Information Notice 1986-06, Failure of Lifting Rig Attachment, While Lifting Upper Guide Structure at St. Lucie Unit 1
SSINS No.: 6835IN 86-06UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF INSPECTION AND ENFORCEMENTWASHINGTON, D.C. 20555February 3, 1986IE INFORMATION NOTICE NO. 86-06: FAILURE OF LIFTING RIG ATTACHMENT,WHILELIFTING THE UPPER GUIDE STRUCTURE ATST. LUCIE UNIT 1
Addressees
Purpose
- This notice is provided to advise licensees of a potentially significant problemthat occurred during the movement of a heavy load over the reactor core. It isexpected that recipients will review this information for applicability to theirfacilities and consider actions, if appropriate, to preclude similar problems attheir facilities. However, the suggestions contained in this notice do notconstitute NRC requirements; therefore, no specific action or written responseis required.
Description of Circumstances
- On November 6, 1985, while lifting the upper guide structure from the St.Lucie Unit 1 reactor vessel, licensee personnel noticed the lifting rig tilt.The lift was immediately stopped, with the lifting rig canted upward about 6inches and the guide structure canted downward about 6 inches at one of thethree attachment points. An attempt was promptly made to lower the'load backto its installed position, but the load cells indicated binding, so the attemptwas terminated after lowering the load a few inches. The 50-ton load was leftsuspended about 8 feet above the reactor core.The licensee declared an Unusual Event. Core alteration containment integritywas enhanced by resuming full use of the airlocks. Temporary primary manwaycovers were installed on bcth hot and cold legs to enhance the nozzle dams.Survey transits were set up and procedures implemented to monitor the rig andload for any shifts in their positions.The licensee and the nuclear steam system supplier, Combustion Engineering,designed and tested a supplementary lifting rig to support the upper guidestructure from the upper portion of the normal rig, using a cable and J-hooksystem. On November 9 with the supplementary rig installed, the load wasjacked to a level orientation and moved to its normal parking position in therefueling pool.8601290056 IN 86-06February 3, 1986 Damage caused during the incident included bending the lifting rig and one ofthe two guide pins that align the rig with the reactor vessel.Discussion:The upper guide structure is shown in Figure 1. It is supported in the reactorvessel by it§..upper flange. It is aligned by eight alignment keys, four at thetop and fourat the bottom. The structure fits down inside the core supportbarrel, just'above the fuel assemblies (see Figure 2). The fuel assemblyalignment plate is the bottom component of the upper guide structure.The lifting rig is attached to the upper guide structure by three verticallyoriented bolts. These bolts are attached from above the water line by torquetools that run down the hollow columns of the rig (see Figure 3). CombustionEngineering's procedure for attaching the rig calls for checking for threadengagement and torquing each bolt to 50 ft-lbs. The licensee's procedureomitted the step concerning the check for thread engagement. Subsequentinspection of the bolt that had pulled loose indicated that part of the lastthread was stripped. It is assumed that this bolt cross-threaded or bound dueto rig to guide structure misalignment during attachment and reached the 50ft-lb torque requirement with only part of one thread engaged. During thelift, the few inches of unengaged bolt shaft were pulled through the liftingrig until the bolt head rested on the rig's surface at the bottom of thecolumn, resulting in an imperceptible tilt. The resulting lateral load wasinitially s6pported by the guide pins. When the rig and guide structure werelifted about 8 feet, where the guide bushings on the lifting rig reached thetapered portion of the guide pins, it is surmised that sufficient lateralmotion was permitted to allow the thread of the improperly engaged bolt to slipfree. This caused the observed motion and tilt.After the guide structure was supported by the supplemental lifting rig andleveled, it was moved to its normal parking position in the refueling pool.The short attachment bolts and torque tools were then replaced with full-lengthbolts.- The long bolts are designed with heads that rest on surfaces at the topof the three hollow columns of the lifting rig. This has the advantage ofmaking anyflmck of full thread engagement more apparent to the personnelattaching the rig. The guide structure was subsequently returned to itsinstalled position using the long attachment bolts.The licensee has not yet decided whether to permanently modify the attachmentbolts. The licensee plans to review all reactor-related lifts for adequacy ofthe procedures to ensure proper lift rig attachment, including provisions formeasuring thread engagement.The potential consequences of dropping heavy loads into the open reactor vesselwere addressed by Unresolved Safety Issue (USI) A-36, "Control of Heavy LoadsNear Spent Fuel." The concern for a UGS drop is that fuel assemblies might besufficiently damaged to release the radioactive gases and iodines held withinthe fuel-clad gap. Under the reduced containment integrity requirements forthe refueling mode, damage to several fuel assemblies might cause the radiationdose limits of 10 CFR 100 to be exceede IN 86-06February 3, 1986 Plant specific calculations were not made for a UGS drop at St. Lucie becausethe NRC determined that further calculations were not required after reviewinginitial calculations previously submitted by other reactor facilities inresponse to Phase II of USI A-36. Some indication of the consequences of aUGS drop at St. Lucie can be gained from calculations performed by CombustionEngineering for a reactor vessel head drop at Waterford 3. The head dropcalculations assumed the reactor vessel head was sufficiently tilted at impactto directly strike the UGS with the UGS at rest in its normal installed posi-tion. The calculated response velocity of the Waterford UGS was 28 feet persecond, and the resulting vertical stresses imposed on the fuel were notsufficient to rupture the cladding.If the St. Lucie UGS had dropped from an 8 foot elevation, its striking velocitywould have been substantially less than the UGS response velocity calculatedfor the Waterford head drop. However, the potential for misalignment of therecesses in the bottom of the UGS (i.e., the fuel assembly alignment plate)with the fuel assembly upper end fitting posts was not addressed by the Waterfordscenario. If substantial misalignment occurred, the fuel could be subjected toadditional axial loading. Significant misalignment could not occur withoutsubstantial impact damage to the eight keys and keyways, which would alsoresult in a reduced striking velocity of the UGS as it reached the fuel. Onthis basis, significant radioactive gas release is considered to be unlikely,although it has not been shown to be impossible.No specific action or written response is required by this notice. If youhave any questions regarding this matter, please contact the RegionalAdministrator of the appropriate NRC regional office or this office.ar Jordan, DirectorDivisio of Emergency Preparednessand gineering ResponseOffice of Inspection and EnforcementTechnical Contacts: S. M. Long, IE(301) 492-7159D. E. Sells, NRR(301) 492-9735
Attachments:
1. Figure 1, Upper Guide Structure Assembly2. Figure 2, Reactor Internals Assembly3 Figure 3, Upper Guide Structure Lifting Rig4. List of Recently Issued IE Information Notices Attachment 1IN 86-06February 3, 1986EXPANSIONCOMPENSATINGRINGCEASHROUDGRIDASSEMBLY.CEA SHROUDSFUEL ASSEMBLYALIGNMENT PLATEFigure 1: Upper Guide Structure Assembly(St. Lucie Unit 1 FSAR-figure 4.2-10)
UPPER GUIDE-STRUCTURE SUPPORTPLATEAttachment 2IN 86-06February 3, 1986CEASHROUDIN-CORE-INSTRUMENTATIONGUIDE TUBEOUTLETCORE' SUPPORTBARRELFUELALIGNMENTPINSCORE-SUPPORTASSEMBLYAm. 3-7/85Figure 2: Reactor Internals Assembly(St. Lucie Unit 1 FSAR figure 4.2-7)
At ta chment3IN 86-06February 3, 1986LIFT POINT FOR CRANE HOOKCLEVIS ASSEMBLYWORKING PLATFORMI NSTRUMENTSTALK OPENING-COLUMNGUIDE BUSHING FORR.V. GUIDE PINa PLACES)-00LIFT BOLTFi gure 3:Upper Guide Structure Lifting Rig(St. Lucie Unit 1 FSAR figure 9.1-8)
Attachment 4IN 86-06February 3, 1986LIST OF RECENTLY ISSUEDIE INFORMATION NOTICEST nfn,'mnfi nNotice No. SubjectDate oTIssueT-Issud tnIssu---- --ud t86-0586-0486-0386-0286-0185-10185-10085-9985-98Main Steam Safety Valve Test 1/31/86Failures And Ring SettingAdjustmentsTransient Due To Loss Of 1/31/86Power To Integrated ControlSystem At A Pressurized WaterReactor Designed By Babcock& WilcoxPotential Deficiencies In 1/14/86Environmental QualificationOf Limitorque Motor ValveOperator WiringFailure Of Valve Operator 1/6/86Motor During EnvironmentalQualification TestingFailure Of Main Feedwater 1/6/86Check Valve Causes Loss OfFeedwater System IntegrityAnd Water-Hammer DamageApplicability of 10 CFR 21 12/31/85To Consulting Firms ProvidingTrainingRosemount Differential 12/31/85Pressure Transmitter ZeroPoint ShiftCracking In Boiling-Water- 12/31/85Reactor Mark I And Mark IIContainments Caused By FailureOf The Inerting SystemAll PWR facilitiesholding an OL orCPAll power reactorfacilities holdingan OL or CPAll power reactorfacilities holdingan OL or CPAll power reactorfacilities holdingan OL or CPAll power reactorfacilities holdingan OL or CPAll power reactorfacilities holdingan OL or CPAll power reactorfacilities holdingan OL or CPAll BWR facilitieshaving a Mark I orMark II containmentAll Westinghousedesigned PWRfacilities holdingan OL or CPMissing Jumpers From Westing- 12/26/85house Reactor ProtectionSystem Cards For The Over-Power Delta Temperature TripFunctionOL = Operating LicenseCP = Construction Permit