Chernobyl — the very name of this town seemed to portend
trouble,
and April 26, 1986 trouble become a reality.
From 1975 to 1986 I lived in Pripyat and worked at the Chernobyl nuclear power plant. Our city was small but very beautiful and neat. In 1986, our city had 51000 inhabitants, the average age of the inhabitants 26 years. I still love this city, often recall it.
At first I worked as an engineer – physicist, then the head of the change of radiation safety on the second queues (3 – th, 4 – th blocks), in the fifth watch. In February, 1986 years was transferred to the department of thermal automatics and measurements because of the reduction of my position. I was assigned to the fifth shift to prepare for the post of senior engineer on duty on measuring equipment on the second block. Was here at the time of the accident.
When the accident happened I heard no explosion, but the floor under his feet came as a major earthquake. Then to us, in the premises of the computer complex "Rock – 2" came the guys from the "Rock – 4" as they have in the room fell suspended ceilings and it was impossible to be there. From their conversations: what, how, and why I have there was a picture of an event. More than 20 years have passed since that day, but every anniversary of Chernobyl catastrophes on television say that it is unknown why the accident occurred and what exploded. So I decided to present my opinion on the matter.
Nuclear reactors of the RBMK – 1000 type have been installed at the Chernobyl nuclear power plant. This means a large power reactor channel, the electric power of 1000 MW. Total thermal power of the reactor — 3200 MW. The diameter of the active reactor areas 11 m, height — 7 m. The whole structure is located in the reactor shaft, which serves as a biological protections. The walls of the mine are three meters thick and are made of heavy concrete (filler — boron steel shavings). Then comes a two – meter layer of serpentinite (what – a kind of pebble with sand) and next is the design of the reactor — the scheme L. This water jacket meter thick. All space within this scheme filled with graphite walls through which passes 2088 channels. Of them 1692 — a technological (channels of fuel). In other channels is located reactor power control system.
There are several hot cells to perform scientific – research works. The fuel is U238 enriched with U235. Degree enrichment — 1.8%. Controlled nuclear reaction goes to U235. Full load reactor — 214 tons of fuel. Two fuel assemblies, each 3.5 m long, are connected together. The length is 7 m, the suspension is welded and the fuel Assembly is loaded into the reactor channel. It consists of fuel elements'. Fuel the element is a zirconium tube filled with uranium tablets. Inside it develops temperatures up to 3000 °C.
Through the reactor passes 35,000 tons of water per hour. Steam capacity of the reactor — 5000 tons of steam per hour. Temperature the water inlet to the reactor is + 265 °C, the outlet of the reactor is + 285 °C, the water Pressure reaches 60 — 70 atmospheres. Therefore, the water does not boil.
The temperature of the graphite stack of the reactor reaches up to 600 °C. Below the graphite masonry is not burned like coal, the reactor space is purged with nitrogen. For this there is a gas circuit. Nitrogen is obtained on local nitrogen – oxygen station. The purpose of the gas circuit — prevent the ingress of oxygen into the reactor space. When the reactor is operating at a power of more than 80%, nitrogen – helium mixture is purged. Helium is used imported.
By the time of the accident, the fourth unit worked for 3 years, it was stopped for major repairs. It was necessary reduce reactor power to 200 MW. Performing operations to reduce power, the operating personnel made a mistake and shut down the reactor completely. In this case, the regulations require to withstand the reactor for 36 hours and only after it is allowed to start a new power rise. This requirement of the regulations was violated.
The staff decided to pick up the reactor and immediately began operations to increase its capacity. Power all increased and increased, and it didn't increase. In the end, it was possible to stabilize the reactor power at the level of 200 MW. How long the reactor worked at such power — I do not know. But if desired, this can be determined by the instrument records. On April 26, 1986, a time of about 1 hour and 25 minutes, an unmanageable increase in reactor power began. In a matter of seconds, in just 3 – 5 seconds, the reactor power increased from 200 MW to 2000 MW. The button was pressed AZ – 5, this means shutting down the reactor entirely, and immediately an explosion occurred, followed by the second.
To explain the physical nature of the accident, let's go back to the dawn of nuclear power. In 1942 in America, the first nuclear reactor was built for scientific research purposes. The operation of the device was observed strange cyclicity — having worked for a while at full power, the reactor suddenly lost it and stood some time in a muffled state. Then again gained power and all was repeated again.
When they began to understand the reasons for this cyclicity, it turned out that among other products of division
U235 unstable iodine – 135 is formed with a half-life of 6.7 hours.
Its decay results in the formation of xenon – 135 (Xe135) with a half-life of 9.1 hours
which has a large neutron capture cross section. When accumulation occurs Xe135
in the reactor core, it absorbs neutrons and the nuclear reaction stops. This phenomenon is called
« iodine pit »
It takes some time, xenon disintegrates, neutrons are not absorbed and again there is a nuclear reaction.
This phenomenon is the basis of the accident at the fourth unit of the Chernobyl nuclear power plant.
It is Obvious that the cause of the accident was a violation of technical instructions by the maintenance personnel operation of the reactor.
Now let's discuss what exploded on the fourth block of the Chernobyl nuclear power plant that night. I don't think it was a thermal explosion. In – first, the power of the explosion was such that the debris of graphite masonry was found at distances of more than a kilometer from stations. In – second, I know this fact: the operational staff of the chemical shop is located in the premises adjacent directly to unit A (reactor unit). At the moment of explosion the woman who was in the room of chemical shop, ripped from his chair and dragged towards the explosion. She was caught for clothes and put in place. This happens when vacuum explosion when gas explodes.
An almost instantaneous increase in the neutron flux density by millions of times was accompanied by a sharp rise in temperature. These two factors led to the fact that the water in the channels of the reactor decomposed into hydrogen and oxygen. Educated the explosive mixture exploded immediately. It probably happened in two stages, as there were two explosions.
Thus, I claim that on April 26, 1986, hydrogen exploded at the fourth reactor of the Chernobyl nuclear power plant.
Read on the Internet many materials on the Chernobyl accident. Among them there is information that the power when the reactor stopped, it did not fall to zero, it remained 30 MW. I guess that doesn't change things. Operating personnel did not pay attention to the process of poisoning the reactor core with xenon. When began the rise of the power, and it did not grow it was necessary to stop and understand what was happening. But the power of the reactor increased and increased. I think we've raised it to 80% of full power. And instead received only 200 MW, as the main part neutron flux was absorbed by xenon. But it's been a-while, the xenon broke and the reactor power immediately rushed to a given level.
The question arises: why does xenon not accumulate during normal operation of the reactor? Under normal operation of the reactor, a powerful neutron flux shoots xenon and it burns out. The loss of reactivity of the reactor is compensated by a slight increase in its power. But when stop the reactor neutron flux is significantly reduced, and iodine 135 produced a lot. Hence it forms the xenon 135 therefore, there is an accumulation of xenon.
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A. Barkar, e-mail: filosof51@yandex.ru
Simferopol April 2009.
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