Fukushima, the worlds worst nuclear accident that is still ongoing
There have been many failures with nuclear power plants from the experimental reactors to fully online commercial installation throughout the relatively short-lived history of nuclear power energy and generation. Many of the early incidents were due to an unknown with the energy. Poor design, containment leaks, runaway thermal reactions and fires with ejected fuel not reaching the cooling ponds, pressure loss of essential coolant and hydrogen build-up due to the boiling of with spent fuel rods that remain active and create their own heat for many years so need to be kept under strictly controlled conditions.
Chernobyl Nuclear Power Plant, Ukraine.
On April 26th at Chernobyl Nuclear Power Plant in Pripyat, Ukraine, a safety test was run on number 4 reactor which is an RBMK-type nuclear reactor that was used extensively throughout the USSR and still is to this day throughout the republics of the former Soviet Union. The test involved dropping the power of the reactor to simulate an electrical power outage to develop a strategy for a safety procedure to continue cooling of the reactor in such an event with the Emergency Core Cooling system (ECCS).
The reactor was only running at half capacity and was supposed to be slowed down to 1000 MWt prior to shutdown but due to operational error it fell to 30 MWt, it took a further hour to get it to 200 MWt and in a stabilized state. Despite this fact the test went on.
Nuclear reactors are self-running beasts once they get up to speed and the correct rate of chain reactors under controlled states are accomplished, it can take months to start up a reactor, at the same time once running they do not like to change course.
On the fateful night, operators came on shift in the control room and were given insufficient instructions with the manuals they were provided for the operational test that the previous shifts operators were supposed to run, lines of information and procedures were crossed out with red pen and notes made beside them that did not make sense, the operators were only experienced in the day to day running of the reactor so did not understand the extra operations involved. Due to the supposed importance of the test, it still went on. The operators proceeded to drop down the power of the reactor as well as turning off several safety mechanisms and only used 6 – 8 control rods when 30 should have been used for a safe shutdown.*
*_Control rods are devices that are lowered into reactor cores to slow reactivity, Chernobyls were made from boron with graphite tips that acted as a neutron absorber.
During the gradual decrease in power for the test there was a sudden power drop to near zero output, the operators managed to partially restore power having to make adjustments to the reactor equipment every few minutes but this made the reactor very unstable. After the test concluded the reactor was put into shutdown but due to the instability of the nuclear reaction and an inadequate amount of control rods, a runaway nuclear chain reaction occurred, this drove up power massively, it is estimated to have been 100x normal peak output power.
This heat and energy output had to go somewhere, part of the fuel cells were ruptured and the fuel inside reacted with the waterways creating huge amounts of high-pressure steam that caused an explosion and destroyed the reactor core. There was then another explosion a few seconds later, this was probably a hydrogen gas build up from the boiling off with the reactor fuel and possible spent fuel rods in the cooling ponds above in the reactor hall.
This event was classed at 7 on the International Atomic Energy Authority (IAEA) scale, the highest given to nuclear incidents.
The reason given for the accident was partial operator error and partial errors in design and safety systems.
The New Safe Confinement (NFC) was built and put into place in November 2016, it covers the original hastily built sarcophagus that was beginning to leak radioactive contamination, the NFC has heavy-duty remote control cranes with interchangeable tools for dismantling and safe handling with eventual storage of the waste.
It is projected to take at least 40 years for the dismantling and storage of reactor fuel to be completed.
Fukushima Daiichi Nuclear Power Plant, Ōkuma, Fukushima Prefecture
On 11th March 2011 a massive undersea earthquake off the coast of Tōhoku in Japan took place, the hypocenter of the earthquake was some 18 miles under the sea. It was the most powerful earthquake ever in Japan and the fourth largest since records began in 1900.
The resulting sudden movement of underlying rock and substrate due to the tectonic plates being forced then suddenly releasing moved a huge volume of seawater that created the tsunami wave.
This tsunami grew in size eventually impacting the Eastern seaboard of Japan causing massive devastation and deaths of many who died of drowning or blunt force trauma, the massive wave at 133 feet (40 metres) in height travelled at 435 mph (700 kph) destroyed everything as in its wake debris was collected, house, cars, everything, this wave of debris did the most damage inland.
The Fukushima Daiichi Nuclear Power Plant is located on the Eastern coast of Japan and so a full collision course from the tsunami was imminent, the massive 45.9 foot (14 metres) wave passed over the sea defence walls flooding the underground backup diesel generators and in turn, cutting the main power lines for the emergency cooling, critically they circulate heat away from the decay reaction in the reactor.
As soon as the earthquake and tsunami were detected, the plants four reactors were automatically shut down – at least the fission reactions were stopped but the heat from the nuclear fuel still needed to be taken away but the backup diesel generators that started initially had stopped and were now flooded underground.
The Tepco engineers went into the car parks and took the 12v lead-acid batteries from their cars to power up some control room gauges, only the basic monitoring tools and dials were enabled in order to see the state of the nuclear cores and control systems.
Attempts were made to power the cooling systems with household generators and long cables, dispute the efforts of the operators, the fission heat continued to grow.
The loss of coolant resulted in three nuclear meltdowns (melt through/China syndrome) as well as three hydrogen explosions from the core and the spent nuclear fuel ponds leaking cooling fluid so not being actively cooled which added to the explosive hydrogen buildup which blew the covers off the reactor vessels as well as the roofs of the buildings, this exposed the cores to the atmosphere.
Even though the reactors were in a new shutdown state nuclear fission was still taking place but as the reactor vessels and cooling rods with the associated systems destroyed, there was no way to get rid of the decay heat automatically. Firefighters were brought in to spray water into the exposed cores later to be replaced by remote control cranes as the radioactivity level was too high for prolonged exposure for humans.
After surveying with 7 different robots had shown mass damage with three out of four of the reactors, there was no easy option to stem the flow of radiation, not only that but cracks had occurred all over the plant including the basements that were and still are allowing natural groundwater and pumped cooling water to run through the plant picking up radioactive isotopes for it then to runoff into the Pacific ocean. There has been significant ambient airborne ionizing radiation and a wide area around the plant has had the top layer of earth removed and bagged for it to sit in ‘dumpy bag’ piles all over the landscape.
Nine years have passed and contamination is still leaking into the environment, various attempts have been tried to stop it with plugging gaps in concrete (that can be accessed safely), ice walls with industrial refrigeration equipment to freeze the groundwater but have proved only partially successful as the refrigerant ‘piles’ driven down into the earth do not reach the bedrock and so groundwater and cooling water that is contaminated bypasses them.
There is so much contaminated water flowing through the power plant that much of it has been pumped up into storage tanks only for them to leak due to sub-standard seals with rushed construction, some have completely leaked with the others being emptied of the contaminants and pumped into newer better containers.
A majority of the water in the tanks (1.1 million tons and growing by 720 tons a day as of February 2020) has been treated with the Multi-nuclide Removal Equipment (ALPS) at the plant but the process having reduced the concentrations of some nuclides like Cesium and Strontium as well as some other elements, it cannot remove the high radiated Tritium within it.
Recently Tepco, the government-run organizations that operate the plant said they want to dump the untreated contaminated water into the ocean, this was met with resistance from the worlds community including scientists and biochemists – the head of the Nuclear Regulation authority Toyoshi Fuketa called the ocean discharge the “only” solution.
All this time on and no real workable plan has been hatched to deal with the breached nuclear reactor vessels and buildings, the exteriors have been recladded but the problems still lie within them, remote control vehicles including robots have not been invented yet that can deal with the deadly radiation and humans can not get near to investigate.
The accident at Fukushima also was a level 7 on the International Nuclear and Radiological Event Scale (INES) but this was after combining three events with three reactors that were very hot and not running at a reduced output. Chernobyl’s one reactor fire was put out in 10 days whereas Fukushimas were never put out and are still boiling away today whilst spilling out Caesium 137 and other elements into the sea everyday.
Tepco have said that an extensive cleanup of the area and decommissioning of the plant will take 30 – 40 years which seems unlikely.