ML20055E602

Discusses Generic Implications & Resolution of Control Element Assembly Failure at Maine Yankee

ML20055E602
Person / Time
Site:	Millstone
Issue date:	07/06/1990
From:	Stolz J Office of Nuclear Reactor Regulation
To:	Mroczka E CONNECTICUT YANKEE ATOMIC POWER CO.
References
TAC-77062, NUDOCS 9007120138
Download: ML20055E602 (7)

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-July 6, 1990 Docket No. 50-336 Mr. Edward J. Mroczka Senior Vice President Huclear Engineering and Operations Connecticut Yankee Atomic Power Company Northeast Nuclear Energy Company P. O.-Box 270 Hartford,. Connecticut 06141-0270

SUBJECT:

GENERIC IMPLICATIONS AND RESOLUTION-Of CEA FAILURE AT MAINE YANKEE (TAC HO. 77062)'

On_ June ~7,.1990, while conducting cold functional _ testing _otthe_ control element assemblies (CEAs) following the Cycle 12 refuelin Yankee,'one CEA could nct be fully inserted in the core. g outage at Maine Subsequent inspection of--the CEA revealed that the end cap was missing from the center CEA finger, the lower stainless steel spacer and boron carbide pellets had fallen out'of the center finger and an axial crack existed at the lower end.

The upper stainless steel spacer was cocked in the bottom of the CEA finger and was causing the center CEA finger to bind against the guide tube. The CEA could not be fully inserted in the core during cold functional testing due to interference from boron carbide pellets that had fallen into the center CEA

. guide tube.

On June 25, 1990, the NRC staff met with the Combustion Engineering Regulatory Response Group (CERRG) to discuss the generic implications and proposed resolution of the CEA failure that occurred at Maine Yankee.. The CERRG concluded that the CEA failure was most likely due to irradiation assisted stress corrosion cracking (IASCC). The CERRG also concluded that the failure mechanism was only applicable to the older Combustion Engineering (CE) CEA design which did not have an absorber plug (other than boron carbide pellets) at the bottom of the center CEA finger.

In order to resolve this issue, the CERRG proposed specific Action Programs for each affected licensee.

The CERRG subn.itted its report to the NRC addressing this issue by letter dated June 26, 1990.

It is our understanding that Millstone Unit 2 is currently operating with 29 CEAs which are vulnerable to the IASCC failure mechanism discussed above and that you intend to implement the Action Program which is included as Enclosure 1 to:this letter. is a request for additional information regarding your Action Program.

Within fourteen (14) days from your receipt of this letter, you are requested to provide your response to our request for additional information and to confirm our understanding that you intend to implement the request, please contact Mr. G. Vissing of my staff at (questions regarding this

}/Q CERRG Action Program for Millstone 2.

If you have any 301)492-1496.

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Mr. Edward J. Mrotzka Millstone Nuclear Power Station Northeast Nuclear Energy Company Unit No. 2 l

cc:

Gerald Garfield, Esquire R. M. Lacich, Manager Day, Berry and Howard Counselors at Law Generation Facilities Licensing City Place Northeast Utilities Service Company Post Office Box 270 Hartford, Connecticut 06103-3499 Hartford, Connecticut 06141-0270 W. D. Romberg, Vice President D. O. Nordquist Nuclear Operations Director of Quality Services Northeast Utilities Service Company Northeast Utilities Service Company Post Office Box 270 Post Office Box 270 Hartford, Connecticut 06141-0270 Hartford, Connecticut 06141-0270 Kevin McCarthy, Director Regional Administrator Radiation Control Unit Region 1 Department of Environmental Protection U. S. Nuclear Regulatory Commission State Office Building 475 Allendale Road Hartford, Connecticut 06106 King of Prussia, Pennsylvania 19406 Bradford S. Chase, Under Secretary First Selectmen Energy Division Town of Waterford Office of Policy and Management Hall of Records 80 Washington Street 200 Boston Post Road Hartford, Connecticut 06106 Waterford, Connecticut 06385 S. E. Scace, Nuclear Station Director W. J. Raymond Resident inspector Millstone Nyclear Power Station MillstoneNuclearPowerStation Northeast Nuclear Energy Company c/o U. S. Nuclear Regulatory Consnisslon Post Office Box 128 Post Office Box 811 Waterford, Connecticut 06385 Niantic, Connecticut 06357 J. S. Keenan, Nuclear Unit r' W

Millstone Unit No. 2 Charles Brinkman, Manager Northeast Nuclear Energy Company Washington t. clear Operations C-E Power Systems Post Office Box 128 Combustion Engineering, Inc.

Waterford. Connecticut 06385 12300 Twinbrook Pkwy suite 330 Rockville, Maryland 20852

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1 ENCLOSURE 2 REQUEST FOR ADDITIONAL INFORMATION RE:

MILLSTONE 2 CEA ACTION PROGRAM 1.

It is our understanding that additional evaluation and analyses are being performed relative is the Maine Yankee CEA failure.

Provide a description of the additional information being developed and what impact this infor. nation may have on your Action Program.

2.

The Action Program defines "old CEA" as one with no AG-IN-CD slug in the center finger and that has achieved high exposure. Recently, CEA degradation was identified associated with one Maine Yankee CEA with only 2732 EFPD exposure. Additionally, one Maine Yankee CEA with only 3415 EFPD exposure failed with loss of end cap and absorber material from the center finger and loss of full insertion capability, Define how many EFPD constitute "high exposure" and clarify your a.

plans and criteria for replacement of old style CEAs.

b.

Provide justification for continued operation with any of the old style CEAs beyond the next refueling outage.

c.

Provide infonnation on the availability of replacement CEAs and the procurement lead time required to replace all old style CEAs.

3.

Your Action Program indicates that only a representative number of old CEAs will be inspected.

Provide more detail on your )roposed inspection program, including a.

the number of old CEAs that lave been discharged, the number planned for inspection and the selection criteria, b.

Provide justification for not inspecting all of the discharged old style CEAs.

c.

Provide your schedule for completing this inspection. Upon completion of this inspection, submit the results to the NRC for our review.

4.

Your Action Program provides for continued operation for the balance of Cycle 10 (about 3 months) with old style CEAs that have exceeded their expected operating lifetime. The cracking of CEAs of the same design at Maine Yankee has been attributed to IASCC. The propagation rate of stress corrosion cracking is known to be a function of stress level (including residual stress), vulnerability of the specific material and operating environment. The vulnerability and propagation rate of Millstone 2 CEAs to IASCC is currently unknown, s

~2-8 Provide your assessment of the current functional capability of the 6.

old style CEAs that are installed in the core.

Include information regarding the latest ECT inspections that have been performed on the old style CEAs that are installed in the core and in the spent fuel pool. Also, include the most recent history of CEA movements and amplifying details which demonstrate the functional operability of the old style CEAs.

b.

Provide your justification for not exercising your old style CEAs inmediately to provide better assurance of safe operation for the balance of Cycle 10.

5.

In the accident analyses, the worst case CEA is assumed to be stuck in the fully withdrawn position during a postulated event. The IASCC CEA failure mechanism could result in a multiple failure rf CEAs to fully insert during the postulated event and must be considi74d, If you plan to operate with-CEAs-of-the old design after the end of cycle 10, provide a comprehensive safety evaluation of the multiple rod failure event that could )e postulated assuming that old CEAs are subject to the Maine Yankee failure mechanism.

If your evaluation cannot be completed in time to support the required response date, provide a description of your planned evaluation and your schedule for completion.

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4 Mr. E. J. Mrockza July 6, 1990 The reporting and/or recordkeeping requirements contained in this letter affect fewer than ten respondents; therefore, OMB clearance is not required under Pub. L.96-511.

Sincerely, Original signed by John F. Stolz, Director Project Directorate I-4 Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation

Enclosures:

As Stated cc w/ enclosures:

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Document Name:

TAC 77062