ML20214Q182
| ML20214Q182 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 09/11/1984 |
| From: | Brandon R, Gridley R GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20214Q102 | List: |
| References | |
| 84NEDO26, NEDO-30767, NUDOCS 8706040272 | |
| Download: ML20214Q182 (16) | |
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l NEDO-30767 P CLASSI l 84NED026 SEPTEMBER 1984 l
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PILGRIM NUCLEAR POWER STATION j
LOSS OF COOLANT ACCIDENT (LOCA)
ANALYSIS UPDATE
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NEDO-30767 Class I 84NED026 September 1984 PILGRIM NUCLEAR POWER STATION LOSS-OF-COOLANT ACCIDENT (LOCA)
ANALYSIS UPDATE
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Approved: /h/A ~ Approved: m Y'//~k R.J.)frgdon, Manager R.LfGridley/ Manager Nucledr Services Engineering Fuel and Ser(ices Licensing Operation NUCLEAR ENERGY BUSINESS OPERATIONS
- GENERAL ELECTRIC COMPANY SAN JOSE, CALIFORNIA 95125 GENER AL h ELECTRIC
NED0-30767 IMPORTANT NOTICE RECARDING CONTENTS OF THIS REPORT Please Read Carefully The only undertal ings of General Electric Company respecting informa-tion in this document are contained in the contract dated January 12, 1971 between Boston Edison Company and General Electric Company, and nothing contained in this document shall be construed as changing the contract. The use of this information by anyone other than Boston Edison Company, 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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NEDO-30767 CONTENTS Page
- 1.
SUMMARY
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- 2. INTRODUCTION 2-1
- 3. ANALYSIS 3-1
- 4. RESULTS 4-1
- 5. CONCLUSIONS 5-1
- 6. REFERENCES 6-1 I
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.- NEDO-30767 I
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- 1.
SUMMARY
An update of the Loss-of-Coolant Accident (LOCA) analysis for the Pilgria Nuclear Power Station (PNPS) has been completed. This update examined the effects of plant modifications made, plant data collected, and analysis bases changed since the last LOCA analysis (Ref.1):
- a. longer stroke times for the core spray injection valves and the recirculation discharge valves,
- b. drilled lower cie plates on all fuel bandles,
- c. higher " shutoff heads" (the vessel pressure at the point of
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incipient flow into the vessel) for the Low Pressure Coolant Injection (LPCI) and Core Spray (CS) systems, and a d. injection of LPCI flow into the broken line for recirculation 2
line breaks of 0.15 ft or smaller.
I This updated analysis has shown thats
- a. The current HAPLHCR limits are adequate to meet the conditions of 10CFR50 Appendix K, and
- b. The effects of the slower valve stroke times are compensated by the effects of the full core drilling of lower tie plates, and the effects of the new analysis basis are compensated by the higher ECCS shutoff heads.
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- 2. INTRODUCTION The most recent LOCA analysis for PNPS was a lead plant type analysis performed in 1977 (Ref. 1). Since that time, several plant modifications affecting emergency core cooling system (ECCS) performance have been made, and new knowledge concerning ECCS behavior has been developed. These changes are:
- a. All fuel bundles with undrilled lower tie plates have been replaced with bundles with drilled lower tie plates (a change that potentially decreases calculated PCT).
- b. The shutof f heads of the LPCI and CS systems have been accurately determined. These shutoff heads are much higher than those assumed in the previous analysis (a change that potentially decreases calculated PCT).
I c. The analysis basis has been changed to assume that LPCI flow is 2
injected into the broken loop for recirculation line breaks of 0.15 f t or less (a change that potentially increasas calculated PCT).
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- d. Modifications have been made to the core spray injection valves which will increase the stroke time from 10 seconds to 15 ! 2 seconds (a change that potentially increases calculated PCT).
- e. Modifications have been made to the recirculation discharge valves which will increase the stroke times f rom 30 seconds to 31.2 2 2 sec-onds (a change that potentially increases calculated PCT).
The effects of going from a partial to a full core loading of bundles with drilled lower tie plates is to improve ECCS performance for large breaks. The higher LPCI and CS shutoff heads will not affect ECCS performance for large breaks where the vessel depressurization is rapid, but will moderately improve the ECCS response to small breaks. The assumption that LPCI flow is injected 2
into the broken loop for recirculation line breaks of 0.15 f t or smaller may make the calculated consequences of these very small breaks more severe. This 2-1
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effect is quite small, however, and reanalyses are not required solely for -
this reason. The last two plant modifications (CS injection valve and recir-culation discharge valve stroke times) could potentially lengthen the effective.
response time of the ECCS during a LOCA which could result in increased cal-culated peak cladding temperatures (PCTs) for large breaks. These two modifi-cations necessitated a re-examination of the PNPS LOCA analyses and the associated operating limit (MAPLHCRs). This analysis was performed to determine if the current PNPS MAPLHCR limits are adequate following the changes.
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- 3. ANALYSIS The updated analysis described in this report was based on calculations performed with the NRC approved General Electric LOCA evaluation models: SAFE, REFLOOD, and CHASTE, and conservatively modeled the effects of the longer valve stroke times, the completed lower tie plate drilling, and the more accurately determined LPCI and CS shutoff heads. The fuel type selected for the analysis was P8x8R at 5000 mwd /T, to give an upper bounding PCT for all fuel types.
The impact of the longer valve stroke times was conservatively modeled.
It was assumed that there is no CS system flow until the injection valve is completely open. This is a very conservative assumption for a gate valve.
. The stroke time of the CS injection valve was assumed to be 18 seconds. This is one second longer than the upper limit of the two-second tolerance band.
The stroke time of the recirculation discharge valve was similarly assumed to be 35 seconds, or 1.8 seconds longer than the upper limit of the two-second tolerance band. It was assumed that any LPCI flow injected into the recircu-lation loop before the discharge valve is fully closed flows backward through the recirculation pump into the downcomer region.
The shutoff heads of the CS and LPCI were assumed to be 270 psig and 260 psig, respectively. These values are 10% below the lowest values determined from vendor data.
The analysis basis was changed to conform to the design basis of the LPCI loop selection logic. The loop selection logic is intended to detect recircu-lation line breaks of 0.15 ft or greater and to inject the LPCI flow into the unbroken loop. For recirculation line breaks of 0.15 ft or less, it was conservatively assumed that LPCI flow was injected into the broken loop resulting in partial loss of LPCI flow out the break.
The analysis assumed the occurrence of the most limiting single failure.
The limiting single f ailures for PNPS had been established previously and are shown in Table 1.
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NEDO-30767 Table 1 POTENTIALLY SIGNIFICANT SINGLE FAILURES FOR PILGRIM LOCA ANALYSIS Systems Remaining Operable After A Failure Recirculation Line Break and Single Failure LPCI Injection Valve 2 LPCS + HPCI + ADS Diesel Generator 1 LPCS + 2 LPCI + HPCI + ADS HPCI 2 LPCS + 4 LPCI + ADS 6
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NEDO-30767 For large breaks, the limiting failure is the LPCI injection valve.
-resulting in loss of the LPCI system. The failure of a diesel generator, resulting in loss of one CS system and two of the four pumps in the LPCI system, is the next most limiting failure. Since the changes in valve-stroke times could affect both CS and LPCI performance, both the LPCI injection valve failure and the diesel generator failure were evaluated for the DBA to verify that the LPCI injection valve f ailure is still limiting.
For small breaks, the dominant variable is vessel pressure response rather than ECCS response time, i.e., the time it takes to depressurize the vessel to the shutoff head of the ECCS pumps is long compared to the system response time. The limiting single failure was and remains failure of the High Pressure Coolant Injection (HPCI) system.
None of the changes will have a significant effect on the trend of calculated PCT versus break size, and a guillotine break of a recirculation suction line remains the most limiting break.
t The limiting small break was identified as 0.1 ft based on analysis of
!- 2 0.07, 0.10, and 0.15 ft breaks assuming LPCI injection into the broken recirculation loop (see Table 2).
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Table 2 PILGRIM SMALL BREAK LOCA RESULTS RECIRCULATION LINE BREAK WITH HPCI FAILURE ONE ADS VALVE ASSUMED OUT OF SERVICE Break Size Peak Cladding Temperature *
(ft2) (*F) Comments 0.15 ft 1513 LPCI injection into broken loop assumed 0.1 ft 1724 LPCI injection into broken loop assumed 0.07 ft 1693 LPCI injection into broken loop assumed
- Based on P8x8R fuel at 5000 mwd /T exposure. Core reflooding occurs before the rated pressure for core spray cooling is reached.
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- 4. RESULTS The results of the analysis of the DBA (guillotine break of a recircula-tion suction line with LPCI injection valve failure) are shown in Figures 1 and 2. These results show that the effect of the slower ECCS response times are slightly more than offset by the full core drilling. The reflooding time is one second earlier than the previous analysis. Calculation of the DBA with diesel generator failure verified that this case is approximately 200*F less limiting than the LPCI injection valve failure.
Results of the PNPS small break analysis are summarized in Table 2. The limiting small break is 0.1 f t recirculation line break with HPCI failure and
- this case is approximately 400*F less limiting than the DBA.
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NEDO-30767 3-15 . CONCLUSIONE Based on the results of these analyses, the following conclusions have been made:
- 1. The effects of' increasing the stroke times of the core spray injection valve and the recirculation discharge valve to 18 seconds and 35 seconds, respectively, are totally compensated by the drilling of lower tie plates in all the fuel bundles.
- 2. No change in MAPLHGR limits is necessary.
- 4. The effects of the change in small break analysis basis are
.l compensated by the higher shutoff heads.
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- 6. REFERENCES
- 1. " Loss-of-Coolant Accident Analysis Report for Pilgrim Nuclear Power Station", NED0-21696, August 1977.
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