Memory Meltdown:
America's Forgotten Nuclear Accident
The mystery
SL-1 vessel background
The accident
The causes The aftermath
DOE SL-1 documents
Ask yourself this question:
Has there ever been a nuclear power plant meltdown that caused
direct fatalities in the United States?
If you are like most people, you will say "no,"
with the possible qualifications that Three Mile Island didn't
directly kill anyone and Chernobyl was outside the US.
What you probably don't know, what almost no one knows, is
that the answer to this question is "yes." But you
shouldn't feel bad about that. An informal poll of dozens of
students, professionals and professors, including several who
teach Physics and one with a graduate degree in nuclear
engineering, failed to turn up the right answer.
The SL-1 nuclear power plant in Idaho suffered a core
meltdown and exploded on January 3rd, 1961, killing three
members of the maintenance crew. The story of the accident is
interesting in itself, but even more interesting is the story
of how no one knows about it.
What is SL-1?
The Stationary Low Power Reactor, or SL-1, was a small
nuclear reactor built by the U.S. Army to explore the
possibility of using such reactors for generating power in the
field.
In particular, the Army wanted to know if small reactors
could work on very remote sites, like the Arctic Circle and
Antarctica.
On January 3, 1961, it blew up, killing three people. The
accident happened when one of the three workers pulled a
control
rod out of the reactor, causing the reactor to "go
critical." (I suspect it went prompt critical) It was the first time an accident in a nuclear
reactor had resulted in fatalities, and the only time such an
event has occurred at a DOE facility.
Because the damage to the reactor could not be repaired, it
was destroyed.
The Stationary Low-Power Reactor Number 1 (SL-1) was built in
the Arco desert 40 miles outside of Idaho Falls, ID near the
start of the Cold War, in 195X. It was a small
first-of-its-kind prototype nuclear reactor with an active
reactor core two feet in height and three feet across. SL-1
was designed to serve as a portable heat and energy plant for
forward radar installations that made up the Defense Early
Warning Line in the northernmost edge of the Americas. SL-1
was powered by Xkg(?) of enriched uranium-235 (235U)
- not alot by today's standards, just short of what is needed
to build a small nuclear bomb. (Compare to Hiroshima bomb?)
The plant generated energy through the fission reaction that
resulted when 235U, in the form of aluminum alloy
fuel rods, was bombarded by neutrons. The heat liberated by
the fission reaction was used to boil steam which in turn
drove a turbine that generated XKw of electricity, a
relatively modest amoug compared to modern nuclear reactors
which typically general XKw.
The reaction was moderated, as all nuclear power plants
are, through the use of control rods. SL-1 had one primary and
four secondary control rods. Each was cruciform shaped,
composed of alumnium alloyed cadmium that, when inserted into
the reaction vessel, absorbed neutrons and stopped the
reaction.
From 1958 to 1961, SL-1 operated without incident.
The SL-1 was a 3MW nuclear reactor designed for electric
power production for remote Arctic stations. It was being
operated by three men on the night of January 3, 1961. It had
a two-month history of sticking control rods and the reactor
had been shut down for maintenance. Work had been done on a
rotating shift basis, and this crew was assigned the task of
reassembling
the control rod devices and prepare for startup.
Tuesday, January 3rd, 1961 was cold in the desert of Idaho,
about 17 degrees below zero. At approximately 9 PM, one or more of the SL-1 plant workers
entered the reactor compartment to re-attach the control
rods to the control rod drive mechanisms. He withdrew the central control
rod 20 inches. This freed up a lot of neutrons. The
reactor immediately went critical, and thereafter prompt critical.
When the SL-1 reactor achieved prompt criticality, a number
of events happened in rapid succession.
- The core power level peaked at 20,000MW for about 4mS.
- Some of the fuel
material reached its vaporization temperature
-
Fuel plates swelled and the
cladding failed, releasing the fuel.
-
A large steam bubble formed in the core, which lifted the
mass of water above it at a rate of approximately 49 m/sec.
-
The withdrawn
control rod was launched into the worker's body, and both the
control rod and worker were launched into the air.
-
This water hammered into the core head
approximately 34 msec later, ejecting the head shielding and
causing the pressure vessel to lift out of its support
structure. (all five metric tons of it)
-
The vessel jumped nearly 3 meters to collide with the
overhead crane before settling back into its original
position.
-
The
steam bubble also caused the pressure vessel to bulge.
-
the operators
were exposed to an integrated neutron flux on the order of
1013 n/cm3. This explains why the victims became radioactive
and could not be decontaminated.
At 9:01 PM, the Atomic Energy Commission (AEC) Fire Station
in Idaho Falls received an alarm
indicating trouble at SL-1.
Emergency crews reached the site
in nine minutes. The building was intact and the
lights were on. At the plant entrance they measured a level of 25 rads/hr.
The crew entered the plant and measured 200 rads/hr as they approached the control room.
Now, at sixteen minutes after the alarm first rang, and due to
the radiation readings being high enough to cause significant
bodily damage, following procedure, they halted
their approach, backed out and waited for backup.
Since your total exposure is related to the dose rate and
the time spent in the radiation field, personnel can rush
through the field quickly and take measurements and try to
assess the damage quickly. On a rush to the reactor, they found it a shambles and
found radiation levels over 500 rads/hr. With protective suits
to prevent getting any radioactive particles on their bodies, they rushed to the reactor building and found two of
the men, one still alive. They found the third man impaled by
a control rod, pinned to the ceiling. This was about
10:30 PM.
The survivor was transported to an
ambulance and traveled several miles with a nurse before an
AEC doctor pronounced him dead.
The third worker could
not be retrieved due to radiation levels in excess of
1000 rem/hour. Once the bodies were removed, they measured
over 400 rad/hr from the bodies, too hot for a normal burial.
Three maintenance workers were killed by the explosion.The body of the one who had been found alive but died in
the ambulance was returned to the SL-1 hot zone. The nurse who
accompanied him was found the next day to have received a
radiation dose of 100-400 rem/hour, an amount equivalent to (something)
(I don't know what something is, but the
numbers above are dose rates, not actual dose. It
depends on how long she spent with the patient).
Several years later she was diagnosed with (some disease)
believed to have resulted from her exposure during the
transport of the patient. The ambulance used in the transport
was decontaminated and subsequently used for several years at
the Eastern Idaho State Fair.
The second worker was found dead on the floor and was left
there for a day while a recovery operation was planned. That
rescue team were exposed to significant amounts of radiation
during their operation.
The third worker had been impaled into the ceiling by the
exploding control rod. His body dangled there for six days
before it could be retrieved.
All three bodies were buried in lead lined caskets. Some
remains that may or may not have been human were buried at the
site.
Twenty three rescue team members received significant doses
of radiation, three of them considered high. But none
displayed signs of acute radiation sickness. I
don't know what happened to those workers. Monitoring of radiation levels around the SL-1 site
revealed a total of ten curies of exposure by the next morning
and a total of more than 50 curies over the month of January,
1961. This level was high but much
lower than it could have been since the reactor building
contained the vast majority of the nuclear core material upon
explosion. This was fortunate, since SL-1's mission to operate
in remote areas did not necessitate a true containment
structure; it was sheer luck that the building's quarter inch
thick steel shell held since it was not designed to do so. At
least 35 acres of desert scrub land was contaminated.
In the subsequent cleanup operations, the reactor and
buildings were demolished and buried as radioactive waste. The
soil and asphalt around the area have been removed and buried.
Today, 36 years later, the cleanup operation continues. The
land, contaminated with low level radioactive debris, is now
under the control of the United States Department of Energy.
The General Manager of the Atomic Energy Commission formed an
SL-1 Advisory Panel to investigate the accident.
The immediate cause of the explosion was obvious: the main
control rod had been rapidly removed from the reaction vessel
by hand causing a chain reaction that exploded the core. But
why had the rod been removed?
The Commission concluded that the most likely explanation
for the meltdown was "malperformance motivated by
emotional stress." Local folklore rumors the accident a
love triangle murder-suicide. But there is no evidence to back
this assertion - no suicide note, no record of despondency - and
other methods of suicide seem so much easier.
Another, perhaps more likely explanation is that the
control rod mechanism became stuck in the extreme cold and was
forced upward. If this is what occurred, it would be a serious
breach of procedure with catastrophic consequences.
The lack of public awareness of the accident at SL-1 is not
surprising. Reports from both sides of the nuclear safety
issue repeatedly mistake the history of US nuclear accidents.
Foe example, the environmental group EarthBase, in a web
report on Three Mile Island, states "the first nuclear
accident in US history occurred on March 28, 1979."
Could the explosion at SL-1 happen today? Probably not,
particularly at a civilian nuclear power plant.
Because of SL-1's small size and simple portable design,
only five control rods were used. The removal of any one of
them would be enough to start a chain reaction and explosion.
Later reactor designs fixed this problem and all current
nuclear reactor designs require that if any one rod is fully
removed, the nuclear reaction can still be halted.
It is important to remember that SL-1 was designed and
built with an urgent Cold War mindset. Pressure existed to
implement the Defense Early Warning Line as soon as possible
to guard against Soviet nuclear attack over the North Pole. It
is possible that this urgency contributed to the accident,
since it was noted that the reactor core fuel design was
inadequate and in need of redesign. If these pressures
contributed to causing the explosion, they are presumably
absent or diminished at this time and do not apply to civilian
power-generating nuclear reactors. Still, the lesson should be
learned so that, when another war hot or cold develops,
urgency in development does not override safety concerns. The
urgency of a wartime climate requires sacrifice on soldiers,
but few projects contain the potential for extreme and
longlasting lethality like a nuclear power plant.
|