ML20155G698
| ML20155G698 | |
| Person / Time | |
|---|---|
| Issue date: | 07/13/1998 |
| From: | Stolz J NRC (Affiliation Not Assigned) |
| To: | Epstein H AFFILIATION NOT ASSIGNED |
| Shared Package | |
| ML20155G702 | List: |
| References | |
| NUDOCS 9811090155 | |
| Download: ML20155G698 (5) | |
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July 13,1998 Mr. Harold E. Epstein l
j IEN Engineering l
19 Garden Road l
Marblehead, MA 09145
SUBJECT:
REQUEST FOR A TECHNICAL REVIEW OF A DRAFT INFORMATION NOTICE REGARDING LEAKS IN THE EMERGENCY DIESEL GENERATOR LUBE OlL PlPlNG AT SEVEP.AL NUCLEAR POWER PLANTS
Dear Mr. Epstein:
l The U.S. Nuclear Regulatory Commission is planning to issue an information notice (IN) discussing leaks in the emergency diesel generator luba oil piping at several nuclear power plants. We ask that you review the enclosed draft of that IN to ensure the technicalinformation is accurate. Your cooperation in this matter is appreciated. Please return any comments you may have as soon as possible. A copy of this request and your response will be placed in the Public Document Room for review by the public. Your response should be mailed to:
U.S. Nuclear Regulatory Commission i
ATTN: Charles D. Petrone MAIL STOP: 0-12D3 Washington, D.C. 20555-0001 Please address any questions you may have on this matter to Chuck Petrone of my staff.
Mr. Petrone can be reached at 301-415-1027 or fax to 301-415-1032. If no comments are received by the close of business July 17,1998, we will assume the technical information in the notice is correct.
Sincerely, original signed by f
John F Stolz, Chief Events Assessment and Generic 9811090155 980713 Communication Branch
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PDR ORG NRRApop Division of Reactor Program Management Office of Nuclear Reactor Regulation k
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Enclosure:
Draft Information Notice DISTRIBUTION _:
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DOCUMENT NAME: G:\\CDPilENENG.LTR - OFFICIAL RECORD COPY j
TMeeive a co )y of this document, indicate in the box C= Copy w/o attachment / enclosure E= Copy with attachment / enclosure N = No copy OFFICE PECB h
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C:PECB RDennig JSb NAL CPetrone l
l DATE 7/097 C[
7 h97 7/h/97 ROUTING AND TRANSMITTAL BLIP FOR NRR/PECB 9
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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555-0001 July xx,1998 NRC INFORMAT!ON NOTICE 98-XX: LEAKS IN THE EMERGENCY DIESEL. GENER LUBE GIL PlPING Addressees All holders of operating licenses for nuclear power reactors, except those licensees who have permanently ceased operations and have certified that fuel has been permanently removed from the reactor vessel.
Purcose The U.S. Nuclear Regulatory Commission (NRC)is issuing this in6rmation notice to alert addressees to leaks in the skid mounted tube oil piping of emer0ency diesel generators (EDGs). The welds in the skid-mounted piping at some plants with Fairbanks Morse (FM)
EDGs were determined to be less than full penetration welds as indicated on the vendor's fabrication drawings. Information is also being provided about actions taken by certain licensees to ensure structuralintegrity of the lube oil piping. It is expected that recipients will review the information for applicability to their facilities and consider this information, as appropriate, in their EDG inspection programs. However, suggestions contained in this information notice are not NRC requirements; therefore, no specific action or written response is required.
Descriotion of Circumstances Several plants, including Crystal River, Millstone, and Vermont Yankee (VY), have experienced problems with degradation of welds in the lube oil and jacket cooling water piping of EDGs during normal operation. Subsequent evaluation showed significant lack of penetration and general lack of quality in the welds, believed to have occurred during manufacture. The Owners' Group for the FM EDGs is pursuing this matter and the three licensees have taken differing corrective actions. The deficiency at VY involved a degraded condition related to welds on vendor-supplied skid-mounted carbon steel piping associated with EDGs, DG-1-1 A and DG 1-18. Some of the welded joints in 'he lube oil and jacket cooling lines have less than full penetration weld configurations as indicated in the vendor's fabrication drawings. The licensee has replaced a section of the lube oil piping, and performed metallurgical examination and destructive load testing of sample welds removed from the system. Based on the examination and testing of the piping, the licensee completed an operability determination which concluded that the EDGs, although degraded, remain operable for both normal operational loads and seismic loads that would be experienced during a postulated design basis earthquake.
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L IN 98 xx July xx,1993 Page 2 of 4 In letters dated September 30,1997, and December 18,1997, the the EDGs at Millstone Unit 2. The failure mod oup re on one of vibration-induced fatigue during diesel operation. Although th o e ue to resulted in a through wall crack in a weld joint resulting in a tube oil leak The most vibration-prone piping and connecting welds have been and W with new piping that conforms to the vendor's fabrication s one At Crystal River, a majority of the skid mounted piping was replace related to the upgrading of the diesel engines.
cations Discussion The main piping systems on the EDG skid consist of tube oil, wate concern since this portion of the piping exper g.
ca cracked weld in this piping section at Millstone 2 and W. It consists o diameter coupling which fits over the 4.5-inch both ends to allow thermal growth and vibration isolation.
e s on in an effort to more clearly understand tile origin mounted piping and the condition of welds en this piping. The original ED s or the skid specifications required the vendor to deliver a seismically qualified pack its intended safety function during a seismic event. specific re A walkdown and visual examination of the potentially affected skid mo welds, it appeared that the welds were most like bead with two additional passes over the single pass resulting in a double cro the skid mounted piping did not exist within the E intentionally deleted in the specifications because FM took exception to utilized their Intemal procedures / processes for the fabrication of the pipin these intemal procedures / processes were equivalent to commercial s industry practice and were deemed acceptable based on many years of operation of their equipment.
and the oil filter was the most highly stressed and vibration. This section of piping was chosen for stress analysis and was consi bounding sample of all skid-mounted piping configurations. In addition, tht this section of piping at W experienced a leak on a welded joint in 199 plant records, the as found condition was a slag inclusion of approximately 3 GIMT
i-IN 98-xx July xx,1998 p
,, g.9 Page 3 of 4 face of this weld with several are strikes. The corrective action for this leak at that time remove the arc strikes, grind the weld and remove visible defects, reweld the piping joint using j
1 approved procedures and conduct a post weld liquid penetrant examination on this and other j
welds on this section of the piping. This section of piping was replaced in late 1997. The balance of the skid mounted piping was determined by the licensee to be degraded but operable.
A major aspect of the basis for continued operation was an analysis performed by the licensee to demonstrate the structuralintegrity of the skid-mounted piping under normal operation and during a seismic event. As stated earlier, the section of the piping between the lube oil pump discharge and the filter was determined to be the most highly stressed and hence it was the
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primary focus of this analysis. Other vulnerable sections of the skid-mounted piping were also analyzed.
A vibration-induced failure mode characterized by fatigue was considered the most likely potential failure mode by the licensee. Such a failure would occur over a long period of time due to propagation of an existing flaw during engine operation resulting in a through wall crack with subsequent leakage. This, in the licensee's view, is not characterized as an abrupt or catastrophic failure. According to the licensee, given the successful operational history of W's diesels, as well as those at other FM supplied units, it is unlikely that imminent failure resulting in complete severance in the remainder of the skid-mounted piping will occur in addition, the licensee argues that, should failure occur, it would likely be characterized as a leak which would be detectable through alarm functions or operator surveillance. With the backup diesel as well as the ovailable W tie line, a safe plant shutdown could be accomplished.
The licensee has also performed load tests on the removed section of the piping from the W EDG which was replaced. Three welds on lube oil pump discharge piping were selected for testing. Both axial and bending loads were applied. The results of the load tests demonstrated that the as-installed welds will withstand loads greater than those which cause stress in the piping to exceed the yield strength of the piping material. Also, the tests demonstrate that these weld geometries have significant strength with respect to the design loads and the B31.1 Power Piping Code allowable stresses, in addition to the leaks in skid mounted piping at Millstone, Crystal River and W, similar leaks have been reported earlier in EDG piping at other plants involving other vendors. An evaluation report (Report No. AEOD/E612, dated 12 December 1986) prepared by the Office of Analysis and Evaluation of Operational Data (AEOD), NRC, related to an oilleak at Zion Unit 2 in 1985 identified similar events at Turkey Point 3, Grand Gulf 1, Duane Amold, Farley 2, g
San Onofre 1, Cooper and Browns Ferry 1. The failed lines were used in the lobe oil, fuel oil and coolant water systems of EDGs The piping failures were caused by vibration fatiguo cracks that resulted from engine induced vibration. In four of the events identified, the cracked lines were made of either copper or brass material, which are considered to be vulnerable to vibrationalloads, in each case, the licensee replaced the piping with carbon steel components.
The AEOD study found that the vibration induced from engine operation produce complex and interacting vibration modes that can affect all components connected to the engine. Lube, fuel and water lines are often subject to relatively high amplitude pulsating loads that may cause
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M[M[ Q IN 98 xx i
July xx,1998 Page 4 of 4 rapid degradation. The pulsating loads aic ery difficult to define at the piping system design stage. Although the loading conditions for this type of vibration have not been generally analyzed in the original piping design, contingency factors for vibration loads have been considered in various design procedures. Section lll of the ASME design code requires that an evaluation for fatigue be made for Class 1 components, but not for Class 2 and 3 components.
It appears that the preoperational and startup tests under the provisions of Section XI, " Test l
Control" of the 10 CFR 50, Appendix B," Quality Assurance Criteria of Nuclear Power Plants,"
l and vibration testing under the dynamic testing requirements of SRP Section 3.9.2 have not,in severalinstances, identified potentially vulnerable locations on the EDGs' skid-mounted piping systems. Regulatory Guide 1.68 and ASME Standard OM-3 " Requirements for Preoperational and initial Start up Vibration Testing of Nuclear Power Plant Piping Systems' provide guidance and acceptance criteria for implementing the above stated requirements.
FM diesel engines in approximately fourteen plants my be affected as a result of inadequate Weld penetration on the skid-mounted piping. Thera are approximately two hundred welds on the skid mounted piping of typical FM diesel engines. Several plants may have already replaced most of the vibration-prone sections of the piping and the vendor has conducted, in some cases, additional metallurgical examinations and tests on the removed piping sections from these plants. This data, however, has not been made available for staff review.
This information notice requires no specific action or written response. If you have any questions about the information in this notice, please contact the technical contacts listed below or the appropriate Office of Nuclear Regulatory Regulation (NRR) Project Manager.
Jack W. Roe, Acting Director Division of Reactor Project Management Office of Nuclear Reactor Regulation Technical contacts:
Jai R. Rajan, NRR 301-415-2788 E-mail jrr@nrc. gov William H. Koo, NRR 301-415-2706 E-mail: whk@nrc. gov Charles D. Petrone, NRR 301-415-1027 E-mail: cdp @nrc. gov
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