2. THE THREAT OF A NUCLEAR EXPLOSION
Dear Colleagues,
[…] I am therefore going to try to reconstruct the events chronologically, using my archives (notes from 1986).
I am very familiar with the construction of the RBMK reactor in which thousands of tonnes of graphite are used as a neutron moderator. We know that when the reactor is functioning normally, all the graphite is contained within a steel cylinder. Slowing down the neutrons in the graphite provides 6 to 7% of the total power of the reactor. In order to maintain the working temperature of the graphite at between 500 and 600 degrees C, the graphite cylinder is filled with an inert gas: a mixture of nitrogen and helium. The heat transfer liquid (water) circulates in the interior of the graphite assemblage.
We know that the accident occurred when errors were made by the staff in the course of an experiment that was dangerous from a nuclear point of view: the experiment was to investigate how, in the case of an emergency shut down of the reactor, it might be possible to use residual calorific emissions to produce extra electricity.
The absorbent rods used in this reactor were shortened and were missing the graphite ends that should fill the channel at the moment when the rods were taken out of the reactor core; as a consequence, when the rods were removed from the active zone, the channel filled up with water (caloporter fluid).
The protocol for the experiment had been submitted to the Minister, the Chief Engineer of the Chernobyl power station, the academic Nikolai Dollezhal, and the scientist responsible for the power station, Anatoli Alexandrov. Despite not having received a positive reply in writing, the management at the power station decided to go ahead with the planned experiment on the 25th April 1986.
The RBMK reactor is particular in having relatively low fuel enrichment (1.8% in uranium-235) and very high positive coefficients of temperature, particularly at lower power levels.
In summer 1986, after the accident, the minister for mechanical construction, E. Slavski, showed me the whole experiment program. According to this program, they needed to lower reactor power to 800MW and then, at this level of power, after the security rods had been lowered, observe the running of the turbo generator through inertia to determine the quantity of electricity produced.
When the experiment began, the reactor power fell to between 60 and 80 MW, and, in accordance with the laws of physics, the reactor fell into an “iodine hole”. In this situation, they should have shut down the reactor, waited two or three days until the short lived iodine isotopes had disintegrated and the power had returned to normal.
According to statements made by those who took part in the experiment, the personnel at the power station took the compensatory rods out from the heart of the reactor, and switched on the complementary circulation pumps in order to pump water into the reactor. The radiolysis of the steam in the channel produced an explosive mixture of hydrogen and oxygen which caused the first thermal explosion at the heart of the reactor.
The result was a deviation in neutron flux, and water that had filled the channels when the absorbent rods were removed started to boil. In two to five seconds, the power of the reactor increased a hundredfold. Ceramic fuel elements (uranium dioxide) with low calorific conductivity deteriorated rapidly under enormous thermal pressure.
It is known that water decomposes most effectively in fuel bursts. There then followed a second detonation of this explosive mixture that tore through the hermetic covering of the graphite and blew off the upper concrete slab (weighing about 1200 tonnes; even today it is still leaning at an angle of 60°). The graphite reservoir was now open to the air. When it burns in air, graphite can reach temperatures of between 3600 and 3800 degrees C. At these temperatures, the zirconium covering the fuel elements and the reinforced tubes in the graphite played a catalytic role, like a spark plug, contributing to the subsequent development of the accident.
The 1700 active channels of the reactor contained 192 tonnes of uranium (1.8% enriched uranium-235). In addition, the maintenance channels contained used cartridges that had been discharged from the reactor.
With graphite burning at such a high temperature, the channels containing the combustible material began to melt (like electrodes in a voltaic arc) and the melted combustible material began to flow downwards and infiltrate the areas where electric cables were housed.
The reactor rests entirely on a concrete slab about 1 metre thick. Underneath the reactor, were solid concrete chambers built to store radioactive waste.
As the personnel continued to pour water into the reactor with the circulation pumps, the water filtered down, of course, into these reinforced concrete underground chambers. A huge risk became apparent. If the material, in the process of fusion, pierced the concrete slab under the reactor, and reached these concrete chambers, it could create conditions liable to cause an atomic explosion. On the 28th and 29th April 1986, the joint members of the department of Physics of Reactors at the Institute of Atomic Energy at the Academy of Science in Belarus, of which I was the director, made calculations that showed that 1300 to 1400 kg of a mixture of uranium, graphite and water constituted a critical mass capable of causing an atomic explosion of 3 to 5 megatons (50 to 80 times more powerful than Hiroshima). An explosion of this magnitude could cause massive radiation lesions in inhabitants within a radius of 300 to 320 km, including the town of Minsk, and contaminating all of Europe to the extent that normal life would be impossible.
I wrote a report on the results of these calculations on May 3rd 1986 at a meeting with N. Sliunkov, first secretary of the Central Committee. What follows is the assessment of the situation that I presented at this meeting: the probability of an atomic explosion was not high because at the moment of the thermal explosion the heart of the reactor had been broken up and dispersed not simply inside the reactor but all around the reactor. They asked me why I could not give a 100% guarantee that no atomic explosion would happen at Chernobyl. I replied that in order to do that I would have to know the state of the concrete slab underneath the reactor. If the slab was unbroken, had no cracks or splits and if no holes appeared later, it would be possible to confirm that there would be no atomic explosion.
But I can tell you one thing with absolute certainty: thousands of railway carriages were brought to the area around Minsk, Gomel and Mogilev and the other towns within a 300 to 350 km radius of Chernobyl to evacuate the population should the need arise.
It was thought that the explosion could occur around the 8th or the 9th May 1986. That is why all possible steps were taken to extinguish the burning graphite before this date. Tens of thousands of miners were brought in to Chernobyl, as a matter of urgency, from Moscow and Donbass, to dig a tunnel under the reactor, install a coil of tubing, and cool down the concrete foundation slab under the reactor to prevent cracks forming. The miners worked in an inferno (high temperatures and high levels of radiation) to save the concrete slab. It’s impossible to truly appreciate the work these men did to prevent a potential nuclear explosion. They worked with no regard for their own personal safety. Most of these young men are ill, a number of them have already died in their thirties.
I compared Nesterenko’s text with the descriptions in Medvedev’s book where he talks about liquid nitrogen being used to “cool down the concrete slab” rather than putting out the fire, and he adds: “I was afraid that the core would pierce the concrete slab on which it rested and that it would collapse into the condensation pool, thus provoking a terrible thermal explosion”. [Author’s italics.] Medvedev is not talking about an atomic explosion. I put the question again to Nesterenko, who replied in more detail on the 6th February.
I can remember quite clearly being called to KGB headquarters in Minsk on the 1st May 1986, where I had a telephone conversation by “high frequency link” (they had a high frequency signal) with Legasov, who was at Chernobyl. He told me that they were thinking of putting liquid nitrogen into the collapsed re
actor. They thought that, as it evaporated, the liquid nitrogen would displace the air (oxygen) and that the graphite would stop burning. But amongst the scientists there was a rumour circulating that when liquid nitrogen is introduced into the active zone (the core of the reactor) it might cause an explosion. People were saying that this had happened before in England. I told Legasov that at our Institute at Sosny, in the research reactor IRT-M, there is a horizontal channel to test materials and studies had been made of magnetic and mechanical characteristics using different samples of metals at low temperatures. In order to do this, we had introduced liquid nitrogen into the channel. No explosion had taken place. I was asked to verify this information, with other people who had participated in the experiment. I also called (it was 2 o’clock in the morning) B. Boiko (who was the director at that time of the Institute of the Physics of Solid Bodies and Semi-conductors at the Academy of Science in Belarus), who confirmed that there had been no explosion. They then let me know that they were sending a helicopter to take me to the site so that I could assess the situation there.
After the accident, while the reactor was still burning (the fire lasted ten days) hundreds of scientists came to the site. They were all studying different things and proposing different schemes to control the situation. You know that 6000 tonnes of lead were poured onto the ruins of the reactor, and this lead evaporated and covered the surrounding area. It is one of the causes of the high level of lead found in children’s blood in the Bragin, Khoiniki and Narovlia districts. One scheme involved miners digging a channel under the foundation of the reactor. During our helicopter flight over the reactor, we tried to locate a route for the lorries carrying liquid nitrogen to reach the ruins of the reactor, displace the air and extinguish the burning graphite.
We know that after the explosion in the reactor, the personnel at the power station continued to pump water into the reactor using all eight pumps at the same time. It is clear that the whole sub-foundation under the concrete base of the reactor was flooded with water. All the scientists feared that if the lava consisting of the materials from the active zone pierced the concrete base, and if the combustible material and the graphite flowed into the concrete chambers underneath the reactor, this critical mass could lead to an atomic explosion. The primary objective was to stop the graphite burning. One of the solutions was to displace the air (containing oxygen). That was why they wanted to bring in liquid nitrogen. Many thousands of tonnes of sand and dolomite were dropped on to the reactor from helicopters. The graphite stopped burning after ten days. But afterwards, there were further outbreaks of fire from this melted mass, between the 15th and 17th May, and radioactive emissions which we detected at a distance of 70 to 100 km from Chernobyl, in the Narovlia region in Belarus.
According to witness statements from all the chemists (Legasov, Gidaspov…) there were two thermal explosions on the 26th April. The fuel elements that exploded and formed a mass of tiny particles created the ideal conditions for the radiolysis (decomposition) of the water vapour into oxygen and hydrogen. When this mixture reaches a certain concentration (7–9%) it explodes.
Under these conditions, ie if between 1,300 and 1,400 kg of water, graphite and uranium had come together, an atomic explosion could have taken place. My opinion is that we came close to a nuclear explosion at Chernobyl. If it had taken place, Europe would have been uninhabitable.
There is a false and dangerous idea currently in the West: with the reactors at Chernobyl shut down, there is no longer any risk of an atomic explosion. But as long as there is combustible nuclear material in the interior of the damaged reactor, it presents a danger not only for Ukraine, Belarus and Russia, but for all the people of Europe.
The European people should, in my opinion, be eternally grateful to the hundreds of thousands of liquidators who, at the cost of their own lives, saved Europe from the worst possible nuclear catastrophe.
V. NESTERENKO,
Corresponding Member of the Academy of Science of Belarus,
Professor, Doctor of Technical Science, and liquidator at the accident
that occurred at the nuclear power station at Chernobyl in 1986.
For thirty six hours, the inhabitants of Pripyat, 2 km from the power station, knew nothing of the volcano spreading its immense invisible evil over objects and beings. The Soviet media remained silent. The spring was exceptionally warm that year. Walking in the town parks, mothers took off their children’s shirts.
3. PRIPYAT: NUCLEAR TRAP
“I often think about Pripyat” writes Medvedev. “Life was great in this ‘nuclear’ town. I watched it being built with my own eyes. When I left to work in Moscow, three residential areas were already being lived in. It was a clean pleasant little town. The quality of life was very good. Newcomers never ceased to marvel at it. Many military personnel wanted to move there for their retirement. Occasionally, after endless problems and endless requests, they won the right to come and live in this paradise, that combined the beauty of nature with every convenience of city life”. 7
7 Op. cit.
Before the accident, Pripyat had a population of 56,000. Today it is deserted, overgrown by vegetation, and will remain forever a ghost town. The classical music emanating from the loud speakers on a wet foggy morning in November 1990 added a touch of surreal madness to this shipwreck from the Soviet era. Yulia Lukashenko stood in front of the house she had abandoned, now surrounded by brambles, and recounted the day of the accident. The day after the accident the people of this town were uprooted from their homes for ever. She had asked and had received permission to accompany us to Pripyat in order that she might “reconcile herself”. She was visiting her home for the first time in the four years that had elapsed. I watched from a distance as she held a piece of paper against the outside wall and wrote in capitals “I’M SORRY!” She was crying.
Q.—Why are you saying sorry? You are not to blame for what has happened to your house.
Y. Lukashenko—I’m a human being. Like all other human beings, I’m responsible for what happens to our planet, the Earth. I am, in a way, to blame for this house. Do you understand? I’m not judging myself as an individual, but in general, as part of humanity. And I feel guilty…
OK. I feel better now. Look over there. I can see the toys my children threw out the window when they chased us out of here. That makes me feel better. I am at home again… (She turns to face the front of the house) Look here, these little red and yellow cubes, and next to them a little yellow wheel. Their toys. There, in the hole, that’s our pen and pencil. I feel good. (She smiles apologetically)
—When did you understand what had happened at the moment of the accident? In the first few hours?
—No. Two weeks later. We only knew that it had been a serious accident two weeks later. But we didn’t know how serious. The morning of Saturday, 26th April, we knew something had happened at the power station. Lessons were interrupted, which was very unusual, discipline was very strict at the school—the teachers had been called in to the office and they were told that during recharging at the power station, there had been a mechanical failure and a fire had started. “The fire is under control (I’m quoting them) and there is no danger. But as a precaution, the children need to be kept at school, they should not go out, close all the windows, wash the floors, (which we did) and explain it to the children. Don’t let them out of your sight”.
Blinded by panic, the people who were responsible for the accident could not accept reality, and for the first thirty-six hours persuaded themselves that the reactor had not been damaged. The decision to evacuate the population was suspended, spontaneous initiatives to protect the children were rejected so as not to alarm people, the town of Pripyat was surrounded by a cordon of armed police, and people were forbidden to leave. It was only on 27th April at two o’clock in the afternoon that the inhabitants were evacuated.
During this time, vaporised nuclear fuel w
as being discharged into the atmosphere and being deposited as a fine dust of radioactive particles which was being inhaled by the people of Pripyat. Water tankers were already washing the town. It was lovely weather. Everyone thought it was in preparation for the 1st May celebrations, a bit early perhaps. But the answer was very different. Samples had been taken from the roads, from the air, and from the dust in the gutters and revealed that 50% of the radioactivity was Iodine-131. On the roads, the level reached 50,000 microsieverts per hour. The average level of natural radioactivity considered “normal” is 0.11 μSv/h. This is the result of radiation from the cosmos and from the earth’s rocks, and is compatible with life. That morning at Pripyat, radioactivity from Iodine-131 was 450,000 times higher than natural background levels. And radioactive iodine, if it is not immediately blocked by a dose of stable iodine, attacks the thyroid gland especially in children.
Y. Lukashenko—During the second or third lesson, I can’t remember now, it was around 10–11 o’clock, they started to distribute tablets, for us and for the children. From that point on, we knew it was really serious.
We went back to the house. We had a powerful telescope. We went out on to the roof of our house and spent a lot of that day watching what was going on at the power station. It’s about 2 kilometres away as the crow flies. The glow of a fire. We couldn’t see any flames, but you could see the fire glowing from the town. We invited the neighbours up there. The telescope passed from hand to hand. We could see the children playing down below in the sand, in their underwear. It was a really hot day. The Mums were out with their pushchairs, and the little ones had no clothes on.
For the last twenty years there has been a deliberate policy of disinformation that has led the world to believe that the disaster at Chernobyl was not, in the final analysis, a very serious accident. Ten days after the accident, the Vice-President of the USSR Council, M. Shcherbina, gave assurances at a press conference convened in Moscow that levels of radioactivity in the immediate vicinity of the reactor were about 150 μSv/h, when in reality it was 150 million μSv/h. The resulting policy decisions had cruel consequences for the people in the Western part of Russia, in Belarus and in northern Ukraine.
The Crime of Chernobyl- The Nuclear Gulag Page 3