Nuclear power is often referred to as a low-carbon source of energy, implying that it would be a good idea to replace our fossil fuel based energy system with one based on nuclear energy. This is part of a dog and pony show, where the problem of climate change is reduced to its current main contributor, human carbon dioxide emissions. The problem with this approach is that replacing fossil fuel based energy with other energy sources is not a solution, if these other energy sources cause climate change through different mechanisms.
This brings us to the nuclear industry’s dirty little secret, known as Krypton-85. Natural processes generate small amounts of Krypton-85. This leads to an equilibrium concentration in the atmosphere of 0.009 PBq. However, nuclear power plants generate Krypton-85 as well. When spent fuel is recycled, Krypton-85 is released into the atmosphere. As a result, Krypton-85 concentrations in the atmosphere have risen dramatically. The concentration in 1973 was estimated at 1961 PBq. In 2000, the concentration was estimated at 4800 PBq, by 2009, this had increased to 5500 PBq.1
Why should we be interested in the Krypton-85 concentration in our atmosphere? Krypton-85 has a number of interesting effects. As a beta-emitter, Krypton-85 is capable of ionizing our atmosphere. This leads to the formation of ozone.2 In the stratosphere, we’re quite happy to witness the formation of ozone, as it protects us against harmful radiation from the sun. On the other hand, in the troposphere, the layer of the atmosphere beneath the stratosphere, the formation of ozone is a big problem. Unfortunately, Krypton-85’s ozone formation in the stratosphere is minor compared to that by cosmic rays.
In the troposphere on the other hand, Krypton-85 is believed to have a significant role in ozone formation compared to cosmic rays. This is especially significant at night, because normally ozone is not generated during the night, as it requires the presence of sunlight. Krypton-85 generates tropospheric ozone, during the day as well as during the night. Normally, Ozone concentrations in the troposphere drop to near zero during the night.3 In the presence of Krypton-85 however, ozone can be created at night as well.
What are the effect of this? Not a lot is known yet, unfortunately, despite the estimated eight orders of magnitude increase of ozone in our atmosphere. What is know about ozone however, reveals a cause of concern. Besides the fact that tropospheric ozone functions as a greenhouse gas, ozone damages plants. It is believed that ozone causes relatively more damage when trees are exposed to it at night, when concentrations are normally very low due to the absence of sunlight.4 Other worrisome effects of Krypton-85 are expected as well. In a 1994 study it was suggested that “there are unforeseeable effects for weather and climate if the krypton-85 content of the earth atmosphere continues to rise”.5 In its global atmosphere watch measurement guide, the World Meteorological Organization warned:
If 85Kr continues to increase, changes in such atmospheric processes and properties as atmospheric electric conductivity, ion current, the Earth’s magnetic field, formation of cloud condensation nuclei and aerosols, and frequency of lightning may result and thus disturb the Earth’s heat balance and precipitation patterns. These 85Kr-induced consequences call for 85Kr monitoring.6
Fortunately, there is good news as well. Thanks to the ongoing global phase-out of nuclear energy, global atmospheric Krypton-85 concentrations are estimated to have peaked back in 2009. If on the hand, a nuclear renaissance occurs after all, we could expect global atmospheric concentrations to continue to increase. It remains to be seen what the subsequent effects of this would be.
1 – http://www.sciencedirect.com/science/article/pii/S0265931X12001816?np=y
2 – Non-CO2 Greenhouse Gases: Why and How to Control? Proceedings of an International Symposium, Maastricht, The Netherlands, 13–15 December 1993
3 – http://earthobservatory.nasa.gov/Features/ChemistrySunlight/chemistry_sunlight2.php
4 – http://treephys.oxfordjournals.org/content/15/3/159.full.pdf
5 – http://www.opengrey.eu/item/display/10068/255704
6 – http://www.empa.ch/plugin/template/empa/*/7530
7 – http://dx.doi.org/10.1016/j.jenvrad.2012.07.006