ML022400842

Advisory Committee on Reactor Safeguards 491st Meeting CRDM Penetration Cracking & RPV Head Degradation Room T-2B3, 11545 Rockville Pike, Rockville, MD, 04/11/2002 - Status Report

ML022400842
Person / Time
Site:	Davis Besse, Oconee, Arkansas Nuclear
Issue date:	04/11/2002
From:	Advisory Committee on Reactor Safeguards
To:
References
BL-01-001, BL-02-001, FOIA/PA-2002-0229, IN-02-011, IN-02-013
Download: ML022400842 (3)

Text

ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 491s MEETING CRDM PENETRATION CRACKING AND RPV HEAD DEGRADATION ROOM T-2B3, 11545 ROCKVILLE PIKE ROCKVILLE, MARYLAND APRIL 11, 2002

-STATUS REPORT Purpose The purpose of this meeting is to hear summaries and discuss the results of the joint subcommittees' meeting on the CRDM penetration cracking and RPV head degradation held on April 09, 2002.

Background and Discussion Axial cracking in the vessel head penetration (VHP) nozzles was found at the Oconee Nuclear Station Unit 1 (ONS1) in November 2000 and Arkansas Nuclear One Unit 1 (ANO1) in February 2001, but was deemed to be of limited safety concern. Subsequent circumferential cracking found at the Oconee Nuclear Station Unit 3 (ONS-3) and Oconee Nuclear Station Unit 2 (ONS-2) in February 2001, raised questions regarding the safety significance and prevalence of cracking in VHP nozzles in PWRs.

NRC Bulletin 2001-01, "Circumferential Cracking of Reactor Pressure Vessel Head Penetration (VHP) Nozzles," was issued on August 3, 2001 to all holders of PWR operating licenses. The Bulletin requested that addresses provide information related to the structural integrity of the VHP nozzles for their facilities and required that all addressees provide a written response to the Bulletin.

Davis-Besse During recent UT examination of VHP nozzles required by NRC Bulletin 2001-01, Davis Besse Nuclear Power Plant found that five VHP nozzles required repair due to cracking in the nozzle adjacent to the J-welds which attach the VHP nozzles to the vessel head. On March 5, 2002, during repair on the nozzles, the licensee identified an unexpected rotation and lateral movement of one of the nozzles during the machining operation. On March 6, the licensee removed the VHP nozzle and discovered significant metal loss from the reactor vessel head, adjacent to VHP nozzle No. 3 where cracking had been identified. The eroded area of the vessel head is 4 to 5 inches across and completely penetrates the low-alloy steel to the stainless steel cladding. Some further undercutting of the low-alloy steel along the stainless steel cladding has been identified. Davis-Besse estimates that the eroded volume contains about 40 pounds of steel.

Examination of the reactor vessel head adjacent to VHP nozzle No. 2 found a smaller area of erosion. This area is up to 3/16 inch from the nozzle and about 1 Y2 inches across.

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The reactor vessel head is fabricated from low-alloy steel, approximately 6 inches thick, with an inner cladding of stainless steel, about 1/4 to 3/8 inches thick.

Information Notice 2002-11 An Information Notice was issued on March 12, 2002 to all holders of operating licenses for PWRs to inform licensees of the finding from the recent inspections and examinations of the RPV head at Davis-Besse. Licensees were asked to review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems.

Confirmatory Action Letter NRC issued a Confirmatory Action Letter to Davis-Besse on March 13, 2002 confirming that Davis-Besse would take the following actions:

1. Quarantine components or other material from the RPV head and CRDM nozzle penetrations for root cause assessment.

2. Determine the root cause of the degradation around the RPV head penetrations.

3. Evaluate the condition throughout the reactor coolant system based on the degradation that occurred on the RPV head.

4. Obtain NRC review and approval of the repair or modification and testing plans for the RPV head, prior to implementation, and prior to restart, obtain NRC review and approval of any modification and testing related to the reactor core or reactivity control systems.

5. Prior to the restart, meet with the NRC to obtain restart approval.

6. Provide NRC with a plan and schedule, within 15 days of the date of this letter, for completing and submitting their ongoing assessment of the safety significance for the RPV head degradation.

And, in accordance with Atomic Energy Act, Davis-Besse is required to:

1. Notify the NRC if their understanding differs from the above.

2. Notify the NRC if they cannot complete the actions on schedule.

3. Notify the NRC when the actions in the CAL have been completed.

NRC Bulletin 2002-01 NRC Bulletin 2002-01 was issued March 18, 2002 to all holders of operating licenses for PWRs. The Bulletin required that within 15 days from the date of the bulletin, all PWR addressees provide the following:

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1. Within 15 days

a. A summary of the RPV head inspection and maintenance programs.

b. An evaluation of the ability of inspection and maintenance programs to identify degradation.

c. A description of any conditions that could have lead to degradation and the corrective actions taken to address such conditions.

d. The plans, basis, and schedule for future inspections of the RPV head and VHP nozzles.

e. The basis for continued operation until the inspections can be performed.

2. Within 30 days The results of inspection.

3. Within 60 days A boric acid corrosion prevention program for ensuring integrity of reactor coolant pressure boundary.

Information Notice 2002-13 NRC issued another Information Notice on April 4, 2002, on recent Davis-Besse experience to alert licensees to possible indicators of reactor coolant pressure boundary degradation including degradation of the reactor pressure vessel (RPV) head material.

Licensees were asked to review the information for applicability to their facilities and consider taking appropriate actions.

Expected Committee Action This is an information briefing.

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