The worst nuclear incident on the land of the US happened on March 28, 1979, as it was the famous Three Mile Island accident, which was a nuclear meltdown in one of the two reactors of Three Mile Island in Dauphin County, Pennsylvania, US. The incident was also rated a five, in the group “Accidents with wider Consequences” on the International Nuclear Event Scale, which has seven as the maximum rate. The accident itself began with the halting of the secondary systems of non-nuclear group, which resulted with the failure of primary system`s relief valve, which was operated by a pilot. The last resulted in the leakage of nuclear reactor coolant in large amounts. As it usually happens in such situations, the technical malfunctions were also complicated by the failures of the operators to manage the situation due to the lack of training, competence of the plant`s operators and human factors. Eventually, a special indicator on the operator`s interface mistakenly showed that there was too much coolant within the reactor; therefore, the operator`s actions manually overrode the emergency cooling systems and released steam pressure. Therefore, the accident was caused by the combination of technical malfunctions and the human factors, which led to the disaster.
The accident escalated the anti-nuclear concerns among not only the usual opposers of the nuclear power, but among the general public also, followed by the new regulations that were supposed to control the nuclear industry. Moreover, the accident has also become the reason for the declination of the project for third reactor`s construction that was already in progress. As for the environmental consequences of the accident, there obviously was a large amount of radioactive iodine release; however, there was no proof that it had severe consequences on the people affected by the accident.
As for the detailed description of the reasons of the accident, everything within the nuclear power plant functioned normally. In the couple of hours before the accident, the second reactor of the plant was functioning almost at full power (97%), while the first reactor was refueling, being shut down. It was the time of 4:00:37 A.M. EST, when the main consequence of the events causing the partial core meltdown started with the secondary loop of the second reactor, which was one of the main steam and water loops in the water reactor.
The real cause of the incident occurred approximately eleven hours earlier, when the operators tried to fix the usual blockage in a condensate polisher, a filter that was designed to clean the water on the secondary loop. In the majority of such cases, the blockage is a common thing for these filters; therefore, it`s also easily removed with the compressed air blowing out the stuck resin within the filter. However, this option didn`t work and the operators decided to clear it with the water simply blowing the air into it. The blockage was removed; however, the small amount of water leaked into the airline of the instrument, causing the steam generators gradually failing. As the generators no longer received any water, the pressure and the heat in the reactor launched the emergency shutdown systems. The nuclear chain reaction was stopped; however, as there was no steam for the turbine, the decay heat was only rapidly growing. Moreover, with the failure of the feedwater pumps, the auxiliary pumps started automatically; although, as the valves had been blocked for the maintenance, the whole system had no possibility to pump any water. The valves` closure was the violation of the regulations of the US Nuclear Regulatory Commission (NRC), which stated that the reactor must also be shut down with the auxiliary pumps, when the last are put to maintenance. NRC officially stated this violation as the key reason for the mechanism’s failure and the incident itself, as a result. As the decay heat wasn`t removed from the primary loop, the pressure of it started increasing, launching the PORV (pilot-operated relief valve) automatically. However, the relief valve stuck open because of the technical malfunctions, despite the standard valve closure after the pressure is released. As the result of opened vault, the coolant water leaked outside, leaving the primary system without any coolant. Eventually, the combination of all the mentioned factors and situations compose the technical side of the incident`s reasons.
The investigation of the user interface of the reactor control system showed the critical problems in engineering of user interface and stated the influence of the human factors on the accident. As it was described above, the valve should have been closed after the pressure within the reactor; however, it remained opened. On the contrary, the indicator on the user`s interface of the reactor showed that the valve closed, as usually. Therefore, due to the bad design of the users interface and the indicator itself, the operators diagnosed an incorrect problem with the reactor. The explanation for them was simple enough, as they had the evidence that the valve has closed; however, the temperature and pressure indicators and the water coolant indicators showed an abnormal states for the closed valve. This uncertainty resulted in the further severity of the accident, as the operators were not able to break the vicious circle of their thinking, as their thoughts contradicted the indicators on the user`s interface. This lasted until the new shift of operators came over, as their fresh way of thinking concluded in the right diagnose of the problem; however, by that time, the major damage to the reactor had already been caused. The operators were not trained to understand the mechanism of the PORV and how the indicators on their interfaces worked, as there was a special indicator for the temperature in the tail pipe located near the pressurizer that could have shown the operators that the temperature remained high; therefore, it could have been easier for them to find out that the valve had been remaining opened for all the time. Moreover, it was not until almost three hours after the beginning of the problem that the launch of the radiation alarms confirmed that the nuclear water reached the detectors. The level of radiation exceeded the expected levels by 300 times; therefore, the plant was severely damaged and contaminated by the radiation. Therefore, the incompetence and lack of training of the operators only escalated the problem and led to the worse consequences of the accident.
Moreover, such confusion in diagnosis of the problem, which occurred at the beginning of the accident made it harder for the officials to proclaim, register and solve this accident. First, a supervisor of the plant announced a site emergency at 06:56 A.M., and manager G. Miller declared a general emergency in 30 minutes, defining the problems with high potential for radiological consequences of high severity to the public. It was not soon enough, when the local officials, including PEMA (Pennsylvania Emergency Management Agency) have contacted the NRC to undertake the serious measures, perceiving them of the hazardous consequences of the incident. When the NRC`s chairman J. Hendrie accompanied by a commissioner V. Gilinsky reviewed the accident and checked all the details of it, they`d stated that the accident was a problem of a big concern; however, it was not a problem of alarm and panic. Gilinsky also reported on the situation to the members of Congress and the reporters, also informing the staff of the White House at 10:00 A.M. However, NRC was also facing the same troubles in retrieving the accurate information about the accident and was accused by the higher official of being ill prepared with the data and needed information.
The third day after the incident was the days of the appearance of the new concern for the officials, as a hydrogen bubble had appeared in the pressure vessel`s dome. A potential explosion of it could not only break the vessel itself, but could also endanger the structure of the containment vessel, which would result in the higher doses of nuclear waste release. Fortunately, the issue was solved, simply venting the bubble into the atmosphere, as there was on oxygen within the bubble, the only substance that could cause the explosion.
Describing the whole accident from the engineering ethics aspect, it should be concluded that the principles of not only engineering, but also the professional ethics weren`t practiced. First of all, the root cause of the incident was the violation of the first and the most important point of the code of engineering ethics, as every engineer must establish the safety of every of his actions as the top priority. The example with the resin cleaning mentioned above states that operators wanted the mechanism to work in any possible way, disregarding the simple safety measures, as an operator should have known that even the smallest amount of water spilled through the airline would cause the irreversible consequences. Secondly, engineers must operate and act only in the areas of their highest competence. That rule was also violated both by the designers of the PORV, operators that weren`t able to manage it in a critical situation and the management of the plant that wasn`t responsible enough to train their employees to perform not only the technical operations, but think wider and find the solutions out of the confusing situations like the one with PORV indicator. The last, but not the least, an engineer must operate with only exact and objective data and report accordingly. The information mentioned above confirmed that this rule was also violated by the management of the plant and the officials regulating its operations.
Therefore, the accident is the bright example of the combination of engineering ethics rules` violations, which could affect not only the plant itself, but the outside environment, and the consequences of these violations could have been more severe, as it`s also mentioned above.
Of course, the accident was investigated thoroughly by a number of federal and state government agencies. However, the most famous and the most successful one was the investigation of President's Commission on the Accident at Three Mile Island, which was set up in April 1979 by Jimmy Carter and it consisted of 12 members, which were not only the specialists of their field of study, but their attitude towards the nuclear energy was neutral. The choice was considered to be as the best for this situation, as the results of the investigation wouldn`t be distorted by the personal attitude towards the nuclear energy usage. The team was headed by the Dartmouth College, John G. Kemeny. During the investigation, the team reported on the local officials responsible for the accident, including the NRC, stating that they lacked the professionalism in maintenance and quality assurance, poor training of the staff, inadequate management and weak communication especially in the questions of important safety measures. The finalized, summarized and documented version of the investigation results was released on October 31, 1979, just when the commission was told to. These results have also concluded that the necessity of the fundamental changes within the organization of the nuclear power plant were critical, including the changes in operations, practices and procedures for the NRC. They`ve also concluded that the operators acted within the areas of their competence; however, nobody has ever taught them how to solve such abnormal situations with the interface and the equipment.
Obviously, the accident wasn`t left without attention for the scholars, as the wanted to receive as much information from the accident in order to prevent the same accidents in future or to solve them in a fasts manner, at least. The incident of The Three Mile Island has become the inspiring note for Charles Perrow to conduct his Normal Accident Theory, which explains the incident as a result of interaction of combination of different failures in a system of high complexity. Furthermore, the TMI has become the brightest example for such type of accidents, as it appeared to be an uncontrollable, unexpected and unavoidable one.
The research also resulted in a conclusion that the failure at TMI was an unavoidable result of the complexity of the whole system, as such complexity was recognized as the reason of imminent failures despite any possible excellence of its management. Therefore, Perrow concluded that such systems would someday suffer from a “normal accident”, which is the explanation of such incident as the result of the system`s complexity that is hard to manage and control. Moreover, he suggested that such systems should be redesigned and simplified in order to avoid any cases of “normal accidents”; otherwise, the whole technology should be abandoned and avoided for the future usage.
The concept of “Normal Accidents” was the inspiration for the intellectual advancements and developments for the 1980s; therefore, the whole conception of risk and safety of the nuclear energy usage was rethought and redesigned. Scientific community recognized the system`s complexity as the main cause of the potential accidents and possible disasters not only in nuclear energy production, but for any other technology; moreover, any technological cataclysm could no longer be the fault of equipment failure and the human factors separately.
As for the aftermath of the accident, it drastically affected the whole nuclear energy industry and the further development of nuclear energy, as during the years following the accident, the number of building nuclear reactors on the territory of the US had been continuously decreasing. Moreover, in the period between 1980 and 1984, more than 50 nuclear reactors were canceled. However, the case hasn`t become the reason for the decay of the nuclear energy for the US, as the community realized that the potential of nuclear energy to replace the oil fuels was the highest, as the oil sources of fuel are still limited and never renewable. Therefore, a number of approximately 53 new nuclear plants at the time of Three Mile Incident was completed under the strict control of the officials, especially in the quality and safety measures.
Obviously, the incident affected the environment, especially around the nuclear plant itself. With the release of radioactive gases into the environment, the sceptics predicted the high cases of death of cancer caused by the radioactivity. However, the official research by the American Nuclear Society refuted these predictions, as they stated that the dose of radiation for every person around the nuclear plant was similar to the one of X-Ray medical radiation; moreover, the average nuclear background for the radiation within the territory never exceeded the normal indexes.
As for the international reaction to the accident, there wasn`t any concerns and fears from the Global Officials, due to the reasons mentioned above and that the consequences of the incident never affected the territory outside the US borders.
The incident has become the great lesson for the plant`s management and local officials; therefore, they`ve done their best to clean out and close the second reactor of the plant and modernize the first generator for the future production. The reactor was continuously improving, especially in the technologies of safety assurance; therefore, it`s still running successfully till nowadays. The future of the second reactor remains murky, despite the fact that it could be used for the future production potentially. The chance of the second reactor usage is still possible in a long-term perspective, when the first reactor will exhaust its powers; however, it`s still officially unconfirmed.
The explanation of the accident from different aspects provides an example of how officials react towards the safety measures and the role of the nuclear power in their country. Statistically, the Three Miles Incident has become the worst nuclear accident in the history of the US; however, there were no severe consequences of this accident, as the incident neither affected the environment dramatically, nor the population. It was the accident caused by the complex of the different factors and eventually, the American governments and scientific society has learnt this lesson to prevent the disasters of the same hazard like Chernobyl and Fukushima had.
References
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