TMI nuclear mishap: a blessing in disguise!

TMI nuclear mishap: a blessing in disguise!

The remedial measures enforced have enhanced the performance of operating nuclear power plants.

On March 28, 2014 the nuclear industry observed the 35th anniversary of the accident at the Three Mile Island (TMI) nuclear power station in Middletown, Pennsylvania, USA. The accident caused a setback to issuing licences to new power plants in that country. The public lost confidence in the regulators and promoters of nuclear energy. An unbiased assessment shows that the accident turned out to be a blessing in disguise, as the remedial measures enforced in the US helped enhance the performance of operating nuclear power plants to enviable levels.

The accident occurred when Unit 2 (900 MWe, pressurized water reactor) at TMI was operating at 97 per cent power. Some equipment malfunctioned; this, together with certain design-related problems and worker errors led to partial melt down of its core. The accident did not kill or injure any plant worker or member of the public. Several competent professional groups which investigated the accident concluded that in spite of serious damage to the reactor, the plant contained most of the radio-nuclides.Because of the concerns about the possibility of radiation-induced health effects, principally cancer, in the area surrounding the plant, the Pennsylvania department of health maintained for 18 years a registry of more than 30,000 people who lived within five miles of TMI at the time of the accident. The department discontinued the registry in 1997, without any evidence of unusual health trends in the area.

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. The review of the accident by the Kemeny Commission set up by Jimmy Carter, the then US president, led to sweeping changes in the emergency response planning, operator training, human factors engineering, radiation protection, and many other areas of nuclear power plant operations. The TMI-2 accident led to the setting up of the Institute of Nuclear Power Operations (INPO) in 1979. They continue to promote excellence in the operation of nuclear plants and accrediting their training programmes.

The lessons learnt from the accident helped. In 1971, 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) of all reactors in USA was 48.4 per cent; it steadily increased and reached nearly 90 per cent in 2002. It remained so till 2010 (90.9 per cent) dipping down to 86.4 in 2012, while 8 US reactors recorded over 100 per cent. The Unit 1 at Three Mile Island recorded a capacity factor of 99.5 per cent in 2012. Nuclear industrial safety accident rate (no of accidents resulting in lost work, restricted work or fatalities for two lakh worker- hours) decreased over 47 fold from 1974 to 2012. 

The American Nuclear Society (ANS) noted that 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 clean up plan successfully. It began in August 1979, with the first shipments of accident-generated low-level radiological waste to Richland, Washington. The cleanup ended in December 1993. The stricken unit received a license from the Nuclear Regulatory Commission (NRC) to remain as a monitored storage facility, to be decommissioned in 2014.

India’s reaction

The owners of TMI-1 modified the plant and revamped the training and operating procedures in the light of the accident. Since then, TMI 1 registered record performance. 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. 

In 2009, NRC renewed its operating licence, extending its life by 20 years to 2034. The current record performance of US nuclear power plants is undoubtedly due to the implementation of remedial measures by nuclear industry post -TMI accident.How did India react to the accident? In 1979, India operated three reactors (Tarapur Atomic Power Station 1&2 and Rajasthan Atomic Power Station -1); five 220 MWe PHWR units were under construction. The Department of Atomic Energy (DAE) constituted a Taskforce under the Chairmanship of MR Rao, the then Head, Reactor Operation Division, Bhabha Atomic Research Centre to study the safety aspects of TAPS and RAPS. The report covered factors such as the reliability and availability of the engineered safety features, human engineering aspects and emergency preparedness in the public domain. The regulatory agency followed up the recommendations of the task force.

(The writer is former secretary, Atomic Energy Regulatory Board)

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