"cold shutdown" that doesn't require coolant circulation?


by HowlerMonkey
Tags: circulation, cold shutdown, coolant, require
nikkkom
nikkkom is offline
#73
Nov15-12, 04:02 AM
P: 549
Quote Quote by mheslep View Post
Just curious: that's due only to the tritium atoms in the water? Not another source?
There is little tritium in BWRs, since they have almost no deuterium, and produce tritium by other means than D+n->T. Tritium production is only significant in heavy water reactors.

Quote Quote by Hiddencamper View Post
While the fuel in BWRs (and PWRs) is solid, all solid material has some miniscule amounts of diffusion.
Not only that. A large BWR contains on the order of 50 thousands of individual fuel rods. With such a large number of rods, it's impractical to ensure that absolutely all of them stay watertight. Thus, BWRs are not stopped when tests indicate that just one single rod ruptured and water is now in touch with its fuel ceramic pellets, washing out some fission products.
Hiddencamper
Hiddencamper is offline
#74
Nov15-12, 04:56 PM
P: 164
Quote Quote by nikkkom View Post
There is little tritium in BWRs, since they have almost no deuterium, and produce tritium by other means than D+n->T. Tritium production is only significant in heavy water reactors.



Not only that. A large BWR contains on the order of 50 thousands of individual fuel rods. With such a large number of rods, it's impractical to ensure that absolutely all of them stay watertight. Thus, BWRs are not stopped when tests indicate that just one single rod ruptured and water is now in touch with its fuel ceramic pellets, washing out some fission products.
Reactor water chemistry is regularly sampled for the difference between diffusion, and actual leakage/seepage/cracking of the fuel. Once ratios of specific elements like iodine and xenon are seen to go outside of normal, in a BWR you can perform suppression testing. What we've found is if you push control rods in near the suspected leakers, you will see a decrease in radioactive inventory in the reactor coolant system. If you then push in 1 or 2 face adjacent controls rods and possibly a diagonal rod it will greatly suppress the amount of leakage from the leaky bundle, almost returning it to 'normal' levels for the reactor. You can then continue operating the unit, albeit with lost effective full power days.

In a PWR, a fuel leak almost always requires the fuel be removed and replaced. PWRs cannot run with a rod full in to suppress it the way a BWR can.
mheslep
mheslep is offline
#75
Nov27-12, 12:17 PM
PF Gold
P: 3,021
Quote Quote by Hiddencamper View Post
It is an (n,p) reaction:

O16 + n -> N16 + p

...
BTW, what happens to the continuously generated hydrogen, the H2 left behind (and the p when it neutralizes)?
rmattila
rmattila is offline
#76
Nov27-12, 01:05 PM
P: 242
Quote Quote by mheslep View Post
BTW, what happens to the continuously generated hydrogen, the H2 left behind (and the p when it neutralizes)?
In a BWR, non-condensible gases end up in the condenser vacuum system, recombiners to recombine most O2 and H2 back to water, then to the off-gas system to be delayed and filtered, and eventually to the atmosphere through the stack.

Hydrogen has a nasty habit of moving with steam in the primary piping and accumulating in places where steam condenses (e.g. inside certain valves), causing fragility issues with certain steel materials.
Hiddencamper
Hiddencamper is offline
#77
Nov27-12, 06:05 PM
P: 164
Quote Quote by rmattila View Post
In a BWR, non-condensible gases end up in the condenser vacuum system, recombiners to recombine most O2 and H2 back to water, then to the off-gas system to be delayed and filtered, and eventually to the atmosphere through the stack.

Hydrogen has a nasty habit of moving with steam in the primary piping and accumulating in places where steam condenses (e.g. inside certain valves), causing fragility issues with certain steel materials.
Another note about this is BWRs usually inject hydrogen into their water to help protect the core and vessel from oxidation. This has some unpleasant side effects like increased radiation rates, fouling of venturis and instrument lines, and plating out of materials (could be good or bad), but is all in all beneficial for the plant as it prevents certain types of stress corrosion cracking.
HowlerMonkey
HowlerMonkey is offline
#78
Oct29-13, 08:38 PM
P: 275
So.......you guys think that a convective loop could be constructed that could deal with a recently shut down or scrammed reactor or do you know of a reactor design of similar power to current reactors that could be shut down and not need continuous power to run cooling pumps?
rmattila
rmattila is offline
#79
Oct30-13, 02:51 AM
P: 242
Quote Quote by HowlerMonkey View Post
So.......you guys think that a convective loop could be constructed that could deal with a recently shut down or scrammed reactor or do you know of a reactor design of similar power to current reactors that could be shut down and not need continuous power to run cooling pumps?
That design gets pretty close:

http://www.rosatom.ru/wps/wcm/connec...11_EN_site.pdf
QuantumPion
QuantumPion is offline
#80
Oct30-13, 12:26 PM
P: 731
Quote Quote by HowlerMonkey View Post
So.......you guys think that a convective loop could be constructed that could deal with a recently shut down or scrammed reactor or do you know of a reactor design of similar power to current reactors that could be shut down and not need continuous power to run cooling pumps?
The GE ESBWR is a boiling water reactor that operates by natural convection. The emergency core cooling system is a huge gravity-fed water tank that can keep the core cool with no offsite power or operator intervention for 3 days, after which it only requires replacing the water inventory at atmospheric pressure.
HowlerMonkey
HowlerMonkey is offline
#81
Oct30-13, 07:29 PM
P: 275
Really glad to see that there are designs that won't "go up" from loss of electrical power or fuel to run diesel generators and pumps.


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