If it ain’t broke, we didn’t build it.
Well not really, it just seems that way.
The need to replace the pressure tubes in CANDU reactors after 25 years or so of operation has always been considered a significant disadvantage of the design. Retubing is very complex since the tubes are integral parts of the reactor core. The whole operation must be done in high radioactivity fields in cramped spaces within the reactor confinement structure. Special remote handling tools and techniques need to be developed on a custom basis since each reactor will be somewhat different. To make matters even more complicated, often the owners “take the opportunity” to replace many other components, steam generators for example, while the reactor is down. The whole process has come to be called refurbishment.
To be fair other types of reactors also need mid-life repairs. In the past ten years or so the tops (lids) of several US light water reactor pressure vessels have had to be replaced due to premature corrosion. This is a big undertaking in itself but is still a much smaller job than retubing a CANDU. Many US reactors are licensed for 40 to 60 year lifetimes and the possibility of an 80 year or longer lifetime is being researched.
Refurbishment of CANDUs has had a chequered history. The first two Pickering reactors had to be retubed in the 1970’s because a poor alloy was originally selected for the pressure tubes. This set the precedent for refurbishment as an expensive and lengthy undertaking. Refurbishing all four of the Pickering A reactors by OPG cost at least $3 billion total for just two of the reactors. It was subsequently decided that refurbishing the other two was too expensive and they were essentially shut down permanently. Bruce Power has been soldiering on for the last few years refurbishing two or three of the four Bruce A reactors at a total cost apparently approaching $4 billion. The New Brunswick reactor overhaul, as reported previously in this blog, continues to be over budget and is lagging months behind schedule with no end in sight.
As for future CANDUs, it’s disappointing to me that the ACR -1000 design envisages refurbishment after 25-30 years. My hope was that they could have avoided this problem by designing more robust pressure tubes. It could be more even difficult to retube an ACR (if one is ever built) because the core has much smaller dimensions – hell in a very small place?
In spite of all its problems, there is an upside to refurbishment. With no possibility of building new reactors for five or ten years or more, it’s the only game in town for Canada’s nuclear industry.
The funding for these projects buys goods and services provided by the many companies, great and small, that comprise the nuclear industry. Without it many of them wouldn’t survive. Cost overruns are mainly labour costs which keep highly skilled engineers employed; preserving the specialized expertise needed to eventually build new reactors. Furthermore, it is apparent that even though refurbishing an existing reactor is costly, it is still much cheaper than building a new one.
So roll on refurbishment, it will likely continue to be the sustaining activity of our nuclear industry for years to come.