ML20198R769
| ML20198R769 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 01/19/1998 |
| From: | Reid D VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| BVY-98-09, BVY-98-9, GL-97-04, GL-97-4, NUDOCS 9801230404 | |
| Download: ML20198R769 (9) | |
Text
VERMONT YANKEE
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NUCLEAR POWER CORPORATION 185 Old Ferry Road, Brattlet,.>ro, VT 05301 7002 (802) 257 E271 January 19,1999 Dowuo A.Rrio BW 93 09 30NIOR VICC PRCSIDENT.
OPERATIONS (802) 258 4102 United States Nucisar Regulatory Commleolon ATTN: Document Control Desk Washington, DC 20665 Refotonose:
M Letter, USNRC to WNPC, Generic Letter 97 04, Assurance of Sufflaient Not Pooltive Suction Head for Emergency Core Couling and Containment Heat Removal Pumps, NW 97153, dated 10/7/97 M
Letter, USNRC to WNPC, Vermont Yankee Dee6 n inspection, Report No. 60-0 271/97 201, NW 97130, dated 8/27/97 M
Letter, WNPC to USNRC,30 day Response to Generic Letter 97 04, BW 97 142, dated 10/31/97 M
Letter, WNPC to USNRC, Submittel of GL 97 04 Response, BW 98-03, dated 1/2/99 s
Subles t Vermont Yankee Nuoleer Power Stellen License No. DPR 29 (Docket No. 90 271)
Generic Letter 97 04 Reauested information On October 7,1997, the Nuclear Regulatory Commiselon leeued Generlo Letter 97 04 whloh raised oor.come which may have generic Iraplicat:ons for Emergency Core Cooling System (CCCS) and containment heat removal pumps. The generlo letter requested, within 90 deye, that llooneeos provide the information outlined below for each of their faciittles:
(1)
Spoolfy the general methodology used to calculate the head loos associated with ECCS suction strainere.
(4
-Identify the required NPSH and the available NPSH.
(4 Specify whether the current design basle NPSH analyels differe kom the most rooent analyone reviewed and approgd by the NRC for whloh a aatety evaluation wat leeued.
'(4)
Spoolfy whether containment overpressure (i.e., contelnment pressure above the vapor pressure of the sump or suppreselon pool fluid was credited in the calculation of available NPSH. Spoolfy the amount of overpressure needed and the minimum overpressure available.
-(II)
When containment overpressure le orodited in the calculation of available NPSH,
\\g confirm that an appropriate containment pressure analyels was done to establish the
(
minkaum containment preneure.
Sy'this letter, Vermont Yankee le providing the requested 90 day response, as detailed in Attachment
- 11. 4 should be noted that on0olng containment analysis has resuhod in identification of additional potential sources of corttainment heat addition tcJiowing a LOCA that le not conaldered in the outront -
' calculations. This leeue has been entered into our corrective action process, compensatory actions under our corrective action pro 0 ram have been impiomonted and these analyses will be corrected, as noosemary, ;
~
V::RMONT YANKun NucLnAn Pownn ConPon ATioN Dookwt No. 50 271 BW 96-09 Pete 2 We truet that the information provkled le r=-+-d to your request; however, should you have any questions or require edditional information, please contact f'Is offloo.
- Sincerey, VERMONT YANKEE NUCLEAR POWER CORPORATION Donald A. Reid Senior Vloe Prooldent, Operations oc:
USNRC Roelon 1 Administrator USNRC Project Manager.WNPS N N'UUg,
USNRC Reeldent inspector WNPS 4
Vermont Department of Public Servloe v
w..
STATE OF VERMONT
)
WINDHAM COUNW Then pereenally appeared before me, Donald A. Rold, who, being duly
' d state %'at he r Vice Proeident, Operations, of Vermont Yankee Nuclear Power Corporation, that he le duty W t _,
file the foregonne document in the name and on the behalf of Vermont Yankoo Nuclear Power Cor ItW,Id I statemente theein oc true to the best of his knowledge and belief.
rs AAAo X e w
Saly A. Sehdetrum, Notary Public My Commiselon espires February 10,1999 o
i.,
m VCRMONT YANK". H NUCLuAR PownR CORPOR ATioN
\\
Vermont Yarace Nuclear Power Corp.
Ikdct No. 50-271 DVY 9849 Page I of 6 ATTACHMENT 1
References:
(a)
Crane Technical Paper No. 410,19th Printing,1980.
(b) letter, USNRC to VYNPC, Vennont Yankee Design Inspection, Repo:t No. 50 271/97-201), NVY 97-130, dated 8/27/97.
(c)
Safety Evaluation by the Office of Nuclear Reactor Regulation Supponing Amendment No. 27 to Facility Operating License DPT. 28, dated 8/2/76.
(d) letter, VYNPC to USNRC, WVY 76 92, dated 7/27/76.
1.
Specify the general methodology used to calculate the head loss associated with the ECCS suction strainers.
Response
The head loss associated with the ECCS suction strainers is a part of the total head loss from the suppression pool surface to the pump suction nonle in the general NPSil evaluation.
The following presents the general NPSil evaluation method, and includes the specific information on the ECCS strainer head loss.
The available NPSil is given as follows:
NPSil (ft) = h, + h,, - h,y - h,,
4 where:
h, = Absolute pressure (in feet) on the surface of the liquid supply level h,, = Static height (in feet) that the liquid supply level is above or below the pump datum h,, = licad (in feet) corresponding to the vapor pressure of the liquid at the temperature being pumped h,, = All suction line losses (in feet) including entrance losses, friction losses, and strainer loss.
The general methodology of evaluating each of the above four terms is discussed below:
5 h,
Vermont Yankee does not currently credit containment pressure above atmospheric in the NPSil evaluation. A nominal value of 14.7 psia for the containment pressure is used, llence h, is calculated as:
h, = (14,7) (144) / p, where p,is the liquid density at the temperature of the liquid being pumped.
' Process Diagrams issued by the reactor vendor for the RilR and Core Spray systems show a toms pressure of 15.8 psia at rated flow and a suppression pool temperature of 165*F.
VCRMONT Y ANKU3 NucLnAn l'Ownn CORI'OR ATION IlVY 98439 Page 2 of 6 h,
110th the Vennont Yankee CS and Rilk pumps are vertical, single stage pumps with in-line suction and discharge nozzles. Thus, the datum of the CS and RilR pumps is taken as the e;cvation of the suction nozzle centerline. The RllR and CS pump suction elevations are obtained from plant "as-built" drawings and are 215' 11" and 215' 9" respectively. Tir elevation of the suppression pool surface at minimum suppression pool level is 227'-l 23/64' (FSAR Fig. 5.2-1). Therefore, h,, is the difference between the elevation of the suppressi'>n pool surface and the elevation of the centerline of the pump suction.
h,,,
The vapor pressure is a function of the bulk pool temperature, h,p.is elven by:
h,p, = P,,, (144) / p, where P,,,is the vapor pressure. Vermont Yankee uses the peak pool temperature for the limiting scenario to bound the NPSit calculation. The peak pool temperatures used in the current NPSil calculations are 176 'F for the long term and 155 'F for the short tenn. The corresponding vapor pressures are 6.869 psia and 4.204 psia respectively, h,,
The key elements in this term are the fouled strainer loss and the suction line loss. Currently, the suction strainers are attached to the suction inlet piping via an entrance tee. In the current NPSil calculation, this entrance tee is included in the suction line loss calculation. The fouled strainer head loss is determined from the clean head loss value and the debris loading expected of a DilA LOCA. Details of the various losses are given below:
i Clean Strainer IIcad less Otw,,,i ): Currently, this it conservatively taken as I ft based on runout flow conditions. The original design basis for strainer head loss was based on the assumption that one of two strainers on each suction line was 100% plugged such that the total pump flow went through the unplugged strainer. The head loss for the unplugged strainer at pump runout flow conditions was specified as I ft. This original design basis assumption has been retained in the current design basis calculations and represents an additional conservatism.
Debris leading Ow): The head loss due to debris loading was evaluated in accordance with Regulatory Guide 1.82, Rev.1, and is based on fibrous insulation debris accumulation. The evaluation was first performed to stipport the recirculation piping modification in 1985. Both rtmout and design flow rates are considered.
l VCRMONT Y ANKCn NucLnAR PownR CORPORATION 11VY 9849 Pap 3 of 6 Vermont Yankee is currently undertaking the installation of larger ECCS suction strainers, in response to Bulletin 96-03. As part of this installation, new strainer head loss and debris loading will be obtained, llead loss test data over the expected flow range will also be furnished by the strainer vendor.
The new ECCS suction strainer head loss information will be provided to the NRC when the Bulletin 96-03 submitta! is made.
Suction 1.ine loss (h% ): As mentioned before, the suction line loss includes the loss due to the entrance tee that connects the ECCS suction strainer to the suction piping. This entrance tee loss as well as losses due to existing valves, pipe fittings, and pipe lengths are expressed in terms of a referenced diameter schedule 40 commercial steel piping. Standard loss factors for elbows, valves, C
and pipe fittings; as well as pipe roughness, are obtained from Crane (Reference a).
Each piping run from the strainer to the pump has been examined using plant as-built piping drawings. The total equivalent lengths of pipe for each run were compared and the longest for each of the Core Spray and RIIR systems were selected to conservatively bound the predicted friction losses in all the piping runs.
Friction losses are based on calculations assuming clean commercial steel pipe and 60 F water using Crane, Appendix H, " Flow Through Schedule 40 Steel Pipe, Water" (Reference a). No adjustments are made for temperature or pipe aging, increasing temperature will decrease friction losses and pipe aging will increase friction losses, therefore the effects tend to cancel each other. For the evaluation of NPSil margins with the new ECCS suction strainers installed, we intend to use a method which will explicitly account for temperature and p'pe aging effects.
The total suction line loss is therefore given by:
h,, a h
+ hu,n, +
h,,.
%,oo.,
2.
Identify the required NPSit (ft) and the available NPSil (ft).
Hrspnts Required NPSit (NPSila) is obtained from pump curves based on witnessed tests performed by the pump vendor. There is a separate set of test data for each of the two Core Spray pumps and the four R11R pumps delivered to Vermont Yankee. A curve fit bounding the required NPSil data was developed for each pump type. The required NPSil for the RilR
~. -. - -
VCRMONT YANKB3 NUCLEAR POWER CORPORATION IIVY 98-09 Page 4 of 6 pumps is based on the data labeled
- Minimum Operable NPSH @ Reduced liend". The basis for the RHR required NPSH was recently reviewed during the AE Inspection (Reference b). At our request, the pump vendor is currently performing additional NPSH evaluations for the RHR and Core Spray pumps in order to provide a more accurate basis for i
interpolating between and extrapolating beyond the NPSH database provided win the pumps.
l The available NPSH (NPSHJ is determined using the methods described in the xmse to question 1. - The most limiting conditions are determined by evaluating the total amm of j
2 Obris accumulation on each active suction strainer for a number of LOCA scenarios. For t
each scenario, the total amount of fibrous debris deposited in the suppression pool is assumed i
to be the same. The distribution of that debris to the strainers is a function of the flow rate l
through each individual strainer in relation to the total flow rate and the number of active suction sites. The amounts of debris on the strainers for each scenario was determined
- {
assuming the operating Core Spray and RHR pumps were operating at their maximum runout
' flow rde for 10 minutes. The short term available NPSH was calculated based on the amount of debris on each strainer, the maximum fiow rate, and the maximum suppression 2
pool temperature at 10 minutes, assumed to be 155'F. This defines the short term NPSH i
margin.
l The long term margin was determined by assuming control room operators would take manual control of the RHR system after ten minutes as described in FSAR Section 14.6.3.3.2, and place one or more RHR pumps in the containment cooling mode, secure pumps no longer required, and to monitor Core Spray flow rate and throttle flow if the Core Spray pumps were to begin to cavitate. FSAR Table 14.6.4C defines the flow rates assumed in the lon -term containment response analysis, 3,020 gpm for a Core Spray pump and 7,000 l
gpm for a RHR pump in containment spray mode. The basis for a Core Spray pump flow j
rate of 3,020 gpm is not given in the FSAR. Current NPSH analyses assumes 3,000 gpm, which is the specified value for rated Core Spray flow. The debris remaining in the l
suppression pool after ten minutes was assumed to be deposited on the remaining active l
t q
2The debris head loss discussed here is based on Regulatory Guide 1.82, Rev. I and f
NUREG-0897, Rev.1. Vermont Yankee plans to install new strainers to meet the requirements of NRC Bulletin %-03 during the Spring 1998 refueling outage. The new strainers are designed l
to improve NPSH margin relative to the current str:.mers.
3 Ongoing ~ containment analysis and design revi.;ws have resulted in a finding that the cur ent licensing analysis for suppression pool temperature did not account for all potential sources of
~ heat addition following a-LOCA.L A Safety Evaluation concluded that suppression pool j
temperature as high as 155'F short-term and 176'F long-term did not involve any unreviewed
. safety questions. Compensatory actions under Vermont Yankee's Corrective Action Program-L have been~ lmplemented to assure pool temperatures do not exceed the values given above under f postulated accident conditions.'-
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1 VCRMONT Y ANKOG NUCLnAR POWER CORPOR ATION IWY 9849 i
Page $ of 6 i
strainers in proportion to their now rates. The long term available NPSil was calculated based on the amount of debris on each strainer, rated pump now rate, and the maximum i
peak suppression pool temperature, assumed to be 176 'F'.
NPSila and NPSII, for the limiting cases for pumps taking suction from the suppression 4
pool following a design basis accident (LOCA), are provided in the two tables below. The first table penains to the limiting short term condition and the second table the limiting long term condition.
I Limiting Short-Term Conditions PUMPS NPSII, (ft)
NPSH (ft) i 4
Core Spray 27.7 28.0 RIIR 22.7 26.3 l.imiting 1.eng Term Conditions I
PUMPS NPSila (ft)
NPSII krI)
A Core Spray 24.1 25.0 RilR 22.6 24.0
- 3. Specify whether the current design basis NPSH analysis differs Irom the most recent analysis reviewed and approved by the NRC for which a safety evaluation was issued.
Response
The Safety Evaluation supporting Amendment No. 27, dated August 2,1976 (Reference c),
addressed modifications made to the RIIR System to install now limiting orifices in the pump
~ discharge lines, The orifices were installed to limit the maximum flow when the RIIR pumps discharge to a postulated broken recirculation loop The Safety Evaluation noted that "VYNPC has calculated that the pumps have a net positive suction head (NPSil) greater than the manufacturer's recommended design value." In a letter to the NRC dated July 27,1976 c
(Reference d), the available NPSil was quoted as 23.7 ft, and the required NPSII as 21 ft.
1
'lhe calculations done in support of the above have been reviewed and compared to the
. current calculations. The principal differences are listed below:
'See previous footnote I
VnRMONT Y ANKlJr1 NucLHAR POwnn CORPORATION HVY 9M9 l' age 6 of 6 Parameter Previous Current (Reference c)
Flow Rate 14,500 gpm (2 pumps into Short tenn: 14,200 gpm (2 broken loop @ 7,250 gpm pumps in intact loop @
l cach) 7,100 gpm each) long-l term: 7,000 gpm (1 pump i
in containment cooling mode)
Suppression Pool 165'F Short term: 155F Temperature long term: 176 F i
Debris licad less Not included as separate Calculated debris head loss term in 1976 term added to specified strainer head loss term Other differences have been compared at the same flow rate and temperature used in the previous (Reference c) calculation The comparison is shown on Table 1.
A search of licensing documents has failed to reveal similar information for the Core Spray
{
System Therefore, Vermont Yankee cannot identify a specific Safety livaluation reviewing and approving an NPSil analysis for the Core Spray System, 4.
Specify whether containment overpressure (l.c., containment pressure above the vapor pressure of the sump or suppression pool fluid) was credited in the calculation of availabic NPSil. Specify the amount of overpressure needed and the minimum overpressure available.
Resnonse Using the llWR Owners group position, Vermont Yankea defines containment overpressure as pressure in excess of atmospheric, not in excess of vapor pressure as stated in the question. On this basis, containment overpressure is not currently credited in the calculation of available NPSil.
5.
When containment overpressure is credited in the calculation of available NPSil, confirm that an appropriate containment pressure analysis was done to establish the minimum containment pressure.
Response
i Not applicable (see response to question 4).
i TABLE 1 Comparison of RIIR NPSH Calculations @ 14.500 gpm,14.7 psia and 165 'F (all values in
- feet *)
Parameter Previous Current Diff rence (P -PJ144)/p, 21.6 22.1 Previor. calculation assumed the standard value for water dermty,62.4 lb/ca. ft. rather than the actui value based on water temperanzre.
Piping Friction anu
-7.5
-7.1 Not all the details are availab'e but what is known is that the previous calculation used a lower Form less equivalent pt.: length arai a lower friction kws per length of pi,e than the current cakulatkm.
The overall result fiw h previous cakulation is slightfy higher because it increased r'se calculated loss by 25% as a conservatism for sizing the RIIR pump discharge orifice Strainer less
-0.7
-1.0 Previous calculation adjusted the strainer krss to account for the lower-than45esigt.. low r:te through strainer. Current cakulation assumes the specified I ft head loss regardless of flow. Both losses are based on the original design basis amuufm that aII flow goes through one strainer with the othat stramer 100% plugged.
Elevation IIcad 10.3 11.2 The basis for the previous calculatkm was not found. 'Ihe current cakulation is based on as-built drawings for the elevatkm of the pump centerlme (215 ft 11 ist) and the. '
= water level in the torus fro n FSAR Figure 5.2-1 W ft I-23/64 in).
Debris less None Scenario Originnt design basis did not accamt for detw s loss as a separate term.
Dependent NPSif.
23.7 25.2 -
Previous calculations did not include a separate debris kns term. Debris loss was incorporated in Debris less the strainer kus term since all flow was assumed to go through one strainer with the cther strainer 100% plugged by debris.
- NPSif, 21.0 22.8 The previous value is taken directly from the RIIR pump curve labeled
- minimum Operable NPSil @ Reduced II.ad* supplied by the vendor. The currem cakulatim uses a conservative curve fit to bound a!! the actual da a poims from tne pump vetskx test report or all four RIIR f
pumps, then reduces that value by 3 ft to represent the Minimum OperabL NTSii.. The value so obtained is conservative relative to the values indicated on the pump curve for Minimum Operable NPSil., thus explaining the difference between the previous and current values.