Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[promecheng]

Is the suppression pool torus on the MK-1 design considered part of primary containment?

 

[Reno Deano]

NEI WEB UPDATE AS OF 2:15 P.M. EDT, TUESDAY, MARCH 15:

Excerpt: An explosion at Unit 2 of the Fukushima Daiichi plant earlier today has damaged the suppression chamber, which holds water and steam released from the reactor core. Personnel not directly supporting recovery efforts have been evacuated from the plant, with about 50 employees remaining, principally to restore cooling water in the reactors.

Later in the day, water level inside the Unit 2 reactor was measured at 1.7 meters below the top of the fuel rods, but it was rising as workers pumped sea water into the reactor, reports said.

Tokyo Electric Power Co. said that an oil leak in a cooling water pump at Unit 4 was the cause of a fire that burned for approximately 140 minutes. The fire was not in the spent fuel pool, as reported by several media outlets. Unit 4 was in a 105-day-long maintenance outage at the time of the earthquake and there is no fuel in the reactor.

 

[Astronuc]

Is the suppression pool torus on the MK-1 design considered part of primary containment?

Yes - it is in the volume that contains the pressure vessel and recirculation system.

If there is no fuel in the core of Unit 4, it means they did a full core offload - and the fuel resides in the SFP or other pool. I've seen thermals coming off older fuel.


This gives a pretty decent explanation of what got the plant in its present situation.
http://blogs.forbes.com/christopher...hat-caused-the-incident-at-fukushima-daiichi/

I don't necessarily agree with the conclusion/remedy regarding fluoride salt fueled reactors.

 

[Texan99]

Suppose a nuclear reactor were successfully shut down with control rods, but then the cooling system immediately failed and no one managed to do a single thing to get it running again. Does anyone really know whether the containment vessels currently in use should be expected to contain the whole meltdown without any significant release of contamination? In other words, I guess steam would build up in there like crazy, but is the vessel up to that task? Or is that just untested territory? In Three Mile Island, for instance, I've read that the core melted down about halfway without breaching the vessel, but I don't know how well the cooling system was functioning.

Special thanks to Reno Deano and Promechang, among others, for your very helpful posts for us laymen.

 

[Texan99]

What is the impact, if any, of a breach of the suppression pool torus on the ability of the containment vessel to hold in all the fissile materials? I mean, suppose you hacked a big hole in the torus. Could melted fuel run out there?

 

[Astronuc]

Suppose a nuclear reactor were successfully shut down with control rods, but then the cooling system immediately failed and no one managed to do a single thing to get it running again. Does anyone really know whether the containment vessels currently in use should be expected to contain the whole meltdown without any significant release of contamination? In other words, I guess steam would build up in there like crazy, but is the vessel up to that task? Or is that just untested territory? In Three Mile Island, for instance, I've read that the core melted down about halfway without breaching the vessel, but I don't know how well the cooling system was functioning.

Special thanks to Reno Deano and Promechang, among others, for your very helpful posts for us laymen.

Some background on TMI-2's accident.
http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/3mile-isle.html

IF the Fukushima plant was able to cool the core, i.e., IF the EDGs had not failed and been able to cool the plants - we wouldn't be having this conversation.

But the ability to cool the cores of Units 1, 2 and 3 failed! That's the critical matter. One unit by itself is bad enough, but three units is three times as bad.

In a normal plant - all the fuel rods could fail. It doesn't matter outside of the utility, as long as the activity is contained in the primary system, and plants are so designed - with the assumption that they have cooling capability so that they primary systems doesn't build up pressure which has to be released. At Fukushima, they lost the cooling capability and that forced the release of fission products into the environment.

Now all other LWR (PWR and BWR) operators must ensure that their own plants will not suffer the same fate.

 

[Astronuc]

What is the impact, if any, of a breach of the suppression pool torus on the ability of the containment vessel to hold in all the fissile materials? I mean, suppose you hacked a big hole in the torus. Could melted fuel run out there?

It depends on where the breach leads to. As long as the breach doesn't lead to the environment, that doesn't affect the public - only the staff that have to deal with whatever part of containment is directly affected by the breach.

Ideally, the fission products stay within the pressure vessel - except for those that have been vented. Otherwise, any fission product in the cooling water that ends up in the torus, will either stay in the torus, or within the primary containment.

Contamination of containment would be a complication of further operation - or complication for decommissioning.

 

[Texan99]

I'm sorry, Astronuc, I'm still not understanding. I do see that the cooling was inadequate, which was why this problem started developing. With normal cooling, the reactor would shut down and gradually cool off. What we got instead was not "zero cooling," but some interruptions or inadequacies in cooling, and some resulting problems with steam and possibly degradation of the fuel rod cladding. At a result we also got explosions here and there that may have put firetrucks out of operation or done some damage to the torus, which might mean that whatever cooling we'd managed to get going again in there was about to get interrupted again, or at least that the cooling system was degraded enough that it couldn't quite keep up for a while. I'm trying to figure out whether it's a huge concern that the cooling might get interrupted or degraded again. Obviously, it's a bad thing for the plant and its owners, but I mean, at this point, assuming that reactor's toast anyway, would a complete loss of the cooling system mean anything more than a lot of slagged-down fuel rods in an intact vessel? And does that answer change when you consider that there may or may not have been a breach in the torus?

 

[Drakkith]

Texan, if we just let the fuel heat up, we would get more Hydrogen buildup. And in addition to the explosive risk from that, the pressure buildup from the evaporating coolant could rupture the containment vessel and building, releasing large amounts of radioactive material into the air.

 

[Texan99]

I realize it's about what's probable. I guess I was just wondering whether it was possible to quit worrying about whether the alternative cooling systems will continue to work, because we continue to get disheartening news about the cooling systems failing, one after the other. I was hoping that we could say, in the end, that no matter what happens with the cooling systems, the vessel will hold, but you're saying no. Rats. Well, I know they're still moving heaven and Earth to continue to provide all the cooling they can, and so far even the compromised cooling has proved adequate to the task of preventing a vessel rupture.

 

[Astronuc]

I'm sorry, Astronuc, I'm still not understanding. I do see that the cooling was inadequate, which was why this problem started developing. With normal cooling, the reactor would shut down and gradually cool off. What we got instead was not "zero cooling," but some interruptions or inadequacies in cooling, and some resulting problems with steam and possibly degradation of the fuel rod cladding. At a result we also got explosions here and there that may have put firetrucks out of operation or done some damage to the torus, which might mean that whatever cooling we'd managed to get going again in there was about to get interrupted again, or at least that the cooling system was degraded enough that it couldn't quite keep up for a while. I'm trying to figure out whether it's a huge concern that the cooling might get interrupted or degraded again. Obviously, it's a bad thing for the plant and its owners, but I mean, at this point, assuming that reactor's toast anyway, would a complete loss of the cooling system mean anything more than a lot of slagged-down fuel rods in an intact vessel? And does that answer change when you consider that there may or may not have been a breach in the torus?

I expect that they are trying to accomplish 2 things: 1) prevent further degradation of the fuel, and 2) prevent pressurization of the containment that would mean venting more steam and/or hydrogen, and more fission products.

In theory, the cooling prevents further degradation, and in fact, less fission gases as the Xe and Kr decay: I -> Xe -> Cs -> Ba and Br -> Kr -> Rb -> Sr. I and Br are volatiles (low boiling/sublimation points), Xe and Kr are noble gases, Cs and Rb are alkali metals (with relatively low melting points), and Ba and Sr are alkaline Earth metals with higher m.p. the corresponding alkali metals.

Ref: http://www.webelements.com/ and http://www.nndc.bnl.gov/chart/ (Zoom 1 or 2 to see details on particlular radionuclides)

The idea is too cool the fuel so that no more fuel fails/degrades, and retain (contain) the fission products in the containment so that they decay away to less radioactive or inert isotopes, which are more manageable. The longer they can keep the fuel cool (and intact) the better, since the expectation is that release of fission products to the environment will be minimized.

 

[DR13]

My roommate was watching the local news (yeah...he does that). They were doing a story on Fermi 2 (in SE Michigan). The news anchor was talking about how dangerous the reactor is since it's 20 years old. Then they go to some intervew with the head of an anti-nuke group leader here in Michigan and he is talking about how Fermi 2 is kinda the same reactor as the one having problems in Japan and how the same thing could easily happen to us. Then the news anchor confirms that she thinks that the plant is also a hazzard (because local news anchors obviously have nuclear engineering degrees).

This was bad enough but then it got worse. They started talking about what would happen if what happened in Japan happened here. YEAH, BECAUSE MAGNITUDE 8.9 EARTHQUAKES AND TSUNAMIS OCCUR IN MICHIGAN ALL THE TIME. I MEAN SERIOUSLY PEOPLE!

This is the problem with the media. Little facts, lots of BS. They don't even talk to someone who is knowledgeable on the subject!

I had to force my roommate to mute the tv until the segment was over.

 

[WatermelonPig]

Hi, not to interrupt conversation but I like would to ask a question: I heard that there was partial exposure of the fuel rods within I believe the third reactor. What exactly does this mean? Did the zircaloy melt? Also, how significant is the height of the fuel rods above the ground in a possible attack on the facility? And do you think this incident will severly affect future power plant construction?

 

[Astronuc]

Hi, not to interrupt conversation but I would to ask a question: I heard that there was partial exposure of the fuel rods within I believe the third reactor. What exactly does this mean? Did the zircaloy melt? Also, how significant is the height of the fuel rods above the ground in a possible attack on the facility? And do you think this incident will severly affect future power plant construction?

There was a headline that indicated that the third reactor at Fukushima experienced partial exposure [to steam] of the fuel rods. The article referred to Unit 3 (the third reactor built, not the third reactor affected). However, a third unit was affected.

The order in which three units experienced cooling problems is Unit 1, Unit 3 and then Unit 2.

The Zircaloy didn't necessarily melt, but it could have reacted (oxidized or corroded rapidly) to the point where it breached. The breaching released the fission gases and volatile fission products into the steam or water as salt water was introduced into the core.

The core sits in a pressure vessel (inches of steel), which is surrounded by several walls (layers) of steel-reinforced concrete.

I expect that designs and construction will receive additional scrutiny in light of the current event at Fukushima Daiichi.

 

[Speedo]

Assuming that the generators had functioned normally, what kind of process would the reactors have gone through after the quake before they were brought back online?

I'm mainly wondering why it wasn't/isn't feasible to bring one reactor online at a low power setting to provide enough power to sustain cooling for the complex.

 

[Drakkith]

Assuming that the generators had functioned normally, what kind of process would the reactors have gone through after the quake before they were brought back online?

I'm mainly wondering why it wasn't/isn't feasible to bring one reactor online at a low power setting to provide enough power to sustain cooling for the complex.

Probably would have remained offline as the waste heat gradually died down. Once the grid was reconnected and everything was verified safe and operational I'm sure they would have started them back up. I don't know how much actual damage the plants sustained from the earthquake, so who knows when they would have been brought back online.

 

[promecheng]

Assuming that the generators had functioned normally, what kind of process would the reactors have gone through after the quake before they were brought back online?

I'm mainly wondering why it wasn't/isn't feasible to bring one reactor online at a low power setting to provide enough power to sustain cooling for the complex.

It's moot at this point since units 1-3 appear to be permanently disabled, and units 4-6 were in outage mode, (not fit for operation), when the earthquake hit. However, even if there was a unit that was fueled and potentially ready to go. There was a 8.9 or 9.0 earthquake that shut the units down for a reason. I think someone said that the plant DBE, (Design Basis Event). earthquake was 7.0 or 7.5. This means that the plant was only designed to withstand up to this event. Being that a 8.9 earthquake is 14 times a 7.5 magnitude one, I'm sure they would have serious reservations about starting a unit back up without a thorough inspection, (which would probably take months or years). For all they know the earthquake could have disabled a number of critical systems necessary for the safe operation of the reactor. This would be too large of a gamble. Additionally I thought I read somewhere that they had significant electrical damage at the plant, so even if they could start a unit and produce steam, (which takes some time to bring up to power), the turbine and switching systems may have been damaged. The bottom line is that you just don't flip a switch to start a plant back up, especially after such a significant earthquake!

 

[Drakkith]

Hi, not to interrupt conversation but I like would to ask a question: I heard that there was partial exposure of the fuel rods within I believe the third reactor. What exactly does this mean? Did the zircaloy melt? Also, how significant is the height of the fuel rods above the ground in a possible attack on the facility? And do you think this incident will severly affect future power plant construction?

1. The partial exposure means that the coolant had dropped so low that parts of the fuel rods had NO coolant high enough to cover them. This is bad obviously.

2. I don't think there is any significance to the height of the fuel rods in the event of an attack.

3. In my opinion it will most definitely affect future nuclear power plant construction, and not in a good way. But mostly because people are ignorant and have zero idea about what radiation and nuclear power really means.

 

[Astronuc]

Assuming that the generators had functioned normally, what kind of process would the reactors have gone through after the quake before they were brought back online?

I'm mainly wondering why it wasn't/isn't feasible to bring one reactor online at a low power setting to provide enough power to sustain cooling for the complex.

They tripped based on the seismic signals. But then they lost the grid - perhaps the local station.

Large equipment like turbines and generators don't like getting shaken very hard - so they would have to inspect 'all' major components. That would take days, especially if they had to compare the data with the design bases.

Because they lost the grid (connection to off-site, and perhaps the local swithyard or distribution system) - the emergency diesel generators came online. They worked! However, a tsunami destroyed the fuel system and apparently some electrical equipment. The slowly lost the ability to the reactor(s). There was no time to even think about a restart - and probably no way to use the electrical power if one did.

Some of that is conjecture because the detailed sequence of events and equipment failure is unknown. While Units 1, 2 and 3 seem to be suffering from the same common mode failure (tsunami damage), there are unique issues with each unit. We won't know for months.


BTW - I want to thank all the contributors for their thoughtful comments and questions.

 

[tkny123]

I'm a humanities guy but I've been doing some reading and have some questions that maybe posters could answer.

1. I heard that the quick path to cold shutdown at Daiini was restoration of grid power then use of its normal pump systems. I heard that grid power was restored to Daiichi but none of the plant's primary and backup feedwater and injection systems are back up or seem to have any chance. Does anyone know why not? Could every single pumping system be disabled? Doesn't that seem unlikely?

2. Is there absolutely no scenario in which the reactor vessel or drywell could be breached? Some in media insist on that. Could someone put some figures to it?
2A. Temperature angle. I read that the melting point of steel is 2800 Faren and zircaloy 2200 F. Also that concrete starts to crumble at 1800 F. Does that mean there is no way a molten core could reach and sustain a temp of > 2800 F? If it could, why couldn't it melt through the vessel?
2B. Pressure angle. Seems like pressure must be able to present a problem and that is the reason for the current "feed and bleed" method. Is there a critical pressure level for the vessel? What has to happen for that level to be reached (i.e., rods totally exposed for x hours with no water?)?

3. Spent fuel rods. If a group of them get totally uncovered by cooling water, what could happen?
3A. Everyone agrees the rods could heat up, then zircaloy cladding melt, then what? If zircaloy melts at 2200 F, wouldn't the concrete under it start to at crumble at 1800 F? Could they sponteously combust, have a conventional fire, that could disperse radioactive material?
3B. I read different things on whether these rods could go "critical", which I understand to means "to restart fission" (but not explode like a bomb). Most in media say "no way" but TEPCO just said it can't rule it out in the case of Unit 4, and it seems like it may have already. See these articles. So can they go "critical" or not?
http://english.kyodonews.jp/news/2011/03/78403.html
http://online.wsj.com/article/SB100...76201643613498376.html?mod=WSJ_newsreel_world
3C. If fresh fission is possible, that's really bad bc it is outside of containment. Freshly fissioned uranium could disperse by fire or explosion (say by hydrogen).

Thanks in advance! I pray for the people of Japan and especially the heros at Daiichi who are sacrificing themselves.

 

[Reno Deano]

The Mark I containment design consists of several major components, many of which can be seen on
page 3-16. These major components include:
• The drywell, which surrounds the reactor vessel and recirculation loops,
• A suppression chamber, which stores a large body of water (suppression pool),
• An interconnecting vent network between the drywell and the suppression chamber, and
• The secondary containment, which surrounds the primary containment (drywell and suppression
pool) and houses the spent fuel pool and emergency core cooling systems.

Technically the Mark 1 torus is outside the Primary containment, but connected by vent ducts.

See the following BWR systems description study guide:http://www.nrc.gov/reading-rm/basic-ref/teachers/03.pdf"

 

[AntonL]

That Nuclear power plants have heated swimming pools (spent fuel storage tanks)
and that the swimming pool heaters can start a meltdown process or catch fire
is news to me. Fukoshima I no 4 reactor fuel rods are all in this indoor swimming pool!

Any discussion on containment primary or secondary is now superfluous

What sort of safety is this!
And that the plant was designed by USA's General Electric the question to ask now is:
How many USA nuclear power plants have heated swimming pools?

 

[AtomicWombat]

That Nuclear power plants have heated swimming pools (spent fuel storage tanks) and that the swimming pool heaters can start a meltdown process or catch fire is news to me. Fukoshima I no 4 reactor fuel rods are all in this indoor swimming pool!

Any discussion on containment primary or secondary is now superfluous

Yes that is pretty much what the Union of Concerned Scientists is saying:
http://allthingsnuclear.org/post/3892719255/spent-fuel-pools-at-fukushima
In particular, "If mechanisms to fill the pool at Unit 4 are broken, or if there is a need to repair the pool, it will be difficult to get workers close enough to do this. If spent fuel has been in the pool for a relatively short time, even if the water level is at the top of the fuel rods, the radiation dose to someone at the railing of the pool would give them a lethal dose in well under a minute. "

I am curious. Is anyone familiar enough with the Mark 1 BWR design to tell me whether the spent fuel pool will drain directly through the gaping hole in the reactor building.

http://www.abc.net.au/reslib/201103/r735227_5964756.jpg

 

[snoopies622]

When they speak of radiation leaks, do they mean only neutrons, alpha, beta and gamma particles - or also other big atomic nuclei that are smaller than uranium nuclei but which will themselves break down and emit more neutrons, alpha, beta and gamma radiation?

Thanks.

 

[Borek]

I believe in this context radiation leak means leak of a radioactive substance, not fact that radiation (be it alpha, beta, gamma) is detectable outside. Sure, when the radioactive substances leak there is a spike in the detected radiation, but it is an effect of the radioactive substances being present outside. As long as the radioactive material is present in the containment at least beta and alpha are almost completely stopped.

 

[AntonL]

When they speak of radiation leaks, do they mean only
neutrons, alpha, beta and gamma particles - or also other big atomic nuclei that are smaller than uranium nuclei but which will themselves break down and emit more neutrons,
alpha, beta and gamma radiation?

Thanks.

radiation leak is a very simple and misleading description
One should speak of radioactive contamination which
contain the original material Uranium as well as the
fission products like Caesium-137 and Iodine-131 both
again highly radioactive and to be avoided.

These fission products have been detected offshore and on-shore

 

[myth_kill]

In the worst-case scenario, one or more of the reactor cores would completely melt down, a disaster that could spew large amounts of radioactivity into the atmosphere.

 

[TCups]

Yes that is pretty much what the Union of Concerned Scientists is saying:
http://allthingsnuclear.org/post/3892719255/spent-fuel-pools-at-fukushima
In particular, "If mechanisms to fill the pool at Unit 4 are broken, or if there is a need to repair the pool, it will be difficult to get workers close enough to do this. If spent fuel has been in the pool for a relatively short time, even if the water level is at the top of the fuel rods, the radiation dose to someone at the railing of the pool would give them a lethal dose in well under a minute. "

I am curious. Is anyone familiar enough with the Mark 1 BWR design to tell me whether the spent fuel pool will drain directly through the gaping hole in the reactor building.

http://www.abc.net.au/reslib/201103/r735227_5964756.jpg

Yikes!

The fuel rods are stored at (3) -- see:

 

[larrymoencurl]

Can nuclear plants be built so excess pressure can be vented without so much risk of hydrogen explosions?

 

[Astronuc]

Can nuclear plants be built so excess pressure can be vented without so much risk of hydrogen explosions?

Yes. TMI-2 successfully contained the hydrogen. Some plants have hydrogen recombiners to safely control of the combustion hydrogen.