Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[tsutsuji]

http://www.tepco.co.jp/tepconews/library/movie-01j.html (last tab) Unit 4 underwater video
http://tepco.webcdn.stream.ne.jp/www11/tepco/download/120210_02j.zip (download)
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_120210_03-j.pdf Diagram

http://www3.nhk.or.jp/news/genpatsu-fukushima/20120210/index.html The visibility was 5 metre. No fuel damage or deformation was observed.

 

[zapperzero]

http://mdn.mainichi.jp/mdnnews/business/news/20120208p2g00m0bu116000c.html "Power firms to install vent facilities in all domestic nuclear plants" (...) "will have a filtering function to remove radioactive substances from vapor before releasing"

A sudden outbreak of common sense, I think it's called.

 

[etudiant]

A sudden outbreak of common sense, I think it's called.

I thought all these plants already have hardened vents.
Are we talking about improved vent actuation methods, that work even if power is lost, or are we talking about filtered emergency venting such as is in place in some Finnish reactors that rmattila has given us helpful insight on.

 

[tsutsuji]

Cabinet investigation committee:

http://icanps.go.jp/eng/120125ShiryouEng.pdf Investigation items for the Final Report

The international experts are invited to participate in a tour to the Fukushima Daiichi NPS on February 23 (Thursday). Please be aware that we will not make any press arrangement for the tour. The meetings with the Investigation Committee will be held on the 24th and 25th of February (Friday and Saturday) at the Keio Plaza Hotel in Shinjuku. The meetings, conducted with simultaneous interpretation, will be open to the press. After the session on February 25 (Saturday), the Investigation Committee and international experts will attend a press conference.
http://icanps.go.jp/eng/120125KaikennaiyouEng.pdf

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20120211/index.html Unit 2 Thermometer:

8 February : 64.1°C
10 February 09:00 : 71.1°C
11 February 03:00 : 71.3°C
11 February 09:00 : 71.3°C

The other two thermometers have further dropped to around 35°C. Tepco said "we are watching the situation. If the temperature rises further than this, we will raise the injection rate".

http://www.nikkei.com/news/category...09180EAE2E2E2;at=DGXZZO0195583008122009000000 :

11 February 17:00 : 69.5°C
11 February 18:00 : 71.2°C

The injection rate was raised by 1 m³/hour to 14.6 m³/hour at 22:45 on 11 February.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20120212/index.html :

11 February 23:00 : 74.9°C
12 February 00:00 : 71.1°C
12 February 01:00 : 69.5°C
12 February 02:00 : 71.9°C

 

[swl]

4. A single sensor data set doesn't make a trend.

I find your interpretation of statistics enlightening.

In other news, TEPCO has increased the reactor-2 cooling water flow to the highest rate since the earthquake. Could they have done this in response to the recent 75 degree indication? And since they increased the flow rate at 15 minutes prior to the public hourly data point, I wonder what the TC indicated prior to the flow increase.

 

[nelle]

I am not surprised by this news.
I have been graphing the hourly temperature data since they released it.

You can see the data here (although it hasn't yet been updated past 4pm on Feb 11): http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/2u_temp2-e.pdf
and the drawing with the location of the 3 temp sensors in question here: http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/2u_temp-keisoku-e.pdf

If this sensor is functioning, and TEPCO seems to think it is, considering the volumes of cooling water they are injecting.

Here are my two charts
Feb 1 thru Feb 10 and Feb 4 thru Feb 11 at 4pm

 

[elektrownik]

2/12 10:00 78.3

 

[tsutsuji]

In December, Tepco released a study in which they calculated an estimate of the proportion of uncovered fuel in each unit. I am curious to know how this estimate is changing for unit 2 with the present temperature values.

http://www.yomiuri.co.jp/science/news/20120212-OYT1T00271.htm?from=main2&from=os4 :

12 February 14:20 82°C

At 15:30 Tepco increased the injection rate by 3 tons/hour to 17.4 tons/hour. No xenon detected.

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_120212_02-j.pdf I can't find the 74.9°C value for 11 February 23:00 here. Instead they wrote "2/11 23:00 71.2".

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_120212_03-j.pdf Here they wrote "2/11 23:00 74.9"

http://www.ustream.tv/channel/%E3%83%95%E3%83%AA%E3%83%BC%E3%82%B8%E3%83%A3%E3%83%BC%E3%83%8A%E3%83%AA%E3%82%B9%E3%83%88-%E5%B2%A9%E4%B8%8A%E5%AE%89%E8%BA%AB%E3%81%AB%E3%82%88%E3%82%8Bustream Video of Tepco's press conference on 12 February afternoon. Junichi Matsumoto: "The probability of a temperature indication failure is high".

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_120212_05-j.pdf (temperature plot) The amplitude of vibration/instability has started becoming greater after 12:00 noon on 12 February.

 

[elektrownik]

"The temperature at the No.2 reactor of the Fukushima Daiichi nuclear power plant keeps rising even after the injection of more cooling water on Saturday night. [...]
TEPCO is set to dump in boric acid to prevent any nuclear criticality later on Sunday and increase the volume of cooling water by 3 tons per hour.

Under new guidelines, the company must keep reactor temperatures at 80 degrees or below, given thermometers’ margin of error of up to 20 degrees."
http://www3.nhk.or.jp/daily/english/society.html

 

[elektrownik]

Reactor 2 90C now

 

[Shinjukusam]

Reactor 2 90C now

Where are you getting that from? NHK is only reporting the highest being 82 at 14:20 Japan time.

 

[elektrownik]

Where are you getting that from? NHK is only reporting the highest being 82 at 14:20 Japan time.

NISA press conference, it was live some time ago on ustream

 

[Shinjukusam]

NISA press conference, it was live some time ago on ustream

Much obliged.

 

[Yamanote]

This can also be seen already in the post from tsutsuji-san:

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_120212_05-j.pdf (temperature plot) The amplitude of vibration/instability has started becoming greater after 12:00 noon on 12 February.

 

[Yamanote]

Some further information from Tepco on this issue:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120212_07-e.pdf

 

[duccio]

The problems arise from the Mark I containment, which is certainly non-optimal for the scenario that evolved at Fukushima. The accident was 'beyond design basis' ... the plant staff had so little time to respond, and the response was muted with complete loss of both off-site AND on-site power

Astronuc, you got my point. More modern designs are better, but BWR + Mark I is still the most common. The actual best practice is to contain the core as much as possible, which works fine when there's nothing else to do as it limits the damages. But I don't remember on which report, I read that one hour after the tsunami there were already 400 people on the plant, including operators, firefighters, contractors... that's an enourmous amount of very flexible power.

If I understand it correctly, after SCRAM, as long as the fuel is submerged under water AND the cladding is intact, there's no major release of radiation, and it's still possible for humans to go inside of the reactor building (and around it).

Right on top of the reactor there's a pool with at least 700 tonnes of water (10 meter diameter times 10 meter of depth, without considering the spent fuel pool side which must remain filled, and the tools pool which on the contrary could also be used for cooling).

Once it is clear that there's no electrical power but there's enough "man power", the RPV could be brought to outside pressure, and then the top plug of PCV and RPV could be pulled so that the pool water would flood the fuel, heat up and evaporate naturally at 100 degrees. 700+ tonnes of water, along with the initial venting of steam, would be enough for a few hours of flooded and cooled fuel (but that's just my guess, I didn't do the math).

Human force would just need to fill the pool with water, but with freedom to go inside and outside the reactor building, that wouldn't be an impossible task.

Your idea is a core element in the design of the newer AP1000 reactors just approved by the US NRC.

(so, it wasn't really "my idea", I shouldn't claim fathership of it ;)

The problem was that the reactors at Fukushima were difficult to depressurize because the valves needed power to be opened. So a bad accident was made much worse.

I believe they are already required to fix it as soon as possible, along with hardened venting pipes. As I do believe that there're ways to make earthquake/tsunami/power-loss resisting valves, and cranes to lift the cover of the reactor (or any other action required by emergency response).

One factor that made me think of this, is that fire hoses, small portable diesel pumps, and even buckets, are really common and cheap, so it should be economically viable for operators to store many of them here and there on the plant. Much cheaper than many other changes they are now forced to do to the plants.

I thought you might be interested in this tidbit from the Washington Post...

Thanks Jim, that material was tremendous, it took me two days to read all the emails but it was worth it. Garwin had to think about it after the accident happened and the core already melted, and as he noted, one of the biggest challenge was the radiation level inside of the building and the debris scattered around (that's why the idea of the charges)

 

[nikkkom]

Once it is clear that there's no electrical power but there's enough "man power", the RPV could be brought to outside pressure, and then the top plug of PCV and RPV could be pulled so that the pool water would flood the fuel

Is this really possible to do w/o electricity? Look at the bolts which keep reactor cover closed:

http://science.soup.io/post/115911576/Nuclear-reactor-core-and-Cherenkov-radiation

They are numerous, and huge. I have hard time imagining how they can be quickly unbolted by hand.

 

[Rive]

They are numerous, and huge. I have hard time imagining how they can be quickly unbolted by hand.

With preinstalled directed explosives it's easy, fast. The steam separator would protect the fuel from the worst of the blast.

However I would be more happy with safety equipments which has more moderate side effects if they goes off accidentally. If the core is already at ambient pressure then any fire truck would be able to refill the RPV without so much risks involved.

Ps.: all this is matter of spare pneumatics control- and feedwater line connections outside the main building. For example. And then no explosives involved.

 

[Yamanote]

I presume that some solutions for proper venting and passive cooling are already available, but at Fukuichi all systems relied on electricity. So it seems that in all considerations a total loss of electric power was never taken into account (or ignored for some reason).

Solutions are there, at least on paper, but they are either not built-in in (old?) plants, or doesn't work under real emergency conditions. So every accident means a new learning cycle (hopefully?).

In the past the containment was designed to contain the radioactive stuff inside under any circumstances, there wasn't even a vent. Now we have seen that this is not an easy job to do, especially when Hydrogen from a core meltdown is involved. In particular cases it might be better or even necessary to release the gases (scrubbed please!) to effectively depressurize the containment and to enable water injection into the reactor core avoiding further damage.

 

[duccio]

I presume that some solutions for proper venting and passive cooling are already available, but at Fukuichi all systems relied on electricity. So it seems that in all considerations a total loss of electric power was never taken into account (or ignored for some reason).

Solutions are there, at least on paper, but they are either not built-in in (old?) plants, or doesn't work under real emergency conditions. So every accident means a new learning cycle (hopefully?).

Indeed. But the more we add, the more there is to mantain and to take into account in case of failure.

I'm not sure that those bolts could be unbolted by hand, or that putting explosive inside a reactor is a good idea (even if it is impressive the degree of control they can achieve on controlled explosions). On that point, maybe feedwater line with standard connections here and there could be a good solution, and maybe some feedwater line connecting the pool to the RPV as well, but there should also be a way for water to evaporate and for steam to go out.

However, I'm not really after a solution, I'm more after some reverse problem solving. Going from the "what should have been there to avoid the emergency" to the "what actually WAS available on the field, once a real emergency started, and how could have we used it better". We don't know what could fail next time, and it's extremely hard to predict and to prevent.

We know we had a heating core, pressure, hydrogen, a pool full of water, and a lot of man power. It was extremely hard for vehicles to get close to the plant because of the hearthquake and the tsunami, but somehow firetrucks managed to reach the plant. Everything else failed, sometimes in unpredictable ways (like DC control panels flooded).

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20120213/index.html :

13 February 10:00 91.2°C

The other two thermometers at the same height indicate 33°C. The other three thermometers located 150 cm lower are in a declining trend. This is giving strength to Tepco's view that the thermometer is broken. But there is no conclusive evidence that it is broken. Tepco maintains the same injection rate while carefully watching the situation.

 

[etudiant]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20120213/index.html :

13 February 10:00 91.2°C

The other two thermometers at the same height indicate 33°C. The other three thermometers located 150 cm lower are in a declining trend. This is giving strength to Tepco's view that the thermometer is broken. But there is no conclusive evidence that it is broken. Tepco maintains the same injection rate while carefully watching the situation.

Is it not equally probable that the sensor is simple near a hot spot, an area of stagnating water flow where fuel may also have accumulated? Given that the interior of the reactor has been seriously damaged, some such development seems more than likely, imho.
TEPCO claims the residual decay heat from the fuel in the reactor is down to about 0.6 megawatts. That will boil a lot of water unless there is really efficient heat transfer, which may be absent given the debris within the trashed reactor.

 

[Shinjukusam]

Is it not equally probable that the sensor is simple near a hot spot, an area of stagnating water flow where fuel may also have accumulated? Given that the interior of the reactor has been seriously damaged, some such development seems more than likely, imho.
TEPCO claims the residual decay heat from the fuel in the reactor is down to about 0.6 megawatts. That will boil a lot of water unless there is really efficient heat transfer, which may be absent given the debris within the trashed reactor.

Yeah, is there a simple to understand diagram showing where on the bottom of the vessel this sensor is located?

might be nice to have a general idea of what is above/beside it.

 

[nikkkom]

So it seems that in all considerations a total loss of electric power was never taken into account (or ignored for some reason).

This is not "seems", it's a fact. TEPCO admitted as much.

Solutions are there, at least on paper, but they are either not built-in in (old?) plants, or doesn't work under real emergency conditions. So every accident means a new learning cycle (hopefully?).

The problem is, TEPCO (and all other operators) was not ignorant about the consequences of the meltdown. They just, at some level(s) of managerial maze, decided to take the risk and not spend money on additional protection.

IOW: we know how to make reactors safer. We also have "lessons learned" from past accidents.
What we do not know is how to make plant owners stop cutting corners and lying to us (and probably to themselves) that their plants are safe.
We do not know how to make them analyze "lessons learned" from past accidents. 25 years after Chernobyl and workers again have no adequate dosimeters? How stupid is that?

 

[elektrownik]

Unit 2 sensor is damaged because it is 250+ C now, and it is impossible

 

[nikkkom]

Is it not equally probable that the sensor is simple near a hot spot, an area of stagnating water flow where fuel may also have accumulated?

The temperature difference of about 30 degrees in two spots of a steamy hot metal enclosure? That's unlikely.

 

[Shinjukusam]

Unit 2 sensor is damaged because it is 250+ C now, and it is impossible

If you're going to fail, fail big.

Where was that announced?

 

[elektrownik]

If you're going to fail, fail big.

Where was that announced?

Here: http://www.tepco.co.jp/nu/fukushima-np/f1/images/2u_temp2.pdf

 

[Shinjukusam]

Here: http://www.tepco.co.jp/nu/fukushima-np/f1/images/2u_temp2.pdf

Got it. Either that's a failure or something really bad just happened. Going by the decrease in every other sensor, I sure hope it's the former.

 

[Rive]

Unit 2 sensor is damaged because it is 250+ C now, and it is impossible

I don't think so. We know nothing about the position of the fuel debris inside the RPV. Some pars of it can be still melted (or just hot).

 

[zapperzero]

Unit 2 sensor is damaged because it is 250+ C now, and it is impossible

Ok, let's take this ball and run with it. What happened? Is a wire or some sort of contact corroding rapidly? That's what it sounds like. Why is this happening? Will it happen to the other two sensors and if so, what then?

 

[elektrownik]

Ok, let's take this ball and run with it. What happened? Is a wire or some sort of contact corroding rapidly? That's what it sounds like. Why is this happening? Will it happen to the other two sensors and if so, what then?

Here is explanation:

In the press conference of 2/13 PM, Tepco announced they lost the heating gauge of reactor 2.
Reactor 2 marked 93.7℃ at 2/13/2012 11:00, but it went to 276.4℃ at 17:00.
Tepco is asserting the heating gauge is broken.

The heating gauge is thermocouple, Tepco tried to check resistance but immediately after the test, the heating gauge indicating 276.4℃. The resistance was about 500Ω. Tepco is asserting the wire is nearly broken.

It is also good to look at this plot: http://www.tepco.co.jp/nu/fukushima-np/f1/images/12021312_temp_data_2u-j.pdf
It is interesting that another sensor plot which was damaged is almost the same like this sensor which is damaged now. Around 2/13 date.

 

[Astronuc]

AFP - Japan's Fukushima [Unit 2] reactor may be reheating: operator
http://news.yahoo.com/japans-fukushima-reactor-may-reheating-operator-234153498.html

Tokyo Electric Power said one of three thermometers on the number-two reactor at the Fukushima Daiichi nuclear plant indicated gradual heating this month and reached 82 degrees Celsius (179.6 degrees Fahrenheit) Sunday.

The temperature was above the 80-degree safety standard newly employed by Japan's nuclear safety authority, prompting the utility to publicise the reading and notify public agencies.

But it remains below the 100 degree level that the government says is needed to maintain the safe state of "cold shutdown".

The utility said it will check the accuracy of the thermometer in question, as two others on the same reactor have been measuring its temperature at around 35 degrees.

As a precaution, TEPCO has increased the volume of water and boric acid solution being poured on the reactor to cool it down.

In a steady-state heat transfer situation, there is a balance between the heat generated (source) and heat transfer (removal). If the temperature in the system is rising, it either means that the heat source is increasing, or the transfer mechanism is reducing such that the heat arrival (at the location of temperature measurement) is greater than the heat leaving. This may happen due to a reduction in flow in the heat transfer method. It could also mean a fault in the thermometer.

 

[Borek]

I have not followed the situation for a long time, so I am not sure about details. What pressures are we talking about? Temperature shouldn't go above boiling point, 276℃ means boiling unless pressure is over 60 atm.