Nuclear Disasters

Chernobyl disaster

The operator error was probably due to their lack of knowledge of nuclear reactor physics and engineering, as well as lack of experience and training. According to these allegations, at the time of the accident the reactor was being operated with many key safety systems turned off, most notably the Emergency Core Cooling System (ECCS), LAR (Local Automatic control system), and AZ (emergency power reduction system). Personnel had an insufficiently detailed understanding of technical procedures involved with the nuclear reactor, and knowingly ignored regulations to speed test completion.

The developers of the reactor plant considered this combination of events to be impossible and therefore did not allow for the creation of emergency protection systems capable of preventing the combination of events that led to the crisis, namely the intentional disabling of emergency protection equipment plus the violation of operating procedures. Thus the primary cause of the accident was the extremely improbable combination of rule infringement plus the operational routine allowed by the power station staff.


In this analysis of the causes of the accident, deficiencies in the reactor design and in the operating regulations that made the accident possible were set aside and mentioned only casually. Serious critical observations covered only general questions and did not address the specific reasons for the accident. The following general picture arose from these observations. Several procedural irregularities also helped to make the accident possible. One was insufficient communication between the safety officers and the operators in charge of the experiment being run that night.

Lucens reactor

The Lucens reactor at Lucens, Vaud, Switzerland, was a small pilot nuclear reactor destroyed by an accident in 1969.

In 1962 the construction of a Swiss-designed pilot nuclear power plant began. The heavy-water moderated, carbon dioxide gas-cooled, reactor was built in an underground cavern and produced 30 megawatts of heat (which was used to generate 8.3 megawatts of electricity). It became critical and the plant was decommissioned. It was fueled by 0.96% enriched uranium alloyed with chromium cased in magnesium alloy (magnesium with 0.6% zirconium) inserted into a graphite matrix. Carbon dioxide gas was pumped into the top of the channels at 6.28 MPa and 223 °C and exited the channels at a pressure of 5.79 MPa and at a temperature of 378 °C.

It was intended to operate until the end of 1969, but during a startup on January 21, 1969, it suffered a loss-of-coolant accident, leading to a partial core meltdown and massive radioactive contamination of the cavern, which was then sealed.


The accident was caused by water condensation forming on some of the magnesium alloy fuel element components during shutdown and corroding them. The corrosion products from this accumulated in some of the fuel channels. One of the 73 vertical fuel channels was sufficiently blocked by it to impede the flow of carbon dioxide coolant so that the magnesium alloy cladding melted and further blocked the channel. The increase in temperature and exposure of the uranium metal fuel to the coolant eventually caused the fuel to catch fire in the carbon dioxide coolant atmosphere. The pressure tube surrounding the fuel channel split because of overheating and bowing of the burning fuel assembly, and the carbon dioxide coolant leaked out of the reactor.

No irradiation of workers or the population occurred, though the cavern containing the reactor was seriously contaminated. The cavern was decontaminated and the reactor dismantled over the next few years.


  • Safety focuses on unintended conditions or events leading to radiological releases from authorised activities. It relates mainly to intrinsic problems or hazards.
  • Security focuses on the intentional misuse of nuclear or other radioactive materials by non-state elements to cause harm. It relates mainly to external threats to materials or facilities.
  • Safeguards focus on restraining activities by states that could lead to acquisition of nuclear weapons. It concerns mainly materials and equipment in relation to rogue governments.


"How to Make Nuclear Energy Safe." TriplePundit. N.p., n.d. Web. 9 Mar. 2016.
"Safety of Nuclear Power Reactors." World Nuclear Association. N.p., n.d. Web. 9 Mar. 2016.
"Safety & Security." Nuclear Energy Institute. N.p., n.d. Web. 9 Mar. 2016.

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