Monday, December 17, 2007

Primer: AECL Maple reactors, MDS, and the Positive Coefficient of Reaction

I was very interested in researching this story, and it has turned out to be most fascinating. I've gone through lots of articles, and scientific papers.

Having picked the Absolutely Worst Spot in the World for a nuclear reactor, AECL has gone on to pick the Absolutely Worst Design. How could they have hit two home runs in a row? It turns out that the original NRU and Candu designs were done by brilliant people brought together by the war. The successor designs were done by techno-bureaucrats, who followed in their place. The location for all this was also picked out by bureaucrats.

As mentioned in a previous primer, the NRU was a brilliant piece of simplicity, although somewhat unsuited for its seismic location. It was an open bathtub of heavy water, with a lattice of hanging fuel bundles, and control rods. Although controlled by the crudest relay buttons, this reactor was kind and stable. If it overheated, by say filling up too much, the heat would create steam voids, and water would evaporate. These pockets of steam could not moderate (slow down) neutrons, and the whole nuclear reaction would slow down. This is like flying a biplane with a stick.

But the AECL techno-bureaucrats wanted to build a fighter jet. They wanted something to generate enough isotopes to Control The world! (market).

They designed and built Maple I and II. So confident were they, that they totally built the thing on the swamp. So confident, they made the coolant in the reactor of light water, with a reflector of heavy water (to save money). So confident was MDS, that they bought these reactors for a few hundred million. Soon, the isotopes would be flowing!

Alas, such are the dreams of mice and men. The Maple reactor has one little thing wrong - A Positive Coefficient of Reaction (PCR), which meant that if the reactor had a power pulse, steam would form in the light water coolant. The light water is a very heavy killer of neutrons, steam is not. The surrounding reflector of heavy water (perfect slower of neutrons) would continue to do its job and send in 'perfect' neutrons. The reaction would run away, and only the brakes of the control rods could stop it.

Now, AECL could probably have overlooked this little quirk, and snuck it past the sleepy (and LIBERAL!) CNSC, except for one inconvenient thing - Chernobyl! That's right, this graphite reactor also had a nasty little problem with PCR, and when things started to blow, inserting the control rods made it worse (and you know what happened).

Poor MDS, stuck with the bag, they put in some few hundred million to try to fix things. They finally gave up, returned the reactors to AECL, receiving $60 million pocket change, and a firm monopoly of all isotopes from AECL in perpetuity.

AECL has now made countless presentations to the CNSC (on the web), saying how smart and wonderful they are, and how they can handle this tiger by the tail. Like an unstable modern fighter jet, they have tacked on 'fly by wire' controls, and other stuff to deal with PCR. The Koreans have one and it works by magic!

In the meantime, they have to operate a 50 year old corroded thing that was to have closed years ago. Thanks to the Beaming Face of Harper, we are assured that there will be no earthquakes in this region. MDS is still making its money, so it has no need to grease things along, but the followers of Harperology may send their offerings, so that He should also abolish the PCR! That way, we can make billions in isotopes, and be ready when the old reactor collapses under its own weight!

I love this story, it's like a movie or a soap opera! Will they tame the PCR? Will Harper ascend to the Heavens in lightning bolts? Will AECL last forever? Will MDS stockholders be happy? Stay tuned....

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