ML20127H138
| ML20127H138 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 11/30/1977 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Stello V Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9211180405 | |
| Download: ML20127H138 (2) | |
Text
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0 l-i NORTHERN 5 TATE 5 POWER COMPANY MIN N E A POLie. MIN N E S OT A 99408
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November 30, 197) 9 gLC5 my :
,4 Mr Victor Stello, Director Division of Operating Reactors s
e/o Distribution Services Branch, DDC, Alti Y
U S Nuclear Regulatory Comission Washington, DC 20555
Dear Mr Stello:
MONTICELLO NUCLEAR GENERATING PIANT Docket No. 50-263 License No. DPR-22 Response to 10/14/77 NRC A'IVS Questions This letter responds to Mr Go11er's October 14, 1977 letter, which questions the use of relays in the Recirculation Pump Trip (RPT) circuitry, which are node by the same manufacturer as relays in the Reactor Protection System (RPS). The referenced letter further states, "Use of identical relays does not fulfill the desired system diversity, in that a comon modo failure similar to that described in WASH-1270 could render both reactor scram and RPT inoperative."
It is our opinion that the diversity requirement is met through functionally opposite application of the relays.
Our description of RPT (NED0-25016) submitted on September 15, 1977 states that the RPI system is " energize to trip" while the RPS is a "de-energize to trip" systen. ':he application of functional diversity to cocanon elements is discussed in detail in Section 4.5.3 of NEDO-25016. The likelihood of a comon cause failure which would adversely affect functional application of these relays is considered acceptably low.
Further pursuit of diversity presents not only unnecessary redundancy, but causes a significant impact on design work completed in the last year.
'Ihe NRC staff safety evaluation dated February 23, 1977 states, "This evaluation presents the results of our review of a proposed RPT modi-fication, which is considered a short tem solution to the anticipated 9211180405 771130 DR ADOCK 05000263 PDR
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Mr Victor Stello Page 2 November 30, 1977 transient without scram, ATWS.
Evaluation of the long term pro-gram, which addresses all the WAsil-1270 requirements and considers the need for additional modifications, will be accomplished for Monticello and other WAslt-1270 Class C plants at a later date."
It further states, "The diversity between the ATWS logic and reactor protection system (RPS) logic has been achieved primarily through the functional application of the logic elements and the location of the logic elements.
. We have detemined that the diversity of this system, based on the above factors, is accepta'ble."
We interpreted your safety evaluation to be concurrence for the entire design, installation and implementation (pending issuance of technical specifications) of the RPT circuitry as proposed; design, procurement of materials and installation activities are presently undervay. We request that your determination on this recent inquiry consider the existence of functional diversity as discussed above and the applicability of the conclusions of your February 23, 1977 safety evaluation.
If our understanding of your concurrence on RPT circuicry is incorrect, please infom us itraediately since current efforts would have to be halted, reinitiated under newly approved criteria, and could cause significant additional delays in the implementation of RPT.
Yours very truly, h.
L 0 Mayer, PE Manager of Nuclear Support Services LOM/IEV/deh cc:
J G Keppler G Charnoff MPCA Attn J W Feman l
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