ML19347E734

Forwards Description of Containment Purge & Vent Sys Isolation Logic Mods Per NRC 791029 Interim Position Re Purge/Valve Operation.Analysis of Isolation Valve Operability Under Accident Conditions Underway W/Vendor

ML19347E734
Person / Time
Site:	Prairie Island
Issue date:	05/06/1981
From:	Mayer L NORTHERN STATES POWER CO.
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 8105130290
Download: ML19347E734 (5)

Text

i T M Northern States Power Company 414 NicoHet Mall Minneapoks. Mmesota 55401 Telephone t612) 330 5500 May 6, 1981

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. , t ,. .c. vh Director  ! ,)d

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Of fice of Nuclear Reactor Regulation P.

U S Nuclear Regulatory Commission .

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i/d 10 $3]> h Washington, DC 20555 Y ,9 PRAIRIE ISLAND NUCLEAR CENERATING PLANT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Containment Purge and Vent System Isolation Logic !!ocifications Our letter dated November 7, 1980 stated that we would provide the hRC Staff with a description of proposed modifications to satisfy item 2(b) of the Interim NRC Staf f Position related to containment purge and vent valve operation. This Staf f Position was transmitted to Northern States Power Company in a letter dated October 29, 1979 from A Schwencer, Chief, Operating Reactors Branch #1, USNRC.

Item 2(b) of the Interim Position requires plant modifications to segregate the containtaent ventilation isolation signals to ensure that reset of c u autom. tic isolation signal does not prevent the other from initiating valv- closure.

Attached is a description of the design change we have initiated to satisfy item 2(b) of the Interim Staff Position. Modification of the Unit 2 logic was completed, as described in the attachment, during the Spring 1981 Unit 2 refueling outage. ,

Modification of the Unit I logic will be completed during the Autumn 1981 Unit I refueling outage.

The analysis of containment isolation valve operability under accident conditions is still being pursued with the valve vendor. An additional deficiency related to electrical separation of Train A and Train B power to the containment purge valve control circuitry, identified in item 2.1.4 of our April 11, 1980 letter, is also in the process of being corrected. Until all deficiencies are fully resolved containment purge valves will remain closed with their air supply isolated.

1 Please contact us if you have any questions related to our modification to the containment vencilation reset logic.

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L 0 Mayer, PE Manager of Nuclear Support Services LOM/DMM/jh cc: J G Keppler G Charnoff b NRC Resident Inspector l

Attachment p sl osis o M6

o Attachment Director of NRR, USNRC May 6, 1981 Design Change 80L622 Modification of Reset Circuit for Containment Ventilation Isolation (CVI)

Description

- The purpose of this design change is to modify the reset circuit for the Contain-ment Ventilation Isolation actuation circuitry to remove the seal-in feature.

The present circuit blocks a second automatic initiation of CVI from occuring af ter a manual reset until af ter trip signals have been removed. For instance, if a safety injection were to occur, causing CVI, and the CVI was reset without resetting safety i.;jection, then a high radiation signal would not cause CVI.

This design change changes the latching relay function from an initie'e block to a reset block (see attached drawings). The CVI will not reset until all trip signals have cleared. Once reset the circut will immediately accept a new trip signal.

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Attachment Director of NRR, USNRC l

May 6, 1981 Page I Safety Evaluation ,

The following areas were considered in the Safety Analysis.

1) Wiring and installation errors

2) Relay Failure

! 3) Operational considerations

1) A wiring error could cause the loss of containment Ventilation Isolation j i (CVI) for the train miswired. The same error could cause a loss of both trains and, hence, a loss of function. QC inspection of the installation  :

I l coupled with operational testing of CVI following modification by STP 2547 and 2J83 will minimize the probability of such an occurrance.

2) A relay failure could cause loss of CVI reset. Due to problems with W'

e stinghouse type BFD relays the reset relay will be replaced with a Type NBFD. It should be noted that the relay will not be required to trip and that contact or relay failure cannot inhibit trip.

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3) Operationally, it will be impossible to reset CVI until af ter all trip

signals have been cleared. Purging will not be possible with a high radiation signal unless the alarm is reset and a bypass is installed to block the High Radiation Trip. The signal from Safety injection is normally reset when [

- appropriate, and assuming no high radiation, purging would then be possible. I This design change does not create a possibility for an accident or malfunction of a different type than previously evaluated in the FSAR, does not increase the ,

probability of occurrance of an accident or malfunction of equipment previously analyzed in the FSAR, and does not reduce the margin of safety defined in the bases for any Technical Specification.

Therefore, it is concluded that the design change poses no additional risk to the health and safety of the public.

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