Chernobyl: Five Fast Facts

The sealing membrane for the new Chernobyl enclosure has been delivered to the site.  Photo courtesy SSE ChNPP.

The sealing membrane for the new Chernobyl enclosure has been delivered to the site. Photo courtesy SSE ChNPP.

By Will Davis

1. The Chernobyl Accident Wasn’t a Nuclear Explosion. The accident at the Chernobyl nuclear power plant reactor no. 4 in April 1986 did destroy the reactor itself as well as the roof of the reactor building, but the explosive forces involved were, first, a steam explosion inside the complex reactor, followed almost immediately by a hydrogen gas explosion similar to those that occurred at Fukushima. No “nuclear yield” was involved—the forces were, instead, explosive expansion of steam and chemical.

2. The “Chernobyl-Type” Reactor Isn’t Common. The type of reactor that experienced the accident in 1986 was also built at other locations around the former Soviet Union, but was never built in an identical form elsewhere. Specific and peculiar problems with the design of this type of reactor (known as the RBMK-1000 model) coupled with operator errors allowed it to get into an unstable condition that is practically impossible with any other kind of reactor; the lack of containment, which all reactors in the United States have, allowed the wide escape of radioactive material once the core was exposed.

3. RBMK Reactors Still Run, But Not the Same. The RBMK type reactors still in operation in some areas of Russia today are not much like the type as it existed in the 1980s. Many changes have been made, in terms of fuel, control rods, safety equipment, and operating procedures. While there has been a push in Europe generally to shut every last one down, in some areas they are a major source of power—and losing that power would plunge the surrounding region into darkness.

4. The Accident Scene is Contained. A very large enclosure, sometimes called “The Sarcophagus,” was quickly engineered and constructed to contain the destroyed reactor and its surrounding heavily damaged reactor building soon after the accident. However, this enclosure proved over time to be leaky and somewhat impermanent after all; thus a new, gigantic enclosure looking a lot like a traditional aircraft hangar (but much larger) has been built and moved over the previous enclosure.

5. Soon-To-Be Sealed. The huge new enclosure over the plant is designed to absolutely prevent release of any materials from inside and to prevent weather from affecting work ongoing inside of it. To this end, this past month the huge seals for the enclosure (seen staged in the photo at the top) have been delivered. According to the site operator, SSE ChNPP, the seals will soon be installed, isolating the environment inside the new structure permanently.

Chernobyl Nuclear Plant as it appeared recently, before the new shelter was put in place.

Chernobyl Nuclear Plant as it appeared recently, before the new shelter was put in place. Units 1 and 2 reactor buildings are nearer at the left, with horizontal dark and light gray stripes. Units 3 and 4 reactor buildings are further; Unit 3’s slanted roof sections can be seen discerning the reactor location. Near to this but not shown are the never finished Units 5 and 6, work on which was halted after the accident.

Learn more about the Chernobyl accident by reading ANS Nuclear Cafe’s post from last year.

ANS member Will DavisWill Davis is a member of the Board of Directors for the N/S Savannah Association, Inc. He is a consultant to the Global America Business Institute, a contributing author for Fuel Cycle Week, and he writes his own popular blog Atomic Power Review. Davis is also a consultant and writer for the American Nuclear Society, and serves on the ANS Communications Committee and the Book Publishing Committee. He is a former U.S. Navy reactor operator and served on SSBN-641, USS Simon Bolivar.

4 thoughts on “Chernobyl: Five Fast Facts

  1. Charles Bergeron

    There were a number of graphite moderated reactors in the US prior to Chernobyl. Use of Graphite as a moderator allows use of un-enriched Uranium as a fuel. Most of these had been shut down prior to Chernobyl and only a few “power” reactors were in service at the Hanford and Savannah River Government sites. They all differed from the RMBK design and had “confinement” buildings if not designed “containment” structures. Long explanation of development General Design Criteria blah blah blah, etc.
    Suffice to say – Chernobyl had nothing to stop release of radioactivity, military sites had some confinement designs that were adequate for “worst case scenarios” and Fukushima era BWRs had containments that were designed for “GDC” “Design Basis Accidents” – which did not include core damage due to zircalloy ignition.
    Zircalloy ignition is what caused the TMI2 and Fukushima accidents to generate large amounts of hydrogen. The large dry containment design of TMI2 was able to contain the hydrogen explosion. The small torus with water suppression containment design of Fukushima was not. This was a known fact and presented in the results of a study done in 1980.
    I personally do not believe that any existing containment design would have survived intact at Chernobyl, but a large dry reinforced concrete structure similar to those at most PWR sites would have retained enough structural configuration to limit the releases.

  2. John Stanke

    Your article lead me to several questions: Wasn’t the Hanford 100 N reactor a similar design? I believe it was shut down as a result of Chernobyl? Also I know all commercial reactors have containments, but don’t BWR have containments that leak? Isn’t this what happened in Japan with wide spread release of radioactive material? It is true that no cantinment is an issue but so are BWR which still exist in the US?

    Regards, JOHN

  3. Charles Bergeron

    Will, I take technical issue with comment 1. The instability that the RMBK 1000 had that caused the explosion was a “nuclear” issue. When the “explosion” at Chernobyl happened I was contacted immediately by high level members of the IAEA. I had presented papers on TMI 2 at IAEA conferences in Europe shortly after that incident and in particular described the various Hydrogen conditions present post severe accident for all common types of reactors and containment sizes. My training and experience on these matters came from Bettis Atomic Power Labs, where Ziracolly was invented.
    They also, incorrectly described the event as a Steam explosion followed quickly by a Hydrogen explosion. I was suspect because of the timing and lack of containment. They got me the best “eyewitness” estimate of the timing of the second explosion and I had a book on the nuclear specifications of the RMBK previously provided to me by the USSR Embassy. Based on these inputs, I estimated that the event was a rapid power escalation resulting in a loss of configuration in the steam cooling tubes. This would result in a steam explosion, but not violet enough to disrupt the lower core area. Vertical steam tubes rupturing at the horizontal headers, probably at the zircalloy to SS transition pieces. It also caused a fast nuclear excursion due to the loss water, since the reactor design and test conditions had put the core and control rods into a positive reactivity state. These excursion was powerful enough to disrupt the entire core assembly. Think SL-1 without a pressure vessel! I provided the IAEA my estimation, but they had already started the Steam – Hydrogen story.
    According to the “eyewitness” account of the two “bangs” there was no time for Hydrogen explosive mixture to develop but it did fit for a “prompt critical excursion”.
    I read a translation of a Russian report that was done several years after the event that was very close to my estimation.
    By the way, Fukushima fit my post TMI 2 predictions for Hydrogen Explosions by Containment Type to a tee.

    BTW, I started some of the Simon Boliver paperwork for her conversion overhaul at NN in ’71? before i went up to Portsmouth. I was Bettis JTG member for the first Posidon and S3G core 3 systems conversions.

  4. I have the hots for Britt Ekland

    Here’s something else. Nature has reclaimed the area around Chernobyl. Plants have overrun the region, and animals now roam the forest. Nature will always win.

    One of my friends is in Ukraine right now. She went to an area near Pripyat (the closest that a person can safely go). She found it bizarre.

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