The third generation of nuclear reactors (gen3) refers to models developed since the 1990s and commissioned in the 2010s, such as the EPR, the first of which was commissioned in Taishan (China) in 2018. They are safer and more efficient than those of generation 2, having integrated systems to prevent situations such as those experienced at Chernobyl and Fukushima from recurring.
Enhanced safety: the focus on 3rd generation nuclear reactors
Since the Chernobyl accident, when we talk about nuclear power, we think first and foremost of accidents and safety. The 3rd generation, developed since the 90s, has put the emphasis on this point. It incorporates the lessons of the two “founding” accidents, Chernobyl (1986 ) and Three Miles Island (1979), then the risk of hijacking (reference to September 11, 2001), then the lessons of the Fukushima disaster (2011).
The main improvements in EPRs therefore concern safety. There have been two main areas of improvement:
- Reducing the risk of serious accidents. This would be around 10 times lower than with generation 2 (Jacoud et al. 2018)
- Reducing damage in the event of a serious accident.
Reducing the risk of nuclear accidents
To avoid the risk of nuclear incidents, measures have been taken to improve the management not only of “internal” events, but also of external aggressions. Buildings are designed to withstand kamikaze aircraft, as well as earthquakes (0.25g acceleration for the EPR).
Another important point is the development of redundancies, i.e. several autonomous systems doing the same thing. If one emergency system fails, others can take over. The human factor, whose importance was highlighted by the Three Miles Island accident, is better managed, notably by increasing system inertia.
Reducing damage in the event of a nuclear accident
There are other ways of limiting damage in the event of a nuclear accident. There are two strategies: retaining the corium in the vessel and releasing the power to the outside (IVR strategy, In-Vessel Retention); or stabilizing the corium in a dedicated area (EVR strategy, Ex-Vessel Retention).
The risk posed by the release of hydrogen during oxidation of the fuel’s zirconium cladding, which caused explosions during the Fukushima accident, is often addressed. For example, 47 “passive autocatalytic recombiners” – materials that naturally recombine hydrogen with oxygen to form water vapor – are installed in EPRs.
A generation of efficient reactors
Another important point is that 3rd generation reactors are designed to be economically attractive. For example, they feature a high availability rate (>90%), shorter refueling times and a life expectancy of at least 60 years. To take advantage of economies of scale, they are generally of high power: 1100 to 1620Mwe (Jacoud et al. 2018)
EPRs
This is the type of 3rd generation nuclear reactor best known in France, since it is the French model. It’s also the one currently under construction at Flamanville. It’s also the oldest, having been developed by Framatome (an EDF subsidiary) and German energy companies since 1992. It has been EUR (European Utility Requirements) certified since 2009.
The containment strategy is EVR: corium is directed and passively cooled in a dedicated room. A filtering system limits any leakage.
Its production capacity is around 4590MWth, transformed into 1650MWe. It runs on enriched uranium and accepts MOX.
Backup systems are designed for “4th-order redundancy”, i.e. there are 4 divisions, each with the components needed to perform the required emergency function. For example, we saw with Fukushima that the malfunction of an emergency pump could prevent the reactor from being irrigated. In this case, there are 4 pump systems that can be activated.
Several EPR reactors are currently finished or nearing completion:
- Taishan 1, in China was coupled to the grid 5 years ago (June 19, 2018) and Taishan 2 the following year (May 2019). Noting abnormally high activity, the operator shut down Taishan 1 during its second fuel cycle, in July 2021. The fuel cladding was damaged. The problem was stress corrosion of the grids holding the fuel. The reactor was restarted in summer 2022.
- Okiluoto 3 in Finland was coupled to the grid last year and reached full power on September 30, 2022. After a few problems, production was restarted.
- Flamanville 3, France
- Hinkley Point C in the UK.
References
- jean-Luc Jacoud, Françoise Ternon-Morin and Philippe Videlaine, “Les réacteurs nucléaires de troisième génération (Gen3): vers une sûreté renforcée.” La Revue de l’Énergie n° 639 – July-August 2018
- A thread on the history of the EPR: https://twitter.com/Mangeon4/status/1539126280674856961
- On the Taishan 1 ruling:
- Minutes of the 61st plenary meeting of the High Committee on June 7, 2022: http://www.hctisn.fr/61e-reunion-pleniere-du-haut-comite-07-06-2022-a214.html
- SFEN, https://www.sfen.org/rgn/defauts-de-gainage-du-combustible-sur-lepr-de-taishan-analyse-de-la-sfen/