ML12038A236

Email from P. Boyle, NRR to R. Martin, NRR Et Al. Ioeb Clearinghouse Screening Summary for Friday, September 09, 2011

ML12038A236
Person / Time
Site:	North Anna
Issue date:	09/12/2011
From:	Patrick Boyle Office of Nuclear Reactor Regulation
To:	Gregory Kolcum, Martin R, Gerald Mccoy Office of Nuclear Reactor Regulation, NRC/RGN-II
References
FOIA/PA-2011-0357
Download: ML12038A236 (3)

Text

Boyle, Patrick From: Boyle, Patrick Sent: Monday, September 12, 2011 8:01 AM To: Martin, Robert; McCoy, Gerald; Kolcum, Gregory Cc: Kulesa, Gloria; Mendiola, Anthony

Subject:

RE: IOEB Clearinghouse Screening Summary for Friday, September 09, 2011 Bob brings up a good point. This is something that the restart team should review as part of their assessment.

Based on my limited knowledge of digital signal processing here are some potential options. Even if both conditions are monitored by the plant process computer (I don't know ifthey are), they could be sampled differently. For example one alarm could be monitored as an interrupt signal and the other could be a polled point. Even if both event occurred simultaneously and were both sampled the same way, a fraction of a second difference can lead to a one-second difference in the time stamp (one sampled 0.1 second prior to the time tick for the clock and one sampled 0.1 second after the clock tick) and if one alarm condition is polled before the other one then the one second difference can be artificially introduced by the data sampling.

Like I said, Bob has a good question here and the team should take a good look at the information when developing their conclusions.

From: Martin, Robert Sent: Friday, September 09, 2011 5:13 PM To: McCoy, Gerald; Kolcum, Gregory Cc: Boyle, Patrick; Kulesa, Gloria; Mendiola, Anthony

Subject:

FW: IQEB Clearinghouse Screening Summary for Friday, September 09, 2011 I would be a bit curious about the conclusion that the North Anna trip occurred I second before the LOOP.

Was the time of the trip and the time of the LOOP measured by the same instrument? If so, what was the response time for the two signals to get from their sensors to the time measuring device? Ifthe time recorders for the two signals are separate, would 1 sec be within the instrument measurement error?

From: Bernardo, Robert Sent: Friday, September 09, 2011 2:13 PM

Subject:

IOEB Clearinghouse Screening Summary for Friday, September 09, 2011 N TE: THIS MMARY IOFFICIAL U, ONLY

• • MAY ON IN SE SITI El PRO RI TARY NRC INTE NAIL USE 0 LY INFOR TI N*'**

SNO FORW RD Y PO TION OU SIDE F NRC WIT UT IRST BTA IN ERMI /I0 F M RIGIN ý Issues for Resolution (IFR): None OpE Forum Postings (COMMS): None Management Requests: None Follow-up/Other Tasks: Seven (7) ......

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4) NORTH ANNA 1 & 2 - ALERT DECLARED DUE TO AN EARTHQUAKE IN THE AREA AND A LOSS OF OFFSITE POWER (8124) - FOLLOW UP INFORMATION Dominion personnel briefed NRC staff on the Earthquake Response and the North Anna Restart Readiness Demonstration Plan during a public meeting on 9/8/2011. A copy of the presentation is available in ADAMS.

(ML11252A006)

Dominion noted that the cause of the negative rate trip (first annunciator out) is still being investigated. At this point, it appears that the grippers for several of the control rods de-energized and dropped RCCAs into the core leading to the negative rate trip. They have confirmed that the flux was decreasing on all four power range channels, but do not have the root cause completed. By their post trip analysis, the trip due to negative flux rate occurred at 13:51:11, followed by the loss of off site power at 13:51:12. Transformers 1-EP-MT-1A, 2-EP-MT-1A, 1B, 1C, all RSSTs, 1-EP-SST-1 C and switchyard transformer #2 tripped due to sudden pressure relay actuations (Loss of off site power). Thus, the negative flux rate trip occurred BEFORE the loss of off site power. Pass to the TRG Leads for AFW, ECCS, Electrical Power, EDGs, Emergency Preparedness, Flooding/Missiles, Spent Fuel Handling, Structural and to NRO. Assigned to Bob Bernardo.

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Outside of Scope

• (i.e, Screened Ireviewed againstLIC-401 criteria for initiatingan "Issue for Resolution" (IFR), which is IOEB's process for conducting further evaluation of an issue to determine what, if any, additionalactions should be taken to communicate and organizationallylearn from OpE.)

i**MN NO E: HIS S ) ARY IS40OFFIOIAL E ONLY/A A

• AYXCgTAIt SENSIT E/EI IROPR/ET RY OI RC INT R *L USE/ ILY INF/ MA qN***A Attendees at Screening Meeting:

Dave Garmon Jesse Robles Rebecca Sigmon Bob Bernardo - by phone Steve Pannier - by phone Bob Beall (NRO) .

Mary Wegner (RES) - by phone 3