Information Notice 2009-20, Degradation of Wire Rope Used in Fuel Handling Applications

Degradation of Wire Rope Used in Fuel Handling Applications

ML092390194
Person / Time
Issue date:	10/07/2009
From:	Brach W, Mcginty T NRC/NMSS/SFST, Division of Policy and Rulemaking
To:
David Beaulieu, 415-3243
References
IN-09-020
Download: ML092390194 (5)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS

WASHINGTON, DC 20555-0001 October 7, 2009 NRC INFORMATION NOTICE 2009-20: DEGRADATION OF WIRE ROPE USED IN FUEL

HANDLING APPLICATIONS

ADDRESSEES

All holders of operating licenses or construction permits for nuclear power reactors. All

licensees who store spent fuel under Title 10 of the Code of Federal Regulations, Part 72, Licensing Requirements for the Independent Storage of Spent Nuclear Fuel, High-Level

Radioactive Waste, and Reactor-Related Greater Than Class C Waste.

PURPOSE

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert

addressees to possible degradation mechanisms affecting wire rope that may have an adverse

impact on safe fuel handling operations. The NRC expects recipients to review the information

for applicability to their facilities and consider actions, as appropriate, to avoid similar problems.

However, suggestions contained in this information notice are not NRC requirements; therefore, no specific action or written response is required.

DESCRIPTION OF CIRCUMSTANCES

LaSalle Refueling Machine

In January 2009, during the twelfth refueling outage at the LaSalle County Station, Unit 2, Exelon Generation Company (the licensee) noted that one of the two redundant wire ropes in

the main hoist of the refueling machine had broken wire strands at the entry to a terminal end

fitting. A refueling operator had noted a sudden movement in the refueling machine while

hoisting a fuel assembly to near the full up position. The refueling staff placed the fuel assembly

in a safe location, inspected the refueling machine, and identified the damaged wire rope. The

licensee quarantined the damaged rope for analysis, replaced the two wire ropes in the main

hoist, and resumed refueling operations.

The licensee conducted an evaluation of the damaged main hoist wire rope. The main hoist

raises and lowers the fuel grapple mounted on the bottom of a telescoping mast. Two separate

wire ropes run from the hoist drum, over equalizer sheaves, and down the inside of the mast, where they terminate at the inner mast section. The two wire ropes normally share the load, but

the design of the hoist allows either wire rope to independently support a fully-loaded mast with

substantial reserve capacity. The broken wire strands occurred at one of the terminal

connections. The wire rope had a rotation-resistant construction, where the inner core strands

are twisted in the opposite direction from the outer strands. The licensee had previously noted

that the wire rope may be subject to side (bending) forces at the terminal fitting when the mast

was stowed in the full up position for maintenance. Analysis of the damaged rope section

revealed that fatigue caused the wire strands to fail. The rotation-resistant construction of the

wire rope used at LaSalle and the presence of the end fitting made inspection of the wire rope at

the damaged location particularly difficult. The licensees corrective actions included fleet-wide

inspection of wire rope in similar use and establishment of a program to replace these wire

ropes on a set frequency.

Beaver Valley Fuel Up-Ender

In October 2007, during a refueling outage at the Beaver Valley Power Station, Unit 1, First

Energy Nuclear Operating Company (the licensee) noted that a stainless steel wire rope failed

completely (all wire strands broken) on the fuel building up-ender. At the time of failure, a new

fuel assembly was in the up-ender. When the supporting wire rope failed, the up-ender pivoted

from a slightly inclined position to a fully horizontal position.

The fuel building up-ender consists of a stainless steel frame that supports one fuel assembly at

a time. The frame pivots from vertical to horizontal positions around a pin support on one end of

the frame. To raise and lower the up-ender, operators use an electric winch connected by a

wire rope through a series of three sheaves to the up-ender frame; thus, within a short distance, a section of the wire rope undergoes bending cycles in three different directions during each

movement of the up-ender.

The licensee determined that fatigue caused the wire rope to fail completely. The failure

occurred between two offsetting sheaves, when the wire rope was near its peak loading. The

licensee found the wire rope had been in service for 24 years, and the failure occurred in a

section of the wire rope that, because of interference from the sheaves, may not have received

a complete underwater visual inspection. Since the failure was limited to the wire rope, the

licensee replaced the failed rope and resumed refueling operations but did not load the new fuel

assembly into the reactor core. Other corrective actions included establishing new repetitive

preventive-maintenance tasks to perform fuel transfer equipment cable and sheave inspections

at both Beaver Valley Power Station Unit No. 1 and Unit No. 2.

Browns Ferry Reactor Building Crane

On October 4, 2007, while making preparations for dry run activities related to dry cask storage

at Browns Ferry, the Tennessee Valley Authority (the licensee) identified the degradation of one

of the main hoist cables for the overhead crane in the reactor building. The degradation

involved the partial untwisting of the wire rope strands within the stationary section of one wire

rope.

The Browns Ferry reactor building has a single-failure-proof crane with two independent wire

ropes. Each wire rope is capable of safely handling the rated 125-ton load. Each wire rope has

one end clamped to the hoist drum, unspools from the drum to the first load block sheave, passes several times between the load block sheaves and the upper sheaves attached to the

trolley, and travels from the final load block sheave to a terminal end fitting attached to the

trolley. The wire rope is stationary (i.e., neither bends around sheaves nor moves with respect to the trolley) at the end between the highest position of the load block and the terminal end

fitting. The crane was fitted with two right regular lay wire ropes. One of the wire ropes was

installed slightly untwisted to reduce the tendency of the load block to twist. The action of the

sheaves as the load block was lowered and raised concentrated the uneven twist in the

stationary section of wire rope, causing the strands to untwist in this area.

The licensee evaluated the physical condition of the wire rope, using the guidelines of the 1976 version of American Society of Mechanical Engineers Safety Standard B30.2, Overhead and

Gantry Cranes (Top Running Bridge, Single or Multiple Girder, Top Running Trolley Hoist),

which the licensee had committed to follow. Consistent with those guidelines, the licensee and

the crane vendor determined that, although the wire rope was somewhat distorted, it retained

sufficient strength to support continued operation. However, the licensee implemented an

enhanced inspection schedule to monitor the condition of the wire rope until the distorted rope

could be replaced. The licensee subsequently replaced the wire ropes.

BACKGROUND

Nuclear power plants use wire ropes in a broad range of material handling applications, including fuel handling, refueling, and dry storage. Safe conduct of these activities depends on

the retention of adequate strength in the wire rope supporting the load. A wire ropes strength

comes from the integration of several individual wire strands into a well-ordered structure.

Damage to multiple wire strands in a single location or loss of the well-ordered structure results

in a substantial reduction in strength and the potential for rope failure.

Fatigue is a common cause of wire rope damage in nuclear plant fuel handling applications.

Each time the wire rope bends and returns to a straight configuration, it undergoes a complete

bending cycle. The wire strands on the outside of the bend experience the greatest change in

stress, and this stress is concentrated at points where individual wires in the outer wire strands

pass over an inner wire strand. Repeated bending cycles lead to hardening and subsequent

brittle failure of individual wires. Thus, fatigue failure is more likely to occur in regions of the

wire rope subject to the most frequent bending (i.e., wire rope that passes around the most

sheaves) during operation.

As multiple wires fail in a single location, the load increases the stress on the remaining intact

wires. Eventually, the remaining wires may have insufficient strength to support the load, and

tensile overload may cause the last remaining wires to fail in a ductile manner.

DISCUSSION

The LaSalle licensee experienced a partial failure (broken wire strands) of one of two wire ropes

supporting the refueling mast at well below the rated load of the wire rope. The broken wire

strands occurred at a point that was subject to small-radius bending and was difficult to inspect

because it was located at an end fitting. While the redundant wire rope had no broken wire

strands, it was subject to similar operating conditions. An installed equalizer assembly provides

a means to compensate for variations in the lengths of the two ropes and maintains

substantially equal rope loading. Had similar damage existed on the second rope and the first

wire rope failed completely, the second wire rope also may have failed because of the sudden increase in its load. Failure of both of the redundant wire ropes could have resulted in a drop of

an irradiated fuel assembly and a consequential release of radioactive material. In situations

where redundant wire ropes are used and are difficult to inspect, licensees may consider

staggered replacement (i.e., replacement of individual wire ropes at widely separated times) or

early simultaneous wire rope replacement (i.e., replacement of both ropes well before wire rope

replacement criteria are satisfied) to avoid operation with both wire ropes in a severely

degraded state.

The Beaver Valley licensee experienced a complete failure of the sole wire rope used to

position the fuel up-ender, with a new fuel assembly in the up-ender. The failure occurred at a

point that was subject to repeated bending around two closely-spaced sheaves, was under

maximum load (i.e., the fuel assembly was near horizontal in the up-ender), and was difficult to

inspect because of the underwater location near the sheaves. Had the event occurred with a

brittle, irradiated fuel assembly in the up-ender, the event could also have resulted in a release

of radioactive material.

The Browns Ferry licensee experienced a distortion (untwisting) of the wire rope structure in one

of the two redundant reeving systems that support heavy loads moved on the refueling floor.

Distortion of the wire rope structure can increase the potential for failure under load because the

individual strands are less likely to share the load evenly. Proper control of the wire rope twist

during the reeving process prevents this type of rope distortion.

CONTACT

This information notice requires no specific action or written response. Please direct any

questions about this matter to the technical contact listed below or, for reactor licensing issues, to the appropriate project manager in the Office of Nuclear Reactor Regulation (NRR).

/RA by RLorson for/ /RA/

William Brach, Director Timothy J. McGinty

Division of Spent Fuel Storage Division of Policy and Rulemaking

and Transportation Office of Nuclear Reactor Regulation

Office of Nuclear Material Safety

and Safeguards

Steve Jones, NRR

301-415-2712 E-mail: Steve.Jones@nrc.gov

Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections. increase in its load. Failure of both of the redundant wire ropes could have resulted in a drop of

an irradiated fuel assembly and a consequential release of radioactive material. In situations

where redundant wire ropes are used and are difficult to inspect, licensees may consider

staggered replacement (i.e., replacement of individual wire ropes at widely separated times) or

early simultaneous wire rope replacement (i.e., replacement of both ropes well before wire rope

replacement criteria are satisfied) to avoid operation with both wire ropes in a severely

degraded state.

The Beaver Valley licensee experienced a complete failure of the sole wire rope used to

position the fuel up-ender, with a new fuel assembly in the up-ender. The failure occurred at a

point that was subject to repeated bending around two closely-spaced sheaves, was under

maximum load (i.e., the fuel assembly was near horizontal in the up-ender), and was difficult to

inspect because of the underwater location near the sheaves. Had the event occurred with a

brittle, irradiated fuel assembly in the up-ender, the event could also have resulted in a release

of radioactive material.

The Browns Ferry licensee experienced a distortion (untwisting) of the wire rope structure in one

of the two redundant reeving systems that support heavy loads moved on the refueling floor.

Distortion of the wire rope structure can increase the potential for failure under load because the

individual strands are less likely to share the load evenly. Proper control of the wire rope twist

during the reeving process prevents this type of rope distortion.

CONTACT

This information notice requires no specific action or written response. Please direct any

questions about this matter to the technical contact listed below or, for reactor licensing issues, to the appropriate project manager in the Office of Nuclear Reactor Regulation (NRR).

/RA by RLorson for/ /RA/

William Brach, Director Timothy J. McGinty

Division of Spent Fuel Storage Division of Policy and Rulemaking

and Transportation Office of Nuclear Reactor Regulation

Office of Nuclear Material Safety

and Safeguards

Steve Jones, NRR

301-415-2712 E-mail: Steve.Jones@nrc.gov

Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.

ADAMS Accession Number: ML092390194 ME0948 OFFICE SBPB:DSS TECH EDITOR BC:SBPB:DSS D:DSS PGCB:DPR

NAME SJones KAzariah-Kribbs GCasto WRuland DBeaulieu

DATE 9/16/09 via e-mail 9/8/09 via e-mail 9/18/09 9/21/09 9/21/09 OFFICE PGCB:DPR BC:PGCB D:DSFST D:DPR

NAME CHawes CMH MMurphy WBrach(RLorson for) TMcGinty

DATE 9/22/09 9/30/09 10/07/09 10/07/09 OFFICIAL RECORD COPY