ML20087D504

Responds to Re Instrumentation to Detect Inadequate Core Cooling.Detailed Analysis of Measurement Errors for Coolant Inventory in Hot Legs & Reactor Vessel Provided

ML20087D504
Person / Time
Site:	Davis Besse
Issue date:	03/09/1984
From:	Crouse R TOLEDO EDISON CO.
To:	Stolz J Office of Nuclear Reactor Regulation
References
1031, NUDOCS 8403130429
Download: ML20087D504 (4)

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TOLEDO

%ms EDISON Docket No. 50-346 A caue P. C A16E v.c.peset Nxww License No. NPF-3 cc m c.;..;n Serial No. 1031 March 9, 1984 Director of Nuclear Reactor Regulation Attention: Mr. John F. Stolz Operating Reactor Branch No. 4 Division of Operating Reactors United States Nuclear Regulatory Commission Washington, D.C. 20555

Dear Mr. Stolz:

This is in response to your letter dated September 6,1983 (Log No. 1360),

concerning the instrumentation to detect Inadequate Core Cooling (ICC).

Toledo Edison provided the schedule for the response on August 9, 1983 (Serial No. 993). Toledo Edison's response for Items 2, 3, 6, 7, 8 and 11 in the Enclosure 2 of your letter was submitted on December 8, 1983 (Serial No. 1003). The response for Item No. 4, 5, 9, 10 and 12 in the same enclosure was submitted on February 10, 1984. Enclosed is the response for the only remaining item (No. 1).

This completes Toledo Edison's response to your original letter (Log No. 1360) for the Davis-Besse Nuclear Power Station Unit No. 1.

Very truly yours, f8 r fW RPC:FYC Attachment cc:

DB-1 NRC Resident Inspector l

'GO)J B403130429 840309 DR ADOCK 0500034 {\gg THE TOLEDO EDISON COMPANY EDISON PLAZA 300 MADISON AVENUE TOLEDO. OHIO 43652

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1, Attachment to TED Letter Serial No. 1031 QUESTION 1:

-Provide a detailed analysis of_the. measurement errors for coolant inventory in the hot legs.and the RV. This analysis should include be~ sides'the overall. estimate of the measurement uncertainty, a table with

' estimates. of error, including limits of uncertainty for each contributing

-factor associated with the transducer. Explafn how the individual errors were combined for the estimate-of the overall error. Discuss the error in

-inventory with the respect to the quantity of. coolant remaining.to cool the core. Evaluate the possibility that a change in containment environment or other conditions affecting the instrument calibration can result in misleading information with respect to the direction (loss or gain) of coolant inventory.

RESPONSE

The RCS liquid level in the hot leg can be represented by the equation:

g = api - pgH pf - p8

where:

L. = Actual level in hot leg H = Vertical distance from the lower tap of the DP cell to the top of the reference leg API = Indicated differential pressure from the DP cell pf = Liquid density in hot' leg i

pg =- Vapor density in hot leg.

Li =- Indicated level in hot leg po = Liquid tensity in reference leg Since api = poli,stherefore:

7 , poli - pgH

. pf - pg 4

. Based-on this formula, . the measurement errors for L can be derived.

dL ,. po , dpf 2 + 2 (dpg)2) g H pf-pg}dLi)2 6 H ,.(dpo)2 po 3

po po )

where:

dL- = Uncertainties associated with the actual level in hot leg (L).

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7-g dLi = -Uncertainty of the-indicated level due to DP transtoitter measurement error.

dpo =- Uncertainty associated with po due to reference leg temperature measurement error.

dpf = Uncertainty of liquid density in hot leg due to T g measurement error.

dpg = Uncertainty of vapor density in hot leg due to pressure measurement error.

The uncertainties or accuracies associated with the DP transmitter is the largest contributing factor.to the overall uncertainty of the level measurement. This is due to the fact that density of water is a rather weak function of temperature (10% variation in temperature such as 20 F in 200 F span translates to only 0.76% variation in water density).

For the DP transmitter the accuracies are:

10.25% (of span) for. hysteresis, repeatability 15.3% for environmental temperature effect (200*F change'in temperature) 10.7% for aging effect 11.43% for static pressure effect Therefore, dLi =

(0.25)2 + (5.3)2.+ (0.7)2 + (1.43)2}\%

= 15.54%

Assume the inaccuracy due'to density effects and other signal conditioning modules combined together-is less_than 2%.

po (at 120*F) = 1/0.016204 = 61.71 lb/ft 8 pf (at 614*F) = 1/0.02433 = 41.10 lb/ft 3 pg (at 1700 psia) = 1/0.23607 = 4.24 lb/ft 3 Therefore,

= 41 424((5.54)2+ (2)2}% in %

= 19.86%

dL = 19.86%

• H

= i0.0986

• 918"

= 190.52"

= 17.54'ft.

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'This kind of inaccuracy ( 7.54 ft..of water) in hot leg and the steam generator tubes translates to 11870 gallons of volume per steam generator loop. Total volume in the RCS below the hot leg (and cold leg) center line. elevation is approximately 20,600 gallons. Therefore, the inaccuracies (9.86%) in level amounts to a maximum of 1870/20600 = 9% of the minimum inventory. The inaccuracy as indicated above, 19.86% includes the maximum effect from possible containment temperature changes (80' to 280*F).

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