Page 6 - 2011 - The 'X' Chronicles Newspaper - March 2011

Fukushima Dai-ichi Nuclear Disaster The Fukushima Dai-ichi Nuclear Power Station Disaster By Lee Boyland This paper is presented in an attempt to explain the complicated technical elements associated with earthquake and tsunami damage done to Japan’s Fukushima nuclear power facility. Before proceeding with a description of how these catastrophes impacted the facility’s reactors, pertinent technical data is provided below. The Fukushima nuclear power facility had six operational nuclear boiling water reactors (BWRs) and two additional large reactors planned. An instant before the earthquake stuck, contain 3-5% U-235. a critical reaction. reactors 1-3 were online. Reactors 4, 5 and 6 Radioactive decay: an isotope emits a Super critical: a nuclear explosion. had been previously shut down for maintenance particle (alpha, beta, or neutron) and changes Nuclear reactors CANNOT reach super and refueling. into a different element by losing or gaining a criticality—they cannot cause a nuclear proton. One element becomes another element explosion. As the prompt critical reaction Reactor Power Rating and heat is produced by the reaction. continues, the fuel rods overheat and melt. In a Operational (Critical) Spontaneous fission: an atom releases weapon, explosives are used to compress the U- No. 1 460 MW March 26, 1971 neutrons and splits into two new atoms of two 235 or Pu-239 into a super critical No. 2 784 MW July 18, 1974 different elements. Part of the mass of the configuration. No. 3 784 MW March 27, 1976 original atom is transferred into heat (E=mc2). Shut down: control rods are inserted No. 4 784 MW October 12, 1978 Both uranium and plutonium atoms can capture into the reactor, absorbing neutrons and No. 5 784 MW April 18, 1978 a neutron, which causes their atoms to split into stopping the chain reaction. If an emergency No. 6 1,100 MW October 24, 1979 two new atoms. occurs, the control system automatically inserts No. 7 and 8 planned for 2013-14 all control rods to immediately stop the chain Isotopes of uranium (U) and plutonium reaction, a procedure know as scramming the (Pu) spontaneously fission, split into two new reactor. Nuclear reactor accidents are classified atoms (two new elements), and when they do Half-life: the time required for half of using the following scale. they release neutrons. When their atoms split, the radioactive isotope to decay. A short half- they produce a pair of new atoms called life means that the radiation will diminish 7 Major Accident - Chernobyl daughter products (new elements). There are quickly. 6 Serious Accident hundreds of daughter product pairs, most of Containment dome (vessel): a steel 5 Accident With Wider Consequences - which are also radioactive and decay. U-235 and and concrete structure built around the reactor Three Mile Island Pu239 are capable of producing a chain core designed to contain the fuel rods if the 4 Accident with Local Consequences reaction—neutrons released causing additional reactor malfunctions. If the fuel rods are 3 Serious Incident fissions. A non-nuclear fuel (i.e., gasoline or exposed to air they become very hot and the 2 Incident natural gas) burns (is consumed) in an engine or zirconium cladding will react with air and 1 Anomaly furnace and the heat produced drives an engine produce hydrogen gas, while the cooling water 0 Below Scale/No Safety Significance or provides heat to a process. A nuclear reactor will flash off as steam. In the latter case, it may employs uranium, which can sustain a chain be necessary to release some of the steam and When the earthquake was detected, the reaction, as its fuel. hydrogen to reduce pressure in the containment automatic control system scrammed reactors 1 - vessel. If cooling fails, the fuel rods may melt, 3. This means that all control rods were A nuclear reaction has four phases: but they will separate and thus will not be inserted, completely stopping the critical configured for a critical or prompt critical reaction. Subcritical: a configuration of the reaction. The containment dome’s purpose is to This paper is based upon the best uranium or plutonium that prevents a chain contain the melted fuel rods and prevent the information currently available. Before going reaction. In other words, one fission does not spread of radioactivity into the environment. further, some basic nuclear terms must be produce another fission, and there is no chain discussed in order to understand what occurred. reaction. Spontaneous fissions will continue, If the cooling system in your automobile producing small amounts of radiation and heat, fails, you have two choices: turn off the engine In very simple terms: but the amount is of no consequence. or continue driving until the engine seizes. Critical: one fission produces one Once the engine is turned off, it begins to cool. Isotope: elements can have variations fission — a self-sustaining chain reaction. A When a nuclear reactor is shut down or caused by a different number of neutrons in nuclear reactor is said to have “gone critical” scrammed, it doesn’t work that way. The their nucleii; and these are called isotopes. An when a self-sustaining chain reaction is daughter products continue to decay and release isotope of an element always has the same achieved. heat. This release of heat can continue for number of protons but has different numbers of Prompt critical: a reaction where one several days, weeks, or years depending on the neutrons. Hydrogen has one proton. Hydrogen’s fission produces more than one fission. Control half-life of the particular daughter elements. second isotope, deuterium, has one proton and rods fabricated from an element that absorbs The longer a fuel rod is in a reactor, the more one neutron. Hydrogen’s third isotope, tritium, neutrons (e.g., boron) are used to control daughter pairs are created, some with very long has one proton and two neutrons. Helium has prompt critical and critical reactions. A reactor half-lives. This means that the core of the two protons and two neutrons in its nucleus. powers up by allowing a controlled prompt reactor must be cooled to remove decay heat. Uranium has 92 protons and has two isotopes of critical reaction to occur until the desired power interest: U-235 has 143 neutrons, and U-238 level is achieved; after that the control rods are Continued on Page 7 has146 neutorns. Nuclear fuel rods usually adjusted to reduce the prompt critical reaction to