ML20079J736

Final Part 21 & Deficiency Rept SD 413-414/79-02 Re Steam Generator narrow-range Level Measurement Errors.To Minimize Errors,Installation of Mirror Insulation to Be Completed Prior to Testing

ML20079J736
Person / Time
Site:	Catawba
Issue date:	01/17/1984
From:	Tucker H DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20079J687	List: ML20079J686 ML20079J736
References
REF-PT21-84-243-000 PT21-84-243, PT21-84-243-000, NUDOCS 8401240404
Download: ML20079J736 (7)

Text

_

DUKE POWER GOMPANY P.O. BOX 33180 CHAMLOTTE, N.C. 28242 HALB. TUCKER TELEPHOhE

m. p.

n (704) 373-4531 December 28, 1983

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Mr. James P. O'Reilly, Regional Administrator U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900

- Atlanta, Georgia 30303 Re: Catawba Nuclear Station Units 1 and 2 Docket Nos. 50-413 and 50-414

Dear Mr. O'Reilly:

Pursuant to 10 CFR 50.55e, please find attached a final response to Significant Deficiency Report SD 413-414/79-02.

Very truly yours, C ad k f a

• . Hal B. Tucker LTP/php Attachment cc: Director INP0 Racords Center Office of Inspection and Enforcement Suite 1500 U. S. Nuclear Regulatory Commission 1100 Circle 75 Parkway Washington, D. C. 20555 Atlanta, Georgia 30339 NRC Resident Inspector Mr. Robert Guild, Eso.

Catawba Nuclear Station Attorney-at-Law P. O. Box 12097 Palmetto Alliance Charleston, South Carolina 29412 21351 Devine Street Columbia, South Carolina 29205 9

8401240404 840117 PDR ADOCK 05000413 S.

PDR

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Duke Power Company Catawba Nuclear Station Final Response to SD 413-414/79-02 Steam Generator Narrow Range Level Measurement Errors Scope The_ steam generator narrow range level' instruments initiate reactor trip and auxiliary feedwater actuation at the low-low level setpoints. - The steam generator narrow range level ~is also used for post-accident monitoring.

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The problem of steam generator narrow range level measurement errors is identified.in significant deficiency report SD 413,414/79-02 and is discussed in Section 7.2.2.3 of-the SER for Catawba Nuclear Station. These errors can be a : result of steam generator. fluid density changes, reference leg heat up'or reference leg boiling. The following provides additional informa-l tion and'a resolution to the aforementioned deficiency.

Resolution

. Reference Leg Heatup

'High energy line breaks inside containment can result in the heating of level measurement reference legs.

Increased reference leg water column

' temperature will result in a decrease of water column density. This decrease in water column density will cause an increase in indicated water level (indicated water level: exceeds actual level).

~

As discussed in the SER,~ Section 7.2.2.3, the reference leg will-be insulated

.to minimize measurement errors due to reference leg heatup. The installation of. mirror insulation on the steam generator level measurement system for Unit 1 l

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is to be completed prior to precritical testing.

A determination of low-low level trip setpoint error is as-follows:

Bottom of Span 0

Normal Channel Accuracy.

5%

Transmitter Errors Due to Adverse Environment

+5%, -15%

Reference leg Heatup Effects

+2%

Totcl Errors

+12%, -20% of Span Minimum Trip _Setpoint Required

+12%

- The normal channel accuracy was achieved by a direct summation error analysis

- ensuring a conservative number. Barton tot 2 transmitters will be temperature

. compensated statically to +5%, -15% of span. The temperature selected for this compensation is the temperature expected inside the electronics housing at five minutes-into'the event. The 2% error assumed for reference leg heatup effects.is due to insulation of the reference leg with mirror insulation.

- ~..

m Attached is a correspondence with Diamond Power Specialty Company (vendor installing mirror insulation at Catawba Nuclear Station) complete with a time versus temperature graph of reference leg heatup. The graph is con-servative in that it represents a faster water temperature rise than would actually be present. The reference leg heatup error was calculated to be less than 2 percent for 5 minutes following the accident.

The minimum low-low level trip setpoint is set at 12 percent of narrow range span. Negative errors provide an earlier trip and need not be considered. No margin of safety above the bottom of the narrow range trip is incorporated since all errors assumed are conservative and are arithmetically combined assuming simultaneous maximum values.

In order to avoid heatup of the reference leg during normal operation, a distance of 12 inches is not insulated down line of the condensate pot.

This uninsulated length will be exposed to the adverse environment and will be a contributor to the total heatup error following an accident. This portion is uninsulated to allow condensate pots and reference legs to cool to ambient under normal operating modes.

Water Density Changes An error in indicated water levels may also be introduced by changes in the steam generator pressure due to the changes in the density of the saturated water and steam in the vessels. The errors which would exist at low power under quiescent conditions is described in Table 1 and were calculated directly, using the following formula:

• II- (pL, cal - pl H

- p, cal + p L

PfP L

g g) + II pf cal - p. cal - I) g I

pf, cal p, cal g

g where:

l E = level error due to density changes in both the vessel and the reference leg, as a fraction of level span, L = true water level in the vessel, above the lower level tap, pf = saturated water density at the pressure of interest, I

p = dry saturated steam density at the pressure of interest, g

H = level span = vertical distance between narrow range taps on steam generator.

H = height of reference leg = maximum vertical distance from lower g

tap to water level in condensing pot on upper tap.

pL, cal = water density at containment temperature and steam generator pressure for which the level indication system was calibrated.

_2_

Reference leg Boiling Boiling could conceivably occur in the reference leg in a single steam generator (affected by the-break) with high containment temperature and depressurization of the steam generator to 42 psia. This condition could only occur following a steam line or feedline rupture inside containment and would be immediately detected by low steam line pressure indication with subseouent safety injection actuation.

If such boiling were to occur, it would cause a major error in the indicated level of the affected steam generator for a short time period, in the extreme case indicating 100%

level when the vessel is actually empty. Due to the extremely low probability of reference leg boiling, it is not included on Table I.

As a precaution, the plant operating instructions will inform operators of the possibility of erroneous water level indications of any depressurized steam generators due to reference leg flashings. -, _.

7..

TABLE I EFFECTS OF TEMPERATURE AND PRESSURE ON STEAM GENERATOR NARROW RANGE LEVEL INDICATION STEAM PRESSURE (psia) 100 300 500 700 900 1100 Reference Leg Temperature Actual

(*F)

Level Error'(fraction of span)

-90 0%

.05

.04

.03

.02

.01

.002 100%

.24

.16

.11

.06

.02

.012 120 0%

.04

.03

.02

.01

.004

.01 100%

.25

. 17

.12

.07

.03

.004 280 0%

.05

.05

.06

.07

.08

.09 100%

.33

.25

.20

.15

.11

.08 340 0%-

1.37

.10

.11

.12

.13

.14 100%

1.66

.30

.25

.20

.16

.13 Basis:

Level Calibration Pressure = 1050 psia L

_ Reference Leg Calibration Temp = 100'F Ratio of reference leg height to tap span (HL/li) = 1.00 Calibrated span = 233.79" @ 1050 psia,100 F Boiling in reference leg is not assumed b

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TRENSMITTED VIA TELECOPIER RECEIVED BY

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• PAGE 1 OF 1 10-7-83 OCT 111983 Jk y&d-~

Diamond Power Specialty Company ag;jy -

Babcock & Wilcox a McDermott company P. O. Box 415

• " *"" ON 43130 October 7, 1983 (614) 687-6'500 590133-100783-1A 4A

' b_,).. f Mr. S. K. Blackley, Jr.

Duke Power Company

1. &.d 'D,

1. d f

4 2.: South Church Street Charlotte, North Carolina 28242 Attention y Mr. R. F. Day )

Cfl0RAL RECURDS[DMS10N USE s

Engineer

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, j-Gentlemen:

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Subj ect: Catawba Nuclear Station Unit #1 MPS Co. P.O. No. C-66733 DPSC Order No. 590133-R Attached you will find a graph summarizing approximate calculation of temper-ature versus time for the situation discu'ssed in the Day / Gilbert /Ehorn telecon of October 3,1983.

Picase note that the solution should not be used above 200*F because the water properties begin to change drastically above that temperature.

In making the calculation we assumed that there was no variation of water temperature with position, i.e. the model is a " lumped" heat transfer model.

Also, the overall heat transfer coefficient is assumed constant with time when in fact it will decrease as the pipe wall temperature increases with time.

This results in a faster water temperature rise than would actually be present.

The physical data used in the analysis is repeated below:

Initial Temperature = 120*F Ambient Temperature (time greater than 0.0 minutes) = 330*F Pressure in Line = ambient pressure (14.7 psia assumed)

Impulse line 0.D. = 0.50 inches Wall thickness = 0.065 inches Insulation: metal reflective, 1/2" actual thickness, SS-4 If you have any questions, please don't hesitate to contact me.

Sincerely, MIRROR INSULATION Unit of Diamond Power Robert R. Ehorn Project Administrator RRE:rm Attachment e -

E. B. Montague

ATTACHMENT 3...

t..mnounnuu non Unit of DIAMOND FOWEft SPECIALTY COMPANY 21C 2

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ORIGIN ATOR -

DATE OCT 0 0_JBB3 o.e.s.c.6aoER uo. [401 %-R CHFCKED.

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