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---
layout: default
title: The Chernobyl Disaster
category: issues
description: Learn about the Chernobyl nuclear disaster
author: nick
byline: true
---
<div class="col-lg-8">
  <p>
    On April 26th, 1986, a nuclear power plant in Chernobyl, Ukraine failed
    violently during a scheduled test of the turbine system. The power of the
    reactor increased out of control from a low-power state, rapidly boiling
    water and causing a steam explosion that blew the roof off the the reactor.
    A graphite fire was ignited, spewing toxic radioactive substances into the
    atmosphere. 31 people were killed during the accident, and it has been
    estimated that the released radiation has caused an additional 4,000 cancer
    deaths.
  </p>

  <p>
    Here, you can find out what caused the Chernobyl accident and why we are
    convinced that nothing like this could happen again. Check the links to the
    right for our collection of information on Chernobyl.
  </p>

  <div class="alert alert-success d-flex align-items-center" role="alert">
    <p>
      <strong>Featured Content Alert!</strong>
      We are extremely fortunate to have some
      <a href="{% link chernobyl-memories.html %}"
        >unique first-hand stories told by two parents of young children</a
      >
      living near Chernobyl when it happened, as well as the reflections from
      <a href="{% link chernobyl-memories-nat.html %}">one of their children</a>
      (who ended up working as a nuclear engineer!)
    </p>
  </div>

  <p class="h3">On this page</p>
  <div class="list-group">
    <a class="list-group-item list-group-item-action" href="#short"
      >What happened at Chernobyl? (short version)</a
    >
    <a class="list-group-item list-group-item-action" href="#sortof"
      >What happened at Chernobyl? (longer version)</a
    >
    <a class="list-group-item list-group-item-action" href="#again"
      >Can Chernobyl happen again?</a
    >
    <a class="list-group-item list-group-item-action" href="#more">More Info</a>
  </div>

  <h2 id="short">What happened at Chernobyl? (short version)</h2>
  <p>
    Because Xenon built up due to a rapid shut-down mainly caused by nearby coal
    plant problem, operators at Chernobyl retracted the control rods all the way
    out of the core only to notice power instabilities due to the inherent
    positive coolant void coefficient of the RBMK reactor and reinsert them. But
    the tips of the rods were graphite, which displaced water without
    introducing neutron poison, thus increasing the power rather than decreasing
    it and the positive void coefficient allowed the reactor to undergo a
    runaway power excursion, resulting in a catastrophic steam explosion and
    graphite fire that killed 30 workers and released radiation in levels that
    were soon detected in Finland.
  </p>

  <h2 id="sortof">What happened at Chernobyl? (longer version)</h2>
  <p>
    The Soviet government ordered the operators of Chernobyl to perform a test
    on their reactor. The test was supposed to measure how long the spinning
    generator would continue producing electricity after the reactor was shut
    down before it slowed and stopped. The test was to happen with the reactor
    at low power. As the operators were about to start slowly and carefully
    bringing the reactor to low power, the utility company called and said that
    a nearby coal plant just shut down unexpectedly and asked Chernobyl to stay
    at full power for a while longer to keep the nearby homes lit. After peak
    hours, the operators brought the plant to low power rapidly. Nuclear
    engineers can explain to you that this kind of shut-down would result in an
    unusually large amount of Xenon build-up in the reactor fuel. Xenon eats up
    neutrons, thus making the chain reaction more difficult to maintain. Because
    of this, the operators were surprised when the reactor went to a lower power
    than they had expected.
  </p>

  <p>
    To get the power of the reactor to its expected value, the operators pulled
    the control rods out further than they would ever do in any normal
    situation. Finally, the reactor went up to the power level needed for the
    test. Unfortunately, the Chernobyl reactor was designed in a dangerous
    manner, allowing the reactor to get hotter if bubbles formed in the water
    coolant flowing past the fuel. As water boiled in certain locations of the
    reactor, this power instability started rearing its head. Apparently, one of
    the operators noticed this highly unstable situation and pressed the button
    to insert the control rods and shut down the reactor. But, an even more
    serious design flaw was in the control rods. The neutron poison in most of
    each rod had a small graphite tip on the bottom. This graphite is not a
    neutron poison (and is usually beneficial to chain reactions). So with the
    control rods all the way out, inserting them for the first few inches
    displaced some water without introducing any neutron poison, and this
    actually increased the power of the reactor. This led to more boiling of the
    water, which resulted in even more power and then positive feedback took the
    reactor power sky-high, immediately boiling all the water to steam. The
    steam pressure was so great that it blew the lid right off the reactor and
    through the roof of the reactor building (which was not one of those steel
    containments, by the way. It was just a concrete building).
  </p>

  <p>
    With no more coolant, the fuel heated up and became molten. Standing
    graphite rods in the reactor ignited into a very hot graphite fire that
    began spewing bits of the radioactive fuel into the open air. The fire took
    over a week to extinguish, costing the lives of about 30 emergency
    responders due to acute radiation poisoning.
  </p>

  <h2 id="again">Can this happen again?</h2>

  <p>
    Modern reactors have reinforced steel-concrete containments domes that would
    not be so easily penetrated by a steam explosion. Control rods are designed
    such that all parts of them are neutron poisons, including the bottom.
    Reactors are designed to have NEGATIVE void coefficients, meaning boiling
    water would result in power decreasing automatically rather than increasing.
    Also, graphite is not typically put in reactor cores. Short answer: no.
  </p>

  <h1 id="more">More info</h1>
  <ul>
    <li>
      <a href="{% link chernobyl-timeline.html %}"
        >Detailed timeline of Chernobyl accident</a
      >
    </li>
    <li>
      <a href="{% link chernobyl-memories.html %}"
        >Memories of a mother and father living ~100 miles from the accident</a
      >
    </li>
    <li>
      <a href="http://www.unscear.org/unscear/en/chernobyl.html"
        >United Nations Scientific Committee on the Effects of Atomic Radiation</a
      >
      - Chernobyl section (very good)
    </li>
    <li>
      <a
        href="https://www.nrc.gov/reading-rm/doc-collections/fact-sheets/chernobyl-bg.html"
        >NRC discussion of effects of accident</a
      >
    </li>
  </ul>
</div>