ML20127M735
| ML20127M735 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 10/31/1972 |
| From: | James Shea US ATOMIC ENERGY COMMISSION (AEC) |
| To: | US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20127M728 | List: |
| References | |
| NUDOCS 9211300450 | |
| Download: ML20127M735 (4) | |
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Files (Docket !h. 50-263)
THRU: g b Of.enann, Chief, ORB #2, L v.R TECi!MICAL SPECL CATION CliAliGE 10 3 - REDUCTICU OF R!ESW F'J'P DISCl!ARGE HEAD FRCG 550 ?] 500 FEET (!DRTdERN STATES PCER CCMPANY - ID!JTICELLD)
Introduction _
By letter dated July 24,1972, :brthern States Power Corpany (U3P) submitted Proposed Chang Ib. 4(1) co reduce the RliRSW ptcp discharge pressure frca 550 feet to 500 feet because operation within the existing nmit has been carrinal since startup. We have reviewed I:SP's letters dated July 24,1972tl) and July 3,1972, " Reporting of Icw Discharge Head on ' A' Loop PiiR Service Water Ptrps"(2) and i3P presentation to the ACRS Subconnittee on September 30, 1972.
~he rinimtn E!B Service Water pttp head requirement was established to accult that an adequate differential pressure would be nnintained in the RHR heat exchanger to prevent leaka;y of the pri::ary system water to the open cycle FJE cervice water system, according to !!SP.
Tne tube-snell sid? differ-ential pressure (mquired at the FJiR systcm heat exchanger to accomolich this is 20 paid 3). HSP has reported that the current minimum RIESW ptcp discharge pressure of 550 feet, as required by the Tecir.ical Specificati0ns, as based in part upon the rarcfacturer's rating l
(3500 cpm at 626 feet) and is unnecessarily restrictive becauce the operatirs rargin is inadequate.
Evaluation I
Conparison between the vendor certified head / capacity curve for the PJiRSW ptcps and the curves obtained frca tests perfomed by USP at Monticello (Figare 2 of reference 2) chows that a flow measurement error of 53 could account for the discrepancy at rated conditions.
He were advised by HSP personnel in a telecon en 10/5/72 that recent rerun test measurements by USP near pump shutoff conditions have lowered the :GP data points plotted en the referenced figure to the proxicity of the pttp certification curve, USP also reported (telecon 10/5/72) that the orifices in the 17-inch ID RHRSW lines at Monticello are 11 inches in dia eter cocpared with a eraller crifice, thcusht to be about 7 inches in dia:neter, used at the vendor's facility. 'Ihe I
calibration accurac' emected for the 11-inen crifice, it was stated i
by HSP, is in the range of 0.5 to 2.05.
.:SP plans to resolve the discrepancy bet';een ptcp behavior at the vendor's facility and the Monticello plant and if necessary to install new calibrated flow retering assemb..ies. We concur with this action.
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As a separate effort, the necessity for the minirna RHRSW pump discharge pressure of 550 feet at 3500 gpm has been reexamined.
The highest 4
j measured pmssure at the heat exchanger of the RHR prirnry coolant water is 315 feet. The measured nnxinum resistance to service water j
flow between pup anc heat exchanger at 3500 epWpump is 62 feet.
The t
j required differential pressure between the tube and shell side is 46 i
feet (20 psi) and the containment pressure during accidents requiring RHR operation could reach 57 feet (25 psi),
she mininun punp discharge pressure at the rated flow of 3500 gpm to assure sufficient pressure at the heat exchanger to prevent prinary coolant water leakage to the river is therefore 460 feet. We concur that the proposed technical specifi-i cation minitun pump discharge pressure limit of 500 feet assums sufficient head pressure to satisfy desig1 requirenents and provides j
an added operating margin of 20 feet. Supportfbr this conclusion is provided by the 10P observation that the minimum differential pressure j
(tube-shell) at the heat exchanger is 66 paid. With a 25 psi allowance i
for containment pressuri:;ation, that diffemntial pressure is nearly 4-4 I
tines the rdnimum requirement of 20 psi. Ibwever, on the assumption that the RHRSW punp discharge pressure reasurements that have been made at j
Monticello are not low, we have concluded that the specified purp discharge pressure may be reduced from the minimum value of 550 feet to 500 feet.
If the NSP neasumaents am later determined to be low, the margin between the pum discharge pressure and the Technical Specifications will be greater than described above and > ump perfornance will be significantly above the 1
level of acceptability, 500 feet.
lending credence to the possibility l
that the HSP flow or pressure reasurements are too low am the results of disassencly, inspection, and teecing of a pump that was retumed to the j
vendor. No pump degradation or mechanical failure could account for the t
pu:"p characteristics observed by USP.
Pump testing by the vendor verified he original pu@ perfomance certification, f
Conclusion There is no evidence of RHRSW pump performance degradation. Punp disassembly
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and inspection together with tests performed at the vendor's plant confirm i
that pump performance is unchanged from the original certification. Since the pump discharge head require ent to prevent - prinary coolant leakage to the river through the heat exchanger is 480 feet, the operating and safety i
nnrgin will be adequate with a technical specification minimum pump discharge i
pmscure of 500 feet instead of 550 feet.
It is likely that biased reasurements have contributed to the apparent reduction'of pump discharge head and NSF will continue to investigate this possibility. A flow neasure-
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nert error of 5% or less, if the pressure is erroneously low, could account i
for the apparent inconsistency of the pump perfomance =between the vendor's-facility and the Monticello plant. We have concluded-that the flow-i pressute neasurements at Monticello may' be in error.
If it is assmed that the lesa conservative USP purp performance measurements are correct, however, e
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there is still sufficient nargin with the pump discharge pressure i
reduced to a r611 mum of 500 feet, to assure that primar/ coolant water i
cannot leak to the river through the heat exchengers when the PJIR system is activated, and we have concluded, therefore, that the Technical j
Specifications should be changed as requested by 13P.
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' arms J. Shea l
Opemting Reactors Branch #2 Directorate of Licensing
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Enclosure:
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References 3
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DL"1ennnn, L:0RB //2 JJShea, L:0RB #2 l
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REFERBK;ES 1.
Change Request No. 4 dated July 24, 1972 - Change the Residual Heat Renoval (RER) Service Water System pump discharge head requirements fron 550 feet to 500 feet.
2.
Reporting of Low Discharge Head on "A" loop RHR Service Water Pumps dated July 3,1972. Service water pipe ID is 17 inches (Figure 1).
Panufacturer's head curve and NSP reasumd ptmp head curve differ by 5% Flow (Figure 2).
"Pased on rieasurements taken during the seven-day repair period, the minimum differential pressure of the heat exchanger, with one EHR ptap and two FuP5d punp operating at rated flow, is 86 paid....
We mininum discharge head required to maintain the 20 paid differ-ential pressure at the heat exchanger is approximately 460 feet."
3 Final Safety Analysis Report (received October 21, 1968) Page 6-2.14 -
" Cooling water for the heat exchangers of the R.*~3 system is pro-vided by four pumps located in the intake structure. Two. service water pumps will deliver cooling water to each of two heat exchangers.
Heat is transferred frcm the primary water to the cooling water and subsequently discharged to the river....
... B e pressure on the tube side of the heat exchanger when FJB service water is flowing is rnintained at a 20 psi differential above the pressure on the shell side with a P controlled valve in order to prevent o
reactor water leakage into the RER service water system and thereby into the river."
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