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Cold shutdown that doesn't require coolant circulation?

by HowlerMonkey
Tags: circulation, cold shutdown, coolant, require
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rmattila
#55
Oct30-12, 12:58 PM
P: 242
Quote Quote by Hiddencamper View Post
As I said, the VVER in this case has a shield building. Also, they are a 72 hour plant that uses a pool of water, similar to the AP1000.
I don't see how the existence of the outer containment is relevant for the feasibility of the steam-air heat exchangers, as they are in any case located outside the containment:



No water needs to be added other than for compensating leaks - the decay heat is dumped directly into air with a closed-loop natural circulation from the SGs.
a.ua.
#56
Oct30-12, 01:09 PM
P: 119
Quote Quote by nikkkom View Post
Here's a sample of the Fukushima jokes from the Internet:

.
These funny stories (anecdote in Russian) have 26 years of history
They come up in the Soviet Union after Chernobyl.
There were a lot of funny stories about his underwear made ​​of lead and a broken rubber band.
Japan badly taught history. Fukushima-received.
Hiddencamper
#57
Oct30-12, 07:31 PM
P: 178
Quote Quote by rmattila View Post
I don't see how the existence of the outer containment is relevant for the feasibility of the steam-air heat exchangers, as they are in any case located outside the containment:



No water needs to be added other than for compensating leaks - the decay heat is dumped directly into air with a closed-loop natural circulation from the SGs.
So when my explosion hits the air cooled heat exchanger and it fails catastrophically I'll make sure that everyone knew you said it would be ok.

Also with regard to the lessons learned, you bolded the very things that I've been pointing out to people. Japan did not incorporate lessons learned, the US already learned those lessons and incorporated it. And we also incorporated lessons learned from Fukushima. There's not a lot of public evidence about this because it all is coordinated through INPO, which is confidential, but the orders we get from INPO are just as mandatory as the ones we get from the NRC.
rmattila
#58
Oct30-12, 10:30 PM
P: 242
Quote Quote by Hiddencamper View Post
So when my explosion hits the air cooled heat exchanger and it fails catastrophically I'll make sure that everyone knew you said it would be ok.
From the protection point of view, the heat exchangers are equivalent to main steam lines, which also contain clean water and can be broken in case of external hazards. In those situations, SBO need not be considered and the emergency feedwater may be credited. The SBO device is not the only way to cool the reactor.

Also with regard to the lessons learned, you bolded the very things that I've been pointing out to people. Japan did not incorporate lessons learned, the US already learned those lessons and incorporated it. And we also incorporated lessons learned from Fukushima. There's not a lot of public evidence about this because it all is coordinated through INPO, which is confidential, but the orders we get from INPO are just as mandatory as the ones we get from the NRC.
Please recheck your quotes - I have not said anything regarding lessons learned. Just been trying to point out the ideas regarding SBO that are currently being discussed internationally especially after the Forsmark incident in 2006, which pointed out the possibility of failures propagating through the electric grid in an unexpectedly widespread manner.
HowlerMonkey
#59
Nov5-12, 07:54 AM
P: 276
Who cares about explosions, missiles, or earthquakes?

Let's start small with simply having no power for........forever with nothing else damaged.
Astronuc
#60
Nov5-12, 08:21 AM
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Quote Quote by HowlerMonkey View Post
Who cares about explosions, missiles, or earthquakes?

Let's start small with simply having no power for........forever with nothing else damaged.
One then has to go with natural convection, hopefully with an intact primary system, or if the primary system fails, e.g., it suffers a LOCA, then containment must be such to allow heat transfer to the environment without failure, or at least with minimal containment breach. In the latter situation, the internal pressure must be controlled via condensation of the steam from the coolant, assuming an LWR. Then the coolant catch/collection system would have to be above the core to ensure it can be returned to the core.

Then there needs to be piping to return collected coolant back to the RPV. One would then need a valve system that is closed during normal operation, and opens only during an accident event.

Otherwise, there is an existing decay heat removal system.

Cold shutdown of an operating reactor core requires coolant circulation in order to remove the decay heat. There has to be some heat removal, otherwise the fuel would heat up to melting temperature, but in an LWR, the cladding would corrode rapidly well below melting temperature.

Decay heat can be somewhat mitigated by operating a reactor at low power density with fuel to low burnup (as is planned in at least one SMR design, and to some extent in a CANDU), but then there is an economic penalty.
etudiant
#61
Nov5-12, 07:06 PM
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Quote Quote by Astronuc View Post

Decay heat can be somewhat mitigated by operating a reactor at low power density with fuel to low burnup (as is planned in at least one SMR design, and to some extent in a CANDU), but then there is an economic penalty.
Very interesting information.
It strongly suggests that CANDU designs are inherently safer.
How large is the 'economic penalty' you indicate?
Could the safety differential justify that difference?
nikkkom
#62
Nov6-12, 05:45 AM
P: 591
Quote Quote by etudiant View Post
Very interesting information.
It strongly suggests that CANDU designs are inherently safer.
How large is the 'economic penalty' you indicate?
More frequent fuel reloading and more voluminous waste. Something like x3 more waste by mass, but which is about x3 less radioactive.
gmax137
#63
Nov6-12, 12:14 PM
P: 844
Quote Quote by etudiant View Post
Very interesting information.
It strongly suggests that CANDU designs are inherently safer.
...
I'm not so sure about that. The decay heat level in the first hours following the reactor shutdown/trip are barely affected by the burnup (for any reasonable burnup). And, I think that the most risk occurs during those early hours, because it seems that the likelihood of core melt is much less at longer times, when decay heat is lower and more operator action (including aid from offsite) is possible.

In other words, lower burnup reduces the decay heat in the long term (days after trip), but that isn't where the big problems are.
rmattila
#64
Nov6-12, 12:51 PM
P: 242
Quote Quote by gmax137 View Post
I'm not so sure about that. The decay heat level in the first hours following the reactor shutdown/trip are barely affected by the burnup (for any reasonable burnup). And, I think that the most risk occurs during those early hours, because it seems that the likelihood of core melt is much less at longer times, when decay heat is lower and more operator action (including aid from offsite) is possible.

In other words, lower burnup reduces the decay heat in the long term (days after trip), but that isn't where the big problems are.
Burnup does indeed not have a big effect, but power density wrt total heat capacity in the core does. CANDU, RBMK and AGR are good in this respect but have other, less favourable characteristics in other fields.
etudiant
#65
Nov6-12, 03:38 PM
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The greater volume of spent fuel is clearly an economic issue.
Is the more frequent refuelling of the CANDU also an issue if the reactor can be refuelled during ongoing normal operations?
Astronuc
#66
Nov7-12, 12:37 AM
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Quote Quote by etudiant View Post
The greater volume of spent fuel is clearly an economic issue.
Is the more frequent refuelling of the CANDU also an issue if the reactor can be refuelled during ongoing normal operations?
CANDU units can do on-line refueling, so they can maintain high capacity factors. The burnups have been in the range of 1-1.5% FIMA, but may now be higher. The enrichments are lower, so the utility does not have to purchase more uranium ore as compared to LWRs using higher enrichment, which partially offsets the increased volume of spent fuel.
mheslep
#67
Nov11-12, 10:46 AM
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Quote Quote by nikkkom View Post
True, BWR water is radioactive
Just curious: that's due only to the tritium atoms in the water? Not another source?
Hiddencamper
#68
Nov11-12, 11:29 AM
P: 178
Quote Quote by mheslep View Post
Just curious: that's due only to the tritium atoms in the water? Not another source?
While the fuel in BWRs (and PWRs) is solid, all solid material has some miniscule amounts of diffusion. As such, some fission products get into the primary coolant, such as Iodine, Cesium, Xenon, and even Boron from the control rods. During normal operation, there are chemistry samples done, and the specific activity of all of these fission products are looked at, as the ratio of the different fission product decay chains is a sign of whether or not the fuel has failed (Cracked) or if it is just simple diffusion of fission products through the cladding material.

Tritium comes not just from hydrogen absorbing neutrons, but also from the boron in the control rods. The B-10 can absorb a neutron and then undergo double alpha decay, leaving behind a tritium atom. Any boron in primary coolant, or any tritium/boron that leaches out of the rods will also increase tritium inventory in the primary coolant.

In all reactors, when the reactor is online, the main source of radiation in the primary coolant loop is N-16. N-16 is a very short lived isotope (several seconds), and is virtually completely gone within a few minutes after shutdown. When the reactor is offline, cobalt-60 (which comes from stellite material in valve seats as well as on control rod blade rollers used for preventing the blades from rubbing the fuel material), Co-60 is the main gamma emitter when the reactor is offline, usually in the form of hot particles which get trapped in the reactor coolant system.


tl;dr most of the fission products and decay chains make it into primary coolant, not just tritium.

Additionally, primary coolant in both BWRs and PWRs is radioactive. PWRs have more tritium because they use Boron as a chemical shim, while the only tritium in BWR coolant is that from neutron capture and leeching. BWRs do not have a secondary coolant loop, but PWRs do, and their secondary loop also has radioactive products in it. PWRs have drastically less, as only things which leech through the steam generator tubes or pass through tube leaks generally get into secondary coolant. Additionally, reclaimed rad-waste water (which is reprocessed for reactor or secondary use) may contain slight amounts of fission products which werent removed in the rad waste system. Secondary cooling loops have rather large levels of tritium however (compared to BWRs) as well, because tritium does not get removed in the normal rad waste process, as it chemically looks the same as normal water, and rad waste processing is primarily chemical/resin/ion exchange based.
mheslep
#69
Nov13-12, 03:40 PM
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Quote Quote by Hiddencamper View Post

In all reactors, when the reactor is online, the main source of radiation in the primary coolant loop is N-16. N-16 is a very short lived isotope (several seconds),
Interesting. Which comes about from dissolved N2 gas in the water, or some nitrate hanging about?
Hiddencamper
#70
Nov13-12, 04:37 PM
P: 178
Quote Quote by mheslep View Post
Interesting. Which comes about from dissolved N2 gas in the water, or some nitrate hanging about?
It is an (n,p) reaction:

O16 + n -> N16 + p

The oxygen is from the water in the reactor vessel.

See http://en.wikipedia.org/wiki/Nitrogen

N-16 is the reason we have a 3 foot thick concrete bioshield around BWR heater bays and turbines.
mheslep
#71
Nov14-12, 03:55 PM
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Quote Quote by Hiddencamper View Post
It is an (n,p) reaction:

O16 + n -> N16 + p

The oxygen is from the water in the reactor vessel.
Ah of course, I should have seen that.

Continuing, the fuel itself is an oxide. I would think that would create problems, rapidly braking the oxide bonds of the fuel in the conversion of O to N.
Hiddencamper
#72
Nov14-12, 04:22 PM
P: 178
Quote Quote by mheslep View Post
Ah of course, I should have seen that.

Continuing, the fuel itself is an oxide. I would think that would create problems, rapidly braking the oxide bonds of the fuel in the conversion of O to N.
The fuel pellet is pretty much lost the moment you do your first heatup on the fuel. It's known to expand, crack, and under some very nasty transients or against heat limits, shatter/vaporize. Over time, due to changes in the composition of the fuel pellet itself, and changes in the cladding, your thermal limits become more limiting and your heat transfer rates get reduced. These are all accounted for in both core design and core modelling, and are validated in real time against actual plant data.


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