Three Teaching Case Studies of Accidents in Nuclear Energy Development in Japan
Author(s):
Hiroshi Iino
New Link TextPresented at the OEC International Conference on Ethics
in Engineering and Computer Science, March 1999
Introduction
Although engineering ethics classes at technical
institutes are common in the USA, they have been rare in
Japan, and were very rare in 1996 when I was asked by the
Kanazawa Institute of Technology to design, implement and
teach a class on engineering ethics for undergraduate
students 1).
The class was named as the "Society and Engineers" and
more than 2500 students finished the class in 5 years. In
teaching engineering ethics, the most effective way would be
to utilize case studies of, say, "hero" engineers,
engineering related accidents or conversely, unethical acts
of engineers. Since Japanese society were confident of the
ethical conduct of engineers and Japanese culture that does
not generally expect individual heroes, acting on their own,
to produce good outcomes, stories of specific heroic conduct
by engineers are rare in the literature. Thus I chose at the
beginning of the class to focus on two cases in nuclear
energy development by a governmental organization that
exemplify the influence of engineering failure and unethical
acts. I chose these two because the facts of those cases have
been fairly well disclosed and analyzed and because the cases
attracted wide public attention in Japan, due to the nature
of the project. But in 1999, a more serious accident of
atomic criticality occurred in a Japanese company and
resulted in death of two workers. I added this case to the
previous two. The analysis of these three cases provides
engineering students with many useful lessons.
Case 1: Fire by Sodium Coolant Leak at Prototype Fast
Breeder reactor, Monju 2
On December 8, 1995, a prototype fast breeder reactor,
Monju, located in Tsuruga City, 350km west of Tokyo, was
operating at 40% power. The Power Reactor and Nuclear Fuel
Development Corp (PNC), a government controlled organization,
operated this reactor. At 19:47 high temperature liquid
sodium coolant at one of the three secondary heat exchangers
started leaking through a broken thermometer sheath (designed
by IH Company, OD: 10mm, ID: 4mm, Length: 150mm) on the
piping and it ignited on contact with air. As shown in Fig. 1, the
primary heat exchangers are designed to take heat out of the
core of the reactor to the secondary heat exchangers, which
then transfer the heat to steam generators for power. Because
of this design, it was a simple fire caused by the leakage of
chemically reactive but non-radioactive sodium coolant. But
due to the delay in shutting down of the reactor, 640kg of
the sodium leaked in 3 hours and caused some unexpected
damage by the fire and chemical reactions to the surrounding
structure.
The sheath was found to have been broken by following
design errors such as,
- The sharp cut edge design of the sheath as shown in Fig. 2, which
caused stress concentration and breakage,
- Neglect of newly established mechanical design analysis
of vibration of the sheath parallel to the sodium flow
and
- The IH company's failure to consider the fact that
liquid sodium is 120 times more heat conductive than water
and to use the another contractor's (the H company's)
better and simpler design for those of the primary heat
exchangers. See Fig. 3.
The PNC had been always asked by neighbors as well as
anti-nuclear organizations whether their nuclear reactors are
absolutely safe. They felt constrained to reply "yes" under
the circumstances. Under these conditions, the initial cover
up of hiding the videotapes taken at the site and of showing
them after editing and the PNC's delay (of about one hour) in
informing the neighboring community agencies of the accident
ignited a fierce protest by the public.
This example teaches the students following lessons:
Influence of quality of engineering works
The small design errors in the cheap component which may
come from lack of competence and care of designers in the IH
Company and JNC as the user, caused the accident
The cover up of the video tapes and delay in informing
others of the accident
The cover up decision was made by managers including
ex-engineers. When I asked our students in the class if they
do the same under the situations, one-third of them said they
might although they think it is a very stupid act. The delay
of informing the accidents is mainly due to lack of the
system oversight and to the bureaucracy within the JNC
organization. These caused loss of public trust in general
and have delayed the several tens of billion dollar project
at least 6 years, although the government wants to resume the
project as soon as possible.
Importance of professional work in accidents
The manuals to handle this kind of the accident were not
made although they had some for other types of sodium coolant
leakage. Manuals are necessary and useful especially in
simple operation. But in accidents like this, which no one
had expected and which are generally much more complex than
those anticipated in manuals, professional judgments are much
more important and necessary. In this case, the air
conditioners, which had not been shut down, continued to
supply fresh air to the fire.
Learning from past experience
The earlier experimental fast breeder reactor, Joyo, which
was designed based on practical experiences by the engineers
of previous generation, had not had any serious sodium leak
accident for 18years since its start of the operation in1977.
Most of these engineers, however, were retired or moved to
other job as time passed. New generation of engineers might
have thought it easy to handle. This is the problem of
transferring and learning engineering experience and skills
between generations.
Responsibility of managers (ex-engineers) to the
public
Engineers know "nothing is absolutely safe". But sometimes
political pressure forces managers to say yes to the public
on the absolute safety question. But the more realistic
question form the public is that the engineers make a maximum
professional effort to eliminate the safety hazard. Engineers
should have realized the responsibility of clarifying the
situation. After a long discussion on the safety including
the following two accidents, the Committee of the Nuclear
Safety Commission in Japan formally declared in "The White
Paper 2000 on Safety of Nuclear Energy (in Japanese)"
approved on March 27, 2001 that "none can say nuclear energy
is absolutely safe".
Case 2: Fire and Explosion at Bituminization
Demonstration Facility in 1997 3
The second accident occurred 14months after the first one
at Tokai Works of PNC, located in Tokaimura, 140km north of
Tokyo. The facility mixes a low radioactive nuclear
wastewater with molten bitumen and evaporates water in a
steam-heated extruder at 180_ and pours the molten mixture
into steel drums (180 liters) to cool down, as illustrated in
Fig. 4. Since
the waste contains a high percentage of sodium nitrate, a
strong oxidation reagent, and bitumen and other organic
chemicals, the mixture is likely to initiate oxidation
reaction by itself at high temperature. Because of the risk,
reagents to retard the oxidation reaction were investigated
before the process started operation in 1982.
Engineers planned an experiment to reduce a flow rate by
10% then 20%. Operators from subcontractors observed lowering
viscosity of the final mixture, an indication of higher
temperature but the thermometer at the exit of the extruder
was not working well for years. When they saw pillars of
flame on the drums being cooled down, they splashed water
from sprinklers for one minute just enough to extinguish the
fire. They reported to the engineers. No engineer responsible
to the operation came to the place before an explosion
occurred 10 hours later and a small amount of radioactive
materials went out of the building. Several tens of workers
had been scheduled to enter the building 40minutes after the
explosion. It was very fortunate that there were no
casualties. I think ordinary engineers could have foreseen
the explosion if they had understood what caused the original
fire and time necessary to cool down the oxidation reaction
in the 180 liter drums. This case can be used to caution the
students against the following mistakes
- Incompetent and inexperienced behavior by the engineers
(stationed at dirty, difficult, unimportant, and unhealthy
working environment),
- Careless experimental design,
- Negligence in watching and examining the
experiment,
- Dereliction of the engineers' responsibility of
checking and controlling workers' safety and the floor
after the fire,
- Some engineers become a kind of managers who do not
want to know and do not know what is going on the operating
floor.
- No accident for 15 years made them smug and think the
operation is completely safe, although there was a similar
accident in Belgium
- Delay in informing community agencies about the
accident.
6. and 7. are common to the first and second
accidents.
PNC in charge of both operations was reorganized into JNC
(Japan Nuclear Cycle Development Corp) because of the two
accidents and their poor handling of the situations despite
their thirty years of substantial technical achievements.
Case 3: Criticality Accident at JCO in 1999, 4
In 1999, a criticality accident at JCO, a subsidiary of
Sumitomo Metal Mining Co., astonished the Japanese people and
the world at large. Three workers were refining an enriched
(the uranium235 concentration was 18.8%) uranyl nitrate
solution for a research fast breeder reactor in Tokaimura,
the same village of the second accident. They were pouring
uranyl nitrate solution from a five-liter stainless beaker
through a funnel into the sedimentation tank that was
installed there (but used for other purpose). When they
poured the fourteenth dose, they saw a blue flash. The total
amount of uranium poured was 16.8 kg, seven times larger than
the maximum allowable quantity for the tank. In order to save
time, they had changed the process on their own and violated
a legal requirement in the operation manuals, which the
company had established a few years before. Three were
immediately hospitalized and two later died because of
excessive neutron and gamma ray exposure. The plant equipment
had been designed with a critically safe slim geometry such
as 117mm in diameter and 3500 mm high (80 liters in volume),
which also prohibited efficient operation. But the roughly
spherical sedimentation tank (450mm in diameter, 600mm high
and 100 liters in volume) was an exception. This was an
"irradiation" accident, not a "contamination" accident. One
hundred and fifty other persons received a radiation
exposure, but it was less than a maximum allowable annual
dose.
Three kinds of the operation are shown in Fig. 5. This was a
special operation for them and, therefore, required some
special care. But no qualified engineers were in charge of
the operation and workers were not educated well for the
operation and accompanying risks partly because the company
was in a difficult financial position, which could not be a
reason of the excuse. This is simply a problem of poor
management and management ethics.
This accident teaches students following lessons:
- Poor management. Managements illegally changed the
operation manuals and they neither allocated qualified
engineers nor educated workers for the operation.
- The management of the operation was so badly controlled
that the workers tried to improve efficiency without
knowledge and approval of qualified engineers. Trust and
good communication between engineers and workers are
essential for safety of any operation.
- Even under such a situation, engineers who were not in
charge of the operation could have pointed out the danger
to the management, when they found them.
Several managers (ex-engineers) including the plant
manager were put on trial and JCO closed all the operation
due to this accident.
Conclusion
These three cases supply students in the class with many
lessons just explained. As engineering ethics education
becomes more common in Japan, case studies of events in other
setting, such as private companies, are being collected for
use in engineering ethics classes. Most of these are in
Japanese.
Acknowledgments
I wish to thank those persons in PNC and JNC who helped me
and were willing to discuss the matters open-mindedly.
Footnotes
Hiroshi Iino
Kanazawa Institute of Technology,
Japan