ML20245J597
| ML20245J597 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 07/31/1988 |
| From: | Hoang H, Stoll C GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20245J595 | List: |
| References | |
| EAS-45-0688, EAS-45-688, NUDOCS 8905040192 | |
| Download: ML20245J597 (19) | |
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L EAS-45-0688 DRF A00-03345 July 1988 EVALUATION OF ECCS PERFORMANCE WITHOUT FEEDWATER COOLANT INJECTION AND WITH NORMAL AC POWER FOR MILLSTONE UNIT 1 NUCLEAR POWER STATION l
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Prepared by:
e - ),. fc C.H.Stoll, Lead Performance Engineer y-Plant Performance Engineering
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Prepared by:
H.X.Hoang, Engineer Plant Performance Engineering
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Approved by:
,A G.L.Sozfi, Ednager Plant Performance Engineering
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l GENER AL h ELECTRIC 8905040192 890425 "I PDR ADOCK 05000245.l p
PNU:
e IMPORTANT NOTICE REGARDING CONTENTS OF THIS REPORT The only undertakings of General Electric Company respecting information in this document are contained in the contract between the customer ano 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; and with respect to any unauthorized use, General Electric Company 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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EAS-45-0688 TABLE OF CONTENTS
- 1. INTRODUCTION................................................
1.
1.3 BACKGROUND
1 1.2 EVALUATION APPROACH....................................
1
- 2. EVALUATION.................................................
2 2.1-SINGLE FAILURES 2
2.1.1 Feedwater Line Breaks 3
2.1.2 Core Spray Line Breaks 3
2.1.3 Large Recirculation Line breaks...................
5 2.1.4 Small Recirculation Line Breaks 6
2.2 ECCS PERFORMANCE 8
2.2.1 Analysis Assumptions 9
2.2.2 Limiting Small Break.............................. 10 2.2.3 Small Break With LPCI Injection Valve Failure..... 10 2.2.4 Large Recirculation Line DBA...................... 11 3.
CONCLUSIONS
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~ ABSTRACT An-evaluation has been performed to determine the potential impact on ECCS performance for the Millstone. Unit 1 Nuclear Power Station with normal (off-site) ac power available and no credit for opera-tion of'the feedwater coolant injection system (FWCI).
The evaluation summarized herein shows that with the current configuration of the Millstone plant, ECCS performance with normal ac power available and without FWCI is less limiting than the current licensing basis.
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EAS-45-0688 1.
INTRODUCTION The purpose of this report is to document the results of an evaluation _ performed for the Northeast Utilities Service Company (NUSCo) for the Millstone Nuclear Power Station Unit 1 (MNPS Unit 1). The evaluation was performed to evaluate the ECCS performance assuming postulated loss of coolant accidents (LOCAs) with normal ac power available but with no credit for the FWCI.
1.1 BACKGROUND
NUSCo is evaluating planned changes to certain electrical switch-ing logic at MNPS Unit 1 which could change the allowable analysis assumptions for certain LOCA scenarios.
More specifically, if these changes were made, credit for FWCI may not be allowed for licensing analyses of LOCAs with normal ac power available.
The current LOCA licensing analyses for MNPS Unit 1 assume the loss of normal ac power in compliance with 10CFR50 Appendix K because this lecds to a more limiting result (due to longer ECCS l
response times) than the case of normal ac power available.
- However, if the FWCI is assumed non-functional when normal ac power is available, the limiting scenario for LOCA analyses is subject to change.
1.2 EVALUATION APPROACH The impact of assuming FWCI non-functional for LOCAs with normal ac power available is performed in three steps: _ _ _ _ _ _ _ _ _ _ _ - - - - - - - - _ - _ _
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EAS-45-0688 T
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- 1. Reevaluate the-potentially limiting single failures assuming
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FWCI is not.avellable whenever normal ac power is available.
2.. Identify any possible new LOCA scenarios not shown to be bounded by current licensing analyses.
3.
Evaluate the scenarios not previously analyzed that could potentially lead to results more limiting than the current licensing basis.
2.
EVALUATION Assuming normal ac power is lost coincident with a LOCA increases the response times of the ac powered emergency core cooling sys-tems (ECCS) because the emergency power sources (i.e.,
the diesel generator and/or the gas turbine generator) must be started before the ECCS pump motors can be started. Therefore, existing licensing LOCA analyses for MNPS Unit 1 are based on the loss of normal ac power coincident with the postulated LOCA.
For the evaluation herein, the availability of normal ac power is assumed to be accompanied by the unavailability of the FWCI which could potentially change the limiting LOCA scenario. Therefore, a reevaluation of the single failures both with and without FWCI available was performed.
'2.1 SINGLE FAILURES The single failures previously considered for licensing LOCA _ - _ - _ _ _ _
EAS-45-0688 l
l analyses and the systems remaining operable (i.e.,
capable of injection to the vesse?.) are shown in Table 1.
The table also l
includes the systems remaining operable assuming the FWCI is not functional. The combinations of available systems are then con-pared and evaluated for each break location to identify postulated scenarios requiring further evaluation.
2.1.1 Feedwater Line Breaks.
The ECCS performance for a postu-lated feedwater line break is unaffected by the availability of FWCI since the ACI is disabled as a result of the break location.
2.1.2 Core Spray Line Breaks.
The core spray line break eleva-tion is above the core and the break flow quality from this break location (after an initial period of liquid loss from the shroud head dome above the core) is higher than for recirculation line breaks. Also the flow area of the largest core spray line break is relatively small compared to a recirculation line break. There-fore, the total inventory mass loss from the core spray line break is much less than from an equivalent sized recirculation line break. Further, the higher two phase quality break flow results in a faster vessel depressurization rate. Both of these factors make the calculated peak fuel cladding temperature (PCT) relatively low for a postulated core spray line break. Based en previous analysis of core spray line breaks for several similar BWRs, the mass loss is not significant enough to remove the liquid in the lower plenum of the vessel (only the coolant in the core itself is affected), - _ ___ ____
1 EAS-45-0688 TABLE 1 SYSTEMS REMAINING FUNCTIONAL FOR VARIGUS BREAX AND SINGLE-FAILURE COMBINATIONS AT MNPS UNIT 1 Current Basis
- Evaluation Basis'**
BREAK SINGLE REMAINING REMAINING LOCATION FAILURE SYSTEMS SYSTEMS RECIRC GAS TURBINE 1CS+2 LPCI+IC+4 ADS 1CS+2LPCI+IC+4 ADS LINE LPCI I.V.
2CS+IC+FWCI+4 ADS 2CS+IC+4 ADS DIESEL 1CS+2LPCI+IC+FWCI 1CS+2LPCI+IC
+4 ADS
+4 ADS FWCI 2CS+4LPCI+IC 2CS+4LPCI+IC
+4 ADS
+4 ADS
.1 ADS 2CS+4LPCI+IC 2CS+4LPCI+IC
+ FWCI+ 3 ADS
+3 ADS I
CORE SPRAY GAS TURBINE
-2LPCI+IC+4 ADS 2LPCI+IC+4 ADS LINE LPCI I.V.
1CS+IC+FWCI+4 ADS ICS+IC+4 ADS DIESEL 2LPCI+IC+FWCI+4 ADS 2LPCI+IC+4 ADS FWCI 1CS+4LPCI+IC+4 ADS 1CS+41PCI+IC+4 ADS l
1 ADS 1CS+4LPCI+FWCI+3 ADS 1CS+4LPCI+3 ADS
+IC
+IC FEEDWATER
. GAS TURBINE 1CS+2LPCI+IC+4 ADS 1CS+2LPCI+IC+4 ADS LINE LPCI I.V.
2CS+IC+4 ADS 2CS+IC+4 ADS DIESEL 1CS+2LPCI+IC+4 ADS 1CS+2LPCI+IC+4 ADS 1 ADS 2CS+4LPCI+IC+3 ADS 2CS+4LPCI+IC+3 ADS
- Nomenclature:
L IC = Isolation condenser LPCI = Low Pressure Coolant Injection l
CS = Core spray System FWCI = Feedwater Coolant Injection System LPCI I.V.
= LPCI Injection Valve n ADS or nADS = n Automatic Depressurization System Valves
- Note: In this evaluation the FWCI is only assumed inoperable when normal ac power is available.. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
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EAS-45-0688 and therefore the flow from one of the ECCS pumps (i.e.,
1 core spray or 1 LPCI) is adequate to replenish the core inventory and 1
to recover the fuel before the fuel cladding heats up enough to 1
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approach the 2200 deg F Appendix K limit.
Therefore, ECCS performance for a postulated core spray line break does not depend significantly on the FWCI to assure that the PCT for this event is not limiting. Postulated core spray line break events without FWCI available will not lead to results more limit-ing than the current MNPS Unit 1 licensing basis analysis.
2.1.3 Large Recirculation Line breaks.
The Isolation Condenser (IC) and the FWCI both have a relatively minor affect on ECCS performance for postulated large recirculation line break events.
The large breaks depressurize very rapidly and therefore the IC (which is designed to remove decay heat at high vessel pressure) has very little affect on the transient. Also, the FWCI (which is designed to provide inventory makeup to the annulus region at high vessel pressure) has a very small impact on ECCS performance for postulated large recirculation line breaks.
Most of the FWCI coolant injected into the downcomer region is directly passed out the recirculation line break. As soon as the annulus water level drops to below the top of the jet pumps (which occurs very rapidly for these large breaks) none of the downcomer liquid is circulated through the jet pumps to the lower plenum and the core. Therefore this coolant is eventually lost out the break before contributing significantly to core cooling. -
EAS-45-0688 For.the case of normal ac power available (where FWCI is assuned J
unavailabic in this evaluation) the core spray and LPCI systems will.also inject sooner (because there is no delny in starting up the emergency power sources) which tends to offset the very small impact of the assumed unavailability of FWCI during large break transients.
l Therefore, the availability of FWCI has a negligible effect on l
ECCS performance for postulated large recirculation line break events and with the FWCI unavailable the current limiting licens-ing basis scenario does not change.
2.1.4 Small Recirculation Line Breaks.
systems contribute significantly to the ECCS performance for non-pipe break events or for postulated small recirculation line breaks. The pertinent break sizes are those small enough that the reactor vessel will not depressurize rapidly unless assisted by l
the ADS. For these postulated breaks, the inventory loss is slower than for large breaks, but because the vessel does not depres-surize rapidly, the core spray and the LPCI do not inject coolant to the vessel until the ADS initiates and depressurizes the vessel to the operating pressure of these systems. When the FWCI is available, coolant is injected at high vessel pressure to help depressurize the vessel and to make up for the inventory loss out the break preventing or significantly delaying core uncovery and ADS initiation. However, without FWCI available, the core begins to uncover when the ADS initiates and ECCS coolant cannot be. _ _ _ _ _ _ _ _ - _ _ -
.a EAS-45-0688 j
injected until the vessel depressurize to the operating pressure
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range of LPCI and core spray. This takes approximately 3 minutes after ADS initiation. Therefore the IC and the ADS capacities can have a significant effect on the ECCS performance for these small breaks when FWCI is not available.
This sensitivity to ADS capacity is further reinforced if the LPCI is assumed to be in-jected into the recirculation loop with the break.
MNPS Unit 1
is equipped with LPCI loop-selection-logic which detects a break in a recirculation loop and injects LPCI into the unbroken loop. However, the design basis of the logic system is to detect breaks larger than approximately 0.1 square feet. There-
- fore, in licensing analyses, break sizes 0.1 square feet and smaller are assumed to be undetected by the loop selection logic and LPCI is assumed to inject into the recirculation loop with a break. The 0.1 square foot break size is also near the upper end of the size range that will not depressurize the vessel rapidly without the assistance of ADS.
Consequently, a postulated 0.1 square ft break in the recirculation loop coincident with the unavailability of FWCI leads to a calculated PCT that is higher than for other small break scenarios. The 0.1 square ft recircula-tion line break coincident with a loss of normal ac power, a failure of the gas turbine, and injection of LPCI into the loop with the break, is the most limiting small break scenario in the current MNPS Unit 1 licensing analyses. The calculated PCT for this small break scenario is only marginally below the calculated PCT for the limiting large break scenario. _ _ _ _ _
g.
EAS-45-0688
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l Examination of Table 1 reveals that for a small break with no FWCI and with LPCI injected into the loop with the break, the only single failures that are not shown to be bounded by the current l
licensing analysis are the LPCI injection valve failure and the l
failure of one ADS valve. The calculated PCT in the small break L
scenario is more sensitive to ADS capacity than to the number of 1
ECCS pumps. Therefore, the failure of one ADS valve will result in higher calculated PCT than the LPCI injection valve failure for this small break scenario.
In
- summary, postulated small break LOCA scenarios are sig-nificantly affected by the unavailability of the FWCI. A small break LOCA with the failure of one ADS valve for a case where FWCI is unavailable is the most limiting case that has not been shown to be bounded by current licensina analyses. The 0.1 squawa ft recirculation line break (with LPCI assumed to be injected into the broken loop) is the most limiting small break scenario for consideration. This scenario should be analyzed to determine if licensing limits are impacted by the unavailability of FWCI when normal ac power is available.
2.2 ECCS PERFORMANCE The ECCS performance with normal ac power and with FWCI unavail-able was analyzed for two small break LOCA scenarios including the limiting small break LOCA scenario identified in the above evalua-tions. The PCT was calculated utilizing the approved licensing evaluation models SAFE, REFLOOD, and CHASTE. _ _ _ _ _
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EAS-45-0688 y
2'.2.1 Analysis Assumptions.
At the time of the previous licens-ing analyses, MNPS ~ Unit 1 had 316 fuel bundles in the core with holes drilled in the lower tie plate. These holes provide a path for leakage flow to the core bypass during normal operation. These
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holes also aid refilling the core after a postulated LOCA by providing a path for draining coolant injected into the bypass (e.g., with. core spray) down to the lower plenum. This' drainage to the lower plenum during postulated LOCAs can decrease the time to recover the core. The current configuration of the core at MNPS Unit l'is with the lower tie plates in all fuel bundles drilled.
Therefore, credit was taken for
" full-core-drilling" in the analyses presented herein.
One ADS valve out of four is assumed to fail and the FWCI is assumed inoperable. The faster response time of the ECCS due to the availability of normal AC power does not affect the ECCS performance for this small break scenario because the time of ECCS injection to the vessel is limited by the time to depressurize the vessel.
The fuel types in the core for the current cycle (cycle 12) are GE7B and GE8B. The most limiting fuel type (GE8B) and the most I
limiting exposure for this fuel (11,000 Mwd /Mt) was assumed in the CHASTE calculation of PCT.
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All other analysis input assumptions were the same as utilized in the previous licensing analyses, j _ _ - _ - _ - _
r EAS-45-0688 I
2.2.2 Limiting small Break.
The predicted vessel water level and pressure time histories for the 0.1 square ft recirculation line break with a failure of one ADS valve are shown in Figure 1.
The PCT calculated utilizing the CHASTE evaluation model fer the most limiting fuel type and exposure is 2070 deg F.
This PCT is below the PCT for the current 0.1 square ft recirculation break scenario
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with the lo; of normal ac power and the failure of the gas tur-bine generator.
Therefore, the failure of one ADS valve with FWCI assumed in-operable is less limiting than the current licensing basis for MNPS Unit 1.
Results for this scenario and other pertinent scenarios are summarized in Table 2.
2.2.3 Small Break With LPCI Injection Valve Failure.
The pre-vious licensing analysis results also displayed a relative peak in the PCT versus break area at the 0.18 square ft recirculation line break with a single failure of the LPCI injection valve. There-fore, to verify that the determination of the limiting small break scenario for this analysis is correct, this 0.18 square ft break size with the LPCI injection valve failure was also reanalyzed utilizing the SAFE and REFLOOD licensing evaluation models with no i
credit for FWCI.
The results of the analysis indicate that even without FWCI, this break is less limiting than the 0.1 square ft break with the gas turbine failure. This result is understandable because the effect of FWCI on the ECCS performance is very small for recirculation i 1
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EAS-45-0688 line breaks this large.
FWCI injects-coolant to the downcomer region of the vessel and can contribute coolant inventory to the core via the flow path through the jet pumps when the downcomer water level is above the top of the jet pumps. For the 0.18 square ft break, the vessel water level in the downcomer region drops below the top of the jet pumps before the FWCI begins to inject coolant into the vessel. The core spray systems inject and nearly restore core water level by the time the water level in the downcomer has been restored to the top of the jet pumps. The high powered fuel node in the core is recovered with coolant within 20 seconds after the downcomer level has been restored to the top of the jet pumps.
Therefore, for this break size, the injected coolant from FWCI can not communicate with the core until the core heatup is nearly terminated with the core spray.
These results confirm that the most limiting small break scenario was correctly identified for this evaluation.
2.2.4 Large Recirculation Line DBA.
To demonstrate the validity of the previous conclusion that the large break results are not significantly impacted by the inoperability of FWCI when normal AC power is available, the recirculation suction line DBA with the LPCI injection valve failure was also reanalyzed with the FWCI assumed inoperable. The analysis was performed with the approved licensing evaluation models SAFE and REFLOOD.
In this analysis, credit was taken for the faster response time of the core spray system due to the availability of normal ac power. _
' : '6 EAS-45-0688 i
O th normal ac power available the time to inject core spray into the vessel is governed by the time (19 seconds) for the vessel to 1
depressurize to the pressure permissive (300 psig minimum) of the core spray injection valve and the stroke time (10 seconds) of the l
injection valve. The vessel water level and pressure time his-tories are shown in Figure 2. The core uncovery and recovery times l
were compared to the previous licensing analysis DBA with the loss of normal ac power and WCI operable. The results are summarized in Table 2. These results indicate that the effect of earlier ECCS injection when normal ac power is available is a 24 second eatJier core reflooding, which more than compensates for the negative effect of assuming WCI inoperable.
3.
CONCLUSIONS Based on the above evaluation, the ECCS performance with normal ac power available and without WCI is less limiting than the current licensing basis. Therefore, the current MAPLHGR limits and the most limiting LOCA scenarios are valid for MNPS Unit 1 even with WCI assumed inoperable when normal ac power is available.
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i EAS-45-0688 TAFLE 2 1
SUMMARY
OF ECCS ANALYSIS RESULTS L'
'REAK SINGLE REMAINING ANALYSIS FAILURE SYSTEMS RESULT l
l RECIRC LPCI I.V.
2 CS+IC 24 secol;ds SUCTION (Normal ac
+ 4 ADS earlier core recovery Power but time relative to the FWCI assumed licensing basis scenario inoperable)
RECIRC GAS TURBINE 1 CS+2 LPCI+ IC 2150 Deg F SUCTION (Licensing
RECIRC 1 ADS 2 cst 4 LPCI+IC 2070 Deg F SUCTION (Normal ac
- +3 ADS PCT 0.1 Sq ft Power but FWCI assumed inoperable)
RECIRC LPCI I.V.
2 CS + IC Total Time Core is SUCTION (Normal ac-
+4 ADS uncovered is less 0.18 Sq ft Power but than for 0.1 sq ft FWCI assumed break scenario inoperable) q
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