ML20199D958
| ML20199D958 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 01/14/1999 |
| From: | Langenbach J GENERAL PUBLIC UTILITIES CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 1920-98-20737, GL-97-01, GL-97-1, NUDOCS 9901200270 | |
| Download: ML20199D958 (4) | |
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I GPU Nuclear,Inc.
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Route 441 south NUCLEAR Post Office Box 480 Middletown, PA 17057-0480 Tel717-944 7621 January 14, 1999 I
1920-98-20737
- U. S. Nuclear Regulatory Commission i
Attn: Document Control Desk Washington, DC 20555
Dear Sir:
Subject:
Three Mile Island Nuclear Station, Unit 1 (TMI-1)
Operating License No. DPR-50 Docket No. 50-289 Generic Letter (GL) 97-01, Response to Request for Additional Information
References:
- 1. NRC Letter to GPU Nuclear, Colburn to Langenbach, " Generic Letter (GL) l 97-01, Degradation of CRDM/CEDM Nozzle and Other Vessel Closure Head Penetrations," Request for Additional Information for Three Mile Island J
Nuclear Station, Unit No.1 (TMI-1) (TAC NO. M98605)," dated August 28,1998.
- 2. Nuclear Energy Institute (NEI) Letter to NRC, Modeen to Lainas, " Responses to NRC Requests for Additional Information on Generic Letter 97-01," dated December 11,1998.
This letter is in response to the NRC's August 28,1998 request for additional information (RAI) regarding Generic Letter (GL) 97-01, Reference 1.
GPU Nuclear is a participant along with the other B&W Owners Group (B&WOG) members in the B&WOG integrated program to address the NRC's requests in GL 97-01. GPU Nuclear has not identified any deviations from the B&WOG integrated program specific to TMI-1. In responding to the NRC's RAI on GL 97-01, the B&WOG has participated with other PWR owners groups and the Alloy 600 Issues Task Group of the EPRI Materials Reliability Project to develop generic responses to the RAI questions where appropriate. The generic response, which included the response to questions I through 5 specific to TMI-1, was submitted to the NRC in a letter from the Nuclear Energy Institute (NEI) addressed to
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Mr. Gus C. Lainas of the NRC on December 11,1998 (Reference 2).
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1920,-98-20737 Page 2 of 2 If you have any questions or comments on this matter, please contact Bob Knight, TMI i
Nuclear Safety and Licensing at (717) 948-8554.
Sincerely, 14 mes W. Langerd;ch Vice President and Director, TM1 MRK Attachment cc: Administrator, NRC Region 1 TMI Senior NRC Resident Inspector I
TMI Senior NRC Project Manager File # 97056
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~ 1920-98-20737 Page 1 of 2 GPU Nuclear Response to NRC Reauest for AdditionalInformation Regardine GI 97-01 The GPU Nuclear response to the generic requests for additional information (RAl), questions 1 through 5, were provided to NRC in Reference 2, where the responses for the RAI questions applicable to the B&WOG mer er plaats were contained in Enclosure 3. The question and N
response for the remaining question specific to TMI-l is as follows:
Ouestion No. 6 Given that the IMI-1 facility experienced an extendedintrusion of thiosulfate ions into the TML-1 RCS, andsince the degradation ofAlloy 600 steam generator tubes at1MI-1 has inpart been attributed to this event, justify why the Alloy 600 CRDMpenetration no::les at IMI-1 are not i
being scheduledfor volumetric inspection in the near term.
Response
TMI-l experienced a thiosulfate intrusion into the primary system in 1981. Steam generator tubes were damaged as a result of thiosulfate induced intergranular stress assisted cracking (IGSAC) during cool-down from hot functional testing. Extensive clean-ups, including peroxide flushes, inspections, evaluations and changes to the reactor coolant system (RCS) water chemistry specifications were implemented after the intrusion. Also, the source contaminant, sodium thiosulfate in the Reactor Building Spray System, was eliminated from the plant design.
Prior to the restrt in 1985, GPU Nuclear instituted an inspection and re-qualification program to determine if sulfur conta:nin nts had caused corrosion of other RCS materials. As documented in the NRC's Safety livaluation for the TMI-l steam generator tube repair and return to i
l operation (NUREG-1019 and its references)', investigation started with the development of an Inspection and Test Plan. This plan was based on an analysis of the existing systems, l
components, and parts and their known susceptibility to corrosive attack in a solution containing l
reduced sulfur species.
The Inspection and Test Plan included a series of functional tests, non-destructive examinations and destructive metallurgical examinations, which were designed to determine the presence of corrosive attack. The results of the twenty-two inspections and tests, which involved over a L
thousand selected components, showed that there was no evidence of a problem in the l
components similar to that seen in the once-through steam generator (OTSG) tubes except for the power operated relief valve (PORV) internals. The component materials, which were determined to be the most susceptible to sulfur-induced corrosion, and which were destructively examined included Alloy 600, Alloy X-75" and Type 304 stainless steel. The destructive i
examinations revealed no evidence ofintergranular attack /intergranular stress assisted cracking (IGA /IGSAC)in any of the selected component materials. Reference 4 of NUREG-1019 specifically discussed the inspections of CRDM nozzles at TMI-1. Surface examination and t
3 NRC Letter from J. F. Stolz to H. D. Ibkill, dated December 21,1984, TMI-l License Amendment No.103, " Steam Generator Tube Repairs and Return to Operation, Three Mile island Nuclear Station, Unit 1 (TMI-1)."
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Page 2 of 2 Eddy Current Testing of CRDM nozzles showed no evidence of degradation. Based on the inspection results and metallurgical examinations, GPUN concluded that the thiosulfate intrusion had no effect on the RCS materials except for the OTSG tubes and power operated relief valve (PORV) internals. The NRC staff stated in NUREG-1019 that they had reasonable assurance that the remainder of the RCS had not been subjected to sulfur-induced corrosion and that the l
materials in the RCS were re-certified for continued safe operation.
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Mitigation of the conditions promoting reduced sulfur corrosive attack in the RCS during cold i
shutdown was also implemented at TM1-1. As documented in NUREG-1019, addition oflithium at 10 times the sulfur concentration reduces the probability of the initiation and propagation of IGSAC. TMI-l has maintained this program since the restan in 1985.
Since the 1985 restart, the Reactor Coolant System (RCS) concentrations of sulfate and total sulfur as sulfate have been monitored regularly. Sulfate concentration has been kept well below the TMI-l chemistry program limit. Thus the environment for IGSAC has been non-existent in the RCS since the 1985 restart.
Inspections of the OTSG tubing during outages subsequent to the thiosulfate intrusion (including the previous outage, the Cycle 12 Refueling Outage, where OTSG tube samples were removed and analyzed in the laboratory)2 have not shown continuing sulfur induced attack on the primary side. Also, no evidence ofdegradation has been observed to date during Inservice Inspection (ISI) and augmented ISI inspections of selected Alloy 600 components in the RCS.
In 1996 the B&WOG performed an investigation of sulfur intrusion at B&W plants as documented in B AW-2301, "B&WOG Integrated Response to Generic Letter 97-01," dated July 1997.' Included in B AW-2301 were sulfur intrusions from other sources, including thiosulfate intrusion. The BAW-2301 report concluded that the potential to have sulfur induced intergranular attack / stress corrosion cracking (IGA / SCC) of CRDM nozzles is very low.
Based on the above, GPU Nuclear concludes that there is currently no basis for scheduling l
volumetric inspections in the near term. However, GPU Nuclear will continue to monitor the j
inspection results at the other B&WOG plants and will evaluate the need for future inspections.
2 GP11 Nuclear Letter, dated May 19,1998 from J. W. Langenbach to NRC, "Results from Cycle 12 Refueling (12R) Outage Pulled Tube Examinations."
' B&W Owners Group letter :o NRC, datu luly 25,1997, Goyal to NRC Document Control Desk, "B&W Owners Group.% onse to Generic Letter 97-01."