Pneumatics & Radioactivity
In the summer of 1968 I was sent by the UKAEA to the Reactor Materials Laboratory (RML) at Culcheth, near Warrington in Lancashire, for a summer project. This turned out to be quite a major undertaking for an 18-year-old undergraduate! Not so much because of the engineering – my UKAEA boss had talked to the staff at Queen Mary College, and knew that I was perfectly capable of coping with the engineering involved – but because of the politics. I didn’t find out about those until I arrived at RML…
My memories are greatly assisted by the fact that I kept the memo from the head of the lab about the project, and carbon copies[1] of the report that I wrote.
I felt very naughty keeping those carbon copies: I was very conscious of having signed the Official Secrets Act as one of the conditions of getting that scholarship. If anyone thinks I’ve committed a crime making my report public...they’re barmy. There’s nothing here that’s of the remotest use to any Enemy, imaginary or otherwise.
The project was to get a pneumatic transport system working, that had been installed at RML but which had “teething problems.” It was supposed to be used to transfer radioactive specimens from one “shielded cell” to another – enclosures designed to keep people safe from the radioactive materials inside them. Teething problems? It didn’t work.
I never went to Harwell to look at the “similar system” there[2]. I decided, of my own volition, to visit a department store in Warrington instead, where they had a similar system, from the same manufacturer, that was actually working. They used it to transfer cash (and cheques) between the tills and the office.
It was this visit that alerted me to the fundamental problem that was preventing the RML system working. It was the flaps that cover the ends of the tubes. They’re thick multilayered pieces of rubberized fabric, hinged at the upper edge. The ends of the tubes aren’t perpendicular to the axis of the tubes, they’re angled, so the flaps are elliptical to cover them. The carriers are sucked up the tubes, fly pretty fast up the tubes, round the curves in the system, and fall out of the other end – thumping the flaps as they exit. Those rubberized flaps are resilient enough to flex when the carrier thumps into them with their felt buffers (that also act as vacuum seals against the tube walls) and then reseal. The sealing of the flaps is important: if the flaps at the receiving end aren’t sealing well enough, the leaks leave the vacuum too weak to lift the carriers...Aha!
The system at RML had been modified, because it had proved too difficult to open the flaps to insert the carriers. Everything done inside the shielded cells had to be done by remote control, because the inside of the cells was too radioactive for human access. The remote handling gear was very sophisticated, but didn’t provide the kind of dexterity needed to handle those flaps. So another student on a previous summer project had donned protective gear (much the same PPE that is so familiar nowadays, for very different reasons) and gone inside the cell, and bolted little metal lips onto the flaps to make it easier to open them. A very neatly done job, with the bolt heads countersunk into the flaps so they didn’t damage the carrier felts.
Unfortunately the strip of metal forming the lips spoiled the resilience of the flaps: it bent as soon as a carrier hit the flap, holding the flap slightly bent so it didn’t seal properly any longer.
I donned PPE and went and changed the lips. Instead of a straight strip with two bolts in line along the major axis of the ellipse, I made them triangular with two bolts side by side, quite close together, near the edge of the flap. The original bolts went back in their old holes with just a small washer under the nuts, so the holes wouldn’t cause a vacuum leak. Time to try it, with heavy but non-radioactive loads in the carriers. Everything worked. Still no leaks after quite a few carriers. Bingo! That was two weeks into the project, but I’d noticed some other issues...
Two weeks, and the system was working. Another six weeks to go. I started looking at those other issues. A system that’s good enough for shuttling cash and cheques back and forth in a department store isn’t necessarily really good enough for shuttling highly radioactive specimens back and forth between shielded cells. The cells are surrounded by thick walls of interlocking lead blocks to stop gamma rays; there are windows in the walls consisting of two sheets of glass a foot apart with concentrated zinc bromide solution between them. But the roof is unprotected against gamma rays: a bird flying through a beam of gamma rays up there wouldn’t get much of a dose, and if an unfortunate bird should perch up there for too long – who cares?
All the specimens had been removed from the cells – put in those lead pots – while the plastic pipes for the pneumatic system were installed. While specimens were in flight between cells they’d be above the roof and potentially exposing people on the ground outside the building, but only for short periods. As long as they didn’t get stuck there for any reason...so plans had been made about what to do if that happened. You can read about it in my report.
But crazily, the design of the system of relays and electrical interlocks to operate the system had several flaws that made it fairly likely that a carrier (or two) would get stuck. I spent the next six weeks ironing them out as best I could. But honestly, the whole set up was a disaster waiting to happen.
And then there’s the question of PPE. Is it really good enough for that job? Hmm. There are two issues with working inside places like that.
Firstly, there’s the risk of contamination with radioactive particles. The specimens that are examined in the shielded cells are mostly bits of used nuclear fuel elements and other components removed from reactors. Getting the specimens ready for lab work involves “decrudding” – removing corrosion products – and machining. This creates a lot of radioactive debris, which is difficult to sweep up and remove by remote control. The operators do their best, but with the best will in the world, there’s some left, especially in the decrudding cell. The PPE is designed to stop you getting any of that debris on you, and when you leave the cell, you remove the PPE very carefully, and it’s disposed of as “low level radioactive waste.” Then you’re checked over with a radiation monitor to make sure you don’t have any radioactive particles on (or worse, in) you – and if you do, someone does their level best to clean them off you. The radiation from a small particle isn’t likely to be sufficient to do you much harm in the short time before it’s removed – but if it’s not removed and ends up inside you, it can be there for much longer, and internal radiation is anyway much worse than external, especially with alpha emitters like plutonium or uranium. (Alpha particles can’t even get through skin – but can do a lot of damage if they’re emitted inside you.)
I watched the chap checking me over for contamination: he was careful and thorough and I was clean.
Secondly, there’s radiation from any bits of radioactive debris that’s left around after working on the specimens – especially in the “decrudding” cell! As long as the actual specimens have been removed before the human enters the cell, it’s hoped that the radiation levels are low enough that as long as you’re as quick in and out as possible, you won’t receive too big a dose. PPE does absolutely nothing to protect you from radiation, which goes straight through it. PPE is purely to keep radioactive contamination off you.
Even if you don’t go inside the cells, there’s always a risk of some exposure for various reasons. so everyone working at place like RML wears a radiation monitoring badge – a bit of photographic film in a very opaque plastic sheath[3] pinned to your chest – and they go off to the lab for evaluation every day. If your exposure is over, or anywhere near, the (rather arbitrary) “safety limit,” you’re moved away from any potential sources of ionizing radiation for a while. How long depends how much your exposure was.
If your exposure is enough to require you to be moved, you hear about it straight away; otherwise you get a report at the end of the week. Except when for some utterly unaccountable reason, the records go missing one week...as happened (for everyone at RML) the week I went into the decrudding cell (and all the other cells) to change those lips. That was fifty-three years ago; so far, so good…
I’m sure some of the permanent staff must occasionally have donned PPE and gone inside the cells – but I couldn’t help pondering, later, that the only people I actually knew about going in there after the cells had started to be used with radioactive specimens were me, one other wide-eyed student, and some innocent employees of a company who made vacuum transport systems normally installed in shops and offices.
Another issue I only pondered later was the origin of all the stupidities in the control system. The system in the department store didn’t have any of those problems. It was much simpler, and relied on the common sense of the operators (or luck) to avoid carriers being sent in both directions simultaneously, or the system being switched off or the power failing with a carrier in transit – or carriers getting stuck for any other reason. As far as I’m aware, they’d never had a problem. But if they had had, it wouldn’t have been a safety issue, just a bit of a hassle for some maintenance worker. The RML system had to have safety interlocks. But they needed to be designed competently, and they weren’t. Whether they’d been designed by a UKAEA engineer or by a vacuum systems company engineer I don’t know, I didn’t at the time think to consider the question, although of course I studied the original drawings. Sadly I had no means of taking surreptitious copies – and in those days I was far too innocent to take them even had I had the facility. I felt quite impudent keeping a copy of my own report and drawings.
[1] My £750 p.a. tax free UKAEA scholarship was a very good income for a student in those days. Among other luxuries I’d splashed out on was a portable typewriter – an Olivetti Lettera 32. At some point, I forget exactly when, I briefly left this on a table in the coffee bar at Queen Mary College while I went to get another coffee – and by the time I got back, it had gone. I was typewriterless for a few years, until I got my beloved Hermes.
[2] I did visit Harwell years later, for other reasons.
[3] These days it’s probably something electronic – but it wouldn’t really surprise me if they still use film.