ML18059A680
| ML18059A680 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 02/11/1994 |
| From: | Rogers D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEIN-92-082, IEIN-92-82, NUDOCS 9402240393 | |
| Download: ML18059A680 (5) | |
Text
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1 Palisades Nuclear Plant:
27780 Blue Star Memorial Highway, Covert, Ml 49043 February 11, 1994 Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 David w. Rogers Plant Safety and Licensing Director DOCKET 50-255 - LICENSE DPR PALISADES PLANT - NRC INFORMATION NOTICE 93 PROPOSED REVISED INFORMATION NRC Information Notice (IN) 93-82, "Recent Fuel and Core Performance Problems in Operating Plants," contains information with respect to the Palisades failed fuel event that does not conform with the facts as determined by our investigation and as reported in our August 16, 1993 (Attachment, Reference 1) and our September 30, 1993 (Attachment, Reference 2) submittals.
We understand that IN 93-82 is being revised based on some corrections or clarifications being supplied by Westinghouse, General Electric, and the Perry Plant. Therefore, we are submitting the following corrections and clarifications in order that they also can be included in the revised IN 93-82.
The following are proposed changes and discussion supporting their implementation.
The proposed changes are being submitted to assure that a common understanding of the facts exists between CPCo and the NRC.
If the staff does not agree that our proposed changes are valid, please notify us so further discussion can be initiated to ensure the existence of a mutual understanding of the facts in regard to the Fuel Assembly 1-024 failed rod event.
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David W Rogers Plant Safety and Licensing Director CC Administrator, Region III, USNRC NRC Resident Inspector - Palisades Attachment 181.154 I
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ATTACHMENT Consumers Power Company Palisades Plant Docket 50-255 Proposed Revisions to IN 93-82 February 10, 1994 3 Pages
Attachment Proposed Revisions to NRC Information Notice (IN) 93-82 A.
IN 93-82 Page 2, Paragraph 3 States:
"Inspection of (the defective) fuel assembly and others from the batch of 16 fuel assemblies revealed that the spacer springs had relaxed and there was up to 90 percent through-wall fretting wear at mid-grid locations, predominately on the corner rods of affected assemblies."
Discussion:
1 Stating that spacer springs had relaxed is technically correct, however, it is misleading to so state without also stating that the relaxation which took place was both expected and within design limits (Reference 1).
The statement that up to 90 percent through-wall fretting existed is generally incorrect. The failed fuel rod had 100 percent through-wall fretting; however, none of the other fuel rods showed more than 44 percent through-wall fretting.
Suggested Changes:
Delete the reference to spacer spring relaxation and change through-wall fretting value to 44 percent so the sentence reads:
"Inspection of this fuel assembly and others from the batch of 16 fuel assemblies revealed that there was up to 44 percent through-wall fretting wear at mid-grid locations, predominately on the corner rods of affected assemblies."
B.
IN 93-82 Page 2, Paragraph 3 States:
"Although the typical exposure for these fuel assemblies was only 80 percent of the design life, they had been subjected to the reactor environment and fast flux exposure during five cycles of operation.
Tests by SNP confirmed that the lengthy service life was a contributing cause to spring relaxation."
Discussion No tests were done by Siemens Power Corporation (SPC) to confirm that the lengthy service life was a contributing cause to the spring relaxation.
Consumers Power is considering the lengthy service life to be a potential contributing factor leading to the failed rod event.
Until the root cause is better understood, Consumers Power is conservatively limiting the number of fuel cycles that a fuel assembly of the bi-metallic spacer design will be used to four (Reference 2).
The basis of the limit lies more with the reactor environment in general, since the fast flux exposure will be always verified to be within the bounds of the design.
Suggested Changes:
Delete reference to tests done by SPC.
Delete reference to fast flux exposure, since this was determined not to be an issue by itself. The new wording could be:
"Although the typical exposure for these fuel assemblies was only 80 percent of the design life, they had been subjected to the reactor environment during five cycles of operation.
Consumers Power is considering the lengthy service life to be a potential contributing factor leading to the failed rod event. Until the root cause is better understood, Consumers Power is conservatively limiting the number of fuel cycles that a similarly designed fuel assembly can be used to four cycles."
2
3 C.
IN 93-82 Page 2, Paragraph 4 States:
"Flow mixing spacers in neighboring fuel assembly locations and the low power of the peripheral fuel assemblies adjacent to the core baffle produced a hydraulic mismatch that caused cross flow into the peripheral fuel assemblies."
Discussion:
At the time of the Augmented Inspection Team exit, issues of cross flow were still being addressed by CPCo and SPC (Reference 3). The subsequent work by CPCo and SPC evaluated core cross flow as not being the root cause.
The follow up by NRR stated that the qualitative evaluation performed to address this issue was adequate.
Consumers Power is considering the area of cross flow to be one in which further improvements should be made, especially considering the recent industry experience with fuel failures at the core periphery and associated root cause discussions.
At this time, Consumers Power does not have any data to suggest cross flow, particularly from adjacent assemblies, is a root cause or a key contributing factor for the 1-024 failed rod event.
Suggested Changes:
Suggest the Page 2, Paragraph 4 sentence referred to above be deleted, or be rewritten to reflect that this is a possible theory by insertion of the words "may have" so it reads:
"Flow mixing spacers in neighboring fuel assembly locations and the low power of the peripheral fuel assemblies adjacent to the core baffle may have produced a hydraulic mismatch that caused cross flow into the peripheral fuel assemblies."
References:
- 1.
CPCo letter, dated August 16, 1993, from Gerald B. Slade to NRC, "Docket 50-255 License DPR 20 - Palisades Plant - Reply to Request for Additional Information Regarding Recent Fuel Failure Event"
- 2.
CPCo letter, dated September 30, 1993, from Gerald B. Slade to NRC, "Docket 50-255 License DPR 20 - Palisades Plant - Root Cause, Corrective Actions and Independent Assessment Regarding Damage to Fuel Assembly 1-024 and Inadvertent Lifting of fuel Assembly SAN-08
- Fuel Accountability and Failure Detection"
- 3.
NRC letter, dated August 31, 1993, from William L. Forney to CPCo Gerald B. Slade, "NRC Region III Augmented Inspection Team (AIT)
Review of the July 1 and July 6, 1993, Palisades Fuel Handling Events"