, the engine could use high pressure turbocharging to boost the power. I’m sure it could work very well.

        The only problem I can see is that because the NH3 would have to be under pressure to keep it liquid, a leak could cause serious problems if a person were near it. On the other hand, NH3 is slightly lighter than air so it would rise and escape. And, running vehicles on butane and propane doesn’t seem to cause problems even though those gasses also have to be pressurized to keep them liquid.

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