• Thursday, Jul 29, 2021
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OP-ED: Surprising fact: Nuclear power is safe

  • Published at 01:43 am July 18th, 2021
Chernobyl nuclear power plant
Chernobyl nuclear power plant. Power plants of today are far safer BIGSTOCK

The mistakes of the past are not repeated in today’s power plants

Millions of people (over 4 million according to WHO) are killed by outdoor air pollution every year. Most of these deaths can be attributed to pollution from burning fossil fuels, yet we think of fossil fuels as safe. 

On the other hand, relatively few people have been killed by nuclear power in its 70 year history. However, Chernobyl and Fukushima have convinced the world that nuclear power plants are unsafe.

We can objectively compare the safety of power from different sources by comparing deaths per thousand terawatt-hours (of electric power) from each source. Power from coal causes about 100,000 deaths per thousand terawatt-hours. Power from natural gas causes 4,000 deaths per thousand terawatt-hours. These are big numbers. 

Solar power causes only 440 deaths per thousand terawatt-hours, a much low number. Most readers will be surprised to learn that nuclear power is statistically the safest, causing only 90 deaths per thousand terawatt-hours (these figures are from Statista.com and Forbes).

The Chernobyl accident

The Chernobyl accident is the only nuclear accident in which a large number of humans were killed by radiation or sickness caused by radiation. It’s uncertain how many people have died of causes related to Chernobyl radiation exposure; there are many estimates. 

According to a report by UN experts in 2005, 50 deaths were caused by radiation poisoning, and rates of cancer in the area indicated that 4,000 more people who were exposed to radiation were likely to die (or had already died). 

However, the Russian Academy of Sciences estimated that between 112,000 and 125,000 of the “liquidators” (people who worked to clean up the area) had died of radiation-related illnesses by 2005. Even if the higher estimate is correct, 125,000 deaths is small compared to 4 million killed by fossil fuel pollution. Every year.
The cause of the accident was a serious design flaw combined with poor operator training.
Every nuclear power plant has control rods. A nuclear chain reaction is sustained by neutrons released by the fission (splitting) of uranium atoms. Control rods are made of neutron-absorbing materials.

When control rods are lowered into the reactor core, they are supposed to stop the chain reaction. However in the case of the Chernobyl reactor, the control rods were tipped with a length of graphite. 

Graphite is a moderator, which accelerates the nuclear chain reaction (and increases the heat produced in a reactor). Moderators are never used to make control rods.
The reactor was designed so that the graphite end of the control rod would not normally be withdrawn from the core. If it was withdrawn, reinserting it would certainly cause a power spike.

The operator at the time of the accident had probably not been properly trained, and was probably not aware of this possibility. The control rods were fully withdrawn before a test of the safety system. This was the fatal error that led to the disaster.
The coolant circulation pumps were turned off to test the safety system; reactor temperature then predictably spiked. This was expected, and was part of the test. In response to this temperature spike, the control rods were reinserted to stop the chain reaction.

However, as soon as the graphite ends of the control rods entered the reactor core, they increased the heat output further, precisely when it needed to be decreased. The heat spike overheated the core, vaporizing water (coolant), and causing a high pressure steam explosion which blew up the reactor.

The Chernobyl reactor did not have a “containment building” to contain an accidental release of high-pressure radioactive steam. This was another design error; water-cooled reactors in Western Europe and North America are always built with a containment building.

The Fukushima accident

In the Fukushima accident, one person was killed by radiation. 2,202 were killed during the evacuation of the area; they were mostly elderly or seriously ill patients who did not not survive being moved. 

The Tohoku earthquake and tsunami (which flooded the reactor site and led to the nuclear accident) caused about 15,000 deaths, but those deaths were not caused by the nuclear accident.

The Fukushima accident was also caused by serious design flaws. 

When the earthquake hit, the reactor was automatically shut down. However, a reactor requires cooling even after shutdown, as unstable “fission products” (isotopes produced by uranium fission) continue to fission and generate heat even after the reactor has been turned off. 

AC power from off-site was not available because of the earthquake; however, the reactor was still being cooled with power from generators (on site) until the tsunami flooded the site and stopped the generators. 

The plant had eight hours of backup power from on-site batteries. It also had backup generators, but these could not be started, as the switches were in a basement which had been flooded by the tsunami. 

So once the backup battery power was exhausted, the coolant circulation pumps could not be powered. The core overheated, and water (coolant) inside reacted with zirconium in the cladding of the uranium fuel rods, producing explosive hydrogen gas. 

Hydrogen gas explosions blew holes in the containment buildings of the reactors, allowing radioactive steam (vaporized coolant) to escape.

The generators and switches should all have been on high ground, to ensure backup power even if the site were flooded. The sea wall should have been high enough to prevent the site from flooding.
The Chernobyl and Fukushima design flaws have both been studied in detail. All existing nuclear plants have been examined for similar design flaws; many have been corrected, and many have been shut down. These design flaws will not be repeated in any future nuclear plant.

Nuclear plants today are objectively safe; their safety is ensured by redundant cooling systems (so the reactor will not overheat even if one cooling system fails) and by huge containment buildings (to capture any escaping radioactive steam). All this costs money, which is why nuclear plants are expensive to build.

The next generation of nuclear reactors will probably be sodium-cooled fast reactors (like the Natrium reactor which will be built in Wyoming, USA) or molten salt reactors (like the prototype which is being built in Wuwei in China). 

These new reactor designs simply can’t overheat; a small increase in temperature will stop the chain reaction. Mistakes by the operators will not cause serious accidents; they will merely cause the reactors to temporarily shut down. These idiot-proof designs will also be much cheaper to build than conventional nuclear reactors. 

It is extremely unlikely that accidents like Chernobyl and Fukushima will ever be repeated. To solve the climate crisis, we must phase out fossil fuel power plants. It is well-known that much of Bangladesh will probably be permanently inundated as sea levels rise. 

It is also very likely that agriculture on our remaining land will become less productive as the climate gets hotter. Our future depends on phasing out fossil fuels; the only realistic way to do this is with more nuclear power. It’s time to get over our fear of nuclear power.

Kazi Zahin Hasan is a businessman living in Dhaka.

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