ML20073M911

Forwards Safety Analysis for Early Auxiliary Feedwater Actuation Due to Wide Range Level Indication Sys power- Dependent Decalibr.Consequences Acceptable Through End of Cycle 5

ML20073M911
Person / Time
Site:	Calvert Cliffs
Issue date:	04/13/1983
From:	Lundvall A BALTIMORE GAS & ELECTRIC CO.
To:	Clark R Office of Nuclear Reactor Regulation
References
NUDOCS 8304220286
Download: ML20073M911 (26)

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BALTIMORE GAS AND-ELECTRIC" CHARLES CENTER P.O. BOX 1475. BALTIMORE, MARYLAND 21203 ARTHUR E. LUNOVALL, JR.

vscc PRESIDENT Suppty April 13,1983 Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555 ATTENTION: Mr. R. A. Clark, Chief Operating Reactors Branch #3 Division of Licensing

SUBJECT:

Calvert Cliffs Nuclear Power Plant Unit 2, Docket No. 50-318 Wide Range Steam Generator LevelInstrumentation System (WRSGLIS), Power-Dependent Decalibration Gentlemen:

During initial startup of U'it 2 Cycle 5 with the new Wide Range Steam Generator n

Level Instrumentation System (WRSGLIS), a power-dependent decalibration was observed. The WRSGLIS decalibration was due to dynamic effects at the lower sensing points of the new instruments, resulted in the wide range indicated lesel being lower than the actuallevel, and could result in early actuation of AFW flow.

Evaluation at startup determined' that the limiting Design Bases Event (DBE) impacted by early AFW initiation, the Steam Line Break Event, might not show acceptable results for the more negative moderator temperature coefficient associated with end of cycle 5 but that acceptable consequences would result through a burnup of at least 3000 MWD /MTU.

The enclosure presents the analyses and results which demonstrate acceptable consequences through the end of cycle 5.

l Very truly yours, BALTIMORE GAS AN ELECTRIC COMPANY

__ &: A&2_ -

'A, E. Lundvall, Jr.

f Vice-President - Supply Q) i AEL/MEB/Imt Enclosure (40 copies) l l

8304220286 830413 l

PDR ADOCK 05000318 P

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Office cf Nuclear Regulation April 13,1983 Page 2 cc:

J. A. Biddison, Esquire G. F. Trowbridge, Esquire D. H. Jaffe P. W. Kruse 4

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4 ENCLOSURE SAFETY ANALYSIS FOR EARLY AUXILIARY FEEDWATER ACTUATION DUE TO WIDE RANGE LEVEL INDICATION SYSTEM POWER-DEPENDENT DECALIBRATION 1

Introduction The Steam Line Break (SLB) event was analyzed in depth for Calvert Cliffs Unit 2 Cycle 5 in Reference (1). ' This enclosure documents the results of analyses performed to envelop a power-dependent decalibration in the Wide Range Steam Generator Level Indication System and to provide additional flexibility in the AFW flow setpoints.

The level indication decalibration was observed during startup with the new Wide Range (WR) Level Indication System and is due to dynamic flow effects at the lower pressure tap of the WR Level Differential Pressure transmitters. - The WR Level indicated at power is lower than the actual (narrow range) level and could result in earlier actuation of AFW flow than considered in Reference (1).

The limiting Design Bases Event (DBE) impacted by early AFW initiation is the Inside-Containment Steam Line Break event with loss of AC power on turbine trip. This event was analyzed for full power (HFP) and zero power (HZP) conditions assuming AFW system runout flow of 1300 gpm was initiated at the time of the Steam Line Break. All other analysis assumptions and initial conditions were identical to those of Table 3-1 and.

3-2 of Reference (1). These tables, with the changes highlighted, are repeated in Tables 1 and 2 for completeness. The HFP and HZP moderator cooldown curves (Figures 1 and 2) are also identical to those of Reference (1) (Figures 3-1 and 3-2 respectively) and are likewise included for completeness.

Results SLB Inside Containment 2

The sequence of events for the 6.305 ft SLB with Loss of AC (LOAC) on turbine trip initiated from HFP conditions is given in Table 3.

The reactivity insertion as a function of time is presented in Figure 3. The NSSS responses during the transient are given in Figures 4 through 8.

The results of the analysis show that the HFP SLB causes the secondary pressure to rapidly decrease until a reactor trip on low steam generator pressure is initiated at 1.7 seconds. The CEAs drop into the core at 3.1 seconds and terminate the power and heat flux increases.

The AFW system runout flow of 1300 gpm is initiated at the time of the Steam Line Break. This flow is assumed to be unaffected by any electrical transient due to LOAC, l

and is directed in its entirety to the ruptured steam generator until the AFW block valves are completely shut.

E A LOAC power on turbine trip is assumed to occur at 3.1 seconds. At this time, RCPs start coasting down and the diesel generators start coming on line. At 13.1 seconds, the diesel generators reach full speed and the shutdown sequencer is initiated to l

load emergency systems. At 17.0 seconds the safety injection actuation analysis setpoint j

is reached and diesel generators switch from the shutdown sequencer to the LOCA sequencer to load emergency systems. At 22.0 seconds the HPSI pump is loaded on line and at 52.0 seconds the HPSI pump reaches full speed.

The Steam Generator Isolation Analysis Setpoint is reached at 1.7 seconds. At 2.6 l

seconds, the MSIVs begin to close and are completely closed at 14.6 seconds. The l,

blowdown from the intact steam generator is terminated at this time.

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An AFW isolation signal based on steam generator differential pressure is initiated -

- at 2.9 seconds. At 22.9 seconds, the AFW block valves associated with the steam generator with lowest pressure (i.e., ruptured steam generator) are completely closed and all AFW flow is directed to the intact steam generator.

The continued. blowdown - from the ruptured steam. generator causes the core reactivity to approach criticality. The ruptured steam generator blows dry at 109.1 seconds, which terminates the cooldown of the RCS. A peak reactivity of -0.05% at 144.0 seconds is obtained. A peak R-T-P of 7.5%, consisting of 4.2% fission power and 3.3% decay power, is produced at 144.5 seconds. A transient minimum DNBR of 1.56 at 140.0 seconds is obtained.

The negative reactivity inserted due to boron injection via the HPSI pump terminates the approach to criticality and the core becomes more suberitical.

2 The sequence of events for the 6.305 ft SLB with LOAC on turbine trip initiated from HZP conditions is given in Table 4. The reactivity insertion as a function of time is presented in Figure 9.

The NSSS response during the transient are given in Figures 10 through 14.

The results of the analysis show that the HZP SLB causes the secondary pressure to rapidly decrease until a reactor trip on low steam generator pressure is initiated at 1.3 seconds. The CEAs drop into the core at 2.7 seconds and terminate the power and heat flux increases.

The AFW system runout AFW flow of 1300 gpm is initiated at the time of the Steam Line Break. This flow is assumed to be unaffected by any electrical transient due to LOAC, and is directed in its entirety to the ruptured steam generator until the AFW block valves are completely shut.

A LOAC power on turbine trip is assumed to occur at 2.7 seconds. At this time,

.RCPs start coasting down and the diesel generators start coming on line. At 12.7 seconds the diesel generators reach full speed and the shutdown sequencer is initiated to load emergency systems.

At 22.4 seconds, the safety injection actuation analysis

- setpoint is reached and the diesel generators switch from the shutdown sequencer _ to the LOCA sequencer to reload the emergency systems.

At 27.4 seconds, the diesel generators load the HPSI pump on line and 30.0 seconds later (i.e., at 57.4 seconds) the HPSI pump reaches full speed.

The Steam Generator Isolation Analysis Setpoint is reached at 1.3 seconds. At 2.2 seconds, the MSIVs begin to close and are completely closed at 14.2 seconds. The blowdown from the intact steam generator is terminated at this time.

An AFW isolation signal based on steam generator differential pressure is initated at 3.4 seconds. At 23.4 seconds, the AFW block valves associated with the steam generator with lowest pressure (i.e., ruptured steam generator) are completely closed.

AFW to the ruptured steam generator is terminated, and all AFW flow is directed to the intact steam generator.

The continued blowdown from the ruptured steam generator causes the core reactivity to approach criticality. The ruptured steam generator blows dry at 108.5 seconds, which terminates the cooldown of the RCS. A peak reactivity of +.13% at 130.5 seconds is obtained. A peak R-T-P of 2.32%, consisting almost entirely of fission power is produced at 157.5 seconds. A minimum transient DNBR of 2.6 at 160.0 seconds is obtained.

l

- The negative reactivity inserted due to boron injection via the HPSI pump terminates the reactivity excursion and the core becomes and remains suberitical.

SLB Outside Containment The primary purpose for analyzing the SLB outside containment is to calculate site boundary dose since, when compared to the inside containment break with respect to R-T-P, it is less adverse. Two sources of radioactivity contribute to the site boundary dose:

the initial activity in the steam generator, and the activity associated with primary to secondary leakage. These activities are not affected by increased AFW flow. Therefore, the results forwarded in Reference (1) remain unchanged.

Conclusions The results of the Steam Line Break inside containment shows that post-trip minimum DNBR is above the design limit of 1.3.

These bounding cases demonstrate acceptable results by means of somewhat more HERMITE credit than was used for the Reference (1) analysis. The increased HERMITE credit is, however, entirely justifiable.

The SLB outside containment results in a site boundary dose which is within 10CFR100 guidelines. Therefore, the results of the SLB event with LOAC power on turbine trip are acceptable for Unit 2 Cycle 5, even with the runout AFW flow assumed herein.

References

1. A. E. Lundvall to R. A. Clark letter dated 11/17/82, " Supplement 1 to Fifth Cycle License Application" i

TABLE 1 KEY PARAMETERS ASSUMED IN THE INSIDE CONTAINMENT STEAM LINE BREAK EVENT INITIATED FROM HFP Parameter Units Cycle 5 Initial Core Power MWt 2754.0 Initial Core Inlet Temperature F

550.0 Initial RCS Pressure psia 2300.0 Initial Steam Generator Pressure psia 860.0 Low Steam Generator Pressure psia 600.0 Analysis Trip Setpoint 1

Auxiliary Feedwater Actuation

% Wide Range Steam (1)*

Analysis Setpoint Generator Level Indication Steam Generator Differential psid 250.0 Pressure Analysis Setpoint Safety Injection Actuation Signal psia 1645.0 Minimum CEA Worth Available

% delta Rho

-6.89 at Trip i

Doppler Multiplier 1.15 Moderator Cooldown Curve

% vs. density See Figure 1 l

Inverse Boron Worth ppm /% delta Rho 95.0 Effective MTC x 10 delta Rho / F

-2.2 Beta Fraction (including uncertainty)

.0060 l

• change from Reference (1)

(1) NA - 1300 gpm AFW flow is initiated at the time of SLB.

4 TABLE 2 KEY PARAMETERS ASSUMED IN THE INSIDE CONTAINMENT STEAM LINE BREAK EVENT INITIATED FROM HZP Parameter Units Cycle 5 Initial Core Power MWt 1.0 Initial Core Inlet Temperature OF 532.0 Initial RCS Pressure psia 2300.0 Initia1 Steam Generator Pressure psia 900.0 Low Steam Generator Pressure psia 600.0 Analysis Trip Setpoint Auxiliary Feedwater Actuation

% Wide Range Steam (1)*

Analysis Setpoint Generator Level Indication Steam Generator Differential -

psid 250.0 Pressure Analysis Setpoint Safety Injection Actuation Signal psia 1645.0 Minimum CEA Worth Available at Trip

% delta Rho

-5.2 Doppler Multiplier 1.15 Moderator Cooldown Curve

% vs. density See Figure 2 Inverse Boron Worth ppm /% delta Rho 90.0

-4 Effective MTC x 10 delta Rho / F

-2.2 Beta Fraction (including uncertainty)

.0060

• Change from Reference (1)

(1) NA - 1300 gpm of AFW flow is initiated at the time of SLB.

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1 TABLE 3 SEQUENCE OF EVENT FOR INSIDE CONTAINMENT STEAM LINE BREAK EVENT WITH LOSS OF AC POWER ON TURBINE TRIP INITIATED FROM HFP Time (sec)

Event Setpoint or Value 2

0.0 Steam Line Break Occurs 6.305 ft 1

0.0 Auxiliary Feedwater is 1300 gpm Initiated; All Flow is Directed to the Ruptured Steam Generator i

1.7 Low Steam Generator Pressure 600.0 psia Analysis Trip Setpoint is Reached; Steam Generator Isolation Analysis Setpoint is Reached 2.6 Trip Breakers Open; Main Steam Isolation Valves Begin to Close; Main Feedwater Isolation Valves Begin to Close 2.9 Steam Generator Differential delta P = 250.0 psid Pressure Analysis Setpoint is Reached r

3.1 CEAs Enter Core; Loss of AC Power on Turbine Trip; RCP Coastdown Begins; Diesel Generator Start Coming on Line;-

Main Feedwater Rampdown Begins 13.1 Diesel Generators Reached Rated Speed Following LOAC Power; Shutdown Sequencer Initiated 14.6 Main Steam isolation Valves Completely Close 17.0 SafetyInjection Actuation 1645.0 psia Analysis Setpoint is Reached; LOCI Sequencer Initiated 19.0 Pressurizer Empties 22.0 Power Provided to High Pressure Safety Injection Pumps

TABLE 3 (continued) -

- Time (see)

' Event Setpoint or Value 22.9 AFW Block Valve Completely 1300 gpm Closed; All Flow Directed to Undamaged Steam Generator 23.1 Main Feedwater Rampdown 8% of full Completed power feedwater flow 52.0 High Pressure Safety Injection Pump at Full Speed 82.6 Main Feedwater Isolation Valve Completely Closed 109.1 Affected Steam Generator Blows Dry 144.0 Peak Reactivity

-0.051% delta Rho 144.5 Peak Return to Power 7.5% of 2700 MWt F

TABLE 4 SEQUENCE OF EVENT FOR INSIDE CONTAINMENT STEAM LINE BREAK EVENT WITH LOSS OF AC POWER ON TURBINE TRIP INITIATED FROM HZP Time (sec)

Event Setpoint or Value 2

0.0 Steam Line Break Occurs 6.305 ft 0.0 Auxiliary Feedwater is 1300 gpm Initiated; All Flow is Directed to the Ruptured Steam Generator 1.3 Low Steam Generator Pressure 600.0 psia

' Analysis Trip Setpoint is Reached; Steam Generator Isolation Analysis Setpoint is Reached 2.2 Trip Breakers Open; Main Steam Isolation Valves Begin to Close; Main Feedwater Isolation Valves Begin to Close 2.7 CEAs Enter Core; L.oss of AC Power on Turbine Trip; RCP Coastdown Begins; Diesel Generators Start Coming on Line 3.4 Steam Generator Differential delta P = 250.0 psid Pressure Analysis Setpoint is Reached 12.7 Diesel Generators Reached Rated Speed Following LOAC Power; Shutdown Sequencer Initiated l

14.2 Main Steam Isolation Valves Completely Close 17.7 Power Provided to High Pressure Safety Injection Pumps 22.4 SafetyInjection Actuation 1645.0 psia Analysis Setpoint is Reached; LOCI Sequencer Initiated i

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TABLE 4 (continued)

Time (sec)

Event Setpoint or Value 23.4 AFW Block Valve Completely Closed; All Flow Directed to Undamaged Steam Generator 26.9 Pressurizer Empties 27.4 Power Provided to HPSI Pump 57.4 High Pressure Safety Injection Pump at Full Speed 108.5 Affected Steam Generator Blows Dry 130.5 Peak Reactivity

+.127% delta Rho 157.5 Peak Power 2.32% of 2700 MWt

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