ML20148M069

Technical Evaluation Rept for Natural Circulation,Boron Mixing & Cooldown at Waterford Unit 3

ML20148M069
Person / Time
Site:	Waterford
Issue date:	03/31/1988
From:	Jo J, Perkins K BROOKHAVEN NATIONAL LABORATORY
To:	Office of Nuclear Reactor Regulation
Shared Package
ML20148M072	List: ML20148M069
References
CON-FIN-A-3843, RTR-NUREG-0787, RTR-NUREG-787 NUDOCS 8804050231
Download: ML20148M069 (21)

Text

, j Ahhment TECHNICAL EVALUATION REPORT 10R THE NATURAL CIRCULATION, BORON HIXING AND C00LDOWN AT WATERFORD UNIT 3 J.H. Jo and K.R. Perkins Containment & Systems Integration Group l l

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Department of Nuclear Energy l Brookhaven National Laboratory l Upton, New York 11973 1

1 March 1988 Prepared for U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Washington, D.C. 20555 Contract No. DE-AC02-76CH00016 FIN A-3843

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ABSTRACT This report reviews the conformance of the Waterford Unit 3 nuclear plant operation and equipment with the requirements of Reactor Safety Branch Tech-nical Position 5-1 regarding boron mixing and cooldown under natural circula-tion conditions. The utility has referenced the San Onofre tests as demon-strating the Waterford capability.

The BNL review indicates that the plants are suf ficiently similar to allow Waterford Unit 3 to take credit for the San Onofre test results.

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l TABLE OF CONTENTS Page ABSTRACT.............................................................. iii ACKNOWLEDGMENTS....................................................... vii

1. INTRODUCTION...................................................... 1-1

2. APPLICABILITY OF THE SONGS TEST TO WATERFORD UNIT 3............... 2-1

3. CONCLUSIONS....................................................... 3-1 4

REFERENCES........................................................ 4-1 l

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, ACKNOWLEDGMENTS This work was performed for the Planning, Program and Management Support Branch, NRC/NRR. Mr. B.L. Grenier is the Project Manager and D. Katze and R.C. Jones, DEST /RSB, are the Technical Monitors. C.-Y. Liang, DEST /RSB, and E. Branagan DRPEP/RPB, have also provided considerable assistance to the project.

The authors are also grateful to Ms. S. Flippen for her excellent typing of the manuscript.

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" 1. INTRODUCTION While cooling own under natural circulation conditions on June 11, 1980, the St. Lucie Unit 1 primary system coolant flashed and produced a void in the reactor vessel upper head, which forced water into the pressurizer. At the time of the event there was concern that the void formation would interrupt natural circulation and inhibit decay heat removal. However, the voiding was controlled by depressurization and eventually the reactor was brought to shut-down cooling sys'?n (SCS) entry conditions. Based on the NRC review of the event, a nulti-plant action item (MPA B-66) was initiated which requires that all pressurized water reactors (PWRs) implement procedures and training pro-grams to ensure the capability to deal with such events. In Generic Letter (GL) 81-21, dated May 5, 1981, the licensees were required to provide an assessment of their facility orocedures and training program including:

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1. a demonstration (e.g., analysis and/or test) that controlled natural circulation cooldown from operating conditions to cnid shutdown con-ditions, conducted in accordance with plant procedures, .would not re-sult in reactor vessel voiding.  ;

2. verification that supplies of "condensate-grade" auxiliary feedwater i are sufficient to support plant cooldown methods. The Reactor Sys- I tems Branch Technical Position (RSB 5-1) requires an adequate supply ,

of auxiliary feedwater stored in safety grade systems. l

3. a description o' the plant training program and the provisions of emergency procedures (e.g., limited cooldown rate, response to rapid change in pressurizer level) that deal with prevention or mitigation of reactor vessel voiding.

It should be noted that at the time GL 81-21 was issued, procedures for natural circulation cooldown with upper head voids were not generally availa.

bl e. Since then, Conbustion Engineering (C-E) has issued an analysis l sup-porting natural circulation cooldown with voids and subsequent testing at Palo

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Ve rrie2 has demonstrated cooldown and depressurization with void fo rmati or,. '

While the NRC staff considers natural circulation cooldown without voids as more desirable, cooldown with voids may be acceptable providing it can be I

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. 1 can be accomplished using only safety-grade equipment and approved procedures, and operators have adequate training in the use of these procedures.

Additional requirements for pre-operational testing are set forth in the Standard Review Plan under RSB 5-1. This technical position essentially requires that a Class 2* plant demonstrate that it can be brought from hot l standby to cold shutdown under the natural circulation conditions using only l systems which are safety grade and with only onsite or offsite (not both) power available and assuming a single failure.

RSB 5-1 also requires that PWR pre-operational and initial startup test programs shall include tests with supporting analyses to (a) confirm that adequate mixing of borated water added prior to or during cooldown can be achieved under natural circulation conditions and permit estimation of the times required to achieve such mixing, and (b) confirm that cooldown under natural circulation conditions can be achieved within the limits specified in the emergency operating procedures. Comparison with performance of previously tested plants of similar design may be substituted for these tests.

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In response to these requirements, Louisiana Power and Light referenced the natural circulation cooldown and boron mixing test which was to be con-ducted at Unit 2 of the San Onofre Nuclear Generating Station (SONGS) as being applicable to Waterford Unit 3. The SONGS natural circulation test was per-formed on July 27, 1983 and the results were presented in CEN-259, "An Evalua-tion of the Natural Circulation Cooldown Test Performed at the :an Onofre Nuclear Generating Station." 3 BNL reviewed the test report and issued a Tech-nical Evaluation Report (TER).4 The specific items addressed by the SONGS natural circulation cooldown test included a demonstration of the ability to mix boron under natural circu-lation, an evaluation of reactor vessel upper head cooldown rates with and "RSB 5-1 divides plants into three classes for the purpose of implementing the requirements for plant heat removal capability for compliance with its posi-tion. The classification was based on the acte when CP (construction permit) or PDA (preliminary design approval) applications were docketed and/or an OL (operating license) was issued. Recommended implementation for a Class 2 plant is specified in the position letter. Waterford Unit 3 is a Class 2 pl a nt.

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, without operation of the control el ement drive mechanism cooling fans, an assessment of the adequacy of seismic .. Category I condensate supply and an evaluation of the adequacy of the safety grade nitrogen supply for the atmo-spheric dump valves. A subsequent tests at San Onofre addressed the perfor-mance of the residual heat removal (RHR) system with only natural circulation ir. the primary system. The purpose of this report is to evaluate the applica-bility of the SONGS test results and analyses to Waterford Unit 3 with respect to the requirements of RSB 5-1.

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. 2. APPLICABILITY OF THE SONGS TEST TO WATERFORD UNIT 3 The C-E nuclear steam supply systems (NSSS) can be divided essentially into two categories with respect to the requirements of RSB 5-1, namely Pre-System 80 and System 80. The most significant distinction between these two categories of plants is the relative size of the reactor vessel upper heads.

The volume of the reactor vessel upper head (RVUH) of the Pre-System 80 design is approximctely half of that of the System 80 design. SONGS Units 2 and- 3 and Waterford 3 belong to the Pre-System 80 design. Accordingly C-E stated that the procedures that would be employed by Waterford 3 to meet RSB 5-1 would be identical to that employed by San Onofre.3 Specifically, following plant cooldown to the shutdown cooling system (SCS) initiation temperature (350*F), the system pressure would be maintained near nomal operating pres-sure for a fifteen hour hold period until the RVUH had cooled sufficiently to depressurize the reactor coolant system (RCS) and place the plant on shutdown cooling without foming a stean bubble in the upper head.

The applicability of the SONGS test results to Waterford Unit 3 depends on the similarity in design between the two plants. Waterford Unit 3 and ,

SONGS Unit 2 are virtually identical: 6 The rated core themal output is iden-ti cal . Total coolant flow rate and operating conditions are identical. Sizes and configurations of the reactor' pressure vessels (including the upper head),

steam generators and pr essurizers of both plants are identical. The bypass flow rate and loop Ap are also similar. The only significantly different parameters between these two plants with respect to natural circulation, bcron mixing, cooldown and depressurization are the supply of seismic Category I condensate feedwater for the steam generators and the supply of nitrogen for control of the atmospheric dump valves (ADVs). Accordingly, the conclusions developed" for SONGS based on the test results 3 appear to apply to Waterford Unit 3 with the exception of the supplies of cooling water and nitrogen.

These conclusions are reiterated in the next section.

The amount of safety grade condensate water and the volume of nitrogen required to bring the plant at Waterford 3 to SCS initiatien conditions can be assumed to be equal to those at SONGS Unit 2 since the rated themal output, 3 total RCS water volume, total RCS netal nass and the upper head configurations j

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'of both plants are identical. The maximum estimate of the cooling water re-quired is about 350,000 gallons based on several conservative assumptions out-lined in Reference 4. This estimate includes the additional cooling water to remove the decay heat during the prolonged upper head cooldown period (about 38 hours4.398148e-4 days <br />0.0106 hours <br />6.283069e-5 weeks <br />1.4459e-5 months <br />) when the control element drive mechanism (CEDM) cooling fans are not avail able. The condensate storage tank at Waterford Unit 3 contains a minimum of 170,000 gallons of safety grade cooling water according to Waterford Tech-nical Specifications. Additionally, 350,000 gallons of seismic Cathgory I cooling water are available from the wet cooling tower basins. Therefore, a sufficient supply of cooling water i s available from seismic Category I sources even for a prolonged plant cooldown.

With respect to nitrogen usage by the ADVs, the Waterford 3 FSAR6 states that "Seismic Category I accumulators are provided for atmospheric dump valves, sized to maita .in the valves operable for 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />." This is compara-ble to 38 hours4.398148e-4 days <br />0.0106 hours <br />6.283069e-5 weeks <br />1.4459e-5 months <br /> which is the estimated cooldown period. It should be noted also that the ADVs at Waterford are equipped with manual handwheels and that the SONGS test demonstrated that ADVs could be marually operated via nanual handwheels in the event the nitrogen supply should become depleted.

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3. CONCLUSIONS The applicability of the SONGS natural circulation cooldown test to Waterford Unit 3 was assessed. It was concluded that the two plants (San Onofre and Waterford) are sufficiently similar in design so that the SONGS test results 3 apply equally well to the Waterford plant. The conclusions de-veloped4 previously for San Onofre are reiterated below.

1) The tests at San Onofre demonstrate that adequate natural circulation can be established at Waterford and the plant is capable of removing the decay heat by natural circulation using only safety-grade equip- I ment.

2) Adequate boron mixing can be achieved in about one hour of operation at hot standby with natural circulation in the main flow path of the l RCS and using only safety-grade equipment. l

3) Relatively unborated water entering the RCS from the upper head and pressurizer will not have a significant effect on criticality as long )

as depressurization is conducted carefully to limit the size of the l possible void formation. (Note that the plant's emergency procedures I have not been reviewed but C-E 3 indicates that Waterford would use the same procedures as San Onofre.)

4) Boron injection may be conducted prior to cooldown without filling up the pressurizer even when letdown is not available. However, it appears desirable to allow the pressurizer level to decrease during the natural circulation prior to boron injection. Operation of the auxiliary spray may be necessary to naintain pressure control during i boron injection. '

5) The test at San Onofre adequately demonstrated that cooldown to the l SCS initiation temperature can be accomplished while maintaining ade-quate subcooling during natural circulation using only safety-grade equipment.

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, [,' 3-2 J The upper head can be cooled without void formation when the CEDM 6) cooling fans are in operation, l

7) The test at San Onofre demonstrated that the Waterford RCS can be depressurized to the SCS initiation pressure under natdral circula-l tion using the auxiliary spray. However, if the letdown is not available the pressurizer level would increase substantially (about 40%) and it may be necessary to use the head /ent valve to depressur-ize, especially near the end of the depressurization period, l

8) The estimated cooling time for the San Onofre upper head without the CEDM fans operating, varied from 15.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> (C-E analysis) to about ,

38 hours4.398148e-4 days <br />0.0106 hours <br />6.283069e-5 weeks <br />1.4459e-5 months <br /> (BNL). The size of the upper head at Waterford is identical to San Onofre so the cooling time without fans and without any upper head nixing (38 hours4.398148e-4 days <br />0.0106 hours <br />6.283069e-5 weeks <br />1.4459e-5 months <br />) would also apply to Waterford. )

9) Calculations performed for San Onofre indicate that the pressurizer level at Waterford would have to be maintained at 60% or higher to  ;

maintain the RCS pressure above the saturation pressure corresponding to the upper head fluid temperature during the prolonged period of upper head cooling.

10) The supply of safety grade cooling water (520,000 gallons) at Water- i ford is much greater than the maximum estimated usage (350,000 gal-lons) for the prolonged upper head cooling period even if the CEDM fans are not available.

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11) Only one motor-driven auxiliary feedwater (AFW) pump is sufficient to c supply the necessary cooling water throughout the postulated tran-sient.

12) Sufficient ADV capacity would be available during most of the cool-down period with the cooldown rate of 50*F/ hour. However, it may be necessary to lower the cooldown rate if one of two ADVs would not be

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.- i The supply of safety grade nitrogen for the ADVs is not quite suffi-

, 13) cient for the longest possible cooldown period. However, the ADVs are also operable via mar.ual handwheels in the event that the nitro-gen supply should become depleted.

14) The strategy for pressure control should be very carefully planned when the pressurizer heaters and the letdown system are not availa-bl e. Both of the available safety-grade pressure control systems (charging and auxiliary spray) require injection of additional water into the system. Without letdown this may result in overfilling of the' pressurizer (and water-solid operation). Occasional use of the head vent valve may be preferable to extended auxiliary spray opera-tion.

15) The capability to cooldown to cold shutdown conditions, once SCS entry conditions are reached, has not been evaluated but a test at San Onofre5 indicated that SCS cooling would be prolonged unless the reactor coolant pumps (RCPs) are available to circulate water through the steam generators. Since the SCS has an unlimited heat sink no safety concerns are expected to arise due to the prolonged SCS opera-tion.

16) The NRC requirement to demonstrate that the SCS can be remotely ini-tiated from the control room has not been addressed at Waterford.

In summary, it is concluded that the Waterford Unit 3 plant is in compli-ance with the requirements of RSB 5-1 with the exception of demonstrating re-mote initiation of the SCS.

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.- *4 . REFERENCES e' t

1. "Natural Circulation Cooldown Reanalysis for CESSAR-F Computer Sinulation of a Natural Circulation Cooldown," Letter from A.E. Sherer, C-E, to D.G.  ;

Eisenhut, NRC, LO-83-074, August 12, 1983. .

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2. "An Evaluation of the Natural Circulation Cooldown Test Performed at the Palo Verde Nuclear Generating Station," Arizona Nuclear Power Project.

Revision 0, February 1987.

3. "An Evaluation of the Natural Circulation Cooldown Test Performed at the San Onofre Nuclear Generating Station," Combustion Engineering, CEN-259, January 1984 4 "Technical Evaluation Report for the Natural Circulation, Boron litxing and Cooldown Test Performed at San Onofre Nuclear Generating Station " Brook-haven National Laboratory, Technical Report A-3843, October 1987.

5. "Remote Initiation of Shutdown Cooling Test Perforned September 16-17, 1985 at the San Onofre Nuclear Generating Station Unit 3," Letter Report  !

from M.0. Medford, SCE, to G.O. Knighton, December 27, 1985, Docket No. '

50-362. '

6. "Final Safety Analysis Report for Waterford Steam Electric Station Unit No. 3," Docket No. 50-382, December 1986.

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