ML20090L681
| ML20090L681 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 12/16/1975 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Ziemann D Office of Nuclear Reactor Regulation |
| References | |
| 14066, NUDOCS 9102120521 | |
| Download: ML20090L681 (9) | |
Text
.
g HSp NORTHERN STATES POWER COMPANY MIN N R A POLle. MIN NM SOT A 99409 December 16, 1975 6
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, g fO Mr. D. L. Ziemann, Chie f j,
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Operating Reactors Branch W.
Division of Reactor Licensing U. S. Nuclea r Regula tory Commission D
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d-Dear Mr. Ziemann MONTICELLO NUCLEAR GENERAYING PIANT Docket No. 50-263 License No. DPR-22 Relief Valve Line Restraints Inside Torus Your letter dated August 27, 1975 requested that an analysis be per-formed to confirm the adequacy of relief valve line restraints inside the torus at the Monticello Nuclesr Generating Plant. Your letter also requested that an inspection of the relief valve lines and their re-straints inside the torus be conducted for indications of damage or degradation.
Attached is a report entitled, " Structural Analysis of Safety / Relief valve Discharge Line Restraints Within Torus." he report demonstrates that loadings on the restraints will not exceed yield during a relief valve opening event.
%is report, along with our letter to you dated October 17, 1975, on the same subject, should provide the information requested in your let-ter dated August 27, 1975.
The restraint loadings were obtained from the Bechtel Power Corporation's current dynamic load model.
his model will be refined by the results of the Safety / Relief Valve test program planned as part of the Mark 1 Containment Long-Term Program Yours very t ruly, O-
@? w L.O. Mayer, PE D'
Manager, Nuclear Support Services E
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J. G. Keppler N
G. Charnoff M PCA--a t tn; J. W. Fe rman 9102120521 751216 PDR ADDCK 0' 5006!!63 P
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1 Structural Analysis of Sa fety/ Relief Valve Discharge 1,ine Restraints Within Torus 1.
Introduction Monticello has eight relief valves and discharge lines.
The lines inside the torus are identical and equally spaced around the torus.
The layout and detailed restraint design inside the Lorus is as shown on attached drawings (enclosures 1 and 2).
The lines inside the drywell are not iden-tical so the analysis was based on the shortest line which provides the largest losds on the torus supports.
2.
b athods of Analysis a.
Computer Code for Calculation of Relief Valve Discharge Flow Transients The code is based on a non-steady, one dimensional flow analysis.
The flow along the discharge pipe axis is divided into three regions; steam flow region, an air flow region and a vater flow region.
The steam flow through the relief valve, causes the air originally in the pipe to flow (undergoing compression) in the direction of the water slug at the down-stream end of the pipe.
This in turn induces a water flow at the discharge end of the pipe.
These three flows are treated separately while satisfying the proper conditions at the interfaces.
Steam and air are treated as per-feet gases and water compressibility is accounted for.
No condensation is assumed.
Frictional losses are taken into consideration while gravitational terms have been neglected in the analysis.
The solution of the basic equations (continuity, nomentum and energy) govern-ing the flow is carried out using the method of characteristics. A finite dif ference solution using a specified time interval scheme for the distance time grid has been adapted for the numerical computations.
In this scheme, the pipe is divided into a suitable number of nodes at which the code de-termines the time changes of the following set of flow variables: velocity, pressure, sonic speed and density.
Starting from the initial conditions (no flow in the pipe) the code computes the flow variables at each node at the end of the first time otep.
Incremen-ting the time and using these conditions new values are obtained at the end of a new tira step, etc.
The code models the valve flow as an upstream boundary condition.
It con-siders the valve opening time as well as the valve opening characteristica (valve area - time and valve flow coefficient-opening dependence).
The steam /
air interface is tracked at each time step. Also, the location of the air /
i 4
l 2-J I,
i water interface is determined at etch time step.
The downstream boundary condition models the water flow through the pipe vent to the suppression i
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pool.
It allows for possible exit loss.
a The cooe determines the time at which water clearing ends.
This instant 4
]
marks the substitution of the downstremn end condition by a different model, a ram's head--attached air bubble modct.
The use of this downstream boundary l'
is continued until all the air originally in the pipe is discharged out of the pipe. At this instant, a developing steam jet model is adapted as downstream end boundary condition.
This growing steam jet is continued until it reaches j
a steady state at which time a steady jet model is assumed at the downstream i
end boundary.
7 i
The code in its current.fonn has been used to predict Quad Cities test data (NED0-10859). A good agreement was obtained between the calculated values and the test data both in the magnitude and time phase of the pressure trace up to the end of water slug clearing.
Less favorable agreement prevailed during the attached air bubble and the developing steam jet phases. Quad I
Cities test data indicate that the conditions leading to the most severe j
pipe loading occur during the initial phase of the transient, i.e., during the water slug clearing phase. Accordingly, it has been decided to use the
]
code in its current form to predict piping forcing functions only to the end t
I of water clearing.
4 The program development effort is being continued to resolve the discrepancies encountered during the post water slug clearing.
Current plans call for check-ing the code results with more test data, when available.
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b.
The structural analysis was based on the American Institute of Steel i
Construction (AISC) Specification for the Design, Fabrication and Erection of Structural Steel for Buildings - Sixth Edition.
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c.
Dynamic Load Factor
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A dynamic load factor was calculated and used for the loads imposed on the restraints.
3.
Results a.
The basic parameters used in the analysis are as follows:
1)
Safety / Relief Valve Manu facture r:
Target Rock Model:
67F Set Pressure:
1068 psig l
Accumulation:
3%
Flow Coefficient, K:
8 0 100% OPEN i
i ASME Rated Flow:
879,571 lbm/hr j
Valve Opening Time:
0.035 sec t
4 t
.~
e 3-
- 2) Discharge Piping Inside Torus Size:
10" Sch 80 Material:
A106 Cr B except for pipe stub in vent header, which is A333 Gr 6 3)
Torus Condition Water Temperature:
130F Air Temperature:
130F Water Level Elevation:
909.46 ft.
Initial Water Depth:
4.985 ft.
b.
The results of the analysis are shown graphically on Figures 1 and 2.
Note that the maximum net force or. run J-K is 36 kips, c.
The forcing function ahown in Figures 1 and 2 was utilized in the computer code STARDYNE 3 to determine the resulting stress in the relief valve discharge line and restraints. 1ht results of utie analysis gra as follows:
Peak Bending Stress in RV restraint 27,000 psi at Restraint B Peak Stress in Pipe 20,000 psi The design yield stress for the RV restraint s (ASTM A36) is 36,000 psi (lowest actual material ytid stress from the certified material test reports is 42,000 psi).
The peak stress in the RV re.'traints is 75% of design yield stress and 64% of actual yield stress.
The code allowable stress as determined by the AISC-6th Edition, for this type of design is 22,000 psi.
The predicted stresses are well below yield stress but above code a'.lowable.
The SRV test program, planned as part of the MKI Containment Long Tenn Program will be used to verify the calculated fluid flow forcing functions and determine the resulting stresses on the RV restraints.
4.
Limitations and Conclusions a.
Limitations--
The analysis only considered the ef fects of water-slug clearing.
Possible concurrent ef fects such as pool swell, an operational basis earthquake or safe shutdown earthquake are not included (but deemed to be very small compared to the primary loads.)
b.
Conclusions--
The calculated loads on the restraints are below the design yield stress for ASTM A-36 material, i
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lJI:C it.3-BlutJYllN FOR. P/.llT 50 DOC 1'.!
.4ATFRIAL
- (iI.fAPOR AHY I OHM) o l
CONTfiOL NO:E/C 4 b_
8 FILE-F ROM: Nor t.hern S tates Pwr DATE OF DOC DATG REC'D t.T R l \\.'X RPT OTHER Minneapolis, Mn
..LO_hucL 12_-10._75 12-1r-75 XXX TO:
ORIG CC OTHER SENT 12C PDR TX Mr Ziemann one signed SENT LOCAL PDR
-u CLASS UNC L ASS PROPllUO INPUT NO CYS REC'D DOCKET NCA XXXXX 1
50-263 DESCRIPTION:
ENCLOSURES:
Ltr te our 8-27-75 Itr.....trans the following:
Adol into concer ning Relict Valve Line Restraints inside Torun...(40 cys' enc 1 rec)
PLANT NAME: Monticello FOR ACTION /INFL RMATION_ _ _ _ _ _ _ _ 12-20-75 eht BUTI til (L)
SCHWE NCE R (L) Z l H.', A N N ( L )
REG AN (E)
REID(L)
W/ Copies W/ Copies
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STOL% (L)
DICKER (E)
LE AR (L)
W/ Copies W/ Copies W/ Copies W/ Copics PA Rii (L)
VASSAL LO (L)
KNiGHTON (E) spins W/ CW,ies W/ Copies W/ Copics.
W/ Copies KNIEL (L)
PURPLE (L)
YOUNGBLOOD (E) trH W/ Copies W/ Copics W/ Copies W/" Copies
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7 SCH R O E DE R GRIMES
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BRAllMAN OGC. ROOM f%0CA MACCAllY GAMMILL H. GE ARIN (L)
SALTZMAN
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ME LTZ CASE PAWLIC K I DALLARD P. KRiiUTZER (E)
SHAO SPANG LE R J. LEE (L)
PLANS s
BOYD ST E ll.O M, nt).T.nmocy(L)
MCDONALD MDORE (L)
HOUSTON ENVIRO S. REED (E)
CHAPMAN DEYOUNG (L)
NOVAK
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DUBE (Ltr)
SKOVHOLT (L)
ROSS DICKER S. SilEPPARD (L)
E. COUPE GOLLER (L) (Ltr)
IPPOLITO KNIGHTON M. SL ATE R (E)
PETEliSON P. COI.LIN3 TEDESCO YOUNGBLOOD H. SMll H (L)
HAR1 FIELD (2)
DENISE J. COLL 11:s REGAN S. TEElS (L)
KLECKER J1EG..OPR L AIN AS PROJECT LDR G. Will.l AMS (E)
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