ML20246Q366

Discusses Second Appeal Associated W/Diversity Requirements for ATWS Rule (10CFR50.62).Proposed Application Lacks Necessary Degree of Equipment Diversity Between Alternate Rod Injection & Reactor Trip Sys Per ATWS Rule

ML20246Q366
Person / Time
Site:	Browns Ferry
Issue date:	03/17/1989
From:	Thadani A Office of Nuclear Reactor Regulation
To:	Grace D BWR OWNERS GROUP
Shared Package
ML20245D855	List: ML20245D851 ML20245D878 ML20246Q366
References
NUDOCS 8903290025
Download: ML20246Q366 (2)

Text

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MAR 171989 Mr. Donald N. Sasco, Chairman BWR Owner's Group c/o Gpu Nuclear i Upper Pond Road Butiding E Parsippany, NJ 07054

Dear Mr. Grace:

SU8 JECT:

DIVERSITY REQUIREMENT OF ATWS RULE (10 CFR L3.62)

References:

1.

Letter, D. N. Grace (8WROG) to F. Miraglia (NRC),

"8WR ATWS Diversity Discussions," dated 12/8/88

2. Letter D. N. Grace (BWROG) to A. Thadani (NRC),

"BWR ATWS Diversity," dated 1/3/89

3. Letter T. E. Murley (NRC) to D. M. Grace (BWR06),

" Diversity Requirement of ATWS Rule." dated 8/8/88 -

4.

Letter, T. E. Murley (NRC) to L. W. Eury (CP&L),

" Diversity Requirement of ATWS Rule." dated 8/8/88 During our meeting on January 12, 1989, the staff had the opportunity to review your second requirements appeal presentation associated with the diversity for the ATWS-Rule.

The discussion surrounding the diversity issue in this instance involves a BWROG proposal to use an analog transmitter trip unit (ATTU) in the ulternate rod injection (ARI) system; and, we note

' that similar units provided by the same manufacturer are currently being used in the reactor trip systems (RTS) at most of the BWROG power plants. The NRC s

~ taff finds that this proposed application lacks the necessary degree of equipment diversity between the ARI and RTS systems to meet the diversity requirements specified in the ATWS-Rule. For this reason, the staff finds the proposed applications as discussed to be unacceptable. Our position on this issue is further discussed below.

In your presentation two major points were presented:

(1)

The diverse analog transmitter trip unit will cost approximately

$8000 to 12000/ unit (variance is based on quantity purchased) with a lead time for delivery of about 6 months; and, I

(2)

The reactor water low level alam (level 4) analog trip unit is diverse from trip units in trip channels for levels 1, 2, and 3. Also, with a postulated common mode failure of the analog trip units in levels 1, 2, and 3 you stated that there is about 15 minutes for operator action to prevent damage.

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s Donald N. Graca .

, MAR 171989 The cost estiestes provided at this meeting are higher than those previously suggested to the staff by the BWR06. However, the cost factors and lead time presented in item (1) above are considered by the staff to be consistent with (encompassed by) the original rulemaking process. With respect to operator intervention which is your argument presented in item (2), the staff's position is that operator action can only be used as a backup function to automatic initiation. l Your analysis and conclusion'that the frequency of such a loss of feedwater ATWS is a negligible contributor to risk because of the necessary combinations of failures and the time available for operator action was considered previously by the staff following your first appeal of the staff's position on ATTU diversity.

While you added a quantitative estimate of this frequency at the January 12 l meeting, we contin'io to believe that such numerical estimates of common mode failure likelihoi are questionable. As stated in previous letters (References '

3 and 4), the disersity required by the ATWS rule is intended to ensure that common mode failures that could disable the electrical portion of the existing reactor trip system do not affect the capability of the ARI system to perfom its required design function. It continues to be the staff's position that -

hardware / component diversity is required to prevent common mode failures frost-simultaneously disabling both the existing RTS and ATWS preventive / mitigative 1 systems. Thus, based on the discussion provided in this letter and our pre- (

vious letters of last August, the staff again concludes that the information- '

presented in the January 12, 1989 meeting does not constitute a valid argument to change the staff's original position regarding the ATWS rule diversity re-quirements.

Sincerely,

- :,:...i ~ ...- , 7.. , 7 ,.... p Ashok C. Thadar.i, Assistant Director for Systems Division of Engineering & Systems Technology Office of Nuclear Reactor Regulation l

cc: T. Murley F. Miraglia L. Shao 1 \

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