Three Teaching Case Studies of Accidents in Nuclear Energy Development in Japan

Author: Hiroshi Iino

Kanazawa Institute of Technology, Japan

Presented 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,

1. The sharp cut edge design of the sheath as shown in Fig. 2, which caused stress concentration and breakage,
2. Neglect of newly established mechanical design analysis of vibration of the sheath parallel to the sodium flow and
3. 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

1. Incompetent and inexperienced behavior by the engineers (stationed at dirty, difficult, unimportant, and unhealthy working environment),
2. Careless experimental design,
3. Negligence in watching and examining the experiment,
4. Dereliction of the engineers' responsibility of checking and controlling workers' safety and the floor after the fire,
5. Some engineers become a kind of managers who do not want to know and do not know what is going on the operating floor.
6. No accident for 15 years made them smug and think the operation is completely safe, although there was a similar accident in Belgium
7. 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:

1. Poor management. Managements illegally changed the operation manuals and they neither allocated qualified engineers nor educated workers for the operation.
2. 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.
3. 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

• 1. Hiroshi Iino "Teaching Engineering Ethics in Japan", International Conference of Engineering Education, Oslo, Norway, August6-10, 2001, 8D2, pp35-41 and revised version published in a special issue of the International Journal for Engineering Ethics (IJEE), in press
• 2. Refer to JNC's detailed technical explanation in English of Monju and the accident at http://www.jnc.go.jp/zmonju/mjweb/index.htm
• 3. For technical detail in English, refer to N. Sasaki, T. Koyama, E. Omori, A. Maki and T. Yamaniuchi "Study on the Cause of the Fire and Explosion Incident at Bituminization Demonstration Facility at PNC Tokai Works", Spectrum798, Denver, Colorado, U.S.A., September 13-18, 1998
• 4. For final report on the accident in Japanese, refer to "Report from Investigation Committee for Criticality Accident in Uranium Treating Plant" December 24, 1999, pp.1-141