Wednesday, November 17, 2010
"U.S. Atomic Energy Commission
Idaho Operations Office
SL-1 The Accident: Phases I and II
Describes this nuclear accident from the point of view of the Atomic Energy Commission.
Considering the time, this film report is exceptionally candid about the vulnerabilities of nuclear reactors. This first civilian reactor accident was especially gruesome in that one of the reactor operators was shot into the ceiling by an expelled reactor vessel plug and control rod. Views of the internal wreckage are fascinating. The cause of this accident has never been determined, although operator error has been alleged.
Documentaries of this quality are rare in the U.S. nuclear community, at least for the general public.
Producer: U.S. Atomic Energy Commission; Creative Commons license: Public Domain
The SL-1, or Stationary Low-Power Reactor Number One, was a United States Army experimental nuclear power reactor which underwent a steam explosion and meltdown in January 1961, killing its three operators. The direct cause was the improper withdrawal of the only movable control rod. The event is the only fatal reactor accident in the United States.
The facility, located at the National Reactor Testing Station approximately forty miles (60 km) west of Idaho Falls, Idaho, was part of the Army Nuclear Power Program and was known as the Argonne Low Power Reactor (ALPR) during its design and build phase. It was intended to provide electrical power and heat for small, remote military facilities, such as radar sites near the Arctic Circle, and those in the DEW Line. The design power was 3 MW (thermal). Operating power was 200 kW electrical and 400 kW thermal for space heating. NASA system failure studies have cited that the core power level reached nearly 20 GW in just four milliseconds, precipitating the reactor accident and steam explosion.
On December 21, 1960, the reactor was shut down for maintenance, calibration of the instruments, installation of auxiliary instruments, and installation of 44 flux wires to monitor the neutron flux levels in the reactor core. The wires were made of aluminum, and contained slugs of aluminum-cobalt alloy.
On January 3, 1961 the reactor was restarted after a shutdown of eleven days. Maintenance procedures commenced, which required the main central control rod to be withdrawn a few inches; at 9:01 p.m. this rod was withdrawn almost to the top of the core, causing SL-1 to go prompt critical. In four milliseconds, the heat generated by the resulting enormous power surge caused water surrounding the core to begin to explosively vaporize. The water vapor caused a pressure wave to strike the top of the reactor vessel. This propelled the control rod and the entire reactor vessel upwards, which killed the operator who had been standing on top of the vessel, leaving him pinned to the ceiling by a control rod. The other two military personnel, a supervisor and a trainee, were also killed. The victims were Army Specialists John A. Byrnes and Richard L. McKinley and Navy Electrician's Mate Richard C. Legg.
Reactor principles and events
Fission produces neutrons with a wide range of energies. In all light-water-moderated reactors (LWR), to sustain fission of the U-235 the reactor core needs to have water present to moderate (slow down) the neutrons produced by the nuclear reaction. This process is called "thermalizing" and increases the probability of the neutrons causing fission. When reactivity is inserted in the reactor core, more neutrons are available and power rises. Several factors limit the increase in power.
The first limiting factor is that, given a proper initial spectrum of neutron energies, water has a negative reactivity coefficient. Having a negative reactivity coefficient means that, as the water heats up, the molecules are farther apart (water expands and eventually changes phase) and neutrons are less likely to hit hydrogen atoms, so fewer neutrons are thermalized by collisions with the hydrogen in the water and the probability of fission decreases. This removes reactivity from the core. The lower the temperature, the closer the molecules, the greater the number of neutrons thermalized and the greater the core reactivity. It is also possible to design a reactor core that has an entirely different neutron energy spectrum such that it has conditions for which water has a positive reactivity coefficient. A graphite-moderated, water-cooled reactor like the RBMK reactors at Chernobyl may have a positive reactivity coefficient for coolant (water) temperature."
This is a shorter clip showing the recovery process.
"This clip shows the post-emergency response to this radiation accident to recover bodies of the two workers killed. This clip is taken from the U.S. Atomic Energy Commission's (AEC) film, SL-1 The Accident: Phases I and II. It describes, using real and recreated film footage, the events surrounding this 1961 nuclear accident, the initial emergency response and the early response to protect the public and the environment. Three workers were killed in this incident, the first worker fatalities associated with nuclear power. For more information on the Sl-1 and this tragic incident, link to http://en.wikipedia.org/wiki/SL-1 . The entire 40 minute film is available for viewing and downloading at the Internet Archives."