Japan Earthquake: nuclear plants

rmattila

An INPO report containing a narrative of the events:

http://www.power-eng.com/content/dam...a%20report.pdf

A new version of the "steam or no steam at unit 1:s IC at 18:18", and mentioning that it was the IC, not HPCI, that was cycled at Unit 1 between 15:03 and the tsunami.

clancy688

Two things I discovered by skimming through the report:

Unit 2 - If I read the section about Unit 2 correctly (and I'm not really sure I did, perhaps NUCENG could look over the sections regarding Units 1-3? There's a certain emphasis on venting valves), then Unit 2 never vented. The workers established a vent path, but a rupture disc never failed, even though the pressure was higher than the pressure needed to break it.
So when Unit 2 finally depressurized, it wasn't done through venting - but through containment failure.

Unit 3 - RCIC didn't fail on March 14th, it failed on March 12th at 11:36 local time, HPCI provided core cooling until the morning of March 14th. Was that fact known before?

SteveElbows

The link to that report is currently broken. Try this one instead.

http://www.nei.org/resourcesandstats...-power-station

SteveElbows

It does not seem to me like there is much in the way of new information in this report, but it is presented in a way that makes it easier to spot such details. We already knew that they had numerous problems trying to vent reactor 2, and although Im not sure we spent much time talking about it. The fact that venting never happened does not strike me as new, although prior to this latest report Im not sure it was ever specifically stated that rupture disc never failed.

Checking the info from that report with a couple of other sources such as NISA analysis of events, my brief summary of venting details for the three reactors is as follows:

Reactor 1
RPV fell to PCV pressure levels without any mention of SRV valves having been deliberately opened
PCV pressure fell somewhat, and radiation levels at plant increased, before there was any venting.
Early venting attempts were only partially successful or not successful at all for hours on the 12th.
Venting was eventually confirmed, backed up by visual evidence of venting via stack.

Reactor 2
Numerous problems when trying to get various vent paths opened.
SRV's opened on more than one occasion.
PCV pressure didn't rise significantly when RPV pressure first fell, suggesting PCV leak.
RPV pressure increased several times after initial SRV opening, requiring further SRV opening activity to be performed.
PCV pressure then went higher, but the indicated drywell pressures went much higher than the suppression chamber ones.
Venting still didn't work.
Tried to vent directly from drywell to get round the issue of lower s/c pressure compared to d/w pressure, but there was still no indication of success.
Sound near suppression chamber, pressure indication for s/c went to 0, drywell pressure fell over the next few hours.

Reactor 3
RPV pressure fell when HPCI started.
RPV pressure increased when HPCI failed.
Attempts to vent not successful.
PCV containment leaking may have occurred.
Venting succeeded, with visual confirmation of venting via stack. SRV opened at about the same time and RPV pressure fell as expected.
Problems keeping vent path open at certain times in the subsequent days, which sometimes affected ability to continuously inject enough water.

SteveElbows

TEPCO have released a large number of previous unpublished videos, taken over many months.

http://www.tepco.co.jp/en/news/110311/111111-e.html

zapperzero

It says there
<quote>These motion pictures are available until the end of December. </quote>
so make copies

nikkkom

This was the first "extended SBO + all EDGs off" scenario, and it resulted in a total, 100% SNAFU: not a single reactor unit was saved.

It's actually worse than that: out of three active reactor units affected, FOUR blew up (counting 2nd unit's infamous "load bang in the torus area"): they managed to blow up even the unit with reactor switched off, opened and unloaded. That's quite an achievement.

Tell me how I can trust nuclear industry after this. Am I to believe French or US nuclear stations are better prepared, when more natural and conservative conclusion is 'French and US nuclear stations just didn't have their "extended SBO + all EDGs off" scenario. Yet. Just wait'?

clancy688

Great line, I really had to laugh out loud. Both hilarious and depressing.

I agree, trust is gone, for me, too. I was totally pro-nuke before Fukushima, but now I'm against it.
But overall I'd say that damn tsunami probably chose the one plant out of all those 500 stations in service worldwide which was actually the most vulnerable against such an attack. Pretty bad luck I'd say. And keep in mind that the whole station was from the same generation as Chernobyl and even TMI.
(By the way, we had three major accidents in civil NPPs and all of them happened in Units designed and built in the late sixties...)

zapperzero

I blame the pot. On a more serious note, I think it has been definitively proven unwise to operate NPPs that are past their design life.

Oh, if only decommissioning one were not such an involved and costly affair.

Most Curious

Is this a technical forum - or a political one?

With enviornmental whackos preventing construction of coal fired base load plants and opposing ALL new nukes what PRACTICAL alternative is there? Hard to shut down an operating plant when there is nothing to replace it!!

These kooks would have us all freeze to death in the dark.

If I choose to be anti-nuke I want it based on sound science, NOT political considerations or activist driven pseudo science.

I come here to study and learn science.

clancy688

You ought to check out this thread.
It's closed but there were some good pro and contra nuke arguments going on.
And then there's the "more political" thread here.

I think I'll answer to the rest of your post in that one. ;)

tsutsuji

http://www3.nhk.or.jp/news/genpatsu-...00_hoanin.html The NISA declared that Tepco's report on Xenon was valid.

http://www3.nhk.or.jp/news/genpatsu-...00_kanshi.html Tepco said it would implement a system to measure Xenon continuously, for the purpose of being able to quickly assess criticality. Concerning temperature measurements, Tepco said that there is a 20°C uncertainty, so that in order to be sure to achieve 100°C as requested by the "cold shutdown" requirement, the thermometer values have to be below 80°C.

http://www3.nhk.or.jp/news/genpatsu-...hyo-shiji.html and http://www3.nhk.or.jp/news/genpatsu-...650_30nen.html The ministers of Industry (Edano) and Nuclear accident (Hosono) have asked Tepco to prepare a schedule where spent fuel pool fuel removal is started within 2 years after completion of step 2. This is one year earlier than recommended in the report from the middle and long term commission that was completed on 9 November. Concerning molten fuel removal, the start is within 10 years.

http://www3.nhk.or.jp/news/genpatsu-...5_tsuruga.html The NISA is asking Japco to provide the operation data of the isolation condenser of Tsuruga unit 1 over the past 10 years because it is similar to the one of Fukushima Daiichi unit 1, and it might shed light on what went wrong at Fukushima Daiichi.

nikkkom

How did you figure that out?
Do a mental exercise: imagine that all EDGs on all NPPs on the planet have vanished into thin air; then cut all power - put all NPPs into extended SBO.
Can you honestly say that F1 would be the only station where in this mental experiment events would take the worst turn? All other ones would be better off? That's statistically unlikely.

We were told that they are upgraded with new safety systems and thus are safe. We ended up with station personnel not knowing how to turn on ICs and/or vent containment without electricity.

clancy688

Um, nope. I rather meant that the SBO only happened because the tsunami "chose" the single one plant which would actually lose everything if hit.
True, other plants will probably live through the same experience if confronted with a multiple-day SBO. But the actual event (earthquake + tsunami) may not be enough to trigger such a SBO at other stations.
A NPP will suffer meltdowns if confronted with a long and total SBO. And a plane will crash if all engines fail and can't be restarted. That's why you engineer those things the way that this shouldn't happen. But at Fukushima, nobody apparently thought of the obvious, a giant tsunami inundating the whole plant, and that triggered the SBO.
In my opinion, the problem is not the SBO. It are the events which could lead to SBOs. Or high-pressure meltdowns. Or whatever else. The events which no engineer thought of when constructing the plant. And those events exist, as Fukushima proved.

Is it even possible to turn ICs on/off and/or vent the containment without electricity? I honestly don't know.

NUCENG

I am not sure I can add much to what you have read. I have one criticism as this report is a narrative and does not provide references on how each statement was developed. As a result I think we need to review the vast amount of claims, statements, descriptions and timelines to find support or conflict. OTOH, this is exactly the kind of event summary that can make that a manageable exercise.

The narratives of units 1 to 4 are all plausible as far as I can see. I was sceptical about the Unit 3 source for the hydrogen explosion in unit 4, but the recent photos of damage on the 4th floor are persuasive, if not conclusive. I thought that the reverse flow through the unit 4 SBGT filters was problematic. But this report explains that unit 3 was able finally to vent at a fairly high containment pressure. It clarifies that the SBGT system dampers fail open. It confirms there are no backdraft dampers to prevent flow to the adjacent unit.

From the descriptions I note a new issue that may affect other multiple unit sites. The military term is fratricide and refers to casualties to friendly forces close to a an intended target. Unit 1 explosion damaged response equipment at unit 2. Unit 3 explosion damaged additional response equipment for other units. The issue here is the physical separation of units or location of emergency hookups to shield the equipment and workers from failures in adjacent units.

On Unit 2 There are two things to point out. First RCIC probably failed due to inability to cool or rediuce pressure in containment. RCIC exhausts to the suppression pool and the combination of low steam pressure and high exhaust pressure was the probable cause of RCIC failure. I see nothingin the report that indicates unit 2 containment venting was successful. Containment failure of the torus is still a likely explanation for the "loud noise."

I had seen the reports that unit 3 had HPCI running when the preferred system should have been RCIC which failed. This is another example of an issue that needs careful investigation. The number of work-arounds and alternative methods tried by operators to vent containments, operate SRVs, provide alternate power to instruments, and to reenergize other systems was very impressive. But it is probable that some of these methods were subject to delays to figure out how to do them. In my experience, some of these methods are proceduralized and exercised at US plants.

Hope this helps the discussion.

NUCENG

The report explains that the containment vent valves had manual operation capability and that operators eventially provided additional pneumatic pressure (compressor and air bottles) and alternative power from batteries to operate the system. In addition to remote operation from the control room theat means there were multiple ways to operate the valves, including manual and alternate power.

NUCENG

nikkom, a mental exercise probably doesn't belong on this thread. But while you're at it why not throw in a loss of gravity accident?