Once Chernobyl - but please with return ticket

Author: Dr. Klaus Hassmann, Cluster Energietechnik, Dr. Dipl. Phys. Theobald Fuchs, Nuremberg (as of May 2016) In 1986, the reactor disaster in Chernobyl happened. 30 years after this terrible event, the press and numerous media report extensively about the accident and its consequences. The objective of this article is not to repeat the events for the umpteenth time. It goes back in time to the weeks after the accident and describes how experts tried to understand what might have happened there. By means of impressive photos impressions from a two-day stay of these years on site are described in the 2nd part.

In the media a reactor accident in Ukraine was pointed out, nothing more. Only when from a bad weather zone in Scandinavia, later also in Central European countries a very high soil contamination of even heavy volatile reactor-typical fission products was reported, specialists began to occupy themselves not only in Germany with the processing of this factual situation. After evaluating the weather conditions, it soon became clear that this radiation contamination had rained down from a radioactive cloud that could be assigned to the country of origin, Ukraine.

Tracking down the events at Chernobyl

The technical basis in Germany for research was the knowledge gained from the federal government's R&D project on core meltdowns, for which more than DM 100 million had been spent by 1986, as well as the risk study for the pressurized water reactor Biblis B. When the fuel in the reactor core is overheated, first highly volatile noble gases are released, followed by medium-volatile fission products such as iodine, cesium, tellurium and antimony at over 1500 degrees C, and finally, at over 2200 degrees C, low-volatile ones such as strontium, barium, molybdenum, ruthenium, lantanum, neptunium, cerium and plutonium. The latter, in particular, have a very long lifetime until the radiation drops to levels that are harmless to humans and animals. For the most part, fission products of the 2nd category and all of the 3rd category are released bound to particles (aerosols). The decay series of the elements can be read in the list of nuclides of all known elements.

Very tenaciously, the information leaked out that Chernobyl was water-cooled, graphite-moderated reactors; the moderator slows down the neutrons and ensures that the particles necessary for a self-sustaining chain reaction remain in the area of the reactor core. Reactor physics was used to study these materials for their behavior under various system and component failures. It was found that a steep power ramp could have occurred in the core with the consequence that the heat removal mechanisms were no longer sufficient and the fuel together with surrounding components heated up rapidly until the original geometry in the core together with the pressure-resistant enclosure was lost due to thermodynamic processes such as melting, perhaps also evaporation and their mechanical effect. The high temperatures led to a massive release of even low-volatility fission products. This "chaotic fast" phase change in combination with a significant change of the original geometry will have stopped the chain reaction and thus the heat generation (except for the residual heat of the fission products remaining in nuclear material). The imminent massive release of radioactivity could no longer be influenced by interventions of the operating crew. The consequence: destruction of the reactor pressure vessel and building barriers; also the reaction of graphite (fire) and metals (H2 generation) with water vapor, both at very high temperature, will have contributed to the destruction and direct release of radioactive noble gases and aerosols into the open.

Visit to Chernobyl exclusion zone in June 2014

On the way from Pripyat to the village of Chernobyl, which is located south of the cooling water lake, our tour guide says at a certain point: have your dosimeters ready! And off we go. Inside the minibus rolling along the road, a chorus of alarm tones begins to whistle. The dose rises above ten times the limit of 3 microsieverts per hour. On the bus, mind you. Not alpha and not beta, only gamma radiation penetrates sheet steel, we learn that in school. After 20 seconds and 500 meters, the spook is over just as abruptly as it began. And as chance would have it, two Przewalski's horses, a rare species that has made its home in the exclusion zone, are grazing quite unmoved in the ditch.

Our tour guide, after the many years he has been working for the Ukrainian Ministry of Information, knows countless spots where radioactivity rises to life-threatening levels, often within just a few tens of centimeters. Hot spots, he calls the spots that set off the alarm of all dosimeters, one of which each of us carries. They can be completely inconspicuous patches of moss, where invisibly a tiny speck of dust glows with full force for all eternity. Or the ever-moist spot under the outlet of a gutter, where over decades the radiant dirt from the roof has been deposited with the rainwater. Or a huge grab made of steel, which was parked between two collapsed apartment blocks.

To get the unimaginable quantities of concrete to the site of the disaster, where a weatherproof, radiation-proof enclosure had to be erected over the coking reactor core in the greatest haste, an entire cement plant was built on the edge of the zone and a concrete transfer station just before the turnoff to Pripyat. The "clean" trucks from outside backed up a ramp, four or five abreast, to the sharp edge at the end, where large steel hoppers were set up. Below them waited the contaminated trucks that would later end up in the high-security graveyard for vehicles and helicopters. The ramp still stands as it was last used, the last hundredweight of concrete that was no longer needed congealed into gray stalactites hanging from the steel scaffolding. The turnaround area and the dusty access road immediately set off the alarm of the Geiger counters.

We ourselves are allowed to enter the zone only in closed shoes, long pants and long-sleeved tops. The alpha and beta radiation is thus prevented from burning our epidermis. Against the gamma local dose rate only the good old radiation protection rules help anyway: Keep the residence time short and the distance large. The safest way, of course, would be not to enter the exclusion zone at all. Later, back in our accommodation in Kiev, I will immediately stuff my sneakers in the trash.

In the backyard of the garage a yellow bus, half overturned leaning against a tree, a stately birch tree growing in the middle of a crumbling truck tire. In front of the hospital, a gynecological treatment chair that pranksters have dragged in front of the front steps. In a devastated classroom, a mountain of gas masks, with colorfully printed pages from textbooks draped over them. A gymnasium, with studded walls behind which moss and ferns sprout from damp walls. My receptivity reaches its limit, I can no longer keep up with looking, marveling, snapping - and shuddering. The flood of bizarre horror pictures does not want to take an end.

Pripyat was founded in 1970 and until 1986 an insignificant city with scarcely 50,000 inhabitants, as they were stomped in the Soviet Union routinely from the ground. Everything was there: a police station, a fire department with a watchtower and three garages for the fire trucks, a swimming pool with a diving tower and a large glass front, a hospital, a stadium with bleachers, a soccer field and a tartan track, five schools, twelve kindergartens in operation, one under construction as more and more children were born. A wealthy, progress-oriented nuclear elite lived here, the population had an average age of only 27, mostly engineers and technicians. Today, everything is gone, everything devastated. The residents were allowed two hours to pack their belongings, then they had to leave their homes. 120 minutes, a World Cup quarterfinal match with overtime, to pack a complete life. They were taken away by 2,100 buses brought from Kiev and all over Ukraine, forming a line 20 km long. In extreme haste and under the merciless command of an overtaxed general. Everything else was left behind: radios, stoves, dishes, furniture, cars, bicycles, beds, the pets.

My conscience is constantly calling, not least in a 12-story apartment block, in one of the Soviet showcase apartments, at the sight of mint-green wallpaper that has come off the wall all by itself and rolled to the floor. I remind myself during the tour never to forget the mercilessness with which the disaster threw hundreds of thousands of lives off track, plunged most of them into chronic misery, and caused quite a few to decay and die before their time. Twenty-eight years later, I walk through the bedrooms of these people, taking pictures and admiring the socialist wooden floorboards that covered the floors, even if they are now covered with a finger-thick layer of lime that trickles from the ceiling. Most especially, however, I admonish myself to remember that the fine dust that covers the streets and roofs outside, under which unsuspecting people once made their homes, comes from the ruptured core of a nuclear reactor.

Do not touch anything! Do not sit down anywhere! Do not put anything in your mouth!

By evening, the dosimeter has already become an object that is part of everyday life. Like a wristwatch or a handphone, you carry it with you, unconsciously looking at the display regularly, otherwise only remembering when the alarm goes off. In the barracks, where we eat and spend the night, I'm afraid to touch anything at first, I'm not even afraid of the cutlery. Sitting down is also an effort, although we are assured that this part of Chernobyl has been thoroughly decontaminated. That is how deeply the lesson of the day among the contaminated ruins has burned into our minds.

I feel helplessness, powerlessness, disappointment. The deceived belief that natural sciences, engineering, in general the human mind could gain control over nature. What was once said in the Soviet Union? "Our nuclear power plants pose no risk whatsoever. They could even be built in Red Square. They are safer than our samovars."

The most dangerous human ability of all: hubris.

... and this is how it looks today in the restricted area around Chernobyl and Pripyat

(Photo credit: Dr. Dipl. Phys. Theobald Fuchs)