PEER REVIEW: Dr. Saji’s Comments on IC at 1F1 and Thoughts On Unit 2
I am posting these here to save space on the live blog chat. Dr. Saji’s new comments sent via email have some insight into the IC (isolation condensers) and early hours at unit 1. He also comments on what he thinks is going on at unit 2 and he concurs with what most of us have been assuming. This is for reference , not for broadcast distribution. Thanks.
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II. RELAP analysis of “short-termed station blackout.”
Among the bulk of report, I found an interesting viewgraph, which describes the RELAP analysis of the short-termed SBO, where the loss of off-site power is aggravated with further gradual depletion of batteries. It is a transition phase before going into the “long-tem SBO”. In the latter, the damaged plant lost all measures of core cooling and should eventually goes into a melt-down. I am very much interested in the attached viewgraph (in Japanese, refer the following http – Ko-ichi),
http://www.nisa.meti.go.jp/shi
since their conclusion is much different from my vision of the current core state, based on my “back of an envelope” assessment. The analysis is about operation of IC (isolation condenser) for 1F1. This passive residual hear removal system should have successfully helped preventing the gross-core melt in my view. I believe 1F1 plant has not went so far into the “long-tem SBO”.
On page 6, their modeling is illustrated in a block diagram. I immediately noticed that the SRV (Safety an Release Valve) is not correctly configured in the modeling. The SRV is installed in the Main Steam Line, from which steam is released into the suppression pool, during the “feed and bleed” operation. The safety valve function works even without the battery power, since it is with a spring action. Perhaps because of this, on page 9, the rate of water level decrease is shown very fast, down to TAF in just 1.5 h after the arrival of tsunami. I estimated 5 hours or longer. In addition, their analysis does not incorporate the TEPCO’s new findings described in their December 22 Internal Investigation Committee Report. The report indicates that an operator opened the MO-3A valve at 21:30 of March 11, to restart IC-A and confirmed release of steam from the secondary side of IC, indicating successful operation of the IC. This crucial operator action was motivated by knowing that IC should work, even without additional cooling water supply on the secondary side, as long as 10 hours.
In addition, I began to suspect the turbine-driven HPCI may have worked, at least temporarily, although its operational status was not confirmed from the control panel. It is because the observed water level is one meter or so higher (TAF +200mm at 21:19 of March 11) than my estimation of the reactor water level, which assumes no additional water injection. My estimation simply follows the water level by calculating the amount of the reactor water released by evaporation. I introduced this issue more in detail in Earthquake (170, Dec 16-23). Although there are some questionable issues, I strongly request continuation of this kind of assessment, instead of SBO=core-melt type analyses.
III. Update of the mysterious temperature rise in 1F2
I introduced this issue a week ago. Although this issue attracted a lot of media attention last week, it was concluded as a failure of the thermocouple (TE-2-3-69H1). The temperature plot was released as attached (as below – Ko-ichi).
http://www.tepco.co.jp/en/nu/f
TEPCO also quickly performed an environmental test using an insulation damaged thermocouple with cable, and found that high temperature readings are induced. Later, the reading showed below freezing temperature, indicating that such a failure is likely. However, TEPCP’s conclusion does not dismiss a possibility that something did occur inside of the PCV locally, near the thermocouple. TEPCO put this sensor out of service for monitoring the core status.
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