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Using CO2 Sensors in Nuclear Applications

Safety is a top priority for nuclear power plants. CO2-cooled reactors are inherently safer than water-cooled reactors, but it is essential to prevent, detect, and repair CO2 leaks to maintain safe operation. Infrared sensors from Edinburgh Sensors provide the ideal leak detection solution for nuclear research and nuclear power plants
.

Nuclear power stations convert energy stored in nuclear fuels such as uranium or plutonium into electricity. Energy is released using nuclear fission reactions; neutrons are fired at nuclear fuel rods to form excited nuclei that split into smaller nuclei, free neutrons, heat, and radiation. The heat is then moved away from the nuclear reaction core to generators, producing electricity.1-4

Nuclear power plants provide several advantages compared to fossil fuel plants including low carbon electricity generation. Small amounts of nuclear fuel provide large amounts of electricity, so nuclear power generation is often more cost effective and reduces fuel mining impacts compared with fossil fuels.1-4

Safety of nuclear power is a major concern
Catastrophic large-scale nuclear accidents in Chernobyl and Fukushima have resulted in widespread public fear of nuclear power generation. However, modern plant design processes emphasize safety; as a result, the overall risk of accidents at nuclear power plants is low and continues to decline.5

Major nuclear accidents, like those at Chernobyl in 1986 and Fukushima in 2011, are typically 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. Neutrons released during nuclear fission initiate a chain reaction that generates a large amount of heat and controlling the chain reaction is vital.2-4
There are many different nuclear power plant designs currently in operation, with varying ways to control 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
While water cooling provides high power density and therefore excellent thermal efficiency, systems that use water as the primary coolant have several drawbacks, including the risk of explosions during meltdown events.2-4

If there is a power cut and the system's water pumps fail, the fuel rods can reach very high temperatures, at which point water splits, producing 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
Using CO2 as the primary coolant in a nuclear reactor is inherently safer than using water, as CO2 is less reactive and does not pose a risk of exploding. CO2 is also more flexible in terms of operating temperatures and pressures, resulting in a more stable system that responds more slowly to catastrophic faults than water-cooled reactors. However, reactors that use CO2 coolants have lower power densities than water-cooled reactors, resulting in larger reactors and reduced efficiencies.2-4,9

Current and future nuclear power plants utilize CO2 cooling
The first CO2 cooled nuclear reactors were Magnox reactors, which were commissioned in the 1950s-1970s. However, Magnox reactors were never able to reach high efficiencies, and most have now been decommissioned.

The Magnox reactor led to the development of advanced gas reactors (AGR), which used new materials that enabled the reactor to operate at higher temperatures, increasing efficiency. Fourteen AGR reactors are presently in operation in the United Kingdom.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 important to detect CO2 leaks. A CO2 leak can leave the reaction core with no coolant and 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

Infrared sensors are ideal for monitoring CO2 levels and detecting leaks. Infrared sensors are easy to use and provide rapid online measurements of CO2 concentrations in a package that is robust, reliable, low-maintenance, and long-lasting compared with other gas composition sensors.

Edinburgh Sensors are a leading supplier of high-quality infrared gas sensing solutions, including continuous CO2 detectors. While some infrared sensors suffer from the effects of temperature or pressure variations, sensors from Edinburgh sensors offer extensive temperature and pressure correction to ensure 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 meet stringent UK regulations and are accredited for use in nuclear plants. EDF Energy, who currently operate eight AGR power stations in the UK, rely on Edinburgh Sensors to ensure their CO2 is stored correctly and to detect any leaks. EDF Energy have 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

1. '
Nuclear Energy'


2. 'Nuclear Energy' - Ferguson CD, Oxford University Press, 2011
.
3. 'Nuclear Power: A Very Short Introduction' - Irvine M, Oxford University Press, 2011.

4. 'Nuclear Power' - Breeze P, Academic Press, 2016.

5.
'Safety of Nuclear Power Reactors'

6. 'A Study of the Fukushima Daiichi Nuclear Accident Process' - Ishikawa M, Springer, 2015.

7. 'Lessons Learned from the Fukushima Nuclear Accident for Improving Safety of U.S. Nuclear Plants' - National Research Council, National Academies Press, 2014.

8. 'The 2011 Fukushima Nuclear Power Plant Accident' - Hatamura Y, Abe S, Fuchigami M, Kasahara N, Iino, K Woodhead Publishing, 2014.

9. '
High Temperature Gas-cooled Reactors Lessons Learned Applicable to the Next Generation Nuclear Plant'

10.
'Description of the advanced gas cooled type of reactor (AGR)'

11. '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.

12. '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.

13.
'Guardian NG'

14.
'Edinburgh Sensors'


Edinburgh Sensors,
a division of Edinburgh Instruments, is a world-class customer-focused provider of high quality gas sensing solutions. Since 1980, we have designed and manufactured a comprehensive range of gas sensors based on non-dispersive infrared (NDIR), fail safe gas sensing technology. The application of our continued research and development has contributed to several major advances in the world of infrared gas sensing and delivered a comprehensive portfolio of products for the detection of CO, CO2, CH4 and various refrigerants.
For more information, please contact :-

Edinburgh Sensors - A division of Edinburgh Instruments Ltd.
2 Bain Square, Kirkton Campus, Livingston EH54 7DQ. UK
Tel: +44(0)1506 425300
Fax: +44(0) 1506 425320
Email:
sales@edinst.com
Web: www.edinburghsensors.com

December 2018

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