Friday, December 14, 2007

A primer on the Canadian Nuclear path to glory

I realize that some people are making fun of this whole nuclear business in Canada, but other people can't laugh along unless they've had some serious background on the whole issue. So, now I put on my serious hat, and offer this to help others.

I've had something like 29 years in the nuclear business, so I think I'm as good as the Conservatives! The mere fact that my many alter egos find everything so ridiculous should not put me at a disadvantage compared to those who are totally humourless. I started my career as a Geotechnical Engineer, working on the foundations for two nuclear plants - Bruce B, and Darlington. I also helped review Pickering B. I was a bright young thing and learned everything about Candu, because the plant was going to sit on the foundation, draw water through tunnels, and put it's waste in the facilities I was helping to design.

I have recently re-researched the history of nuclear stuff in Canada. It is actually difficult sifting through all the AECL-generated fluff, or avoiding the nasty Greenpeece versions. Somewhere in middle is a very human story of people muddling along to try and help Canada.

The history of nuclear in Canada is very much tied up with the nuclear bomb. The first man-made nuclear reactor in the world was done by some crazy guys in Chicago, who shoved some enriched U235 together, until the Geiger Counters went wild, and their eyebrows tingled.

This was the critical concept. A small hunk of U235 all by itself spontaneously generated neutrons, but they just zoomed away and went into people. But U235 has a great property that it can latch onto a neutron travelling at just the right speed, vibrate a lot, and then split apart. When it splits, it generates more neutrons, and other radioactive stuff. We are lucky that sometimes it takes a while to split, which allows the reaction to be controllable.

Nevertheless, they soon realized that knocking together bits of Uranium with a screwdriver was not ideal, and set about to scale it up. The US used graphite in big piles of bricks (hence, 'nuclear pile'). Their attention was solely on the prize of producing Plutonium for bombs. Graphite was extremely dangerous (think Chernobyl!), but this was war!

The graphite acted as a 'moderator' which meant that the high-speed neutrons could be slowed down to just the right speed to split the Uranium. This was necessary for a controlled reaction. But there was another moderator - heavy water, which is a rare form of water with extra neutrons in the hydrogen. The world's only supply of heavy water had been purified in Norway, constantly being shipped ahead of the German advance. It finally made it to England, and then to Montreal.

So, at this point, the US was churning out Plutonium, and they thought it would be great if the Canadians did it a different way. They pumped a lot of money into Canada to create a super-secret installation disguised to look like a miltary base, right in the middle of a great big swamp north of Ottawa. This was Chalk River.

With their big supply of heavy water, the Canadians did it different. They had a big bathtub, and they hung uranium fuel rods like icicles. Then they pumped in the heavy water, and at a certain level, it became a 'hot tub', full of neutrons. If they filled it too much, it became super-hot (super-critical), which had a good chance of blowing up. If this happened, they had suspended control rods, which dropped down into the tub, absorbing neutrons, and killing the reaction.

Needless to say, these crazy guys had a lot of accidents, where people got majorly zapped with neutrons, and it never bothered anyone! I like to think that a good dose of neutrons counteracted the smoking.

All of this was ready, the day the war ended. The Americans no longer had any interest in the Canadians, and gave them this wonderful present. Now the Canadians had to figured out what to do with it! So, they cranked up the reactor and made neutrons! In 1957 they made the biggest reactor bathtub in the world, the famous NRU, of nuclear fiasco fame. This was no super-safe baby, they cranked it up for neutrons! If the water level went too high - poof! If it went too low - poof! And you were relying all the time on those rods dropping cleanly. Needless to say they had accidents, since this really was 'research reactor' run by absent-minded professors.

Since they had nothing better to do, they bombarded all sorts of things with neutrons to see what happened. They made Cobalt for the first cancer machines, and they made medical isotopes. Such a large bathtub could churn out lots of isotopes!

Needless to say, somebody figured out that having scientists monkey around with water levels, and floopy rods was no way to have a commercial reactor, where you wanted lots of power. They changed the design, still having a big bathtub, but shoving in the fuel sideways in pressure tubes. Thus began the great Candu era!

Over the years, they have realized that the original design was a bit too dependent on gravity behaving itself. And we all know that earthquakes can upset that assumption. The first and most important thing was building on a good foundation, not a swamp. The second was to make the control rods spring loaded, and able to insert under high lateral forces. As well, all the surrounding buildings were built for earthquakes.

Today the new Candu stations are pretty good for earthquakes. What about the old NRU? I can only shudder. The building is on ground that will amplify ground motions about 100 times. It is probably all brick and block walls. The bathtub can slosh out all the water, which makes the fuel rods explode. The control rods won't drop under violent shaking. The containment building won't hold. Still, most likely, the great big poof of radioactivity would spread over a fairly empty area, and flow down the Ottawa River, where it would be diluted. Not really that bad.

*All of this can be found by Google searching, and looking up Wikipedia. I left out all references, because I wanted to.

2 comments:

Tom near SRS said...

Do you know why Canada continues (as official policy?) to refuse to clarify the history of reprocessing Canadian spent fuel in Europe (Belgium, Itlay and perhaps at Sellafield in the UK)? Why are they hiding this apparently experimental program and that Canadian-origin plutonium was separated? Canada, of all counties , should come clean about its plutonium dabblings but so far has failed to even report to the IAEA about this. Or was the plutonium or sold or transferred to the Europeans? The mystery continues but not for too much longer. For now, this remains a blot on Canada's non-proliferation standing.

Harold Asmis said...

I'm sure they made a boot-load of plutonium at NRU over the years. That's what it was designed to do! The stuff coming out of a regular Candu is not useful for bombs.

Thank you for the comments. I think they are the best part of a blog. Sometimes, I feel like making up my own!!