Capacity Factor Learning Curve

The learning curve for nuclear power plant operation can lead to a slow increase in capacity factor. However this leads the nuclear industry to be ‘locked in’ to existing technology.

The graph below shows the average capacity factor for all US nuclear plants by year.

capacity factor US
Capacity Factors for US Nuclear Plants1

You can see that it has increased considerably from about about 50-60% in the seventies to about 90% now. The increase is for several reasons including increased fuel burnup. However, the main reason is that the operators gained a better understanding of how to maintain and operate the plants.

If we look at the capacity factor for Finnish nuclear power plants we see a similar picture. However, on this graph I have plotted the capacity factor against the number of years of operation.

Finland capacity factor
Capacity Factor vs Years of Operation. Data from the World Nuclear Association Database2

I have also plotted a trend line for each reactor (I chose a power curve since this tends to be the form of learning curves3).

Again there is a general increase in the capacity factor with time and that the newer plants do better than the older plant.

One of the factors behind this is that two types of reactor predominate – the pressurised water reactor (PWR) and boiling water reactor (BWR)  so a lot of experience was gained on the same reactor type. At present over 88% of all power from nuclear power stations comes from PWRs or BWRs4 and there has been little change in design from the earliest reactors to the new reactors proposed for Hinkley and Sizewell.

Palisades_PWR EPR_PWR
Palisades reactor vessel (1960’s)5 European Pressurised Reactor (EPR) reactor vessel (2010’s)6

The USA and Finland have some of the highest capacity factors for nuclear in the world. This has not been true of the UK who went it alone with the Magnox and Advanced Gas Cooled reactors (AGR):

Capacit5y Factor vs Year for UK Nuclear Reacotrs
Capacity Factor vs Year for UK Nuclear Reactors.Data from the World Nuclear Association Database2

The capacity factor is consistently awful with one notable exception – the only PWR at Sizewell which has an average capacity factor of over 84%. In 2010 it did drop below 50% due to ‘excess moisture in the containment’ which incidentally turned out to be a leak of a gallon a minute – however that will probably be the subject of a future post.

The affect of the learning curves for running nuclear power stations means that currently we are ‘locked in’ to PWR or BWR designs with very few alternatives entering the market. Without massive public subsidy this is likely to remain the case.

While there is a positive learning curve for capacity factor (for PWR and BWR in the USA and Finland at least) the learning curve for nuclear power construction is negative – i.e. they get more expensive the more that you build7,8.

One of the reasons for the slow/negative learning curve is that very few large units are built and operated. Although the International Atomic Energy Authority (IAEA) boast of at total of 15,247 reactor years of experience the wind industry is currently getting over 225,000 turbine years of experience every year9.


1 Nuclear Power Plant Operations, 1957-2011, US Energy Information Administration (

2 World Nuclear Association Database (

3 Experience Curve Effects, Wikipedia (

4 Nuclear Power Stations In The World, IAEA 2013  (

5 Palisades PWR Schematics, Univertisty of New Mexico (

6 European Pressurised Reactor (EPR) Schematics, Univertisty of New Mexico (

7 Does nuclear power have a negative learning curve?, Climate Progress 2011 (

8 An assessment of the costs of the French PWR programme 1970-2000, Arnulf Gribler, International Ins;titute for Applied Systems Analysis, Austria, 2009 (

9 How Mnay WInd Turbines Are There In The World, Global WInd Day (


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