ML20148F080

Discusses Causes of Reactor Vessel Overpressurization & Measures Taken to Avoid or Reduce Overpressurization Probability.Requests Util Evaluate Sys Design Re Overpressurization Susceptibility

ML20148F080
Person / Time
Site:	Yankee Rowe
Issue date:	08/11/1976
From:	Schwencer A Office of Nuclear Reactor Regulation
To:	Groce R YANKEE ATOMIC ELECTRIC CO.
References
NUDOCS 8011030755
Download: ML20148F080 (4)

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Docket 1.o., 50-29 AUG 1 1 1976  :

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Yankee Atomic Electric Company ATTH: 1:r. Robert H. Groce Licensing Engineer E ,

20 Turnpike 90ad "

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Westborc, Massachusetts 01581 THIS DOCUMENT CONTAINS unu enen: POOR QUAllTY PAGES _

.3 P.E: Yankee-Rowe ,

A number of reported instances of reactor vessel overpressurization is C

in Pressurized Water Reactor (PWR) facilities have occurred in E which the Technical Specifications inplementing 10 CFR Part 50 Appendix G linitations have been exceeded. The majcrity of cues '

have occurred during cold shutdown'in which the prinary systen  :

has been in water solid conditions. These overpressurization . y events have been initiated by a varicty of causes, including the  :

iollowing: g ,

(1) Isolation of RHR systen/ letdown system while charging to a m vtater solid primary system, i _ .

(2) Thornal expansion f ollowing the starting of a pritary coolant pinp due to stored ther6al energy in steam generators, j

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• i (3) Inacvertent actuation of safety injection accurulators, and i j

K) Initiation of operation of a reactor coolant puap or a high pressure safety injection pump.

In essentially all of the events reported, a single corsonnel error, ec;uipient nalfunction or procecural deficiency has been sufficient 1 to cause the event. 1 i

Ue believe that appropriate steps should be taken prcaptly by ll

'd all PUR licensees to nininize the likelihood of soditional occurrences of reactor vessel overpressurization. To that end we rccently .j conpleted a series of nectings with several PWR licensecs and  :

NSSS suppliers in which we discussed the reported overpressur- j ization events and assessed the neasures that are currently being ;1 enplcyed to either avoid or reduce the probability of similar occur- g l rences,or to control the pressure transient to loss than Appendix f ]

G linits.

na Examples of those ueasures ioentified by the variouc a s u u, m m, ,wm..>.

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~ kW (1) Complete avoidance of water solid conditions by either maintaining I a pressurizer steam bubble or by providing a low pressure nitrogen

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blanket in the pressurizer when a steam Dubble cannot be maintained, g i b

(2) Disabling High Pressure Injection and Safety Injection pumps =d by disconnecting electrical power supplies when at low prinary y~q system tepperatures, g ,

(3) Installation of dual setpoint pressurizer power relief valve (s) .

to provide protection' against exceeding Appendix G limits -

while at low primary system temperatures, (4 ) hinimization of time. at water solid conditions.and upgracing =!

plant procedures to include appropriate warnings and cautions a when'such operations are necessary, and 5 (5) Installation of relief valves in charging pump discharge lines '

with a. setpoint to provide protection against exceeding Appendix  ; . .,

G 11 nits.

2 it was noted.in our discussions with the PWR licensees that, for the najority of those plants involved, not all potential overpressurization p -

events would be prevented by the measures they had identified l and that soli.e of the remaining neasures may have Undesir6ble effects on - j reacter safety. 1

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Lasec on the infor.mation gathered to date, we have concluced that .i all PUR licensees should evaluate their system designs to deteruine -

1 Specifically, you 4 susceptibility to overpressurization events.

shculd provide the following: )

(1) /.n anclysis of the pseactor Cocient Systen (RCS) response 3 to prcssure transients that can occur during startup and [ ]

shutuown. Any design icodifications detereined to be necessary . j to preclude exceecing Appendix G limits cre to be incorporated i; in this analysis. The analysis should include a plot of pressure i j as a function of tine until temination of the event. The j:

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analysis should assume the most lir..iting initial conoitions i; (e.g., one RHR train operating or available for letdown, i other components in norr:a1 operation when the system is water ,

I solid such as pressurizer heaters and charging pumps, and ene or more reactor coolant pumps in operation) with the '

worst single failure or operator error as the initiating event. _

Justification should be provided for the choice of limiting 2!

conditions and worst single failure or eperator error assumed j in the analysis, .j i

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n FF, (2) /. description of those cesign codifications deteminod to be necessary, inclu,iino cauip: ent perfomance specifications and K systo:1 operational secuences. The design basis used in the choice of ecuipment should be included, and F (3) A schedule for the prompt innle1entation of the preposed design [-

"ed i fic atio ns r The basic criteria to be applied in detemining the adecuacy of over-preu.urizatior, protection are that no sincle enuipment failure or single operator error will result in Anpondix 6 linitations beinn exceeded.

For tnase situations in which the necessary design chances identified cannct he innle ented within the next few ror.ths, you should identify [I short-torn neasures to reduce the likelihood that overprrsturization F events will occur in the interin period until the pomenent design [

chsrees can be '1ade. Short tem n:asures should be identifien senarately for iniodiatt ic'nle:1cotation witbin the tems and conditionr. of your ,

license. Short tem neasures nicht ir.clude sone combination of, but ['

urul." not De lir,ited to, the follo in- rugnestions:

(1) Procedural chs.v:cs to ninimize ine tia'. in which the ori..ory systco is in a patrr solid ccm:itien,

( .. ) Ue:rcuinc. cxitting plant procedures nr.a ministrativ r.cntrol s to assure tre t approcrine '.a rrin::s and certions

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SURNAME P DATC h

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-Yanken Atomic . Electric Conpany AUG 1 i 676 E E

L Mo'difications to preclude or nininize the probability of reactor vessel overpressurization events are plant dependent and the exanples given nay or nay not be adaptable to your specific system design. Consideration '

must also be given to the potential effects of both the short tem and ..E

-long tern neasures you consider to assure that other aspects of nuclear ,

safety are not cc^ promised. q

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To verify conpliance with Appendix G pressure-ter.iperature linits during il startup and shutdewn, you should assure that the appropriate instrtr1en-tation -is installed to provide a continuous pemanent record over the [r full. range of both pressure and tenperature. This instrumentation should p be in service during long periods of cold shutdown as well as during f startup and shutdown ' operations. Reliance upon the plant computer to F reconstruct a pressure transient is not considered sufficient because ;i of the likelihood.of conputer downtine especially during plant shutdown r conditions.

Ue request that you notify. us within 20 days after receipt of this letter that you will provide all the information recuested within 60 drys or explain why you cannot meet this schedule and provide the schedule that i ..

you will nect, b This recuest for :eneric infornation was opproved by CAO under a blantet j clearance num9er 3-1802P5 (R0072); this cir4arance expires July 31, 1077.  :  :

Si ncerely, Original signed by 1

A. Sc henter, Chic f Operatin; Peactors Brr.nch e l l Division of Operatino neactors

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DISTRIBUTION J cc: 'ir. Donald G. Allen, Preside'it NRC PDR VStello E Yankee Atonic Electric Concany Local PDR Dross 20 Turnpike Road Docket TBAbernathy Westboro, Nssachusetts 01581 KRGoller JRBuchanan l TJCarter ACRS(16) j Greenfielo Public Library OELD' 402 ' :in Street 01&E(3)

Grn iicid,izssachusetts 01581 ASchwencer a GZech  :

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Iorm ATC-3tB (Rev 9 53) ALChi 0240 W u. s. ooVERNMENT PRINTING OF FICEI 1974 636146

Yankee Atomic Electric Company ,. , ,..

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cc: Mr. Donaid G. Allen, President Yankee Atomic Electric Company 20 Turnpike Road Westboro, Massachusetts 01581 Greenfield Community College 1 College Drive Greenfield, Massachusetts 01301

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