I recently saw a report that failure of a piece of safety equipment had “no impact on public health and safety”. If so, why is it there?
I was going to write this post several months ago. However, a recent comment on one of my posts has prompted me to write it now.
What originally sparked this post was an incident at Calvert Cliffs nuclear power plant in the USA in April 2015. Following a power cut to the plant, an emergency generator started but tripped after 11 seconds. The same generator had failed to start in a similar incident in 2010. Also, one of the three saltwater pumps also failed to restart1.
The Nuclear Regulatory Commission (NRC) said that “there was no impact on public health and safety”. This is a statement from the organisation that is meant to be overseeing health and safety at nuclear sites in the US. It was not from the site owners or the press. So if such equipment has no impact, why is it there?
A similar event happened at Hunterston power station in Scotland in December 1998. During what is now called the Boxing Day Storm, the power station lost grid connection. The reactor was shut down, diesel generators started and cooling was quickly restored. When grid connection was restored, the diesel generators and emergency cooling system were turned off. However, grid connection was then lost for a second time. However, the diesel generators had been set to manual rather than automatic and failed to start and there was no cooling to the reactor. Staff (working mainly in the dark) eventually restarted the diesel generators and cooling was restored2. However, despite an on-site emergency being called, the operators stated: ” that no radiation was released and there had been no danger to staff or the public.”3
The comment on one of my posts which I mentioned above prompted this post4 says:
Small fires due to the contact of minutes amounts of water/humidity with sodium did happen at Superphenix and other FBR-Na, but none has been serious.
So do we need to worry if nothing serious5 happens?
Let us say you are driving along in your car and after several miles you notice that your brakes are not working properly. You come off the road a few times, so do you think “but none has been serious” and so “there had been no danger to myself or the public”. Hopefully you do not since there is of course a probability that you will not be so lucky next time and you will kill yourself or one or more members of the public.
It is important to realise that a large scale nuclear accident has a much bigger consequence than a car crash. Fukushima and Chernobyl were lucky escapes. Cooling water was restored to the spent fuel ponds at Fukushima in time, and they did not have major fires. At Chernobyl miners dug underneath the plant and a large concrete slab stopped the core from melting down and reaching the groundwater.
Since the consequences are so large, the probability of such an accident must be extremely low – the nuclear industry often quotes a figure of 1 in 1 million reactor years or even 1 in 10 million reactor years.
To achieve this, a nuclear power plant should have back-up systems and even back-up systems of back-up systems in case the initial system fails. Let us look at a very hypothetical situation – the numbers will not be realistic, the system will be over simplified, but it will give you an idea of what is happening.
- Let us say that the probability of the complete loss of off-site power is 1 in 10.
- The probability that the diesel back-up do not work is 1 in 100
- The probability that the back-ups for the back-ups do not work is 1 in 100
- The probability that this loss of power causes a meltdown and a radioactive release is 1 in 10
So the overall probability is 1/10 x 1/100 x 1/100 x 1/10 which is 1 in 1 million. However, if we have lost off-site power then the probability of loss of off-site power is 1.0 – i.e. it has actually happened. Therefore, the overall probability is 1 x 1/100 x 1/100 x 1/10 which is 1 in 100,000. If the backup power supply does not work, the probability is 1 x 1 x 1/100 x 1/10 which is 1 in 1000.
So in the two examples I give at the beginning of this post, even the loss of outside power would have considerably increased the risk to the public. The failure of the back-up generators would have increased the risk even more.
The nuclear industry and their proponents (unfortunately including various ‘nuclear regulators) see nuclear accidents, even large ones such as Fukushima6, as nothing more than a problem with public relations.
1 NRC Sends Special Inspection Team to Calvert Cliffs Nuclear Plant, Nuclear Regulatory Commission, April 13 2015 (http://www.nrc.gov/reading-rm/doc-collections/news/2015/15-016.i.pdf)
2 The United Kingdomรขโฌโขs National Report On Compliance With The Obligations Of The International Convention On Nuclear Safety, UK Department of Trade and Industry, 2001 (http://www.onr.org.uk/cns2.pdf)
3 Nuclear alert at Scottish plant, BBC, December 30, 1998 (http://news.bbc.co.uk/1/hi/uk/244765.stm)
4 Comment By Roberto Kersevan on my post Energy Density of Uranium (http://www.plux.co.uk/energy-density-of-uranium/#comment-2229)
5 One person was killed and 4 injured at an explosion at the French Rapsodie FBR in 1994 – see Fast Breeder Reactor Programs: History and Status, International Panel on Fissile Materials, February 2010 (http://fissilematerials.org/library/rr08.pdf).
6 Revealed: British government’s plan to play down Fukushima, The Guardian, 30 June 2011 (http://www.theguardian.com/environment/2011/jun/30/british-government-plan-play-down-fukushima)
Leave a Reply