ML20082P699

Suppls 901206 Response to Generic Ltr 90-06, PORV & Block Valve Reliability:Addl Low Temp Overpressure Protection for Lwrs. PORV Power Supply Mods Delayed to Refueling Outages 5 & 4 for Byron Units 1 & 2,respectively

ML20082P699
Person / Time
Site:	Byron, Braidwood
Issue date:	08/27/1991
From:	Chrzanowski D COMMONWEALTH EDISON CO.
To:	Murley T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
References
GL-90-06, GL-90-6, NUDOCS 9109110014
Download: ML20082P699 (4)

Text

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August 27,1991 Dr. Thomas E. Murley, nirector Office of Nuclear Rea' Regulation U.S. Nuclear Regulator, ommission Washington, DC 20555 Attention: Document Control Desk

Subject:

Pressurizer PORV Power Supply i

References:

(1) D. Taylor to NRC Letter dated December 6,1990, providing the Commonwealth Edison response to l Generic Letter 90-06. '

(2) August 21,1991 Telecon, CECO (A. Checca, D. Chrzanowski, et al) and NRR (A. Hsia) 1 Daar Dr. Murley: .

)

l Reference (1) provided Commonwealth Edison's response to Generic Letter 90-06,

' Power Operated Relief Valve and Block Valve Reliability" and " Additional Low-Temperature Overpressure Protection for Light Water Reactors". Along with our schedule for submitting changes to Technical Specifications to comply with the Generic Letter, this response provided details on upcoming modifications to the PORV power supplies at Byron and Braidwood.

Byron Station is modifying their schedule for installing the modification discussed in our response to Generic Letter 90-06. During the Referen::e (2) teieahone conversation with NRC Staff a callinitiated to inform NRR of this change, several issues related to the Generic Letter and the CECO response required clarification. The purpose of this letter is to document the conclusions reached in that discussion.

Issue 1 - Delay of the Byron PORV Power Supply Modification CECO requested, and NRC Staff agreed, to allow Byron Station to modify their schedule for the installation of the PORV Power Supply Modification. This proposed modification was, as stated in Reference 1, schedu!ed for installation at the upcoming Byron Unit 1 outage (B1RO4) starting September 1991 and at the Unit 2 outage (B2AO3) in February 1992. The modifications will now be ddayed to the outages listed in the response to issue 2 provided below.

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, ' 9109110014 910827 j PDR ADOCK 05000454 l P PDR 090050 ZNLD/1176/1 [8/ ,

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/ U.S. NRC September ?.1991

Background

The original modification as currently installed at both Braldwood units, changed the power supply for the PORV auxillary relays from a non safety related power supply to an uninterruptible instrument bus. The need for this modification was identified after a Loss

. Of Offsite Power event which occurred at Byron in 1987.

In the summer of this year, the Byron Technical Staff was reviewing the Lessons Learned Information from a spring 1991 Loss of Offsite Power event at Zion Station.

During this event both pressurizer PORVs lost power for automatic operation. The Technic . Staff transferred the information from this event to their review of the upcoming PORV power supply modification and identitled an enhanced power configuration for the modification. This enhancement would prevent the loss of automatic control for both PORVs in the event of a f ailure of an instrument bus.

. The power configuration recently installed at both Braidwood units will be modified _

to the new, enhanced design, however, the development time of this new modification i precludes installation at the upcoming Byron and Braidwood outages. ,

Issue 2 - Provide the revised modification schedule for all four Byron and Braidwood Units. ,

Our revised schedule for installation of the PORV Auto and Arm Low Ternp enhanced power supply is: 1 Byron Unit 1 B1ROS 2/93  ;

Byron Unit 2 B2RO4 8/93 i Braldwood Unit 1 A1RO4 3/94 ,

Braidwood Unit 2 A2RO3 3/93 i Because refueling outage dates are fluid, these dates are approximate.

Backgtound This revised modification, as well as the original version installed at Braidwood, provides features that are not required by the PORV design basis. The Byron /Braidwood power supply configuration for the PORVs is already in full compliance with Generic  ;

Letter 90-06. This modification is not a Generic Letter requirement and therefore the schedule change does not impact our compliance with 90-06.

Issue 3 - Describe the difference between the 1E power supply to the PORV auto l function mentioned in Reference 1 and the now proposed uninterruptible power supply. .

The statement in the CECO response to Generic Letter 90- 06 that described the proposed power supplies to auto functions in the modification as 1E was not correct. The '

power supaly in the current modification and in the new proposed design both have a supply to tie auto and arm low temp functions that is uninterruptible. The manual functions of the PORVs have always been supplied with 1E power.  ;

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ZNLD/1176/2 i l

l U.S. NRC S::ptember 6,1991

Background

The 1E classification is for electrical equiament and systems that are essential to emergency reactor shutdown, containment iso lation, reactor core cooling, and containment and reactor heat removal, or are otherwise essential in preventing significant release of radioactive material to the environment. During normal operations, AC power is supplied from the Svstem Auxiliary Tra;mformers (SATs), or from the SATs and Unit Auxiliary Transformers (UATs) concurrenTt y. In emergency situations, the diesel generators will supply power directly to 1E buses. During the switchover to the Diesel supply power will be temporarily lost.

Uninterruptible power supplies prevent fluctuations and interruptions in power to  !

sensitive loads such as vitalinstrumentation. Power is normally supplied to the l uninterruptible loads by the AC bus through an inverter, which converts the AC to DC  !

then back to regulated AC. In event of a loss of a 4 KV AC bus, the inverter will switch to DC from the 1E battery. If an inverter f alls the instrument bus can be manually switched to a constant voltage transformer and the action statements can be entered.

Issue 4 - Clarify the Generic Letter requirements for the PO'3V power supply, manual and auto functions.

Specifically, the Generic Letter proposed a Technical Specification surveillance to verify the emergency power supply to the PORVs. The recommended wording being; "The emergency power supply for the PORVs and block valves shall be demonstrated OPERABLE at least once per 18 months by:

a. Manually transferring motive and control power from the normal to the emergency power bus, and

b. Operating the valves through a complete cycle of full travel."

The Commonwealth Edison response explained that this proposed surveillance is not applicable to Byron or Braidwood since; "The OPEN and CLOSE functions of the PORVs at Byron and Braidwood Stations are supplied with IE power.

This power configuration is consistent with the Byron /Braidwood design bases and Safety Analyses and exceeds the requirements of the Generic Letter by providing a 1E power source for PORV manual operation.

Also as a clarification to our original response, the block valves for the PORVs are, and have always have been, supplied with 1E power. This was not stated in the original response ZNLD/1176/3

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• U.S. NRC Septnmber 6,1991 ,

Background

The 3ower supply arrangement, without any enhancements, is in full ,

compliance with 1UnEG 0737," Clarification of T MI Action Plan Requirements", E'-..un ll.G.1 " Emergency Power for Pressurizer Equipment" Also, as discussed in the Generic Letter and ir the supporting NUREG 1316,

" Power Operated Relief Valv6 and Block Valve Relit.bility", the role of the PORV ir, mitigating a steam generator ttbe rupture requires enhanced PORV reliability which is one of the reasons for the Generic Letter actions. However this "new" safety related function only requires manual operation.

Our internal commitment to modify circuitry is an action beyond the scope of the Generic Letter. This position is supported by the Generic Letter itself, in attachment A-3, the basis of the proposed surveillanco requirement states that the backup power suurce testing is;"...provided for either PORVs or block valves,..., where the, are installed with non-saf aty-grade power sources..."

If there are any questions or comments, please contact me at (708) 515-7292.

Sincerely, n r.

D i 3. a o$/ I cc: A. Bort DvM, Regional Adminis*rator-Rill R. Pulsifer, Project Managor-NRR i

/. Hsla, Project Managor-MRR S. DuPont, Senior Resicent inspector (Braidwoed)

W. Kropp, Senior Re Aent Inspector (Byron) i i

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