By: Donald Jones, P.Eng., retired nuclear industry engineer, 2014 April
It has been 35 years since the small loss of coolant accident (small LOCA) at Three Mile Island (TMI) Unit 2 caused the loss of the plant. Rod Adams has some interesting views on the event and its precursors on his informative pro-nuclear website, Atomic Insights, http://atomicinsights.com/tmi-operators-took-actions-trained-take/ including some from licensed reactor operators and shift supervisors.
CANDU has not been immune to small LOCAs but none resulted in the kind of damage and infamy that inflicted TMI Unit 2 although a pressure tube failure at Pickering A unit 2 in 1983 did result in the retubing of all four Pickering A reactors. It is worth remembering that no one was injured and that there were no long term health effects from TMI. Small LOCAs are much more likely to happen than large break LOCAs. Unlike TMI the CANDU small LOCAs reviewed below originated in the primary heat transport (PHT) system and not in the balance of plant. There have been other CANDU significant events that did not originate in the PHT system but these did not progress to small LOCAs. For those interested in a TMI comparison all CANDUs after Pickering operate with a degree of boiling at reactor core outlet at high powers (nominally 4 percent on CANDU 6 and Darlington) and onset of boiling results in a spike in pressurizer level. Pickering does not have a pressurizer.
The TMI event occurred near the end of the CANDU 6 design process in which I was involved and it was reviewed in detail and resulted in little or no design changes but did result in a continuing emphasis on ergonomics. To the best of my knowledge and memory what follows is a description of all the major CANDU small LOCAs. This does not include precursor events and events that caused acute leaks of heavy water.
Karachi Nuclear Power Plant (KANUPP), Pakistan Read the rest of this entry »