It's really quite an accomplishment that Canada's developed an exportable technology, but they aren't as safe as the LWR reactors that most countries use. One problem is that the piping is much more complicated than other reactors, so the possibility of springing a leak is much higher. CANDU reactors also have a positive void reactivity coefficient, which means that they're much more dependent on electronics to prevent power excursions. They also produce and leak tritium at a much higher rate -- it's not clear that this is a real problem, but it's very detectable. The economics of running on natural uranium aren't so good now that gas centrifuges can refine uranium more efficiently than the old gas diffusion plants.
Nobody will argue that a CANDU reactor properly operated will produce weapons-grade plutonium, but a country that's able to build CANDU reactors domestically could construct CANDU derivatives which would be useful for proliferation.
I wouldn't say that BWR reactors are categorically unsafe, but looking at the operating history, I think PWR reactors have a better record, even leaving Fukushima out. I don't know if BWR reactors or derivatives like the ESBWR have a future at this point. The Mark I BWR at the Fukushima site lacked many of the safety upgrades that have been made at other countries... Regulators in the US were aware of the problem that blew the roof off several of the reactors in the 1980s and took steps to prevent that step in the accident progression -- and don't kid yourself it wasn't significant, because a collapsed building is a dangerous environment that makes it hard to work around the reactor, particularly when you want to get in and get out fast to minimize your radiation dose.
I'd really like to see small PWR reactors with natural convection like mPower from B&W and the NuScale reactor. I think these can be very safe and also, being factory constructed, control the cost escalation that scares utilities away from investing in nuclear. I'd also like to see a realistic plan for fuel management -- we don't know the whole story at Fukushima yet, but spent fuel was part of the problem, and having a plan that's better than stacking it up at reactor sites is important.
Very interesting. I trained at a student reactor (TRIGA) but that was a while ago we didn’t learn that much about real-world considerations. I remember being told that CANDU happened to be near price parity with LWR in general, but that this was basically a coincidence and would change someday.
Do you have any remarks on “generation IV” reactors like VHTR and MSR? I’m particularly curious about PBR – seems like a cute idea with some possibly showstopping bugs.
Right now there's no real answer for disposal of carbide (VHTR/PBR) or fluoride (MSR) fuels. Geological disposal and reprocessing are credible for today oxide fuels, but not for these. A fuel damage incident happened at the Oak Ridge MSR about 30 years after it was shut down -- radiolysis caused the production of F gas, which in turn caused the production of UF6, which migrated out of the drain tanks into carbon traps. There were no serious consequences, but enough U233 was involved that there could have been a criticality accident.
There is a grassroots thorium movement behind the MSR these days -- they're a bunch of smart, wonderful, and idealistic people but they're running against a headwind. The U.S. government is not interested in radical innovation in the nuclear space because it may open up new paths to proliferation. I think the most credible MSR concept is Moir and Teller's idea of having clusters of reactors built in huge underground bunkers. Small, modular reactors are exciting, but I find it hard to believe that online reprocessing would be practical for something small that isn't being watched over by a team of specialists.
Prehaps I'm a dinosaur but I till think FBRs on the plutonium cycle may have a market in the long term. It would take a long time for this to replace the LWR because of the slow rate Pu gets generated, but the amounts of Pu available in spent fuel would be sufficient to open up new markets for small modular reactors that are highly proliferation resistant. (A sodium fire probably kills you if you try to open it up, and then there's so much Pu240 you'll never make a bomb of it)
It's really quite an accomplishment that Canada's developed an exportable technology, but they aren't as safe as the LWR reactors that most countries use. One problem is that the piping is much more complicated than other reactors, so the possibility of springing a leak is much higher. CANDU reactors also have a positive void reactivity coefficient, which means that they're much more dependent on electronics to prevent power excursions. They also produce and leak tritium at a much higher rate -- it's not clear that this is a real problem, but it's very detectable. The economics of running on natural uranium aren't so good now that gas centrifuges can refine uranium more efficiently than the old gas diffusion plants.
Nobody will argue that a CANDU reactor properly operated will produce weapons-grade plutonium, but a country that's able to build CANDU reactors domestically could construct CANDU derivatives which would be useful for proliferation.
I wouldn't say that BWR reactors are categorically unsafe, but looking at the operating history, I think PWR reactors have a better record, even leaving Fukushima out. I don't know if BWR reactors or derivatives like the ESBWR have a future at this point. The Mark I BWR at the Fukushima site lacked many of the safety upgrades that have been made at other countries... Regulators in the US were aware of the problem that blew the roof off several of the reactors in the 1980s and took steps to prevent that step in the accident progression -- and don't kid yourself it wasn't significant, because a collapsed building is a dangerous environment that makes it hard to work around the reactor, particularly when you want to get in and get out fast to minimize your radiation dose.
I'd really like to see small PWR reactors with natural convection like mPower from B&W and the NuScale reactor. I think these can be very safe and also, being factory constructed, control the cost escalation that scares utilities away from investing in nuclear. I'd also like to see a realistic plan for fuel management -- we don't know the whole story at Fukushima yet, but spent fuel was part of the problem, and having a plan that's better than stacking it up at reactor sites is important.