The curious case of the expanding standpipe28 September 2001
In this month’s feature former CEGB employee Jessica James tells NEI about a cautionary tale of a minor transgression in the past that came back to haunt Hinkley Point A – at great expense – many years later.
Many years ago, employees at Hinkley Point A found a number of distorted standpipes. The problem called into question the viability of all the Magnox reactors. NEI asked former Central Electricity Generating Board (CEGB) employee Dr Jessica James what happened.
“It’s a long time now since I worked in the nuclear industry – too much thinking about it makes me feel my age,” said Jessica.
“When I started I was part of a nationalised industry, the CEGB. When I left, a few months later, I was part of Nuclear Electric, the nationalised rump of the proud company, having been briefly employed in the interim by National Power Nuclear which had a transient existence before the UK government of the day (Conservative – in those days Labour wasn’t into privatisation) realised that the public were unlikely to want to buy shares in a company that had decommissioning costs on the horizon.
“I was a summer student in 1989 in Bristol, working at the CEGB laboratory. I was not a direct observer of all the events which I am about to describe, though those I did not witness were reported to me by highly reliable people, many of whom had PhDs, and not all of the conversations took place down the pub!”
Jessica’s story is a salutary one, reminding us that human error and carelessness on even the smallest scale can have long-term repercussions.
At the Bristol labs the research team supported a large number of different reactors over the country, but had particular responsibility for the Hinkley Point A site.
The Bristol team were, according to Jessica, “a bunch of clever and dedicated folk with whom I was privileged to work. The team participated in the annual outage of the reactors, when they were ceremoniously taken offline to be tested and tapped and tweaked to check that it would be safe to let them run on for another year.”
This had taken place without major incident for a long time, and people had started to believe that the good old Magnox workhorses would go on for several decades longer than they were designed for.
Jessica tells of an unfortunate occasion during an outage: “A fuel rod was being carefully extracted from its close-fitting standpipe when it stuck. And remained stuck. The force being applied to extract it was cautiously increased, but perhaps not cautiously enough: The rod broke off and half of it remained down the core.
“This was terribly bad news. Bad because someone was going to have to spend a long time fishing for it with equipment not really designed for the purpose, but worse because the cost of maintaining the reactor offline was about £10,000 per hour – and that’s in 1989. These days I work in a bank, so with the benefit of my financial acumen I can tell you that, using the Retail Price Index as a proxy for the rate of inflation, £10,000 then is worth about £15,000 now. Which is, over the course of a few days spent fishing for a bit of fuel rod, a lot of money.”
The mystery unfolds
Eventually the offending fuel rod segment was extracted. But no-one was happy as it transpired that this wasn’t the first time that a rod had jammed, though upon previous occasions it hadn’t actually broken.
“The bizarre fact that linked all the cases of distorted standpipes was, at this point, they had only been discovered in reactor 1, and not in reactor 2,” said Jessica.
“This was peculiar. The reactors had been simultaneously constructed by the same team of construction workers, yet no hint of a problem had ever appeared at reactor 2. As they were built at the same time of year, this couldn’t even be explained by the possibility that water had seeped into the concrete of one but not the other.
“The reactor was switched back on, but the team knew that they had to do something about it. The thought of subsequent breaks occurring during future outages was very horrible, and a number of standpipes seemed to be affected.
“So they built, in a very short time, a complex and beautiful rig whose job it was to measure the inside diameter of all the standpipes in reactor 1 core.
“The research team usually named the rigs in an acronymic fashion, and this one was no exception. It was dubbed HASTEE, the first two letters standing for Hinkley A but I cannot remember what collection of words was strung together to achieve the rest. It was meant to commemorate its speed of design and construction.”
Jessica went on to describe the rig. “HASTEE was a rather amusing thing to look at. A long extendable steel shaft was topped with a globular head surrounded by three inflatable rubber seals. In operation, the head and shaft were lowered into the standpipe and the seals inflated. Water was pumped into the space above it and the standpipe diameter was accurately scanned using ultrasound.
“Tests on an artificial ‘standpipe’ in the lab seemed to give good results. The problem was serious enough that a special outage, known as ‘The Mini-Outage’, was applied for and obtained. Mindful of the vast quantities of money which were draining out of the CEGB every second that the outage continued, the team set to work.”
“All went well. HASTEE did its stuff, and the readings flooded in. The team worked around the clock in shifts. Because of the nature of the problem, it was pretty easy to tell which were the standpipes with the curious bulging that might in future trap the fuel rods or the control rods, and they were noted, to be sealed off and left empty in the future. The Mini-Outage was deemed a success, and HASTEE was mothballed until the next regularly scheduled outage, to become part of the regular array of checks.
“Fortunately, though there were a number of affected standpipes, the number was low enough not to compromise the operation of the reactor.
“The results of the ultrasound scans were interesting. The bulge only occurred in a particular part of the standpipe, where the diameter abruptly changed from the fairly wide access area at the top to the smaller bore which could contain fuel rods or control rods.”
Jessica went on to explain that the diameter of both the concrete surround (muff) and the metal pipe made this change, and the bulge appeared to be caused by some corrosive material which had adhered to the concrete before the inner metal standpipe was inserted.
The reactor was allowed back on line, but several questions remained. What was that stuff? And why only in reactor 1, not reactor 2?
The plot thickens
Jessica explained that, at this point, a rumour began to circulate around the station. The corrosion was consistent with some liquid being poured down the concrete outer pipe and pooling at the point where the diameter narrowed. Apparently the station manager speculated that urine contamination was the reason for the corrosion. Whether it was meant as a joke or not, the theory became quite popular.
Jessica explained that, during construction of Hinkley Point A, the construction workers who had been building reactor 1 were further from the site facilities than those working on reactor 2.“Could it really be the case that several hundred thousand pounds worth of research time and equipment was a result of the construction workers using their initiative when nature called?”
Jessica was not sure as to what happened next. What is certain is that an article appeared on the front page of The Times on 6 November 1986 reporting a problem that threatened not only the continued safe operation of reactor 1 at Hinkley Point A, but also cast doubt on the viability of all Magnox reactors. The article triggered a parliamentary enquiry on “standpipe distortion at Hinkley Point A power station and the cost of decommissioning Magnox reactors.”
One of the witnesses called to give evidence to the energy committee was John Large of the consulting firm Large & Associates (L&A). In a memorandum to the committee, L&A stated:
Apparently, no physical tests on the materials, that is the standpipe steel tubing or the concrete, have been undertaken by the CEGB since the discovery of the defects in 1983.
In the absence of such positive information and data the CEGB can only speculate on the cause of the distortion and assumed corrosion of the standpipe tubing. Such speculation has included the quite absurd claim that a construction worker urinated in the muff cap concrete mix at the time of construction; that a pinch of salt was added to the concrete mix; or that the seaside salty air has eventually initiated corrosion of the standpipe steel.
In the end no-one ever found out what the cause of the corrosion was. Another distorted standpipe was discovered at unit 2, bringing the total number of affected standpipes at the station to four. The most likely origin of the problem was in the construction stage through contamination of one or more batches of concrete mix. Unfortunately, we are not likely to ever find out what the exact nature of the contamination was.
In any case, careless quality control at the construction stage was likely to have led to, about a quarter of a century later, the discovery and very expensive attempt at solving the mystery of the distorted standpipe. In fact, it almost had far more serious consequences for the Magnox fleet, and the UK’s nuclear industry as a whole.
“There’s not much more to tell,” said Jessica. “I remember reading recently that the decision was made to finally stand down the dear old Magnoxes.
“But I’ll never forget it as an example of how a few moments of thoughtlessness can cause endless trouble and expense, years down the line.”