ML030870341
| ML030870341 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 02/05/2003 |
| From: | NRC/OCIO |
| To: | |
| References | |
| FOIA/PA-2003-0018 | |
| Download: ML030870341 (16) | |
Text
NRC Assessment of Davis Besse Head Degradation 0
- Ad 0I 1*
0A Jack Grobe, Chairman of the Davis Besse Restart Panel, Region III Office, United States Nuclear Regulatory Commission Mark Kirk, Senior Materials Engineer, Office of Nuclear Reactor Research, Division of Engineering Technology, United States Nuclear Regulatory Commission VG 1
Overview of Presentation
- Wastage found in the vessel head m Scope of analysis performed by RES
- Finite element model (and basis of model)
- Failure criteria
- Next Steps m Lessons Learned VG 2
Reactor Vessel Head VG 3
Boric Acid Deposits on Head Source: EPRl/DEI N
w I -zki S Naule#
Pouible Lejking fbagem
/
,N
-3N6NI.~
<0 0~O 7-Affected Area at RP-lo Addu.inalAffected Area t lP-l Additional Affected Area at RF-12 Additional Affected Aea at RF-13 VG 4 S
Location of Head Corrosion Reactor Vessel Head Degradation Location Control Rod Drive Mechanism Ns Area of Davis Besse Reactor Vessel Head Degradation Reactor Vessel Head Stainless Steel Cladding Layer VG 5
(D
=3" CD (D
(D CD ar) 4 ii 53 o
.0 ii, 55 cr c O (D En CD CD~
rl-o 0
M.
Nozzle #3 Corrosion Cavity 1..
'42 1 4 VG 7
Initial Repair Proposed VG 8
Head Cavity Removal
_2 OOf2. 5. 14 I VG 9
Removed Head Cavity VG 10
Scope of Analysis Performed by RES
"* Analysis of vessel in as-found condition
"* Initial deterministic analysis
"* Probabilistic analysis
"* Analysis of potential future states
"* Cavity growth leading to cladding failure at pressures in the range of the operating pressure (2165 psi)
"* Estimates of the additional operation time needed to achieve failure at pressures in the range of the operating pressure (2165 psi)
VG 11
Basis of Finite Element Model Wastage Geometry (upper-bounded from April "02 licensee measurements)
Cladding Tensile Properties (lower-bounded from available data) t'rm
-C
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.AMA -
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2i AOWt, dat. ma 550 °f Am 015 02 True Strain (.)
2IA'l
st cfw Cladding Thickness (minimum repofted by licensee 0.24-in.)
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-4 4AM 4W 4M 4W SIn U.
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N Design of the Head 80 60 20I 0
I F - 2
'-0 I
1 I
-L-4 True Strain (-)
k'6,ln DD2 M Ow
Finite Element Model VG 13
4tI
4 44 1
117T II.
- N.
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.7 4
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Failure Criteria
-4 Calibrated to disc burst tests reported by P. Riccardella [ASME "72 PVP]
-4 6-in. diameter
-) 1/8 and 1/4-in. thick
-4 Experiments used to quantify uncertainty and bias in using FE analyses to predict rupture of an unsupported membrane subjected to pressure loading
-4 This statistical distribution is then used along with 3D FE model of Davis Besse cavity to assess probability of cladding rupture in the "as found" condition AIBS-C WBSW SPWiM"f spociffln 2Flw...
Fllur.
Geonielry C
- 35304, 15 i
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2 4
6 B
10 12 14 VIG 14 PeiueIe)
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3 5 -----
--i -i -
T -
i I - -
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Normal Distribution I,
Mean
= 1.0975 SStd Dev 0.12 2.5 meal]
1 098 (a
median = 1 008 0
2 Weibull Distribution Location = 0 825 I
Scale
=0308 C13 1.5 -I 1.5 Shape 2 302 I-I 0.5
$60.8 1
1.2 1.4 Exp. Burst Press u rePred icted Burst Pressure, a! 07,1010"2 1(1 ptw
Findings & Next Steps
- Complete preliminary analysis to determine probability of failure for the "as found" vessel condition utilizing simplified configuration head
"* Further analysis could be performed including definitive measurements of 9 Cavity geometry e Cladding thickness & thickness variation
- Cladding tensile properties made directly on the Davis Besse head
"* Calculation of cladding rupture probabilities associated with larger wastage areas
"* Estimation of the time needed for the boric acid corrosion to progress from the as-found condition to the size of these larger wastage areas VG 15
Lessons Learned
" Significance analysis may need to consider other factors
"* Precursors were apparent to plant engineers
"* Increased accumulation of boric acid deposits on head and color changes in these deposits
"* Boric acid deposits in Containment Air Coolers necessitated frequent cleaning
"* Corrosion deposits on Radiation Element Filters caused frequent clogging
"* Effective engineering organizations understand the limits of their knowledge and analysis VG 16