What Do Nuclear Chain Reactions and Epidemics Have in Common?

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What Do Nuclear Chain Reactions and Epidemics Have in Common?

Date: April 23^rd 2020

Author: Dr. Leon Cizelj

Category: En.vision

Topic: Electricity , Economy , En.vision , Nuclear Energy

A lot, in fact. Let us start with the fact that both can be controlled. While the chain reaction in a nuclear reactor was first controlled more than 75 years ago, Covid-19 has, in Slovenia at least, been controlled very effectively over the past week or two, according to the latest data. Both are also something people need to learn to live with. However, thanks to the in-depth, long-term public engagement with science, I expect this process will be much quicker with Covid-19.

I am deeply grateful to all the government officials, workers in power plants and health care, energy system operators, and those in charge of other critical infrastructure for doing an outstanding job addressing and coping with the Covid-19 threat. I am also grateful to scientists for putting their wealth of knowledge and curiosity as well as scarce budget resources to use, plunging into studying and making sense of the situation. My special thanks go to Dr Matjaž Leskovar of the Reactor Engineering Division of the Jožef Stefan Institute, whose sheer interest and experience in modelling hypothetical serious nuclear accidents had made him well-equipped for monitoring and predicting the epidemic. I deeply appreciate his courage to issue, as early as 25 March, a simulation that predicts the covid-19 epidemic in Slovenia until the end of April – a simulation that has turned out to be remarkably accurate. A big thank you also goes to the team behind ‘Science on the Street’, an initiative promoting science, for making possible and producing the online video lecture entitled ‘What Do Nuclear Chain Reactions and Epidemics Have in Common?’. The lecture is available here https://youtu.be/nxcMd0sY3So (in Slovenian).

What is typical of a chain reaction – in an epidemic or in a nuclear reactor – is exponential growth: the number of new patients or neutrons in a reactor at any given time is proportional to the number of all patients (or neutrons) at that time. Sessa, the mathematician who invented the game of chess, is credited with providing a great example to illustrate exponential growth. To reward him, his ruler asked him to choose the prize. Sessa humbly asked for one grain of rice on the first square of a chessboard, two grains on the second, four on the third, etc. Happy with his choice, the ruler sent his servants to get a bag of rice. Soon, the servants let him know they cannot and will never be able to produce a bag of this size (see figure).

If Sessa had asked for, say, twenty grains on each square of the chessboard, this would have been a practicable, manageable prize, one very much like the process in a nuclear reactor. In the reactor, the same number of neutrons (patients) emerge at any given time, resulting in a steady, stable chain reaction. To keep the reaction stable, especially to prevent the escalation into exponential power growth, the right technical solutions are required. Negative feedback loops are their key feature, automatically managing the power of the reactor, along with a range of effective checks to stop the chain reaction if necessary. This has allowed for commercial-scale operation of nuclear reactors for more than 65 years.

An illustration of Ray Kurzweil's second half of the chessboard principle (Ray Kurzweill, Wikipedia, By Andy0101 (talk) – Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=10700518

Something similar will happen with the spread of Covid-19. There are known ways to stop this chain reaction. Now we need to learn how to control it. While automatic management would be ideal, this will require some changes to our daily lives. Good hygiene (protection, disinfection) and less physical contact with other people seem to be the most obvious ones. Meanwhile, stronger checks like the currently prescribed social distancing, or vaccine at some point in future, are also available and have, to some extent, been tested.

The key to success lies in our own heads. As the ruler’s promise of a prize in the legend of Sessa, rice and a chessboard suggests, human intuition struggles to understand the implications of exponential processes. Therefore, more science and a higher level of trust in experts seem to be vital – yet another similarity between a nuclear chain reaction and the Covid-19 epidemic.