Japan Earthquake: nuclear plants

Shinjukusam

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

elektrownik

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

Shinjukusam

Much obliged.

Yamanote

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

Yamanote

Some further information from Tepco on this issue:

http://www.tepco.co.jp/en/nu/fukushi...20212_07-e.pdf

duccio

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.

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

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.


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

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

http://science.soup.io/post/11591157...nkov-radiation

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

Rive

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

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-...213/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

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

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

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

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

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

Shinjukusam

If you're gonna fail, fail big.

Where was that announced?