Japan nuclear disaster risk seen receding fast

[Statistical]

The risk of a major radiation leak in Japan is subsiding as stricken nuclear reactors cool, but there will be major clean-up costs and three reactors will probably be written off, experts said on Monday.

A massive earthquake and tsunami on Friday knocked out cooling systems at a nuclear plant in Fukushima, eastern Japan, triggering a race to flood reactor cores with seawater and stop radioactive uranium fuel from melting and leaking out.

A natural decaying process means that the amount of heat the fuel produces has fallen dramatically, by more than 90 percent, experts said on Monday.

-----------------------------------------------

http://www.reuters.com/article/2011/03/14/japan-nuclear-radiation-risk-idUSLDE72D19720110314

Some insights.

On operating the three plants
There is no probably about it. All three plants are dead. They will never produce a single MW of electricity ever again. Plant failure, combined with damage from overheating, explosions, and seawater mean it would be impossible to certify them again and likely more expensive to try rather than simply build a new replacement plant. A new plant would also have the advantages of being larger, more efficient and safer design (including passive safety - self cooling). Japan may or may not build new nuclear reactors but these three are finished. Since time is your best ally if containment remains intact likely they will seal it, monitor it, and wait a couple years (maybe a decade) before decommissioning the plant (which will be tricky given the damage and could take years longer to finish).

On disaster receding.
Fission has been halted in the reactors so the remaining risk is heat from nuclear decay. You can' halt fission by absorbing neutrons but you can't stop nuclear decay and when it happens it produces heat. The good news is know the nuclear decay heat falls exponentially. These reactors put out roughly 500MW of electricity at peak power. To do that the plants produce about 1500MW of heat (1500 MWt). Now the second the earthquake hit the reactors scrammed. Control rods were inserted and the fission chain reaction halted. That helps. The heat output would have declined about over 90% within minutes. All that remains is the heat produced by natural nuclear decay (which is magnitudes less than active fission).

At the point of SCRAM heat output would be down to about 100 MWt. 1 hour later the heat output has declined to about 20MWt. 1 day later the heat output is down to about 6MWt. 1 week from SCRAM heat output is down to 3MWt.

Time is on the side of the operators. If they can prevent the RPV (reactor pressure vessel) from getting so hot it melts, and prevent the pressure from getting so high it bursts the RPV then physics will take care of the rest. Heat output will continue to decay until it reaches a point the reactor is "cold", that doesn't mean physically cold but lacks the thermal energy to melt anymore fuel, or damage the RPV.

[pokerfan]

1. k&r for good news! (nt)

[TomClash]

2. Best news all day

Thanks! :thumbsup:

[tabatha]

3. Why have they asked for international help then?

I don't know if this report makes much sense.

"A senior nuclear industry executive has told the New York Times that Japanese nuclear power industry managers are "basically in a full-scale panic". The executive is not involved in managing the response to the reactors' difficulties but has many contacts in Japan. "They're in total disarray, they don't know what to do," the executive added."

[Statistical]

5. The RPV needs to remain intact.

The reactor pressure vessel has undergone extreme stress, Japan will need expertise to avoid doing something that cause the RPV to breach. Also cleanup is going to be very complex and will require expertise to avoid secondary contamination (mistakes or failures that cause an unnecessary and avoidable release of radioactive material after disaster is contained).

Radioactive output decays according to physics. Many of the isotopes in a reactor have a very short half life. Some measured in minutes, others measured in hours. As they decay off they don't add heat to the output. Heat output can only decline not rise. The heat output now is far less than when the disaster happened.

Without fission it is impossible for heat output to ever rise. Imagine a bonfire that has burned out. Lots of coals and they are hot but 2 hours later it will be cooler, a day later much much cooler, a week later you wouldn't even be able to register any heat. The bonfire coal may be very hot but they will only get cooler over time. Similar concept here. Fission is the "fire" once fire it out all that remains the "coals" which is nuclear decay.

[joeybee12]

4. Now they're saying most likely the rods in reactor 3 are melting...

far from over.

[Statistical]

7. Neither I nor the article said anything about "over".

Nuclear decay falls off exponentially over time. That is a law of physics not an oped. Time has elapsed since the SCRAM so the heat output of the reactor is much lower. The output will continue to decline and in the absence of new fission it will never increase.

All the fuel can melt as long as the RPV remains cool enough to avoid the RPV from melting or bursting. Eventually the fuel will go "cold". The risk is less now than yesterday because the heat output is lower and will continue to decline very predictably. Eventually the heat output will be insufficient to melt through the RPV.

[SpoonFed]

19. I'm no expert but...

I find some problems with your reasoning based on what I saw discussed at a press conference early this morning.

The scenarios is something like this...

1) the reactor is shut down normally, ie SCRAM
at this point it is getting cooler

2) cooling breaks down
at this point it is getting warmer

3) venting/breach/whatever, the coolant escapes
at this point it is getting warmer
if it is not replaced at a sufficient rate go to step 4
if not go to step 1

4) the rods are exposed
at this point it is getting warmer
the casings are deteriorating, it's gonna melt soon
if the coolant is quickly replaced, go to step 1

5) the rods start to melt
circulation and proper cooling are compromised
if at this point coolant is reapplied go to step 6
flow is hampered, some the rods are perhaps melting together
if the melting is sufficient, go to step 7

6) rods are no longer exposed
if coolant is properly circulating again and dissipating sufficiently, go to step 1
if not go to step 3, there is a coolant problem

7) the melted mess makes a pool at the bottom of the vessel
at this point it is getting warmer

8) the pool reaches criticality again and sustained reaction resumes
at this point it is getting warmer and totally not in control anymore
since it's in a blob at the bottom, maybe inside vessel, maybe outside

9) good luck cooling that by human means
???
profit

[Statistical]

20. If I could clarify.

The warmer isn't a measure of heat output but rather insulation (ability or inability to transfer heat).

For a given heat output say 1 MW the local temperature will vary depending on how quickly effectively you can MOVE (transfer) that heat. So while the temperature may rise or fall based on how effective the cooling methods are the core thermal output (thus ability to produce higher temps in the future) is continually falling.

If pump breaks and cooling stops the core may get warmer but output is still declining. Good analogy is coals of a campfire. They may be hot but they can only get cooler over time. Fission is the fire, nuclear decay is the coals.


Criticality is impossible without:
1) sufficient number of neutrons - which is why control rods (absorbing neutrons and breaking chain reaction) and born is being added to seawater.
2) water to moderate the neutrons - slow them down.

Things could get worse. If they can't keep the reactor "cool enough" the fuel could melt the RPV and containment could be lost. However the thermal potential of the fuel is declining over time so as time goes on the likelihood that can happen decreases. Eventually the fuel will have insufficient thermal energy to melt steel at which point the situation would be "contained".

[SpoonFed]

38. You're not clarifying, you're repeating.

This recent article:
http://www.bbc.co.uk/news/world-asia-pacific-12733393
has the best Orwellian doublethink I've seen in a while:

"International nuclear watchdogs said there was no sign of a meltdown but
one minister said a melting of rods was "highly likely" to be happening."

I've also just watched an analyst describe the reason for the falling water levels
is that there is already melting and hence the disappearing water levels, in the
form of compression into steam, exacerbating the exposure of the rods and temperatures,
or just all out loss of containment. Your choice, both seem to be worse.

As for the eventuality that the fuel will have insufficient thermal energy to do anything
bad, I do agree in that I believe in the eventual heat death of the universe.

[spanone]

6. headline msnbc: Fuel rods likely melting at third Japanese reactor Water levels drop at plant

SOMA, Japan — The uranium fuel rods at a third nuclear reactor within a stricken Japanese power complex are likely to have started melting after water levels dropped precipitously twice on Monday, officials said.

The water drop left the rods no longer completely covered in cooling water, thus increasing the risk of a radiation leak and the potential for a meltdown at the Unit 2 reactor, Tokyo Electric Power Co. said.

Workers managed to raise water levels after the second drop Monday night, but they began falling for a third time, according to Naoki Kumagai, an official with Japan's Nuclear and Industrial Agency.

TEPCO later said it had resumed work to pump sea water into the unit by opening a valve on the reactor's pressure vessel.

http://www.msnbc.msn.com/id/42066534/ns/world_news-asiapacific/

[dkofos]

8. I think reuters is blowing radioactive smoke up the rectal opening.

[tabatha]

9. yup

[Teaser]

11. basis?

.

[rhett o rick]

15. Where are you getting your info? Are you disappointed? nm

[Thunderstruck]

30. Why is questioning the veracity of "official" information now considered

disappointment that a catastrophe may be averted?

[rhett o rick]

33. So you dont believe that they are getting the situation under control?

And you are glad that a catastrophe was avoided? I missed that in your post.

[Thunderstruck]

36. I don't have any reason really not to believe them but some people are

justifiably skeptical of what the Japanese officials are reporting. On Yokoso News the translators were describing the anger being expressed by the reporters at the press conferences of Sec Endano, saying the reporters were "violently" asking questions in anger because they did not feel the official was being completely honest in his reports. The Japanese are notorious in their dishonesty when it comes to nuclear energy.

All I'm saying is that just because someone isn't smellin' what the Japanese officials are cookin' doesn't mean that they are disappointed that a catastrophe has been averted.

Do you REALLY need an answer to your question: "And you are glad that a catastrophe was avoided?" I mean, really?

[rhett o rick]

41. self delete

[Thunderstruck]

42. Another explosion and a 10,000x increase in radiation, officials in tears on CNN

http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=439&topic_id=645098&mesg_id=645098

[SpoonFed]

40. Seriously?

> So you dont believe that they are getting the situation under control?

Hahahah. They've been getting it under control since the very beginning!

And they've been doing a great job and it's almost done so now they are
asking the international community for help in planning the celebration
after party.

And I quote:

"After insisting for three days that the situation was under control, Japan
urgently appealed to US and UN nuclear experts for technical help on preventing
white-hot fuel rods melting. "

http://www.telegraph.co.uk/news/worldnews/asia/japan/8382139/Japan-crisis-meltdown-alert-raises-spectre-of-nuclear-nightmare.html

[Duende azul]

43. So this is now a question of "belief"?

Did you belief them in the first place, when everything was reported as under control?

Let´s wait and see.

And it strikes me as extremely ugly to insinuate someone may be disappointed in a catastrophe avoided. If that´s not personal attack, I don`t know what is.
You might consider apologizing to the persons in question.

Btw: There is no catastrophe avoided. They have one at hands. What hopefully may be avoided is the really big one.

[kristopher]

35. Two reasons:

The first is that the "official" line is weighted by vested interest on the part of "officials" to favor the nuclear industry.

Second is that nuclear supporters are very strongly inclined to be people who have a great deal of trust in authoritarian cultural institutions like the nuclear industry and it's governmental sponsors.

And yes, if challenged I can support the statement with research from the nuclear industry itself.

[yodermon]

10. and what of the spent fuel pools located at the top of the buildings?

Are they not worthy of mention?

You know, the ones that supposedly survived this:

[Junkdrawer]

13. They're still working on those talking points.....

Give 'em a break. It's been a busy weekend.

[Statistical]

14. Heat output of spent fuel in ponds is much much lower.

They don't require active cooling. They simply need a mechanism to replace any water that is lost. If they can inject millions of gallons of water into the core I would assume that they can refill the cooling pond if needed. While one needs to ensure the spent fuel remains under water is requires much less attention than the reactor core (which is still producing significant albeit dropping thermal output).

[rhett o rick]

17. If you have information that conflicts, plez share. Otherwise it sounds like you are disappointed

that it wasnt the huge disaster as many were hoping.

[Old and In the Way]

12. Lets all hope this report is true.

When the smoke clears, someone's on the hook for $100's of billions in scrap and we need to have a real conversation about the efficacy of our energy choices. No question that nuclear power is the investment choice of energy corporations, but is that the best choice for the people who need to live with the consequences?

[Chris_Texas]

21. If nuclear were the choice of the biggest energy companies

You would have been fed a steady diet of love for nuclear rather than the irrational fear your were fed instead. the big enerby companies prefer oil and coal -- there's far more money in it. Here's a hint: the big environmental groups are no more "grassroots" than the tea parties. Their money comes from the same mega-corporations that most assume they hate.

You think Exxon-Mobile doesn't like making hundreds of billions a year off oil? You think they WANT the people to have essentially free power? Consider this: if you factor even some minor cost-benefits of mass production, the United States could have likely replaced 100% of it's gas and coal fired powerplants with nuclear for no more investment than the cash we handed out to the banks with the Bush bailouts -- let alone adding in Obama's stimulus. Instead of feeding bonus checks and toxifying the planet, that money COULD have provided everyone in America with free or extremely low cost power. Imagine having NO power bill... imagine the stimulative impact THAT would have on the economy.

Big-energy doesn't like that idea one bit.

[SlimJimmy]

16. Best discussion I've seen on DU since this happened. K&R

[LAGC]

18. Never underestimate the ability of man...

...to conquer and prevail over whatever nature throws our way.

K & Fucking R.

[Junkdrawer]

22. You should correct the scientists at the Union of Concerned Scientists....

They're posting a graph that doesn't seem at all like an exponential decay graph...



Clearly they don't know as much as you do....

[Statistical]

23. Did you not notice the time measurements aren't linear?

The slope of the graph is flat because the distance between days is uneven. Also the chart doesn't show the distance between 0 days and 1 day which is the largest decay in heat output. If it did the distance between day 0 and day 1 would be nearly 2x as wide as the distance between day 1 and day 2.

"Clearly they don't know as much as you do...."
No clearly you don't know how to read a chart. Nuclear decay is a very well understood phenomenon. It isn't subject to oped or bias. The heat output of the reactor will continue to decay making the problem easier to manage as time goes on. The most critical hours where right after the SCRAM when heat output was much higher. Had the pumps not worked for the first hour, or the batteries for next 8 it is entirely possible the reactor would have simply melted down before any contingency could be devised.

In essence the disaster workers can "get away" with less and less water pumped each day increasing the margin of safety.

[Junkdrawer]

27. As I read this graph, it's taking longer and longer periods of time....

to lose the same delta of energy.

[Statistical]

28. Exactly. Which is exactly what I indicated.

Full reactor power - 1500 MWt
At SCRAM - 100MWt (90% reduction in matter of minutes)
After 1 hour ~ 20MWt (75% reduction after ANOTHER 1 hour)
After 1 day ~ 6MWt (70% reduction after ANOTHER 23 hours)
After 1 week - 3 MWt (50% reduction after ANOTHER 6 days)

Would you agree that dealing with 3MWt of heat is far easier than dealing with 100MWt (thermal output at point of SCRAM) or 1500MWt (thermal output prior to SCRAM).

You look at it as in the future the reactor won't lose energy as fast. I look at it as the reactor has 93% less energy than when it SCRAMED and 99.8% less energy then when it was operating.

Although the timeline is slowing down there is still "good" news. In another week the output of the reactor will fall by about another 25% increasing further the margin for safety. In a month the output of the reactor will fall by over half.

[Junkdrawer]

29. The decay curves are good news/bad news things....

and everything depends on how much decay is necessary before the rods won't melt down when uncovered - because they seem to be having an increasing difficult time keeping the rods covered.

[Statistical]

31. That I agree. I could do some quick number crunching this evening to get a ballpark figure.

You are right though, the bad news for the containment team is that most of the help they are going to get from physics has already happened.

Still I look at is as good news is the output is much lower today and will be lower tomorrow, next week, next month. This provides a margin of error. Without water (or a delay in water) the fuel would melt through the RPV is a longer amount of time today than it would a day ago. Likewise it will take longer for fuel to melt through the RPV in the future.

[Junkdrawer]

25. Posted wrong spot.

[jtuck004]

24. Great post, perhaps it will calm some nerves...

But I am concerned that the "pressure" part of the inner vessel has been compromised on at least one, and perhaps two, of these. Even after the rods are "coals", they heat the water to well over boiling - (takes about 4-5 years to get them cool enough to trasport in the casks on a truck).

Without that pressure it's like a car with a loose radiator cap and an engine you can't shut off - even with a constant supply of water it can flash into steam which can prevent further water flow and cause explosions that further damage the pipes (which may well have been damaged by the earthquake). To prevent such an explosion they are venting that steam (and hydrogen), but that releases radioactive material into the air, some of which has a half-life of 30 years or so. I think they are mis-reporting this on purpose, so as not to alarm people.

That's the thing that concerns me the most. You have to keep the water contained and it has to be under pressure. At this point it looks like that is not happening. I used to work with steam turbines, and it was the same problem even with conventional boilers.

The good news is that the design of the reactor is such that it should contain the pool of material at the bottom. (If it doesn't it burns through, enters the ground, and then you have big, uncontrolled, radioactive steam clouds until it solidifies what is around it). But that is unlikely unless there has been damage to the inner cladding.

Still, it is far safer than the coal being burned in our electrical plants today, and even in a worst case scenario probably won't hurt as many people, IIRC.

"Assuming a 1 percent ash release to the atmosphere (Environmental Protection Agency regulation) and 1 part per million of uranium and 2 parts per million of thorium in the coal (approximately the U.S. average), population doses from the coal plant are typically higher than those from pressurized-water or boiling-water reactors that meet government regulations."

http://www.sciencemag.org/content/202/4372/1045.abstract

[Statistical]

26. I don't believe (based on information available which I admit is limited)

that the ability of RPV to maintain pressure has been compromised.

Actually if anything on reactor #2 the pressure relief valves failed to open so they couldn't pump any more water in (steam only compacts so much). They finally got the valves open so they are adding more water now.

Essentially the process is something like this:
1) close steam relief valves (water boils at higher temp under pressure)
1) Add water to reactor till full.
2) Attempt to cool reactor via heat exhanger (only partially sucessful)
3) Since reactor has insufficient cooling the temp and pressure in reactor will rise.
4) Open valves to release steam.
5) Go to Step #1.

As long as they can keep releasing and building pressure they can cool the reactor more efficiently (steam under pressure boils at higher temp thus has more energy that is more energy removed from the reactor core per unit of water. Without ability to increase pressure (and thus increase boiling point) you are right cooling the reactor gets much harder but not impossible. Technically it is the same operation it just requires significantly more water as each unit of water boils "easier" and thus carries away less energy. It takes more water to move the same amount of energy.

In essence by controlling pressure they can reduce the amount of water necessary for cooling.

[jtuck004]

47. The reason I think it does have a leak is because they are having to vent the steam.

If it was under pressure, ie a closed system with the proper pressure, the steam could be controlled. It's not, which means there is a leak, and thus the reason for the venting of steam with radioactive particles. With the rods at a much lower temp than when they were operating should dramatically reduce the amount of heat, so the only other explanation I can come up with is that there is a pressure leak.

The other reason is because I heard the government reports that they are able to get water in, but it was not raising the level in the reactor. That shouldn't happen if there is containment. We had the same issues on navy boilers, with the same outcome. Except then we could turn the fire off.

That said, you may be correct. But if there is pressure there is no real reason, other than damage, that they should not be able to cool it sufficiently to prevent having to release steam to the atmosphere when the pressure gets too high.

Too far away, information flow sucks - I guess we will see over the next few days.

[Obamanaut]

32. This will certainly be a blow to the 'doom and gloom' faction. nt

[Whisp]

34. the people here wanting revolutions and catastrophies

will be dissapointed, I am sure.

but I am happy happy joy joy relieved.
still not over till it's over but looking good.

[roamer65]

37. They were scheduled for decomission a year or so back...

I have read. Unfortunately they decided to run them for another 10 years.

[Jersey Devil]

39. Just as I thought, no problem at all

People should learn that nukes can be fun! As Americans we've known that for a long time.

http://www.youtube.com/watch?v=0lX9IU1qWmA

[Generic Other]

44. Not what is being reported on Japanese television

They are talking about meltdowns. What the hell? Isn't there enough confusion without deliberate misinformation?

[senseandsensibility]

45. Glad to hear

I hope the world learns something from this disaster.

[Thunderstruck]

46. How's that working out for you?

http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=102&topic_id=4770692&mesg_id=4770692