ML030870341

Slide Presentation, NRC Assessment of Davis-Besse Head Degradation

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 Jack Grobe, 0I 1*

0A Chairmanof the Davis Besse Restart Panel,Region III Office, United States Nuclear Regulatory Commission Mark Kirk, Senior MaterialsEngineer, Office of Nuclear ReactorResearch, 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 I -zki S Naule#

Pouible Lejking fbagem

/

,N -3N6NI.~

<0 0~O w

S 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

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

ii 4 cr c 53 o

.0 O (D En (D

CD ii, CD ar) 55 CD~

rl-o 0 M.

Nozzle #3 Corrosion Cavity

,* '-. , .. -,* . 1..

'42 14 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

Design of the Head Basis of Finite Element Model Wastage Geometry (upper-boundedfrom April "02licensee measurements)

I I

Cladding Tensile Properties I \ ,,I -L-(lower-boundedfrom available data) K ii 44- - - -fl4 -a- -a

.4- - - - N - - - - - a 80 t'rm ," ' - -C114 992 rc7, .. - - - S... a 4S *-* -. a a 4

*a,. 61.64 list" Cladding *4- *4fl -"

• Mi H

U.

fl S..

U.

• 4W a4

-4J 60 *4- -0*

.dj.l.d %%l I (

.,,.m Thickness 0- 44W Sf0 - U. JAN IAN a Hotboth S%.I04curisnC.

ror B .. du. .C..... tt a 94.359 (minimum repofted - 4W Sf0 - M* -U uniform elangtion - I 15'

.AMA - - .AA V'--

by licensee -

-4 4AM 4W 4M 4W SIn U.

4AM 20I 1FI'm 5-;7

,sP. 2i 0.24-in.) r N F - 2 .5/I k'0

'-0 AOWt, dat. ma550°f 005 015Am 0 02 True Strain (-) k'6,ln DD2 M Ow True Strain (.) 2IA'l st cfw 1

• Finite Element Model VG 13

44 1 4tI 4 -.

117T II.

- N. I Failure Criteria

.7 . 4 I

-4 Calibrated to disc burst tests reported by P. Riccardella [ASME "72PVP]

-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 9 along with 3D FE model of Davis Besse cavity to assess probability of cladding 3 5----- --i-i - - T- iI - - - I - --

rupture in the "as found" condition Normal Distribution I, Mean = 1.0975 SStd Dev 0.12 AIBS-C WBSW SPWiM"f spociffln Fllur. Geonielry C 2Flw...

2.5 meal] 1 098 (a median = 1 008 35304, 15 i 0 2 Weibull Distribution ABS-C; A5338 -- Location = 0 825 I

/  !*.,"ar A'5338 C13 I-1.5 -IScale 1.5 Shape

=0308 2 302 I

o.C* B* / 45 VG 14pdra 0.5 0 2 4 6 B 10 12 14

$60.8 1 1.2 1.4 VIG 14 PeiueIe) U1I' .;. d Exp. Burst Press u rePred icted Burst Pressure, a! 07,1010"2 1(1ptw

Findings & Next Steps

• Complete preliminary analysis to determine probability of failure for the "as found" vessel head condition utilizing simplified configuration

"* 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