Chalk River - The First Nuclear Reactor Accident in History

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[JimBiddle.]

So safety officer and the fate of the locality, comes down to 4 buttons? Making Homer's job in the Simpson's seem plausible.

[sheldonpetrie]

As a Canadian I had never heard of this, like ever, until very recently. The fact that the team was led by Jimmy Carter is just another notch in the incredible life of accomplishments for that man.

[bradlevantis]

Imagine being the accountant when someone pops in and says “hey, you up for trying to put out a radioactive core fire after your break?”

[FatherDraven]

Twenty grand doesn't feel like enough compensation for a 50 year late program. They probably spent more money flying politicians about to discuss the idea than the entire program paid out.

[bnjzinr]

Thank you for covering this topic. My Grandfather was in the Canadian Military and was sent as part of the clean up team. I’m so glad this is finally coming to light.

[taylor]

Please, please, please, 3 Mile Island was not a public health disaster. The radiation released was less than the background radiation you would receive from just standing in Boston.

[spencerleava]

Simon, I do need to correct two major mistakes you made in the video. A moderator in a nuclear reactor slows neutrons, neutrons at different speeds have different probabilities of doing something (ie: fission, absorption ect) when they hit a nucleus. In simple terms, in a nuclear reactor it brings neutrons to the correct speed needed to allow fission to occur. The role of the moderator is not to absorb neutrons, or to slow a reaction: without a moderator a reaction cannot occur at lower enrichment levels.

Heavy water is an ideal moderator specifically because it does not absorb neutrons easily. Using heavy water as the moderator is what actually allows CANDU reactors (the kind Canada uses for generating electricity) to use unenriched uranium as their fuel, and one of the safety features is that to stop the reaction all you need to do is add normal water to stop the reaction. How the reaction was actually stopped was that they drained the heavy water from the calandria: no moderator, no fission.

I think this mistake stems from the fact that most reactors nowadays use normal "light" water as the moderator. Light water does also absorb neutrons, so there is a bit of a balancing act in how it affects the reaction. The neutron absorption of light water is also why light water reactors need to use enriched fuel. For these reactors, they have what is called a negative void coefficient, which means that if the water boils the reactor slows down: less water lower moderation. The NRX kept the heavy water used as the moderator, and the light water used for cooling separate which caused it to have a positive void coefficient, which means that if the cooling water boils the reaction speeds up. Less light water means less neutron absorption meaning the reaction speeds up.

I know this can sound a lot like technobable, and to be fair I only have a basic understanding of nuclear reactors myself, but understanding the roles played by each component of a reactor is essential in understanding how nuclear accidents happen. I know I shouldn't volunteer others, but there is another youtuber whom I believe still lives in prague called Thunderf00t who I believe still lives in Prague as well who has worked with nuclear reactors. He is also another brit : P. Perhaps it may be worth firing a message when covering nuclear topics, he may be able to help you catch tricky errors when it comes to nuclear topics.

[amb]

I drive through Chalk River/Deep River a couple of times a year, heading to Ottawa. I also grew up in Elliot Lake, Ontario, once the "uranium capital of the world", which likely supplied this reactor. Yet, I never knew about this incident before today. Yikes.

[KingCrusoe]

I'm fascinated by how the operator had thought he said buttons 3+4, but actually said buttons 1+4, thus causing the control to input an incorrect command before the correction was able to be relayed.

I work at a coal plant, so obviously not quite so dangerous, but whenever any operators or control make commands/requests to one another, there is always AT LEAST 1 repeat on either end before anything is actually clicked or changed so that the likelihood of that kind of mistake happening is nearly null. Some operators even repeat these things more than 1 to make extra sure.

Lucky that this mistake was caught so soon, but also unfortunate that it was able to happen in the first place.

[tkskagen]

I don't know what upsets me more, the 30 years of suffering, or the fact that it took almost another 20 years for compensation...

[johntrottier]

It took me a while a some research to understand what Simon was saying and how the accident occurred.
The first thing I needed to understand is that even though the reactor was water cooled and moderated by heavy water, it's actual design was much more on par with the designs of the Hanford Reactors.
In other words the fuel models were square Aluminum Cans with aluminum fuel tubes inside the cans. The space between the tubes was to be kept full of cooling water (normal H2O) pumped through each of the cans. This was river water is strictly for cooling and is NOT supposed to boil (the same as at Hanford).

These cans sit is a pool of heavy water contained by the calandria (reactor vessel). Thus the heavy water replaces the graphite used in the Hanford reactors. The numerous horizontal control rods of the Hanford reactors were not needed because the output of the reactor was controlled by the level of heavy water in the calandria. The vertical rods performed the emergency safety function (as at Hanford) but also could be used to control what modules were going to receive enough neutrons to take part in the chain reaction.

For this last test, the control rods were positioned to direct the neutron flux to the test item that was being irradiated. The reactor was running at a low power level controlled by the level of the Heavy Water. (sound familiar?)
A maintenance man turned the wrong valves, which started raising the rods. The supervisor saw it, got the valves shut, but power was still rinsing. Pushing the wrong buttons just made it worse.
The power surge cause the river water to boil inside the fuel cans. And just like Chernobyl, this reactor design has a Positive Temperature Coefficient. The water boiling created steam voids which created MORE reactivity in the core, which increased power, which increased boiling, until the elements melted and the Heavy Water was drained.

The government agencies had a program of checking the river downstream for radioactivity. After the accident the found some samples with low levels of radioactivity. They labeled the samples as CRUD, for Chalk River Unidentified Deposit.
The samples are long gone, but the term lives on in the US Nuclear Navy, where CRUD is the term for radioactive deposits found in primary piping.

[samking]

Not an accident. But it would be interesting to hear one on the Nuclear testing in Australia. In particular the nuclear Tank (a centurion tank that was placed near an explosion). Many Australian Servicemen who were used as labour during the testing were treated terribly when they started getting sick.

[PhanieDaemonia]

This video is an almost word-for-word translation of an article published in the canadian magazine "Québec science" October-November 2021 edition. I hope the original author got recognition for her work!

[Squeezmo]

In Navy Nuclear Power, We called surface contamination: CRUD… after Chalk River Unidentified Discharge.

[jimbobur]

2:35 No it doesn't absorb the neutrons, it absorbs some of their kinetic energy. A neutron moderator slows down fast neutrons produced by fission reactions. This reduces their kinetic energy into a range that makes it more likely for them to trigger further fission reactions in the fuel.

[pamelamays]

Jimmy Earl, a legend for eight decades and counting.

[natecody]

I just knew it was Jimmy Carter you were alluding to. The guy just radiates heroism.

[adamfoster]

Thank you simon and to the gang for covering some local history :)

[cocomojoe]

Super weird. Recently discovered all your channels and been binging my way through. I’m from Deep River, right next to Chalk River, and both my parents worked at AECL, and my Uncle still does. I had done some reading about the accidents but hadn’t heard of the compensation efforts at all. My family all worked/work in the IT department, but I still remember them coming home wearing their dosimeters, and there was one time in my childhood when they tested the meltdown siren and that noise lives in my brain for eternity. Love your content, and thanks for spreading the word about this. I’m sure I must have met some of the workers who helped with the cleanup and I never had any idea.

[LadyCooper]

I was not expecting jumpscare Peter MacKay at 13:48 😂