ML20070M554
| ML20070M554 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 03/20/1991 |
| From: | Devine J GENERAL PUBLIC UTILITIES CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20070M559 | List: |
| References | |
| 5300-91-084, 5300-91-84, C321-91-2073, TAC-79166, NUDOCS 9103210292 | |
| Download: ML20070M554 (17) | |
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5 ElE W Pa's ppany New Jersey 07054 201 316 7000 TELEX 136 482 Writer's Direct Dial Number, March 20, 1991 C321-91-2073 5300-91-084 U. S. Nucicar Regulatory Commission Attn:
Document Control Dock Washington, DC 20555 centlemon Subjects Oyster Crook Nuclear G9norating Station (OCN05)
Docket No. 50-219 Licvnse No. DPR-16 Oystor Crook Drywell Containment References (1) NRC letter dated 2/14/91, "Requent for Additional Information on Oyster Creek Drywell Stroso and Stability Analysis (TAC No. 79166)."
(2) GPU Nuclear letter dated 12/5/90, " Oyster Creek Drywell Stream and stability Analysis (With Sand)."
In the Reference (1) letter, the NRC requested additional information on the Oyster Creek Drywell stress and Stability Analysis (With Sand) submitted by GPU Nuclear, Reference (2).
This information requent consisted of nino (9) questions on the stress and stability analysis plus two (2) general questions on the original dr; sli quality assurance and control programs and the drywell on-line thickness monitoring program. providon the requested additional information for each of the Il Reference (1) questions.
If you have any queestions or comments on this submittal or the overall drywell corrosion program, please contact Mr. Michael Laggart, Manager, Corporatt, Nuclear Licensing at (201) 316-7968.
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g 5300-91-084-e t,20-01-8073 Page 2 Attachment JCD/Rt./ pip ect Administrator, Region 1 Senior NRC Resident Inspector Oyster Cret). NRC Project Manager l
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ATTACHMENT I GDU NUCLEAR RESPOfLSElQ COMMENTS AND REQUEST FOR ADDITIONAL INFORMATION QMSE REPORTS lh'DEX NO. 91 AND 9 2 AN_ASME Vill EVALUATION OF THE OYSTER CREEK DRYWELL STRESS AND STABILITY ANALYSIS i
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l PARTI STRES_SANALYSIS P1:C3212073
1.
Eggt 2-3. first paragtgph i
Reference is made to Table 2-1 which shows the 95 percent confidence thickness values in the locally corroded areas of the drywell. The basis and method of calculating these projected thicknesses should be explained. Furthermore, the anticipated date for reaching these projected thickness should be specified.
EtulLEttLilai The following two (2) sheets present the basis and method of calculating the Table 2-1 rwjectd thicknesses. The Table 2-1 thicknesses do not represent the minimum coom require thicknesses but rather the thicknesses projected to exist at the start of the 14R Outage (October 1992), assuming a corrosion rate calculated from inspection data taken through April 1990.
It should be noted that the very conservative limiting corrosion rate will decrease as additional data is obtained.
Recent data obtained during our 13R Outage confirms this assumption.
GPU Nuclear will routinely update and document the revised corrosion rate in their safety evaluation which is available for tiRC inspection.
Should future data indicate that the April 1990 corrosion rate assessment is not conservative, the NRC will be notified immediately.
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2.
Pace 2-5...first paragraph The last sentence states that "given a design which satisfies the l
general code intent, as the oyster Creek drywall does as originally constructed, it is not a violation of Subsection NE requirements for the
-I membrane stress to be between 1.0Smc and 1.1Smc over significant distances." Further justification for the licensee's position should be provided. L'nder what conditions would this become a code violation?
In other words, at what goint does the " local" region become a " general membrane" region? Has the opinion of the code Committee been solicited regarding this matter?
If reference is to be made to code Case N-480,
.the specific portions of the Code Case as it applies to the Oyster Creek drywell situation should be fully explained.
1 Reoronat:
The use of an allowable primary membrane stress greater than 1.0 Smc and
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4 1ess than 1.1 sme is justified based upon the f act that the Code in NE-3213.10 recognizes that primary membrane etress intensity may exceed Smc for some portions of the vessel.
Further, the code limits the j
maximum meridional distance over which local primary stress may exceed 1.1 Sme, but it places no limit on the distance for which the stress may exceed 1.0 Smc but be below 1.1 smc.
This intermediate distance, shown as
- X" on the attached figure, while not defined by the Code is j
large relative to VRt due to the large attenuation length of these stresses. Therefore, the portions of the drywell which are corroded i
such that the primary stress is in excess of 1.0 sme but lose than 1.1 Smc are determined in this analysis to be in compliance with code.
This allowable is not interpreted to be global in the sense that stresses everywhere would De permitted to equal 1.1 Sme.
However, for a vessel that originally complied with the Code, increases beyond 1.0 Smc in localized areas of undefined size are acceptable.
If the shell were to continue to corrode (a case considered here hypothetically), primary membrane stress would increase at some point i
beyond 1.1 Sme.
In that case, evaluation would be required according to Code rules for a shell subjected to stress to greater than 1.1 Sme, taking into account all regions which may be within 2.5 VRt of the area in question, per the definition set forth in NE-3213.10.
l The opinion of the. Code Committee has not been solicited. The discussion of Code N-400 is used only to demonstrate that similar code rules have been applied to situations involving corroded safety related structures.
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3.
Pace 5-2. Section 5.4 This section states that "the membrane stresses for the degraded j
thickness condition were obtained by scaling upwards the calculated stresses for the nominal thickness case (Table 5-2) by the thickness ratio."
It should also be explained how the primary membra a plus bending stresses shown in Table 5-3 were obtained.
It appears that the combined stress was scaled upwards linearly by the thickness ratio.
However, the bending portion of the stress should be scaled by thu square of the. thickness ratio. Also, the effect of stress concentrations due to the change of thickness should be addressed.
Response
Both the membrane and membrane plus bending stresses for the degraded thickness case were obtained by scaling upwards the calculated stresses for the nominal thickness case by the thickness ratio.
We agree that the bending stresses should be scaled by the square of the thickness ratio and combined with membrane scaled by the thickness ratio when calculated in this manner, the membrane plus bending stresses in all the drywell regions will be less than 1.5 S,e, the Code allowcble value for primary membrane plus bending stresses. The highest membrane plus bending etress magnitude will be 28620 psi in the upper sphore.
Thic value is less than the allowabic value of 29000 pai.
New tables for the strusses in the degraded region are attached.
The ef fect of change in thickness on the membrane and membrane plus bending stresses is already included in the axisymmetric finite element model. All plates at changes in thickness are tapered to minimize local effects.
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ORF # 00664 INDEX NO. 9 3, REY. I 1ABLE 5 lb comparison of Calculated Stresses to Code Allowable Values
( 95% Projected Drywall Wall Thicknesses Above Lower Sphere)
Limiting load Combination Y 1 Orywell Region Stress Calc. Stress Allowable Categ.
Magnitude Max.
Stress (Psi)
(psi)
Cylinder Prim Memb.
19850 21200 (t=0.619in.)
Prim. Memb. +
21010 29000 Bending Upper Sphere Pritt. Memb.
20360 21200 (t=0.677in.)
Prim. Memb. +
28620-29000 Bending Middle Sphere Prim Memb.
19660 21200 (t=0.723in.)
Prim, Memb. +
24930 29000 Bending 58
ORF # 00664 INDEX NO 9 1. REY. 1 TABLE 5 3 Comparison of Calculated Stresses to Code Allowable Values
( Projected Drywell Wall Thicknesses )
Limiting Load combination V 1 ( Except as Noted)
Orywell Region Stress Calc Stress Allowable Categ.
Magnitude, Max.
Stress (psi)
(psi)
Cylinder Prim Memb.
19850 21200 (t0.619in.)
Prim, Memb. +
21010 29000 Dending Upper Spherieni Prim Memb.
20360 21200 (t=0.677in.)
Prim. Memb +
28620 29000 Bending Middle Spherical Prim. Memb.
19660 21200 (t=0.723in.)
Prim, Memb +
24930 29000 Bending l
4 4.
hppendix P a,gge 21, eggend narA2I.81h The last nentence states that
- impact testing would not be required by the present code rules unless the LST (lowest metal service temperature) were leso than 30'r, and the oyster Creek drywell material would not require impact testing.* Earlier in this section it is stated that an LST of 30'r was used for the Oyster Creek design basis.
Is the LST for the drywell monitored by any plant operating procedures or the Technical specifications? Have studies and plant operating history demonstrated that the drywell shell temperature is not expected to be lower than 30'r for all loading conditions?
P&ELtDLts The drywell tenperature has been routinely monitored for the past five years. The lowest temperature recorded during outages is 67 r and the 0
lowesttemperatureduringoperationis100r.
Both temperatures are well above the LST of 30 F.
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i 5.
Annendim F. pAQ.t. lt.;(1K31. E n 2tAtb What is the basie for performing the sand sensitivity study with a i
nominal sand stif fness of 366 poi / inch and a sr.no stif f ness of 80
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percent of the nominal value?- Were studies and/or tests performed to j
support these assumptiona? Otherwise, the sensitivity study should be conducted further with iower stiffness values.
The licensee's letter of December 5,-1990 indicates that structural calculations assuming the sand removed would be completed by December 31, 1990.
The results of these studies should be provided to demonstrate the sensitivity of the stresses to the assumed sand stiffness, f
l Responsgt i
CE Report Index 9-3 entitled 'An ASME section VIII Evaluation of Oyster Creek Drywell for Without Sand Case Part 1 Stress Analysis
- submitted March 4, 1991 demonstrates Code compliance without sand.
Therefore, sensitivity of stresses to variations of the cand spring stiffness is not a concern.
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Part ll - S.tabilliy Analy.als i
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6.
Pace 2-3.
Section 2.3 This section states that the method described in Reference 2-5 was used to quantify the effect that the orthogonal tensile stress has on reducing the ef fect of imperfections on the buckling strength.
The sensitivity of the results should be studied by using other methods which also address this effect.
Reenonses A study has been made of the test data contained in 44 references by Clarence D. Miller of CBI to investigate the eensitivity of reducing the effect of imperfections due to orthogonal tensile stress (see attached referenced report dated February 28, 1991).
In addition, a design equation has been developed which is a lower bound of all test data.
This has been compared to that used in CE Report Index 9-2.
Referring to Figure 3 in the attached report, equation 3 is the recommended lower bound while equation 11 is the curve used by GE.
This figure demonstrates that the values CE used are conservative relative to that from equation 3 which is supported by all test data.
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.SUPPLEMERTIOEESEQMSESQJi Technical Report CDI 022891, 'Effacts of Internal Pressure on Axial compression strength of cylinders,"
dated rebruary 20, 1991.
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