ML19208A795

Interim Deficiency Rept Re Steam Generator Water Level Measurement Sys Errors.Westinghouse Pursuing Resolution on Generic Basis for Plants Under Const.Westinghouse Ltr Re Substantial Safety Hazard Encl

ML19208A795
Person / Time
Site:	Catawba
Issue date:	08/20/1979
From:	DUKE POWER CO.
To:
Shared Package
ML19208A790	List: ML19208A789 ML19208A795
References
SD-413-414-79, SD-413-414-79-0, NUDOCS 7909170479
Download: ML19208A795 (1)

Text

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DUK2 POWER COMPANY CATN/BA NUCLEAR STATION Report No. : SD 413-414/79 02 ,

Report Date: August 20, ' 979 Facility: Catawba Nuclear Station - Units 1 and 2 Identification of Deficiency: Steam Generator Water Level Measurement System Errors Description of Deficiency:

This deficiency is as described in the attached June 22, 1979 letter, NS-TMA-2104, from T M Anderson, Manager, Nuclear Safety, Westinghouse to Victor Stello, Director, Office of Inspection and Enforcement, US Nuclear Regulatory Commission. Westinghouse reported this deficiency to the NRC as a substantial safety hazard under 10CFR21 for operating plants and as a significi. deficiency under 10CFR 50.55(e) for plants under construction.

Analvsis at _afety Imolicaticn:

The safety implications of this deficiency are also presented in the attached Westinghouse letter (NS-TMA-2104). This letter outlines the diverse backup signals that are provided in the plant design for reactor trip and auxiliary feedwater initiation. Due to the above mentioned backup signals, and since this deficiency was identified during the plant construction phase prior to operation, the health and safety of the public were not affected.

Corrective Action:

Westinghouse is pursuing resolution of this deficiency on a generic basis for plants under construction. Upon finalization of this generic solution, the specific corrective action for the Catawba Nuclear Station will b'e outlined in a subsequent report to NRC.

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J. " r- m2-June 22, 1979 NS-TMA-2104 Mr. Victor 5 llc 3 -

Director, Of fi a of Inspection and Enforcement V U.S. Macle Lerulatory Commission East hest Tr. e s Building 4300 Ecst UM t Highway Bethesda, "r land 20014

Dear Mr. Stelio:

Suisject: Steam Generator Water Level This is to confirm my telephone conversation of June 21, 1979 with Mr.

Norman C. Moseley, Director, Division of Reactor Operation and Inspec-tion and Mr. Samuel E. Bryan, Assistant Director' for Field Coordination.

In that conversation, I reported that Westinghouse had infonned its utility custcmers of corrections that should be applied to indicated steam generator water level and recomt. ended that they incorporate those

&g. corrc: tion; in the steam generator low water level protection system setpoints and emergency operating procedures for operating plants as appropriate.

High energy line breaks inside containment can result in heatup of the steam generator level measurement reference leg. Increased reference leg water column temperature will result in a decrease of the water column density with a consequent apparent increase in the indicated steam generator water level (i.e., apparent level exceedirg actual level). This potential level bias could result in delayed protection signals (reactor- trip and auxiliary feedwater initiation) which are based on-16w-low steam Senerator water level. In the case of a feedline rupture,'this adverse environment could be present and could delay or prevent th Tprimary signal arising from declining steam generator water level (low-low steam generator level). The following is a list of backup signals available in those Westinghouse plants which take credit in their Final Safety Analysis Reports for steam generator water level trip with an adverse contair. ment environment: overtemperature delta T; high For pressurizer pressure; containment pressure and safety injection.

other high energy line breaks which could introduce a similar positive bias to the steam generator water level measurement, steam generator level does not provide the primary trip function and the potential bias would not interfere with needed protective system actuation.

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Westingnouse has advised all customers with affected operating plants that the potential temperature-induced bias in indicated level can be compensated for by raising the steam generator low-low vater level setooint. For immedicte action, Westinghouse has recommenced a change in the allo rable water level setpoint sufficient to accommodate the bias (up to 107. of level) which could result from containment temperatures up to 280'F. Conta',. ment analyses following a secondary high energy line break on typical plants have shcwn that a containment high oressure signal would be generated before tne containe nt temperature reaches 280*F. Thus, postulation of all water-level measure cent errors occurring simultaneously in the adverse direction results in the containment high pressure signal becoming the primary protective functicr. following some feedline rupture events, i.e., for those cases in which the containment tcmperature exceeds 280 F before a steam generator low-low water level trip is actuated, the high containment pressure signal crovides protection. The combination of the revised low-low water level setpoint and the high containment pressure signal will provide reactor trip and auxiliary feedwater initiation following a feedline rupture and will ensure that the feedline break criteria stated in the Safety Analysis Reports continue to be met. Some applicants may choose to use plant-specific containment analyses, possibly combined with changes in the containment high-pressure setpoint, to justify reducing the bias introduced due to reference leg heatup which must be accommodated in the steam generator low-low water level setpoint.

p The potential steam generator level measurement bias also has implications for v post-accident monitoring considerations. Since the post-accident environment for hi;h energy line breaks can exceed 280*F. the level bias can exceed the 10% limit which must be considered for protection system actuation. A positive bias of up to 20% can ba anticipated for an extreme environmental condition. .;

The appropriate bias most be coupled with instrumentation and other process r errors, to determine tne required range of indicated level to be maintained during post-accident monitoring to ensure that the steam generator tubes are fully covered and the steam generator is not water solid. Westinghouse has provided all of its customers with operating plants witt. information to enable them to modify their emergency operating procedures to ensure that suitable steam generator level temperature bias allowance _ f s made.

In a related area, it'has been fottnd that aMWnitdam generator-ld51 miy also be introduced by changes in steadi generater_ Pressure, due to changes in steam generator fluid densities. Westinghouse has quantified this effect for all of its customers with op~Er'ating plantsr Wehinghouse has notifNi%il "

customers with operating plants that such a bias will exist in thele.el indi-cation of all steam generators and that the operator should be instructed to monitor steam generator pressure, as well as level, to ensure that the potential bias is reflected in his post-accident recovery actions.

Also, following depressurization of any steam generator, boiling could conceivably occur in the reference leg and cause a major bias for a short time period.

Westinghouse has notified all customers with operating plants that the water level indication in the depressurized steam generators may be erroneous due to the t4 potential boiling in the reference leg.

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For plants under construction, customers have been advised of the above af fects ,

and the options open to them for corrective action will be reviewed in a timely manner. The NRC will be advised of proposed resolutions for these olants.

The attached tables have been supplied to all customers. They have been informed that we are reporting this to you as a potential substantial safety hazard under 10CFR21 in operating clants and as a significant deficiency under 10CFR50.55(e) for plants under construction.

Should you have any questions on this material, please contact Mr. K. R. Jordan (412/373-4795).

Very truly yours, Westinghouse Electric Corporation s .

T. M. Anderson, Manager Nuclear Safety JPC:kk cc: Mr. Nonnan C. Moseley Director, DRO&I Mr. Samuel E. Bryan Asst. Director, DRO&I

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- Correctwn to indicated steam generator water level for Reference Leg Heatup ef fects efu2 to post-accident contair. cent _.

temaer;'. ore (before reactor trip)

- Maximum containment temperature Correction to S/G Level, reached before reactor trip, F  % of Span 90 0%

200* 4%

280 10%

320* 13%

8 - - . - _.

400* 20%

.g ' . -_

+' BASIS:

.- . Level Calibration Pressure < 1000 psia

_., N . F .- -

- = ~ ~ - -

_ Reference Leg Caliura' tion JegeraturE 1- 90*F

= -

_n m-Heig'ht of_Referenca Ng_.< ] . h Level 5.o.an

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J, o; u_., ., ,, .e . >o

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• • = .-e- e..,e,m y. .p.e e q>w.... _

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TABLE 2 Corrections to allowable indicated steam generator water level for Reference Leg Heatup and Pressure changes following a high-energy line break, to assure that true level is between the level taps Correction To Corrections to Containment Mininum Allowed Maximum Allowed Temperature Indicated Level, Indicated Level.

% of Span  % of Span

• F 90 +1 -4 200* +6 -4

-4 g 280* +11

-4 320* +14

+21 -4 400* \

C BASIS:

- Level Calibration Pressure < 1000 p.sia__

Refere6ce Leg Calibration TerJeTacu_ri-z-50*F ,

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Height of Reference Leg < Ll x tevel Span Pressure > 50' psia Pressure < 200 psi + Calibration Pressure Boiling in the Reference Leg is not assumed.

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