Chernobyl
Páginas: 19 (4731 palabras)
Publicado: 27 de septiembre de 2011
THE CAUSES OF THE CHERNOBYL EVENT
by Jacques FROT*
The Number 4 reactor of the Chernobyl nuclear power plant in the Soviet Ukraine suffered a power excursion on April 26, 1986, at about one o'clock in the morning, in the midst of a low-power test requested by the Moscow authorities. In a few seconds the power increased to about 100 times its nominal value. The light water coolant, no longerable to carry off the enormous amount of heat generated, evaporated in a fraction of a second leading to a steam explosion at 1:23:44 (local time). The reactor was destroyed. In the following ten days or so, about 12 exabequerels (exa = 10^18), about 300 MegaCuries, of radioactive isotopes would be injected into the atmosphere, significantly contaminating an area of about 150 000 squarekilometers (about 60 000 square miles - about the area of the state of Iowa, for example) inhabited by some 6 million people. It also caused a measurable increase in the level of ionizing radiation in most of Europe.
The Chernobyl event had two components:
.The explosion of the RBMK reactor;
.The effects on the health of the surrounding population.
We will examine these causesseparately because the effects on the health of the population were not an inevitable consequence of the explosion. However, certain causes of a political nature had a significant impact on both aspects of the event.
Before Chernobyl, the reader will recall, the civilian nuclear industry had suffered two major accidents: the UNGG reactor at Windscale in Great Britain in 1957 and the pressurized waterreactor (PWR) at the Three Mile Island power station in the USA in 1979. Each of these accidents was classified as level 5 of the International Nuclear Event Scale (INES -created after the Chernobyl event) which has eight levels, from 0 to 7. Contrary to what the public commonly believes, no one died or was injured in these two accidents, and epidemiological studies have not revealed any adverseeffect on the health of the population around those sites.
A. THE CAUSES OF THE EXPLOSION OF THE CHERNOBYL REACTOR
This 1000 Megawatt-electric RBMK reactor is graphite-moderated and cooled by light water. In addition to electrical power, it produced weapons-grade plutonium-239. Accordingly, the fuel could not be irradiated for long periods of time, and the reactor was equipped with a systemto load and unload fuel elements without shutting down the reactor.
The causes of the explosion were of three types:
A-1. Design errors,
A-2. Faults of management and errors committed by the operating staff,
A-3. Political.
A-1. Design Errors
A-1-1 The RBMK reactor core is unstable below 700 Megawatts-thermal, about a quarter of full power. In simple terms, at low power thereactor is difficult to control and any tendency toward a runaway chain reaction is automatically and rapidly amplified. This very dangerous feature is characteristic of the RBMK design. Fortunately, it is absent in Western designs as well as in the Soviet VVER pressurized water reactor. In reactors other than RBMK, any tendency to a runaway chain reaction is, thanks to the reactor core design,automatically squelched. The Chernobyl explosion occurred during a test at low power, that is, at a moment when the reactor was unstable. Russian nuclear engineers knew of this instability as did French and British experts. The Soviet authorities were warned well before the Chernobyl accident, but the warning fell on deaf ears. One might compare the situation to a bus on a twisting mountain road witha non-functioning steering wheel !!
A-1-2 In the RBMK reactor the control rods are inserted s l o w l y. Full insertion takes about 20 seconds, while it takes less than 2 seconds in other reactors throughout the world. This is much too slow to prevent runaway of the core while it is operating in the unstable mode. And the RBMK reactors don't have emergency control rods with fast insertion....
by Jacques FROT*
The Number 4 reactor of the Chernobyl nuclear power plant in the Soviet Ukraine suffered a power excursion on April 26, 1986, at about one o'clock in the morning, in the midst of a low-power test requested by the Moscow authorities. In a few seconds the power increased to about 100 times its nominal value. The light water coolant, no longerable to carry off the enormous amount of heat generated, evaporated in a fraction of a second leading to a steam explosion at 1:23:44 (local time). The reactor was destroyed. In the following ten days or so, about 12 exabequerels (exa = 10^18), about 300 MegaCuries, of radioactive isotopes would be injected into the atmosphere, significantly contaminating an area of about 150 000 squarekilometers (about 60 000 square miles - about the area of the state of Iowa, for example) inhabited by some 6 million people. It also caused a measurable increase in the level of ionizing radiation in most of Europe.
The Chernobyl event had two components:
.The explosion of the RBMK reactor;
.The effects on the health of the surrounding population.
We will examine these causesseparately because the effects on the health of the population were not an inevitable consequence of the explosion. However, certain causes of a political nature had a significant impact on both aspects of the event.
Before Chernobyl, the reader will recall, the civilian nuclear industry had suffered two major accidents: the UNGG reactor at Windscale in Great Britain in 1957 and the pressurized waterreactor (PWR) at the Three Mile Island power station in the USA in 1979. Each of these accidents was classified as level 5 of the International Nuclear Event Scale (INES -created after the Chernobyl event) which has eight levels, from 0 to 7. Contrary to what the public commonly believes, no one died or was injured in these two accidents, and epidemiological studies have not revealed any adverseeffect on the health of the population around those sites.
A. THE CAUSES OF THE EXPLOSION OF THE CHERNOBYL REACTOR
This 1000 Megawatt-electric RBMK reactor is graphite-moderated and cooled by light water. In addition to electrical power, it produced weapons-grade plutonium-239. Accordingly, the fuel could not be irradiated for long periods of time, and the reactor was equipped with a systemto load and unload fuel elements without shutting down the reactor.
The causes of the explosion were of three types:
A-1. Design errors,
A-2. Faults of management and errors committed by the operating staff,
A-3. Political.
A-1. Design Errors
A-1-1 The RBMK reactor core is unstable below 700 Megawatts-thermal, about a quarter of full power. In simple terms, at low power thereactor is difficult to control and any tendency toward a runaway chain reaction is automatically and rapidly amplified. This very dangerous feature is characteristic of the RBMK design. Fortunately, it is absent in Western designs as well as in the Soviet VVER pressurized water reactor. In reactors other than RBMK, any tendency to a runaway chain reaction is, thanks to the reactor core design,automatically squelched. The Chernobyl explosion occurred during a test at low power, that is, at a moment when the reactor was unstable. Russian nuclear engineers knew of this instability as did French and British experts. The Soviet authorities were warned well before the Chernobyl accident, but the warning fell on deaf ears. One might compare the situation to a bus on a twisting mountain road witha non-functioning steering wheel !!
A-1-2 In the RBMK reactor the control rods are inserted s l o w l y. Full insertion takes about 20 seconds, while it takes less than 2 seconds in other reactors throughout the world. This is much too slow to prevent runaway of the core while it is operating in the unstable mode. And the RBMK reactors don't have emergency control rods with fast insertion....
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