Nuclear Power Safety
To date there have only been two major reactor accidents in nuclear power plants worldwide – Chernobyl and the Three Mile Island. The Three Mile Island accident took place in the USA in 1979 and there was containment of the radiation, whereas the accident that took place at Chernobyl, (Ukraine) in 1986 allowed significant radiation to escape as there was no provision for containment.Details of the accidents at the respective plants are noted below:
Three Mile Island
In 1979, the number 2 reactor at the Three Mile Island plant in Harrisburg, Pennsylvania, USA was destroyed due to a cooling malfunction, which caused the core to melt. Essentially the reactor’s core became exposed and caused up to one third of the fuel to melt. The problem was exacerbated due to a lack of training and poor tools available to the operators that were called to incident. Conflicting messages were sent to the public with regards to the incident, which resulted in panicking the public unnecessarily as there was some radiation escape, however, the releases were not serious and did not pose a heath threat. Reassuringly, the containment unit worked as designed and despite a significant core meltdown, the reactor maintained its integrity and retained the fuel within.
The 1979 accident at went on to affect utilities all over the world. Several of them were felt immediately. Any plans for further nuclear power plants were dealt a serious blow in the United States and plants that were under construction faced huge modifications in response to the Nuclear Regulatory Commission (NRC). The cost for the operators skyrocketed as they faced additional delays and increased outlays for construction.
Residents brought a lawsuit against the plant claiming injury, however, this was dismissed and the judge found that there was insufficient evidence that radioactive releases had brought about enough harm to justify the case progressing.
Regulators and the nuclear industry had to fundamentally change how they thought about safety after the Three Mile Island accident. There was a widespread culture within the NRC and the utilities companies that such an incident could not possibly happen, which in turn could have stood in the way of an effective response to the incident. The accident also showed that a combination of freak events could occur, that those individual events in themselves were not foreseeable and that the some interaction was important and determined the actual risk. Prior to the Three Mile Island accident, regulators and the industry thought about planning for accidents in a more isolated context, in other words, this pipe break or not. This overall thinking was reflected in the design of the control area at the Three Mile Island power plant. The control room had over 600 individual alarms, which were useful in tracking the performance of individual systems and very useful if one individual system developed problems. However, when the incident occurred, several of the alarms went off which overwhelmed the control room crew and contributed to a slower response time.
The complexity of a nuclear generating plant is not unrivalled, chemical plants are known to be complex. However, utilities were not used to that level of complexity. For example, fossil fuelled plants are not as complex and if a problem should occur, the plant can be shut down with little chance of an incident affecting the surrounding area.
The Three Mile Island accident shook the public’s faith in nuclear power and the government and utilities handling of it. It has been noted that the valve that had failed in the Three Mile Island plant had malfunctioned 11 times before at other nuclear plants; however, the NRC had not taken any corrective action or issued any warning to other operators.
Chernobyl
In 1986, at Chernobyl, Ukraine the most catastrophic nuclear power plant accident occurred when a test was conducted to see whether an emergency shut down could be conducted safely in the event of a loss of power. Clearly in this case it could not. Within two seconds, there were two explosions and the power in the plant quickly rose to approximately 120 times its rated capacity. The fuel rods exploded, and the cooling water flashed into steam. Throughout this the pressure from the
steam increased and it breached the reactor structure and escaped into the environment. Although Soviet reactors did not have a containment vessel, the reactor was encased in cement. This 1,000 pound slab of cement was tossed aside.
For the first time, the lethal radioactive contents of a large power reactor were exposed to the atmosphere. The graphite control rods caught fire and smouldered for seven days spewing out radioactive releases into the air. It took 11 days to extinguish the fire and cease the radioactive releases.
Approximately 30 workers died fighting the fire and another several hundred had radiation sickness. Although these people recovered, they are at risk for cancer related illnesses. Officials ordered the evacuation of 135,000 people and parents sent their children away voluntarily. The monetary costs of the incident probably reached up to $10 billion and approximately 50,000 square miles of land became contaminated due to the incident. There were isolated incidents of high radioactivity readings in food, such as reindeer in Scandinavia, sheep in Wales, and fish in Switzerland.
After the Chernobyl power plant disaster, the soil in the region contained elevated levels of radioactivity, which means that the food chain will remain contaminated for some years. An exclusion zone was created in the affected area and at least some of the wildlife that inhabits it has absorbed high levels of radiation. Approximately 100,000 residents were permanently relocated.
Despite detailed knowledge of the radioactive fallout, the health effects cannot be
Determined easily as considerable non-radiation health related impacts related to anxiety and stress have been documented by researchers of which could be partly attributable to having to relocate en masse with little or no contingency plans.
Researchers do expect higher than normal deaths from cancer for years to come and there have been some 2,000 reported cases of child Thyroid cancer. This is a highly treatable disease, however, these cases could have been avoided by the ingestion of iodine tablets. However, there were not elevated levels of leukaemia when a 1993 report was conducted. Researchers found this surprising because after Hiroshima and Nagasaki, leukaemia was the earliest sign of long-term radiation effects. Various studies contain estimates of 5,000, 14,000, 600,000, or even one million additional deaths from cancer due to the Chernobyl disaster. The most common estimates are around 10,000-50,000. Thirty-five thousand cases would mean an increase in the cancer rate of approximately one-half percent, whereas the smaller estimates are not as large as the expected number of cancer related illnesses from coal and or the probability of dying in a car accident.
An incident such as this terrible disaster raises questions as to whether an event such as this could happen in North America or Western Europe. Most analysts would not compare the Chernobyl plant with an American plant or any other commercial plant outside of Eastern Europe. The main differences are the lack of a containment structure, the unstable reactor design, faults in the reactor design, and the non-routine operation during the test.
posted by Admin @ 10:57
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