IAEA Briefing on Fukushima Nuclear Accident (24 March 2011, 22.30 UTC)

[OKIsItJustMe]

http://www.iaea.org/newscenter/news/tsunamiupdate01.html

Fukushima Nuclear Accident Update Log

Updates of 24 March 2011

Staff Report

IAEA Briefing on Fukushima Nuclear Accident (24 March 2011, 22.30 UTC)

On Thursday, 24 March 2011, Graham Andrew, Special Adviser to the IAEA Director General on Scientific and Technical Affairs, briefed Member States on the current status of nuclear safety in Japan. His opening remarks, which he delivered at 15:30 UTC at the IAEA headquarters in Vienna, are provided below:

Current Situation

As far as the reactors at the Fukushima Daiichi site are concerned, there is some good news to report from the last 24 hours, although the overall situation is still very serious.

With AC power connected, instrumentation continues to be recovered in Units 1, 2 and 4. Workers returned after being evacuated from Units 3 and 4 on March 23, following confirmation that black smoke emissions from Unit 3 had ceased.

Reactor pressure is increasing in Unit 1, pressure readings are unreliable in Unit 2, and stable in Unit 3 as water continues to be injected through their feed-water pipes. The temperature at the feed-water nozzle of the Reactor Pressure Vessel (RPV) is decreasing at Units 1 (243 ºC) and 3 (about 185 ºC), and stable at Unit 2 (about 102 ºC).

Units 5 and 6 are still under cold shutdown, they are undergoing maintenance using off-site AC power and existing plant equipment.

Dose rates in the containment vessels and suppression chambers of Units 1 and 2 have decreased slightly.

Radiation Monitoring

The IAEA radiation monitoring team made additional measurements at distances from 21 to 73 km from the Fukushima nuclear power plant. At distances between 34 and 73 km, in a westerly direction from the site, the dose rate ranged from 0.6 to 6.9 microsievert per hour. At the same locations, results of beta-gamma contamination measurements ranged from 0.04 to 0.4 Megabecquerel per square metre.

At distances between 30 and 32 kilometers from the Fukushima Nuclear Power Plant, in a north westerly direction from the site, dose rates between 16 and 59 microsievert per hour were measured. At these locations, the results of beta-gamma contamination measurements ranged from 3.8 to 4.9 Megabecquerel per square metre. At a location of 21 km from the Fukushima site, where a dose rate of 115 microsieverts per hour was measured, the beta-gamma contamination level could not be determined.

The second IAEA monitoring team has started their work today in Fukushima and Tokyo. Measurements will be taken to determine more precisely the actual radionuclides that have been deposited.

On-site monitoring by the Japanese authorities at the Daiichi NPP produced new data on March 23 for radionuclide concentrations in the air from samples collected between 19 and 23 March. Of the six radionuclides monitored, only iodine-131 was found to be in excess of the limits set by Japan. Overall, the dose rates reported on the site have decreased from 1930 to 210 microsievert per hour between 21 to 23 March.

There continues to be considerable daily variation in the deposition of iodine-131 and caesium-137 reported in 10 Prefectures. Recent rainfall and the resulting wet deposition may help explain the increased deposition in Tokyo. As measured by the Japanese authorities for the Shinjuku district of Tokyo, iodine-131 deposition increased by 36,000 Becquerel per square metre from 22 to 23 March, and caesium-137 deposition by 340 Becquerel per square metre.

Monitoring of the marine environment by ships of the Japanese Ministry of Education, Culture, Sport, Science and Technology has now begun. Seawater and air samples were collected on 23 March in coastal waters, at distances of about 30 km off-shore. Dose rate measurements were also taken. Results from 24 March indicate surface seawater concentrations at eight locations ranging from 24.9 to 76.8 Becquerel per litre for iodine-131, and 11.2 to 24.1 Becquerel per litre for caesium-137. Radionuclide concentrations in dust in the air above the sea were also measured. The results are being assessed by experts from the IAEA's Marine Environment Laboratory.

New data provided by the Japanese authorities has been made available concerning radionuclide concentrations in foodstuffs, milk and drinking water. Sampling has been most thorough and extensive in the Fukushima and Ibaraki Prefectures. Of the 11 varieties of vegetables sampled from 18 to 22 March iodine-131 and caesium-137 levels exceed limits set for food and drink ingestion. Permissible levels of iodine-131 and caesium-137 (one sample) were also exceeded in nearly all of the milk samples taken in Fukushima and Ibaraki Prefectures between 16 to 21 March. In addition, permissible levels of iodine-131 were exceeded in drinking water samples taken in the Fukushima and Ibaraki Prefectures and in Tokyo from 17 to 23 March. Further sampling and analysis will be carried out in the days ahead by the Japanese authorities. A joint FAO/IAEA mission to Japan will be undertaken to provide advice and assistance on sampling strategies, analysis and the interpretation of data collected by the Japanese authorities related to food contamination.

In summary, radioactivity in the environment, foodstuffs and water is moving more to the forefront, as some technical concerns related to the status of the reactors at the Fukushima Daiichi site appear to be slightly less acute in some respects. However, the overall situation on the Fukishima site remains very serious.

Fukushima Daiichi Nuclear Accident Update (24 March, 17:30 UTC)

Japanese Seawater Samples Show Signs of Radioactive Materials

Japanese authorities today provided the IAEA with data on seawater samples they collected on 22 and 23 March, after detecting iodine and cesium in the water near the Fukushima Daiichi nuclear power plant. (http://www.iaea.org/newscenter/news/2011/fukushima220311.html#seawater">See earlier update.)

A vessel from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) collected water samples at several points 30 kilometres from the coastline and found measurable concentrations of iodine-131 and cesium-137. The iodine concentrations were at or above Japanese regulatory limits, and the cesium levels were well below those limits.

The IAEA's Marine Environmental Laboratory in Monaco has received the data for review.

Fukushima Daiichi Nuclear Accident Update (24 March 17:25 UTC)

Japanese Workers Treated for Radiation Exposure

Japanese authorities today reported that three workers at the Fukushima Daiichi nuclear power plant were exposed to elevated levels of radiation. The three were working in the turbine building of reactor Unit 3 and have received a radiation dose in the range of 170-180 millisieverts.

Two of the workers have been hospitalized for treatment of severely contaminated feet, which may have suffered radiation burns. The workers had been working for about three hours in contact with contaminated water.

The IAEA is seeking additional information.

Fukushima Daiichi Nuclear Accident Update (24 March, 15:00 UTC)

The IAEA today released updated summary slides on reactor conditions at Fukushima Daiichi nuclear power plant.

→ http://www.slideshare.net/iaea/table-summary-of-reactor-unit-status-at-of-24-march0600-utc">View Table

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[FBaggins]

1. Could be evidence that #2's containment is compromised.

Can't tell for sure without a pressure reading, but that temperature looks suspicious.

Was #2 the unit that workers were injured in stepping into water?

[OKIsItJustMe]

2. Re: Was #2 the unit that workers were injured in stepping into water?

No, that was unit #3.

[Statistical]

4. Why is it suspicious?

It has been almost two weeks since fission has halted. Heat output of reactor will only decline with nuclear decay. 5 & 6 are in cold shutdown (<100 deg @ 1 atm of pressure).

Had the reactors not overheated to begin with (retaining days worth of heat) all 6 would be in cold shutdown a long time ago.

[FBaggins]

5. The reactor is identical to the one sitting next to it

virtually so anyway. They wouldn't have activity levels drop off at dramatically different rates. They're both still putting off plenty of heat.

I haven't thought this through entirely yet, but when the only option you have for cooling is to inject water and (eventually) let off steam, you can't get down to 102 for long without also being at 1 ATM. One of the things I speculated on when the tors burst was that, while it would release lots more radiation, it would be easier to cool. You don't have to "inject" water (force it in against high pressure), and steam would release on it's own (and not through a filter).

I think the result would be water temperatures that stayed right at the 1ATM boiling point, so when I see that I assume that I was right. "Activity levels are way down" is true, but it's equally true for the reactor sitting right next to it. They don't have to be at the same temperature and pressure because they didn't have identical releases of steam... but I don't see how they could be this far apart.

I'm open to other possibilities. I just haven't thought of one that fits.


5 & 6 are in cold shutdown (<100 deg @ 1 atm of pressure).

And working pumps got them down to that level before the event occurred. They don't add to the discussion.

[Statistical]

6. Well your assumption and conclusion are wrong.

"One of the things I speculated on when the tors burst was that, while it would release lots more radiation, it would be easier to cool. "

Actually the reverse is true. Lower pressure = lower boiling point thus it takes less energy to boil a given unit of water. Less energy to boil means less energy is removed from the core. Pumping water into a core at 20 atmospheres of pressure removes nearly 3x the thermal energy (heat) compared to pumping the same amount of water into a core at 1 atm.

"I think the result would be water temperatures that stayed right at the 1ATM boiling point, so when I see that I assume that I was right. "Activity levels are way down" is true, but it's equally true for the reactor sitting right next to it. They don't have to be at the same temperature and pressure because they didn't have identical releases of steam... but I don't see how they could be this far apart."

Well first the 108 deg isn't water temp it is core temp. If you pumped a small amount of water into core at only 1 ATM eventually there would be no water (flashed into steam) and the core temp would be far higher than 108 deg.

As for the temp delta, #3 was without water for a longer period of time. The nuclear decay was roughly the same so the energy didn't disappear. A small amount was removed via conduction to the RPV but that isn't enough. So more thermal energy built up inside the core. Temperature of a system is simply the delta between energy in and energy out.

You can think of the core (or any material) as a thermal battery. The melting point of nuclear fuel is 2500 deg and the core weighs between 70 to 200 tons depending on configuration. That is a massive thermal battery. Even without fully melting the fuel it can "store" as huge amount of thermal energy. It is going to take more "energy out" (via water boiling to steam) to remove that stored energy (plus the new energy continually added via nuclear decay).

[FBaggins]

7. I don't see anything in what you're saying here that convinces me of that.

Actually the reverse is true. Lower pressure = lower boiling point thus it takes less energy to boil a given unit of water. Less energy to boil means less energy is removed from the core. Pumping 100,000 gallons of water into a core at 20 atmospheres of pressure removes nearly 10x the thermal energy (heat) than pumping 1000,000 gallons of water into a core at 1 atm.

Yep... but what you're missing is that there's a limit to how much water you can inject to a sealed system. You're playing a game with temperature and pressure until you have to release some steam. You can't just keep adding water.

In an OPEN system you just keep pouring water on it and the steam keeps flowing away. Each gallon carries away less thermal energy, but there are far more gallons available to do the work.

Well first the 108 deg isn't water temp it is core temp. If you pumped a small amount of water into core at only 1 ATM eventually there would be no water (flashed into steam) and the core temp would be far higher than 108 deg.

Yep... it would flash to steam and then the steam would flow out of the system and new cold water would replace it. But how do you get the temperature DOWN to the boiling point of water in a sealed environment?

Keep in mind that it isn't possible for the core to be BELOW the boiling point of water because there are no pumps taking hot water out and cooling it. If this is a sealed system and a pressure well above 1 ATM... how would the temperature be below boiling? The activity level of the core hasn't fallen that far. Heck, the activity level of the spent fuel pools is higher than that.


Temperature of a system is simply the delta between energy in and energy out. That's true, but there have been days since then. We're talking about a system that is (reasonably) under control.

[Statistical]

8. There are the same gallons available for work.

Under pressure
1) close valbes
2) inject water (say 100,000 gallons)
3) while that injection is occuring (over course of hours
a) water is turning into steam
b) as a result pressure is rising and helping cooling
5) when pressure gets too high release valves and vent steam
Repeat

No pressure
1) pump in water.
2) boils at much lower temp and amount of thermal energy removed is much less

Unpressurized system may be simpler but it is never more efficient. It can never removes as much heat as a pressurized system. It also has the advantages of a) you can't superheat the steam, b) you have no control over the timing of steam releases.

"In an OPEN system you just keep pouring water on it and the steam keeps flowing away. Each gallon carries away less thermal energy, but there are far more gallons available to do the work."
No there aren't far more gallons. Gallons are still limited to pump output. With boiling point of 100 deg C you will never cool the reactor. This is why keeping reactor pressurized is standard proceedure in a loss of coolant accident. You need to avoid pressure getting too high but you never run the reactor open. I mean they could run all 6 reactors open if they wanted. Just open steam release valves and never close them. The fact that they don't should indicate that it would be horribly inefficient to do so.

[FBaggins]

9. Why are the "same gallons" available?

The difference here isn't just that one is less efficient at heat transfer.

It's that in one case you are limiting your release of heat into the environment (because it comes with radioactive steam and some nasty friends)... in the other case you're constantly releasing steam. You don't have a choice. It may be bubbling through a pool of water in the torus, but it's just flowing out from there.

With boiling point of 100 deg C you will never cool the reactor.

Well... the boiling point in this case would be higher since it's saturated with salt (pretty darn close to the temperature recorded in fact), but that's beside the point. If what you're saying were true, it would be impossible to cool the core by dropping it in a cool river with the water flowing past.

No pressure
1) pump in water.
2) boils at much lower temp and amount of thermal energy removed is much less


3) water becomes steam and leaves the system
4) pump in more water and repeat. or just keep pumping water continuously.


I think the other point you're missing is that you're concentrating on the relative number of calories involved in steam creation at various pressures... but ignoring the fact that the fresh water must first be heated from, say, 55 degrees to boiling. Very little fresh water in the closes system... unlimited fresh water in the open one.

[Statistical]

10. Once again same amount of water in both systems.

They pump water into the pressurized reactor until pressure in reactor is higher than what pump can handle. At that point you stop, release steam, pressure drops below what the pump can handle, you close valve and continue to pump as much as you can.

There is no (minimal) reduction in the amount of cooling water used just a 300% increase the efficiency of the water. Trying to cool an unpressurized reactor is stupid. It serves no purpose. By pressurizing the reactor you transfer 3x the amount of energy with the same amount of water.

Your claim is that reactor #2 is broken thus it is unpressurized so it has superior cooling. Why not simply unpressurize all the reactors? If it is superior why not just depressurize all the reactors? You keep going back to this unsupported conclusion that an open system would result in power water flow. The limit on water flow is the flow rate of the pumps. Period. They can control the amount of pressure via venting so they can choose the optimal balance between pressure and water flow.

So
Open system - limit of water = pump capability
Closed system - limit of water = pump capability

Open system - horrible thermal efficiency
Closed Sysrem - superior thermal efficiency

Ever reactor in Japan was cooled by maintaining pressure in the RPV to make cooling water more effective. They could make the pressure in every reactor 1 ATM but they didn't. If as you falsely claim it is superior then why didn't they? Oh yeah because it would serve absolutely no purpose other than to REDUCE the amount of cooling with the added bonus of making steam releases uncontrollable.

Less cooling and less control now that is a winning combination.

[FBaggins]

11. Why?

They pump water into the pressurized reactor until pressure in reactor is higher than what pump can pump.

And if the pressure never rises because it isn't a closed system? They pump and pump and pump. There is no limit to the amount you can put in there because it's all flowing out when it turns to steam.

The reported radiation level in the water the exposed workers steped in ("3.9 million becquerels of radiation was detected from 1 cubic centimeter of water") sure implies that something more than steam releases through the normal filters.

I think it's steam released into the torus cooling to water and overflowing out of whatever breach caused the problem in the first place.

You keep reaching this unsupported conclusion that an open system would result in power water flow. The limit on water flow is the flow rate of the pumps. Period.

Sorry... that doesn't make sense. They have NOT been running the pumps continuously. They inject a given amount of water and wait for the temperature and pressure to grow. At this point they may only be injecting water every day or two. The pump's pressure limit is a limiting factor in one case, but not the number of gallons it can pump per day.

They could make the pressure in every reactor 1 ATM but they didn't.

Obviously they COULD, but it would involve unrestrained releases of radiation. So they don't WANT to (even if it would bring temperatures down faster - because the temperature isn't an issue at 150 or 200 or 250 degrees). In this case they might not have a choice.

[Statistical]

12. Either way it is the same amount of release yet they choose to keep reactor pressurized.

Option A)
leave stem vent open. Water in -> Steam out. No rise in pressure. Inefficient Cooling

Option B)
Periodically open/close steam vent. Water in -> Steam builds (rise in pressure and improved cooling) -> Vent Steam.

In option B you are essentially storing the steam in RPV before releasing it in batches. Either way there is the going to be the same activity release.

"Sorry... that doesn't make sense. They have NOT been running the pumps continuously. "
Yes they have. Where do you get this idea from? It takes a massive amount of flow to cool a reactor. The pumps are running constantly. The spraying ops are more manpower intensive so they do them for batches of time. The injection pumps have been running nonstop.


"The pump's pressure limit is a limiting factor in one case, but not the number of gallons it can pump per day."
Pressure is a scale not on or off. RPV can handle up to 75 atmospheres of pressure. They can by controlling time between venting choose a pressure anywhere between 1atm and 75atm. They also have data showing flow rate at various pressures, the max pressure of the pumps and cooling efficiency at each level of pressure. They can optimize cooling to maximize energy flow.

Even IF the pumps weren't run continually you can still maximize cooling. You simply keep the pressure in optimal range. High enough to improve cooling and low enough to not overload the pumps.

Energy out = efficiency * water flow.
In open system you have no control over efficiency and all pumps have finite flow capacity.

In closed system you have two variables you can use to mazimize energy flow. The relationship between the variables is no linear. i.e you could chose 30% higher pressure which results in 50% higher efficiency but only 15% less flow. MAXIMIZING COOLING PERFORMANCE.

Nobody tries to cool a unpressurized reactor. You don't depressurize a reactor by choice until it is in cold shutdown.

[FBaggins]

14. Sigh... I'll leave it for now with two questions. We'll know soon enough either way.

Nobody tries to cool a unpressurized reactor. You don't depressurize a reactor by choice until it is in cold shutdown.

1) Who said they had a choice?

2) Doesn't my theory better explain the highly readioactive water under the plant? The levels don't fit overflow from the fuel pools. Do we need to speculate about a different route of exit from the core?

[applegrove]

3. I sent this link to my brother in japan the other day and he is using it. Thanks for posting.

[wtmusic]

13. K&R. nt