United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-06: Failure of Lifting Rig Attachment While Lifting the Upper Guide Structure at St Lucie Unit 1

                                                            SSINS No: 6835 
                                                            IN 86-06       

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, DC 20555

                              February 3, 1986

Information Notice No. NO 86-06:   FAILURE OF LIFTING RIG ATTACHMENT WHILE 
                                   LIFTING THE UPPER GUIDE STRUCTURE AT ST 
                                   LUCIE UNIT 1 

Addressees: 

All nuclear power facilities holding an operating license (OL) or a 
construction permit (CP) 

Purpose: 

This notice is provided to advise licensees of a potentially significant 
problem that occurred during the movement of a heavy load over the reactor 
core It is expected that recipients will review this information for 
applicability to their facilities and consider actions, if appropriate, to 
preclude similar problems at their facilities However, the suggestions 
contained in this notice do not constitute NRC requirements; therefore, no 
specific action or written response is 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 6 inches and the guide structure canted downward about 6 inches at one 
of the three attachment points An attempt was promptly made to lower the 
load back to its installed position, but the load cells indicated binding so 
the attempt was terminated after lowering the load a few inches The 50-ton 
load was left suspended about 8 feet above the reactor core 

The licensee declared an Unusual Event Core alteration containment 
integrity was enhanced by resuming full use of the airlocks Temporary 
primary manway covers were installed on both hot and cold legs to enhance 
the nozzle dams Survey transits were set up and procedures implemented to 
monitor the rig and load 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 guide 
structure from the upper portion of the normal rig, using a cable and J-hook
system On November 9 with the supplementary rig installed, the load was 
jacked to a level orientation and moved to its normal parking position in 
the refueling pool 


8601290056 


                                                           IN 86-06        
                                                           February 3, 1986 
                                                           Page 2 of 3     

Damage caused during the incident included bending the lifting rig and one 
of the 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 
reactor vessel by its upper flange It is aligned by eight alignment keys, 
four at the top and four at the bottom The structure fits down inside the 
core support barrel, just above the fuel assemblies (see Figure 2) The fuel
assembly alignment plate is the bottom component of the upper guide 
structure 

The lifting rig is attached to the upper guide structure by three vertically
oriented bolts These bolts are attached from above the water line by torque
tools that run down the hollow columns of the rig (see Figure 3) Combustion
Engineering's procedure for attaching the rig calls for checking for thread 
engagement and torquing each bolt to 50 ft-lbs The licensee's procedure 
omitted the step concerning the check for thread engagement Subsequent 
inspection of the bolt that had pulled loose indicated that part of the last
thread was stripped It is assumed that this bolt cross-threaded or bound 
due to rig to guide structure misalignment during attachment and reached the 
50 ft-lb torque requirement with only part of one thread engaged During the
lift, the few inches of unengaged bolt shaft were pulled through the lifting
rig until the bolt head rested on the rig's surface at the bottom of the 
column, resulting in an imperceptible tilt The resulting lateral load was 
initially supported by the guide pins When the rig and guide structure were
lifted about 8 feet, where the guide bushings on the lifting rig reached the
tapered portion of the guide pins, it is surmised that sufficient lateral 
motion was permitted to allow the thread of the improperly engaged bolt to 
slip free This caused the observed motion and tilt 

After the guide structure was supported by the supplemental lifting rig and 
leveled, it was moved to its normal parking position in the refueling pool 
The short attachment bolts and torque tools were then replaced with 
full-length bolts The long bolts are designed with heads that rest on 
surfaces at the top of the three hollow columns of the lifting rig This has
the advantage of making any lack of full thread engagement more apparent to 
the personnel attaching the rig The guide structure was subsequently 
returned to its installed position using the long attachment bolts 

The licensee has not yet decided whether to permanently modify the 
attachment bolts The licensee plans to review all reactor-related lifts for 
adequacy of the procedures to ensure proper lift rig attachment, including 
provisions for measuring thread engagement 

The potential consequences of dropping heavy loads into the open reactor 
vessel were addressed by Unresolved Safety Issue (USI) A-36, "Control of 
Heavy Loads Near Spent Fuel" The concern for a UGS drop is that fuel 
assemblies might be sufficiently damaged to release the radioactive gases 
and iodines held within the fuel-clad gap Under the reduced containment 
integrity requirements for the refueling mode, damage to several fuel 
assemblies might cause the radiation dose limits of 10 CFR 100 to be 
exceeded 


                                                           IN 86-06        
                                                           February 3, 1986 
                                                           Page 3 of 3     

Plant specific calculations were not made for a UGS drop at St Lucie 
because the NRC determined that further calculations were not required after
reviewing initial calculations previously submitted by other reactor 
facilities in response to Phase II of USI A-36 Some indication of the 
consequences of a UGS drop at St Lucie can be gained from calculations 
performed by Combustion Engineering for a reactor vessel head drop at 
Waterford 3 The head drop calculations assumed the reactor vessel head was 
sufficiently tilted at impact to directly strike the UGS with the UGS at 
rest in its normal installed position The calculated response velocity of 
the Waterford UGS was 28 feet per second, and the resulting vertical 
stresses imposed on the fuel were not sufficient to rupture the cladding 

If the St Lucie UGS had dropped from an 8 foot elevation, its striking 
velocity would have been substantially less than the UGS response velocity 
calculated for the Waterford head drop However, the potential for 
misalignment of the recesses in the bottom of the UGS (ie, the fuel 
assembly alignment plate) with the fuel assembly upper end fitting posts was
not addressed by the Waterford scenario If substantial misalignment 
occurred, the fuel could be subjected to additional axial loading 
Significant misalignment could not occur without substantial impact damage 
to the eight keys and keyways, which would also result in a reduced striking
velocity of the UGS as it reached the fuel On this basis, significant 
radioactive gas release is considered to be unlikely, although it has hot 
been shown to be impossible 

No specific action or written response is required by this notice If you 
have any questions regarding this matter, please contact the Regional 
Administrator of the appropriate NRC regional office or this office 


                                   Edward L Jordan Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  S M Long, IE
                    (301) 492-7159

                    D E Sells, NRR
                    (301) 492-9735

Attachments:
1   Figure 1, Upper Guide Structure Assembly
2   Figure 2, Reactor Internals Assembly
3   Figure 3, Upper Guide Structure Lifting Rig
4   List of Recently Issued IE Information Notices

Page Last Reviewed/Updated Tuesday, November 12, 2013