ML102110536
| ML102110536 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 02/26/2010 |
| From: | Downing T, Travieso-Diaz M - No Known Affiliation, Northern States Power Co, Pillsbury, Winthrop, Shaw, Pittman, LLP |
| To: | Atomic Safety and Licensing Board Panel |
| SECY RAS | |
| Shared Package | |
| ML102110525 | List: |
| References | |
| 50-282-LR, 50-306-LR, ASLBP 08-871-01-LR-BD01, RAS 18326 | |
| Download: ML102110536 (17) | |
Text
tl Xcel Energy*
EC-0441 EC Closeout Package REV.O Report Date: 10/30/2009 tl Xce.I Energy*
EC-0441 EC Closeout Package REV.O Report Date: 10/30/2009
EC Number:
0000015044 Revision:
000 Engineering Change EC Number:
0000015044 000 Facility PI Status/Date:
CLOSED 10/24/2009 Type/Sub-type:
EVALI EC
Title:
EVALUATION OF THE IMPACT OF CONTINUING REFUELING CAVITY LEAKAGE DURING 1R26/2R26 ON CONCLUSIONS OF EC 14139 THAT CONSIDERED THE EFFECTS THROUGH 25 REFUELING OUTAGES. DOMINION ENG. R-4448-00-01 Mod Nbr:
KW1:
KW2:
KW3:
KW4:
KW5:
Master EC Work Group Temporary Outage Alert Group E-PRGM MGR Aprd Req. Dt.
WO Required N
Image Addr Exp Insvc Date Adv Wk Appvd Alt Ref.
Expires On Auto-Advance Priority Auto-Asbuild Caveat Outst Resp Engr DWNT01 10/30/2009 EC Number:
0000015044 Revision:
000 Engineering Change EC Number:
0000015044 000 Facility PI Status/Date:
CLOSED 10/24/2009 Type/Sub-type:
EVALI EC
Title:
EVALUATION OF THE IMPACT OF CONTINUING REFUELING CAVITY LEAKAGE DURING 1R26/2R26 ON CONCLUSIONS OF EC 14139 THAT CONSIDERED THE EFFECTS THROUGH 25 REFUELING OUTAGES. DOMINION ENG. R-4448-00-01 Mod Nbr:
KW1:
KW2:
KW3:
KW4:
KW5:
Master EC Work Group Temporary Outage Alert Group E-PRGM MGR Aprd Req. Dt.
WO Required N
Image Addr Exp Insvc Date Adv Wk Appvd Alt Ref.
Expires On Auto-Advance Priority Auto-Asbuild Caveat Outst Resp Engr DWNT01 10/30/2009
Units and Systems Facility PI Attributes Unit o
Attribute Name Value SCRN NO SIMULATOR SYSTEM HEALTH EVALNO PORC DTE PRIORITY RANKING Topic Notes Topic DESCRIPTION JUSTIFICATION NOT REQUIRED REVIEWER COMMENTS Cross References XRef Number AR AR EC 01160372 01201071 0000014139 Affected Documents Milestone System ZC Updated By DWNT01 Notes
System Description
CONTAINMENT VENT Last Updated 10/11/2009 This evaluation is an extrapolation of a previous evaluation to show the CoOO nclusions remain valid. The evaluation does not support a change to any stD 0 ructure, system, component, procedure, design basis, or technical specificao 0 tion and is not used as a basis for operability. Screening is not required 0 0 An engineering evaluation EC# 14139 was performed by Dominion Engineering to assess the potential for degradation of containment concrete, reinforcing bar, and containment vessels due to refueling cavity leakage through 25 refueling cycles. Evaluation EC# 15044 assesses the impact of continued leakage through 1 R26 and 2R26 on the conclusions of the original evaluation. The original evaluation was performed in conjunction with RCE01160372 and was procured safety related under the vendor appendix B program as specified in contract 00026901.
The original evaluation was procured to support RCE01160372. The new evaluation extrapolates the original results for an additional outage to show the conclusions remain valid. Both the evaluation and the referenced Dominion evaluation are attached in sharepoint under the EC Pkg folder.
Reviewer comments were included within the engineering evaluation. All comments were resolved.
Status APPROVED APPROVED CLOSED Date 12/02/2008 10105/2009 05/11/2009 Reference Description Refueling Cavity Leakage Corrective Actions and the LRA Leakage from Ceiling in Regen HX Room EVALUATION OF EFFECT OF BORATED WATER LEAKS ON
- CONCRETE, REINFORCING BAR Milestone APPROVED BY Date 10/13/2009 ID WTRS02 Name Myers, Sonja K Reg By APPROVED Notes: Tom Downey is qualified to prepare EC-Evaluations. Lora Drenth 00 is qualified to prepare and review EC-evaluations.
00 I concur no 50.59 screening is required.
00 I approve this EC.
Units and Systems Facility PI Attributes Unit o
Attribute Name Value SCRN NO SIMULATOR SYSTEM HEALTH EVALNO PORC DTE PRIORITY RANKING Topic Notes Topic DESCRIPTION JUSTIFICATION NOT REQUIRED REVIEWER COMMENTS Cross References XRef Number AR AR EC 01160372 01201071 0000014139 Affected Documents Milestone System ZC Updated By DWNT01 Notes
System Description
CONTAINMENT VENT Last Updated 10/11/2009 This evaluation is an extrapolation of a previous evaluation to show the CoOO nclusions remain valid. The evaluation does not support a change to any stD 0 ructure, system, component, procedure, design basis, or technical specificao 0 tion and is not used as a basis for operability. Screening is not required 0 0 An engineering evaluation EC# 14139 was performed by Dominion Engineering to assess the potential for degradation of containment concrete, reinforcing bar, and containment vessels due to refueling cavity leakage through 25 refueling cycles. Evaluation EC# 15044 assesses the impact of continued leakage through 1 R26 and 2R26 on the conclusions of the original evaluation. The original evaluation was performed in conjunction with RCE01160372 and was procured safety related under the vendor appendix B program as specified in contract 00026901.
The original evaluation was procured to support RCE01160372. The new evaluation extrapolates the original results for an additional outage to show the conclusions remain valid. Both the evaluation and the referenced Dominion evaluation are attached in sharepoint under the EC Pkg folder.
Reviewer comments were included within the engineering evaluation. All comments were resolved.
Status APPROVED APPROVED CLOSED Date 12/02/2008 10105/2009 05/11/2009 Reference Description Refueling Cavity Leakage Corrective Actions and the LRA Leakage from Ceiling in Regen HX Room EVALUATION OF EFFECT OF BORATED WATER LEAKS ON
- CONCRETE, REINFORCING BAR Milestone APPROVED BY Date 10/13/2009 ID WTRS02 Name Myers, Sonja K Reg By APPROVED Notes: Tom Downey is qualified to prepare EC-Evaluations. Lora Drenth 00 is qualified to prepare and review EC-evaluations.
00 I concur no 50.59 screening is required.
00 I approve this EC.
Milestone Milestone CLOSE DSGNVERIFY Date 10/24/2009 10/12/2009 ID LDWHIP01 N111195 Name Whipple, Linda D Drenth, Lora D Req By CLOSED Notes: Comments on form QF-0528 attached to evaluation under ECPkg folder in shareD D point.
PREPARED (EVL) 10/11/2009 DWNT01 Downing, Thomas R H/APPR Document References Facilty PI Doc-Type EC Sub-Type Doc #
0000015044 Rev 000 Minor Rev Date 10/24/2009 Milestone Milestone CLOSE DSGNVERIFY Date 10/24/2009 10/12/2009 ID LDWHIP01 N111195 Name Whipple, Linda D Drenth, Lora D Req By CLOSED Notes: Comments on form QF-0528 attached to evaluation under ECPkg folder in shareD D point.
PREPARED (EVL) 10/11/2009 DWNT01 Downing, Thomas R H/APPR Document References Facilty PI Doc-Type EC Sub-Type Doc #
0000015044 Rev 000 Minor Rev Date 10/24/2009
QF-0528 (FP-E-MOD-07) Rev. 1 tl Xcel Energy~
DOCUMENT NUMBERI TITLE:
1 2
3 4
ITEM REVIEWER'S COMMENTS In the purpose section, the impression given was that the contact of the borated water with the containment vessel was not to continue beyond refueling outage 1 R26. I believe that the actual intent of this evaluation is to evaluate conditions through the 2th cycle of operation (until shutdown for 1 R27). Please clarify purpose section.
The Dominion evaluation did not consider 5 mils as a conservative corrosion rate. It gave 5 mils as an example of a corrosion rate from a particular test. I suggest that if you choose to use a less conservative corrosion rate than the 7 mils per year assumed in the Dominion evaluation, you will need to more assertively make your point as to why a less conservative corrosion rate remains acceptable. The 7 mils per year assumption was not added as a margin of conservatism, but was a value taken from the Boric Acid Corrosion Guidebook There should be some discussion in the corrosion portion as to how this affects margin management. It should be clear to the reader what type of margin has been lost by a possible 0.19 inch of wall thickness loss.
Please page number the evaluation, page x of y, to allow verification that all pages are included.
The evaluation has been reviewed per the requirements of FP-E-EVL-01 Rev. 3 Section
5.3. Reviewer
Design Review Comment Form Sheetjof-1 REVISION:~ __ DATE:
jQ/11/Q~
PREPARER'S RESOLUTION Adopted suggested langua~e that references the 2t fuel cycle.
Revised evaluation to reference 7 mils as a conservative corrosion rate and added quote from Dominion report that states range of.002 to
.007.
Added paragraph to demonstrate that margin was significant based on the pressure stress < 'Y2 the yield strength and the change in margin is < 1 %.
Page numbers added to header.
Purpose section has been clarified. LKD Revised evaluation uses the Dominion evaluation corrosion rate and explains why increased wall loss will not affect conclusions of the Dominion report. LKD Discussion on available margin and the impact on ASME code design thickness has been explained.
Page numbers have been added.
No additional comments.
Date: ID 13 ~
Page 1 of 1 QF-0528 (FP-E-MOD-07) Rev. 1 tl Xcel Energy~
DOCUMENT NUMBERI TITLE:
1 2
3 4
ITEM REVIEWER'S COMMENTS In the purpose section, the impression given was that the contact of the borated water with the containment vessel was not to continue beyond refueling outage 1 R26. I believe that the actual intent of this evaluation is to evaluate conditions through the 2th cycle of operation (until shutdown for 1 R27). Please clarify purpose section.
The Dominion evaluation did not consider 5 mils as a conservative corrosion rate. It gave 5 mils as an example of a corrosion rate from a particular test. I suggest that if you choose to use a less conservative corrosion rate than the 7 mils per year assumed in the Dominion evaluation, you will need to more assertively make your point as to why a less conservative corrosion rate remains acceptable. The 7 mils per year assumption was not added as a margin of conservatism, but was a value taken from the Boric Acid Corrosion Guidebook There should be some discussion in the corrosion portion as to how this affects margin management. It should be clear to the reader what type of margin has been lost by a possible 0.19 inch of wall thickness loss.
Please page number the evaluation, page x of y, to allow verification that all pages are included.
The evaluation has been reviewed per the requirements of FP-E-EVL-01 Rev. 3 Section
5.3. Reviewer
Design Review Comment Form Sheet j of:J.
REVISION: _____ _ DATE:
jQ/11/Q~
PREPARER'S RESOLUTION Adopted suggested langua~e that references the 2t fuel cycle.
Revised evaluation to reference 7 mils as a conservative corrosion rate and added quote from Dominion report that states range of.002 to
.007.
Added paragraph to demonstrate that margin was significant based on the pressure stress < 'Y2 the yield strength and the change in margin is < 1 %.
Page numbers added to header.
REVIEWER'S DISPOSITION Purpose section has been clarified. LKD Revised evaluation uses the Dominion evaluation corrosion rate and explains why increased wall loss will not affect conclusions of the Dominion report. LKD Discussion on available margin and the impact on ASME code design thickness has been explained.
Page numbers have been added.
No additional comments.
~~
Preparer: Tom DOwning~
Date: ID/nl~
Page 1 of 1
QF~0527 (FP-E-MOD-07) Rev. 3 1
1 tl Xcel Energy~
D.sign Review Checklist EC Number or Document Number I Title I Revision Number: EC 150441 EVALUATION OF THE IMPACT OF CONTINUING REFUELING CAVITY DURING 1R26/2R26 ON CONCLUSIONS OF EC 14139 THAT CONSIDERED EFFECTS THROUGH 25 REFUELING OUTAGES. DOMINION ENG. R~4448~00¥01 Verifier's Name I Discipline: Lora Drenth / Boric Acid Corrosion Program OWner DESIGN REVIEW CONSIDERATIONS:
ti2
~
- 1.
Were the inputs correctly selected and incorporated into design?
- 2.
Are assumptions necessary to perform the design activity adequately described and reasonable? Where neceS5a~, are the assumretions identified for subsequent re-verifications when the detal ed design activit es are completed?
- 3.
Are the appropriate quality and quality assurance requirements specified?
- 4.
Are the applicable codes, standards, and ref;Julatory requirements includln~ issue and addends properly identified and are their requirements for design met.
- 5.
Have applicable construction and operating experience been considered?
0 0
- 6.
Have the design interface requirements been satisfied?
0 0
cgJ
- 7.
Was an appropriate design method used?
0 0
cgJ
- 8.
15 the output reasonable compared to inputs?
cgJ 0
0
- 9.
Are the specified parts, equipment and processes suitable for the required application?
0 0
cgJ
- 10.
Are the specified materials compatible with each other and the design environmental 0
0 cgJ conditions to which the material will be exposed?
- 11.
Have adequate maintenance features and requirements been specified?
0 0
cgJ
- 12.
Are accessibility and other design provisions adequate for performance of needed 0
0 cgJ maintenance and repair?
- 13.
Has adequate accessibility been provided to perform the in-service inspection 0
0 cgJ expected to be required during the plant life?
- 14.
Has the design properly considered radiation exposure to the public and plant 0
0 cgJ personnel?
- 15.
Are the acceptance criteria incorporated in the desi9n documents sufficient to allow 0
0 cgJ verification that design requirements have been satisfactorily accomplished?
- 16.
Have adequate pre-operational, sUbseguent periodic test and inspection 0
0 cgJ requirements been appropriately specified, including acceptance criteria?
- 17.
Are adequate handling, storage, cleaning, and shipping requirements specified?
0 0
[gJ
- 18.
Are adequate identification requirements specified?
0 0
cgJ
- 19.
Are requirements for record preparation, review, approval, and retention adequately specified?
0 0
cgJ
- 20.
Have Design and Operational Margins been considered and documented?
cgJ 0
0 COMMENTS: D None
[gJ Attached (Use Form QF-0528)
D In EC Topic Notes Form retained in accordance with record retention schedule identified in FP-G-RM-01.
QF~0527 (FP-E-MOD-07) Rev. 3 1
1 tl Xcel Energy~
D.sign Review Checklist EC Number or Document Number I Title I Revision Number: EC 150441 EVALUATION OF THE IMPACT OF CONTINUING REFUELING CAVITY DURING 1R26/2R26 ON CONCLUSIONS OF EC 14139 THAT CONSIDERED EFFECTS THROUGH 25 REFUELING OUTAGES. DOMINION ENG. R~4448~00¥01 Verifier's Name I Discipline: Lora Drenth / Boric Acid Corrosion Program OWner DESIGN REVIEW CONSIDERATIONS:
ti2
~
- 1.
Were the inputs correctly selected and incorporated into design?
- 2.
Are assumptions necessary to perform the design activity adequately described and reasonable? Where neceS5a~, are the assumretions identified for subsequent re-verifications when the detal ed design activit es are completed?
- 3.
Are the appropriate quality and quality assurance requirements specified?
- 4.
Are the applicable codes, standards, and ref;Julatory requirements includln~ issue and addends properly identified and are their requirements for design met.
- 5.
Have applicable construction and operating experience been considered?
0 0
- 6.
Have the design interface requirements been satisfied?
0 0
cgJ
- 7.
Was an appropriate design method used?
0 0
cgJ
- 8.
15 the output reasonable compared to inputs?
cgJ 0
0
- 9.
Are the specified parts, equipment and processes suitable for the required application?
0 0
cgJ
- 10.
Are the specified materials compatible with each other and the design environmental 0
0 cgJ conditions to which the material will be exposed?
- 11.
Have adequate maintenance features and requirements been specified?
0 0
cgJ
- 12.
Are accessibility and other design provisions adequate for performance of needed 0
0 cgJ maintenance and repair?
- 13.
Has adequate accessibility been provided to perform the in-service inspection 0
0 cgJ expected to be required during the plant life?
- 14.
Has the design properly considered radiation exposure to the public and plant 0
0 cgJ personnel?
- 15.
Are the acceptance criteria incorporated in the desi9n documents sufficient to allow 0
0 cgJ verification that design requirements have been satisfactorily accomplished?
- 16.
Have adequate pre-operational, sUbseguent periodic test and inspection 0
0 cgJ requirements been appropriately specified, including acceptance criteria?
- 17.
Are adequate handling, storage, cleaning, and shipping requirements specified?
0 0
[gJ
- 18.
Are adequate identification requirements specified?
0 0
cgJ
- 19.
Are requirements for record preparation, review, approval, and retention adequately specified?
0 0
cgJ
- 20.
Have Design and Operational Margins been considered and documented?
cgJ 0
0 COMMENTS: D None
[gJ Attached (Use Form QF-0528)
D In EC Topic Notes Form retained in accordance with record retention schedule identified in FP-G-RM-01.
Evaluation of Potential Impact of Continued Refueling Cavity Leakage ill 1 R16
- 1. Purpose This evaluation will review the impact of the c(mtinuance through the unit 1 twenty~seventh cycle of operation, 2009 and continue to spring 20 It. This evaluation is 14139, which considered the effects through 26 plant operation. The evaluation is also applicable to unit 2 as the Dominion was generic to both units.
- 2. Methodology As per EC# 14139 and Dominion Engineering Evaluation R~4448*OO~Ol Rev. ()
- 3. Acceptance Criteria As per EC# 14139 and Dominion Engineering Evaluation R~4448~OO-01 Rev. 0
- 4. Inputs As per EC# 14139 and Dominion Engineering Evaluation R-4448-00-01 Rev. 0
- 5. References As per EC# 14139 and Dominion Engineering Evaluation R-4448-00-01 Rev. 0
- 6. Assumptions As per EC# 14139 and Dominion Engineering Evaluation R-4448-00-01 Rev. 0
- 7. Analysis I or 3 The evaluation performed by Dominion Engineering considered the effects of degradation in four discrete areas: first, a bounding computation of the maximum credible corrosion of the containment lower ellipsoidal shell; second, a computation ofthe worst case depth of attack of the concrete by dissolution of the cement; third, a check that the effects of carbonation will not have rendered any rebar more susceptible to corrosion; and fourth, a computation of the maximum credible rebar corrosion for bars that are exposed to borated water flowing through cracks in the concrete.
The Dominion Engineering evaluation considered that a conservative corrosion rate to apply for determining the maximum credible wall loss of the containment shell would be 7 mils per year, and when considered to apply over 36 years, would have a resultant 0.25 inch of wall loss. From section 4.2 of the evaluation "Tests at ambient temperature indicate that the rates of corrosion of steel in aerated, concentrated (and in one case saturated) boric acid solutions range between 0.002 to 0.007 inch per year (Section 4.4.1 and page 4-35 of the Evaluation of Potential Impact of Continued Refueling Cavity Leakage ill 1 R16
- 1. Purpose This evaluation will review the impact of the c(mtinuance through the unit 1 twenty~seventh cycle of operation, 2009 and continue to spring 20 It. This evaluation is 14139, which considered the effects through 26 plant operation. The evaluation is also applicable to unit 2 as the Dominion was generic to both units.
- 2. Methodology As per EC# 14139 and Dominion Engineering Evaluation R~4448*OO~Ol Rev. ()
- 3. Acceptance Criteria As per EC# 14139 and Dominion Engineering Evaluation R~4448~OO-01 Rev. 0
- 4. Inputs As per EC# 14139 and Dominion Engineering Evaluation R-4448-00-01 Rev. 0
- 5. References As per EC# 14139 and Dominion Engineering Evaluation R-4448-00-01 Rev. 0
- 6. Assumptions As per EC# 14139 and Dominion Engineering Evaluation R-4448-00-01 Rev. 0
- 7. Analysis I or 3 The evaluation performed by Dominion Engineering considered the effects of degradation in four discrete areas: first, a bounding computation of the maximum credible corrosion of the containment lower ellipsoidal shell; second, a computation ofthe worst case depth of attack of the concrete by dissolution of the cement; third, a check that the effects of carbonation will not have rendered any rebar more susceptible to corrosion; and fourth, a computation of the maximum credible rebar corrosion for bars that are exposed to borated water flowing through cracks in the concrete.
The Dominion Engineering evaluation considered that a conservative corrosion rate to apply for determining the maximum credible wall loss of the containment shell would be 7 mils per year, and when considered to apply over 36 years, would have a resultant 0.25 inch of wall loss. From section 4.2 of the evaluation "Tests at ambient temperature indicate that the rates of corrosion of steel in aerated, concentrated (and in one case saturated) boric acid solutions range between 0.002 to 0.007 inch per year (Section 4.4.1 and page 4-35 of the
Evaluation of Potential Impact ofColltillllcd Refueling Ctwity Leakage in IR26 Boric Acid Corrosion Guidebook, Rev. 1 [16]).
conservative for the current application the steel containment vessel will be burrcl'cd concrete,"
Dominion Engineering then proceeded to conservatism and evaluation of a possible function of the containment. The evaluation concluded would not impact the safety function of the containment that any actual corrosion discovered in the field would to requirements of the ASME Section XI Code for acceptability.
By extrapolating the evaluation to account for an additional fuel of exposure to the assumed conditions, the 36 year is increased to 37.5 years, and the calculated maximum credible wall from inch to 0.26 inch. The conclusions of the evaluation, which considered 0.25 inch of wall loss remain valid as the 0.01 inch change is smull compared to the nominal 1.5 inch wall thickness and does not significantly the impact on the safety function of the containment vessel which was based 011 a comparison of the 11.6ksi pressure stress to the 34ksi yield stress of the material. From section 4.2 of the Dominion evaluation "For example, using a remaining thickness of 1.25 inches, the axial tensile stress at the thinned area is given by PR12t (page 298 in
[20]) where R is the radius (105 '/2 52.5' 630" ), P is the accident design pressure of 46 psig, and t is the remaining thickness, taken as 1.25 in. This indicates an axial tensile stress of -11,600 psi, which is far below the yield stress of 34.0 ksi (Table 1-8 in Chapter (1) 1-12 of [21]) at the accident design temperature of 268°F (Sheet 12 in [12]), let alone the tensile strength of about 70 ksi.".
The Dominion evaluation noted that there is signi f1cant mMgin as the 11.6ksi pressure stress is less than half the material yield stress, and less than 20%
of the material minimum tensile strength. As pressure stress is proportional to the shell thickness of 1.5", a change from an assumed thinning from.25 inch to.26 inch would change the available margin by less than 1 % and does not change the conclusions ofthe evaluation. As noted above, any wall loss below the 1.5" design thickness would need to be evaluated in accordance with ASME section IX under the site IWE program for acceptability.
The Dominion Engineering evaluation of the worst case depth of attack on exposed concrete due to dissolution of the cement considered the exposure time to be 25 refueling outage pool-flood periods of 15 days each. The computed depth of attack was 0.31 inches. The correlation is a function of t to the 0.5 power.
Adding an additional 15 day exposure period increases the calculated depth of attack to 0.32 inches. The Dominion evaluation then compared this depth of attack against the various thicknesses of grout or concrete cover used in the design of Prairie Island's containment concrete structures. The conclusion that this loss of concrete section in a wall that varies from 4 to 5 feet thick may be considered insignificant is not affected by the increase of one 1I100th of an inch.
The Dominion Engineering evaluation noted that at one specific point around the fuel transfer tube, the design concrete thickness may be less than a foot, in which Evaluation of Potential Impact ofColltillllcd Refueling Ctwity Leakage in IR26 Boric Acid Corrosion Guidebook, Rev. 1 [16]).
conservative for the current application the steel containment vessel will be burrcl'cd concrete,"
Dominion Engineering then proceeded to,'1<'.ti"*"""
conservatism and evaluation of a possible function of the containment. The evaluation concluded would not impact the safety function of the containment Vtc","",,,
that any actual corrosion discovered in the field would to requirements of the ASME Section XI Code for acceptability.
By extrapolating the evaluation to account for an additional fuel of exposure to the assumed conditions, the 36 year is increased to 37.5 years, and the calculated maximum credible wall from inch to 0.26 inch. The conclusions of the evaluation, which considered 0.25 inch of wall loss remain valid as the 0.01 inch change is smull compared to the nominal 1.5 inch wall thickness and does not significantly the impact on the safety function of the containment vessel which was based 011 a comparison of the 11.6ksi pressure stress to the 34ksi yield stress of the material. From section 4.2 of the Dominion evaluation "For example, using a remaining thickness of 1.25 inches, the axial tensile stress at the thinned area is given by PR12t (page 298 in
[20]) where R is the radius (105 '/2 52.5' 630" ), P is the accident design pressure of 46 psig, and t is the remaining thickness, taken as 1.25 in. This indicates an axial tensile stress of -11,600 psi, which is far below the yield stress of 34.0 ksi (Table 1-8 in Chapter (1) 1-12 of [21]) at the accident design temperature of 268°F (Sheet 12 in [12]), let alone the tensile strength of about 70 ksi.".
The Dominion evaluation noted that there is signi f1cant mMgin as the 11.6ksi pressure stress is less than half the material yield stress, and less than 20%
of the material minimum tensile strength. As pressure stress is proportional to the shell thickness of 1.5", a change from an assumed thinning from.25 inch to.26 inch would change the available margin by less than 1 % and does not change the conclusions ofthe evaluation. As noted above, any wall loss below the 1.5" design thickness would need to be evaluated in accordance with ASME section IX under the site IWE program for acceptability.
The Dominion Engineering evaluation of the worst case depth of attack on exposed concrete due to dissolution of the cement considered the exposure time to be 25 refueling outage pool-flood periods of 15 days each. The computed depth of attack was 0.31 inches. The correlation is a function of t to the 0.5 power.
Adding an additional 15 day exposure period increases the calculated depth of attack to 0.32 inches. The Dominion evaluation then compared this depth of attack against the various thicknesses of grout or concrete cover used in the design of Prairie Island's containment concrete structures. The conclusion that this loss of concrete section in a wall that varies from 4 to 5 feet thick may be considered insignificant is not affected by the increase of one 1I100th of an inch.
The Dominion Engineering evaluation noted that at one specific point around the fuel transfer tube, the design concrete thickness may be less than a foot, in which
Evaluation of Potential I mpact of Continued Refueling Cavity Leakage in tlU6 case the loss of 0.31 or 0.32 inches should be evaluation is subsequently performed elsewhere. then 0.32" should be addressed. Otherwise. such a change insignificant compared to the conscrvatisms employed in original value, such as the somewhat arbitrary doubling rate proportional constant to account f()of unceltainties in specific behavior from chemistry di in the concrete The Dominion Engineering evaluation of the protection by the hydroxides and the loss of said protection due to carbon dioxide in the air over time), determined that carbonation may penetrated approximately 1.2 inches into the concrete over the course of This was based on a curve fit and extrapolation of data from NUREG/CR-6924, which covered 25 years. By repeuting the same exercise~
of 36 years, we find that the calculated penetration goes from 1.18 inch to 1.21 inch, which does not change the value in the Dominion eVaiuati()n, which rounded to two significant figures. Thus, the conclusions are unaffected, The Dominion Engineering evaluation considered the corrosion of rebar that is exposed to boric acid leakage through crucks in the concrete. It used a corrosion rate of 0.007 inch per year and an exposure of30 days per refueling outage for each of25 outages, for a total time of750 days or 2.05 years. Thus the calculated upper limit ofrebar corrosion was found to be 0.014", Extrapolating this value to 26 refueling outages worth of exposure results in an increase in corrosion depth from 0.014" to 0.015". The Dominion evaluation judged 0.014" of rebar corrosion to be insignificant without detailed analysis. Therefore, 0.015" would be similarly insignificant, in light of the supporting data of no visible signs of rebar corrosion such as concrete spalling or rust staining at the leakage locations in containment.
- 8. Conclusions The conclusions reached in the Dominion Engineering evaluation (EC# 14139),
when results are extrapolated for an additional refueling cycle of exposure, remain valid.
Evaluation of Potential I mpact of Continued Refueling Cavity Leakage in tlU6 case the loss of 0.31 or 0.32 inches should be "'~'''U'-'
evaluation is subsequently performed elsewhere. then 0.32" should be addressed. Otherwise. such a change insignificant compared to the conscrvatisms employed in original value, such as the somewhat arbitrary doubling rate proportional constant to account f(}f unceltainties in specific behavior from chemistry di in the concrete The Dominion Engineering evaluation of the protection by the hydroxides and the loss of said protection due to carbon dioxide in the air over time), determined that carbonation may penetrated approximately 1.2 inches into the concrete over the course of This was based on a curve fit and extrapolation of data from NUREG/CR-6924, which covered 25 years. By repeuting the same exercise~
of 36 years, we find that the calculated penetration goes from 1.18 inch to 1.21 inch, which does not change the value in the Dominion eVaiuati()n, which rounded to two significant figures. Thus, the conclusions are unaffected.
The Dominion Engineering evaluation considered the corrosion of rebar that is exposed to boric acid leakage through crucks in the concrete. It used a corrosion rate of 0.007 inch per year and an exposure of30 days per refueling outage for each of25 outages, for a total time of750 days or 2.05 years. Thus the calculated upper limit ofrebar corrosion was found to be 0.014", Extrapolating this value to 26 refueling outages worth of exposure results in an increase in corrosion depth from 0.014" to 0.015". The Dominion evaluation judged 0.014" of rebar corrosion to be insignificant without detailed analysis. Therefore, 0.015" would be similarly insignificant, in light of the supporting data of no visible signs of rebar corrosion such as concrete spalling or rust staining at the leakage locations in containment.
- 8. Conclusions The conclusions reached in the Dominion Engineering evaluation (EC# 14139),
when results are extrapolated for an additional refueling cycle of exposure, remain valid.