Japan: Map details radiation at N-plant site

Yomiuri Shimbun ^ | 04/26/11

[TigerLikesRooster]

Map details radiation at N-plant site

Tokyo Electric Power Co. has released to the public for the first time a map of its Fukushima No. 1 nuclear power plant that shows results of a survey of radiation levels at the site.

The map released Sunday shows high levels of radiation in different parts of the site, including 300 millisieverts per hour from debris near the No. 3 reactor, the outer building of which was damaged in a hydrogen explosion more than a month ago.

The map, which shows radiation levels at about 230 locations within the nuclear plant complex, indicates the dangers of working at the plant for long periods.

A TEPCO spokesperson said the information revealed by the map would not affect the timetable for stabilizing the reactors that was released by the firm this month.

[TigerLikesRooster]

P!

[meyer]

Looks like the debris around 3 is the biggun!

[justa-hairyape]

They supposedly have removed or buried the nasty debris around #3. So as of right now no known debris is emitting over 100 micro sieverts per hour. The water they are piping (called hose) from #2 to the filtration station supposedly has 1,000 micro sieverts of radiation in it at any point in time. According to the article. So we do not want that pipe or hose springing a leak.

[justa-hairyape]

Oops...replace micro....with milli

[meyer]

Yeah, that water in the basement of unit 2 is nasty stuff. My opinion, for what it's worth, is that the primary containment of unit 2 is cracked or breached, probably either a pipe or where something enters the containment structure from outside. The fracture is low enough in the containment that the water that they're flooding into the core of 2 is leaking out. But they can't know for sure until they get a visual, and they can't do that (even with a robot) until the basement is drained. Evidence is the highly radioactive water and the fact that 2 is at roughly atmospheric pressure. I think they've got the temperature of #2 under control, but they've got to find the leak and stop it.

Unit 1 is holding pressure, and they're pumping N2 in to dilute the H accumulating at the top of the primary containment sufficiently so that an explosion will not occur within. They could still vent it, but if they don't have to, then why do it. I think they've got #1 reactor under control, even though it is still above "cold shutdown".

Unit 3 is a bit of a mystery. Again, the reactor temperature is under control, though still not down to "cold shutdown" level. They're pumping water in, but as far as I know, the pressure within containment is still atmospheric meaning that there's possibly a leak above the water level (again, IMHO).

The spent fuel pools are still an issue, but I think they're now able to keep them cool at least. I don't know for certain, but I think they actually have a circulation system set up on unit 2's spent fuel pool. #4 seems to be the most troublesome, but considering that it has the newest and largest quantity of spent fuel, it should be. They're pumping a good deal of water in there every day, for a few hours. I'm sure that it's evaporating, since it's still quite warm, but I also wonder if there's a leak.

I notice that they've made significant advances in the off-site power, adding a higher-voltage source and connecting that into whatever switchgear they're using. I suspect that they're going to shoot for reduncance ASAP, but building new substations takes time. And I think that given the damage that the tsunami caused, they're doing a lot of rebuilding right now.

This has been a very interesting, almost captivating event. I look at it more from the position of the engineers and operators on-site though I have absolutely no experience in nuclear other than having to deal with nuclear plant operators on occasion (not nearly as user-friendly as coal-plant operators). I do, however, have a good deal of electrical experience in substations, coal-fired plants, and hydro plants. Nuclear adds a very significant dimension to the equation, and perhaps that is why I've been so interested in this event.

[justa-hairyape]

Agree with your assessments of #1 and #2.

.....Unit 3 is a bit of a mystery.

Yes there are some weird stories floating out there about #3. One is that the reactor blew up. Another is that a nuclear explosion of some kind happened in the pool. Don't think any of those are true, but that was one big hydrogen explosion. Certainly had to experience damage to its spent fuel pools.

.....#4 Spent Fuel Pools... but I also wonder if there is a leak.

Others are wondering also.

#Fukushima I Nuke Plant: Reactor 4 Spent Fuel Pool May Be Leaking

...I notice that they've made significant advances in the off-site power,

Read an article about them rewiring the power lines so that if they lose off-site power again they can get it from another source. They apparently have three separate sources each one run to a pair of reactors.

Rewiring starts at Fukushima Daiichi

....and perhaps that is why I've been so interested in this event.

There are more interesting aspects to this event then the general public will ever know. The Japanese PM was expecting a worse case scenario of losing eastern Japan and Tokyo the first couple of nights. And neither is out of the woods yet. Watching one of the Worlds most closed societies actually open up, is quite a site. Hopefully DC will be open up one day. DC's lies have gotten so bad that they routinely violate the laws of physics now.

And people who think better regulation could have avoided this problem, need to realize that the regulators in government will always have limited knowledge about the subject they are attempting to regulate. For example.

Govt was unaware of hydrogen explosion risk

[justa-hairyape]

Even Gundersen has a theory on the #3 explosion. His video however does have a very nice comparison sequence showing the difference between #1 and #3 explosions. It is early on in this video.

Gundersen Postulates Unit 3 Explosion May Have Been Prompt Criticality in Fuel Pool

[meyer]

Read an article about them rewiring the power lines so that if they lose off-site power again they can get it from another source. They apparently have three separate sources each one run to a pair of reactors.

I noticed an interesting setup in the plant's transmission system as compared to the typical plant in the US. It appeared that the 6 generating units operated in pairs and didn't have a large, common switchyard. Instead, they seem to have one transmission line per generator, possibly switchable to the second line, although that is hard to tell since the stepup transformers seem to be under a roof. In contrast, at TVA's Browns Ferry nuclear plant, all 3 units generate through their respective step-up transformer to a common bus that feeds 5 500-kV transmission lines. Any one of those lines can provide off-site power to the plant, as can two 161 kV transmission lines that feed the plant's auxiliary loads from two different directions.

Govt was unaware of hydrogen explosion risk

Interesting. After TMI, the regulators in the US required BWR plants to add a hardened ventilation system to the reactors specifically to vent hydrogen gas that would occur if fuel rod cladding were to break down and react with water in the event of a 'loss-of-cooling' situation. The vents take the hydrogen gas/reactor gas OUT of the building, bypassing the internal upper areas of the outer "secondary" containment building. If you weren't aware, Browns Ferry uses the same GE Mk I BWR reactor that is used at Fukushima Dai'ichi nuclear plant. There's an excellent construction image of Browns Ferry that clearly shows the reactor core and torus.

They did a PR tour at Browns Ferry recently, pointing out the differences between it and Fukushima I. Among them, there is a fire hose on the top floor that can be used to douse the spent fuel pool if needed. And, there were additional redundant diesel generators added post 9/11 at all US nuclear plants.

[meyer]

Pictures from the press tour at BFNP (Browns Ferry Nuclear Plant):

http://www.tva.com/news/pix/index.htm

Each link takes you to another picture. This is roughly the same stuff that they have in Fukushima, so it should give some perspective as to what the plant should look like. It was particularly interesting to see the spent fuel pools with the crane system and all.

[justa-hairyape]

Apparently it was the Japanese government officials that were unaware of potential hydrogen explosions. The plant operators were aware of the problem. Unfortunately the final decision to vent steam had to be made from a Japanese government official due to protocol and the potential to violate emission laws. In the US, the plant operators have the authority to make the call. As far as I am concerned, during a nuclear power plant emergency, there are no higher controlling legal authorities then the plant operators.

[meyer]

I think that the hydrogen issue was mostly blown off as something with a probability of close to zero. However, a total loss of power incident probably has about the same probability. I mean, they were prudent in building to the “expected” worst-case earthquake and tsunami, only to find out many years later that it was woefully insufficient.

You’re right about one thing - US plant operators have the authority to make the call in emergency situations. In fact, the senior reactor operator on duty, I believe, is the top authority in a nuclear plant. Probably varies from one company to another, but somebody has to be in the position of authority, and the closer they are to the action, the more accurate and timely their decision will be.

I think that I’d be inclined to violate emissions laws if the situation warranted, and I would say that this situation warranted taking such action. Then again, I’m not sure that they totally expected that there’d be enough hydrogen concentration in the released (vented) reactor gasses to create a potentially explosive situation inside the building. At least not on the first one. After that, maybe they should have considered it. It wasn’t until a week or so later that they perforated the roof on Unit 5 and 6 reactor buildings as a precaution, even though those units were not in nearly as bad of shape (they had at least 1 diesel generator available shortly after the tsunami to give some cooling circulation on those units).

Side note, and totally unrelated - it just started raining, which is good. I put an acre of fertilizer down today and it needs to be washed in. :)

[justa-hairyape]

There is one thing I find puzzling about the hydrogen explosion story. Those tall chimney stacks are supposed to be the vents for the plant. Read one article that stated a vent of the reactor would send the venting products up those tall stacks to safely vent away from the plant buildings. How could that venting process have leaked inside the reactor building ? Or is that story wrong which states a vent from the reactor would go over and up the stacks ?

[meyer]

I'm not quite sure about those tall chimney "tower" stacks. They may be to vent off high pressure steam in the event of a unit trip (when a steam-driven generator trips, the main steam valves to the turbine slam closed while the main generator trips, and all fuel sources are also tripped, which in the case of a nuke would mean that the control rods are inserted). The sudden closing of the main steam valves would leave enormous steam pressure in the loop. In an ordinary coal-fired steam plant, this would be vented to the atmosphere through a pressure relief valve. Maybe that is the purpose of the stack, although I would think that with a BWR, that pressure would instead be releived into the torus.

I'll try to find out more about the stack. Could be that the relief system didn't work as designed due to failure of equipment necessary to open the valve. I really don't know.

[justa-hairyape]

The article I read stated that the pressure release required manually operated valves to be opened. And those valves were supposed to direct the steam to one of the tall chimney stacks. And yes, the Suppression Torus is supposed to be where steam condenses back into water during a shutdown. In normal hot operation the used steam condenses back to water in the Turbine building condenser. There are some who have filed complaints that the emergency condensation system is flawed. In fact, three GE engineers resigned about that design flaw back in the 1970’s. There is supposedly a better (more expensive) way to handle the steam during an emergency shutdown.