ML20024G468

Notifies That on 720614,low Discharge Head on Loop a RHR Svc Water Pumps Occurred

ML20024G468
Person / Time
Site:	Monticello
Issue date:	07/03/1972
From:	Mayer L NORTHERN STATES POWER CO.
To:	Anthony Giambusso US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9102120517
Download: ML20024G468 (7)

Text

{{#Wiki_filter:_ _ _ _ _ _ _ _ _ _ _ e JJ e NORTHERN STATE 5 POWER COMPANY M I N N E A P O L,t e. M I N N E s oTA 55401 July 3, 19'72 4 W 0) s k l Mr. A Giambusso , jJ dlfQ - &( i( kbN \\ Deputy Dimtor for Reactor Projects ~ $hg 'g 7 Directorate of Licensing MA k k United States Atomic Energy Commission J N ( - 11 Washington, D C 2054'i 3 0, j Q N, Ibar Mr. Giambusso: CvS,QT bf MONTICELID NUCLEAR GENERATING PLAlff Docket No. 50-263 License No. DPR-22 Reporting of Lov Discharge Head on "A" loop RHR Service Water Pumps A condition occurred at the Monticello Nuclear Generating Plant recently which we are reporting in accordance with provisions of 6.6.B.1 of Appendix A, Technical Specifications, of the Provisional Operating License DPR-22. The Region III, Regulatory Operations Office has been notified of the occur-rence. On June 14, 1972 during a regular quarterly surveillance test, verification could not be made that either pump No.11 or No.13 on EHR Service Water (RHRSW) loop "A" was able to deliver 3500 gpm at the 550 ft head required by the Technical Specifications. Based on uncorrected pressure gage readings at the pump discharge flange, the maximum head was found to be 5-6% below the required level (517 feet and 520 feet for pumps No.11 and No.13 respectively. ) As required by Technical Specification 3 5.C.4, the RHRSW pumps were declared inoperable, thus rendering RRLSW loop A inoperable. 'lhis condition was re-ported to AEC Regulatory Operations by telegram on June 14, 1972. RHRSW loop "B" was demonstrated to be operable in accordance with Technical Specification 3 5.C.3 The minimum RHR Service Water pump head requirement was established to ensure that an adequate differential pressure vould be maintained in the RHR heat exchanger to prevent leakage of primary system water to the open-cycle RHR Service Water system. The differential pressure required is given as 20 psid en page 6-2.14 of the Monticello FSAR. At no time has the capability to main-sain this limit been threatened. During the seven day repair period, attention was first focused on possible pump degradation. No.13 pump was dismantled and completely inspected by the manufacturer's representative. No mechanical problems were detected 1 which would indicate degraded pump performance. All case wearing rings were s 9102120517 720703 nm PDR ADOCK 05000263 e." O # 3 g PDR.

NORT IRN STATES POWER cob ANY Mr. A Glanbusco July 3,1972 replaced and clearances were machined to manufacturer's specifications. While work vac underway on the pump, the flow orifice,10-97A, was removed for in-spection. The orifice utili::es a clip-on instrument flange which is seal velded to the pipe as shown in Figure 1. The seal velds left a beveled edge adjacent to the orifice pressure taps. It was suspected that the orientation of the pressure taps with respect to the beveled edges were upsetting the measurements. Following discussions with the orifice manufacturer, a filler ring vac fabricated and installed to provide a smooth.rusition at the ori-fice plate. The installation was reviewed and approved by the plant Opera-tions Committee. In the course of this work, accessible sections of line (three feet) upstream and downstream of the orifice were cleaned and painted. Flov tests indicated a net increase in head of approximately 20 feet using either the No. 11 or No. 13 pump. This indicated that the work on the No.13 pump had no significant effect on its perfomance. The only conclusion that can be drawn on the basis of investigations per-formed to date is that the obse-ved 20 foot head improvement with either pump must be attributed to work performed on the flow metering assembly. As additional verification, system tests will be run at two week intervals until sufficient assurance is attained that system degradation is not tak-ing place. It was the opinion of the manufacturer's representative that the pumps were in excellent running order and no further improvement in discharge head could be anticipated without significantly modifying the pumps. At this point, it was appropriate, in line with other activities, to reexamine our measurement philosophy. Tbe RHRSW pumps are a vertical-centrifugal type with ei ht stages. S The bowl assembly at the last stage discharge is located 15 vertical feet be-lov the nominal discharge flange elevation. The applicable Technical Spec-ification requires that in order for a RER Service Water pump to be considered operable, it must be capable of delivering "3500 gpm against a head of 550 feet." Nomal plant praci,1ce in determing this head consisted of taking an uncorrected pressure gage reading at the discharge flange. This practice, though conservative, is inconsistent with " head" definitions generally used by industry and with the pump manufacturer's certification data. In addi-tion, it is unduly res',rictive in demonstrating the head capacity of the RHRSW pumps. The 550 foot limit is based in part on what was considered an acceptable margin below the manufacturer's rating. As shown on Figure 2, head capacity measurements taken on three of the four pumps reveal a charac-teristic significantly different than that shown on the manufacturer's cer-tified pump curve; the head-capacity characteristic for the fourth pump is not expected to differ substantially. Althou6h the pumps are able to meet the required 20 psi heat exchanger differential with nmple margin, the Technical Specification head requirement selected from the certified pump curve leavec no operating rargin. The pump manufacturer is working with us to explain the test curve-pump performance deviation.

i NORT RN STATEG POWER cob ANY Mr. A Giamburro July 3, 1972 Baced on mencurements taken during the seven day repair period, the minimum differential preccure of the heut exchanger, with one RHR pump and two RiIRSW pump operation at rated flow, ic 86 poid. Figure 3 demonstratec the June ik, ar-found condition and the subsequent improved condition in relation to the requirements on the cycten. The minimum discharge head required to maintain the 20 peid differential precsure at the heat exchanger in approximately 460 feet. Following considerable internal review, including the Operations Committee and the Safety Audit Committee, it was agreed that the apparent low pump head condition did not compromise plant eafety. In this context then, it was considered appropriate to define the required head as the total pump developed head rather than the static head meacured at the discharge flange. On this basic, the 550 foot requirement was met with some margin. The "A" RHR Service Water loop vas declared operational on June 21, 1972 following diccuselon of our findings with AEC Directorate of Licensing and Regulatory Operations personnel. It is our intention to submit a request for a change of the Technical Speci-fication miniman head requirement. This change would bring our Technical Specification requirement in line with realistic overall plant requirements. An Abnormal Occurrence report vill be available at the site for the Regula-tory Operations inspectors. Yours very truly, x"G. i L 0 Mayer, P.E. Director of Nuclear Support SeIvices .4M/br cc: B H Grier ( Attachmente

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AFC DI&fRIIGTION FOR FART SO DOCCT mTERIAL (TiMORARY FORM) CONTROL NO: 3673 FROM: Northern States Power Co. DATE OF DOC: DATE REC'D LTR MEMO RPr UIRER Minneapolis, Minn. 55401 L.O. Hayer 7-3-72 7-6-72 1 TO: ORIG CC UnIER SENT AEC FDP b Mr. A. Ciambusso 3 signed 37 SEh'f LOCAL IDR hFROPINFO INIVf NO CYS REC'D DOCKET NO: CLASS: 40 50-263 DESCRIPfl0N: Ltr rpt a condition which occurreiNCLOSURES: on 6-14-72 involving low discharge head on "A" loop RRR service water pumps w/attchd Fig. 1,2 & 3........ FLAlff NAMES: Monticello Plant FOR AC'lio:i/INFORMATION. p DL 7-6-72 BUfLER(L) LNIEL(L) VASSALLO(L) F41EMANN(L) INIGiff0N(LNV W/ Copies W/ Copies W/ Copies W/kCopies W/ Copies CLARK (L) SCIfa'ENCER(L ) H. DENTON CHI'IV00D(FM) W/ Copies W/ Copics W/ Copies W/ Copics W/ Copies GOLLER(L) STOLZ(L) SCHEMEL(L) DICKER (ENVIRO) W/ Copics W/ Copies W/ Copies W/ Copies W/ Copies INTERN @ DISTRIBUTION .2 OtEO FILE @ MfELLO-L OLLIER-IARAS-L L/A P4R % R. HENDRIE ) MASON-L L/A BWR G rud MOORE-L ENTON-L OIT.R (2) $ LANGE-L GRDCS-L BROWN-L L/A P4R C-RM P-506 PfWLIC[I-L GAMMILL-L WILSON-L L/A PWR NTZING & JfAFF KHOMPSON-L ENIGHTON-ENVIRO IARI-L L/A WR QIAIGUSSO-L ESCO-L DICKER-ENVIRO SMITH-L L/A WR t/boYD-L-WR ONG-L PROJ LDR ETVIRO: GEARIN-L L/A EWR DEYOUNG-L-NR INAS-L DIGGS-L L/A ffJLLER-L-ENVIRO SHAO-L SALT 4 MAN-IliD. TEETS-L L/A bdK0VHOLT-L-OFER _JENAROYA-L McDDNALD-FLANS WADE-L L/A ENVIRO UTH-L FAORRIS-RO NUSSBAUMER-FM BRAIT!!AN-A/T CCARY-L UBE-L SMILEY-FM RARLESS-ENVIRO IROEDER-L J. CA SE-L P. COLLINS-L d fRNA STEELE l-LOCAL PDR Minneapolis, Minn. 1-SAN /LA/NY--FDR -IYrII-(IAUGHLIN ) 9-NATIONAL LAB'S 1-CHIEF WATER REACTORS -NSIC-(BUCHANAN) ANL/ORNL/B.WL l-RD....E. HALL F-309 GT 1-ASLB-YORE /SARYE l-R. CARROLL-0C, GT WOODWARD /H. Sr. 1-R. CATLIN, A-170, GT l , J.-C. MILES-C-459, GT 1-CONSULTANT' S M.6 cyS ACRS-HOLDING NEWMARI/BLUME/AGBABIAN l-DR. GERALD S. LELLOUCHE l BROOIEAVEN NATIONAL IAB l l l}}