ML20198K697
| ML20198K697 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 05/31/1986 |
| From: | Brown P, Stacey J YANKEE ATOMIC ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20198K690 | List: |
| References | |
| YAEC-1552, NUDOCS 8606040113 | |
| Download: ML20198K697 (19) | |
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NATURAL CIRCULATION COOLDOWN AND BORON MIKING Applicability of Tests Perfomed at Diablo Canyon Unit I for Conformance to BTP RSB 5-1 Paragraph E Seabrook Station Public Service Company of New Hampshire May 1986 i
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Prepared By:
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Reviewed By:
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Approved By: i (M
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Yankee Atomic Electric Company Nuclear Services Division 1671 Worcester Road Framingham, Massachusetts 01701 B606040113 860601 PDR ADOCK 05000443 E
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!l DISCLAIMER OF RESP 0NSIBILITY This document was prepared by Yankee Atomic Electric Company
(" Yankee"). The use of information contained in this document by anyone other 3
than Yankee, or the Organization for which the document was prepared, is not authorized and with respect to any unauthorized use, neither Yankee nor its
, 'I officers, directors, agents, or employees assume any obligation, responsibility, or liability or makes any warranty or representation of the material contained in this document.
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4 TABLE OF CONTENTS I
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, a 1.0 PURPOSE.......................
2.0 SPECIFIC REQUIREMEliTS............................................
2 s,
s 3.0 SAFETY-CRADE SHUTDOWN AT SEABROOK................................
3 4.0
SUMMARY
OF DIABLO CANYON TEST....................................
5 4.1 Acceptance criteria........................................
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4.2 Test Description...........................................
6 4.3 Chronology.................................................
7 5.0 COMPARISON OF SEABROOK DESIGN FEATURES AND DIABLO CANYON.........
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I 6.0 EVALUATION.......................................................
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6.1 Method of RCS Depressurization.............................
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6.2 Upper Head Temperature.....................................
12 6.3 Boron Source...............................................
12 6.4 RHR Initiation Pressure....................................
13 6.5 RV In t e rn a l s...............................................
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7.0 CONCLUSION
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8.0 REFERENCES
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1.0 PURPOSE Branch Technical Position RSB 5-1 (Reference 3) and Regulatory i
Guide 1.139 (Reference 7) require testing with supporting analysis to (a) confirm that adequate mixing of borated water added prior to, or during,
.i cooldown can be achieved under natural circulation conditions and permit estimation of the times required to achieve such mixing, and (b) confirm that
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cooldown under natural circulation conditions can be achieved within the limits specified in the emergency operations procedures. Comparison with the 1
performance of previously tested plants may be substituted for these tests.
Seabrook committed to perform a comparison study in RAIs 440.113 (Reference 14) and 640.29 (Reference 4).
This was confirmed in Paragraph 5.4.7.5 of the Seabrook SER (Reference 2):
Verification of adequate mixing of borated water added I
to the RCS under natural circulation conditions and f
confirmation of natural circulation cooldown ability will be accomplished either by reference to the results of the test from a plant of similar design or actual testing at Seabrook. The staff will require that the applicant provide a report justifying the applicability of the results of the boron mixing and natural circulation tests to be conducted at Diablo Canyon to the Seabrook design. If the Diablo Canyon tests are not completed or do not provide results that support the Seabrook design, the staff will require the applicant to perform such tests at Seabrook during startup after the first refueling.
This is listed as License Condition 5 in Section 1.9 of the SER.
On March 28 and 29, 1985, testing to meet these requirements was performed at Diablo Canyon, Unit 1.
The results of these tests were published in WCAP-11095 (Reference 1).
The test was successfully performed and all objectives and acceptance criteria were met. This report provides the required comparison and establishes the applicability of the Diablo Canyon test to the Seabrook design.
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2.0 SPECIFIC REQUIREMENTS r
1.
Operators must be capable of taking the reactor from normal operating conditions to cold shutdown using only safety-grade systems which satisfy the requirements of GDC 1 through 5.
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The systems wust have suitable redundancy in components and l
features, and suitable interconnections, leak detection, and isolation capabilities to assure that for on-site electrical power system operation (assuming off-site power is not available) and for off-site power operation (assuming on-site power is not available),
the system function can be accomplished assuming a single failure.
3.
The systems must be capable of being operated from the Control Room I
with either only on-site or only off-site power available. When considering a single failure, limited operator action outside the Control Room is acceptable, if suitably justified.
4.
The systems must be capable of bringing the reactor to cold shutdown, with only off-site or on-site power, within a reasonably short period of time following shutdown, assuming the most limiting single failure.
5.
The Category I water supply for the Auxiliary Feedwater System must have sufficient inventory to permit operation at hot shutdown for at least four hours, followed by cooldown to conditions permitting operation of the RHR System. The inventory needed for cooldown must be based on the longest time needed with either only on-site or only off-site power available with an assumed single failure.
6.
Atmospheric dump valves must be safety-grade.
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k 3.0 SAFETY-GRADE SHUTDOWN AT SEABROOK t
Under the conditions of BTP RSB 5-1, the plant is capable of being i
taken to cold shutdown within a reasonable period of time provided that limited manual actions are performed. Analysis shows that RHR operating conditions can be reached in eight to nine hours, including the time required to perform any necessary action during a four-hour period at hot standby.
l The four key processes involved in cooldown are: heat removal, RCS depressurization, RCS flow circulation, and reactivity control.
I Heat removal will be accomplished by using the Emergency Feedwater System to provide water to the steam generators.
During hot standby, steam will be released from the generators by either the steam generator code safety or power-operated relief valves.
During cooldown, steam will be released by the power-operated relief valves; water for the cooldown will be supplied from the CST.
RCS depressurization is accomplished with the pressurizer power-operated relief valves. To remain at hot standby for four hours and periodically during cooldown, it may be necessary to use the pressurizer heaters. The heaters themselves are not classified as class 1E components; however, two banks of heaters can be powered from Class 1E power supplies (see Reference 14).
t RCS flow circulation is provided by natural circulation from the core to the steam generators. During startup testing, the establishment of stable natural circulation conditions will be verified (see Startup Test Abstract 220, Reference 15).
Reactivity control is accomplished by providing boric acid to the charging pumps from the boric acid tanks. This is done by the boric acid transfer pumps or direct gravity feed. Makeup required in addition to that needed for boration can be provided from the RWST.
All of the systems required for cooldown to RHR operating conditions, with the exception of the pressurizer heaters, are safety-grade systems and satisfy GDC 1 through 5.
1.
i The systems contain suitable redundancy in components and features, j
suitable interconnections and isolation capabilities to assure that the system safety function can be accomplished, assuming the availability of either only on-site power or only off-site power, and assuming a single failure. Leak detection from the described systems can be accomplished via Class IE instruments for systems' level, pressure or flow rates in conjunction with various building sump level alarms and/or semp pump operation.
All systems are capable of being operated from the Control Room with either only on-site or only off-site power available. Should a single failure result in a loss of redundancy in the aforementioned systems, limited operation or action outside the Control Room may be necessary.
A more detailed discussion of this process is found in the exhibit attached to Reference 14.
The Emergency Operating Procedures (References 11, 12, and 13) developed for Seabrook are based on the Westinghouse Owner's Group Emergency i
Response Guides (References 8 and 9).
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4.0 SUMHARY OF DIABLO CANYON TEST j
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The basic objectives of the test were to (1) establish natural circulation using core decay heat; (2) confirm that borated water added to the RCS prior to the cooldown could be adequately mixed with the RCS during the l
i low flow conditions characteristic of natural circulation; (3) maintain hot standby conditions under natural circulation for at least four hours;
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(4) cooldown and depressurize the RCS from hot standby to cold shutdown; and (5) obtain cooldown rates for both the reactor vessel upper head metal and RCS i
l bulk water.
i On March 28 and 29, 1985, the test was performed at DCPP, Unit 1.
The test consisted of tripping the reactor from 100 percent power, stabilizing at hot shutdown for approximately three hours, maintaining hot standby under i
i natural circulation conditions for four hours, tripping the RCPs to initiate natural circulation and boron mixing, cooling down and depressurizing from hot j
standby to the point of initiation of the RHR System, and cooldown to cold shutdown conditions. The test was successfully performe6 and all objectives and acceptance criteria were met.
Comparison of test results with pretest predictions showed good agreement.
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The Diablo Canyon Emergency Operating Procedures are based on the Westinghouse Owner's Group Emergency Response Guidelines.
4.1 Acceptance Criteria The acceptance criteria chosen for the tests were as follows:
o Increase the boron concentration in the active portions of the RCS by 250 ppm or more.
Control plant cooldown under natural circulation conditions to be i
o within Technical Specification limits.
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Maintain temperature of all active portions of the RCS uniformly o
within 1100 F of the core average exit thermocouple temperature.
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Maintain the temperature of the steam generators and reactor vessel I'
o upper head to <450 F when the core average exit thermocouple temperature is 350 F.
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Assure that the RHR System is capable of cooling down the RCS to I
cold shutdown conditions.
Reduce RCS pressure lower than the RHR initiation pressure of o
390 psig.
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o Maintain 50 F subcooling margin for the upper head bulk water j
temperature during cooldown and depressurization.
o Maintain an administrative maximum temperature difference of o
100 F between the core average exit temperature and the upper head bulk water and metal temperatures.
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4.2 Test Description The test included four different operating conditions as follows:
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Approximately three hours during which the plant was stabilized at hot shutdown conditions prior to initiation of natural circulation.
2.
Approximately four hours during which the plant was maintained at hot standby under natural circulation conditions.
During this period, natural circulation was established and the boron mixing test was performed. The boron concentration was stable, indicating complete mixing, in less than one hour.
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Approximately 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br /> during which the plant was cooled down and depressurized from hot standby conditions to RHR System initiation conditions.
During this period, plant cooldown and depressurization testing were performed.
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Approximately four and one-half hours during which the plant was cooled down from RHR initiation conditions to cold shutdown conditions.
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4.3 Chronology q
Time l
(Minutes)
Hot Standby - RCPs Runninr s
O Plant Operating at 100% power, tripped turbine.
10 Reactor shutdown and plant in hot standby conditions.
20 Class 1 equipment alignment begun per test procedure.
90 Steam generator level at 44% narrow range level.
120 Main turbine relatched.
150 Fuse repaired and vital power aligned to pressurizer heater.
165 Class 1 equipment aligned. RCP seal flow about 50 spm.
This period with the RCPs operational resulted in significant cooling j
of the upper head which would not have occurred if natural circulation had been initiated immediately.
Hot Standby - Natural Circulation and Boron Mixing 178 RCPs tripped.
198 Natural circulation verified.
202 BIT injected at 150 gpm.
208 to 220 PORV opens nine times.
221 Letdown established to lower pressurizer level and minimize PORV actuation. This action was not required for cooldown but saved unnecessary wear and cleanup.
I 223 BIT injection complete. Baron concentration. increased i
from 890 ppm to 1.195 ppm.
RCS temperature drifting l:
down.
270 50% of SJAEs secured to minimize steam loss.
During a real event, the SJAEs would have been secured when the MSIVs closed. Presumably, the SJAEs were kept operational to maintain condenser vacuum.
405 Letdown initiated to lower pressurizer level. This was 4
done to prevent PORV actuation. Level was increasing because of RCP seal injection. This action is not required for shutdown.
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6 430 Control of RCP seal injection flow demonstrated by j
manually throttling an isolation valve.
440 Makeup to the VCT is set at 2,000 ppm.
This allows the i
charging pumps to maintain their normal alignment while simulating alignment to the RWST.
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RCS Cooldown/Depressurization to RHR Initiation Conditions i
440 Letdown isolated. Cooldown commenced with 10% ADVs.
Cooldown at 200F/hr.
i 483 Letdown used to lower pressurizer level and primary /
secondary differential pressure. This action not e
required for shutdown.
663 Letdown isolated.
675 CRDM fan secured. CRDM fans were operational to protect l
the CRDMs. Testing demonstrated that for THOT P ants, the WOG ERG had adequately predicted cooldown with or without fans. CRDM fans are not srfety grade and are not required for shutdown.
I 747 Letdown reinitiated.
0 949 Mode 4.
Loops less than 350 F.
i 986 Charging valves and auxiliary spray bypass valves open.
No appreciable depressurization occurred. This contirmed the results of earlier testing which showed that the charging lines must be isolated for auxiliary spray to be effective.
992 Charging valve closed. Depressurization at 8 psi / min.
1,065 Letdown isolated. PORV opened to depressurize the RCS.
Cooldown to Cold Shutdown 1,235 RHR operation begun.
1,261 Remaining operating CRDM fans secured.
1,365 Three CRDM fans re-energized. This was done as part of testing to show effect of fan operation on results.
1,470 Peak RCS boron concentration of 1,325 ppm reached.
0 1,515 Mode 5.
RCS below 200 F.
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S.0 COMPARISON OF SEADROOK AND DIABLO CANYON DESIGN FEATURES Diablo Canyon (Note 1)
Seabrook t.
Reactor Power 3,423 MWt Fuel Assemblies 193 Vessel Height (Exterior) 43'-10" Diameter (Inside) 173" Volume 4,700 ft3 Operating Temperature 620/5600F Hot Les/ Cold Leg Type TCOLD RCPs Model 93Al Best Estimate Flow 100,200 gpm Elevation of Discharge 4'-2-3/4" Above Top of Fuel Assembly Seal Water Injection 8 spm Seal Water Return 3 spm Steam Cenerstors Model F
Height 67'-8" Diameter (Tube Section) 138" Tube Number 5626 Elevation of "U" Tubes Above 40'-7-3/4" Top of Fuel Assembly RCS Piping and Valves Loop Isolation Valves No Hot Leg Diameter 29" cold Les Diameter 27-1/2" RCP Suction Leg Diameter 31" Are there any significant No differences in the RCS piping layout? (See Ref. 20)
Pressurizer Volume 1,800 ft3 operating Temperature 6530F Elevation Above Top of 12'-9" Fuel Assembly
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cycS Borated Water Sources BIT ppm / Volume Not Applicable BAT ppm / Volume 7,000/20,200 gal.
RWST ppm 2,000 Injection Point to RCS RCP Discharge Loops 1 or 4 AFWS CST Volume 400,000 gal. of which 200,000 gal.
dedicated to AFWS RHR 0
Initiation Pressure / Temperature 365 psig/350 F System Pressure Drops (psi) at Best Estimate Flow RV 46.2 S/G 38.6 1.3 Hot Leg Pump Suetion 3.3 Cold Les 3.3 Pump Head 290 ft Total RCS Volume 12,265 ft3 Note 1 -
The information provided by Pacific Gas & Electric is considered confidential information and shall not be given to any third parties without PG&E's writtp,n consent.
- The pressure drop data around the RCS loops are estimated values provided to Pacific Cas and Electric from Westinghouse. o
6.0 EVALUATION 1
There are some differences in the cooldown method and the design of I
Seabrook and Diablo Canyon.
Each is identified and discussed below:
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o Method of RCS depressurization.
o Upper head temperature.
o Boron source.
o RHR initiation pressure.
o RV internals.
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6.1 Method of RCS Depressurization i
.'i At Diablo Canyon RCS depressurization was accomplished primarily
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through the use of the Auxiliary Spray System. A pressurizer PORV was used for the last part of the task. At Seabrook, the intent is to use the PORV to depressurize. The Diablo Canyon test showed that spray and PORV were equally I
effective in depressurizing.
Auxiliary sprays cause the reactor inventory to increase while PORVs cause it to decrease.
During the Diablo Canyon test, reactor inventory increased to the point that the Letdown System was used.
During a design i
basis shutdown, letdown would not have been available. As a result, the PORV would have opened repeatedly, During PORY use, reactor inventory losses will be made up by the e
Charging System. At Diablo Canyon, as the PORV decreased RCS pressure from I,
700 to 350 psig, the Charging System increased pressurizer level from 40% to ll 70%.
Charging is from the RWST (2,000 ppm boron) further increasing the shutdown margin.
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6.2 Upper Head Temperature j
P ant.
That is, the reactor Diablo Canyon is classified as a T l
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vessel upper head temperature is close to the hot les temperature than to the cold leg temperature during operation. Seabrook is a T Plant.
Cold I
During a natural circulation cooldown, there would be virtually no circulation in the upper head. Cooldown of the water in the upper head would be by radiant cooling to the air and CRDM above the reactor or to the water below. The depressurization and cooldown rates aust be limited to ensure that the upper head temperature remains below the saturation temperature to avoid voiding in the upper head.
Since the upper head temperature at Seabrook is less than that at i
Diablo Canyon, this factor is less limiting at Seabrook, 6.3 Boron Source At Diablo Canyon, 900 gallons of 21,000 ppm borated water from the Boron Injection Tank (BIT) was used to achieve the required shutdown margin.
Borated water from the tank was combined with water from the Charging System to provide a combined flow rate of 150 gpm.
The BIT was aligned in this manner for approximately 20 minutes. Thus, the average concentration of the boron injected into the RCS was about 6.300 ppm. Most of the boron was injected in the beginning so the first part of the injection was at a significantly higher concentration.
The Seabrook design does not include a BIT.
Boration will be achieved using the boric acid tanks as the source of water for the Charging System.
The tanks contain 20,200 gallons of 7,000 ppm borated water. This supply is more than adequate to provide the required shutdown margin.
i Borated water enters the Seabrook RCS at a lower concentration and it is injected for a longer period of time than at Diablo Canyon. At all times j
the boron concentration in the RCS maintains an adequate shutdown margin
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throughout the cooldown. Boration of the RCS at Seabrook could be accomplished by using the boron injection portion of the Safety Injection System, if required. Uniform mixing and equal circulation is assured by using l
the main steam atmospheric dumps. However, the preferential method of assuring equal circulation flow is by using the main steam dumps to the condenser. Thus, the mixing of the boron will occur to provide a uniform'RCS boron concentration.
6.4 RHR Initiation Pressure The maximum RHR initiation pressure is 390 psig at Diablo Canyon and 365 psig at Seabrook. During the test at Diablo Canyon, RCS pressure was reduced to less than 375 psig before initiating RHR.
Therefore, the testing is applicable to both situations.
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i' The type of upper support plate at Diablo Canyon is called a top hat.
At Seabrook it is an inverted top hat.
Normally, inverted top hats have fewer Control Rod Drive Mechanisms (CRDM). Seabrook has 57, while Diablo Canyon has 53.
Thus, when the CRDM cooling fans are in use, the cooling rate for the upper head is slightly greater at Seabrook. The CRDM fans are not required for a natural circulation cooldown. As shown in Reference 8, cooldown is the P ants despite differences in upper support plate same for all T l
Cold design. As discussed in Section 6.2 of this study, the upper head temperature P ants. Therefore, the P ants is always less than that for T l
for T l
Hot Cold difference in upper support plate design does not affect natural circulation cooldown or boron mixing.
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7.0 CONCLUSION
l Design features which are important to natural circulation cooldown and t
I boron mixing are substantially the same at Seabrook and Diablo Canyon. As discussed in Section 6.0, those features which are different either are not I
significant or favor Seabrook.
l The testing at Diablo Canyon has proven for both designs that:
4 Boron mixing is esser.tially complete one hour after injection; and l
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o Natural circulation cooldown can be achieved within the limits specified in Emergenc:r Operating Procedures based on the Westinghouse Owner's droup Emergency Response Procedures.
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8.0 REFERENCES
4 1.
WCAP-11095 "Diablo Canyon, Units 1 and 2. Natural Circulation, Boron Mixing, and Cooldown Test, Final Post-Test Report,"
Westinghouse Electric Corporation, March 1986.
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NUREG-0896, " Safety Evaluation Report Related to the Operation of
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j Seabrook Station Units 1 and 2," March 1983.
l 3.
BTP RSB 5-1, " Design Requirements of the Residual Heat Removal System," Revision 2 July 1981.
4.
RAI 640-29, Seabrook FSAR, Amendment 49, May 1983.
j 5.
Regulatory Guide 1.68, " Initial Test Program for Water-Cooled Nuclear Power Plants, " Revision 2, August 1978.
6.
Regulatory Guide 1.68.2, " Initial Startup Test Program to 1
Demonstrate Remote Shutdown Capability for Water-Cooled Nuclear i
Power Plants," Revision 1 July 1978.
7.
Regulatory Guide 1.139, " Guidance for Residual Heat Removal,"
May 1978.
8.
Background Information for Westinghouse Owners Group Emergency Response Guide, ES-0.2, " Natural Circulation Cooldown,"
HP-Revision 1, September 1, 1983.
9.
" System Review and Task Analysis, High Pressure Version,"
Westinghouse Owners Group Emergency Response Guidelines, Revision HP Basic, April 1, 1983.
- 10. NAH-3029, "NSSS Cooldown Study," January 24, 1983.
- 11. Emergency Operating Procedure, ES-C.2, " Natural Circulation Cooldown," Revision 1, September 21, 1984.
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- 12. Emergency Operating Procedure, ES-0.3, " Natural Circulation i
Cooldown With Steam Void in Vessel (With RVLIS)," Revision 1, September 21, 1984.
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- 13. Emergency Operating Proceduro, ES-0.4, " Natural Circulation l
Cooldown With Steam Void in Vessel (Without RVLIS)," Revision 1, September 24, 1984.
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- 15. Seabrook FSAR, Table 14.2-5, " Natural Circulation Test,"
Amendment 56, November 1985.
- 16. EPRI NP-2615. " Natural Circulation Experiments in UTSG Four-Loop Test Facility," September 1982.
- 17. EPRI NP-1676-SR, " Natural Circulation Loops in Pressurized Water i
Reactors and Other Systems," January 1981.
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- 18. EPRI NP-1364-SR, " Experimental and Analytical Investigation of a PWR Natural Circulation Loop," March 1980.
- 19. EPRI NP-2006, " Single-Phase Natural Circulation Experiments on Small Break Accident Heat Removal " August 1981.
- 20. 9763-F-805534, " Reactor Coolant System Loop Pipin!; Arrangement,"
Revision 6.
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