Safety is the primary concern when constructing and running a nuclear power plant, both for the plant itself and the environment outside. This is the main reason that CO2-cooled reactors are preferred over water-cooled reactors. To keep the reactors at a high standard of operation it is essential to prevent, detect, and repair CO2 leaks. Infrared sensors from Edinburgh Sensors provide the ideal leak detection solution for nuclear research and nuclear power plants
Nuclear power stations generate electricity by unlocking and converting the energy stored in nuclear fuels like uranium or plutonium. The energy is released by splitting apart atomic nuclei in nuclear fission reactions. Splitting occurs by firing high energy neutrons at nuclear fuel rods to form excited nuclei that separate into smaller nuclei, free neutrons, heat, and radiation.
The heat energy can be then transferred away from the nuclear reaction core to generators, producing electricity.1-4
Nuclear power plants offer a number of important advantages over fossil fuel plants, including low carbon electricity generation. It requires a much smaller amount of nuclear fuel to produce the same amount of electricity as traditional fuels, even factoring in the greater complexity of the plant. This often makes nuclear power generation more cost effective and reduces the impact of fuel mining.1-4
Safety of Nuclear Power is a Major Concern
There have been several high-profile accidents, such as the Chernobyl and Fukushima melt-downs, leading to a widespread public fear of nuclear power generation. However, this has led to even greater safety measures, and modern plant design processes being built around making structures as safe as possible; this has resulted in the overall risk of accidents at nuclear power plants being low and this continues to decline.5
In the cases of Chernobyl in 1986 and Fukushima in 2011, the meltdowns arose as the result of a series of events involving overheating, fuel meltdowns, and explosions, resulting in the release of large amounts of radioactive material into the environment. A surplus of neutrons cause the fission reaction to cascade and a large amount of heat is generated, which is unable to be contained. Controlling the chain reaction is therefore vital to the safety of the plant.2-4
There are a number of different nuclear power plant designs currently in operation, with varying ways of maintaining stable nuclear fission chain reactions. Some reactors rely on water as the primary coolant, while others use gases such as CO2 or Helium, molten metals or molten salts.2-4
Using Water as the Primary Coolant Increases the Risk of Explosions
Although water cooling provides high power density and therefore excellent thermal efficiency, there are several drawbacks to systems that use water as the primary coolant, most notably the risk of explosions during meltdown events.2-4
If at any point the power to the system's water pumps cuts out, the water ceases to circulate and the fuel rods can reach very high temperatures. These temperatures can be so high that the water molecules split and produce explosive hydrogen and oxygen gas.
This possibility was demonstrated in 2011 when an earthquake and tsunami in Japan led to a power outage at the Fukushima nuclear plant, removing power from the cooling systems, resulting in overheating of the fuel reactors, which were flooded with water and led to explosions that released large amounts of radioactive material into the environment.6-8
CO2 Provides Safer Cooling than Water
To avoid the problem of high-temperature explosions, CO2 may be used in place of water as the primary coolant in a nuclear reactor, making it inherently safer. CO2 also offers greater flexibility in the choice of operating temperature and pressure, producing a more stable system that allows more time to react to catastrophic faults than water-cooled reactors.
There are drawbacks to reactors that use CO2 coolants over water, namely the lower power densities, which results in larger reactors and reduced efficiencies.2-4,9
Current and Future Nuclear Power Plants Utilize CO2 Cooling
The first reactor type to use CO2 coolant were Magnox reactors, which were commissioned in the 1950s-1970s. However, the reactors were never able to consistently reach the high operating efficiencies necessary to keep them in operation and most have now been decommissioned.
Lessons were learned from the Magnox reactor, and they paved the way for the development of advanced gas reactors (AGR). AGRs used new materials that enabled the reactor to operate at higher temperatures, reaching efficiency levels that had eluded the Magnox. First coming online in 1976, there are still fourteen AGR reactors still in operation in the United Kingdom today.2-4,9,10
The latest research into nuclear reactors includes the development of gas-cooled fast reactors, which use supercritical CO2 as a coolant that directly powers turbines without intermediate steam generation, resulting in further increased efficiencies.11,12
Detecting CO2 Leaks is Vital for Safe Nuclear Power Generation
In both nuclear research and routine operation of CO2 cooled nuclear reactions, it is vital that any CO2 leak is detected. A CO2 leak can divest the reaction core of coolant and leave it in danger of overheating. Furthermore, large leaks of CO2 can be dangerous to personnel and the environment, expensive, and disruptive to power plant operation.10
An ideal monitoring and detecting solution is the use of infrared sensors. Infrared sensors are simple to install and use and provide rapid online measurements of CO2 concentrations in a robust, reliable, low-maintenance, and long-lasting unit, when compared with other gas composition sensors.
Edinburgh Sensors is a leading supplier of high-quality infrared gas sensing solutions, including continuous CO2 detectors. Some models of infrared sensors lose accuracy when under the effects of temperature or pressure variations. Edinburgh Sensors products offer extensive temperature and pressure correction to ensure they continue to report accurate results in a wide variety of operating environments, making them ideal for nuclear research and operations.13,14
Figure 1. Guardian NG from Edinburgh Sensors. Image credit: Edinburgh Sensors.
Edinburgh Sensor’s Guardian CO2 NG gas monitors are fully compliant to stringent UK regulations and are accredited for use in nuclear plants. EDF Energy relies on Edinburgh Sensors in their eight UK-based AGR power stations to ensure their CO2 is stored correctly and to detect any leaks. EDF Energy has recently purchased a large number of Guardian NG CO2 monitors units from Edinburgh sensors to support their control systems at their nuclear power stations.13,14
References and Further Reading
- Nuclear Energy’ https://www.edfenergy.com/future-energy/energy-mix/nuclear
- ‘Nuclear Energy’ — Ferguson CD, Oxford University Press, 2011.
- ‘Nuclear Power: A Very Short Introduction’ — Irvine M, Oxford University Press, 2011.
- ‘Nuclear Power’ — Breeze P, Academic Press, 2016.
- ‘Safety of Nuclear Power Reactors’ http://www.world-nuclear.org/information-library/safety-and-security/safety-of-plants/safety-of-nuclear-power-reactors.aspx
- ‘A Study of the Fukushima Daiichi Nuclear Accident Process’ — Ishikawa M, Springer, 2015.
- ‘Lessons Learned from the Fukushima Nuclear Accident for Improving Safety of U.S. Nuclear Plants’ — National Research Council, National Academies Press, 2014.
- ‘The 2011 Fukushima Nuclear Power Plant Accident’ — Hatamura Y, Abe S, Fuchigami M, Kasahara N, Iino, K Woodhead Publishing, 2014.
- ‘High Temperature Gas-cooled Reactors Lessons Learned Applicable to the Next Generation Nuclear Plant’ INL (Idaho National Laboratory) Digital Library
- ‘Description of the advanced gas cooled type of reactor (AGR)’ https://inis.iaea.org/collection/NCLCollectionStore/_Public/28/028/28028509.pdf
- ‘The application of supercritical CO2 in nuclear engineering: A review’ — Qi H, Gui N, Yang X, Tu J, Jiang S, The Journal of Computational Multiphase Flows, 2018.
- ‘Review of supercritical CO2 power cycle technology and current status of research and development’ — Ahn Y, Bae SJ, Kim M, Cho SK, Baik S, Lee JI, Cha JE, Nuclear Engineering Technology, 2015.
- ‘Guardian NG’ https://edinburghsensors.com/products/gas-monitors/guardian-ng/
- ‘Edinburgh Sensors’ https://edinburghsensors.com/about/about-us/
This information has been sourced, reviewed and adapted from materials provided by Edinburgh Sensors.
For more information on this source, please visit Edinburgh Sensors.