Boron and Fukushima
Today, we’re going to look at the Fukushima nuclear accident in 2011 and how Boron helps to contain the radiation and the potential spread of nuclear fallout.
Boron and Fukushima
Boron at Fukushima
In 2011, a severe nuclear meltdown occurred in Fukushima in Japan at the atomic reactor on the coast of Japan. Authorities resorted to spreading a boron compound on the site to halt the spread of radiation.
How did boron help mitigate radiation and meltdown at the time and how does it also act as an inhibitor in the nuclear rods themselves?
In Fukushima on March 11th, 2011 at 14:46 local time, an enormous tsunami wave struck the coastline and led to the reactor melting down in Fukushima. This undersea megathrust earthquake with a magnitude of 9.0 to 9.1 occurred 72 kilometers east of the Oshika peninsula in the Tohoku region. It lasted approximately six minutes causing a huge tsunami. It’s also known as the greatest Japan earthquake.
Boron is widely used in nuclear reactors for shielding, control and safety. Boron absorbs nutrient radiation during fission and controls the reaction’s rate, slowing or stopping it without itself fissioning. In addition to being a clean, reliable, and sustainable fuel for modern living, boron contributes to keeping nuclear power safe.
Plant operators can adjust the quality of boric acid in the reaction, by dissolving high-purity boric acid in the primary cooling circuit, which controls the nuclear reaction rate and its energy production. The use of borates as corrosion inhibitors is possible in some situations where criticality is reached. And this was the case in Fukushima.
So what actually happened that day?
The worst case scenario at a nuclear plant is a breach of the containment vessel. And there was indeed a breach of the containment vessel in Fukushima. At 11:01 on March the 14th, there was a catastrophic explosion in the upper part of the reactor building. And this was caused by a leak in the containment boundary of the plant.
The tsunami, which reached a height of 14 meters following the earthquake, swept over the plant seawall flooding parts of reactors, one to four. The flooding caused the emergency generators to fail and the circulating pumps to lose power. Between 12 and 15th of March the resultant loss of core cooling caused three nuclear meltdowns, three hydrogen explosions, and the release of radioactive contamination in units one, two, and three.
The active reactors immediately shut down the fission reactions that generate power after the earthquake. The reactor’s electricity was cut off and the emergency diesel generators were automatically turned on.
Coolant was circulated through the reactor cores by pumps, powered by electricity. Even after fission has ended, residual decay heat continues to be created however, and removed by this continuous circulation.
Due to this decay, heat from the spent fuel rods, the spent fuel pool in previously shut down reactor four increased in temperature on March the 15th but did not cool down sufficiently and exposed itself. The situation resulted in mitigation measures, which included radiation released into the atmosphere and this forced the government to declare a 20 kilometer radius evacuation zone around the plant.
In the wake of the April earthquake and tsunami in Japan, officials from the Tokyo Electric Power Company TEPCO, began injecting seawater laced with boron into the reactor’s primary containment vessel- boron being an excellent absorber of neutrons in nuclear reactions.
The seawater corroded the fuel elements but boron is not corrosive and is a safe, last ditch cooling method. The uranium 210 boron mix, absorbed the neutrons and stopped the Fukushima reactor’s core from reaching this critical state. This use of boron to cool the reactors was considered a safer option. Engineers pumped seawater laced with boron into two of the three reactors of the Fukushima number one nuclear power plant.
Many years later, decommissioning of the plant is still ongoing after 10 years. There are four types of decommissioning work being conducted at Fukushima. Radiation materials must be encapsulated, cleaned, cooled and stored. The Japanese government is considering using boron to decommission Fukushima.
In a study published in the World Nuclear News Update, scientists showed that water injection was safe but the water needed repumping several times. The Japanese government reported that the situation at Fukushima was worse than a meltdown. The IAEA, the International Atomic Energy Agency, released an updated log on the accident.
The IAEA has also stated the reliability of the system. Aside from the reliability and safety of the nuclear plant, the new research shows that boron is an essential component of the control rods. The scientific community is still trying to fully understand the radiation levels of Fukushima and researchers continue to study the amount of boron released in the spent fuel pool.
These studies are essential for the decontamination of the local area. A one model control rod of the damaged units was exposed to boron to gauge the extent of dampening of the nuclear reaction and researchers used boron carbide control rods to determine the distribution of the boron.
Further research continues to investigate the effects of radiation on the Fukushima area. The study’s authors led by Prof. Rod Ewing of Stanford University are urging the Japanese government to do more to protect the region and the findings of this paper are crucial for decontamination operations at the plant to enable a more thorough understanding of the meltdown conditions.
Besides Fukushima, boron has also been used in a meltdown situation, namely at Chernobyl. In Chernobyl, a large fire raged in the ruins of the number four reactors of the Chernobyl nuclear power plant in 1986. A hospital in the nearby town of Pripyat was overrun with radiation victims. The deadly radioactive dust had drifted all the way out to the Soviet union and even into Sweden. The air above the reactor was glowing where the uranium core had become exposed.
People leading the disaster response decided to dump thousands of tons of sand and boron on the core.
To reduce radiation risk and seal the site, the sand and boron were dumped extensively. This Chernobyl mixture of sand and boron also included clay and lead.
The deadly smoke plumes were contained since the sand covered the exposed reactor and with the help of boron the scientists were able to arrest the nuclear reaction.
The definition of a nuclear chain reaction means gathering radioactive isotopes close enough so the neutral and shoot into space, hits another atomic nucleus and split it. Due to the structure of the nucleus, there’s a certain probability that an isotope will absorb a neutron when it interacts with the neutron.
Boron tends to absorb neutrons and then instantly split apart. However, uranium specifically uranium 2, 3, 5, tends to break apart imediately after taking in a neutron. ???? Hence boron is a good anti-radiation weapon to have for nuclear emergencies.
And that’s all from Borates Today. For more information on the meltdown at Fukushima and other information related to nuclear power plants using boron and boron compounds, please go to Borates Today. Thanks for listening.
