This is true, and was a credited shutdown system at the Pickering A reactors, but was not that reliable as a shutdown technology because it takes too long to drain the moderator. Shut off rods and poison injection are much faster in making a reactor good deep in the negative criticality zone.
In the event of a loss of coolant accident following an earthquake, overheated fuel could deform the fuel channels to the point where they would start to touch the calandria tubes, allowing for heat transfer to the large volume of room temperature heavy water by conduction, which has it's own cooling loop. So it's actually a good thing to keep the moderator in place when you loose coolant (as mentioned, are in separate systems).
I've often read that a CANDU reactor is already designed for use of Thorium as a fuel, but compared to claims in this article, would prove to be an expensive way to burn this fuel.
Of course, a CANDU reactor can burn up old warheads and even the waste a PWR leaves behind, so I have my doubts any of the 7 countries using that reactor would need to switch to a Thorium cycle. By then, perhaps even more ingenious ways to extract power from Thorium may be discovered.
Reading your posts, it sounds like you have some understanding of what you're talking about, but not connecting all the dots.
There is a big difference a half hour after shutdown and 10 years later, and you said it: hot spots. They get hot through activation and will cool down over time and just as you said, the only protection workers have against it is lead if it's hot. Exposing one's self to a 500 mrem/h contact pipe in order to dismantle it and ship it out over a shift without any PPE would reduce the total amount of times you could go in and do the same work, and would qualify for probably some sort of hazard bonus to your wage. If you wait for those fields to drop over time, all of a sudden it doesn't impact you so much.
So, when they say that the plants don't have enough to decommission, is it because the regulator assumes that decommissioning right after final shutdown? It could be that decommissioning won't happen until well after final shutdown.
At the plant I work at, it's the latter plan we have on the books. It will take nearly as long to decommission as the plant was operational, but the exposure to radiation as as low as reasonably achievable, and the cost is minimized that way.
You don't have to wait forever. Just saying, if you want to send in the demo crew a half hour after shutdown, you need more personal protective equipment against radiation, which prolongs the work to be done and increases cost. If you allow for activated products to die down a bit, say a decade or two, you can work with less protection, which decreases cost.
Decommissioning costs and plans are required up here in Canada, and I know it accounts for a lot of the plant to sit vacant for quite some time after you stop using it for just such a reason.
Is everyone sure this is all about money and nothing to do with allowing activated products in the reactors to die down to an acceptable radioactive level for workers to go in and start ripping things apart?
You guys should come up to Canada and see how we do it (essentially an Austrailian ballot). The thing is, Elections Canada is really on the ball. They could teach you guys a thing or two about how to run an election.
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This is true, and was a credited shutdown system at the Pickering A reactors, but was not that reliable as a shutdown technology because it takes too long to drain the moderator. Shut off rods and poison injection are much faster in making a reactor good deep in the negative criticality zone. In the event of a loss of coolant accident following an earthquake, overheated fuel could deform the fuel channels to the point where they would start to touch the calandria tubes, allowing for heat transfer to the large volume of room temperature heavy water by conduction, which has it's own cooling loop. So it's actually a good thing to keep the moderator in place when you loose coolant (as mentioned, are in separate systems).
The 50th Regiment (Gordon Highlanders of Canada) had the nickname "Gay Gordons." However, that was back when gay then didn't mean gay now.
I've often read that a CANDU reactor is already designed for use of Thorium as a fuel, but compared to claims in this article, would prove to be an expensive way to burn this fuel. Of course, a CANDU reactor can burn up old warheads and even the waste a PWR leaves behind, so I have my doubts any of the 7 countries using that reactor would need to switch to a Thorium cycle. By then, perhaps even more ingenious ways to extract power from Thorium may be discovered.
As a fellow John Hunter, I approve his methods.
Reading your posts, it sounds like you have some understanding of what you're talking about, but not connecting all the dots. There is a big difference a half hour after shutdown and 10 years later, and you said it: hot spots. They get hot through activation and will cool down over time and just as you said, the only protection workers have against it is lead if it's hot. Exposing one's self to a 500 mrem/h contact pipe in order to dismantle it and ship it out over a shift without any PPE would reduce the total amount of times you could go in and do the same work, and would qualify for probably some sort of hazard bonus to your wage. If you wait for those fields to drop over time, all of a sudden it doesn't impact you so much. So, when they say that the plants don't have enough to decommission, is it because the regulator assumes that decommissioning right after final shutdown? It could be that decommissioning won't happen until well after final shutdown. At the plant I work at, it's the latter plan we have on the books. It will take nearly as long to decommission as the plant was operational, but the exposure to radiation as as low as reasonably achievable, and the cost is minimized that way.
You don't have to wait forever. Just saying, if you want to send in the demo crew a half hour after shutdown, you need more personal protective equipment against radiation, which prolongs the work to be done and increases cost. If you allow for activated products to die down a bit, say a decade or two, you can work with less protection, which decreases cost. Decommissioning costs and plans are required up here in Canada, and I know it accounts for a lot of the plant to sit vacant for quite some time after you stop using it for just such a reason.
Is everyone sure this is all about money and nothing to do with allowing activated products in the reactors to die down to an acceptable radioactive level for workers to go in and start ripping things apart?
If the ducks first hit open water at Disko Bay, are these ducks intended to be called the Disko Ducks? [Wikipedia]
You guys should come up to Canada and see how we do it (essentially an Austrailian ballot). The thing is, Elections Canada is really on the ball. They could teach you guys a thing or two about how to run an election.
They do. Why do you need a laptop bag without a laptop? The TSA guys must be looking to carry around their new loot with a shoulder strap.