IR 05000327/2004012

Insp Rept 50-346/85-15 on 850327-0412 & 0530.No Violations or Deviations Noted.Major Areas Inspected:Crd Mechanism Malfunction & Damaged Internal Spring Component

ML20127F383
Person / Time
Site:	Davis Besse, Sequoyah
Issue date:	06/20/1985
From:	Danielson D, Jeffrey Jacobson NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
Shared Package
ML20127F364	List: IR 05000327/2004012 ML20127F361
References
50-346-85-15, NUDOCS 8506250140
Download: ML20127F383 (4)

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U.S. NUCLEAR REGULATORY C0tHISSION ,

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REGION III

Report No. 50-346/85015(DRS)

Docket No. 50-346 License No. NPF-3 Licensee: Toledo Edison Company Edison Plaza 300 Madison Avenue 1 Toledo, OH 43652  ;

Facility Name: Davis-Besse Nuclear Power Station, Unit 1 Inspection At: USNRC, Region III, Glen Ellyn, IL

Inspection Conducted: March 27 through April 12 and May 30, 1985 hj<8n kf+-~

Inspector:, cobson Ufle (I D~ ate cd77d&n /1% -

Approved By: D. H. Danielson, Chief 5/7C/IJ Materials and Processes Section D~a te

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Inspection Summary L

Inspection on March 27 through April 12 and May 30, 1985 (Report

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ho. 50-346/85015(DR5])_ '

Areas Inspected: ReviewofControlRodDriveMechanism(CRDM)malfunctionand

damaged internal spring component. This inspection involved a total of 20 inspector-hours in the Region III office by one NRC inspecto >

i Results: No violations or deviations were identifie l f

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DETAILS 1. Persons Contacted Toledo Edison _ Company (TECo)

J. Helle, Director, Nuclear Facility Engineering F. Hiller, Engineer Nuclear Systems & Analysis R. Peters, Manager, Nuclear Licensing T. Murray, Assistant Vice President Nuclear Operations R. Crouse, Vice President Nuclear Babcock & Wilcox (B&W)

T. Brandsberg, NPD G. Domoleski, NPD G. Hayner, LRC A. Lowe, NPD J. Raas, NPD Nuclear Regulatory Commission (NRC)

J. Harrison, Chief. Engineering firanch, DRS Region III W. Shafer, Chief, Projects Branch, DRP Region 111 I. Jackiw, Chief, Projects Section, DRP Region III P. Cortland, Metallurgist, Engineering & Generic Communications Branch, IE R. Cilimberg, Metallurgist, Vendor Program Branch, IE F. Hebdon, Chief, Program Technology Branch, AE0D All the individuals listed above participated in discussions at various times during the inspectio . Review of CRDM Malfunction and Damaged Internal Spring Component On March 16, 1985, the control rod at location E-3 would not drop into the core on demand and had to be driven downward by control room personne On March 22, 1985, control rod drop testing on core location E-3 was performed during a short maintenance outage. After the third test, the CRDM would not withdraw from the fully inserted positio The CRDM was removed and partially inspected at Davis-Bess During this inspection it was noted that the leafspring used to lock the leadscrew nut was broke Following this inspection, the CRDM was shipped to Babcock and Wilcox (B&W), Parks Township, Pennsylvania for disasserbly to identify the cause of malfunctio A study was conducted by performing detailed laboratory inspections and analysis on pertinent subassemblies. It was determined that the CRDM failed due to a pier of a setscrew which had become lodged in the rotor assembly. The se.'-- ew entered the housing from a maintenance tool used

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to handle the leadscrew during refuelings. From this, it was concluded

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l that inspection, tightening, and locking of all fasteners on the CRDM maintenance tooling prior to usage will prevent recurrence of this type of failure. The licensee has committed to review and revise as necessary the appropriate procedures, f Though apparently not involved in the E-3 CRDM malfunction, the broken Icadscrew nut locking leafspring is of particular interest. A failure of I this spring was experienced on another CRDM at Davis-Desse and was related

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to a control rod insertion malfunction on June 24, 1981.

f The spring from the 1981 failure was forwarded to the BOl Lynchburg

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Research Center (LRC? at that time for analysis. Macroscopic, scanning j electron microscopy (SEM) and electron dispersive x-ray (EDX) examination

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techniques were utilized to analyze the failure. The SEM examination revealed that the majority of the fracture surface was intergranular, i; 1.e., cracking occurred at the grain boundaries. In addition, extensive j secondary cracking on the fracture surface was observed. The fracture

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characteristics could have resulted from stress corrosion, corrosion fatigue or sensitized material combined with applied or residual stres None of those mechanisms however, could be proven from the information

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available. The EDX exanination indicated that most of the surface debris

! probably resulted from contamination after removal from the reactor.

l Elements associated with detrimental environments such as Chlorine (Cl) or l Sulfur (S) were not found. In short, the examinations and analysis at 2 that time was inconclusive as to cause of spring failur On March 28, 1985, the site NRC resident inspector visually inspected 12

open CRDM assemblics. Though all loafsprings were partially visible, it was noted that in two CRDM assemblies the spring was not properly seated in the leadscrew locking slot. On March 30, 1985, the licensee visually inspected the open ends of the 40 CRDM assemblics not previously inspecte .

! Of the 40, three additional springs were found to be improperly seated, j All five of the CRDM assemblies with improperly reated springs were removed and disassembled. One of the five springs was found to be cracked

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j and was subsequently sent to B&W LR In addition to replacing the five

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assemblies with improperly seated springs, another six leadscrew assemblies l were chosen at random, removed, inspected, and returned to their positio One additional nut and spring assembly was replaced af ter removal for dye

penetrant inspection. No cracks were found for the other springs that

were inspected, t

l 1he licensee exercised the remaining leafsprings in place to verify spring i integrity. On April 11, 1985, the NRC resident inspector observed the rod

drop time test for all trippable rods and found no abnormal indication ! The above mentioned inspections were carried out as a result of the NRC discussions with the licensee. On April 4, 1985, Region 111 in consent

, with the above, issued a Confirmatory Action Letter (CAL) outlining the

required actions before authorizing restart of the unit. In addition to the above inspection, the CAL required the following:

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Perform an analysis to determine the cause of failure of the !

leafspring including both the 1981, and 1985, Davis-Desse failures and .

a known failure at the Alliance Research Cente !

! Perfom complete chemical analysis of the failed springs to verify (

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proper material typ l Develop a basis for the restart of the unit including a safety evaluation and the results of the failure analysis.

l The NRC Region 111 Staff in conjunction with the NRC IIcadquarters Staff !

transmitted a list of metallurgical concerns to TEco to be specifically l addressed in responding to items 1 and 2 of the CA The licensee provided its formal response on April 11,1985(Serial l

No. 1-512), was found to be acceptable and in conformance with the CA The Region !!! response dated April 12, 1985, granted permission for restart of the unit. The licensee submitted the final report on i May 15, 1985 (Serial No. 1-525), which outlined a program for further l research on the cause of spring breakage. The report concludes that the .

r most probable cause of the spring failure was the mechanical interference

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between the spring and the inside of the CROM when the spring was l improperly seated; that is, not totally engaged in the leadscrew nut. It is believed that the improperly seated springs were initially installed l and left in the improper position until this condition was discovered as previously noted above, j The additional research program to further validate the above conclusion i is scheduled to be complete in December 1985. This is considered an open item pending the inspector's review of the program results (346/85015-01(DRS)).

NRC IE Headquaters metallurgist were involved in the review process i, including trips to B&W in Lynchhurg to participate in the analysis of i failed springs. Mr. Fred Hebdon, Chief, Program Technology Branch, AE00 was contacted by Region 111 to determine if an operational history of leafspring failures existea. No reports of similar failures had been identifie !

The Office of Inspection and Enforcement issued Infonnation Notice No. 85-38 dated May 21, 1985, to alert facilities of the potential for spring breakag . Exit Interview  :

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l The inspector and other NRC staff nembers riot with and conmunicated i via telephone with the licensee representatives denoted in Paragraph 1 i at various times during the period March 27 through May 30, 1985 to discuss the results of the reviews / inspections noted in this repor i The inspectors also discussed the likely informational content of the inspection report with regard to documents or processes reviewed by the l

inspector during the inspection. The licensee did not identify any such .

documents / processes as proprietary.

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