Reactors In Japan After Earthquake

[kowalskil]

Below is a message from a nuclear physicist in Japan (received 3/12/2011)

 

Ludwik

 

================================================

 

Serious rescue efforts for isolated people in destroyed

towns by tsunamis and quake are under way.

Another serious concern is of the stopped nuclear power

plants, Fukushima-I $II with 8 reactors total.

The Fukushima-I#1, 40 years old, has got the first trouble

after its automatic shut-down by the quake, which was caused

by no electricity (an emergent Diesel generator did not work

either) for driving circulation pumps of cooling water.

Consequently, decay heat of U-fuel pins could not be cooled

enough and temperature and steam pressure inside the reactor

vessel elevated continuously. Finally the melt-down of

reactor-core fuel started to happen, as detected by Cs and I

activities outside as the emergency value of reactor vessel

gas was opened to decrease the elevated steam pressure. It

happened an explosion, by mixing hydrogen-gas (generated by

H2O + high-temperature-metal interaction inside reactor) and

oxygen gas at the outside of the reactor steel-container,

which destroyed the concrete walls of the #1 plant building.

The reactor container vessel and reactor vessel were looked

not damaged.

TEPCO (Tokyo Electric Power Corp.) and NISA (Nuclear and

Industrial Safety Agency) decided to fill the inside and

out-side of reactor vessel with sea-water adding borated

acid to cool the reactor. The work was done. Radioactivity

monitors outside showed decrease of radiation level to about

ten times of natural BG, which was about several 100 times

just after the emergency gas-valve opening. Now the reactor

is confined stable. Citizens inside 20 km radius were

evacuated for safety.

(I think, the usage of sea water, emergent use, was chosen

by two reasons: 1) not enough pure-water was not available

at the site, 2) NaCl contained in sea water, as well as

added borated acid (B-10) has significant thermal-neutron

absorption effect which may help avoiding a worst

criticality accident of fallen debris of melt U-fuels into

water pool of container vessel, if happened.)

 

Probably the Fukushima-I#1 reactor will be closed

(disassembled) in near future. But we still need careful

watching what will be going on.

 

Now it is aired that Fukushima-I#3 reactor has got a similar

trouble. They might do similar treatment, not decided yet.

.

[freeztar]

Interesting...

 

Looks like we need some chemists to weigh-in here. Borated acid?

 

A couple of friends have been piping about radiation on the west coast of USA. The neutrons are not a factor, but perhaps there are some isotopes that manage to drift across the Pacific. I assured my friends it was not a worry, but the scientific part of my mind is curious about how we can estimate the amount of radioactive material that left the site and where it is headed. Obviously, any calculation would be inaccurate because of Chaos Theory (a butterfly in Japan...). But it would be neat to see what people come up with and what kind of range can be determined. :)

 

I'll have a go at it a bit later. Need to collect data first...

[CraigD]

A couple of friends have been piping about radiation on the west coast of USA. The neutrons are not a factor, but perhaps there are some isotopes that manage to drift across the Pacific. I assured my friends it was not a worry, but the scientific part of my mind is curious about how we can estimate the amount of radioactive material that left the site and where it is headed.

I don’t think that significant amount of radioactive pollution will reach Hawaii or the American west coast from the ongoing Fukushima I nuclear accidents.

 

So far, the Fukushima reactors appear only to have has steam intentionally vented from within their concrete reactor enclosures, and unintentionally vented when these enclosure were ruptured by a hydrogen explosion inside it. 2 or the plant’s 6 buildings have been breached so far.

 

Although a bad thing, this water should be only slightly radioactive, so the impact of it falling on plants, animals, and into bodies of water and ground water should not be catastrophic. It's good that the steel inner reactor vessels remain intact, so the very radioactive fuel within them can't escape into the air or ground by melting, burning or being pulverized by an explosion.

 

Although I'm sure there are many important differences between them – a major one being that Fukushima’s failure was caused by damage from Friday’s earthquake, while TMI was caused by what should have been a non-critical mechanical failure, followed by a chain of critical operator mistakes - I don't think it's too inaccurate to describe what's happened is the last few days at Fikushima as what nearly happened during the 1979 Three Mile Island accident.

 

At TMI, hydrogen accumulated in the single affected concrete reactor enclosure, but did not explode before it could be removed by various techniques, including venting it into the atmosphere. At Fukushima, despite similar efforts, hydrogen in two of its concrete reactor enclosures have exploded, breaching the enclosures.

 

At both TMI and Fukishima, control rods were successfully inserted – “scrammed” – into the fuel piles of the troubled reactors, reducing their fission rate enough that, although fuel rods and internal components melted, their steel vessels were not melted through when their water-based cooling systems failed. Had the reactors in either case failed to scram, the results would have many times worse, similar to the 1986 Chernobyl disaster, where, during a test of a reactor shutdown procedure, control rods were prevented from being inserted more than 1/3rd of the way into the reactor’s fuel core by an explosion in the core, and the reactor vessel was breached.

[Jay-qu]

I am concerned about the bad PR this may be giving nuclear technology. These reactors, even though 40 years old, survived a magnitude 8.9 earthquake and large tsunami, only having their diesel backup generators (for cooling) knocked out. People consider this unsafe how? A more robust backup cooling system should be able to prevent such events from occurring again. Thus one would hope this event does not halt progress in using and developing nuclear technologies.

[freeztar]

Good point J!

 

We need nuclear power. Any disparaging that happens should be tempered with the cold hard logic that supports such tech.

 

Great post Craig. I was hoping you would chime in. :)

[Qfwfq]

People consider this unsafe how? A more robust backup cooling system should be able to prevent such events from occurring again.

That is pretty much the problem. They could have made a system less prone to failure but they didn't. For one, maybe the Fukushima plant should have had a water tower, to give extra margin; a diesel engine is far from failproof as a backup system. Sometimes people just plain don't think.

 

Typically, in designing the overall system, they are limited by cost issues and they can't make something at such a great cost as not to be worth it. That's why so many plants have been made with safety compromises. In the end, treatment of the radioactive waste is a problem that can't be truly adequately solved at a reasonable cost.

 

I don't think current fission is the way to go and there are too many doubts about fusion as being worked on. I think the only hope is in radically new methods and I'll be waiting until more is disclosed and figured out about Andrea Rossi's approach (still somewhat shrouded in industrial secret).

 

BTW:

So far, the Fukushima reactors appear only to have has steam intentionally vented from within their concrete reactor enclosures, and unintentionally vented when these enclosure were ruptured by a hydrogen explosion inside it. 2 or the plant’s 6 buildings have been breached so far.

 

Although a bad thing, this water should be only slightly radioactive, so the impact of it falling on plants, animals, and into bodies of water and ground water should not be catastrophic.

Radiation levels are reported to be rising near Tokyo. Edited March 15, 2011 by Qfwfq
addendum

[CraigD]

A more robust backup cooling system should be able to prevent such events from occurring again.

That is pretty much the problem. They could have made a system less prone to failure but they didn't. For one, maybe the Fukushima plant should have had a water tower, to give extra margin; a diesel engine is far from failproof as a backup system.

Some quick estimating about water towers in a boiling water reactor cooling system:

• Each Fukushima reactor is a boiling water reactor of about 800 MW (8e8 J/s) electrical output
  
• As a rule of thumb, nuclear electric generators are about 33% efficient, so these reactors are about 2.4 GW (2.4e9 J/s) thermal
  
• The heat of vaporization of water is about 2.3e6 J/kg (we can ignore the heat to raise the water from input to boiling temperature, as its much less than the heat of vaporization)
  
• Therefore, each reactor requires about 2.4e9/2.3e6 = 1000 kg/s, (8.7e7 kg, or 87000 m³ per day) of water
  

Even for a single day supply of water, this is pretty huge, for even a modern water tower (I think the largest are around 12000 m³), so I’d guess each reactor would need to have at around 10 large water towers.

 

For environmental and health reasons (reactor coolant water is radioactive) water passing from these towers through the reactors must be collected in reservoirs for recycling into the towers.

 

Obviously, these water towers would have to be earthquake-proof – and, in a coastal area like Fukushima, tsunami-proof - requiring sophisticated flood barriers and motion isolation and dampening systems. Also, for environmental and health reasons, they must be as leak-proof as possible, including systems to detect and warn of leaks or pre-leak conditions.

 

Put this all together, and I’m picturing a power plant consisting mostly of water towers, needing many times the area of land of the present plant, being many times the cost, and having a lot of new points of potential failure

 

Sometimes people just plain don't think.

My guess is we’re not the first people to think of this. From the above quick estimates, though, I can guess why the engineers that designed Fukushima went with the multiple backup pumped closed cooling systems design instead.

 

My hope is that there won’t be many more boiling or pressurized water cooled fission rectors designed or built. Newer designs, like pebble bed reactors, don’t have loss-of-coolant failure modes at all, so are inherently safer. China plans to have a 250 MW pebble bed reactor online in 2013, and as many as 300 GW by 2050. This, I think, is the right track for future nuclear electric power generation.

 

I don't think current fission is the way to go and there are too many doubts about fusion as being worked on. I think the only hope is in radically new methods and I'll be waiting until more is disclosed and figured out about Andrea Rossi's approach (still somewhat shrouded in industrial secret).

Rossi’s approach is interesting. We’ve been discussing it, although rather sluggishly, in this thread.

 

I’d say it’s not only shrouded in industrial secrecy, but also scientific uncertainty, as nobody appears to be able to more than guess at the exact physics or chemistry of it. Rossi (an engineer by training, not a physicist or chemist) and collaborators calls it “low energy nuclear reaction”, and believes it involves the transmutation of nickel (atomic number 28) to copper (29), while other use the older term “cold fusion” and, I gather from some scattered reading, think hydrogen (1) to helium (2) transmutation is involved.

 

According to Rossi, the wait to see if his approach works won’t be long:

I will start up my 1 MW plant in October [2001], in the factory of a customer, and that unit will work 24 hours per day. You will be invited to visit our 1 MW plant.

(source:

http://peswiki.com/index.php/Directory:Andrea_A._Rossi_Cold_Fusion_Generator#Application:_WO.2F2009.2F125444

)

Rossi also claim an amazingly low fuel cost of energy of less than US$0.03/MWh, which, assuming a conventional steam electric generator, would make this technology about 50% cheaper than coal or natural gas

 

If true, LENR power will likely replace most present day power generation technologies. IMHO, however, this is a pretty big if!

[Qfwfq]

Aaaaahh Craig, I don't think you got my point! :D

 

First of all, as a further backup to the diesel, it only needs to act as a buffer for a duration in which either the diesel failure is responded to, or more drastic emergency measures are taken before the overheating even begins. Second, I see no excessively great problem with a raised reservoir having at least as good seismic proofing as the plant's main structure (if necessary, even without the ground under it being wasted to other purposes). The normally empty collection tank could of course be underground. Mostly though:

Put this all together, and I’m picturing a power plant consisting mostly of water towers, needing many times the area of land of the present plant, being many times the cost, and having a lot of new points of potential failure

Putting this all together in a similar fashion, but for the diesel system, one shouldn't get hugely differing conclusions if one's reasoning is equally flawless. What could the huge difference be due to then?

 

You don't suppose the water needs to be recondensed without leakage in any case, including normal operating? I would have designed the whole cooling system so that the extra tanks are a fairly simple addition to it, just as I would expect the diesel to be. Design should have been such that use of the the reservoir would be a mere opening of a (possibly one single) valve. Of course, if properly concieved, the water in the reservoir would have remained clean for all the time up until the diesel backup failed; thus treatment of it for the radioactivity would only now be necessary as an exceptional case.

 

My guess is we’re not the first people to think of this.

Certaily not, but from your above quick estimates I can see why the avearge engineers did not include the buffer idea, especially if they could only think in terms of it being an alternative to the multiple backup pumped closed cooling systems.

 

My hope is that there won’t be many more boiling or pressurized water cooled fission rectors designed or built.

Absolutely but this doesn't remove the blame for inadequate design of those already existing.

 

Newer designs, like pebble bed reactors, don’t have loss-of-coolant failure modes at all, so are inherently safer. China plans to have a 250 MW pebble bed reactor online in 2013, and as many as 300 GW by 2050. This, I think, is the right track for future nuclear electric power generation.

Certainly an improvement for safety; I would even hope it removes all problems except the one it can't do much about.

 

I’d say it’s not only shrouded in industrial secrecy, but also scientific uncertainty, as nobody appears to be able to more than guess at the exact physics or chemistry of it. Rossi (an engineer by training, not a physicist or chemist)...

As I kinda said in that thread, limiting my remarks because it isn't exactly the nominal topic.

 

If true, LENR power will likely replace most present day power generation technologies. IMHO, however, this is a pretty big if!

Some very competent dudes were at the meetings in Bologna and, in the videos I saw, they don't seem at all skeptical! My main hope is that it won't produce any kind of radioactive waste and, by what I heard the nuclear physicists saying and Rossi replying, it seems it emits a bit of gamma, probably beta (likely minus) and, with almost 100% certainty, does not produce neutrons which are the main cause of troublesome radioactive waste.

[modest]

Some quick estimating about water towers in a boiling water reactor cooling system:

• Each Fukushima reactor is a boiling water reactor of about 800 MW (8e8 J/s) electrical output
  
• As a rule of thumb, nuclear electric generators are about 33% efficient, so these reactors are about 2.4 GW (2.4e9 J/s) thermal
  
• The heat of vaporization of water is about 2.3e6 J/kg (we can ignore the heat to raise the water from input to boiling temperature, as its much less than the heat of vaporization)
  
• Therefore, each reactor requires about 2.4e9/2.3e6 = 1000 kg/s, (8.7e7 kg, or 87000 m³ per day) of water
  

Even for a single day supply of water, this is pretty huge, for even a modern water tower (I think the largest are around 12000 m³), so I’d guess each reactor would need to have at around 10 large water towers.

 

A shut down reactor reduces its power output pretty quick. According to http://en.wikipedia.org/wiki/Decay_heat#Power_reactors_in_shutdown the output will go almost immediately to 7% or less (depending on how old the fuel is) and down to 1.5% after an hour and .4% after a week.

 

This talks a bit about gravity fed passive cooling:

 

The reactors at the nuclear plant, built in the early 1970s, rely on active cooling systems that require electricity. Newer plant designs would lessen or eliminate the need for active cooling, making use of natural convection or a "gravity feed" system to cool reactors in the event of an emergency.

 

In one design, for example, the relatively new Westinghouse AP1000, water is suspended over the reactor housing. If pressure within the system drops, this allows the water to fall into the reactor area, submerging it in enough water to keep it cool.

 

While passive systems could be better in the event of electrical failures, they might not always be the safest systems. Kadak says that in an active system, it's easier to ensure that coolant gets exactly where it needs to be—it's simply pumped to the right location. Designing passive systems, on the other hand, requires complex models of how fluids will behave in a system that could be rendered incorrect if the system is damaged.

 

http://mobile.technologyreview.com/energy/35100/

[modest]

You don't suppose the water needs to be recondensed without leakage in any case

 

I believe the AP-1000 is designed to do that as well. The containment building (scary as this sounds) is to be entirely metal—no concrete. That way, if electricity fails with no backup the rods will passively fall to shut down the reactor and water is set to fall from tanks as it boils out of the pressure vessel. The steam is to condense on the metal containment vessel (no insulating concrete between it and the environment) then fall back down to the tanks and to the reactor.

 

~modest

[freeztar]

This is not good. I also read a report earlier tonight about spiking radiation levels in Tokyo.

 

The Japanese government on Tuesday told workers fighting the meltdown to evacuate after radiation levels skyrocketed at the Fukushima Daiichi plant. The workers were the last defense against a serious meltdown.

 

“All the workers there have suspended their operations,” Japan’s Chief Cabinet Secretary Yukio Edano told reporters at a televised news conference. “We have urged them to evacuate, and they have.” The news comes after the government raised the limits on the amount of radiation to which each worker can be exposed, to 250 millisieverts from 100 misieverts, five times the maximum exposure permitted for nuclear power plant workers in the United States.

 

The change in policy means workers had the opportunity to remain on site longer, helping fight a potential meltdown.

 

 

http://politicallyil....php/lpnh/2472/

[CraigD]

Even more bad news from the Fukushima 1 plant.

 

I’ll leave it to the reader to try sifting through the many news stories on it, but in short, the radiation around the plant has become so high that workers had to retreat about 500 m from it, waited for the wind to carry the contaminated air out to sea, then returned.

 

With their low-power water circulation and replenishing systems failed, spent fuel in on-plant cooling pools have become a problem. At least 1, in the burning #4 reactor building is believe to have lost so much water the fuel rod assemblies are only partially submerged. Radioactive material escaping from these spent fuel rods may now be causing more radioactive contamination than steam from the scrammed reactors.

 

There are conflicting reports that one or more reactor cores may have melted through its inner vessel, though no credible ones I've seen that their buildings’ reinforced floors have been burnt/melted through.

 

I hope today brings good news, and this whole mess gets cooled down and under control. At present, that outcome seems far from certain.

[modest]

I heard at least one nuclear physicist on CNN say, before the spent fuel rods were ever mentioned as a problem, that what everyone really needs to keep eye on are the spent fuel pools. That they are far less shielded and would have taken more damage from the explosions on site, outside the containment buildings... that they would catch fire if exposed to air.

 

Crazy that happened. Could anything else go wrong?

 

The last NHK was saying, their best options to refill and cool the pool is to dump water on the cracked roof of the reactor building perhaps with a helicopter, or to shoot fire hoses at the crack in the side of the building. I'm not sure any plan could sound more reassuring! :o

 

I say it's time we send in Sonny Chiba.

[modest]

Looks like we need some chemists to weigh-in here. Borated acid?

 

I was wondering the same thing. I just heard a Japanese nuclear engineer on NHK say that it is possible for either the fuel in the reactor or the spent fuel pool to go critical if it melts and settles into a unfavorable configuration. The reactor, he said, is designed to prevent it, but there is still the possibility.

 

Boron would help prevent a criticality accident because it has a large neutron cross section. Wiki has a bit about it:

 

Criticality accident prevention

 

Mismanagement or control rod failure was often the cause or aggravating factor for nuclear accidents, including the SL-1 explosion and the Chernobyl disaster.

 

Homogeneous neutron absorbers have often been used to manage criticality accidents which involve aqueous solutions of fissile metals, in several such accidents either borax (sodium borate) or a cadmium compound has been added to the system. The cadmium can be added as a metal to nitric acid solutions of fissile material, the corrosion of the cadmium in the acid will then generate cadmium nitrate in situ.

 

In carbon dioxide-cooled reactors such as the AGR, if the solid control rods were to fail to arrest the nuclear reaction nitrogen gas can be injected into the primary coolant cycle. This is because nitrogen has a larger absorption cross-section for neutrons than carbon or oxygen, hence the core would then become less reactive.

 

As the neutron energy increases the neutron cross section of most isotopes decreases. The boron isotope 10B is responsible for the majority of the neutron absorption. Boron containing materials can be used as neutron shields to reduce the activation of objects close to a reactor core.

 

Control rod--Criticality accident prevention

 

And here is a quote from 2007 that hopefully isn't foreshadowing:

 

As compared to typical nuclear power plant accidents, an SFP accident is slow in its evolution. A loss of cooling situation could take days to evaporate the pool water and hours to heat-up to the point of burning. However, events such as a catastrophic earthquake or intentional sabotage can be very quick in evolution. Should water supply be resumed following such events, the consequence can be mitigated. But if fresh water rather than the required borated water is used, either by administrative error or intentional sabotage, reduction of pool boron concentration may cause a return to criticality. Another consideration is that when water level reaches 3 feet above the top of the fuel, the radiation level may become high enough to prohibit human access.

 

http://www.microsimtech.com/sfp/

 

Scary stuff.

 

http://en.wikipedia.org/wiki/Prompt_critical

 

~modest

[modest]

This is not good. I also read a report earlier tonight about spiking radiation levels in Tokyo.

 

The Japanese government on Tuesday told workers fighting the meltdown to evacuate after radiation levels skyrocketed at the Fukushima Daiichi plant. The workers were the last defense against a serious meltdown.

 

“All the workers there have suspended their operations,” Japan’s Chief Cabinet Secretary Yukio Edano told reporters at a televised news conference. “We have urged them to evacuate, and they have.” The news comes after the government raised the limits on the amount of radiation to which each worker can be exposed, to 250 millisieverts from 100 misieverts, five times the maximum exposure permitted for nuclear power plant workers in the United States.

 

The change in policy means workers had the opportunity to remain on site longer, helping fight a potential meltdown.

 

 

http://politicallyil....php/lpnh/2472/

 

Again, hopefully not foreshadowing

 

A story on Chernobyl from 2006:

 

On the roof of the turbine hall, both gamma and neutron radiation was being emitted by the lumps of uranium fuel and graphite at a rate of 20,000 roentgen an hour; around the core, levels reached 30,000 roentgen an hour: here, a man would absorb a fatal dose in just 48 seconds. It was a full hour before Pravik and his men, dizzy and vomiting, were relieved and rushed away by ambulance. When they died two weeks later in Hospital No 6, Zakharov heard that the radiation had been so intense the colour of Vladimir Pravik's eyes had turned from brown to blue; Nikolai Titenok sustained such severe internal radiation burns there were blisters on his heart. Their bodies were so radioactive they were buried in coffins made of lead, the lids welded shut.

 

Anatoli Zakharov remained on duty at the power station until 2pm, and then cycled home. He drank three litres of apple juice, and went to bed. Shortly afterwards, he was hospitalised in Kiev, where he remained for two months; they told him that he'd absorbed 300REM of radiation. 'That's what they wrote down. But only God really knows what my dose was.' In 1986, he was awarded the Order of the Red Star for bravery; in 1992, he was declared a total invalid. Now, he says the men from Fire Station No 2 never doubted the risks they were taking.

 

'Of course we knew!' he laughs. 'If we'd followed regulations, we would never have gone near the reactor. But it was a moral obligation - our duty. We were like kamikaze.'

 

http://www.guardian.co.uk/world/2006/mar/26/nuclear.russia

 

I hate to say it, but sending a few firefighters into reactor building 4 in hopes that they could get to the spent fuel pool would hopefully avert a huge disaster, but who could ask someone to do that? It's awful to contemplate.

 

~modest

[freeztar]

I hate to say it, but sending a few firefighters into reactor building 4 in hopes that they could get to the spent fuel pool would hopefully avert a huge disaster, but who could ask someone to do that? It's awful to contemplate.

 

~modest

 

Where's Spock when you need him?

 

Today has had some good and bad news. Unfortunately, the rating got raised today from 4 to 5 (out of 7...details here).

In good news, they have finally run power to the plants. Now it's a mad dash to get the pumps working and try to contain the radioactivity. Godspeed Japanese engineers and workers!