ML20236L471
| ML20236L471 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 08/31/1987 |
| From: | Frantz E, Sterrett C WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML20236L463 | List: |
| References | |
| 4021Q, NUDOCS 8711100360 | |
| Download: ML20236L471 (16) | |
Text
{{#Wiki_filter:' r, ;,, 1 ~ ; i s O MILLSTONE UNIT 3-j NATURAL CIRCULATION-SYSTEM COMPARISON f Os ] i Prepared by: C..R. Sterrett-1 'E. R.~Frantz 4 } August <1987 . 1 4 a 4 a s )- 1-h WESTINGHOUSE ELECTRIC CORPORATION . Nuclear Technology Systems.. Division P. O. Box 355' -Pittsburgh, Pennsylvania 15230 O 1 8711100360 871106 DR ADOCK 05000423 PDR .\\ 4021g _-_--_-.___mm.______-_____ _.___n__>_ m
5 i TABLE 0F CONTENTS'. -SECTION-SUBJECT .PAGE ,i 1.0 . INTRODUCTION 1: [{ 2.0 COMPARISON OF DIABLO. CANYON WITH MILi. STONE UNIT 3 4 D .) 3.0' APPLICABILITY Of THE DIABLO CANYON TEST RESULTS '7 1 TO MILLSTONE UNIT 3 3 l q-l l 4.0
SUMMARY
AND= CONCLUSIONS 13 ! '1
5.0 REFERENCES
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3 o .. 3 1.0 ' INTRODUCTION-This Natural Circulation System Comparison Report has been developed to evaluate the plant systems and equipment that affect the natural circulation, boron mixing, cooldown and depressurization capabilities'of~ Millstone Unit 3 relative to the requirements'of Branch Technical Position.RSB 5-1, Design Requirements;for Decay Heat Removal Systems. j (Referer.ce 1). , O 1.1 { Backaround l Circulation of reactor coolant is a key. function in the operation of!the Millstone Unit 3 plant, including operations to place and maintain the plant in the hot standby operational mode 'and in perfonning operations to' take the plant to cold shutdown. During norraal plant operations, at ' least one reactor coolant pump (RCP) is normally operating.to ensure forced circulation of reactor coolant for boron mixing, heat removal and ( pressure control considerations. The loss of forced circulation constitutes an emergency plant conditicn. 1 L Under this plant condition, the plant protection systems will automatically trip the reactor and the plant will-be placed in the hot standby operational mode under natural circulation conditions. The plant is designed to be maintained in this condition until forced circulation l is restored and normal plant operations can be resumed. Natural circulation of reactor coolant is provided with the reactor core as the j heat source and the steam generators as the heat sink. iteam release to-- b-maintain the reactor at hot standby is accomplished via the. steam generator atmospheric power operated relief valves, or the safety valves i io l. if needed. The Millstone Unit 3-systems capabilities needed'to support-l t safety grade cold shutdown are evaluated in Section 5.4.7 of the-J Millstone Unit 3 Final Safety Analysis Report (Reference 2). 's -l L ( 4021q -'1-l- l.
p 1.2 Description of the Diablo Canyon Power Plant Natural Circulation Test On March 28 and 29, 1985, a boron mixing and cooldown test was performed at Diablo Canyon Unit 1. The test began with a trip from hot full power fi conditions at 2130 hours on March 28, and continued until 2245 hours on March 29 when cold shutdown conditions were achieved. In genetal, the ) test consisted of four basic periods as described below: 1) An initial period of approximately three hours'during which the. plant was stabilized at hot standby conditions prior to initiation of natural circulation. 2) A period of 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. ][ 3) A period of approximately thirteen hours during which the plant was j cooled down and depressurized from hot standby conditions to RHR J system initiation conditions. During this period, plant cooldown and depressurization testing was performed. ( 4) A final period of approximately four and one-half hours during which the plant was cooled from RHR initiation conditions to cold shutdown conditions. 1.3 Report Structure The final report for the Diablo Canyon natural circulation test is provided in the Diablo Canyon Units 1 and 2 Natural Circulation / Boron j Mixing /Cooldown Test Final Post Test Report (Reference 3). -This O Millstone Unit 3 report is structured to compare the plant systems and equipment that-affect the' natural circulation, boron mixing, cooldown and depressurization capabilities of Millstone Unit 3 with the Diablo Canyon c systems and equipment. This comparison is used to describe the applicability of the natural phenomena associated with the Diablo Canyon Unit 1 test to Millstone Unit 3. 4021q 4 \\
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L 4 g 'Section 2.0 provides a general. comparison'.between the systems.and. equipment of Millstone Unit 3 and Diablo Canyori, i Section 3.0 provides justification of the appl.icability of'.the Diablo (- Canyon test results to Millstone Unit 3 - u I l , 4 O t I . l i i = ? O 1 s O 4021g l- __.___=_-_-_____:___.__-__
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- i 2.0 COMPARISON'0F DIABLO CANYON WITH MILLSTONE UNIT 3 4
This section; compares the systems and equipment that affeet natural ] circulation of Millstone Unit 3 to those of Diablo Canyon Uni,t 1 in ] sufficient detail to evaluate systems capabilities. I Reactor Coolant System p The general configuration of the piping and components in the. reactor coolant loop is the same in both Millstone' Unit 3 and Diablo Canyon. Both Millstone Unit 3 and Diablo. Canyon'have four loops for heat transfer. Each heat transfer loop contains a steam generator and. a reactor coolant pump (RCP). The Diablo Canyon SG is a Model 51 while the Millstone SG is a Model F. The Diablo Canyon RCP is a'Model,93A while the Millstone RCP is'a Model-93A1. The hydraulic ~ resistances' and elevation differences are not significant and do not adversely affect the j natural circulation flowrates. Also, one loop at each pl6nt is equipped l with a pressurizer. J a r, Pressure control is available at both Diablo Canyon and Millstone Unit 3 q using the normal pressurizer spray valves if.the RCP's are running or the, pressurizer auxiliary spray systems. If both the normal and auxil.iary spray valves are unavailable, the pressurizer PORVs are available at'each plant for RCS depressurization. At Millstone Unit.3, the' pressurizer spray valves and auxiliary spray valves are not safety grade, however, the PORVs are safety-grade Class 1E solenoid operated valves. The PORV block valves are safety-grade and may be used to block PORV paths. O' Auxiliary Feedwater System The auxiliary feedwater systems at both Diablo Canyon and Millstone Unit 3 are capable of supplying cooling to all steam generators using the auxiliary feedwater pumps during the natural circulation cooldown. -The systems will provide water to the SGs from large storage tanks. The' condensate storage t4nk provides this water source at Diablo Canyon, while Millstone Unit 3 uses the. Seismic Category I demineralized water storage tank. The auxiliary feedwater system at Millstone Unit 3 is a 40214,
J q ~. .c safety grade system. Alternate sources of. auxiliary feedwater at' y' Millstone Unit 3 include the condensate storage tank, service water system (safety grade source), and domestic water system. j 4 Main Steam System. The steam generators at.both plants have main steam pressure relievin'g valves (MSPRV) which are: utilized for the plant cooldown. ~ Millstone Uniti, '3 also has'four. main steam pressure relieving bypass valve's (MSPRBV) to; O-ensure a steam release path.is available if the PORVs are not available. At Millstone Unit 3, the MSPRVs:and.MSPR8Vs are safety grade and are powered from Class 1E buses. The' MSPRVs are air operated and-have a t safety function to:close. The' MSPRBVs provide the safety grade' means 'of controlling steam release. Chemical and Volume Control-System (CVCS) i Injection of boric acid int; the RCS is required-to offset xenon decay ^ E and the reactivity change which occurs during plant cooldown. The Diablo Canyon natural circulation cooldown test utilized'the charging pumps to i charge through the boron injection tank (at 20000 ppm boron).in the Safety Injection System. Subsequent charging was aligned from the volume control tank in the CVCS. The boron concentration in the volume control tank was adjusted to 2000 ppm to simulate charging from the refueling water storage tank (RWST). At Millstone Unit 3, four weight percent boric acid is pumped from the safety grade boric acid tanks (at 6300 ppm boron).by the boric: acid transfer pumps to the suction of the centrifugal charging pumps; These ]H pumps are also safety grade and are powered from Class 1E: buses. An h alternate flow path f rom the boric acid tanks.to the' suction of the. U centrifugal charging pumps is available through the safety grade gravity feed valves. A backup source of boric acid is available from the RWS1 (at 2000 ppm boron). The bor'ated water is then iiijected to the RCS via the normal charging line and the RCP seals. A back-up means for injection involves the use of the high pressure injection path through '40210 5-j u i L
I i l -l 1 the Sis. TN. normal charging and the S15 boron injection paths each j contain a Class IE solenoid operated throttling valve that permits variable control of the makeup.,flowrate, ym To accommodate the borated water addition to the RCS, letdown capability b. is normally provided by the non-safety grade normal and excess letdown lines to the CVCS. If both the normal and excess letdown lines are I l unavailable, letdown is provided by the safety grade reactor vessel head vent letdown line to the pressurizer relief tank. Throttling control.of l ,q O the' head vent letdown is provided'by two redundant parallel safety grade l Class 1E solenoid valves. j Residual Heat Removal (RHR) System j l l The RHR systems at both Diablo Canyon and Millstone Unit 3 are low l pressure heat removal systems consisting of~RHR pumps and heat-exchangers. They are designed.to lower the temperature of the RCS from 350'F to cold shutdown conditions. w. l l 1 0 / )' 40214 _ _ _ _ _ _ _ _
1 ~ i l -P 3.0 APPLICABILITY OF THE DIABLO CANYON TEST RESULTS TO MILLSTONE UNIT 3 l ) l I 3.1 Natural Circulation i O The Diablo Canyon natural circulation test evaluation verified that RCS l \\' natural circulation flow could be established, thereby permittin0 boron mixing and RCS cooldown/depressurization to RHR' system initiation conditions. This phase of the test had no specific acceptance criteria and it was evaluated based on the results of the boron mixing and cooldown/depressurization phases of the natural circulation cooldown, test. 1 Th'e Diablo Canyon test results indicated that natural circulation j l flowrates were adequate to ensure.that core decay heat removal, boron l mixing and plant cooldown/depressurization were maintained throughout the ) test. The response of.the RCS temperatures. indicated stable natural' circulation conditions throughout the test. I 17 The Millstone Unit 3 plant and Diablo Canyon Unit 1 have been compared j (Section 2.1) to ascertain any differences between the two' plants that could potentially affect natural circulation flow. The general configuration of the piping and components in each reactor coolant loop is the same in both Millstone Unit 3 and Diablo Canyon Unit 1. The elevation head represented by these components'and the system piping is similar in both plants. Steam generator units were also compared to ascertain any variation that could affect natural circulation capability by changing the effective elevation of the heat sink or the hydraulic resistance seen by the primary coolant. The longer tube bun'dle for ] Diablo Canyon Unit 1 would result in 5-10% higher driving head when-compared to Millstone Unit 3. However, it een be concluded that there are no significant differences in the design of the steam generators in ) g, the two plants that would adversely'affeet the natural circulation characteristics. l I 40214 l
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Canyon, the hydraulic. resistance coefficients were also compared. The-coefficients were generated on'a per loop: basis. The hydraulic: resistance coefficients applicable to normal flow conditions',are as' follows: q e Diablo Canyon ' Millstone-Unit 3 ' [ft/(gpm)2] [ft/(gpm)2] -10 -10 Reactor Core'& Internals. 129.0 x.10 115.1'x 10 ' p -10 Reactor Nozzles 36.1! x 10 ~26.6 x-10 l 1 -10 0' R.C.. Loop Piping 20.9 x 10 '/4.0'x.10 -) Steam Generator 112.0 x 10 118.0'xT10-10; -10 -10 -10 Total Hydraulic 298.0.x 10 283.7 x 10 Flow Coefficient (HFCtot) e? ~~1/2 Flow Ratio Per Loop HFC = tot for Diablo Canyon "" tot for Millstone The general arrangement of the reactor coreand internals is the same in Diablo Canyon and Millstone. The Diablo Canyon vessel inlet nozzle radius is significantly smaller than that of Millstone, as refiteted by the higher coefficient for Diablo Canyon. The flow losses are otherwise very similar for the two plants. The coefficients indicated represent -the resistance seen by the flow in one loop, excluding the resistance. through the reactor coolant pump. The RCP flow resistances.for natural circulation flow conditions are comparable to the flow coefficients given above. However, since the RCP impeller designs for Diablo Canyon and Millstone Unit 3 are nearly identical, the' flow ratio reported above would remain very close to unity. 4021q _ _ _ _ _
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1 q \\ l If the ef fect of the 5-10% increased natural circulation driving head 'for. ,{' Diablo Canyon Unit 1 is'taken into account, the flow ratio would change to approximately.0.99. Considering the slight differences and uncertainties in hydraulic -losses and natural circulation driving heads, the natural circulation loop flowrate for Millstone. Unit 3.is expected to. be within three percent of that for Diablo Canyon.- Slight differences in { reactor power and decay heat levels between the two plants would not be f expected to alter this conclusion. O.J e Wo i 0 4021g - 9.-
p f. y t 3.2 Boron Mixina The'Diablo Canyon boron mixing test evaluation demonstrated adequate boron mixing under natural circulation conditions when highly borated water at. low temperatures-and. low flowrates (relative to RCS temperature and flowrate) was injected into-the RCS. It also evaluated the time delay associated with boron mixing under these conditions. A The acceptance criterion for this' phase of-the Diablo Canyon test was that RCS hot legs (loops 1 & 4) indicate that the active portions of the. RCS were borated such that the boron concentration had increased by 250 ppm or more.- Boron injection was conducted at the Diablo Canyon test using the 20000 ppm borou solution contained in the boron injection. tank (BIT). The-BIT's contents were flushed into the RCS and within 12 minutes, natural circulation had provided adequate mixing to increase the boron f concentration in the RCS by 340 ppm. Following injection, makeup to the VCT was set to provide 2000 ppm boron. This simulated suction of'the j charging pumps aligned to the RWST. The charging pump discharge was ~ aligned to provide seal injection flow to each RCP and charging flow to one RCS loop. This alignment was continued throughout the remainder of the test causing the boron concentration to further increase. ] For the Millstone Unit 3 plant, boron would be injected into the RCS from 4 the $300 ppm boron solution of the BATS through the RCP seals and the normal charging line, if available. Also, as noted previously, a safety O' grade = backup means of boron injection is provided by the SIS flow path. This boron concentration (6300. ppm) at Millstone Unit 3 is less than that used for the successful'Diablo Canyon test. The addition tef a larger quantity of borated water over a longer time period will be required for-O Millstone Unit 3 to achieve a similar change in boron concentration.. However, because natural circulation flow at fli11 stone Unit 3 is expected to be very similar.to the flow ^obtained at Diablo Canyon, adequate mixing. of the boron would also be provided for Millstone Unit 3. 4021g -
s m ,e d 3.3 Reactor Coolant System Cooldown i The cooldown portion.of the test Demonstrated.the capability to cool down the RCS to RHR system initiating conditions at approximately,25'F/ hour y using all four steam generators for' natural circulation. The RHR system l O was.th'en used to cool the RCS to' cold shutdown conditions.. Plant' cooldown was controlled within Technical Specification limits. -All' active portions of the RCS remained within 100*F of the average core exit q temperature. Also, both the steam generators and reactor vessel upper O-head were cooled to below 450'F when the core exit 1 temperature was 350'F. I For' Millstone Unit 3, cooldown capability will be;similar to.Diablo 1 Canyon due to similarities in the design of the RCS. AFW, main steam and RHR systems. The upper head volume for Millstone Unit'3 is higher than that of'Diablo Canyon Unit 1. However, the spray nozzle flow area-for. 1 Millstone Unit 3 is significantly higher. The upper head region for. Millstone Unit 3 is expected to cool at a rate comparable to or exceeding p that of Diablo Canyon 1. RCS cooldown at.a rate exceeding 25 F/ hour would potentially be permitted for Millstone Unit 3. :A:50'F/ hour 1 -1 cooldown rate would be permitted if CROM fans are operating. Initial i plant cooldown will be accomplished via steam release from the main steam system. After RHR system initiation, the RHR system will be used to cool j the plant down to cold shutdown temperatures. l 3.4 Reactor Coolant System Depressurization The depressurization portion of the test demonstrated the capability to O control pressure in the RCS under natural circulation conditions. Pressure control capability included the ability to maintain adequate RCS l pressure without operating the pressurizer heaters and the ability to significantly reduce RCS pressure when needed to initiate RHR system N operation. Three methods of reducing pressure were demonstrated. During the RCS cooldown, pressurizer pressure exhibited a downward trend due to ambient heat losses from the pressurizer. This was followed by operator initiated RCS depressurization using the auxiliary; spray. For auxiliary l spray to be effective, the charging lines to the RCS loops must be 4021q,
p s at isolated. Finally,- depressurization?was ' completed using a pressurizer : .PORV. Each method was determined to be effective.in.reducingsRCS 4 pressure. 0 For Millstone Unit 3 pressure control and depressurization capability. ( j will be similar to Diablo Canyon due to. similarities in the design.of the RCS.and CVCS. Ambient heat losses will' gradually reduce;RCS pressure. Pressurizer PORVs or auxiliary spray will be effective in depressurizing' the RCS 'when needed to permit' RHR system,iriitiation. i l O 4021g ,12 - t [ 'i l . d.. 'i
7; , j-4'.0:I10MMARY-AND CONCLUSIONS- .The Diablo Canyon Unit l' Natural Circulation / Boron Mixing /Cooldown; Test - J (Reference.3)' demonstrated that-the' plant can safely be taken to cold 1 I' shutdown under natural circulation conditions. In order to apply the test' results to Millstone Unit 3. a general j . comparison'(Section 2.0)'of the plant systems and equipment that affect natural c.irculation, boron mixing ~ cooldown and depressurization capabilities has been made between the' Millstone Unit 3 and Diablo Canyon t Unit.1 plants. The Section 3.0 evaluation demonstrates that the Millstone Unit' 3 capabilities are comparable'to those of Diablo Canyon Unit 1. Therefore it is concluded that Millstone Unit-3 meets'the j testing comparison requirement of Branch Technica1'. Position RSB 5-1,. ' Design. Requirements'for Decay Heat Removal Systems (Reference;1). j e( ] O ' C) \\ m 40214,.,
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Sranch Technical. Position RSB'5-1 ! Design. Requirements'for Decay. q Heat Removal Systems,: Revision 2,.luly -1981.. .j n 2.. Millstone Unit:3FSAR Section'$.4.7, Residual Heat RemoYal' System.'- f q 4 cj 3. WCAP-11086, Diablo Canyon Units 1 and 2' Natural Circulation / Boron.- .J 1 .A Mixing /Cooldown Test Final Post Test Report, March,1906.t 1 -.O l 1 i ,1q d .q 1 -{ ( .( a l f C 1 l 4021g - .j 14 - 1 i .1 I}}