ML031040142

E-mail from Douglas Pickett Re Davis-Besse Safety Significance Telecon

ML031040142
Person / Time
Site:	Davis Besse
Issue date:	05/29/2002
From:	Pickett D Office of Nuclear Reactor Regulation
To:	Norris W
References
FOIA/PA-2003-0018
Download: ML031040142 (2)

Text

I1 r are E 1 3 :Gul- D -af-8ese Safety Significance Telecon __ _ _ _

From: Douglas Pickett ' '

To: DB Daily Call; DB0350; Wallace Norris Date: 5129102 12:35PM

Subject:

Davis-Besse Safety Significance Telecon To all:

to We have scheduled a telecon with the Davis-Besse licensee for Thursday, May 30, at 1:00 p.m.Is to better discuss the attached questions concerning the Safety Significance Assessment The purpose I have understand the differences between the licensee's and our contractor's calculated failure pressure.

reserved room 13B4 for headquarters personnel from 1:00 to 3:00 p.m.

We will use the usual conference bridge (301-231-5539 or 800-838-8081) witlascode _ J Information in this record was deleted in accordance with the Freedom of Information Act, exemptions FOIA- -2=s 3-00 IY

b--*

SAFETY SIGNIFICANCE NRC STAFF COMMENTS AND QUESTIONS ON DAVIS-BESSEAPRIL 8, 2002 ASSESSMENT (SIA-W-DB-1IQ-301) SUBMITTED FAILURE CRITERION exceeding 11.15%) used to (1) What Is the technical basis of the failure criterion (e.g., strain specific technical determine the failure conditions of the cladding layer? Provide used in this evaluation.

references in the literature that support the failure criterion in a uniaxial tensile test)

(2) How does the failure criterion (e.g., based on ultimate strain triaxial loading in the cladding account for the effects of biaxial loading in the cladding, or at the edges of the degradation cavity?

the minimum cross-(3) The failure criterion applied in SIA report W-DB-1 Q-301 (e.g.,the strain levels in the sectional strain exceeding the failure strain of 11.15%) allows thickness, leading to very the cladding to exceed the critical strain value entirely through 5 of the SIA report. What large strains at the surface of the cladding, up to 49% in Table average cross-sectional strain, is the technical basis for this approach, as opposed to the or the maximum cross-sectional strain?

to give guidance of the failure (4) Did you explore a continuum damage mechanics analysis growth starts? If criterion once the strains exceed the critical strain where neckinghoid mechanics analysis.

damage not, provide the technical basis for not using a continuum level Is exceeded, so the

[Poisson's ratio of 0.5 no longer applies once this critical strain changing as the voids grow analysis is strictly not valid. (Poisson's ratio is continuously stress redistribution that is at the strains beyond the start of necking.) This results in a not accounted for in a standard elastic-plastic analysis.]

was assumed to be (5) How would the strain values change if the stress free temperature accounted for the the stress relief temperature instead'of 700F, and the analysisat the operating differential thermal expansion of the cladding and head steel temperature of 605OF?

GEOMETRYIMESHING the cladding thickness to (A) Does the size of the degradation cavity and the transition from knowledge regarding the head thickness that was used in the SIA report reflect current In Figure 13 on page 103 the cavity geometry, In particular the undercut area described dated April 15, 2002?

of the Davis-Besse Root Cause Analysis Report (CR2002-0891),

What Isthe transition geometry assumed in the analyses?

to adequately capture (B) Is there sufficient mesh refinement through the cladding thickness any sensitivity studies the bending and shear strains at the edge of the cavity? Describe used to demonstrate the adequacy of the mesh refinement thickness (C) Was the cladding deposited by weld wire? Do the thinner cladding toes? In what direction of weld bead measurements from UT coincide with the locations the degradation cavity?

do the cladding weld beads run relative to the long axis of