For those too young to remember, this happened of April 26, 1986:
The Chernobyl Disaster
whatisnuclear.com
What happened at Chernobyl? (short version)
Because Xenon built up due to a rapid shut-down mainly caused by nearby coal plant problem, operators at Chernobyl retracted the control rods all the way out of the core only to notice power instabilities due to the inherent positive coolant void coefficient of the RBMK reactor and reinsert them. But the tips of the rods were graphite, which displaced water without introducing neutron poison, thus increasing the power rather than decreasing it and the positive void coefficient allowed the reactor to undergo a runaway power excursion, resulting in a catastrophic steam explosion and graphite fire that killed 30 workers and released radiation in levels that were soon detected in Finland.
What happened at Chernobyl? (longer version)
The Soviet government ordered the operators of Chernobyl to perform a test on their reactor. The test was supposed to measure how long the spinning generator would continue producing electricity after the reactor was shut down before it slowed and stopped. The test was to happen with the reactor at low power. As the operators were about to start slowly and carefully bringing the reactor to low power, the utility company called and said that a nearby coal plant just shut down unexpectedly and asked Chernobyl to stay at full power for a while longer to keep the nearby homes lit. After peak hours, the operators brought the plant to low power rapidly. Nuclear engineers can explain to you that this kind of shut-down would result in an unusually large amount of Xenon build-up in the reactor fuel. Xenon eats up neutrons, thus making the chain reaction more difficult to maintain. Because of this, the operators were surprised when the reactor went to a lower power than they had expected.
To get the power of the reactor to its expected value, the operators pulled the control rods out further than they would ever do in any normal situation. Finally, the reactor went up to the power level needed for the test. Unfortunately, the Chernobyl reactor was designed in a dangerous manner, allowing the reactor to get hotter if bubbles formed in the water coolant flowing past the fuel. As water boiled in certain locations of the reactor, this power instability started rearing its head. Apparently, one of the operators noticed this highly unstable situation and pressed the button to insert the control rods and shut down the reactor. But, an even more serious design flaw was in the control rods. The neutron poison in most of each rod had a small graphite tip on the bottom. This graphite not a neutron poison (and is usually beneficial to chain reactions). So with the control rods all the way out, inserting them for the first few inches displaced some water without introducing any neutron poison, and this actually increased the power of the reactor. This led to more boiling of the water, which resulted in even more power and then positive feedback took the reactor power sky-high, immediately boiling all the water to steam. The steam pressure was so great that it blew the lid right off the reactor and through the roof of the reactor building (which was not one of those steel containments, by the way. It was just a concrete building).
With no more coolant, the fuel heated up and became molten. Standing graphite rods in the reactor ignited into a very hot graphite fire that began spewing bits of the radioactive fuel into the open air. The fire took over a week to extinguish, costing the lives of about 30 emergency responders due to acute radiation poisoning.
Which brings us to this week:
Scientists don’t understand why…
Andrei Tapalaga / History of Yesterday
Sept 17, 2021
Underneath reactor 4 there is still nuclear fuel that is active and which will take around 20,000 years for it to deplete. The uranium is too radioactive for anyone to live in the city and since the incident, the European Union had created a shield around the reactor which should not allow for the radioactive rays to come out.
“Chernobyl officials presumed any criticality risk would fade when the massive New Safe Confinement (NSC) was slid over the Shelter in November 2016.”
“The €1.5 billion structure was meant to seal off the Shelter so it could be stabilized and eventually dismantled.”
However, many other parts around Chernobyl have also been affected due to prolonged exposure, some more than others, and many of them have not been contained as they were not presenting any major radioactive activity until now. Neil Hyatt, a nuclear chemist from the University of Sheffield had mentioned that there is a possibility for the uranium fuel to reignite on its own.
Hyatt also offered a simple explanation on how this is possible, just like charcoal can reignite in a barbeque, so can nuclear materials that have once been ignited. He as well as a handful of nuclear chemists have mentioned previously the possibility of the uranium from Chernobyl to reignite, but the scientists from Ukraine that are responsible for managing the nuclear activity within the vicinity never really listened, until now…
Recently... sensors have detected a constant increase in the level of radioactivity. It seems that this radioactivity is coming from an unreachable chamber from underneath reactor 4 that has been blocked since the night of the explosion on the 26th of April, 1986.
Nothing to see here...
The explosion at Chernobyl in 1986 brought down walls and sealed off many rooms and corridors. Tonnes of fissile material from the interior of a reactor were strewn throughout the facility and the heat it generated melted sand from the reactor walls with concrete and steel to form lava-like and intensely radioactive substances that oozed into lower floors.
One chamber, known as subreactor room 305/2, is thought to contain large amounts of this material, but it is inaccessible and hasn’t been seen by human or robotic eyes since the disaster.
Now, researchers have seen a spike in neutron emissions from the room, with levels increasing around 40 per cent since the start of 2016. This points to a growing nuclear fission reaction, so researchers are trying to determine if this surge will fizzle out, as previous spikes in other parts of the ruins have done, or whether they will need to find a way to access the room and intervene.
I’m sure it’ll be fine if we just leave it alone….
Professor Neil Hyatt is the Royal Academy of Engineering and Nuclear Decommissioning Authority's research chair in radioactive waste management.
Speaking to LADbible about recent developments that nuclear reactions had been detected from deep within the mummified plant - 35 years after its core exploded in what is widely viewed as history's worst nuclear disaster - he says it's time to act.
"If we don't take it down, it's going to fall down," says Professor Hyatt, who teaches at Sheffield University.
"The original shelter was built as a temporary facility to stabilise a situation and the New Safe Confinement is essentially the same thing - to buy us time. [But] it only buys us around 100 years or so…
"That probably tells you it's going to take at least 50 years, if we started today, probably at a cost of about £900 million, to decommission Chernobyl.
"These are orders of magnitude, and the reason is because we still don't know everything we need to know to decommission it, about the material inside."
He adds: "If we don't take it down, it's gonna collapse eventually. If you've bought yourself 100 years, you really need to start cracking on with the dismantling - probably in the next 20 years.
Make no mistake, this is an ongoing disaster, not a footnote or relic of history:
Richard Stone/ Science
5 MAY 2021
Chernobyl officials presumed any criticality risk would fade when the massive New Safe Confinement (NSC) was slid over the Shelter in November 2016. The €1.5 billion structure was meant to seal off the Shelter so it could be stabilized and eventually dismantled. The NSC also keeps out the rain, and ever since its emplacement, neutron counts in most areas in the Shelter have been stable or are declining.
But they began to edge up in a few spots, nearly doubling over 4 years in room 305/2, which contains tons of FCMs buried under debris. ISPNPP modeling suggests the drying of the fuel is somehow making neutrons ricocheting through it more, rather than less, effective at splitting uranium nuclei. "It's believable and plausible data," Hyatt says. "It's just not clear what the mechanism might be."
The threat can't be ignored. As water continues to recede, the fear is that "the fission reaction accelerates exponentially," Hyatt says, leading to "an uncontrolled release of nuclear energy."
And it’s not just Ukraine’s problem:
‘Disasters know no borders’ says Guterres, 35 years on from Chernobyl nuclear accident
26 April 2021/ UN News
Marking the 35th anniversary of the accident, Secretary-General António Guterres said that together, “we can work to prevent and contain [disasters]… support all those in need, and build a strong recovery”.
Never forget
As one of the most serious nuclear accidents in history, nearly 8.4 million people in the three countries were exposed to radiation, according to the UN.
Some 350,000 were forced to leave their homes in severely contaminated areas, which left a deeply traumatic and lasting impact on their lives: “Their suffering must not be forgotten”, said the top UN official…
While the Organization had helped the people in the areas surrounding Chernobyl at the onset, four years after the accident the Soviet Government acknowledged the need for international assistance.
That same year, 1990, the General Assembly adopted a resolution calling for “international cooperation to address and mitigate the consequences at the Chernobyl nuclear power plant”. This began the UN’s participation in the recovery effort.
In 2002, the world body announced a shift in the Chernobyl strategy, with a new focus on a long-term developmental approach.
And in 2019, a new safety casing over the old shelter was completed and given to the Government of Ukraine. It was achieved with €2.2 billion in donations from over 45 nations.
A memorial to those who took part in the cleanup of the Chernobyl nuclear power plant disaster stands in Vasily Gulay’s hometown of Rechytsa, Belarus.
Gulay, now 67, was one of the cement workers sent from the state-run oil company Belorusneft to reinforce the foundation of the exploded reactor two weeks after the accident on 26 April 1986.
The memorial at Rechytsa, 165 kilometers north of Chernobyl, bears a list of names of cleanup crew members, called liquidators, and images of a helicopter and a fire engine. Gulay believes a cement mixer should be depicted too…
Gulay worked at the Chernobyl site twice, in May and October 1986. The second time the task was to drill a 2-kilometer-deep well to hold the solution left from washing buildings.
“And they [bureaucrats] claimed that my work was not directly connected with the cleanup operation. It took me four years to achieve the right to retire at 50!” Gulay told Euroradio.
In 2007, Chernobyl liquidators who did not have disabilities were stripped of benefits such as higher-tier health care and medication, health resort packages, and free public transport. In 2012, they also lost their liquidator status and were placed in the general category of Belarusians affected by the disaster.