>CANDU runs on natural uranium so the waste products are actually less radioactive than what we take out of the earth, as well CANDU can burn nuclear waste from light water reactors alleviating the need for Yucca mountain.
There is less uranium in the waste, but there will be fission products and trans-uranium elements just like in the fuel of regular reactors. Radioactivity of uranium is hardly a problem, when dealing with spent fuel. In short term (less than 100 years) fission products produce most of the radioactivity. In long term trans-uranium elements are the problem.
>Lets look at it's meltdown profile, CANDU reactors need heavy water to function, if you replace the heavy water with light water fission stops, no meltdown. Also before the reactor would ever get to that point the fuel bundles deform, halting meltdown.
Halting a normal fission chain reaction is hardly a source of accidents in any current nuclear reactor design. Decay heat is produced in the spent nuclear fuel of CANDUs just like in Fukushima or Three Mile Island.
CANDU is an interesting reactor design, but there is none as great alternative as you propose. However, various active and passive safety measures may get you very close. I don't know CANDU design so well, that I could judge those.
Interesting, I thought the large heat sink inherent in the CANDU design essentially ensured that with no human interaction that CANDU reactors would failsafe. My understanding was such that the 'reactor' might be destroyed but the design was such that the failure cascade would not release radioactive materials outside of the containment units.
As I said, I don't know the safety systems of CANDU :)
Large heat sink buys you time to get the cooling working again. Ultimately the heat must be transferred out somehow. In modern reactor designs these systems are usually designed to passively for very long times. With CANDU's it is very likely to be the case too.
In nuclear engineering one must always consider also the chance, that not everything is working as designed (like the destroyed diesel generators and external power sources at Fukushima). PRA (Probabilistic Risk Analysis) is used for that. PRA analysis are used for detecting most vulnerable systems in a nuclear power plant and this information is used to design new safer reactor types and to update the old ones little by little to be still safer. Harsh weather, seismic activity etc. is also considered in these analysis, but sadly in Fukushima even detected vulnerabilities didn't lead to improvements in time.
Even, if everything is done as well as possible, there is still a chance (although with modern designs almost arbitrarily small) that under certain conditions all the safety systems will fail. An ultimate example of such an event, would be a 100 km meteorite smashing the plant to atoms.
We agree on older plants being not as safe as new ones. My original sentence was about things you just can't prepare for (with any reasonable means). After that I just wanted to say, that it is possible to build plane-safe NPP.
There is less uranium in the waste, but there will be fission products and trans-uranium elements just like in the fuel of regular reactors. Radioactivity of uranium is hardly a problem, when dealing with spent fuel. In short term (less than 100 years) fission products produce most of the radioactivity. In long term trans-uranium elements are the problem.
>Lets look at it's meltdown profile, CANDU reactors need heavy water to function, if you replace the heavy water with light water fission stops, no meltdown. Also before the reactor would ever get to that point the fuel bundles deform, halting meltdown.
Halting a normal fission chain reaction is hardly a source of accidents in any current nuclear reactor design. Decay heat is produced in the spent nuclear fuel of CANDUs just like in Fukushima or Three Mile Island.
CANDU is an interesting reactor design, but there is none as great alternative as you propose. However, various active and passive safety measures may get you very close. I don't know CANDU design so well, that I could judge those.