Nuclear engineer identifies ‘weakest link’ at Unit No. 4 — “Potential catastrophic drain down” of fuel pool (PHOTOS)

Published: June 15th, 2012 at 4:19 pm ET
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Nuclear Engineer Identifies Mechanism for Potential Catastrophic Drain Down of Fukushima Unit 4 Spent Fuel Pool
Enformable
Lucas W. Hixson
June 14, 2012

During a review of events concerning the status of Fukushima Unit 4, nuclear engineer Chris Harris identified the “weakest link” which may initiate a spent fuel pool draindown event.

A major portion of the water in the Fukushima Unit 4 Spent Fuel Pool remains over the Fuel because of the, “Refueling Bulkhead and Bellows” Seal (see drawing above).

Although this component has received little attention, its integrity is vital to maintaining Spent Fuel Pool Level.  This is because in the current configuration (Refueling Mode) of Unit 4 and the known problem of leaking Refueling Slide Gates, the Drain Down of the Spent Fuel Pool could occur via Failure of the “Refueling Bulkhead and Bellows”.

Source: Chris Harris, Enformable

The Gate is a long rectangular “dam” in the side of the Fuel Pool which can be removed after the Reactor Refueling Cavity Well is filled so that Fuel can pass through the opening (Slot). The Fuel Handling Machine is then able to pass the fuel safely submerged. The Gate has seals so that the Fuel Pool doesn’t drain into the Cavity and dangerously expose Fuel Assemblies when not in Refueling Mode.

TEPCO noted that the refueling gate seal is maintained by adequate pool water levels, and may be lost in the event of a LOCA sequence.

The leakage through the Gate is caused by an apparent physical distortion which causes an unintended Flow Path between the Reactor Refueling Cavity Well and the Fuel Pool. Evidence of this condition includes a January incident where Fuel Pool water level had been maintained by water from the Reactor Refueling Cavity Well.

If the Gate were undamaged and installed correctly, then there should have been no direct communication between the Well and the Pool.

Because the damaged Gate provides a non isolable Flow Path, any loss of water from Reactor Refueling Cavity Well will Drain the Fuel Pool to the Bottom of the Gate.

[...]

Source: Chris Harris, Enformable

Read the full report here

Published: June 15th, 2012 at 4:19 pm ET
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17 comments to Nuclear engineer identifies ‘weakest link’ at Unit No. 4 — “Potential catastrophic drain down” of fuel pool (PHOTOS)

  • I wonder if the new 'cover' on sfp4 will interfere with water cooling of fuel

    Posted Nuckelchen's vid of the cover placement at Reality Check
    World-wide Fukushima fallout forecasts also there
    http://realitycheck.no-ip.info/nnn.html

    Other radiation monitoring links at the rc rad forum
    http://realitycheck.no-ip.info/forum/index.php/board,24.0.html

    Senator Wydens contact info here somewhere. I wonder if he feels better now
    http://www.usa.gov/Contact/Elected.shtml


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  • gottagetoffthegrid

    flood the primary conainment vessel (inverted lightbulb structure. problem solved.

    well that assumes there isnt a cracked and leaky supression chamber.


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    • farawayfan farawayfan

      Sorry SFP is completely separate. Wish it were that simple.


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      • faithhopelove

        "Sorry SFP is completely separate."

        But isn't the article (Chris Harris) suggesting that loss of water from Reactor Refueling Cavity Well will Drain the Fuel Pool into the drywell? So as 'gottagetoffthegrid' suggests, if the drywell (inverted lightbulb structure) were filled with water, then even if the Gate were to leak, the water level could be maintained.


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    • faithhopelove

      "…well that assumes there isnt a cracked and leaky supression chamber"

      But how could a simple hydrogen explosion in unit 4 have damaged the reactor's supression chamber if the reactor was open at the time?

      For that matter:

      (1) how could a simple hydrogen explosion have blown out those thick concrete walls in unit 4?
      (2) how could those thick concrete walls in unit 4 been blown out, without severely damaging the unit 4 SFP? (In other words, are most of the original contents of SPF 4 still there?)


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  • Greetings friends…

    Your friend tacomagroove has been a busy bee this week! So I will give a short insight into this article… Before I get into the real news… First off the cover…

    Suppose there is a large crack in the fuel pool, due too the weight of the cover tearing the building in half… That would be bad. But wouldn't using helicopter drops of seawater be impossible? Food for thought…

    Now my news…


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  • For the last few days I've been surfing the west coast for tsunami debris… I now have several samples / items of Japanese origin that I will be sending to potrblog team for rad sampling. Will upload pics when I get home.

    Emmy. 2012


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  • homeenergyexpert homeenergyexpert

    Another study at the NUCLEAR AND INDUSTRIAL SAFETY AGENCY that I found posted on the Embassy of Japan website in DC, is very informative on Reactor #4 and #3.
    http://www.nisa.meti.go.jp/english/index.html

    Causes and Countermeasures:
    The Accident at TEPCO’s Fukushima Nuclear Power Stations

    May 25, 2012 The Integrity evaluation of the reactor building at unit4 in the Fukushima- Daiichi nuclear power plan (Good pictures and diagrams of retrofits)

    Technical Knowledge of the Accident at Fukushima Dai-ichi Nuclear Power Station
    of Tokyo Electric Power Co., Inc. (Provisonal Translation)

    PressReleases
    PressMay.25.2012Regarding Direction of Implementation of Seismic Safety Evaluation in Unit 4 at Fukushima Dai-ichi Nuclear Power Station, Tokyo Electric Power Company (TEPCO)(PDF:47KB)
    PressApr.19.2012Seismic Damage Information (the 400th Release)(As of 14:00 April 19, 2012)

    Check it out as it has some very good data.


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  • many moons

    Where did the original cover to the fuel pool go???
    I think they never had one and that was a good thing because then they could fill the pool with the hose…Tons off concrete ontop of an already damaged building doesn't sound like a good thing…I wonder how important it was to get the fuel pool covered since it's been stable without it…man these TEPCO folks make me nervous!!!!


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  • markww markww

    Let me know if there are gamma products. when you post your findings

    Mark


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  • chrisk9

    This is an excellent article in many respects and it's assumptions seem to be very logical. Notice how it postulates about the possibility that even Fukushima Dani would have to be evacuated if spent fuel pool #4 loses its water. It also talks about the spent fuel pool gate and leakage problems that it has. This is the weakest link to the fuel pool. If they know it is leaking that is bad news. Note the references to dose rates if just one fuel bundle is dropped and exposed. My only critique of the article is that it mixes BWR issues with some PWR ones which confuse things a bit.
    The cover on the spent fuel pool will do nothing to it's integrity, were talking hundreds of pounds versus a pool holding hundreds of tons of fuel.


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