ML20248F495
| ML20248F495 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 06/02/1998 |
| From: | Alexion T NRC (Affiliation Not Assigned) |
| To: | Cottle W HOUSTON LIGHTING & POWER CO. |
| References | |
| GL-97-04, GL-97-4, TAC-MA0045, TAC-MA0046, TAC-MA45, TAC-MA46, NUDOCS 9806040299 | |
| Download: ML20248F495 (12) | |
Text
,
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[
e Mr. Wilitm T. Cottle Juna 2, 1998 President and Chief Executive Officer STP Nuclear Operating Company I-South Texas Project Electric Generating Station P. O. Box 289 l
Wadsworth,TX 77483
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION ON 90-DAY RESPONSE TO GENERIC LETTER 97-04, SOUTH TEXAS PROJECT (STP), UNITS 1 AND 2 (TAC NOS. MA0045 AND MA0046)
Dear Mr. Cottle:
The staff issued Generic Letter (GL) 97-04, "Arsurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps" on October 7,1997. The GL requested that licensees provide information necessary to confirm the adequacy of the not positive suction head available for emergency core cooling and containment heat removal pumps. By letter dated December 30,1997, STP Nuclear Operating Company submitted its
. 90-day response to GL 97-04.
The staff has reviewed your response and has concluded that additional information is needed for items 1,2, and 3 of the GL. Enclosed are examples of responses, with the plant-specific information deleted, which the staff has found acceptable. Please note that the enclosed examples are only guidelines of the type of information that the staff needs to conduct its review and are included for your convenience. After reviewing the enclosed examples, please re-evaluate your submittal, revise as necessary, and provide the revised response within 60 days from the date of this letter. Should you have any questions, please contact me at (301) 415-1326.
Sincerely.
l ORIGINAL SIGNED BY:
Thomas W. Alexion, Project Manager Project Directorate IV-1 l
Division of Reactor Projects lil/IV Office of Nuclear Reactor Regulation Docket Nos. 50-498 and 50-499-
Enclosures:
Sample responses cc w/encis: See next page s-I i
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June 2,1998 Mr. William T. Cottle President and Chief Executive Officer STP Nuclear Operating Company South Texas Project Electric Generating Station P. O. Box 289 Wadsworth, TX 77483
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION ON 90-DAY RESPONSE TO GENERIC LETTER 97-04, SOUTH TEXAS PROJECT (STP), UNITS 1 AND 2 (TAC NOS. MA0045 AND MA0046)
Dear Mr. Cottle:
The staff issued Generic Letter (GL) 97-04, " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps" on October 7,1997. The GL requested that licensees provide information necessary to confirm the adequacy of the not positive suction head available for emergency core cooling and containment heat removal pumps. By letter dated December 30,1997, STP Nuclear Operating Company submitted its 90-day response to GL 97-04.
The staff has reviewed your response and has concluded that additional information is needed for items 1,2, and 3 of the GL. Enclosed are examples of responses, with the plant-specific information deleted, which the staff has found acceptable. Please note that the enclosed examples are only guidelines of the type of information that the staff needs to conduct its review I
and are included for your convenience. After reviewing the enclosed examples, please re-I I
evaluate your sui:mittel, revise as necessary, and provide the revised response within 60 days from the date of this letter. Should you have any questions, please contact me at (301) 415-1326.
Sincerely, hv
\\fts/
Thomas W. Alexion, Project M nager i
Project Directorate IV-1 Division of Reactor Projects lil/IV Office of Nuclear Reactor Regulation Docket Nos. 50-498 and 50-499
Enclosures:
Sample responses cc w/encis: See next page I
i e
l;.
Mr. William T. Cottle l
STP Nuclear Operating Company South Texas, Units 1 & 2 i
t cc:
l Mr. David P. Loveless Jack R. Newman, Esq.
Senior Resident inspector Morgan, Lewis & Bockius l
U.S. Nuclear Regulatory Commission 1800 M Street, N.W.
l P. O. Box 910 Washington, DC 20036-5869 l
Bay City, TX 77414 l
Mr. Lawrence E. Martin A. Ramirez/C. M. Canady Vice President, Nuc. Assurance & Licensing City of Austin STP Nuclear Operating Company L
Electric Utility Department -
P. O. Box 289 l
721 Barton Springs Road Wadsworth,TX 77483 Austin, TX 78704 Office of the Govemor l-Mr. M. T. Hardt ATTN: John Howard, Director Mr. W. C. Gunst Environmental and Natural City Public Service Board Resources Policy P. O. Box 1771 P. O. Box 12428 San Antonio, TX 78296 Austin, TX 78711 Mr. G. E. Vaughn/C. A. Johnson Jon C. Wood Central Power and Light Company Matthews & Branscomb P. O. Box 289 One Alamo Center Mail Code: N5012 106 S. St. Mary's Street, Suite 700 Wadsworth, TX 74483 San Antonio, TX 78205-3692 INPO Arthur C. Tate, Director Records Center Division of Compliance & Inspection 700 Galleria Parkway Bureau of Radiation Control i
Atlanta, GA 30339-3064 Texas Department of Health l
1100 West 49th Street
{
l Regional Administrator, Region IV Austin, TX 78756 j
U.S. Nuclear Regulatory Commission
[
611 Ryan Plaza Drive, Suite 400 Jim Calloway Arlington,TX 76011 Public Utility Commission of Texas Electric Industry Analysis D. G. Tees /R. L. Balcom P. O. Box 13326 Houston Lighting & Power Co.
Austin, TX 78711-3326 P. O.- Box 1700 Houston, TX 77251 Judge, Matagorda County Matagorda County Courthouse 1700 Seventh Street Bay City, TX 77414
Nuclear Station Response' to NRC Generic Letter 97-04 l
l Per the above referenced generic letter, licensees were i
l requested to provide information on five issues relating to net positive suction head for Emergency Core Cooling System (ECCS) pumps.
The exact requests, and the specific j
responses, are included in the following:
L 4
i 1.
Specify the general methodology used to calculate the head loss associated with the ECCS suction strainers. -
i In order to determine various " flow and design issues relating to ECCS sump performance, contracted '
to construct a 1:3 scale model of the containment sump and to conduct extensive hydraulic testing.
The general methodology used in calculating suction strainer and vortex suppressor head loss was the gathering of empirical data during test runs with various flow and screen blockage conditions, and compiling this data to determine a loss coefficient.
The complete report is provided by the Report
" Assessment of Flow Characteristics within a Reactor Containment Recirculation Sump using a Scale Model".
The bounding case for suction screen head loss is given by maximum flow for the Residual Heat Removal (RHR) and l
Containment Spray pumps.
Using the loss coefficient determined by the above report for 50% strainer blockage, I
this maximum head loss was calculated to be feet. Since i
the location of the-sump screens is feet above the sump floor, the suction pressure added by the elevation head would more than compensate for the maximum head loss across the suction strainers.
The calculation for the limiting-case available net positive suction head for the ECCS and Containment Spray pumps assumed a sump level of 0, and therefore no suction screen head loss was included.
This is one of several conservatism contained in the minimum NPSH calculations.
The following discussion on general NPSH calculation methodology is extracted from the FSAR, Section 6.3.2.14.
"The Emergency Core Cooling System is designed so that l
adequate net positive suction head is provided to system pumps in accordance with Regulatory Guide 1.1.
To ENCLOSURE 1
O Page 2
-')
_,e demonstrate that adequate NPSH is provided for the ECCS
. pumps, it is not necessary to provide a graph of NPSH as a function of time; it is only necessary to demonstrate that the NPSH is adequate under the worst limiting conditions.
Adequate net positive suction head is shown to be available for all pumps as follows:
1.
Residual Heat Removal Pumps The net positive suction head of the residual heat removal pumps is evaluated for normal shutdown operation, and for both the injection and recirculation modes of operation for the design basis accident.
The recirculation mode of operation gives the limiting NPSH requirement for the residual heat removal pumps, and the NPSH available is determined from the following equation:
NPSH[ actual]
(h) containment pressure - (h) vapor
=
pressure + (h) static head - (h)1oss To evaluate the adequacy of the available NPSH, several l
L conservatism are applied:
No increase in Containment pressure from that a.
present prior to the accident is assumed.
b.
The Containment sump fluid temperature is assumed to be
'*F even though the maximum temperature reached is approximately
. *F.
c.
Tne static elevation head is calculated from the floor elevation of the sump (elevation
'+
")
instead of the available water level. The elevation of the RHR pump is
'+
(Centerline of discharge pipe).
d.
The head loss is evaluated based on all pumps running at the maximum calculated runout flow with conservatively assumed junction factors.
The required NPSH is based on one pump running at a e.
maximum calculated runout flow of gpm.
.)
x Page 3
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._ /
2.'
Safety Injection and Centrifugal Charging Pumps The net positive suction head for the safety. injection pumps and the centrifugal charging pumps is evaluated for both the injection and recirculation modes of operation for the design basis accident. The end of the injection mode gives the limiting NPSH requirement for the safety injection pumps and the centrifugal charging pumps, and the NPSH available is determined from'the following equation:
NPSH[ actual] = (h) containment pressure
.(h) vapor pressure + (h) static head - (h)1oss To evaluate the adequacy of the available NPSH, several conservatism are applied:
- a. The Refueling' Water Storage Tank (RWST) fluid temperature is assumed to be
- F.
- b. The static elevation head is calculated taking no credit for water level above the bottom of the RWST (elevation
'+
").
- c. The head loss is evaluated based on all pumps running at the maximum calculated runout flow with conservatively assumed junction factors.
- d. The required NPSH is based on one pump running at its maximum calculated runout flow."
t In summary, although head loss across the sump suction screens and vortex suppressor were not incorporated in the calculations for minimun available NPSH, the more limiting assumption of 0 sump level was used.
If actual elevation and suction screen head loss were incorporated into the available NPSH calculation, results would be slightly higher i
than the current conservative values.
i
L Required NPSH and available NPSH (for the most limiting l
flows and operating modes) are given for the ECCS and containment spray pumps by the following table:
i
Pcg3 4
- ??\\
~
.; Required Available NPSH NPSH (feet)
(feet)
Injection Cold Leg Recirc.
Pump Min. RWST Minimum Level Sump Level i
')
(.
')
Containment
^'
Spray A Containment Spray B
.s Safety Injection A Safety
~
Injection B Residual Heat Removal A Residual Heat Removal B Centrifugal Charging A Centrifugal Charging B
- 3. Specify whether the current design-basis NPSH analysis differs from the most recent analysis reviewed and approved by the NRC for which a safety evaluation was issued.
Current design-basis NPSH analysis is unchanged, and still accurately reflected by the general methodology discussion in the FSAR, as related in the issue 1
. response.
This item was last formally reviewed by the NRC in the SER.
NRC Reauest
.m
\\
1.
Specify the general methodology used to calculate the head loss associated with the emergency co-e cooling system (ECCS) suction strainers.
88ElstBE De basic taethodology used for determining pump not positive suction bead (NPSH) involves a comparison of the difference between the total available suction head (absolute head measured at the pump impeller eye) and the vapor head (absolu.e) of the pumped fluid. His basic methodology is reflected in the following equation-NPSH = h,- h,,, + 4. - 6 where:
h, = atmospheric head, absolute pressure (in feet ofliquid) on the surface of the liquid being pumped.
h,,, = vapor head, the head in feet corresponding to the vapor pressure ofliquid at the temperature being pumped.
h, = static head, static height in feet that the liquid supply level is above the pump impeller eye.
- h. = friction head, all suction line losses (in feet) including all sump screen and form losses as well as friction losses through piping, veives and finings.
In applying this basic relationship to the ECCS and containment spray pumps for the sump recirculation mode, the following conservative methodologies and assumptions were used to establish each term:
h, Absolute pressure on the surface of the liquid supply level.
His term is defmed as the product of the containment pressure and the specific volume of the liquid being pumped. De calculations assume that the containment pressure is atmospheric (14.7 psia). His assumption is consistent with NRC Regulatory Guide 1.1 which states that no credit is to be taken for post-accident containment pressurization. De specific volume of the sump fluid is conservatively assumed to be that of water u
F. De assumed
'F water temperature represents the maximum post accident sump flulJ temperature.
h,,, - Vapor pressure of liquid at the temperamre being pumped.
His term is defined as the product of the saturation pressure for the temperature of the liquid being calculations pumped and the specific volume of the liquid at that temperature. The conservatively assume that the saturation pressure and specifs volume of the sump fluid is that of water at.
'F. De assumed
'F water ;.w.une represents the maximum post-accident sump fluid temperamre.
h, - Static height of the pumped fluid above the pump impeller eye.
Dis term is defined as the elevational difference between the su. face level of the fluid being pumped and the center of the pump impeller eye. De.
calculations use the difference ENCLOSURE 2
between the calculated containment sump level during recirculation and the ECCS and containment
~
spray pump suction elevation for the static head. Containment sump levels are assumed to be conservatively low for both large break (LBLOCA) and small break (SBLOCA) loss of coolant accidents. Calculations which use methodologies and assumptions which minimize sump level have been performed for both accidents to confirm that the assumed coo % ment sump levels are less than fue calculated minimum sump levels.
- h. = Friction head losses (in feet)in the suction line including hetion losses through piping, i
i valves and fittings as well as sump screen and form losws.
l This term is defined as the head loss due to flow resistance encountered by the pumped fluid in the l
i pump su: tion line. De calculations maximize the tienon bead loss by the conservative calculation and nummarian of the following parameters:
I. Sump screen and form losses which address head losses from the sump inlet screen to the residual best removal and containment spray pump suction piping. his value was empirically established for based on scale model testing performed prior to plant l
operation. The testing measured pressure head losses for the actual sump configuration I
and established a corresponding loss coefficient for the sump configuration. De loss coefficient relates actual sump screen, form and suction piping entrance head losses to the fluid velocity in the pump suction piping. These losses were calculated for con ervatively high pump flow rates. (These calculated losses assume that the sump screen is free from blockage. Sump mereen blockage has been evaluated separately as described in the response to item 2.)
j
- 2. Se. tion line fiction losses which consider the p! ping length, size (schedule), relative rughness, fitting resistance (i.e, piping elbows, reducers, see connections, gate valves and check valves) and fluid velocity. The calculations establish an equivalent pipe length for the actual length of straight pipe and a!! associated fittings and valves in the ECCS and containment spray pump suction piping. The maximum established equivalent piping length is combined with conservatively high pump flow rates, actual pipe inside j
diameters and an empirically determined friction factor to establish bounding suction line friction losses.
)
)
A
i NRC Reausst m,
)
.i
&tannag The following is a senmary of the available NPSH and the required NPSH for the ECCS pumps.
tilggt Available NPSH Raouired NPSH ExcessNPSH Residual Heat Removal (LBLOCA)
- A
.A A
l t'aa*=iamaw Spray (LBLOCA)
A A
,A Residual Heat Removal (SBLOCA)
A
,A A
(No Containment Spesy)
Residual Heat Removal (SBLOCA)
A A
9 (With Containment Spray)
A A
.A SafetyIrdection (LOCA)
A A
A (Hot Leg Recirculation)
Safetyinjection (LOCA)
A A
A (Cold Leg Recirculation)
Centrifugal Charging (LOCA)
R A
A (Hot Leg Recirculation)
Centrifugal Charging (LOCA)
A A
A (Cold Leg Recirculation)
During the containment sump recirculation mode of operation, the residualheat removalpur 3 and containment spray pumps take suction fkom the containment sump. De safety indoction pumps at 3e high pressure centrifugal charging pumps take suction kom the residual heat removal pump discharge. As indicated above, available NPSH has been evaluated for the residual heat removal pumps and the containment spray pumps when aligned to the containment sump. The 9vailable NPSH has also been evaluated for the safety injection and high pressure centrifugal charging pumps when aligned to the residual heat removal pump discharge. No other ECCS pumps take suction frorn the containment sump or are supplied by pumps which take suction tom the containment sump during the sump recirculation mode of 8Perstion.
Since thare are significant differences between ECCS pump Ametional requirements and coat tament sump levels for the LBLOCA and SBLOCA recirculation mode of operation, the available NPSH be been evaluated for both accident conditions for the pumps directly aligned to the containment sump. Additionally, since the size and locatum of a SBLOCA will determine if the containment spray system will be activated, an evaluation of the available SBLOCA recirculation mode NPSH has been performed with and wisbout actuation of the containment spray system for the pumps which take suction directly tom the containment sump.
ll 9
The safety injection pumps and high pressure centrifugal charging pumps have similar flow requirements for both the large break and small break loss.of coolant accidents. A single evaluation has been performed for both accidents when the pumps are operating aligned to the residual heat n moval pump discharge piping.
Since there are slight differences in the safety irdection and centrifugal charging pump flow distributions 4
between reactor coolant system cold leg injection and hot leg injection, the available NPSH for the safety l
l
i$ection and centrifugal charging pumps has been evaluated for irdection hto both the reactor coolant system bot legs and cold legs.
De available NPSH values for the residual heat removal and containment spray pumps were established using the methodology described in the response to item 1. De available NPSH values for the safety injection and centrifugal charging pumps were calculated in a similar manner with output 6cm a hydraulic model of the ECCS which conservatively establishes the pump suction pressure based upon operation of a single residual beat removal pump.
)
i The required NPSH for each pump was established 6cm the equipment manufacturer's performance test curve for the required flow rete. De difference between the residual best removal pump required NPSH for
)
LBLOCA and SBLOCA conditions is based upon the different pump performance requirements. For a LBLOCA, the reactor coolant system pressure decreases below the pump shutoffhead and a conservatively
)
large residual beat removal pump flow is assumed. For a SBLOCA, the reactor coolant system pressure remains above the pump shutoff head and no hot leg or cold leg idection flow is provided by Ibe residual best removalpumps.
The availabic NPSH values listed above assume that the sump screen is Dee Dom post accident debris blockage. A separate evaluation of head losses associated with sump screen blockage has been performed.
De evaluation uses an empirical relationship which establishes sump screen head loss as a ihnction of fluid 3
I velocity, sump screen mesh size and an empirical discharge coefficient established for rectangular mesh screens. This relationship was benchmarked for the surnp configuration by comparison of predicted head losses to actual head losses measured during scale model testing for clean sump screens (no blockage) and 50% screen blockage. De evaluation established that with both trains ofresidual best j
removal and containment spray pumps in operation at conservatively high flow rates, the increase in sump screen hrad loss from 0% screen blockage to 90% screen blockage would be
. A for a LBLOCA and ft for a SBLOCA. Given the excess NPSH values listed above and the results of a containment debris transport study which confirms that less than 90% screen blockage will occur under accident conditions, adequate NPSH is available to address worst case sump screen blockage.
m NRC Reauest 3.
Specify whether the current desip-basis NPSH analysis differs hem the most recent analysis reviewed and approved by the NRC for which a safety evaluation was issued.
Resnonse De original NRC approval of the available NPSH calculations for ECCS operation is documented in the initial plant safety evaluation report (Section 6.3.3 of NUREG-
., including Supplements I and 2).
Since the issuance of the initial plant safety evaluation report, the design-basis NPSH calculations have been upgraded as part of the 1986-1987 Design Calculation Program performed in accordance with the Nuclear Performance Plan. Under the calculation upgrade program, the original calculations were given a general revision to include a clear purpose, verifiable input assumptions, uniform methodologies and clear acceptance critena. The revised calculations were classified as " essential" and were subjected to an ind==d-at review to establish technical adequacy. While the Design Calculation Program was evaluated by NRC and found to be acceptable in the
. Nuclear Performance Plan safety. evaluation report (Section 2.3 ofNUREG.
. Volume 2), the revised NPSH calculations produced under the program were not specifically addressed by NRC.
De technical changes made to the available NPSH calculations during the calculation upgrade program involved the addition of conservatism to the assumed ECCS flow rates, the addition of conservatism to the assumed containment sump bulk fluid temperature, the refmement of the containment sump level calculations to reflect revised containment spray flow paths between upper and lower containment and the evaluation of containment sump screen blockage.
I
De changes made (3 add conservatism b the assumed ECCS flow rates and containment sump bulk temperature are consistent with the NRC evaluation in Section 6.3.3 cf NUREG-
, Supplement 1. Le bulk containment sump temperspare was increased 6om T to
.T to reflect the maximum expeced temperature. He containment sprey flow rate assumed in the analysis was increased to contain a level of conservatism similar to that cited for the residual best removal pumps (i.e., a conservative flow rate above expected pump runout condnions).
De changes made to the sump level eatentatians for containment spray drainage were made to be consistent with the resolution of the "ECCS Water less Outside Crane Wall / Air Return Fan Operability" issue described in Section 3.9 ofNUREG- -
, Volume 2. De containment sump level calculations were revised to reflect plant modifications perfortned in 1988-1989 designed to drain convala'amat spray inventory diverted Aom the active sump back to abe active sump.
The evaluation ofsump screen blockage was perfonned in accordance with the resolution of the
" Containment Coatings" issue described in Section 3.7 ofNUREG.
, Volume 2. The evalnation is descrhd in the response to item 2. The evaluation confirms that adequate ECCS pump NPSH is svallable for the maximum expected containment sump screen blockage under accident aaadiriaan Since the completion of the calculation upgrade program, the available NPSH calculanons have been revised to reflect a 1991 modification to the containment spray system. The assumed containment sprey flow rate was conservatively increased tom spm to spm as part of a design change which evaluated system operation with a bigber head containment spray pump rotating element.
In summary, the current design oasis NPSH analysis differs tem the analysis reviewed and approved by the NRC as part of the original plant safety evaluation. The majority of the changes made to the analysis were performed as part of the Nuclear Performance Plan to address issues evaluated by abe NRC anfery evaluation contained in NUREG-
, Volume 2. The balance of the changes were performed to support a plant modification which was evaluated under 10 CFR 50.59 criteria. The current design basis analysis continues to meet the requirements of NRC Regulatory Guide 1.1 for consideration of sump bulk temperature and containment pressure.
i i