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Sodium-cooled reactors: The solution to climate change

  • Published at 05:00 pm February 1st, 2020
Rooppur nuclear power plant
Rooppur nuclear power plant Bigstock

Employing it could prove to be invaluable to our world in the future

The concentration of carbon dioxide in the atmosphere is now over 400ppm. Scientists think that this will cause the earth to heat up, and will melt enough polar ice to raise the sea level by 15 to 25 metres in the future. Please note that Dhaka is only a few metres above sea level.

Thousands of power plants around the world burn fossil fuels. The world needs an alternative to fossil fuels; to reduce the level of CO2 in the atmosphere, we must dramatically reduce the consumption of fossil fuels.

The problem with sunlight and wind is that these are intermittent sources of power. Many cities experience winters with very little sunlight; many cities experience seasons with little or no wind. Modern cities need continuous power; solar and wind cannot provide this without expensive battery storage, which no city or utility has been willing to buy. 

That’s why after billions of dollars of investment in solar and wind power, there is not a single major city which is powered exclusively by solar or wind. Most utilities which have invested in solar or wind power use fossil fuel power as backup. That’s why big investments in solar and wind power have not significantly reduced emissions of CO2.

Hydro-power is a good source of clean energy, but creating hydro-power requires building dams and flooding large areas; this is politically impossible in any densely-populated country. In Bangladesh, the construction of the Kaptai Dam and the displacement of the Pahari people in the area that became Kaptai Lake created resentment which contributed to an insurgency in the Chittagong Hill Tracts region of Bangladesh. 

Nuclear power is, in fact, the only non-fossil energy which can easily be scaled up to replace fossil fuels. Nuclear power has become unpopular; the accidents at Chernobyl and Fukushima have convinced many people that nuclear power is inherently dangerous. Germany and Japan have shut down many nuclear plants since Fukushima.

The nuclear plants at both Chernobyl and Fukushima, like most nuclear plants which exist today, used water-cooled reactors. The accidents at both of these plants were caused by failures in the circulation of coolant, which caused the reactor core to overheat and melt down. 

In the 1950s, a different type of reactor was designed and tested at Argonne National Laboratories in Idaho; the EBR-II (Experimental breeder reactor II) which was cooled with liquid sodium. The use of liquid sodium as a coolant has huge advantages; reactors cooled with water must be operated under very high pressure, and overheating of the water coolant can cause a high-pressure steam explosion (which happened at Chernobyl). 

Liquid sodium coolant does not have to be pressurized. As the reactor vessel does not have to withstand high pressure, it can be designed to expand thermally if temperature goes up. The core of EBR-II sat in a pool of liquid sodium inside a metal reactor vessel. This design has important implications for safety. 

In April 1986, scientists at Argonne conducted a test: With the EBR-II reactor at full power, they turned off the coolant circulation. This would have caused a meltdown in any water-cooled reactor, but the design of EBR-II made such a meltdown impossible. As the core heated up, the heat was conducted by the liquid sodium to the metal reactor vessel, which then experienced thermal expansion; this thermal expansion of the vessel allowed neutrons to escape the core; this ended the chain reaction, and led the core to cool down without any human intervention. 

This kind of safety (safety which is designed into the nuclear plant, and which does not depend on operators doing the right thing) is known as “passive safety.” 

Many tests were conducted at Argonne to test the IFR (Integral Fast Reactor) design, which was a liquid sodium-cooled reactor design (like EBR-II) but with significant improvements on the EBR-II design. Reactors built with the IFR design will not need fresh uranium fuel; they can be fuelled with reprocessed spent uranium fuel (radioactive waste), which today’s water-cooled reactors cannot burn. The world has thousands of tons of radioactive waste in storage; in its present form, it will have to be stored for at least 10,000 years. 

However, if this waste is reprocessed and “burned” in reactors built using the IFR design, it will only be radioactive for a few centuries (as opposed to millennia) after being “burned.” So the next generation of nuclear reactors will reduce the world’s stock of radioactive waste; they will not add to it. 

Unfortunately, the US, after having developed the IFR technology, never used it; they stopped building nuclear plants because of pressure from the anti-nuclear movement. Russia has commissioned two commercial nuclear plants cooled by liquid sodium; BN-600 (commissioned 1980) and BN-800 (commissioned 2015). China has commissioned a small, experimental sodium-cooled reactor, CEFR (commissioned 2012), and obviously intends to build commercial sodium-cooled reactors. Russia and China are leading the way; tomorrow’s nuclear plants will be sodium-cooled plants which will not melt down, and which will gradually use up existing stocks of radioactive waste.

Chernobyl and Fukushima have convinced us that nuclear power is unsafe, but the truth is that nuclear plants are far safer than fossil fuel energy. The World Health Organization estimates that outdoor air pollution kills 4.2 million people every year; a significant number of these deaths can be attributed to pollution from burning fossil fuels. In the long term, fossil fuels threaten to make much of our planet unliveable; nuclear power is a far better alternative. 

The nuclear technology presented here is described in detail in the book "Plentiful Energy: The Story of the Integral Fast Reactor" by Charles Till and Yoon Chang (2011).

Kazi Zahin Hasan is a businessman and an avid reader.

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