28 April 2009
The US nuclear power industry learnt many lessons from the accident. These led to make US nuclear power plants enviably efficient and safe. In 1980, the average capacity factor (the ratio of electricity produced compared with the maximum electric power a plant can produce, operating at full power all the year around) for US nuclear power reactors was 56.3%; it increased steadily and remained consistently above 90% for the past ten years. Sixteen of the 104 reactors had capacity factors of over 100% in 2008. According to the American Nuclear Society (ANS), the clean up after the accident offered unique technological and radiological challenges. It took 12 years. So far the utility spent nearly US$973 million. The decommissioning team shipped 342 fuel canisters safely for long-term storage at the Idaho National Laboratory. More than 1000 skilled workers carried out safely and successfully the clean up plan developed by a team of specialists. It began in August 1979, with the first shipments of accident-generated lowlevel radiological waste to Richland, Washington. In the cleanup’s closing phases, in 1991, approximately one percent of the fuel and debris remains in the vessel. The team emptied the last remaining water from the TMI-2 reactor in 1991. The cleanup ended in December 1993. The Unit 2 received a license from the NRC to remain as a monitored storage facility, to be decommissioned in 2014.- by Dr K S Parthasarathy
Lessons from TMI Accident: US Nuclear
- by Dr K S Parthasarathy
March 28, 1979 is a day every one in nuclear power industry wants to forget. It was on that fateful day the most serious accident occurred at Unit 2 of the Three Mile Island nuclear power plant in Middletown, Pennsylvania, USA. The accident did not kill or injure any plant worker or member of the public
The unit 2 (900 MWe, Pressurized Water Reactor) was operating at 97% power; some equipment malfunctioned; this, together with certain design-related problems and worker errors led to partial melt down of its core. It shook the confidence of the public.
The clean up measures to mitigate the effects of the accident were very expensive. But the environmental impact of the accident was not high. The US Nuclear Regulatory Commission (NRC) reported that the average radiation dose to 2 million people in the area was about one millirem, compared to the dose due to natural gamma background radiation of about 100 125 millirem for the area; the maximum dose to a person at the site boundary would have been less than 100 millirem.
Several independent groups of respected professionals investigated the accident comprehensively and concluded that in spite of serious damage to the reactor, most of the radionuclides were contained; the actual release had negligible effects on the physical health of individuals or environment. (NucNet release March 23).
According to NRC the accident “brought about sweeping changes involving emergency response planning, reactor operator training, human factors engineering, radiation protection, and many other areas of nuclear power plant operations. It also caused the U.S. Nuclear Regulatory Commission to tighten and heighten its regulatory oversight “(NRC Fact sheet, March 2009).
The Kemeny Commission set up by Jimmy Carter, the then US president, to investigate the accident made comprehensive recommendations.
The US nuclear power industry learnt many lessons from the accident. These led to make US nuclear power plants enviably efficient and safe.
In 1980, the average capacity factor (the ratio of electricity produced compared with the maximum electric power a plant can produce, operating at full power all the year around) for US nuclear power reactors was 56.3%; it increased steadily and remained consistently above 90% for the past ten years. Sixteen of the 104 reactors had capacity factors of over 100% in 2008.
According to the American Nuclear Society (ANS), the clean up after the accident offered unique technological and radiological challenges. It took 12 years. So far the utility spent nearly US$973 million. The decommissioning team shipped 342 fuel canisters safely for long-term storage at the Idaho National Laboratory.
More than 1000 skilled workers carried out safely and successfully the clean up plan developed by a team of specialists. It began in August 1979, with the first shipments of accident-generated lowlevel radiological waste to Richland, Washington. In the cleanup’s closing phases, in 1991, approximately one percent of the fuel and debris remains in the vessel.
The team emptied the last remaining water from the TMI-2 reactor in 1991. The cleanup ended in December 1993. The Unit 2 received a license from the NRC to remain as a monitored storage facility, to be decommissioned in 2014.
TMI-2 cleanup operations produced over 10.6 million litres of accident-generated water that was processed, stored and ultimately evaporated safely.
Early in the cleanup, the team completely severed TMI-2 from any connection to TMI Unit 1. The owners do not anticipate any further use of TMI-2.
Over a dozen major independent health studies of the accident showed no evidence of any abnormal increase of cancers around TMI years after the accident (ANS, 2005). Specialists do not expect any adverse health effect among the populations living in the area is as the radiation doses to the population were negligible.
In June 1996, Harrisburg US District Court Judge Sylvia Rambo dismissed a class action lawsuit alleging that the accident caused health effects.
The National Cancer Institute studied the cancer mortality rates around 52 nuclear power plants including TMI and nine US Department of Energy facilities at the request of US Senator Edward M. Kennedy, chairman of the Senate Committee on Labour and Human Resources.
The study concluded that the survey has produced no evidence that an excess occurrence of cancer has resulted from living near nuclear facilities.
During TMI-2 accident, TMI-1 was shut down for refuelling. It remained shut down till October 1985. TMI-1 received all the benefits from the lessons learnt from the accident at TMI-2.
According to the World Nuclear Association, When TMI-1 restarted, its owners, General Public Utilities pledged that they would operate the plant safely and efficiently; they desired that it would become a leader in the nuclear power industry (WNA, 2001). The plant lives up to their expectations.
The owners of TMI-1 modified the plant and revamped the training and operating procedures in light of the lessons of TMI-2.
Since then, TMI-1 clocked many creditable records. In 1997, TMI-1 completed the longest operating run of any light water reactor in the history of nuclear power worldwide - 616 days and 23 hours of uninterrupted operation. (That run was also the longest at any steam-driven plant in the U.S., including plants powered by fossil fuels.) In October 1998, TMI employees completed three million hours of work without a lost-work day accident. In 2008, it clocked a capacity factor of 106.7%.
The licence to operate TMI-1 expires on April 19, 2014. On January 8, 2008, the utility owners have applied to operate the reactor for an additional 20 years. The NRC has issued the safety evaluation report (NRC release, March 13). Three Mile Island Alert, a nuclear watchdog founded in 1977 has opted not to oppose the plant owner’s (Exelon) application to re-license the plant through 2034.
The record performance of all US nuclear p ower plants post TMI may gradually remove the stigma attached to them because of the TMI accident.
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