ML20148E915

Requests Info within 120 Days Re Proposed Plant Design &/Or Procedural Mods Necessary to Assure Acceptably Low Public Safety Risk Due to Water Hammer Events.Damaging Water Hammer Events Affecting safety-related Sys Should Be Reported

ML20148E915
Person / Time
Site:	Yankee Rowe
Issue date:	09/02/1977
From:	Schwencer A Office of Nuclear Reactor Regulation
To:	Groce R YANKEE ATOMIC ELECTRIC CO.
References
NUDOCS 8010310693
Download: ML20148E915 (4)

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a Yankee Atonic Electric Conpany ATTH: !!r. P.obert 11.- Groce ==

Licensing Engineer 20 Turnpike Road Westboro, Massachusetts 01581 t Gentl emen:

RE: Y/MEE-ROWC AT0i!IC POWER STATIDH y .

-l The NRC staff continually reviews experience froa operating reactors to assure that an cdequate level of safety is maintained at each individual c E

nuclear plant and for the total population of nuclear plants. As new k technical information and operating experience becomes available, the i ]E URC evaluates whether such infonmation could significantly alter the h; +1.

previously deternined levels of safety. In this regard, we have noted v1 that there have been about 50 reported water hanmer events in light water b d reactors some of which resulted in structural damage to safety significant p systens. Of these, approxiaately 20 water hanners have occurred due to the rapid condensation of steau in feedwater lines in plants with 1.'estinghouse F[

and Cor45ustion Engineering designed steam generators. While for the nost part danage frota these events has been limited to piping supports, one event in the feedwater line of a pressurized water reactor did result in a significant piping failure. None of the events to date has resulted in {

an acverse impact on the health cod safety of the public. It is possible, '

however, that water hamners could lead te more severe consequences; although it woulu be expected that the probchility of such events is very low. ,

because of the continuing cccurrence of water hamcer events, the N3C staff ,

has been evalostir.g available operating experience, actively discussing  ;

with nuclear stcan supply vendors and architect /engineerina firns ways of I reducing the treauency and consequences of such events, anc utilizing technical consultants to e, ore definitely exanine water hanner phenomena.

A copy of the report of our principal consultant, CREAP.E. is ettsched (Enclosure 1) for your infornation.

As a result of our efforts to date, we believe that rater hamers due to the rapid condensation of steam in the feedwater lines of stean generators represent a safety concern and that further actions by licensees are n

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Yankee Atomic Electric Company SEP 0 21977 Ef 5

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warranted to ass' re that an acceptably Icw risk to public safety due to .

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such events is naintained. The staff has concluded that such assurance would be provided if it can be deconstrated that the feedwater lines and feedwater spargers would remain sufficiently filled with water to preclude '

water hammer under normal and transient operating conditions. Accordingly, 2

you are requested the following to subait within 120 days of the date of this letter, inforcation: b _

il (1)

Proposed plant design and/or precedural modifications, if any, which ere necessary to assure that the feedwater lines and

'if spargers remain filled with water during normal as well as transient operating conditions. Supporting evaluations and analyses,.and any necessary procedural testing, should be provided to denonstrate the system performance. We recognize ....

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that there may be various design and/or procedural options '

available which will satisfy this objective and that, in -

some cases, existing plant designs may already incorporate such provisions. For exanple, we believe that provisions such as the use of top discharge feedwater spargers, and autvaatically initiated operatio of auxiliary feedwater systens, could maintain the feedwater lines and sparger full of water. In addition, it appears that steam generator feedwater system design characteristics nay, in some cases, r inherently maintain a filled status by virtue of the elevation of the sparger, the closure rate of the feedwater control valve, prompt availability of auxiliary feedwater, etc. ,.

Proposed codifications will be reviewed and approved on [

the basis of their effectiveness to reliably noir.tcin the feedwater lines and spargers fillcd with water on a plant specific basis.

t (2) An assessment of your proposed design and precedural nodifi- '

cations in terms of the impact or interaction with the safety '

design bases and supporting safety analyses for the plant.

(3) .

A schedule for implementation of the proposea design and procedural todifications. r f

U511e existing Technical Specifications contain reportine requirements '

applicable to water hanmers, the staff has developed additional guidance reparding the type of events to be reported. Specifically, all future dancging water henner events occurring in safety-related systens or J

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-. q occurring in other systems that affect safety-related systems should *=

be reported. A fomat for the reports is enclosed. Damaging water c hancer events are those events that result in: (a) danage to pipe [2 supports or pipe insulation, (b) pipe displacement, or (c) failure 1:.~

of pipes or components. =1 Approved by GAO, B-180225 (R0072), clearance expires July 31, 1980. .-

Approval was given under a blanket clearance specifically for identified E generic problems.

Sincerely, 9

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..1 A. Schwencer, Chief H Operating Reactors Branch #1 Division of Operating Reactors [1l

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Enclosures:

1. Report by CREARE on _

t!ater Hanmer Phenomena

2. Fonnat for Report ,, _

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Yankee Atomic Electric Company SEP 0 21977 cc: Mr. Donalb G. Allen, President iv Yankee Atomic Electric Company

20. Turnpike Road Westboro, Massachusetts 01581 Greenfieh' uolic Library 402 Main Street Greenfield, Massachusetts 01581 a 4!

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