Replace the RPV

19 January 2011

Here’s a crazy idea. A few weeks ago I was fortunate to be the chairman of a lively PLIM/PLEX conference in Chicago. The event’s first speaker, Fred Polaski, a former Exelon life extension executive, said that many nuclear stations could probably be run beyond even 80 years of life. And in addition to the many safety-related component replacements that have already occurred in nuclear power plants, he proposed an even more radical project: replacing an entire reactor pressure vessel.

I felt an incredulous buzz in the room as he said that. The idea of cutting out the pulsing heart of a nuclear power plant is outrageous.

But perhaps on second thought the idea is not so crazy. He pointed out that in his early working days at Philadelphia Electric Power, there was absolutely no idea that the stations would be getting an extra life extension, as so many have recently. And it is unlikely that he would have conceived then of the possibility of cutting off, removing, replacing, and reattaching the steam generator, pressuriser, or reactor vessel heads, or engineering dissimilar metal welds, as many utilities have in recent years. And the RPV may well limit the life of a reactor, especially in its ability to withstand the thermal shock of emergency cooling water flow.

Actually changing the RPV would carry the technical, regulatory, economic and timescale risks of a first-of-a-kind operation, and the burden of associated theoretical and regulatory paperwork required. But the industry has faced down those demons before.

Polaski went on to say, “Why not? We removed reactor vessels when we decommissioned plants.” The most prominent example is the decommissioned RV of the 1100MWe-class Trojan PWR reactor in Oregon, which according to an EPRI report (1003029) was left intact, filled with grout, and removed in one piece. Despite its mass—930t—and the extent of its radioactivity—two million Curies—the vessel was still successfully moved to the Hanford site. (However, I can find no analogue in the case of BWRs: both 1000MWe-class commercial BWRs Shoreham (from the USA) and Wuergassen (Germany) were decommissioned by segmentation into many smaller pieces).

Many sites have become familiar with cutting a hole in containment to replace steam generators and/or pressurizers. Inside containment, nuclear cutting techniques have developed in response to the demand for in-situ segmentation work for decommissioning reactors. So it just might be technically possible to cut the old reactor out and remove it without destroying the whole plant. That would probably be the easy part.

Only main vendors can manufacture, qualify and validate a new reactor vessel, and many of the original manufacturers of popular designs from the 1970s have since been subsumed into other companies (for example, Konvoi and Combustion Engineering). The loss of expertise involved in those changes would make a direct replacement of an older design from many manufacturers difficult.

Probably the utility would want a fresh load of reactor internals also, which would include control rod drive mechanisms. All of these would need to be quality managed within the as-measured tolerances of the original plant, and qualified by the vendor and the statutory safety regulator at many stages of construction. This is not an easy or inexpensive task. But on the other hand the vessel could be assembled and tested (and then disassembled again for transport and installation) in a controlled factory environment.

Finally there would need to be all of the handling and connection issues involved in installing the RPV, including dissimilar metal welds between vessel and pipework, and a large-scale commissioning programme akin to starting up a new unit.

It is unclear whether all of this work would end up cheaper, on a EUR/MWe generated basis, than a new Gen-III+ reactor set up next door; the station would not have as long a lifetime as a brand-new one. Perhaps it would only be worth investigating should a relatively modern station begin to run into serious problems. Still, sometimes it is the crazy ideas that just might work.

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