ML20199C175
| ML20199C175 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 01/23/1998 |
| From: | Dromerick A NRC (Affiliation Not Assigned) |
| To: | Cruse C BALTIMORE GAS & ELECTRIC CO. |
| References | |
| TAC-M99880, TAC-M99881, NUDOCS 9801290162 | |
| Download: ML20199C175 (7) | |
Text
3anmry'23,1998 Mr. Charles H. Cruse Vice President - Nuclear Energy i
Baltimore Gas and Electric Company Calvert Cliffs Nuclear Power Plant 1650 Calvert Cliffs Parkway Lusby, MD 2C657-4702
)
SUBJECT:
REVIEW OF CONTAINMENT TENDON EVALUATION REPORT - CALVERT CLIFFS NUCLEAR POWER PLANT, UNIT NOS.1 AND 2
- (TAC NOS. M99880 AND M99881)
]
Dear Mr. Cruse:
The NRC staff has reviewed the enclosed Containment Tendon Evaluation Report. In performing the review, the staff visited the Calvert Cliffs pla7t site and communicated with Messrs. Gary J. O'Connell and Mark A. Wright, BGF personnel involved in the subject issue.
They provided clarifications regarding some areas.,f the report and the staff now has a better understanding of the report.
In the report, BGE, the licensee, evaluated, as a short-term action, the continued operability of the containment on the basis of the number of broken tendon wires so far discovered and on the number of wires expected to be broken by applying a Weibull distribution modeled after the statistics of the steam generator tube cracking. The staff has some reservations about the appropriateness of this model. Also, as a temporary measure, the tendon wires in the vicinity where excessive corrosion has been discovered were re-greased. BGE has under consideration a number of options for long-term corrective action ranging from increasing the frequency of 1
inspection to rept,ir and replacement of the corroded tendons. The licensee indiceted that it will make a decision as to which long-term action is to be tsken in the first quarter of 1998. In order to assure continued containment integrity, the licensee should have a long-term action plan with clearly defined and scheduled actions in place prior to restart from the Calvert Cliffs Unit No.1 j
spring 1998 refueling outage.
" Y' Original Signed by:
Alexander W. Dromerick, Senior Project Manager Project Directorate I-1
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Division of Reactor Projects -l/11 Office of Nuclear Reactor Regulation I
Docket Nos. 50-317 and 50-318 h
Enclosure:
Safety Assessment Report "g gy ec w/ enclosure: See next page
_ DISTRIBUTION:
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' attachment / enclosure "N" = No copy 0FFICE PS {Pp d lE LAPol*1;OV l
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DATE u9te '/98 01/ 4 998 01/ @ 98 01/
/98-01/ /98 Official Record Copy 9901290162 980123 PDR -ADOCK 05000317 P
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January 23i 1998 Mr; Charles H. Cruse m-[
Vice President - Nuclear Energy F
Baltimore Gas and Electric Company Calvert Cliffs Nuclear Power Plant --
1850 Calvert Cl6ffs Parkway l
Lusby, MD 20657-4702
SUBJECT:
REVIEW OF CONTAINMENT TENDON EVALUATION REPORT - CALVERT CLIFFS NUCLEAR POWER PLANT, UNIT NOS.1 AND 2 (TAC NOS, M99880 AND M99881)
Dear Mr. Cruse:
The NRC staff has reviewed the enclosed Containment Tendon Evaluation Report.. in performing the review, the staff visited the Calvert Cliffs plant site and communicated with Messrs. Gary J. O'Connell and Mark A. Wright, BGE personnel involved in the subject issue.
- They provided clarifications regarding some areas of the report and the staff now has a better understanding of the report.
= In the report, BGE, the licensee, evaluated, as a short-term action, the continued operability of the containment on the basis of the number of broken tendon wires so far discovered and on the number of wires expected to be broken by applying a Weibull distribution modeled after the
- statistics of the steam generator tube cracking. The staff has some reservations about the appropriateness of this model. Also, as a temporary measure, the tendon wires in the vicinity where excessive corrosic.1 has been discoverso were re-greased. BGE has under consideration a number of options for long-term corrective action ranging from increasing the frequency of inspection to repair and replacement of the corroded tendons. The licensee indicated that it will make a decision as to which long-term action is to be taken in the first quarter of 1998. In order -
to assure continued containment integrity, the licensee should have a long-term action plan with clearly defined and scheduled actions in place prior to restart from the Calvert Cliffs Unit No.1 spring 1998 refueling outage.
Original Signed by:
Alexander W. Dromerick, Senior Project Manager Project Directorate 11 Division of Reactor Projects - 1/11 Office of Nuclear Reactor Regulation
. Docket Nos. 50-317 -
and 50-318
Enclosure:
Safety Assessment Report cc w/ enclosure: See next page -
DISTRIBUTION:
" Docket File A.' Dromerick OGC PUBLICT S. Little -
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.PDI-1 R/F-
_ S. Bajwa T Hanis (SE only)
B. Boger '
= C. P. Tan.
C.' Hehl, Region i DOCUMENT NAME:G:\\CC12\\CCM99880.ER-To receive a copy of this' document, indicefs in the box: "C" = Copy without attachment / enclosure "E" = Copy with 4
1
! attachment / enclosure -- "N" = No copy OFFICE Mgppk1
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NUCLEAR REGULATORY COMMIS810N WASHINGTON, D.C. 30e06-0001
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January 23,1996 Mr. Charles H. Cruse Vice President - Nuclear Energy Batimore Gas and Electric Company Calvert Cliffs Nuclear Power Plant 1650 Calvert Cliffs Parkway Lusby, MD 20657-4702-
SUBJECT:
REVIEW OF CONTAINMENT TENDON EVALUATION REPORT - CALVERT CLIFFS NUCLEAR POWER PLANT, UNIT NOS.1 AND 2 (TAC NOC. M99880 AND M99881)
Dear Mr. Cruse:
The NRC staff has reviewed the enclosed Containment Tendon Evaluation Report. In
- performing the review, the staff visited tr.e Calvert Cliffs plant site and communicated with Messrs. Gary J. O'Connell and Mark A. Wright, BGE personnel involved in the subject issue.
They provided clarifications regarding some areas of the report and the staff now has a better understanding of the report, in the report, BGE, the licensee, svaluated, as a short-term action, the continucd operability of the containment on the basis of the number of broken tendon wires 40 far discovered and on the number of wires expected to be broken by applying a Weibull distribution modeled after the statistics of the steam generator tube cracking. The staff has some reservations about the appropriateness of this model. Also, as a temporary measure, the tendon wires in the vicinity where excessive corrosion has beeri discovered were re-greased. BGE has under consideration a number of options for long-term corrective action ranging from increasing the frequency of inspection to repair and replacement of the corroded tendons. The licensee indicated that it will make a decision as to which long-term action is to be taken in the first quarter of 1998, in order to assure continued containment integrity, the licensee should have a long-term action : an with clearly defined and scheduled actions in place p ior to restart from the Calvert Cliffs Ura No.1 spring 1998 refueling outage.
Sincerely, Alexdhder W. Dromerick, Senior Project Manager Project Directorate 1-1 Division of Reactor Projects - t/Il Office of Nuclear Reactor Regulation Docket Nos. 50-317 -
and 50-318
Enclosure:
Containment Tendon Evaluation Report cc w/ encl: See next page
t Mr. Charles H. Cruse C,alvert Cliffs Nuclear Power Plant Baltimore Gas & Electric Company Unit Nos.1 ar.d 2 cc:
Presider.
Mr. Joseph H. Walter, Chief Engineer Calvert County Board of Public Service Commission of Commissioners Maryland 175 Main Street Engineering Division Prince Frederid, MD 20678 6 St. Paul Centre Baltimore, MD 21202-6806 James P. Bennett, Esquire Cnunsel Kristen A. Burger, Esquire B.'timore Gas and Electric Company Maryland People's Counsel P.O. Box 1475 6 St. Paul Centre Baltimore, MD 21203 Suite 2102 Baltimore, MD 21202-1631 Jay E. Silberg, Esquire Shaw, Pittman, Potts, and Trowbridge Patricia T. Bimie, Esquire 2300 N Strcet, NW Co-Director Washington, DC 20037 Maryland Safe Energy Coalition P.O. Box 33111 Mr. Thomas N. Pritchett, Dimetor Baltimore, MD 21218 l
NRM I
Calvert Cliffs Nuclear Power Plant Mr. Loren F. Do,'atelt 1650 Calvert Cliffs Parkway NRC Technicall.aining Center Lusby, MD 20657-4702 5700 Brainerd Road Chattanooga, TN 37411-4017 Resident inspector U.S. Nuclear Regulatory Commission l
P.O. Box 287 l
St. Leonard, MD 20685 Mr. Richard I. McLean, Manager u
Nuclear Programs Power Plant Research Program Maryland Dept. of Natural Resources Tawes State CWee Building, B3 l
Annapolis, MD 21401
- Regional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 l
I ne k
- UNITED STATES g
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i NUCLEAR REGULATORY COMMISSION WAsHINeToN, D.C. SeseM001 l
I OfflCE OF NUCLEAR REACTOR REGULATION SAFETY ASSESSMENT REPORT f
CALVERT CLIFFS NUCLEAR POWER PLANT. UNIT NOS.1 AND 2 CONTAINMENT TENDON ENGINEERING EVALUATION REPORT l-
1.0 INTRODUCTION
On August 28,1997, the Baltimore Gas and Electric company (BGE), licensee of the Calvert Cliffs Nuclear Power Plant, submitted a letter rr. port informing the staff of the discovery of
- abnormal degradation of the vertical tendons during the 20th year tendon surveillance of Unit i 1
. required by Technical Specification 4.6.1.6. It was in the process of performing the inservice inspection of all vertical tendons. On October 28,1997, after completion of the inspection of all the vertical tendons, the licensee submitted the "Comainment Tendon Engineering Evaluation Report."
i According to BGE, out of 202 vertical tendons,63 were found to be severely corroded and 19 of l
these tendons have 117 broken wires. Six of these tendons were detensioned and were not retensioned for the sake of the safety of the inspection personnel due to the potential for tendon L
rupture during rotonsion:ng. As a short term measure, BGE regreased the tendon wires in the vicinity where excessive corrosion has been found to be occuning. On the basis of the number of wires which are not broken and the number of wires detensioned as compared to the number of wires required to meet the minimum required tendon force and by using a Weibull distribution to predict future wire breakage, the licensee justified the continuing operability of the containment untilit decides on a long term resolution in the first quarter of 1998. The licensee has under consideration a number of options for the long-term corrective actions. In the meantime, the licensee is in the process of inspecting all the vertical tendons in Unit 2, 2.0 EVALUATION j
In reviewing the report, the staff had a number of questions which need clarification. In order to expedite the review and to witness the tendon lift-off on Unit 2, the NRC staff visited the plant.
site. After talking to the BGE pers annel involved in the tendon inspections and the preparation of the report, the staff has a better anderstanding of the report.- The lift-off tests of the vertical tendons are basically performe.1 from the top with one exception. The liftoff forces as shown in the Appendix B Table of the rr. port are the average of the three readings taken at liftoff unless noted otherwise. The As-Fotnd and the Average are mostly the same for the tendons. The double end stressed (DES)isndons are tendons around large openings and are supposed to have li't-off tests from both rends.- In Table 1 of the report, the reason that the conditions of only 19 tendons are listed is because they are representative of the remaining 63 tendons. Six of 1
these tendons were detensoned for more thorough inspection. It was determined that there is j
abnormal degre dation of ver tical tendons and decisive action is required.
~
Therefore, any further invristigation by detensioning more tendons would not be of any use, because the 't.ontainmen*. Integrity would be put in jeopardy and for personnel safety the detensioned 10ndons in the corroded state should not be retensioned. According to the licensee,
^ the Weibull distr;5utior was used to show that the number of wires expected to be broken will be Enclosure
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within such limits as to not affect the integrity of the containment. The staff has reservations on -
the application of the Weibull distributic.7 because of the limited amount of data on tendon wire l
failure. Therefore, its role in the licensee's decision process should be minimal.
F The licensee has provided the short term as well as the long-term corrective actions. The short-term corrective action which has been implemented consists of local regressing and sealing the grease cans with silicone to slow further degradatibn and to ensure operability until the long.
term corrective actions are implerrented. The staff Ands the short-term corrective action to be acceptable.
The five~ options being considered by BGE for long-term corrective actions are summarized as follows:
- 1. Determine if an auditional examination or an increased frequency of examination is needed to assure the continued operationalintegrity of the containment.
- 2. Determine th6 feasibility of repairing the tendons by cutting off the corroded portions and rebuttoning the tendons.
- 3. Replace the affected tendons with new tendons; l
- 4. Determine if the criteria to allow tendons to be accepted "as is" can be developed.
This requires the use of equipment to detect wire breaking.
- 5. A combination of items 3 and 4.
In addition, BGE is also evaluating the replacement of the grease in all vertical tendons regardless of the option chosen.
BGE indicated its plan to complete the required evaluation and make a decision on the long-term i
resolution during the first quarter of 1998 after the completion of the inspection of the Unit 2 containment which, being of similar design to Unit 1, is expected to have'the same level of p
degradation as Unit 1.
Of the five options for the long-term corrective actions, evidently option 3 is the most reassuring.
- The prime consideration should be positive assurance of continued containment integrity, in view of the fact that the top heads of the vertical tendons can be regarded to be located in the
- " gutter" of the dome roof, there will be a continuous potential threat of water intrusion into the grease cans and contact with the tendon wires, it appears that BGE had the problem in mind in considering the replacement of all of the grease. The effectiveness of the regressing should be
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verifled by a program ofinspections.
- it is to be noted that throughout the report, there is not mention of the lower end of the vertical tendons. Therefore, inspections of the lower ends should be performed.
3.0 CONCLUSION
The staff has reviewed the report submitted by the licensee. Through a visit to the site and a meeting with the licensee's personnel involved in the inspection and in preparing the report, the
3 staff obtained pertinent clarification and has a better understanding of the problem and its prospective resolution. The licensee has indicated that a decision on the long-term resolution will be made in the first quarter of 1998, in order to assure long-term containment integrity as required by Technical Specification 3.6.1.6(b), the licensee should have a long-term plan with clearly defined and scheduled actions in place prior to the restart from Calvert Cliffs Unit No.1, in the spring 1998 refueling outa'ge. The licensee should not rely on the prediction of wire breakage through Weibull distribution based on the statistics of steam generator tube failures to make any long-term corrective action decision.
Principal Contributor: C.P. Tan Date: &nuary 23,1998