Hydrogen Deflagrations In BWR MK-I Reactor Buildings

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Sherrell Greene
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Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by Sherrell Greene » Mar 12, 2011 10:33 pm

Guys,

During the early-mid1980s, ORNL had an extensive NRC-funded BWR severe accident analysis program. One of the severe accident sequences we focused on during that time was an unmitigated complete station blackout. You will find a short paper by Steve Hodge at the URL below, that summarizes several of our "lessons-learned" from that analysis. It appears the Fukushima sequence was similar in some ways to the accidents we analyzed. However, the ANS reports I've read this evening appear to indicate a small-break LOCA (SBLOCA) also occurred at some point during the accident and that the plant operators purposely vented the primary containment into the reactor building to reduce PC pressure... We looked at BWR-4 / MK-I accidents. The Fukushima unit is a BWR-3 with an isolation condenser. ANS indicated the Fukushima operators used the isolation condenser to cool the reactor until a small-break LOCA occurred, followed by actuation of the Reactor Core Isolation Cooling System (RCIC), which ran until the batteries were exhausted. Thus the Fukushima accident sequence is different from the "standard" unmitigated SBO sequence discussed in Steve's paper.

http://www.osti.gov/bridge/purl.cover.j ... 78-B1kbTJ/

For those of you who have the time and interest, you can find at the URL below a paper I wrote in 1987 in which I looked at a station blackout-driven hydrogen deflagration in a MK-I reactor building. My analysis began with an the worst case assumption of "core-on-the-floor" in the drywelI. I used the specific parameters of the Browns Ferry plant - a larger (BWR-4) reactor than the Fukushima BWR-3. My scenario assumed molten core breeched the drywell liner and vented the H2-rich drywell atmosphere into the reactor building. Based on this evening's reports, the Fukushima plant (thankfully) did not proceed to a "core-on-the-floor" scenario, and we do not know a how/where the primary containment was vented into the reactor building. Whatever the details of the "front-end" of the Fukushima accident, according to the ANS, it eventually resulted in injection of hydrogen from the Zr-H2O reaction in the over-heated fuel cladding into the reactor building. Though the reactor building modeled in the paper is almost certainly different than that of the Japanese plant, the analysis gives one a feel for how these events occur and the expected results.

http://www.osti.gov/bridge/purl.cover.j ... 51-nR29Hq/

There was also a paper, "The Role of BWR Secondary Containments in Severe Accident Mitigation: Issues and Insights From Recent Analyses," in Nuclear Engineering and Design, Volume 120, Issue 1, 1 June 1990, Pages 75-86. I don't seem to have a pdf of that handy, but if you curiosity is really triggered, I'm sure you can find it somewhere.

Per ANS this evening, the plant is now under diesel power and they are pumping borated sea water into the reactor vessel. Let's hope this terminates the accident progression.

Take care,
Sherrell

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Kirk Sorensen
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Re: Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by Kirk Sorensen » Mar 13, 2011 8:37 am

Thanks Sherrell...this is great information and I think many of us (certainly myself) are getting a crash course in the design of the Mark 1 BWR.

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Re: Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by arcs_n_sparks » Mar 13, 2011 9:10 am

Sherrell,

Thank you as well; very useful information.

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Re: Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by jaro » Mar 13, 2011 12:15 pm

Thanks for the paper !
Sherrell Greene wrote:Secondary containment above the reactor building is provided by a…. refuelling bay which is constructed of corrugated sheet meta walls that contain large blowout panels to provide protection from the effects of tornados and steam line breaks.

The refuelling bay siding is designed to withstand internal pressure in excess of 57.6 lb/ft^2 (2758 Pa) without structural failure. Pressures in excess of 50 lb/ft^2 (2394 Pa) will, however, be relieved by blowout panels in the siding.
I was wondering about those blowout panels -- presumably the Fukushima refuelling bays have them too, although they certainly didn't work for the hydrogen deflagration !

I know that modern turbine buildings have blowout panels, as there is a fair bit of hydrogen in steam turbine machines during normal operation.

Also, one wonders why some big doorways to the refueling bay aren't opened, when one is about to vent hydrogen into the building ! ...its not like it was something that happened accidentally.

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Re: Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by Cyril R » Mar 13, 2011 1:24 pm

Jaro, looking at the video footage it appears the detonation and shock wave started above the primary building, perhaps jetting inwards to the top section of the building that blew out (it is not inerted with nitrogen in contrast to the primary containment). So perhaps the blowout panels worked fine but the quantitity of hydrogen was big enough to blast the weak non-nuclear top section off. This does mean a big amount of the top fuel section must have been badly damaged. In that light, the decision by TEPCO to flood the primary with sea water makes sense - they were expecting zero salvage already. Financially, this plant is toast.

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Re: Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by USPWR_SRO » Mar 13, 2011 1:40 pm

And it's final shutdown for decommissioning was to be March 22nd 2011 anyway.

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Re: Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by Cyril R » Mar 13, 2011 2:15 pm

Yeah, that's probably why TEPCO was not very bothered about the use of seawater cooling.

I just wactched the news. First 5 minutes were about the nuclear plants in Japan, lots of stupid journalists that don't understand even the basics of how reactors work talked about the 'catastrophe' that the Japanese nuclear plants were in. Then there was 1 minute of footage which was like 'oh yeah and 10,000 people also died by the quake and tsunami and hundreds of thousands were made homeless'. Almost like an afterthought (!). Gee that's not nearly as important as the nuclear plant hypebole with zero radiation casualties eh? They did mention how 190 people were 'contaminated' with radiation.

Disgusting, how these journalists are disrespecting the Japanese emergency to engage in hyperbole. It makes me feel ashamed of being a Europe citizen.

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Re: Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by jaro » Mar 13, 2011 3:15 pm

A great quote from WNN:
The area around the plant was hit very hard by the tsunami and around 200 homeless people are sheltering in the power plant's administration building.
Fukushima, that is.

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Re: Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by USPWR_SRO » Mar 13, 2011 3:46 pm

Which?

Fukushima Daiichi (Unit 1 there blew its Rx building apart)

or:

Fukushima Daini

alexterrell
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Re: Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by alexterrell » Mar 13, 2011 3:50 pm

Would it not make sense to have a few heavy trucks - perhaps military derivatives with caterpillar tracks - with mobile generators stored a few km inland, away from the plant, in hardened shelters? That way if all the diesel generators are knocked out (say by an EMP weapon, or a Tsunami), power can be brought to the reactor within an hour.

What sort of power do the diesel generators need to generate?

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Re: Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by Lindsay » Mar 13, 2011 3:55 pm

alexterrell wrote:Would it not make sense to have a few heavy trucks - perhaps military derivatives with caterpillar tracks - with mobile generators stored a few km inland, away from the plant, in hardened shelters? That way if all the diesel generators are knocked out (say by an EMP weapon, or a Tsunami), power can be brought to the reactor within an hour.

What sort of power do the diesel generators need to generate?
I imagine that you would need MW of backup power, some number between three and ten MW, which is not easy to rig up quickly unless your auxiliary electrical systems have been specifically designed to allow this.

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Re: Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by alexterrell » Mar 13, 2011 4:00 pm

Lindsay wrote:
alexterrell wrote:Would it not make sense to have a few heavy trucks - perhaps military derivatives with caterpillar tracks - with mobile generators stored a few km inland, away from the plant, in hardened shelters? That way if all the diesel generators are knocked out (say by an EMP weapon, or a Tsunami), power can be brought to the reactor within an hour.

What sort of power do the diesel generators need to generate?
I imagine that you would need MW of backup power, some number between three and ten MW, which is not easy to rig up quickly unless your auxiliary electrical systems have been specifically designed to allow this.
A couple of these http://www.offshore-technology.com/cont ... e-as5.html
and a few 20 ton diesel trucks?

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Re: Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by USPWR_SRO » Mar 13, 2011 4:20 pm

One or two Diesel Gen sets rated for 2-5MWe each would be needed.

Something like this would be ideal: http://www.fairbanksmorsenuclear.com/en ... ckPA6B.php

The problem is these are not something you walk down to Wal-mart and pick up. They are long lead time items and they need regular maintenance even when not running.

You can do what you suggest but it won't be simple or cheap.

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Re: Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by Lindsay » Mar 13, 2011 5:47 pm

I think that something like this might be a better fit, somewhere around 1.2 - 1.5 MW each, road barge or heavy lift helicopter (?) transportable. With prior planning and the right equipment, multiple units could be paralleled to meet bigger loads.

There is still that issue of having the receiving party all geared up to be able accept such a connection which would carry its own risks. For any key infrastructure that needs electricity to operate, these plugin systems can be a powerful ally in any civil emergency and should be more widely used IMHO. If there is a shortage of units in a major event, then the government disaster management services get to decide who gets priority, until more can be airfreighted in from wherever.
CATXQ2000.pdf
(459.33 KiB) Downloaded 185 times

alexterrell
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Re: Hydrogen Deflagrations In BWR MK-I Reactor Buildings

Post by alexterrell » Mar 13, 2011 6:16 pm

From here: http://morgsatlarge.wordpress.com/2011/ ... -reactors/
Within the 8 hours, another power source had to be found and connected to the power plant. The power grid was down due to the earthquake. The diesel generators were destroyed by the tsunami. So mobile diesel generators were trucked in.

This is where things started to go seriously wrong. The external power generators could not be connected to the power plant (the plugs did not fit). So after the batteries ran out, the residual heat could not be carried away any more.
Seems like a lack of emergency drills (as in practices)

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