Why do some nuclear power plants have smoke stacks?

[jim hardy]

Common sense dictates that a nuke plant shouldn't just open its windows. All the ventilation air is collected and exhausted up the stack so it can be monitored. If activity goes up unexpectedly, dampers close to bottle things up while plant guys figure out what's happening.The stack is there as an ounce of prevention not a pound of cure.

A lighthearted yet sensible look at the subject here:
http://www.scientificamerican.com/article/coal-ash-is-more-radioactive-than-nuclear-waste/

The popular conception of nuclear power is straight out of The Simpsons: Springfield abounds with signs of radioactivity, from the strange glow surrounding Mr. Burn's nuclear power plant workers to Homer's low sperm count. Then there's the local superhero, Radioactive Man, who fires beams of "nuclear heat" from his eyes. Nuclear power, many people think, is inseparable from a volatile, invariably lime-green, mutant-making radioactivity.

Coal, meanwhile, is believed responsible for a host of more quotidian problems, such as mining accidents, acid rain and greenhouse gas emissions. But it isn't supposed to spawn three-eyed fish like Blinky.

Over the past few decades, however, a series of studies has called these stereotypes into question. Among the surprising conclusions: the waste produced by coal plants is actually more radioactive than that generated by their nuclear counterparts. In fact, the fly ash emitted by a power plant—a by-product from burning coal for electricity—carries into the surrounding environment 100 times more radiation than a nuclear power plant producing the same amount of energy.

Key phrase there is : "carries into the surrounding environment" .
We go to great lengths to keep our high activity stuff bottled up and out of the surrounding environment.
Some of Fukushima's got out.

 

[nikkkom]

Venting from the wetwell achieves a reasonable decontamination factor prior to release, especially if being vented to an elevated release point. Which is why even post Fukushima, wetwell vents in the US do not require filters. The cost of the filter does not justify the added decontamination factor. These studies are all available through EPRI by the way, with regards to severe accident venting in Mark I and II containment structures. The wetwell venting, especially when sprays are utilized, are as high as a dedicated external filter.

Which is a faulty logic because a filter on a vent line works in *addition* to any wet scrubbing in the primary containment. In particular, it would work even if, you know, an "unthinkable" happens and wet scrubbing fails to occur.

Remember, BWRs have a wet pool to scrub fission products in.

Remember, there are now thousands of square kilometers with their population evacuated around a BWR station in Japan which failed its wet scrub.

*This* attitude of not being capable of acknowledging the truth even when it is right into your face is what made me lose faith in the nuclear industry.

(This post is not directed personally at you, Hiddencamper.)

 

[mheslep]

Remember, there are now thousands of square kilometers with their population evacuated around a BWR station in Japan which failed its wet scrub.

Seems to me Fukushima makes HC's point, not yours, as in that case what additional safety is provided by filters whose function clearly would have become moot when the containment seal was blown at the time of the explosions? To my mind the lesson of Fukushima is the guaranteed removal of sufficient decay heat before it induces a destructive explosion, not the indeterminate use of what remains after an explosion.

 

[Hiddencamper]

A filter at Fukushima would not have been beneficial as the evidence seems to show that the reason for a lot of the release was due to containment system failures. An engineered filter only works if your containment is intact. Yet unit 3 it appears the dry well head "burped" and there were penetration failures. Unit 2 was speculated by ANS in 2012 to have large containment failure when there was an explosion sound in the vicinity of the suppression pool. Not as sure about unit 1. But a filter would not have provided additional scrubbing in those scenarios, while the pool would (up until vessel failure and hot debris ejection), and the containment, if water was added, would have been more capable of absorbing fission product releases.

Now there is an argument that Fukushima could have vented early if they had passive filters. Remember these units have active filters installed (standby gas treatment system). I argue that it wouldn't have mattered, there are noble gasses that do not hold up in charcoal adsorpers or hepa filters which still dictates you delay the release, because the noble gas inventory is a large contributor to the early release.

 

[etudiant]

A filter at Fukushima would not have been beneficial as the evidence seems to show that the reason for a lot of the release was due to containment system failures. An engineered filter only works if your containment is intact. Yet unit 3 it appears the dry well head "burped" and there were penetration failures. Unit 2 was speculated by ANS in 2012 to have large containment failure when there was an explosion sound in the vicinity of the suppression pool. Not as sure about unit 1. But a filter would not have provided additional scrubbing in those scenarios, while the pool would (up until vessel failure and hot debris ejection), and the containment, if water was added, would have been more capable of absorbing fission product releases.

Now there is an argument that Fukushima could have vented early if they had passive filters. Remember these units have active filters installed (standby gas treatment system). I argue that it wouldn't have mattered, there are noble gasses that do not hold up in charcoal adsorpers or hepa filters which still dictates you delay the release, because the noble gas inventory is a large contributor to the early release.

I'd thought the noble gases were not scrubbed from either nuclear plants or nuclear fuel processing facilities. Is this incorrect?
The document here: http://www.areva.com/EN/operations-2332/gaseous-releases-annual-statement.html suggests the release by the Areva La Hague processing facility is about 280,000 Terabequerels of noble gases, 3,000 times as much as the tritium and C14 releases.

 

[Hiddencamper]

I'd thought the noble gases were not scrubbed from either nuclear plants or nuclear fuel processing facilities. Is this incorrect?
The document here: http://www.areva.com/EN/operations-2332/gaseous-releases-annual-statement.html suggests the release by the Areva La Hague processing facility is about 280,000 Terabequerels of noble gases, 3,000 times as much as the tritium and C14 releases.

That's correct. My argument is a passive filter vent at Fukushima would not have changed the outcome. Japan would not have vented early when they should have, because the noble gas release still would have been high, even with a passive filter. Later in the event the containment systems were damaged precluding effectiveness of a passive filter. It would not have substantially decreased the release either in the actual case of a hypothetical case.

 

[etudiant]

Why would concern about a noble gas release prevent the Japanese from venting early given the presence of a passive filter for the other emissions?
Is there some legal or health constraint?

 

[mheslep]

I imagine Xe-135, w/ half life of some hours, is the primary concern

 

[Hiddencamper]

Why would concern about a noble gas release prevent the Japanese from venting early given the presence of a passive filter for the other emissions?
Is there some legal or health constraint?

In Japan you need to get permission to vent containment.

There is an argument out there that if the plants had a filtered vent, they would have been more likely to vent early when it would have helped. But this isn't true because the government still controlled when the first vent occurred and you still would have had a large noble gas release.

I think it's unlikely that the Japanese government would have allowed early venting even with an installed filter.

 

[nikkkom]

Seems to me Fukushima makes HC's point, not yours, as in that case what additional safety is provided by filters whose function clearly would have become moot when the containment seal was blown at the time of the explosions? To my mind the lesson of Fukushima is the guaranteed removal of sufficient decay heat before it induces a destructive explosion, not the indeterminate use of what remains after an explosion.

Wrong.

I read Fukushima accident timeline.

Personnel was afraid to vent the containment because they knew this will result in some of-site contamination. So for a time they were hoping they can be able to contain the accident without venting. When they realized it's not to be, they did not have enough time to organize orderly venting happen.

So it all ended as an uncontrolled venting through damaged containment.

You may notice that Japanese are now installing filters on all vent lines on all NPPs. Looks like they agree with me, not with NRC.

 

[Hiddencamper]

Wrong.

I read Fukushima accident timeline.

Personnel was afraid to vent the containment because they knew this will result in some of-site contamination. So for a time they were hoping they can be able to contain the accident without venting. When they realized it's not to be, they did not have enough time to organize orderly venting happen.

So it all ended as an uncontrolled venting through damaged containment.

You may notice that Japanese are now installing filters on all vent lines on all NPPs. Looks like they agree with me, not with NRC.

U.S. SAGs and EOPs for boiling water reactors have you vent prior to exceeding the PCPL. Unlike Japan which has you wait until you are twice the PCPL. (Primary containment pressure limit). Twice the PCPL is the ultimate design limit of the containment for the mark I/II plants.

Just that directive alone, the difference in the emergency procedures, creates problems. And they were waiting for approval to vent after they decided to.

 

[mheslep]

Wrong.

I read Fukushima accident timeline.

Personnel was afraid to vent the containment because they knew this will result in some of-site contamination. So for a time they were hoping they can be able to contain the accident without venting. When they realized it's not to be, they did not have enough time to organize orderly venting happen.

So it all ended as an uncontrolled venting through damaged containment..

That all may be true, but what does any of it have to with the one relevant point, which is how do the filters help in any way to prevent a Fukushima like accident. Namely, the rejection of the decay heat after loss of cooling.