CLIMATE CHANGE – NUCLEAR SAFETY
Nuclear power plants already faces issues that may be related to climate change: floods, heat waves, storms, invasion of jellyfish and seaweed, rising sea levels, etc. With global warming, some of these natural events may be more severe. Is the nuclear fleet ready to face those threats?
Nuclear power plants must be prepared to resist particular climatic hazards. Events like floods or heat waves can have a serious impact on their cooling system. Flooding is one of the major risks to which nuclear power plants must be prepared. To cool their reactors, these facilities use large amounts of water, 40 cubic meters per second and per reactor, which necessarily places them close to a river or the sea. This water dependence puts them at other risks: lack of available river water, blockage of access to cooling water by plant debris, jellyfish or sea weed bloom in the filter grids.
Safety checks following the Fukushima disaster in Japan in March 2011, when a 10 meter-high sea wall was overtopped by a tsunami, have shown that nuclear plants are at greater risk of catastrophic flooding as a result of climate change. Nuclear plants can be flooded and it happened several times.
In Bordeaux, on 27 December 1999, the Martin storm has made reached the seawater beyond the dikes oh the Blayais nuclear plant and the water has crept in utility tunnels. The reactors were immediately shut down by EDF, but the damage was done: electrical systems had to be shut down, including two of the four cooling circuits of reactor 1. As the plant still had electricity, pumping operations were started quickly, preventing a major accident. These operations lasted for weeks. The incident was rated level 2 on the INES scale.
In Britain, after discovering in May 2013 that one of their reactors at Dungeness would be at risk of inundation by seawater during a storm, the owners, EDF Energy, quietly shut it down. Dungeness is built on a shingle beach beside the English Channel. The company informed the Office for Nuclear Regulation that it was being shut down as a precaution. The reactor remained off-line five months in 2013 while a new sea wall was constructed.
HEAVY RAIN – SEA LEVEL RISE
Changes in rainfall regime may impact the behavior of cooling water supplies (rivers, streams, groundwater) and transmission lines. A change in the rain regime can in the long term change the bearing capacity of the underground. Even if the principal facilities (e.g. reactors) might not be concerned, related structures, piping and cabling can be.
Moreover, predicted increases in sea level may cause inundation of some sites. Many existing nuclear power stations are located on coastal sites because of the need for an isolated location with a plentiful supply of cooling water. Many are built at very low elevations, and are consequently highly vulnerable to the rising sea levels which global warming is expected to bring.This will be particularly true in the southeast of England.
Nuclear power may face difficulties in working because of the heat. A rise in temperature may affect the performance of the cooling systems. During the brutal heat wave in 2003, a quarter of French reactors had to be shut down. Normally, the cooling system pumps water, uses it to cool the reactors and then rejects the heated water into the environment. But in case of a heat wave, cooling waters are collected in smaller quantities, they come out of the plant warmer than usual, with the possibility of damage to the flora and fauna. Each nuclear plant has standards for the tolerated heating of the water, which is of the order of one to several degrees. During the heat wave of 2003, EDF had obtained derogations to reject abnormally warm water in rivers. The proposed new nuclear power station in Paks is supposed to reduce capacity when cooling water emission temperature limits are reached. When this happens more frequently, this will influence the economic performance of the reactor.
In the face of climate change, heat peaks will still force to reduce nuclear power performance or to dump too hot water in natural environments. In France, over the last thirty years, the frequency and intensity of heat waves has increased. And that’s not all, since there are three in four chance that the number of days of heat waves will increase to 5 to 10 days in the southeast of France in the twenty-first century.
JELLYFISH AND SEAWEED BLOOM
Power plants in Europe do get closed down due to cooling water intake problems. Large amounts of jellyfish and seaweed more frequently block the cooling water inflows of nuclear reactors. In recent decades, dozens of cases were observed where jellyfish and seaweed caused the partial or complete shut down of coastal nuclear plants. In 2011, for example, in Scotland, two of the Torness reactors had to be shut down in the space of one week, when the seawater, used as a coolant, has been invaded by jellyfish. In France, the small ‘rose-de-mer’ jellyfish closed the Paluel nuclear plant, and in Sweden in the USA, plants have been closed down with massive influxes of larger umbrella- type jellyfish. Jellyfish are abundant in Europe coastal waters through the summer months and warmer conditions (often attributed to ‘global warming’) and exacerbate this risk.
To explain this phenomenon, there is a climate-related mechanism: it could be a combination of elevated temperatures in the oceans and some environmental changes, such as overfishing and ocean acidification. It could be that the rising acidity of the oceans – related to the increased level of carbon dioxide in the water- reduces the number of sea- shell animals (that need lots of calcium) but do not touch the jellyfish. In this new non-competition environment, jellyfish could take the opportunity to multiply.
All nuclear plants need large quantities of water for cooling so all must be built close to the sea, large rivers or lakes. This makes them vulnerable to sea level rise, storm surges and to the possible collapse of large dams upstream from poor construction, floodwater or seismic activity.
The vulnerability of power plants to risks of flooding and overwhelming heat raises the question of cooling systems of the nuclear reactors. Besides the issue of seismic risk and probability of flooding, it is important to ask how long time of autonomy have nuclear power plants to ensure cooling a reactor if it ever stops completely?
Since nuclear plants are designed to operate for as long as 60 years and need around a further century to decommission, accelerating sea level rise and more intense rainfall may present serious problems. The risk of a serious nuclear accident remains always above zero as a result of unexpected phenomena from climate change.
Rapport sur l’inondation du site du Blayais survenue le 27 décembre 1999, Institute for Nuclear Protection and Safety (IRSN), 2000. http://www.irsn.fr/FR/expertise/rapports_expertise/Documents/surete/rapport_sur_l_inondation_du_site_du_blayais.pdf
Greenpeace Study, “The impacts of climate change on nuclear power stations sites”, 2007. http://www.greenpeace.org.uk/files/pdfs/nuclear/8176.pdf
 Report lead by Jean Jouzel, “Le climat de la France au 21è siècle”, volume 4, 2014. http://www.developpement-durable.gouv.fr/Le-climat-de-la-France-au-21e.html
 British Environment Agency, “Cooling Water Options for the New Generation of Nuclear Power Stations in the UK”, 2010. https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/291077/scho0610bsot-e-e.pdf