ML031530402
| ML031530402 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 05/05/2002 |
| From: | Bass R, Nilesh Chokshi, Matthew Kirk, Norris W, David Rudland, Wilkowski G, Williams P Engineering Mechanics Corp of Columbus, Materials Engineering Branch, Oak Ridge |
| To: | |
| References | |
| FOIA/PA-2003-0018 | |
| Download: ML031530402 (11) | |
Text
.,I NRC Assessment of Margin Available at Davis Besse toSn 0t UT-RATTELLE Mark Kirk. Wally Norris, Nilesh Chokshi RES/DET/MEB Paul Williams, Richard Bass I
Oak Ridge National Laboratory Gery Wilkowski, Dave Rudland Engineering Mechanics Corporation of Columbus ACRS Briefing: Materials and Metallurgy & Plant Operations Subcommittees USNRC Headquarters. Rockville, MD.
5th May 2002 VGT~:
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Overview of Presentation a Deterministic assessment of margins
- Scope of investigation
- Analytical tools
- Findings to date
- Next steps
- Further deterministic analysis
- Probabilistic analysis VG 2
RES Assessment of Davis-Besse "Margins"
- Margin left in condition that existed at March
'02 shutdown
- How much
- More pressure, or
- More wastage could have been tolerated without failure?
FOOTPRINT OF WASTAGE AREA Done Jnderway Aea Likely not necessary in optionssment of repair <
view of current licensee plans to procure and modify Midland head VG 3
Analytical Tools submodel il__LLL-1:
Wastage modeled as pit at top of head Most realistic representation of the geometry of both the wastage area and the overall head design VG 4 More refined cladding model (than possible in 3D)
Allowed easier investigation of additional wastage area needed to produce failure
-- l l
l~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-
Details of Analyses l
l
Ax-Metri FEC7 P = Design (2165 psi) or higher T = Operating (6000F), no gradients Material Properties On next page.
- All penetrations modeled Geometry 0 Straight walled 3D cavity Axial pit at apex of head
- Geometry digitized from early photo.
- Failure occurs when the average through-thickness equivalent plastic strain in the cladding exceeds 5.5%
Failure m 5.5% corresponds to the strain at the beginning of Criteria plastic instability. Derived from
- 11.15% strain in a uni-axial tension test
- Assumption that "failure" occurs at same stress level under uni-axial and bi-axial loading.
VG 5
Material Stress-Strain Properties RPV Steel Cladding 140 140 r-
-r Base RPV Steel i
12 900 120 600 120 -
Clad 3081308L Weld l
0.2% offset yleld strength = 30.96 ksi 1800 100 -
68 F ultimate tensile strength = 69.65 ksi a-OF B0 54 F
600 100 log. strain at UTS
=0.1115 100 212~~~~~~~~~~~~~~~~~~~~~
801OF k
)
600 u 60:'
2 400 60 600 'F
-500 U
lu
~60-j--'j40 200
-1300 20 40 200 0-
- j.
0 20~
0 0.05 0.1 0.15 0
0.02 0.04 0.06 0.08 0.1 0.12 Effective Plastic Strain 03;14102.K2 htw Effective Plastic Strain 0412O2.K p1 VG 6
Summary of Findings
-+
As-Found Condition At o erating pressure (2165 psi) the 3D FE model pre icts 2 0/o plastic strain in the cladding
- No failure predicted relative to assumed failure criteria Pressure =2.165 ksi VG 7
Summary of Findings 4> Margin on Overpressure Depending upon
- The particular failure strain (5.5°/0 vs. 1O%)
- The strain value (average, minimum, etc.)
- Cladding thickness (design, average measured, minimum measured) used in the analysis, different margins on overpressure result:
- SIA (Industry) 3D Analysis: Pfaij /roper
= 2.1 -261
- ORNL (NRC) 3D Analysis: P-Poper = 1.4-2.0
- EMC2 (NRC) 2D Analysis: (Pfail / Poper 1.1-3 Note: Only the most pessimistic overpressure margins-do not exceed the SRV set-point of VG 8
Summary of Findings 4 Additional Cavity Growth Needed to Fail ArisL(rOmtWt*
Owhi)mv lan
§r (y%da t^'II3 li i 'sl sI-j.(1tire WdJ About 1.9-in, more wastage needed (along maximum rowth axis) to cause 1ilure at the operating pressure, assuming 5.50/0 failure strain (average through thickness
- Average thickness cladding
- Appropriateness of axi-symmetric model VG 9 I
14003-k rnsiliul lonti ccn r 0.
thco X
X g
Illick cliitlliiit ilh.5 vcrn,e.
st ;rul zroi thickness 0
2 4
6 8
10 12 14 16 18 20 2:
Ul,mtI ol He*d Com,o;ol aC1ddV flcknet.297 1(t0*i)
.~~~~~~~0tsV cAtwh55
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2
Next Steps
- Better definition of failure criteria
- Calibration relative to appropriate data, if data is available
- Determination of significance of different failure criteria (for probabilistic analysis up to 2500 psi)
- Cavity growth rate
- Growth rate data
- Growth models Probabilistic analysis VG 10
Next Steps (details)
Re-analyses using ORNL "best-estimate'" 3-D FE model of existing cavity up to 2500 psi to quantify failure probabilities Further evaluation of clad failure criteria by analyzing measured data obtained from (6-in. dia. x 0.25 in.
thick.) SS burst disks 3-D FE analyses of cavity growth scenarios to refine estimates of critical wastage area at Poper VG 11