Lessons Learned From�Early Accidents at Los Alamos
Richard “Dick” Malenfant
Los Alamos National Laboratory - Retired
UK Webinar August 17, 2023
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UNCLASSIFIED | 1
ABSTRACT��The results of an experiment can never be considered a failure. Analyses of the results often suggest modifications to theories and procedures to improve the understanding of the underlying principles. In a similar way, observation and analyses of accidents suggest modifications to procedures and behavior to minimize repetition.
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Although I have worked in the field for over
fifty years, I do not feel that I have been accepted
by the Criticality Safety Community – because…
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Although I have worked in the field for over
fifty years, I do not feel that I have been accepted
by the Criticality Safety Community – because…
I have spent a large portion of my life making
systems critical – rather than keeping systems
from going critical!
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Nevertheless, it has been my privilege
to have worked with GIANTS…
Hugh Paxton
Dixon Callihan
Gordon Hansen
John Orndoff
Bob Keepin
Bob Long
Bob Jefferson
Gene Plassmann
Dave Smith
Raemer Schreiber
and others….
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ALWAYS REMEMBER --
You don’t
Plan
To Have An Accident!
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BECAUSE
An Accident is an
UNPLANNED Event
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Ac-ci-dent
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Sub-Critical Multiplication
In order to participate fully in the analyses
of the following accidents, it is necessary
to have an appreciation for the concept
of sub-critical multiplication.
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Sub-Critical Multiplication
Subcritical multiplication is the process of
using source neutrons to maintain an
equilibrium neutron population when keff is
less than 1.
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What I would like to have you take from my
presentation:
Neither the Code of Federal Regulations, ANSI Standards, DOE Orders, nor even training prevents
ACCIDENTS!
Safety is a state of mind, attention to detail, and a result of experience…
Although you cannot teach safety, you can study
the lessons of the past and avoid repeating the environment that has resulted in accidents!
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In considering the details of the following three
accidents, I would like to make them personal
by putting us in the position of the participants.
Where do you find the cross-sections to use for
your calculations?
How accurate are they?
Nevertheless, results of calculations are often
reported to four or more significant figures.
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How does your computer program treat the
n-2n reaction in beryllium?
Is it important to know this?
Is the keff resulting from that treatment of the
n-2n reaction correct?
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Nuclear reactions occur in a time frame of micro-sec.
How long is a micro-sec?
There are 86,400 seconds in a day.
Round that off to 100,000 sec./day
There are approximately 1,000,000 seconds in 10 days
The relationship of a micro-sec. to a second is about
the same as the relationship of a second to ten days!
0.000001/1.0 = 1.0/1,000,000
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What is the best reflector for a fast system?
Water
Tungsten Carbide
Beryllium
Steel
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Is the human body a good reflector?
What is the only element in the periodic table that
cannot 180 deg backscatter?
How many collisions are required for a neutron to
be returned from a water reflector?
What is the average solid angle subtended by a
sphere in a close fitting box?
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One of the most difficult calculations to make is
the kinetic reaction of a solution of fissionable
material.
Why?
The reaction is affected by the formation of
radiolytic bubbles of gas that reduce local density,
modify the power density distribution, alter the
chemical composition, and migrate out of
the solution.
We could spend all week exploring the phenomena!
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All of that being said, please:
Close your notes, and turn off your cell phones.
You are limited to using a slide rule, pencil,
nuclear cross-sections that you have measured
or can infer from work on the Water Boiler,
and a table of logarithms to evaluate kinetics
of the following reactions in fast systems.
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In 1944, Emilio Segré and his group in Pajarito
Canyon determined that the Pu240 in reactor produced
plutonium would result in pre-initiation if used in a
gun-type weapon.
This resulted in a redirection of the laboratory effort.
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Nevertheless, work continued on the use of uranium in
a gun-type weapon.
However, there had never been a demonstration of
a chain reaction sustained by prompt neutrons alone,
and the cross-sections for fast fission are not well
known.
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With that in mind, a proposal was made by
Otto Frisch to construct and operate a machine
to demonstrate a nuclear reaction sustained
by prompt fissions alone.
When the proposal was described to a Safety
Committee including Enrico Fermi and
Dick Feynman, the latter observed that this…
“was just like tickling the tail of a sleeping dragon”
Hence, the machine became known as The Dragon
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“A chain reactor (The “Dragon”) was constructed so that by dropping a slug through an assembly (both of active material), a divergent chain reaction supported by prompt neutrons alone was achieved for about 1/1000 second. In this short time neutron multiplications up to 1012 were obtained. Various measurements were made which permitted calculation of the generation time in two independent ways; from the shape, and from the size of the neutron burst which occurred when the system became prompt neutron supercritical; these calculations agreed reasonably well with each other, and also with the time obtained from a Rossi time-scale experiment. The neutron bursts produced by the reactor were used in other experiments on delayed neutrons, gamma-rays, the effect of intense radiation on coaxial cable, and on living animals.”
ABSTRACT, LA-397
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The
Dragon
Machine
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In two excursions the energy release
resulted in heating and expansion of
the slug causing it to stick in the
annulus. The burst was larger than
anticipated resulting in personnel
radiation exposures of 25 rep –
similar in today’s units to 25 rad.
There were no long-term effects.
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Participants in the
experiments with
the Dragon
included:
Otto Frisch
Philip Morrison
Klaus Fuchs
Harry Daghlian
Louis Slotin
Jim Osborn
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The second accident occurred on August 21, 1945.
Harry Daghlian, the sole participant, was working
alone, at night, to complete an experiment started
earlier in the day. He was stacking tungsten carbide
blocks around a plutonium sphere.
The exact details of what happened are not known
because the only other person present – the Security
Guard - was apparently not actually observing the
experiment although he did report a “blue flash”.
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The Daghlian Accident – August 21, 1945
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Although there were no eyewitnesses except for the security guard who wasn’t looking, Jim Osborn
had worked with Harry Daghlian and was perhaps
the last person to see him before the accident. He documented his recollections in the February 2003 Newsletter of Children of the Manhattan Project.
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The third accident occurred on May 21,1946 and it
involved 8 participants.
Louis Slotin planned to go to the Pacific to participate
in nuclear weapons tests. His position at Los Alamos
was to be taken by Al Graves. On the afternoon of
May 21, 1946 Graves requested a demonstration of the
measurement of the “crit.” Slotin agreed and proceeded
to lower a hemishell of beryllium on to a plutonium
sphere supported in another hemishell of beryllium.
An excursion occurred and the “blue flash” was observed
by others in the room.
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At this point I would like to make the following
observations.
Both Harry Daghlian and Louis Slotin:
* were experienced researchers,
* knew what they were doing,
* were fully aware of the consequences,
* were doing work that they had done before.
However, something went wrong!
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Raemer Schreiber was in the room where the accident occurred. He presented the following observations to Darol Froman, Deputy Director, in a memo written on May 28, 1946.
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1. Slotin was not, by any possible Interpretation, guilty of what legal minds like to call “criminal negligence.” The monitors were set up and running, an adequate number of observers were
present who, by their silence, agreed to the procedure, and he had provided a safety device in the form of wedges to keep the tamper from dropping if it slipped. The fact that this safety
device failed does not alter the situation as far
as this point is concerned.
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2. The assembly was made too rapidly and
without adequate consideration of the details
of the method. A “dry run” without the
active material to check the details of the
mechanical operations should have been
made.
with the assembly should have remained
in the room.
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a neutron monitor could have prevented the
accident. The neutron rise was too rapid to have
the reaction stopped by any devices that I have
seen used at Los Alamos.
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remote control would have eliminated the
hazard from this particular “burst”, it might well
have become a real explosion with equal or
greater damage to personnel in spite of
shielding walls unless a positive and fast-
acting safety device were part of the
assembly. In this case, Slotin was that safety
device.
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Schreiber went on to recommend a list of guidelines.
Although they were specific to the conduct of
critical experiments, I believe that they form the
basis of nuclear criticality safety to this day.
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new set of rules will not prevent more
accidents. As stated in item (1) of the
preceding section, the existing rules were
nominally complied with. In addition to the
restatement of rules, there must be a
continuous and vigorous campaign to keep the
people participating in this work aware of the
potential danger in every assembly. Perhaps
the work should be rotated among a number of
people. As soon as a person ceases to be
nervous about the work, he should be
transferred to another job.
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in detail a considerable time in advance.
The plan should be sent to several responsible
people, any one of which could veto the plan
or ask for a clarification.
one or more observers whose job would be to
stop any procedure which they consider
hazardous.
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done by remote control provided that this
control incorporates safety devices guaranteed to
stop the reaction in the shortest possible time.
be kept, possibly with a running commentary fed
into a wire recorder and either a movie camera
or an automatic still camera.
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reduced to a routine matter to be “run through
before lunch.”
be kept up to date. This file would be valuable
as a guide in making future assemblies and
could also be evidence for removing assemblies
known to be safe from the rather severe
restrictions which will undoubtedly be imposed
on all untried assemblies.
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In other words:
Regulations do not prevent
accidents - people do.
Study the accidents of the
past – to avoid repeating
them.
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Never take anything
for granted!
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Keep the law of unanticipated consequences
in mind at all times.
I recommend
“The Black Swan”, by Nassim Nicholas Taleb
(now available in paperback)
“The Limits of Safety”, by Scott D. Sagan
“Inviting DISASTER”, by James R. Chiles
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THE ACCIDENT
Richard E. Malenfant
American Nuclear Society 1995 Annual Meeting
June 25-29, 1995
Philadelphia, Pennsylvania
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LAMD-120, Series A, REPORT ON ACCIDENT OF AUGUST 21, 1945 AT OMEGA SITE, August 28, 2945,
Paul Aebersold
Dr. Louis Hemplemann
Louis Slotin
LA-3861, REVISED DOSE ESTIMATES for the
CRITICALITY EXCURSION at LOS ALAMOS SCIENTIFIC LABORATORY, May 21, 1946
December 1967
Dale E. Hankins
G. E. Hansen
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“A Summary of Accidents and Incidents Involving
Radiation in Atomic Energy Activities”,
June 1945 thru December 1955. D. F. Hayes
LA-13638, “A Review of Criticality Accidents”,
Thomas P. McLaughlin et. al.
RAK-2. “Accidents in Nuclear Ships”, December,
1996, P. L. Olgaard, Riso National Laboratory,
DK-4000 Roskilde, Denmark. This document can be
Obtained from NKS Secretariat, P.O. Box 49,
DK-4000 Roskilde, Denmark.
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