ML20090L783
| ML20090L783 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 07/30/1976 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Ziemann D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9102120658 | |
| Download: ML20090L783 (5) | |
Text
{{#Wiki_filter:-. _ _ Q NORTHERN STATES POWER COMPANY M I N N E A P O L.18. M I N N E G OT A 59401 July 30, 1976 ff h moerpc,og s s c-*.*: 'd' j ' ,f q[} s 6 MG g gtg T (n.S ef o I Hr D L Ziernann, Chief ,m 15 W '7 Operating Reactors Branch #2
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g'.,,,, f T. (%6 C Division of Operating Reactors U S Nuclear Regulatory Cccanission G i j Washington. DC 20555 W: s ( .s N ' W. g W-Dear Mr Ziemanni FOffrICELID NUCLEAR '.ATITG PIA!T1' Docket No. 50-263 Lievuse No. DPR-22 Supplement to June 7.1976 Imtter Concerning LPCI Design Our June 7,1976 letter stated that Mo...icello was not vulnerable to the potential LPCI deficiency identified in your May 20, 1976 letter. We have been requested verbally by members of your staff to supply the follwing additional information in support of our conclusion. We analysis was done for the base case of two pumps in a single LPCI loop pumping into the postulated broken recirculation loop assuming throttle valves to be vide open. Runout flow was found by plotting the system dynamic head-f1w curve on tha pump characteristic curve and noting the f1w at the point of intersection of the two curves. Knwing runout flow, the NPSH available was calculated. Available NPSH (atmospheric head + clevation head - f riction head loss in suction piping - l vapor pressure head + dynamic head) exceeds the required NPSH (found from characteristic pump curve). It is therefore concluded that no cavitation will occur. ( LPCI consists of two systems, each having two pumps. A single auction line supplies the two pumps in each system frcan a eccanog torus ring header. De dis-charge lines fro:n the two systems are cross tied so that either system can discharge into either recirculation loop. We case of two pumps discharging into a broken recirculation loop is more severe than the other two cases postulated in your letter for IMR-3 plants with Loop Selection Logic Systems. (This is identi?.ed as Case I in the attached Figure 1.) For the case of four LPCI pumps injecting into a brellen recirculation loop (Case II) the system dynamic head is greater, causing runout flow to be less, re-sulting in a larger available NPSH. (The total f1w of the four pumps in Case II is the sa:ne as that of Case I, resulting in the same loss in the suction screens and ring header.) For the case of three pumps providing f1w to the unbroken loop (Case III) the pumps must be looked at individually. For the LPCI system having two operable ND 9102120658 760730 PDR ADOCK 05000263 S PDR
NORTHEhN OTATED POWER COMPANY D L Ziemann July 30, 1976 pumps, the f1w is less than in Case I and therefore the available NPSil is greater. For the LPCI loop having only one operable pump, the f1w will be much less than the total f1w from the two pumps in Case I which discharge to the broken loop. Since almost all of the friction head loss in the suction piping occurs in piping coninon to the two pumps of the 1101 system, the NPSil available to the single operational pump in Case III will be greater than that of Case 1. Figure 2 shws the runout f1w for the Case I systen head to be 4500 gpm per pump. This is based on a water temperaturn of 145 F (Figure 5.2.16, FSAR). At this f1w the NPSit required is 26.6 feet of water absolute and N!P required is 555 which is less than KlP requirement at pump rated conditions. At this f1w the friction head loss in the suction line is 10.47 feet of water (based on loss through suction strainer, 20" torus ring header, 20" pump suction line and 14" suction line). F1w through the suction strainer and torus ring header was based on operation of two core spray pumps at rated capacity, two !JCI pumps at rated capacity and two LPCI pumps at the runout flow. The available NPSil is 28.68 feet of water: 33.60 feet (atmospheric pressure) + 11.63 feet (elevation dif ference betveen torus level and pump center line) -10.47 feet (friction head loss) - 7.75 feet (vapor pressure of water at 145 F) + 1.67 i et (dynamic head). Rigorous anasysis was completed for "B" 1101 loop. Comparison of system isometrics shws no signi.'icant difference in configuration of "A" and "B" loo, It is safe to conclude that :-sults of "B" loop analysis are typical of "A" loop. In accordance with Safety Guide 1, the calculation of available NPSit does not take credit for containment pressurization. It is believed that in a real situation the margin of available NPSl! over required NPS!! would be substantially increased due to containment pressurization. It should also be stated that pump cavitation is not equivalent to pump damage and failure, as this request for information seems to imply. In fact, in certain applications pumps operate continuously in a state of cavitation. On the basis of the characteristic pump brake horsepwer and motor current at tunout f1w, and the available NPSil at runout f1w, we conclude that the Monticello LPCI pumps are not subject to cavitation or motor overload in the runout condition. Yours very truly, 0. r-L 0 Mayer, PE Manager of Nucicar Support Services IDM/MHV/ak cc: J G l'eppler G Charnof f MPCA Attn: J W Ferman Attachments
I Case I. Two Naps into 11roken Loop i 3 I ) T ]) 'V to intact l A recirc loop 9 F J L r v to broken A recite loop r Case II. Twr Nmps into Broken Mop ) O) L2 to intact F1 recirc loop } O) t V .A _ to broken rectre loop f Case III. Ihree Pumps into Intact Loop } V to intact l -O recirc loop i ,.c - J ' --+d,M' R inoperable f Li to broken 71 recirc loop i Figure 1. Postulated Failure Configurations l l .,....._.__.-._..-.._~-.,.-.......,....,-..,-.,_-.....,~,._,...m.-,, _ _ _ _. _ _., _... -, -... _.. _. -. _...., _., - -. ~.....
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