Thermal System Coupling – from the 2019 ANS Winter Meeting

by Will Davis, from the 2019 ANS Winter Meeting

It’s no secret that public will and a great deal of marketing have combined to legislate large amounts of renewable energy onto parts of the US grid (and indeed grids around the world.)  The challenges that this brings are particularly severe for nuclear energy, which is commonly threatened when expected to operate in an environment where everything else has to “get out of the way” for renewables.  The question is:  Can nuclear play a role if it’s coupled with some kind of energy storage?  The early answers seem to be well into the “yes” range, as was explained today during an excellent technical session featuring a number of speakers.

A Tough Environment

“The problem is,” said Dr. Charles Forsberg today, “that when large amounts of renewable energy come onto the grid driving the price of electricity near zero or negative, nuclear simply cannot compete.”  Forsberg showed graphs depicting trends in California’s costs of electricity that demonstrated the change in daily electricity pricing; in 2012, before large amounts of solar PV (photovoltaic) power were on the grid the price was relatively stable throughout the day, but nowadays the price peaks right before and right after the solar PV flood onto the grid happens.  Worse, while the PV is gorging the grid with electricity no one needs, the price of electricity bottoms out or even goes negative.  Forsberg referred to this phenomenon as “price collapse,” and it’s directly tied to the solar PV phenomenon on the West coast.

Further, Forsberg pointed out that the actual overall wholesale cost of electricity in Europe has done nothing but climb as renewables have crowded onto the grid.  Crowded, that is, in nameplate capacity only – they still underperform at some times and at night, meaning that fossil backup has to be ready at all times.  This phenomenon could actually help base load plants over time, he pointed out.

Not Ready for Prime Time

Some might say, “well, just load follow with the nuclear plants and they’ll get along with renewables!”  This idea ignores the fact that nuclear plants – at least, large GW scale ones – have to run at higher or high constant power to make money.  As Prof. Mohamed Ali of Khalifa University, UAE pointed out today, there are significant problems with load following.  He said that load following actually leads to between 25 and 35% higher fuel costs, leads to a shorter fuel cycle length (time) and increases the risk of component wear in the plant.  Although some plants, like those in France, were designed (later plants) or modified (earlier plants) for load following and even instantaneous grid frequency control, this isn’t the best use for large GW scale plants.  What then could be the solution?

Energy Storage – Good for Renewables, Better for Nuclear

The coupling of nuclear plants with some sort of energy storage isn’t a new idea, but what was presented newly today were developments that make the actual operation of nuclear with storage as part of a mid-term-future, integrated grid seem much more realistic and likely.

Robert M. Field and Anna Maria Kluba presented today on Korea Electric Power Company / KEPCO International Graduate School research into combining heat storage with an almost totally conventional, “as-built” APR1400 nuclear plant.  This plant was the last widely built standard plant in Korea before the present swing over to nuclear fear and a halting of new builds in that country, and the design is also design certified by the US NRC.

The novel part of their proposal is the addition of a thermal oil circuit to take heat from the conventional steam cycle (with various takeoff points being considered) and then a large body of contained, crushed rock to store the heat energy.  When called for, the heat would be returned to the steam cycle by reversing the oil heat transport and providing feedwater at an elevated temperature.  An important point of the studies is to compensate for reactivity changes driven by the altered cycles; automatic controls are expected to be used to relieve operators of the need to monitor and control the more complicated system.

The above concept is intended to allow the nuclear plants at 1 GWe or greater to simply run at full power all the time, which certainly would help economics – but Charles Forsberg points out that it may prove out that an entirely new, synergistic and integrated energy system may be what is called for.  His ideas center around the ability to divert energy to either industrial uses or storage as the need dictates; of course, the primary product would normally be electricity in most cases.  However, he very sharply includes a “cheap energy buy-back” portion in his integrated power plant design that allows electricity to be bought by the plant when wholesale cost has been driven to nothing by renewables; the energy is stored as heat, and then sold back to the grid when power costs rise.

However it is done, it seems clear now that there is motion inside the industry to get nuclear working with storage – which is one of the things the renewables folks say will spread their preferred power source world-wide.  It looks, at first and even second take, that very large scale (i.e. non-electrochemical battery) heat storage could help nuclear far more, at least in terms of reliable and resilient power generation.  Just when these concepts will reach market, though, no one can say.

Will DavisWill Davis has been a member of the Board of Directors for the N/S Savannah Association, Inc. He has been a contributing author for Fuel Cycle Week, and wrote his own popular blog Atomic Power Review. Davis is also a consultant and writer for the American Nuclear Society, and serves as Vice Chair of ANS’ Book Publishing Committee. He is a former U.S. Navy reactor operator and served on SSBN-641, USS Simon Bolivar.  His popular Twitter account, @atomicnews is mostly devoted to nuclear energy.  He enjoys collecting typewriters and model trains and especially spending time with his nephew, Dawson.  

 

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