Nuclear Reactors and Natural Disasters

[aerius]

Speaking of reactors, I read that the Advanced Candu Reactor will require enriched fuel.

Seems like it lost one of it's major pros thjere to me, I mean not having to process fuel was a big cost saver and it also gave the CANDU-6 the ability to burn all this other stuff and have this nice fuel cycle. The ACR can't do this from what I see, but its cheaper to build, though since it'll require more infrastructure WRT fuel now I dunno if the final cost isn't higher anyway?

The current CANDU design is pretty nice but it does have a few issues, the core size for a given power output is a lot larger than other designs and it's a complete plumbing nightmare with tons of high pressure pipes all over the place. It also requires a huge amount of heavy water since the core is so big and the water is used as both the coolant and moderater. ACR simplifies the design with a smaller core and less plumbing, it also uses light water cooling so it doesn't need as much heavy water to run the reactor.

Downside is it now has to use slightly enriched fuel, but it still retains the ability to use a thorium cycle and burn MOX fuels.

[someone_else]

You need a significant fraction of the plant's own output rating to support it, It think usually about 10% but don't quote me on that, and most nuclear reactors produce at least 1 GW of electrical power.... not easily met

I'm quoting you on this.
Meanwhile I did some snooping around, this guy, that seems to be an old BWR worker, claimed a rhr pump (one needed for waste heat removal from each core) needs around 1.5 MW, and that service pumps (the ones needed to pump water in the pools I guess) would need 0.7-0.5 MW.

Yeah, that's quite feat for a RTG, maybe a SRG can do it. But it is somewhat "new and untested technology" to the contrary of diesel generators and RTGs, so it may not be deemed reliable enough before it gets more mature.

If half the generators were on one side of the reactor, and half on the other this would not have happened.

Why? The wave would have still reached those generators with a dangerous strenght when returning back to the sea. The only way to save them would have been placing them in a small bunker on the hillside imho.

so that the power cable runs would be short. That way less risk of an earthquake breaking an underground cable and causing power failure that way.

underground cables? isn't better placing them above the ground (in a cover to resist weather) and keeping spares? (or placing them only if needed since they have batteries that last days already)

Yeah, I know nothing about it but I dare nitpick .

[Magis]

Yes, it is possible.

There are CANDU accident scenarios, such as large loss-of-coolant accidents, that have the potential to lead to catastrophic core damage and failure of containment. However, these accidents are estimated to be very infrequent. According to current probabilistic risk assessments, such accidents are only expected to occur once every million operating years.

[EDIT] As an addendum, I will also say that if, like Fukushima, a CANDU plant were subjected to a total station blackout for more than a few days, containment failure would be almost unavoidable, and the accident progression would look pretty much the same as Fukushima, maybe excepting the troubles at the spent fuel bays.

[Magis]

It's also designed so that it has natural convective cooling in the event of a total power loss, the water will move itself through the pipes to a degree even if all the pumps are down. In the event of a core shutdown with total power loss the water will still circulate and remove residual heat from the reactor core.

The natural convective cooling capability of a CANDU is pretty limited. Soon after a loss of forced convection, the cooling regime will at first be single-phase thermo-siphoning, and then two-phase thermo-siphoning before moving on to what is known as intermittent buoyancy induced flow. These flow regimes will keep the fuel bundles below their melting temperature for one to two days.

The reactor design that achieves the best natural circulation cooling is the BWR.

[Ellindsey]

Speaking of reactors and natural damages, in the recent tornadoes in Virginia a plant had its switchyard taken out by a tornado. The diesel generators were undamaged and kicked in for emergency cooling, the plant shut down safely, and they were later able to reconnect external grid power.

World Nuclear News