In early 2019, four French EDF scientists wrote a 22 page report on load following in French nuclear reactors. The English version was first published on April 1 2020 but this has only recently been brought to my attention (ie mid Jan 2021).
This report is instructive and worrying, and requires careful reading. In essence, it discusses how French nuclear engineers have managed to retrofit and configure France’s reactors so that they can follow the diurnal loads increasingly required by France’s electricity needs.
It should be borne in mind that EDF’s 58 nuclear reactors are very old and past their sell-by dates. Most are between 30 and 40 years old with an average age of 33 years in 2018.
Some background is necessary to explain why this report was written. French reactors have been operating since the 1980s. Since their gross output has usually exceeded French domestic requirements, especially at night, much is exported to France’s neighbours ie UK, Belgium, Netherlands, Germany, Italy and Spain. Large amounts were until recently also sent to large pumped storage schemes in Switzerland at night. These transfers have been at a considerable financial loss to EDF and the French Treasury as the prices for such supplies are understood to be low. In addition, during the day, France imports significant amounts of electricity- mainly from the renewables in Germany.
In recent years, increasingly large amounts of French renewable energy (RE) have come on line. The EDF report states that since 2010, about 2 GW of renewable energy have been added annually to French generation capacity. In 2017, French wind power capacity was 13.6 GW and solar energy capacity 7.7 GW. Together, they total more than 21 GW, compared with 92 GW for nuclear power in France, ie 22% of nuclear’s capacity. Although more recent figures are not yet published, it is estimated that French renewables’ capacity is now over 25% of nuclear’s capacity.
For the future, the French Transmission System Operator (RTE) forecast in 2017 annual increases in wind capacity of 1.5 – 2 GW and in solar capacity of 1.4 – 1.8 GW up to 2023. Beyond 2023, the pace of development was expected to continue, reaching 40 to 51 GW wind capacity and 28 to 36 GW solar capacity by 2030.
These data and forecasts present serious problems for EDF’s nuclear reactors. In a nutshell, they mean that EDF needs to reduce their nuclear electricity outputs to make space for increasing RE supplies. The obvious method is to shut down its older reactors, but EDF has resisted this so far, apart from the Fessenheim station.
Instead, EDF’s engineers have opted to reduce reactor outputs by adapting them to follow electrical load. This is not stated in the report, but that is essentially what has been happening. For about 30 years, French engineers have been introducing novel techniques – in particular “grey” control rods and boric acid regimes – so that their reactors could be ramped up and down to follow daily diurnal loads.
Readers may be aware that nuclear utilities in all other nuclear countries do not do this as it is considered unsafe. Ramping up and down is restricted to approximately yearly episodes during refuelling and maintenance. Daily ramping up and down certainly does not occur in UK or US reactors.
The reason is as follows. The most dangerous time in the operating regimes of nuclear reactors is when they are powering up or powering down, because the balances of fast neutrons, slow neutrons, xenon levels and boric acid concentrations have to be strictly controlled during these episodes. Ramping up and down is usually done in UK and US reactors slowly over two or three days. To get these tricky balances wrong, as happened at Chernobyl in 1986, is to court disaster.
Annual Number of Transients (ie ramping up or down)
The 2019 EDF report states that, for the period 2000-2017, the annual average number of transients were
- 70 transients for each of its 20 x 1300 MWe reactors,
- 40 transients for each of its 34 x 900 MW reactors,
- 30 transients for each of its 4 x1450 MW reactors.
In the more recent “World Nuclear Performance Report 2020” by the World Nuclear Association, performance-report-2020-v1.pdf.aspx (world-nuclear.org), Stephane Feutry, Head of Nuclear Power Performance at EDF (and lead author of the 2019 EDF report) states
“Most of the nuclear reactors in France can reduce their power twice a day, every day, going down to 20% of nominal power in half an hour. However, this theoretical capability is not always used. On average, a reactor performs 15 variations per year, but this figure is increasing because more and more renewable electricity is being injected into the grid.” (See pages 15-17).
This probably means 15 x 2 = 30 transients per year. This is similar to, but lower than, the more detailed figures given in EDF’s 2019 report.
To ramp from 20% up to 100% of rated output within 30 minutes, and then to do the reverse 8 hours later, and to do this perhaps on a daily basis as the French EDF are apparently doing at some reactors is considered extraordinary.
Although the above reports state that EDF’s reactors can do this, the report remains silent on
(a) exactly how many reactors in the EDF fleet actually do this,
(b) whether they are ramping up by the full 80% or less than that, and
(c) how often they do this.
As for (a), a reliable French contact estimates that load following has occurred at perhaps as many as 40 EDF reactors – perhaps at their less old reactors. As for (b), the EDF report states that variable increases occur depending on the required reduction. And for (c), the 5th para of page 2 above indicates that rampings occur approximately once a week at each reactor.
When I first read this report, my initial reaction was surprise, followed by the question as to whether there had been reported incidents or accidents during such ramping episodes. Teething problems are experienced when practically all new technologies are introduced, so that, realistically speaking, we should expect some to have occurred here.
Apparently not – not even minor ones. The EDF report does not mention the words “accident” or “incident” far less discuss how many there might have been. Instead it states that there has been no “noticeable or unmanageable impact on safety or the environment”.
In other words, any incidents or accidents either were not reported to or not noticed by the media, or were considered “manageable” by EDF engineers.
This is not reassuring, given the nuclear industry’s past history of secrecy, coverups, and equivocations.
By my reckoning, probably about 40 rampings (ie up + down) occur at French reactors each week, (ie 2,000 per year) though some of these will be by small amounts. This is a rough estimate but it is an uncomfortably high figure given the advanced age of the EDF’s reactors. Basically, EDF embarked on a large safety experiment without consulting French (and other) citizens: this amounts to technological hubris.
The conclusion is that the French Government should be pressed to establish a programme of planned closures for all French reactors over the next few years. But the deeply entrenched institution of French nuclear power means that this is unlikely to happen anytime soon, sad to say.
I thank Yves Marignac and Paul Dorfman for their comments on an early draft of this article. Any errors which remain are my sole responsibility.