Technical Topics - Corrosion In the Nuclear Power Industry (and of Bells!]
by the Technical Secretary, Douglas Hills

This month I thought I'd talk about Corrosion in the Nuclear industry. Pretty big field you may say and you'd be right. There is an EFC working party (no 4) devoted to this area and they always put on an interesting session at EuroCorrs. (In this connection we are hoping here at the Institute to get the Corrosion Engineering Division workgroups going again and maybe feed into the EFC group. Nick Smart (email address below) is involved with this.


My own time working in the nuclear industry was some time ago now (late 70's - a different age!). I will recount here a couple of memories from that time.

One experience I had was crawling/walking/ climbing around inside an ACR (Advanced Gas Reactor) taking samples (chloride level) shortly after it had been working. Part of the reactor (not the core!) had filled up with sea water - the operators detected a water leak, thought it was boiler water (it was in fact cooling water!) and had responded by trying to boil it off! This led, as one can imagine, to some pretty severe corrosion problems in the Sub-Boiler annulus and well up the walls of the containment vessel which was insulated with Triton and stainless steel foil (The latter was reduced in places to "toast"!). Despite this major accident the clean up was done effectively and was completed within a couple of years and to my knowledge this reactor has been operating reliably since.

I also remember working on the Thermal Reactor Assessment exercise. Particularly we had to decide whether the tendency for steam generator tubes in PWRs (Pressurised Water Reactors - Sizewell B is one of these) to corrode would make opting for that type of reactor a mistake. An environment of concentrated caustic solution at high temperature can crack a lot of alloys and finding a suitable alloy (Inconels 600, 800 and 825 were the choices available back then) was important Anyway, the decision was made that the technology could cope and I presume our faith was justified. The corrosion problems specifically associated with radioactivity (like enhanced oxidation of zirconium used for fuel tubes which I also worked on) seemed generally to be predictable and could be allowed for.

Overall I was impressed back then by the UK nuclear industry (and I still am!).The stations (at least AGRs which were what 1 was most familiar with) were high output, efficient, reliable and contained in small non intrusive buildings and apparently safe (cows grazing right beside them!).There are of course still corrosion challenges for example in the currently operating UK nuclear stations, many of which having been pushed beyond their original design lives.

Also important are end of life problems eg. with some Magnox reactors there have been difficulties with storage of waste fuel rods that are kept in ponds which have to be inhibited.There is also the very important and contentious issue of nuclear waste disposal. Stainless steel is currently the preferred containment material for intermediate level waste in UK but maybe more sophisticated alloys (like the famous Alloy 22 which is supposed to have the lowest corrosion rate long term of any non precious metal alloy and which will probably be used for high level radioactive waste disposal in the U.S.) may be considered.

Should there be "new build"? Have the technical and human problems that have led to some of the high profile negative publicity for nuclear energy been solved? Well the last fifty years has been a learning experience for both builders and operators of nuclear plants. So nuclear is now a mature technology and these problems should not occur again. Overall then (I'm afraid I'm moving into politics here!) my view is that we should go for "new build" in UK mainly because nuclear power stations are virtually carbon neutral and this is the big issue right now. The French generate over 80%of their power by nuclear and are a good example of how to do it with PWRs. That route is supportable with much reduced waste, intrinsically safe design, 60-year lifetimes probably, and frequent replication of designs instead of our perpetual "one-offs" or two at best. Well that is probably enough on that - maybe it will stimulate some correspondence from people working currently in the industry!


Returning to copper corrosion (a previous TT article) and my musical interests, I went round one of the only two bell foundries in UK (JohnTaylor in Loughborough) last week. JT cast big bells (130 a year!) from a high tin bronze. Another important line for them is refurbishment. According to our guide, when bells come back for this, no attempt is made to clean the patina or verdigris from the outside. It apparently makes no great difference to the sound, looks OK and if you do clean it off it grows again "just as thick" within two years (I presume the growth is logarithmic (log to base 30!) as some bells are nearly 1000 years old and have not disintegrated!) What old bells often do need is a retune {it was not made clear whether corrosion contributes to the falling out of tune - or whether they were never in tune in the first place) and for that reason metal has to be removed from the inside. A couple of pictures illustrate this very interesting visit.

As usual I am happy to receive any comments: Douglas@Harrbridge.freeserve.co.uk. Thanks are due to John Haigh and Nick Smart {nick.smart@serco.com) for correcting some of the author's misconceptions. Any errors left are his own!