ML20027C577

From kanterella
Jump to navigation Jump to search
Responds to NRC Request for Clarification of Util 820715 Ltr Re Errors in BWR Water Level Indication.Existing Emergency Operating Procedures Adequate for Successful Termination of Bounding Event Resulting in Ref Leg Flashing
ML20027C577
Person / Time
Site: Fermi DTE Energy icon.png
Issue date: 10/11/1982
From: Tauber H
DETROIT EDISON CO.
To: Kintner L
Office of Nuclear Reactor Regulation
References
EF2-60-002, EF2-60-2, NUDOCS 8210180188
Download: ML20027C577 (3)


Text

u Harry Ttutor

[kr It nd Constructe MI lyp EUN?E"k$a?"Ee*22s

<3ta> 237m October 11, 1982 TF2 - 60,002 Mr. L. L. Kintner U. S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Division of Licensing Washington, D. C. 20555

Dear Mr. Kintner:

References:

(1) Enrico Fermi Atomic Power Plant, Unit 2 NRC Decket No. 50-341 (2) Letter, H. Tauber to B. J. Youngblood, EF2-57,987, July 15, 1982 (3) NEDE-24801, " Review of BWR Reactor Vessel Water Level Measurement",

April, 1980

Subject:

Errors in BWR Water Level Indication This is in response to an NRC Staff request for further clarification of the Reference 2 letter. .

The Fermi 2 water level measurement system which uses the cold reference leg design exclusively provides the level signals for both display and automatic actuation purposes. Temperature compensating columns (Yarways) are not used for any application in the Fermi 2 level design.

l A review of the various accident scenarios analyzed in the General Electric NEDE-24801 report (Reference 3) was made by Detroit Edison. It was determined that

, the most limiting case with respect to level errors

( for a Mark I containment design was the small break accident where the vessel remains at pressure for one half hour followed by a fast depressurization by I manual actuation of ADS (paragraph 2.3 3 of Reference 3).

l The analysis indicates that flashing in the reference leg would occur at the point when the reactor vessel pressure is decreased to the saturation pressure of the reference leg. For the bounding case (see Figure 2-8 of Reference 3), this is approximately 3200F or 90 psia.

"-~

B210180188 821011 '

PDR ADOCK 05000341 A #

i PM

Mr. L. L. Kintnar Ochter 11, 1982 EF2 - 60,002 Page 2 ,

The magnitude of the initial flashing phenomenon is calculated to be less than 20 percent of the vertical drop of the reference leg in the drywell proper. For the Fermi reference leg design with an actual vertical drop of 18 inches in the drywell, the flashing error would be approximately 4 inches of indicated water level. Even if the entire reference leg portion in the drywell is assumed to boil off, the maximum possible indicated error (18") will not seriously impact plant safety. Use of ADS requires that ECCS pumps are operating. In addition, complete ECCS pump actuation will have been called for due to high drywell pressure -- a signal diverse from level. The high drywell pressure actuation will occur before drywell temperature reaches the reference leg satura-tion temperature. In addition, automatic initiation of HPCI and RCIC is at level 2 ( 99 inches above the active fuel). Manual control levels are also desired to be above this range if possible. As a consequence, a level error of 18" under the worst conditions does not impact adversely manual or automatic actions.

In any csse, the BWR emergency procedure guidelines being developed provide specific cautions and guidance to the operator to be aware of this phenomena.

Caution No. 6 of the guidelines gives specific caution to the operator when drywell temperature approaches the saturation temperature for the reactor vessel. In addition, the drywell temperature portion of the con-tainment control guideline keys the operator to the correct procedure when the temperature begins to approach this point.

Detroit Edison has provided a degree of enhancement in the Fermi 2 level measurement system which allows it to withstand a reference leg break and an additional single failure. By improving the diversity of the power supply feeds to the reactor level measurement transmitters, the Fermi design is able to provide con-tinuity of water level indication in the unlikely event that one division reference leg fails and the opposite division instrument power supply is lost. c This system capability provides level information which allows the operator to terminate this very unli-kely event using procedure-based manual actions.

a Mr. L. L. Kintner Ochter 11, 1982 EF2 - 60,002 Page 3 As a direct result of the very small level error which results if the Fermi 2 level measurement system is challenged by the bounding event which results in reference leg flashing, Detroit Edison has concluded that the existing emergency operating procedures are adequate for the successful termination of this event and other less significant events.

Should you have any additional questions, please contact Mr. Larry E. Schuerman, (313) 649-7562.

Sincerely, e ,

cc: Mr. B. Little