ML20150D119

Drywell Temp Analysis

ML20150D119
Person / Time
Site:	Pilgrim
Issue date:	08/31/1987
From:	Sozzi G GENERAL ELECTRIC CO.
To:
Shared Package
ML20150D110	List: BECO-88-051, Forwards GE Rept EAS-98-0887, Drywell Temp Analysis, Providing Revised Drywell Temp Profiles Requested in NRC .Temp Profiles Determined Based on 30 & 10 Minutes of Drywell Spray Initiation Time ML20150D119
References
DRF-T23-00614, DRF-T23-614, EAS-98-0887, EAS-98-887, NUDOCS 8803230100
Download: ML20150D119 (62)

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EAS-98 0887 DRF T23 00614 AUGUST 1987 i

DRWELL' TEMPERATURE ANALYSIS FOR PI14 RIM NUCLEAR POWER STATION E. H. Hoffmann S. G. Terrill P. T. Tran s

L. L. Chi Approved by:

G. L. Sozzi, Manager Application Engineering Services 8803230100 800315 PDR ADOCK 05000293 P

PDR GENERAL $ ELECTRIC

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IMPORTANT NOTICE REGARDING CONTENTS OF THIS REPORT Please Read Carefully The only undertakings of General Electric Company respecting infortnation in this document are contained in the contract between the customer and General Electric Company, as identified in the purchase order for this report, and nothing contained in this document shall be construed as changing the contract. The use of this information by anyone other than the customer or for any purpose other than that for which it is intended, is not authorized; snd with respect to any unauthorized use, General Electric makes no representation or warranty, and assumes no liability as to the completeness, accuracy, or usefulness of the information contained in this document.

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i ABSTRACT The dryvell airspace response to a spectrum of pipe breaks is calculated in order to define the response envelope for equipment qualification purposes for the Pilgrim Nuclear Power Station.

The maximum calculated dryvell airspace temperature is 330 F for a duration of. 10 minutes. The effects of operator action to initiate dryvell spray and the response of equipment inside the drywell were also determined.

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TABLE OF CONTENTS Ea!&

ABSTRACT 1-1

1. INTRODUCTION

2.

SUMMARY

AND CONCLUSIONS 2-1 3-1

3. MODEL DESCR!"TIONS 3.1 SHORT-TERM COUPLED REACTOR AND CONTAINMENT MODEL 31 3.2 LONG-TERM HEAT AND MASS BAIANCE MODEL 31 4."INITIAL CONDITIONS AND ASSUMPTIONS 4-1 4.1 INITIAL CONDITIONS 4-1 4.2 MODELING ASSUMPTIONS 4-2 4.3 ASSUMPTIONS FOR DRYWELL SPRAY TIME 4-4 4.3.1 Assumed Operator Action Time for ADS 4-4 4.3.2 Conservative Operator Action Time for 45 Containment Sprays 4.3.3 Realistic Operator Action Time for 45 Containment Sprays

5. ANALYSIS RESULTS FOR CONSERVATIVE DRYWELL SPRAY TIME 5-1 5.1 IBA LOCA ACCID NT SEQUENCE 5-2 l

5.1.1 1.00 ft Steam Break 5-2 5.1.2 0.50 ft Steam Break 53 5.2 IBA LOCA ANALY IS RESULTS 5-4 5.2.1 1.00 ft Steam Break 54 5.2.2 0.50 ft Steam Break 5-5 5-6 5.3 SBA LOCA ACCIDgNT SEQUENCE 5-6 5.3.1 0.10ft}SteamBreak 5.3.2 0.01 ft Steam Break 5-7 5,4 SBA LOCA ANALY IS RESULTS 5-8 5.4.1 0.10 ft Steam Break 5-8 l

5.4.2 0.01 ft Steam Break 5-9 l

l 5.5 DRYWELL TEMPERATURE PROFILE FOR CONSERVATIVE 5-9 l

DRYWELL SPRAY TIME l

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, r TABLE OF CONTENTS (CONTINUED) l EaSa l

6. ANALYSIS RESULTS FOR REALISTIC DRWELL SPRAY TIME 6-1 l

6.1 IBA LOCA ACCID NT SEQUENCE 62 6.1.1 1.00 ft Steam Break 6-2 I

6.1.2 0.50 ft Steam Break 63 6.2 IBALOCAANALYgISRESULTS 6-4 j

6.2.1 1.00 ft Steam Break 6-4 2

L 6.2.2 0.50 ft Steam Break 6-5 6.3 SBA LOCA ACCIDgNT SEQUENCE 6-6 g

6.3.1 0.10 ft Steam Break 66 2

6.3.2 0.01 ft Steam Break 67 6.4 SBA LOCA ANALY@IS RESULTS 68 6.4.1 0.10ftjSteamBreak 6-8 6.4.2 0.01 ft Steam Break 68 L

6.5 DRWELL TEMPERATURE PROFILE FOR REALISTIC 68 DRYWELL SPRAY TIME 6.6 TEMPERATURE RESPONSE OF DRYWELL EQUIPMENT 69 f

7. REFERENCES 71 APPENDIX A A1 FIGURES FOR CONTAINMENT TEMPERATURE RESPONSE WITH CONSERVATIVE DRYWELL SPRAY TIME B1 APPENDIX B FICURES FOR CONTAINMENT TEMPERATURE RESPONSE WITH REALISTIC DRWELL SPRAY TIME f I

.m LIST OF TABLES AND FIGURES g

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Table 2 1:

Pilgrim Drywell Temperature Envelope for 2-2 Conservative Drywell Spray Time Table 2 2: Pilgrim Drywell Temperature Envelope for 2-3 Realistic Drywell Spray Time Table 6-1: Time when Setpoints for Drywell Spray 6 10 have Exceeded Figure 2-1: Short-term Drywell Temperature Responsa 24 Envelope for Conservative Drywell Spray Time Figure 2-2: Long-term Drywell Temperature Response 2-5 Envelope for Conservative Drywell Spray Time Figure 2-3: Short term Drywell Temperature Response 2-6 Envelope for Realistic Drywell Spray Time Figure 2 4: Long-term Drywell Temperature Response 2-7 Envelope for Realistic Drywell Spray Time Figure 3-1: Coupled Reactor and Containment Model 3-3 5-10 Figure 5-1: ContainmengAirspaceTemperatureResponse to 1.00 ft Steam Break with Conservative Drywell Spray Time 5-11 Figure 5-2: ContainmengAirspaceTemperatureResponse to 0.50 ft Steam Break with Conservative Drywell Spray Time 5-12 Figure 5-3: Containmeng Airspace Temperature Response to 0.10 ft Steam Break with Conservative Drywell Spre.y Tirne 5-13 Figure 5-4: ContainmenjAirspaceTemperatureResponse to 0.01 ft Steam Break with Conservative Drywell Spray Time 6-11 Figure 6-1: ContainmengAirspaceTemperatureResponse to 1.00 ft Steam Break with Realistic Drywell Spray Time 6-12 Figure 6-2: ContainmenyAirspaceTemperatureResponse to 0.50 ft Steam Break with Realistic Drywell Spray Time

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LIST OF TABLES AND FIGURES (CONTINUED) fact i

1 Figure 6-3: Containmen! Airspace Temperature Response 6-13 to 0.10 ft Steam Break with Realistic j

Drywell Spray Time 1

Figure 6-4: Drywell Equipment Temperature Response 6 14 N

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INTRODUCTION In the event of a postulated Loss-of-Coolant Accident (IDCA), high energy coolant is released from the reactor vessel.

For pipe breaks inside the drywell, this release of liquid or steam would quickly increase the temperature of the drywell, including the airspace, the walls, and any structures inside.

Safety-related equipment inside the dryvell mur,t be capable of surviving certain conditions of this environment in order to meet the equipment's design objective.

The NRC (i,n Reference 1) requires safety-related equipment to be qualified for use up to 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> e t 340 F.

Alternatively, a plant specific containment temperature analysis can be performed to justify relaxed requirements, I

if appropriate.

This analysis was performed to provide the plant unique containment response for the Pilgrim Nuclear Power Station (PNPS). The plant unique containment response to the spectrum of IhCAs was calculated in order to determine the drywell airspace temperature response envelope.

The analysis was performed in compliance with the guidelines presented in Reference 1.

Heat transfer from the drywell airspace to the drywell walls was considered, as outlined in Appendix B of Re ference 1.

The analysis considered the effect of the drywell airspace temperature response to a conservative dryvell spray time and to a realistic drywell spray time.

The calculated response envelopes are to be used for equipment qualification purposes in lieu of the h7C generic envelope.

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2.

SUMMARY

AND CONCUJSIONS Long-term limiting 1ACAs have been evaluated to find the bounding l

drywell airspace temperature response envelope.

The envelope is to be used for equipment environmental qualification for PNPS.

Assumptions l

were chosen which maximize the drywell temperature peak following break initiation. The temperature response is dependent on the initiation of drywell spray.

A conservative 30 minute drywell spray was assumed for all break sizes.

The temperature response for this conservative spray tige is shown in Table 2-1 and Figures 2-1 and 2 2.

The calculated peak dryvell temperature never exceeds the limit of 340 F set by the NRC.

The calculated peak temperature of 330 F exists for 10 minutes after which the temperature drops to below 255 F af ter one-half hour.

The analysis of conservative operator action time for drywell spray 'shows

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that the setpoints which require the operator to initiate drywell spray will occur early in the accident.

This supports a more realistic operator action time of 10 minutes for drywell spray initiation for 2

2 breaks larger than 0.01 ft and 30 minutes for breaks 0.01 ft or smaller.

The calculated temperature envelope using the realistic operator action time for drywell spray is shown in Table 2-2 and Figures 2-3 and 2 4.

The temperature envelope based on the realistic operator action time for drywell spray can be used for equipment qualification pending on NRC acceptance.

2-1

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TABLE 2-1 DRWELL TEMPERATURE ENVELOPE FOR CONSERVATIVE DRWELL SPRAY TIME Drywell Temocrature ( F1 Time from LOCA Initiation 330 0 - 10 min 320 10 20 min 310 20 - 25 min 281 25 - 30 min 255 - 201 linearly 0.02 - 0.28 days 201 - 180 linearly 0.28 - 0.90 days 180 - 160 linearly 0.00 2.02 days 160 - 141 linearly 2.02 5,50 days 141 - 130 linearly 5.50 11.0 days 131 - 120 linearly 11.0

- 33.0 days 120 - 110 linearly 33.0 - 150.0 days 110 - 106 linearly 150.0 365.0 days 2-2

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TABLE 2-2 DRWELL TEMPERATURE ENVELOPE FOR REALISTIC DRWELL SPRAY TIME Time from LOCA initiation Drywell Temperature ( F) 0 - 10 min 330 10 - 30 min 281 0.02 - 0.28 days 255 - 200 linearly 0.28 - 0.90 days 200 - 180 linearly 0.90 2.02 days 180 - 160 linearly 2.02 - 5.50 days 160 - 140 linearly 5.50 - 11.0 days 140 - 130 linearly 11.0 - 33.0 days 131 - 120 linearly 33.0 - 150.0 days 120 110 linearly 365.0 days 110 - 106 linearly 150.0 i

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PILGRIM NUCLEAR POWER STATION SHORT TERM DRYWELL TEMPERATURE ENVELOPE 350 340 -

330 C

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310 -

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Figure 2-1: Short-term Drywell Temperature Response Envelope for Conservative Drywell Spray Time

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PILGRIM NUCLEAR POWER STATION LONG TERM DRYWELL TEMPERATURE ENVELOPE 340 l

320 -

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300 -

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Figure 2-2: Long-term Dryvell Temperature Response Envelope for Conservative Drywell Sorav time

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SHORT TERM DRYWELL TEMPERATURE ENVELOPE 350 340 -

330 C

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Figure 2-3: Short-term Drywell Temperature Response Envelope for Realistic Drywell Spray Time

PILGRIM NUCLEAR POWER STATION LONG TERM DRYWELL TEMPERATURE ENVELOPE

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340 320 -

300 -

C 280 -

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Figure 2-4: long-term Dryvell Temperature Response Envelope for Realistic Dryvell Spray Time

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MODEL DESCRIPTIONS To model each of the transients and evaluate the drywell airspace temperature up to one year elapsed time, two sets of calculations are made. The first calculation evaluates the short-term response and the second evaluates the long-term response.

3.1 SHORT TERM COUPLED REACTOR AND CONTAINMENT MODEL The first calculation uses the General Electric proprietary computer code SH EF. (Reference 2) to calculate the drywell temperature response for the early part of the transient: from initiation of break flow until the drywell spray actuates and equilibrium conditions are approximately met.

This code is a coupled Reactor Pressure Vessel (RPV) and containment thermal hydraulic model. This model performs fluid mass and energy balances between the reactor primary system and the dryvell and wetwell.

The outputs include vessel water level and pressure, break flow and enthalpy, and drywell and wetwell ai'; space temperatures. The various modes of operation of all the important auxiliary systems are modeled, such as the Safety Relief Valves (SRVs), Main Steam Isolation Valves (MSIVs), Emergency Core Cooling Systems (ECCS), Residual Heat Removal (RMR) syster2 and feedwater.

Figure 31 illustrates the code model of the reactor vessel, dryvell, wetwell, and some of the reactor auxiliary systems present at PNPS.

3.2 LONG TERM HEAT AND MASS BA1ANCE MODEL After the early dynamic response dies out, the governing phenomenon is characterized by a quasi steady heat and mass balance. Therefore, the response out to one year elapsed time uses a simpler model.

Energy is l

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added to the s.ystem by the decay heat of the reactor and the RHR pump heat and is *;emoved by the RHR heat exchanger.

Energy is transferred within the system by the break flow and the ECCS and RHR flows. The temperature of the drywell is found by taking a mass weighted average of the break and drywell spray enthalpy.

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Figure 3-1 Coupled Reactor and Containment Model I

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4 INITIAL CONDITIONS AND ASSUMPTIONS l

4.1 INITIAL CONDITIONS l

The following initial conditions were used in the analysis:

The reactor is operating at 102% of rated thermal power (2038 MVt).

a.

i b.

The suppression pool is at 90 F, corresponding to the maximum operating pool temperature.

c.

The suppression pool water volume is at the minimu.'n technical specification limit of 84,000 cubic feet, d.

The drywell, airspace is at a temperature of 135 F, and the airspace is at the high relative humidity (1004) level for normal power ope.ca tion,

The wetwell airspace temperature is at the maximum temperature for e.

normal power operation (90 F) at maximum relative humidity (1004).

4.2 MODELING ASSUMPTIONS l

The following assumptions were used in the analysis to model the

,i event sequence and the system response:

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Emergency power is available, b.

The normal automatic functions of the plant safety systems are available unless specified otherwise, The May Vitt decay heat curve (Reference 3) is used.

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Control Rod Drive (CRD) flow is assumed to decrease from its rated value of 5.833 lbm/see to zero within one second after the event initiation.

Loss of the CRD flow is due to the Loss of Offsite I t Power (LOOSP) and LOCA signals.

The steam line breaks were assumed to be at the steam sapply line e.

of tha High Pressure Coolant Injection (HPCI) system, effectively disabling the HPCI system.

This maximizes the blowdown time for these breaks since no cold HPCI water refills and depressurizes the vessel.

However, the Reactor Core Isolation Cooling (RCIC) system is available for high pressure inventory makeup, which precludes actuation of the Automatic Depressurization System (ADS) for the very small breaks.

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The Main Steam Isolation Valves (MSIVs) close in 3 seconds after a one half second delay following the event initiation, which represents the minimum MSIV closure tine. This is conservative since h ;;c. vide s for the nrt severe isolation and therefore increases vessel stored energy, which must ultimately be delivered to the contain=ent.

1 The control volume of the reactor includes the reactor vessel, the g.

recirculation lines, and the main steam lines up to the inboard MSIVs.

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The drywell heat sink includes the dryvell steel liner, the vent the reactor pedestal, and the shield wall.

system, i.

Lov values for the condensing beat transfer coefficient were used, based on the NRC's formulation of the Uchida correlation found in i

Appendix B

of Reference 1.

Experiments have shown that I

condensation heat transfer rates can be much higher. For example,

see the discussion related to the Tagami correlation in Appendix C I

of Reference 1.

Also, J.J. Cabajo (Reference 4) suggests heat transfer coefficients four to five times higher than the Uchida or Tagami correlations, based on experimental evidence.

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The RHR system is dedicated to containment tipray, rather than reactor vessel level control.

The reactor vessel level can be maintained by the RCIC and Low Pressure Core Spray (LPCS) systems.

P One of the two independent Residual Heat Removal (RHR) systems is univailable.

Calculations have shown that the RRR failure represents the worst single failure.

1.

The drywell airspace contains a homogeneous air / steam mixture, m.

Vessel injection is stopped at vessel high water level (level 8).

Although LPCS has no automatic high level shutoff, it is assumed that the operator will act to prevent the LPCS system from filling the vessel above this level.

This is conservative since the water level will remain below the level of the main steamline, and the break flow from a steamline break would continue as a steam flow, rather than a liquid flow.

n.

The initial containment conditions are set to yield low pressures which result in higher drywell tecperatures.

o.

The Moody Slip Flow Model is used for the break flow calculation.

p.

The feedwater pumps are assumed to coast down to zero flow in seven seconds following the break initiation, due to the lh0SP.

q.

The operator will perform the necessary actions specified in the Emergency Procedure Guidelines (EPG) to mitigate the consequences of the accident.

This includes initiating nanual depressurization system with the ADS and the drywell and vetwell sptays based on containment conditions.

The specified containment conditions and the bases for the assumed time for operator action are discussed in

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1 4.3 ASSUMPTIONS FOR OPERATOR ACTION TIME During an accident event, the operator can take several actions to mitigate the consequences of the accident.

He can initiate the ADS to facilitate the initiation of the low pressure system.

This will have ar effect on the long term response of the containment airspace tempera-ture.

He can also terminate the heatup of the drywell by initiating drywell spray.

Initiation of the drywell spray has a significant effect on the containment temperature response since the drywell spray will rapidly terminate the superheat conditions of the steam inside the drywell.

The EPG provide specific instructions to initiate ADS, j

drywell and wetwell sprays during an accident event (Reference 5).

Therefore, the analysis assumes that the operator will perform these functions in accordance with the EPC.

In theory, the operator will perform the manual actions specified in the EPC as soon as the symptom requiring those actions have been detected.

In practico, some delay may occur because of the potentially chaotic situation during a IDCA event, especially during the initial portion of the event.

The operator may not be able to track the symptoms immediately or he may need some time to confirm that the correct indicated signals are being received.

For these reasons, various delay times for the manual actions were evaluated in the analysis.

The assumed delay times and their bases are described be' w.

4.3.1 Assured Operator Action Time for.ADji The ADS will automatically initiate on low water level and high dryvell pressure signals.

However, for very small breaks where the j

reactor water level decreases slowly, the ADS is assumed to be initiated manually based on drywell temperature exceeding 281 F for over 10 minutes.

This assumption is conservative comparing to the standard 10 minute time for manual action used for the LOCA analysis to determine the adequacy of core cooling for compliance with 10CFR50 Appendix K.

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i 4.3.2 Conservative Operator Action Tiee for Contain-ent Sorays In accordance with the EPG, the emergency operating procedures for PNPS require that the drywell spray be actuated if either the drywell temperature exceeds its design value of 281 F or the wetvell pressure exceeds 11 psig.

The wetvell spray is actuated before the vetvell pressure exceeds 11 psig, since actuation of the wetwell spray has no significant adverse impact on plant equipment due to the lack of moisture sensitive equipment in the wetvell.

For a

large or intermediate break event, the drywell temperature and the wetvell pressure would exceed these limits within the first five minutes of the event.

For a small treak event, the heat input from the break to the containment can be so slow that the drywell and vetvell parameters may not reach these limits until 30 minutes into the event.

For conservatism, the analysis assumes that the operator will initiate the drywell and wetwell sprays in 30 minutes after event initiation for all break sires, although the monitored drywell and wetvell parameters may exceed the prescribed EPG limits.

The 30 minute operator action time for containment sprays has been accepted by the NRC (Reference 6).

The analysis and results for the conservative time for drywell and wetwell sprays are presented in St.ction 5 of this report.

4.3.3 Realistic Operator Action Time for Containment Sorays l

Although the operator may not be able to initiate dryvell and wetwell sprays instantaneously during a LOCA event when either the I

dryvell temperature or wetwell pressure has exceeded the prescribed limits, the 30 minute operator action time is very conservative.

The

' i operator has been trained in accordance with the EPG.

The EPC provides specific guidelines for the operators based on the observed symptom of the reactor.

In general, during a LOCA event, the operator's actions are focused in two areas:

maintaining core cooling and containment integrity.

For the large or intermediate break events, the core cooling will be automatically performed by the LPCS or the Rim system in the Low Pressure Coolant Inj ec tion (LPCI) mode, k'i thin 10 g

minutes of the event, the core cooling is established for these sires of 4-5 d

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breaks and the LPCI function of the RHR can be diverted for contain: cent sprays.

In fact, once core spray flow has been established, the operator c:an manually bypass the nocessary interlocks to initiate the containment sprays to ensure contain=ent integrity.

For a small break event, the containment response to the break is slow.

'W e demand for immediate core cooling is not as severe.

For most events, HPCI or feedwater will be available.

Even if the break is at the HPCI line, a very small break does not necessary defeat the HPCI operation and the RCIC may be * #ficient for core cooling.

Consequently, the operator does not }

• focus primarily for core cooling durin, a small break e

event as h to during a large or intermediate break event. Thus, he 4

can deterna.ua and perform the necessary actions to provide containment cooling if the situation requires such actions.

For these reasons, it is realistic to assume that the operator can initiate containment sprays within the first 10 minutes of eve.;* witiatien for breaks where the drywell temperature and wetvell preu, has exceeded the EPG 1.mits before the 10 minute time frame.

For the very small breaks where the drywell temperature or vetvell pressure does not exceed the limits within 10 minutes of event initiation, the analysis will assume that the containment sprays will be initiated at 30 minutes.

The results of the realistic operator action time for containment sprays are presented in Section 6 of this report.

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5.

ANALYSIS RESULTS FOR CONSERVATIVE DRWELL SPRAY TIME The peak drywell temperature due to a li)CA is primarily determined by the censtant enthalpy decompression process of saturated fluid from reactor to drywell conditions.

Therefore, steam line breaks were ar.alyzed since they result in a superheated drywell environment.

A 2

2 spectrum of break sizes from 1.0 ft to 0.01 ft vers evaluated to provide a complete a.3 bounding envelope of the drywell temperature re,sponse, including both elapsed time and temperature.

Steam line 2

breaks larger than 1.0 ft have been found to result in significant two phase break flow due to vessel level swell.

The drywell temperature resulting from two-phase flow would be the saturation temperature at the drywell pressure.

This is considerably less than the superheat conditions obtained from the steam line breaks due to the constant enthalpy decompression of high pressure saturated steam.

Steam line 2

breaks smaller than 0.01 ft would not produce sufficient heat to raise the drywell temperature to above 281 F.

Drywell temperature responses for liquid line breaks for PNPS are documented in Reference 7.

The results of the analysis for the spectrum break sizes with conservative operatur action time for containment spray are presented in j

this section.

The first four subsection presents the details of the event sequence and the analysis results for the 1.0 and 0.5 ft breaks l

of the inter"aediate break accident events (IBA) and for the 0.1 and 0.01 ft breaks of the small break accident events (SBA).

The results for the entire break spectrum are then summarized in Subsection 5.5 to present a drywell temperature envelope for the conservative operator action time for PNPS. The drywell temperature response for break.= other than those listed above are presented la Appendix A of this report.

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5.1 IBA 14CA ACCIDENT SEQUENCE 5.1.1 1.00 ft Steam Break Time (sec)

Event Descriotion 0

IBA occurs during normal plant operation 2

(1.00 ft HPCI steam supply line break).

Automatic reactor scram on LOOSP.

3 Drywell airspace temperature reaches 281 F.

3.5 MSIVs fully closed (after 0.5 second delay).

7 Feedwater flow to vessel stopped at the end of pump / motor coastdown period.

8 Wetwell pressure reaches 11 psig.

j 50 RCIC system begins coolant injection to RPV.

l 141 LPCS system begins coolant injection to RPV to restore vessel water level.

1800 Drywell spray and wetwell sprays are activated

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through operator action.

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5.1,2 0.50 ft Steato Break l

Time (sec)

Eyent Descriotion 0

IBA occurs during normal plant operation 2

(0.50 ft HPC. steam supply line break).

Automatic reactor scram on LOOSP.

3.5 MSIVs fully closed (after 0.5 second delay).

7 Feedwater flow to vessel stopped at the end of pump / motor coastdown period.

9 Drywell airspace temperature reaches 281 F.

18 Wetwell pressure reaches 11 psig.

71 RCIC system begins coolant injection to RPV.

300 LPCS system begins coolant injection (after pump shutoff head is reached in the vessel) i;i to restore vessel water level.

1800 Drywell spray and wetwell sprays are activated through operator action, q

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5.2 IBA LOCA ANALYSIS RESULTS 2

5.2.1 1.00 ft Steam Break The model described in Section 3.1 was used to evaluate the system response up until the time that the drywell spray flow stabilizes the drywell conditions.

The model described in Section 3.2 was used to evaluate the response after drywell spray initiation.

The short-term response for the 1.00 ft break is given in Figure. 1, while the long-term results are summarized and presented in Figure 2 2 for all the breaks analyzed.

q The reactor scrams immediately after initiation of the pipe break due to the LOOSP.

The primary system isolates within 3.5 seconds (the

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actual isolation time due to a lh0SP event would be much longer, since the power for the isolation logic is derived from the motor generator t'

(MG) sets, which have a finite coastdown period).

The feedwater flow coasts down to zero by 7 seconds.

Inj ection from RCIC begins at 50 seconds but the RCIC flow is not effective for this size break.

A Inj ection from LPCS begins at 141 seconds and begins to reflood the vessel, as the drywell airspace begins to cool off.

The drywell temperature reaches 281 F within the first 3 seconds of 1

the event.

The drywell temperature reaches its first peak of N

approximately 300 F early in approximately 8 seconds due to the vessel blowdown.

The peak drywell temperature of 330 F is reached in

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approximately 78 seconds of the event.

3 At 1800 seconds the drywell and wetwell sprays are manually actuated.

The sprays are initiated since the spray initiation setpoints l

of 281 F drywell temperature is reached in 3 seconds and the setpoint of N

11,psig wetwell pressure is reached in 8 seconds.

The drywell p

temperature prior to the spray initiation is 256 F, considerably below l

its peak tecperature value and close to the saturation temperature of l

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5-4

the dryvell pressure.

Therefore, the initiation of the drywell sprays does not drop the resulting drywell temperature significantly.

Only a 4 F temperature drop is noted.

In the shcrt-term evaluation, the drywell temperature remains at 252 F after the initiation of the dryvell spray up to 20 a.nutes.

At this point the RRR is initiated to remove decay heat.

The drywell temperature will decrease initially but as the decay heat is still greater than the RHR heat removal rate and the containment temperatures soon begin to rise again until, at about 17000 seconds, the drywell airspace reaches a second peak of 199 F.

Thereafter the drywell tepperature decreases gradually.

2 5.2.2 0.50 ft Steam Break 2

The short term response for the 0.50 f t break is given in Figure 5-2.

The long-term results are being enveloped in Figure 2-2.

The overall response is similar to the 1.00 ft break response, except that the increased vessel blowdown time maintains relatively high drywell temperatures and delays LPCS injection until the LPCS pump shutoff head is reached in the vessel.

Again both the drywell and wetwell spray initiation setpoints are exceeded quite early, 9 and 18 seconds, respectively, which requires immediate manual spray initiation per EPG requirements.

By assuming the conservative 30 minutes of operator action time to initiate containment spray, the containment temperature is at 266 F before spray actuation.

In this case, the effect of the containment spray on the containment airspace temperatures can be better seen in the figure.

The drywell temperature shows a sudden decrease as the drywell sprays actuate, due to the de-superheating of the dryaell as

'if the airspace and spray water come into equilibrium.

However, the temperature drop in this case is only approximately 15 F.

b i

5-5

i_ -

i l

5.3 SBA LOCA ACCIDENT SEQUENCE 2

5.3.1 0.10 ft Steam Break I

Time (sec)

Event Description O

SBA occurs during normal plant operation (0.10 ft HPCI steam supply line break).

Automatic reactor scram on LOOSP.

3.5 MSIVs fully closed (after 0.5 second delay).

7 Feedwater flow to vessel stopped at the end of pump / motor coastdown period.

125 L'etwell pressure reaches 11 psig.

170 Drywell airspace temperature reaches 281 F.

193 RCIC system begins coolant injection to RPV.

770 Operator begins manual depressurization of the reactor with the ADS valves.

d 951 LPCS system begins coolant injection to RPV to r

restore vessel water level.

d 1800 Drywell and wetwell sprays are activated through operator action.

]

a 56 x

=uuL 4

2 5.3.2 0.01 ft steam Break Time (see)

Event DescrioL12D 0

SBA occurs during normal plant operation 2

(0.01 ft HPCI steam supply line break).

Automatic reactor scram on LOOSP.

3.5 MSIVs fully closed (after 0.5 second delay).

7 Feedwater flow to vessel stopped at the end of pump / motor coastdown period.

361 RCIC system begins coolant injection to RPV.

i 1209 Wetwell pressure reaches 11 psig.

1765 Drywell airspace temperature reaches 281 F.

1800 Drywell and wetwell sprays are activated through operator action.

2365 Operator begins manual depressurization of the reactor with the ADS valves to initiate long term core cooling with LPCS.

i u

h1 d

5-7 s

i 5.4 SBA IDCA ANALYSIS RESULTS 2

5.4.1 0.10 ft Steam Break The short-term and long-term responses are provided in Figures 5-3 and 2-2, respectively.

Again, the overall response is similar to the IBA results, except for a further increase in reactor blowdown time.

However, the containment spray initiation setpoints are still exceeded quite early requiring prompt spray system actuation as in the IBA

1 analysis.

However, with the conservative spray time assumption, the dr.ywell temperature rises to its peak of 325 F at approximately 800

-1 seconds. Thereafter, the combined effect of ADS and LPCS begins to cool off the reactor vessel as well as the drywell. The ADS actuation at 770

!I seconds is prompted by the drywell temperature exceeding 281 F for ove 10 minutes.

This is conservative since the operator would initiate AD" earlier based on the vetwell pressure setpoint.

At 1800 seconds, the drywell temperature is lowered to 261 F.

Initiation of the drywell spray drops the temperature to approximately 250 F with steady decrease in the drywell temperature thereafter.

2 5.4.2 0.01 ft Steam Break Figures 5-4 and 2-2 give the short-term and long-term results of the drywell temperature response, respectively.

Here the response is unique since such a small steam break would require quite some time to depressurize the vessel.

The reduced break flow does not allow for superheat conditions in the drywell until the drywell walls reach the drywell airspace saturation temperature.

This is because the heat transfer at the wall switches from a condensation heat transfer mechanism (with a high heat transfer coefficient) to a nateral convection heat transfer mode.

The effect of this switch can be clearly seen in Figure 5-4, where the departure from saturation conditions in 5-8 J

, n w -..

i l

i

'l the drywell occurs at about 700 seconds.

The drywell temperature then hl rises to a peak of 281 F just before the drywell sprays actuate at 1800 seconds.

The drywell spray reduces the drywell temperature by approximately 40 F.

4 5.5 DRWELL TEMPERATURE PROFILE FOR CONSERVATIVE DRWELL SPRAY TIME The drywell temperature profile for the conservative drywell spray time is developed by combining the results of the drywell temperature 2

responses for steam line breaks from 1.00 to 0.01 ft The break sizes 2

evaluated are 1.00, 0.75, 0.5, 0.25, 0.10, 0.075, 0.050 and 0.01 ft The detail sequence of event and the drywell temperature responses for 2

the 1.00, 0.50, 0.10, and 0.01 ft are presented in previous subsections.

The drywell temperature response for the remaining br.eaks listed above are shown in Appendix A.

The results of the these breaks were combined to produce a bounding drywell temperature profile for PNPS, assuming a conservative drywell spray time.

The results of this temperature profile are shown in Table 2-1 and Figures 2-1 and 2-2.

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E 6.

ANALYSIS RESULTS FOR REALISTIC DRWELL SPRAY TIME Based on the analysis results for the conservative drywell spray time, Table 6-1 presents a summary of when the drywell temperature and the wetwell pressure would exceed the setpoints for spray initiation.

This table shows that, except for the very small breaks. the setpoints for initiation of the drywell.and wetwell sprays would be reached in a 2

relatively short time.

For the very small breaks (less than 0.01 ft ),

th,e dryvell temperature rises too slow to be a concern for equipment environmental qualification. These results support the reasons given in Subsection 4.3.3 that the operator would initiate the dryvell spray in a relatively short time and that a 10 minute spray time would be a 2

[

realistic assumption for breaks larger than 0.01 ft For smaller breaks, the 30 minute assumption would still be used.

a The results of the analysis for the spectrum break sizes with realistic operator action time for containment sprays are presented in this section.

The first four subsection presents the details of the 2

event sequence and the analysis results for the 1.0 and 0.5 ft breaks of the intermediate break accident events (IBA) and for the 0.1 and 0.01 ft breaks of the small break accident events (SBA).

The. results for the entire break spectrum are then summarized in Subsection 6.5 to present a drywell temperature envelope for the realistic operator action time for PNPS.

The drywell temperature response for breaks other than those listed above are presented in Appendix B of this report.

l l

l l

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i a : L w w w ~.: m '

6.1.IBA LOCA ACCIDENT SEQUENCE 2

6.1.1 1.00 ft Steam Break Time (sec)

Event Descriotion O

IBA occurs during normal plant operation 2

(1.00 ft HPCI steam supply line break).

Automat'ic reactor scram on LOOSP.

j 3

Drywell airspace temperature reaches 281 F.

3.5 MSIVs fully closed (after 0.5 second delay).

7 Feedwater flow to vessel stopped at the end of pump / motor coastdown period.

8 Wetwell pressure reaches 11 psig.

50 RCIC system begins coolant in'jection to RPV.

141 LPCS system begins coolant injection to RPV to restore vessel water level.

600 Drywell spray and wetwell sprays are activated through operator action.

62

2 6.1.2 0.50 ft Steam Break Time (sec)

Event Descriotion 0

IBA occurs during normal plant operation (0.50 ft HPCI steam supply line break).

Automatic reactor scram on LOOSP.

3.5 MSIVs fully closed (after 0.5 second delay).

7 Feedwater flow to vessel stopped at the end of pump / motor coastdown period.

9 Drywell airspace temperature reaches 281 F.

18 Wetwell pressure reaches 11 psig.

71 RCIC system begins coolant injection to RPV.

300 LPCS system begins coolant injection (af ter pump shutoff head is reached in the vessel) to restore vessel water level.

600 Drywell spray and wetwell sprays are activated through operator action, t.

1 #

9 6-3

4

- u a 3 _. ~, s u ~ wm* r i JM%e@U

~^

6.2 IBA IDCA ANALYSIS RESULTS 2

6.2.1 1.00 ft steam Break The model described in Section 3.1 was used to evaluate the system response up until the time that the dryvell spray flow stabilizes the drywell conditions.

The model described in Section 3.2 was used to evaluate the response after drywell spray initiation.

The short-term response for the 1.00 ft break is given in Figure 6-1, while the lo.ng-term results are summarized and presented in Figure 2-4 for all the breaks analyzed.

The reactor scrams immediately af ter initiation of the pipe break due to the LOOSP.

Tb4 primary system isolates within 3.5 seconds (the actual isolation time due to a LOOSP event would be much longer, since the power for the isolation logic is derived from the motor generator (MG) sets, which have a finite coastdown period).

The feedwater flow coasts down to zero by 7 seconds.

Inj ection from RCIC begins at 50 seconds but the RCIC flow is not effective for this size break.

1 Inj ec tion from LPCS begins at 141 seconds and begins to reflood the vessel, as the dryvell airspace begins to cool off.

The drywell temperature reaches 281 F within the first 3 seconds of the event.

The drywell temperature reaches its first peak of approximately 300 F early in approximately 8 seconds due to the vessel blowdown.

The peak dryvell temperature of 330 F is reached in approximately 78 seconds of the event.

At 600 seconds the drywell and wetwell sprays are manually actuated.

The sprays are initiated since the spray initiation setpoints of 281 F dryvell temperature is reached in 3 seconds and the setpoint of 11 'psig wetwell pressure is reached in 8 seconds.

The drywell temperature prior to the spray initiation is 259 F, considerably below its peak temperature value and closer to the saturation temperature of 6-4

the drywell pressure.

Therefore, the initiation of the drywell sprays does not drop the resulting drywell temperature significantly.

Only a 11 F temperature drop is noted.

In the short-term evaluation, the dry'rell temperature remains at 252 F after the initiation of the drywell spray up to 20 minutes.

At this point the RHR is initiated to remove decay heat.

The drywell temperature will decrease initially but as the decay heat is still greater than the RHR heat removal rate e,nd the containment temperatures soon begin to rise again until, at about 17000 seconds, the drywell airspace reaches a second peak of 197 F.

Thereafter the drywell temperature decreases gradually.

i 2

6.2.2 0.50 ft Steam Break The short-term response for the 0.50 ft break is given in Figure 6-3.

The long term results are being enveloped in Figure 2-4.

The overall response is similar to the 1.00 ft break response, except that the increased vessel blowdown time maintains relatively high drywell temperatures and delays LPCS injection until the LPCS pump shutoff head is reached in the vessel.

Again both the drywell and wetvell spray initiation setpoints are exceeded quite early, 9 and 18 seconds, respectively, which requires immediate manual spray initiation per EPG requirements.

By assuming the realistic 10 minutes of operator action time to initiate containuent spray, the containment temperature is at 285 F before spray actuation.

In this case, the effect of the containment spray on the containment airspace temperatures can better seen in the figure.

The drywell temperature shows a sudden decrease as the drywell sprays acu

e, due to the de superheating of the drywell as the airspace and spray water come into equilibrium.

The initial temperature drop in this case is approximately 30 F.

6-5

6.3 SBA LOCA ACCIDENT SEQUENCE 2

6.3.1 0.10 ft Steam Break

\\

Time (see)

Event Description 0

S3A occurs during normal plant operction 2

(0.10 ft HPCI steam supply line break).

Automatic reactor scram on LOOSP.

3.5 MSIVs fully closed (after 0.5 second delay).

7 Feedvater flow to vessel stopped at the end of pump / motor coastdown period.

125 Wetvell pressure reaches 11 psig.

170 Drywell airspace temperature reaches 281 F.

193 RCIC system begins coolant injection to RPV.

600 Dryvell and wetwell sprays are activated through operator action.

770 Operator begins manual depressurization of the reactor with the ADS valves.

951 LPCS sys".em begins coolant injection to RPV to restore vessel water level.

66

. I

2 6.3.2 0.01 ft steam Break Time (sec)

Event Description 0

SBA occurs during normal plant operation 2

(0.01 ft HPCI stcam supply line break).

Automatic reactor scram on LOOSP.

3.5 MSIVs fully closed (after 0.5 second delay).

7 Feedwater flow to vessel stopped at the end of I

pump / motor coastdown period.

361 RCIC system begins coolant injection to RPV.

1209 Wetwell pressure reaches 11 psig.

1765 Drywell airspace temperature reaches 281 F.

1800 Drywell and wetwell sprays are activated through operator action.

2365 Operator begins manual depressurization of the reactor with the ADS valves to initiate long term core cooling with LPCS.

i 67

M 6.4 SBA IDCA ANALYSIS RESULTS 6.4.1 0.10 ft Steam Break The short-term and long-term responses are provided in Figures 6-4 and 2-4, respectively.

Again, the overall response is similar to the IBA results, except for a further increase in reactor blowdown time.

However, the containment spray initiation setpoints are still exceeded quite early requiring prompt spray system actuation as in the IBA analysis.

With the realistic spray time assumption, the drywell temperature rises to its peak of 320 F before spray actaation.

Actuation of the drywell spray reduces the drywell temperature to 251 F, the saturation temperature of the drywell pressure.

Thereafter, the combined effect of ADS and LPCS also contributes to cool off the reactor vessel and the drywell. The ADS actuation at 770 seconds is prompted by the drywell temperature exceeding 281 F for over 10 minutos.

This is conservative since the operator would initiate ADS earlier based on the wetwell prest are setpoint.

6.4.2 0.01 ft Steam Break Since the drywell spray time for this break size is unchanged from the conservative operator action time, the drywell temperature response fpr this break size is unchanged from the results presented in Subsection 5.4.2.

Further discussion for this break is not required.

6.5 DRWELL TEMPERATURE PROFILE FOR REALISTIC DRYWELL SPRAY TIME The drywell temperature profile for the realistic drywell spray time is developed by combining the results of the drywell temperature 2

responses for steam line breaks from 1.00 to 0.01 ft The break sizes 2

evaluated are 1.00, 0.75, 0.5, 0.25, 0.10, 0.075, 0.050 and 0.01 ft 68

s+-

The detail sequence of event and the drywell temperature responses for 2

the 1.00, 0.50, 0.10, and 0.01 ft are presented in previous subsections.

The drywell temperature response for the remaining breaks listed above are shown in Appendix B.

The results of the these breaks combined to produce a bounding yet realistic drywell temperature were profile for PNPS.

The results of this temperature profile are shown in Table 2-2 and Figures 2-3 and 2-4.

6.6 TEMPERATURE RESPONSE OF DRWELL EQUIPMDIT The temperature response of equipment inside the drywell was also evaluated using the realistic drywell spray time.

A 1 ft steel plate was used to represent equipment inside the drywell.

A lumped parameter model (infinite conductance) was used to determine the temperature response of the steel plate after achieving the drywell saturation temperature due to condensation heat trans fe r in the dryvell.

Only natural convection heat transfer in a steam environment is modeled, using a convective heat transfer coefficient of 10 Btu /hr-ft - F.

The drywell temperature is obtained from 'an assumed drywell temperature 2

envelope for a 0.5 ft break. Various thickness of the steel plate were evaluated and the results are shown in Figure 6 5.

The results show that the steel plate temperature is dependent on the thickness of the steel plate and is usually lower than the drywell airspace temperature.

For example, a 0.5 inch thick steel plate, which can be used to bound the response of a 12 inch diameter schedule 80 penetration in the drywell, reaches a maximum temperature of 290 F before being cooled by the actuation of the drywell spray.

The temperature response for other equipment inside the drywell can be determined by applying the correct thickness shown in Figure 6 5.

69

TABI E 6 1 TIME kTEN SETPOINTS FOR DRWELL SPRAY HAVE EXC TIME (sec) kHEN TIME (sec) kTEN DRWELL TEMPERATURE VENELL PRESSURE PREAK SIZE (ft 1 EXCEEDS 281 E EXCEEDS 11 esig 1.00 3

8 0.75 5

12 0.50 9

18 0.25 80 45 0.10 170 125 0.075 222 173 0.050 296 256 0.010 1765 1209 6 10

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PILGRIM PILGRIM MSL BRE0K DW TEMP ANA_YSIS 2

POOL TEMPERATLRE 2.,

i

,h OW AIRSPACE TEMP 7

i WW AIRSPACE TEMP 280.

[

't 3-ZW Z1J 180.

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1. 2x10' TIME-SEC Figure 6-2: Containment Airspace Temperature Response to 0.50 sq f t Steam Break with Realistic Drywell Spray Time

~

'80.

~

PILGRIM PILGRIM MSL BREFM OH TEMP ANALYSIS 2>

i POOL TEMPERRTlRE

,, _, 2 2 OH RIRSPACE TEMP v, 7 s WH RIRSPACE TEMP 280.

t1-g La __

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2 Q_

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TIME-SEC Figure 6-3: Containment Airspace Temperature Response to 0.10 sq ft Steam Break wit h Realistic Drywell Spray Time l

r J

'-x,.

PILGRIM DRYWELL TEMPERATURE ANALYSIS 330 --

Heatup of 1 ft**2 Steel Plate Assumptions 320 -

I - Surface area - 1 ft**2 2 - Natural Convection only

/16" (h-10. btu /hr-ft**2-degf) 3 - Initial temperature equals 310 -

1/8..

DW saturation temp (=250 F) 4 - Infinite Conductance O

h 300 -

.1 1/4" e

e s

290 -

i

/

a.

~

h

~

k ssumed DW Temo Proff1_e

\\

1/2" A

k s

[-

270 -

1" Thick 260 -

250 1

I I

I I

3 I

I 6

6 4

i i

O O.4 0.8 1.2 i.6 2

2.4 2.8 (Thousands)

Time (sec)

Figure 6-4:

Drywell Equipment Temperature Response

o 7.

REFERENCES 1.

"Environmental Qualification of Safety,Related Electrical Equ!.pment", U.S. Nuclear Regulatory Commission, NUREG-0588, Rev. 1 July 1981.

2.

C.

T.

Young, "SHEX-04 User's Manual", General Electric Company, NEDE-30911, August 1985.

3.

"Mark I Containment Program Load Definition Report", General Electric Company, NEDE 21888, Rev. 2, November 1981.

4.

J.J. Cabajo, Nuclear Enrincering and D9EiJ:D, 65 (1981),

pp. 369-386.

5.

"Emergency Procedure Guidelines Revision 4",

BWR Owners Group, NEDO 31331, March 1987.

6.

Letter, J. R. Wojnarowski to H. R. Denton, "Dresden Station Units 1 and 2 Quad Cities Station Units 1 and 2 Drywell Temperature Profile NRC Docket Nos. 50-237, 50 249, 50 254, and 50 265", September 5, 1985.

1 1

(

7.

E.

H.

Hoffmann, "Pilgrim Nuclear Power Station Drywell Wall Temperature Analysis", General Electric Company, MDE-254-1185, November 1985.

(

I 71 6

A_

4 e

i APPENDIX A FIGURES FOR CONTAINMENT TEMPERATURE RESPONSE WITH CONSERVATIVE DRYWELL SPRAY TIME A1

i-

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EPP l

RMM l.

MS LEE 2

I TTT ER S A i

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PILGRIM PILGRIM MSL BREfM DW TEMP ANALYSIS fd-POOL TEMPERATLRE m

i 2

DW RIRSPACE TEMP 2

2 s WW AIRSPACE TEMP Y

280.

1 Y

2 2

O_

Z LU W

Y s

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0 1.2 1.8 2. 11 : 1 0 '

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TIME-SEC Containment Temperature Response for 0.25 sq ft Steam Break

- Conservative Drywell Spray Time

i 380.

PI'LGRIM PILGRIM MSL BREM OW TEMP ANALYSIS

-.~ -

i POOL TEMPERATLRE DW RIRSPACE TEMP 2

WW AIRSPACE TEMP 3

2 280.

11-l O_

Z

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I-Z ttJ 180.

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2. tb10' TIME-SEC Containment Temperature Response for 0.075 sq f t Break

- Conservative Drywell Spray Time O

]h i

l 380.

PILGRIM-PILGRIM MSL OREM DW TEMP ANALYSIS POOL ~ TEMPERATLRE DW AIRSPACE TEMP 2

4 WW AIRSPACE TEMP i

s 280.

2 x

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0.6 1.2 1.8

2. 4x10 TIME-SEC Containment Temperature Response for 0.050 sq ft Steam Break

- Conservative Drywell Spray Time I

i APPENDIX B l

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FIGURES FOR CONTAINMENT TEMPERATURE RESPONSE l

VITH REALISTIC DRWELL SPRAY TIME i

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