ML15218A272
| ML15218A272 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/09/1997 |
| From: | Birmingham J NRC (Affiliation Not Assigned) |
| To: | Foster W BABCOCK & WILCOX OPERATING PLANTS OWNERS GROUP |
| References | |
| PROJECT-693 NUDOCS 9705150242 | |
| Download: ML15218A272 (7) | |
Text
May 9, 1997 Mr. W. W. Foster, Chairman B&WOG Steering Committee P.O. Box 10935 Lynchburg, VA 24506-0935
SUBJECT:
REQUEST FOR INFORMATION RELATIVE TO THE HIGH PRESSURE INJECTION/MAKEUP LINE CRACK FOUND AT ON~Ef N.L-2-J
Dear Mr. Foster,
On April 22, 1997, plant operators at Oconee Unit-2 began a reactor shutdown because of an unidentified reactor coolant system boundary leak rate greater than 1 gallon per minute. Oconee personnel later identified the leak to be from a crack in the high pressure injection/reactor coolant makeup line (HPI/MU) at the nozzle/thermal sleeve area. On May 1 and 6, 1997, the NRC held a conference call with representatives of the Babcock and Wilcox Owners Group (B&WOG) and Framatome Technologies, Inc. to discuss the details of the crack and the potential generic safety implications for other B&W plants.
The purpose of this letter is to request information regarding the generic safety implications of the HPI/MU line crack at Oconee Unit-2 for other B&W designed plants. This letter also requests certain information regarding any completed or planned actions by the Owners Group and licensees to assess the condition of the HPI/MU lines at B&W plants and to preclude the occurrence of similar cracking at those facilities. NRC requests that the B&WOG provide a response to the attached questions by May 29, 1997.
You should address your response to the NRC Document Control Desk and reference B&WOG Project No. 693.
As part of our longer-term followup of this issue, the staff requests the results of the computational fluid dynamics analysis currently in progress, and long-term stress analysis that may be required.
If you have any questions on this matter, please contact me by phone, 301/415 2829 or by email, jlb4@nrc.gov.
Sincerely, Original Signed By:
Joseph L. Birmingham, Project Manager Generic Issues and Environmental L)
Projects Branch Office of Nuclear Reactor Regulation cc: See attached page
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Attachment:
List of Questions On HPI/MU Line Crack Project No. 693 DISTRIBULION:
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 May 9, 1997 Mr. W. W. Foster, Chairman B&WOG Steering Committee P.O. Box 10935 Lynchburg, VA 24506-0935
SUBJECT:
REQUEST FOR INFORMATION RELATIVE TO THE HIGH PRESSURE INJECTION/MAKEUP LINE CRACK FOUND AT OCONEE UNIT-2
Dear Mr. Foster:
On April 22, 1997, plant operators at Oconee Unit-2 began a reactor shutdown because of an unidentified reactor coolant system boundary leak rate greater than 1 gallon per minute. Oconee personnel later identified the leak to be from.a crack in the high pressure injection/reactor coolant makeup line (HPI/MU) at the nozzle/thermal sleeve area. On May I and 6, 1997, the NRC held conference calls with representatives of the Babcock and Wilcox Owners Group (B&WOG) and Framatome Technologies, Inc. to discuss the details of the crack and the potential generic safety implications for other B&W plants.
The purpose of this letter is to request information regarding the generic safety implications of the HPI/MU line crack at Oconee Unit-2 for other B&W designed plants. This letter also requests certain information regarding any completed or planned actions by the Owners Group and licensees to assess the condition of the HPI/MU lines at B&W plants and to preclude the occurrence of similar cracking at those facilities. NRC requests that the B&WOG provide a response to the attached questions.by May 29, 1997. You should address your response to the NRC Document Control Desk and reference B&WOG Project No. 693.
As part of our longer-term followup of this issue, the staff requests the results of the computational fluid dynamics analysis currently in progress, and long-term stress analysis that may be required.
If you have any questions on this matter, please contact me by phone, 301/415 2829 or by email, jlb4@nrc.gov.
Sincerely, Joseph L. Birmingham, Project Manager Generic Issues and Environmental Projects Branch Office of Nuclear Reactor Regulation cc: See attached page
Attachment:
List of Questions On HPI/MU Line Crack Project No. 693
May 9, 1997 REQUEST FOR INFORMATION BABCOCK and WILCOX OWNERS GROUP CRACKING IN HIGH PRESSURE INJECTION/MAKE UP (HPI/MU) LINES
- 1.
Nozzle/Thermal Sleeve Design and Confiquration
- a.
Provide a complete description of the thermal sleeves in each HPI or HPI/MU nozzle.
Include drawings as necessary. Identify installation characteristics (rolled, doubled rolled, etc.)
- b.
Identify the materials used in the fabrication of the nozzle, safe end, piping, and pipe/safe-end weld. Identify whether the nozzle, safe end, and piping are wrought or cast.
- c.
Describe any HPI or HPI/MU thermal sleeve upgrades, replacements, modifications. Indicate when changes were made and reasons for the changes. Indicate if repairs or modifications recommended by B&W Document No. 77-1140611-00 were implemented.
- d.
Provide detailed schematic or isometric drawings of the HPI and HPI/MU systems within the containment.
- e.
For each HPI nozzle and HPI/MU nozzle, provide the results of the detailed stress analysis performed pursuant to the recommendations of B&W Document No. 77-1140611-00. Identify expected usable lifetime.
- 2.
System Operation
- a.
Describe the method of operation of the HPI/MU system. Include flows, warming (bypass flow) valves.
Include periodic tests and their flows. Describe how operation comports with recommendations of B&W Document No. 77-1140611-00, including the bases for any deviation from these recommendations.
- b.
Describe cycling frequencies for HPI/MU line(s) during startup/shutdown and normal operation.
- c.
Provide cycles of inadvertent initiation of HPI.
Identify design cycles.
- d.
Discuss the differences or similarities between the event at Crystal River 3 in 1982 and that at Oconee Unit 2 in 1997 with regard to the HPI/MU nozzle degradation mechanism, and failure modes. Discuss the analysis performed at the facility in response to the Crystal River 3 event in 1982 and provide results of that analysis. Also, describe changes in operation implemented in response to the Crystal River 3 event in 1982, and changes in operation implemented in response to the Oconee 2 event.
Attachment
2
- e. Provide any thermocouple data regarding temperature profiles in the HPI and HPI/MU lines.
- f. Provide the updated "Matrix of Facts" (Table 1 of B&W Document No.
77-1140611-00).
- 3.
Inservice Inspection Program
- a. Provide a description of the inspection program established for the facility as a result of the Safe-End Task Force effort after the 1982 Crystal River 3 event. Indicate whether or not it conforms to B&W Document No. 77-1140611-00 and the bases for any deviation there from. Identify documents submitted to NRC regarding implementation of this program at the facility.
- b. Provide a history of all examinations (volumetric, surface and visual) of the HPI nozzle, safe-end and pipe/safe-end weld and adjacent piping and of the radiographic or visual examination of the thermal sleeves in each unit. Specify type, date and results.
- c. Identify the method used to perform the volumetric examination, the scope of the examination, the qualification procedure for determin ing whether cracks exist in the inspected material, and the results of the inspection. Describe any mockups that were used to qualify the UT inspection methods, including how representative the geometry and materials of the joint are represented by the mockup and the type of reflector e.g., EDM notch, fatigue crack, etc., were used.
- d. Compare the materials in the calibration block to the materials in the HPI line.
- e. Provide the bases supporting the frequency of inspection of Ultrasonic Testing, Radiographic Testing and Volumetric Testing, of the welds in each unit. Indicate if the conduct of the examinations deviated from the program/commitments described in response to 3.a, above.
.4.
Fracture Analysis
- a. Provide a fracture analysis to determine the critical flaw size required to fracture the HPI/MU piping under normal loads during either HPI injection or make-up conditions.
- b. In determining the margins-to-failure, identify all assumptions and inputs into the analysis, including stresses and material characteristics.
- c. Determine the sensitivity of the critical flaw size and margin-to failure on the existence of the complex flaw geometry, i.e., 3600 internal part through crack and through wall cracking.
3
- d. Determine the sensitivity of the critical flaw size and margin-to failure on the uncertainty in the mechanical and thermo-hydraulic loads at the pipe/safe-end weld.
- e. Based on the root cause of the cracking experienced at Oconee 2 in April 1997, provide an assessment of the time to initiate and propagate a crack through the wall of the piping at your facility.
- 5.
Other Configurations Identify other similar configurations, e.g., rolled-in thermal sleeves in areas of large coolant temperature differences, of piping existing in safety-related systems in the plant. Show that they are not susceptible to cracking from the same mechanism identified in the root cause investigation.
- 6.
Safety Implications
- a. Describe how the failure of one.or more HPI lines in a unit is analyzed, and describethe analyzed consequences.
- b. Describe the limiting single failure and what equipment is relied on to mitigate the potential accident.
- c. Review the Probabilistic Risk Assessment for each plant to assess the risk significance of this event. Provide the results of the assessment, and state the actions that would be taken to reduce the potential risk.
- 7.
Compensatory Actions
- a. Describe what actions have been taken to prepare the operators for a potential HPI pipe break for each operating unit.
- b. Describe the plant program for leakage monitoring and acceptance criteria. Indicate if any restrictions or administrative controls have been implemented in response to the Oconee 2 event.
BAW Owners Group Project No. 693 cc: Mr. J. H. Taylor, Manager Licensing Services B&W Nuclear Technologies P.O. Box 10935 Lynchburg, VA 24506-0935 Mr. R. B. Borsum B&W Nuclear Technologies Suite 525 1700 Rockville Pike Rockville, MD 20852-1631
&W Owners Group Project No. 693 cc:
Mr. J. H. Taylor, Manager Licensing Services B&W Nuclear Technologies P.O. Box 10935 Lynchburg, VA 24506-0935 Mr. R. B. Borsum B&W Nuclear Technologies Suite 525 1700 Rockville Pike Rockville, MD 20852-1631