Thanks to more great reporting from the Globe and Mail, we now know that the Canadian Nuclear Safety Commission (CNSC) has thrown the rule book out the window when it comes to ensuring the safety of our aging CANDU reactors’ pressure tubes.
As CANDU reactors age, the hundreds of pressure tubes inside the core of the reactor are subjected to deterioration caused by the intrusion of hydrogen gas into the metal walls of the pipes. This “embrittles” the metal, making the pressure tubes more likely to crack, break or burst.
A broken pressure tube causes a “loss of coolant” accident (LOCA). A worst case LOCA scenario requires a “fast shutdown” – failure to do so can lead to radioactive releases or even a fuel meltdown.
Ontario’s nuclear operators have recently discovered that their mathematical models of what hydrogen levels should be in aging pressure tubes are not even remotely accurate. Samples taken from tubes at the Bruce Nuclear Station have found levels far higher than predicted, meaning a much higher risk of embrittlement and bursting. Ontario Power Generation (OPG) has discovered a similar disconnect between models and real-world results in some of the Pickering reactors.
The CNSC’s response has been to theorize on what might be causing this discrepancy and then to work to find reasons to keep reactors operating despite hydrogen uptake levels in pressure tubes far exceeding CNSC standards. As the Globe reports, when its first “workaround” for ignoring the discrepancy between theoretical models and real-world results didn’t hold water, the CNSC tried again. When its second justification for ignoring the problem also proved flawed, it fell back on the alarming idea that it was alright to simply hope that reactor safety systems will compensate correctly when a pressure tube fails.
The CNSC, Bruce Power and OPG still have no validated explanation for why some tubes have hydrogen levels not only far higher than predicted but also far beyond levels previously considered acceptable by the CNSC. These levels violate the terms of the companies’ operating licences, but they are carrying on as if everything is fine.
Two independent nuclear experts think that is a very risky strategy for the people of Ontario. Dr. Gordon Edwards and Dr. Frank Greening have sent us some thoughts on why the CNSC’s actions fly in the face of common sense and safety.
We wholeheartedly agree with the conclusions they have reached:
· The Bruce B reactors should be shut down or derated (ramped down) to no more than 70% of full power as a precautionary measure.
· The four Pickering B reactors should be shut down as they have never been retubed and are past the age when they should have undergone a complete refurbishment.
· The two operational Pickering A reactors should be shut down until or unless a second fast shutdown system is added to them – they are the only CANDU reactors operating in the world with only one fast shutdown system.
What you can do
Please ask the CNSC’s boss, Natural Resources Minister Jonathan Wilkinson, to step in and order the CNSC to take proper precautionary measures to protect our safety.