Question
Asked 8th Feb, 2015

Why is nuclear power neither a dispatchable nor a non-dispatchable energy source?

Please see Fig 1 in the attached paper. Nuclear power is considered neither a dispatchable nor non-dispatchable energy resource.
I am new to this area, but from my understanding the conventional power plants, such as coal, gas, oil, hydro plants, they can adjust their power outputs. Some have a quicker response, e.g. a few minutes for hydro, and some are slower, e.g. up to a few hours for the coal plant.
For the renewable energy sources (RES), from the technical perspective, the outputs can be adjusted. For instance, the big wind farm (Not sure this is correct, but it is possible in techniques). Some smaller generators, e.g, the rooftop PV system, cannot be adjusted. However, from the policy perspective, the power from the RES will have the priority and therefore should not be curtailed unless causing issues. I understood to consider these resources as non-dispatchable energy.
What about the nuclear? For me, i think it is a dispatchable energy resource even the response time can be very long given it take longer time for the reactor to respond. 
Many thanks in advance.
Regards
Chao

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Popular Answers (1)

9th Feb, 2015
Erik Strub
University of Cologne
In general, nuclear is often used as basic load energy, because adjustment time is longer (than gas, for example), because the adjustment cannot exceed certain levels (after reducing power output, you can not go immediately back to the old power due to "reactor poisoning effects") and last not least, adjustment means stress to reactor strucure which might be an issue with authorities.
So in principle, nuclear is dipatchable, but only within certain limits, and the British regulations may (I don't know) not allow for dispatch.
However, some of the German NPPs at least work at variable load to compensate for renewables.
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All Answers (12)

9th Feb, 2015
Erik Strub
University of Cologne
In general, nuclear is often used as basic load energy, because adjustment time is longer (than gas, for example), because the adjustment cannot exceed certain levels (after reducing power output, you can not go immediately back to the old power due to "reactor poisoning effects") and last not least, adjustment means stress to reactor strucure which might be an issue with authorities.
So in principle, nuclear is dipatchable, but only within certain limits, and the British regulations may (I don't know) not allow for dispatch.
However, some of the German NPPs at least work at variable load to compensate for renewables.
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9th Feb, 2015
Leonardo S. A. Martins
IBM
I guess such discussion is analogous to whether or not hydro is renewable. It doesn't really matter in the great scheme of things. It's just a consequence of our deepest needs for clear and crisp taxonomy definitions.
After the large-scale introduction of renewables, nuclear is not the king of low variable cost anymore. In the old times, it would just serve as the most basic load supply. Period. Nowadays, however, as in the German case pointed out in the other reply, there appears the need to modulate nuclear to account for renewable generation.
9th Feb, 2015
Bacha Seddik
G2Elab
Completely agree with L Martins and E. Strub . The question is more a subject to debate knowing that the  nuclear plants are controlled , monitored and and be used (iare used) for ancillary services. The drawback of such system is its low dynamics.
in general any production system even wind farm and solar PV can be dspatchable , the real challenge is to forecast the availability of the primary source for a given horizon.
10th Feb, 2015
Dharmasa Hemadrasa
Caledonian College of Engineering, Oman
It is a great question.
10th Feb, 2015
Nicholas Sion
Intercan Technologies
To respond one must go to basics. Nuclear is based on the fission process, i.e. neutrons initiating the chain reaction that releases heat and some extra neutrons to continue and expand the chain reaction. Nuclear is a heat source and nothing else. When neutrons are removed the chain reaction falters to a halt and reactor power is reduced . This also releases a noble gas, radioactive Xenon-122 [half life 20 h approx.] and Xenon 127 [half life 36h]. Xenon gas is a neutron absorber. To increase power extra neutrons must be generated to sustain the chain reaction and increase power; but they would be absorbed by the Xenon until the half life is reached. Hence once the reactor has reduced power, the station operators must wait some 36 h before feeding in the extra neutron. This makes a nuclear reactor steady for base loads. Its power cannot be adjusted frequently and rapidly.
Renewable energy changes like a yo-yo at the whim of nature. But it is free. Public sentiment and legislation has made renewables energy connected to the grid. But the grid cannot store extra energy. So it is a mistake to reduce nuclear power whenever the sun shines and the wind blows. Hydro power and gas plants are used to accommodate this variability. 
Germany, is increasing its renewable energy and its grid [that is connected to the European grid] is becoming increasingly unstable . Some countries [Czeck Republic and another country] have disconnected their own grid system from Germany to gain stability. Major factories and manufacturing plants in Germany have brought in their own generators to stabilize their required power supply.
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11th Feb, 2015
Abdul Aziz Sangi
University of Illinois, Urbana-Champaign
Hydro, Fossil Fuel and Nuclear power are with us since last many decades. We fairly understand dynamics of power plants having any one of above as primary Fuel.  Wind, Solar and other renewable energy sources are relatively new. 
It will take a decade or so to develop technology so that we can store solar and wind power  during off demand hours and use it during peak hours. 
Further at present we have regional grids only. But in thirty or forty years from today. We may have globally connected grid systems. 
This will allow better load management with less environment degradation
11th Feb, 2015
R. Brian Peters
US ITER Project Office
 Nuclear is generally considered to be a base load power source and thus non-dispatchable  because it is power output cannot be changed in a timely manner for reasons well described by Nicholas above.  Coal plants and be ramped up and down  to address  term fluxuation but take several hours to bring on line and are not considered dispatchable in the short term sense but can be dispatched in a predictive feed forward control sense.  in the current mix of sources Natural gas turbines and Hydro power are typical dispatchable sources that can respond quickly to demand increases, on the order of 10s of minutes to bring on line.  renewals such as wind and solar are not considered dispatchable due to their intermittent availability
This is my limited understanding of the topic  hope is tis of some help.
Brian
15th Feb, 2015
Ian Hore-Lacy
World Nuclear Association
There seem to be two definitions of dispatchable in play above.  Nuclear is normally considered dispatchable because it can meet demand when required, this being normally base-load, ie 24/7.  It is not usually readily or rapidly variable in output, though French reactors are designed for load-following (unusual for PWRs, easier for BWRs).  See Load-following section in our France paper: http://www.world-nuclear.org/info/Country-Profiles/Countries-A-F/France/
Wind and solar are definitely not dispatchable - try bringing on wind on a calm day or solar at night!
25th Oct, 2016
Mayokun Olutogun
Karlsruhe Institute of Technology
Technically, nuclear power plants have been shown to be dispatchable in the load following mode with the use of Small Modular Reactors, see paper below. However, the process involves an inefficient operation of the plant, exposes it to thermo-mechanical stresses and it's economically not a good option. That's why in power systems, dispatchability is not a purely isolated technical concept and we always speak of "economic dispatchability" usually provided by natural gas plants or hydropower plants
18th Aug, 2017
Myriam Tonelotto
Sciences Po Paris
Just an addendum to the remarks above : 
1) French NPP do, for a share of the existing plants, provide follow-up to the electricity demand. But usually this follow-up will be programmed, the national utility  (EFD) knowing when there will be demands peaks due to weather or cultural context (holidays etc). The PWR that do follow-up are able to disminish there output since they're working at a cruise production of  around 80%. They will decrease their production for instance of a share of 70% during night time and regain cruise power output in the morning. (see graph of a typical day here : https://www.edf.fr/sites/default/files/contrib/groupe-edf/premier-electricien-mondial/cop21/solutions/pdf/cop21-solutions_flexibilite-nucleaire_vf.pdf
2) Only liquid fueled power reactors would be able to do much better, such as European MSFR (Molten Salts Fast breeder Reactor) jointly developed by CNRS in Grenoble and Orsay, Joint Research Centre in Karlsruhe, Delft University of Technology, Paul Scherrer Institute in Switzerland, Nuclear Physics Institute in Řež, Czech Republic. This reactor (does not exist yet ! but unlike start-up projects its investigation is carried by renowned public /academic labs, and belongs to the GEN IV Forum), thanks to the fact that fuel and coolant are one and only thing, and that it is liquid so free to expand, possesses a unique quality : a very negative feedback coefficient. This means that when the grid is asking for more power output, it will simply withdraw more calories from the reactor for steam production/electricity generation in turbines; as the fuel is cooled, it retracts, and allows, to put it in simple words, the atom nucleus to get a bit closer so to increase the chances for neutron encounter and therefore fission. As the the fission increases, the fuel heats up and rejoins the output level required in a couple of minutes. On the contrary, when the grid demand decreases, less calories will be withdrawn. The liquid fuel will heat up, expand, and therefore decrease the number of fissions. Todays French PWR do also have, of course, negative feedback coefficient (unlike Tchernobyl RBMK for instance : uncontrolled fissions = more heat = more fission = more  heat = core meltdown). But first, the heat transfer has to get from the uranium pellets to the cladding and then to the coolant (light water) - this takes much longer ; second, poisoning gas, as mentioned above, will also develop, whether in MSFR they will be bubbled out permanently from the liquid fuel instead of being trapped by the cladding ; third, the stress of temperature changes on a pressurized vessel creates fatigue, which is the main reason why brutal output changes are avoided, since they shorten up the reactor lifetime span.  (MSFR does not need pressure to be kept liquid  and ensure smooth heat transfer as water does : molten salts temperature in the reactor core is around 700° C and they don't not boil before 1300°).
3) A liquid fueled reactor such as European MSFR would therefore be able to follow up not only demand peaks, but also combination with a huge share of intermittent renewables, since its output would be able to adjust with no fatigue nor runaway the sudden lack of electricity production of a large windmill farm or to the contrary its sudden input.
Such reactor, once more, does not yet exist, it is currently investigated through the SAMOFAR security assessment project. You will find more info here (http://samofar.eu). But it is  avery promising technology, since it also solves in the easiest way the minor actinides burden.
PS1 : please note that I'm a film director, not a nuclear reactor scientist. My knowledge comes from sharing for my film with researchers working on MSFR as well as Chinese researchers working on TMSR in Shanghai (SINAP) and US researchers in ORNL. For German and French readers you'll find some general public info here  : http://future.arte.tv/fr/thorium
PS2 : forgive my poor English.
10th Nov, 2017
Mohammad Naser Hashemnia
Islamic Azad University Mashhad Branch
If renewable energy sources are not dispatchable, then what is really the meaning of active and reactive power control in wind/solar systems as many publications are focused on?

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