ML20217G733

Insp Rept 70-7001/97-10 on 970919-980216.No Violations Noted.Major Areas Inspected:Operational Controls,Maint Programs,Engineering Design,Event Root Cause Evaluation & Classification & Reporting of Event

ML20217G733
Person / Time
Site:	07007001
Issue date:	03/27/1998
From:	Hiland P NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
Shared Package
ML20217G714	List: ML20217G712 ML20217G733
References
70-7001-97-10, NUDOCS 9804020503
Download: ML20217G733 (16)

Text

i U.S. NUCLEAR REGULATORY COMMISSION REGION lli Docket No: 70-7001 Report No: 70-7001/97010(DNMS)

Facility Operator: United States Enrichment Corporation Facility Name: Paducah Gaseous Diffusion Plant Location: 5600 Hobbs Road P.O. Box 1410 Paducah, KY 42001 Dates: September 19,1997 through February 16,1998 inspectors: K. G. O'Brien, Senior Resident inspector C. A. Blanchard, Fuel Cycle Inspector R. B. Landsman, Senior Decommissioning inspector Approved By: Patrick L. Hiland, Chief Fuel Cycle Branch Division of Nuclear Materials Safety 9804020503 990327 PDR ADOCK 07007001 C PDR l

EXECUTIVE

SUMMARY

United States _ Enrichment Corporation Paducah Gaseous Diffusion Plant NRC Special Inspection Report 70-7001/97010(DNMS)

On September 18,1997, during the routine transfer of empty 10-ton uranium hexafluoride cylinders from railroad cars to a staging area, the vertical shaft of a cylinder hauler grappler-catastrophically failed, allowing an empty cylinder to drop two feet to the concrete staging area. I The empty cylinder was not breached, no releases of uranium hexafluoride occurred, and no 1 personnel were injured. The cylir.ders were used to transport enriched uranium hexafluoride between the Paducah and Portsmouth Gaseous Diffusion Plants and normally contain a small amount, less than 50 pounds, of uranium bearing material when empty. As an immediate response to the dropped cylinder, management evacuated personnel from the immediate area of the cylinder and initiated an investigation of the event.

The NRC conducted a special inspection of the event and related issues. Overall, the

' inspection results indicated that non-rigorous initial engineering of the cylinder hauler design and inadequate corrective actions for a previous cylinder hauler failure significantly contributed to the current event. . In addition, a generic weakness was identified related to the identification and implementation of training for nonsafety-related activities.

Focus areas for the inspection included operational controls, maintenance programs, engineering design, event root cause evaluation, and classification and reporting of the event.

Significant findings in the focus areas were as follows.

- Operational supervision for cylinder movements was not always cognizant of the requirements for performing some cylinder movement activities. As a result, some cylinder movements were made using improper techniques or using equipment not properly designed for the task.

- Inadequate classroom and incomplete on-the-job training, combined with weak training staff knowledge, contributed to weak' management oversight of routine mobile crane and cylinder hauler operations.

- The current preventive maintenance program for the cylinder haulers was noted to be adequate. However, only limited vendor guidance was available to direct proventive maintenance on the grappler.

- Appropriate actions were taken to ensure that the generic aspects of mobile crane and cylinder hauler component failures were properly addressed. However, the certificatee {

was not proactive in identifying changes to the cylinder haulers, made by the vendors to correct generic design or performance problems.

- The quality inspection program for the mobile cranes and cylinder haulers was j inconsistent and included several weaknesses. The weaknesses involved a lack of 1 detailed guidance to ensure consistent inspections and a lack of engineering involvement in the specification of requirements for inspections following modification l activities.

Modification of the grappler, to include additional rotational and tilt stops, was performed without an engineering evaluation of the modifications. The modifications appeared to 2

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s significantly reduce the time to failure of the Paducah Allied Wagner NCH-20 cylinder hauler.

- A lack of rigorous engineering evaluation of the initial and modified cylinder hauler designs significantly contributed to the grappler shaft failures. The lack of an adequate .

engineering evaluation of the design was due, in part, to the absence of a program or plant policy by which to control the design and use of nonsafety-related equipment.

- Design weaknesses, similar to those that contributed to the Allied Wagner NCH-20 grappler shaft failure, were observed involving other cylinder haulers, i.e., the ATP cylinder hauler grappler had visible structural weld cracks.

- The plant staff failed, in 1995, to aggressively pursue a documented root cause evaluation of the cylinder hauler grappler shaft failure, which occurred after only a few hundred hours of operation. The 1997 cylinder hauler grappler shaft failure occurred, in part, due to the previous inadequate assessment of the 1995 failure.

- The plant staff and management's immediate response to and evaluation of the event for classification and reporting was appropriate and consistent with the site emergency response plan and current reporting requirements.

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Report Details 1.0 - Purpose of SpecialInspection Following initial review of a September 18,1997, drop of an empty 10-ton cylinder used to transport enriched uranium hexafluoride, the NRC conducted a special inspection to examine the circumstances surrounding the event. The special inspectum charter included evaluations of the mobile crane (cylinder hauler) design, modification control, plant staff performance, the effectiveness of the certificatee's root cause investigation, and the effectiveness of the corrective actions. The special inspection charter is included as Attachment 1 to this report.

2.0 Event Description On September 18,1997, at approximately 8:45 a.m. (CST), plant staff were removing empty 10-ton cylinders, used to transport enriched uranium hexafluoride between the Paducah and Portsmouth Gaseous Diffusion Plants, from railroad cars. The equipment used to remove the cylinders from the railroad cars and place them on a concrete pad

' for temporary storage was an Allied Wagner NCH-20 cylinder hauler. During removal of

' the third empty cylinder from the railroad cars, the grappler catastrophically failed at the vertical shaft connecting the grappler to the cylinder hauler boom. The failure resulted in the cylinder and grappler dropping approximately 2 feet to the ground. The dropped cylinder contained a small quantity of uranium bearing material; however, the cylinder was not breached.

3.0 Operational Controls [ Charter item No.1)

The inspectors reviewed the operational controls implemented for the movement of cylinders containing uranium hexafluoride including management oversight, operating ,

procedures, and operator training. 1 3.1 Managament overnight On September 18,1997, management oversight of cylinder movement activities was provided by the supervisor for the mobile crane operations. The supervisor was at the 1 work location and generally observed the cylinder movements and actions of the cylinder hauler operator. Following the event, the inspectors interviewed the supervisor and determined that the supervisor had not identified any problems with the cylinder transfers completed immediately prior to the event. The supervisor indicated that the operator's activities, on the day of the event, were typical and were consistent with management expectations.

During discussions with the supervisor, the inspectors determined that the supervisor was generally familiar with the mobile cranes and the cylinder haulers, but was not a qualified operator for the cylinder hauler involved in the event. In addition, the supervisor was not aware that several of the operator's actions on the day of the event were inconsistent with current vendor guidance for operation of the cylinder hauler.

' Some of the inconsistent actions included cylinder hauler travel with an elevated and extended load, and lifting loads in excess of the limits delineated on a load chart posted in the cylinder hauler operator cab. The supervisor believed that the cylinder hauler, involved in the event and routinely used for the movement of empty cylinders, was appropriate for the task and had been properly designed for all routine cylinder hauler 4

activities. The supervisor indicated that site engineering staff specifically designed the Allied Wagner NCH-20 cylinder hauler for the movement of empty cylinders.

The inspectors noted that during the special inspection, management identified another example of a fork-lift improperly being utilized to move used, empty cylinders.

Specifically, the weight of the cylinders being moved by the fork-lift was greater than the fork-lift load limit. Management and staff indicated that the fork-lift had been used to perform the involved activities for some time, without assurance that the equipment was properly sized and matched to the work effort.

Conclusions The inspectors determined that supervision was not always cognizant of the requirements for performing some work activities associated with the movement of cylinders used to contain uranium hexafluoride. As a result, some cylinder movements were made using improper techniques or using equipment not properly designed for the task. Because safety-related activities were not involved, the findings do not represent a violation of NRC requirements.

3.2 Operating Procedures The inspectors discussed with the mobile crane supervisor the operating procedures used to guide and control mobile crane and cylinder hauler activities involving the movement of cylinders. The supervisor indicated that a system of classroom and on-the-job training were the primary methods used to guide mobile crane and cylinder hauler activities. As a result, very few operations-related procedures existed relative to {

the mobile crane and cylinder hauler operations. This approach to mobile crane and I cylinder hauler operations was consistent with generalindustry practices and guidance included in applicable national standards.

The inspectors noted that the operational procedures, that did exist, were primarily those provided in the vendor manuals and those developed by the plant staff to conduct -

daily pre-startup checks of the mobile crane and cylinder haulers. The inspectors l reviewed the vendor manuals associated with the cylinder hauler involved in the event and determined that the manuals provided information regarding the cab controls but did not discuss operations associated with the grappler, in addition, the manuals did not include information on the load chart, located in the operator's cab, or information relative to cylinder hauler movement with a suspended load. Finally, the inspectors noted that the vendor manuals were not controlled or maintained current.

Conclusions The inspectors determined that management did not rely upon operations-related procedures to direct cylinder hauler activities. Instead, a combination of classroom and on-the-job training was used to ensure operators were knowledgeable of the applicable operations requirements and management expectations. The inspectors noted that this l approach was consistent with general industry standards. l 3.3 Iranng The inspectors interviewed the operators involved in the cylinder drop event on September 18,1997, and reviewed the classroom and on-the-job training program and l l

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t materials used to instruct operators authorized to operate the mobile cranes and cylinder haulers. Based upon the interviews, the inspectors concluded that the operators were not aware of some fundamental aspects of mobile crane and cylinder hauler operations. Specifically, the operators were not cognizant of: 1) boom angle and length limitations applicable during mobile crane and cylinder hauler movement with a suspended load; 2) lifting limitations that were a function of both boom angle and length, and; 3) grappler orientation requirements during both lifting and transporting loads. The inspectors noted that some of these limitations were indicated on a load chart posted in the Allied Wagner NCH-20 cylinder hauler operator cab. The limitations were not posted in the Allied Wagner NCH-35 mobile crane operator cab. At the time of the event, the cylinder hauler boom was positioned at an angle and extension beyond the vendor specified limits, as indicated on the load chart.

The inspectors reviewed the training program used by management to ensure that operators and supervisors were knowledgeable of the mobile crane and cylinder hau!er operational controls and safety features. The inspectors also discussed the event with the training staff. Although the training department library included many training modules applicable to stationary and mobile crane operations, the inspectors determined that none of the modules applied to the Allied Wagner NCH-20 cylinder hauler used to move the empty cylinders. In addition, the training staff were not aware that operation of the Allied Wagner NCH-20 cylinder hauler was not covered by either a classroom or on-the-job training module. The training staff believed that the cylinder hauler was similar to and therefore covered by a module associated with a much larger mobile crane, the Allied-Wager NCH-35. The Allied Wagner NCH-35 mobile crane was sold by the same manufacturer. The inspectors also determined that the training staff were not aware that mobile crane and cylinder hauler load lifts were controlled using load charts which specified load limits based upon both boom extension and angle.

Finally, during discussions with the mobile crane and cylinder hauler operators, supervisors, and the training staff, the inspectors determined that the training ,

management had identified inadequacies with some of the operators' training records during the week prior to the event. In response to the finding, management had scheduled the operators to attend classes to complete the previously missed training; however, none of the operators' authorization to operate the mobile cranes or cylinder ,

haulers was suspended. The inspectors reviewed the missed training and determined l that the training did not contain information directly related to the causes for the event.

3.4 Conclusions inadequate training staff knowledge and incomplete classroom and on-the-job training contributed to weak operator knowledge and management oversight of routine mobile crane and cylinder hauler operations. However, the training program weaknesses did not appear to directly cause the failure that occurred on September 18,1997.

4.0 Maintenance Programs [ Charter item No. 2)

The inspectors evaluated the adequacy and implementation of the maintenance program for the cylinder haulers, including the preventive maintenance, lessons learned, )

and quality inspection programs.

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i Preventairve Maintenance

- 4.1 The inspectors reviewed the cylinder hauler preventive maintenance (PM) program and

~ determined that the current PM inspection frequency was consistent with the vendor's PM guidelines. The inspectors noted that the certificatee had increased the frequency of PM activities, from yearly to quarterly, approximately a year ago, in order to make the program consistent with the vendor's recommendations.

The inspectors discussed the activities performed during routine PM with the maintenance garage manager. The manager indicated that cylinder hauler preventive maintenance was based on the vendor manual guidance, with some limited input from the reliability engineering group. Through a review of the vendor manuals for the Allied Wagner NCH-20 cylinder hauler, the inspectors determined that the manuals did not include preventive maintenance guidance for the grappler. The vendor field representative, sent to the plant following the failure, indicated that the Allied Wagner NCH-20 chassis was used as a base for several applications using different

. attachments, including the grappler. Therefore, the vendor manuals addressed only the Allied Wagner NCH-20 chassis and not the grappler.

The inspectors also reviewed the preventive maintenance activities for the Allied Wagner NCH-35 mobile crane and determined that adequate vendor guidance was available and was being followed. The inspectors attributed the differences in vendor manuals between the two cylinder haulers to the vendor's building of the Allied Wagner NCH-20 as a multi-use system versus sole use designation for the Allied Wagner NCH-35.

The inspectors reviewed various PM records for the cylinder haulers and noted that many of the records were incomplete and vague. Some PM records were also missing.

The amount of detail, describing the PM activities performed during routine and daily inspections, was limited. In addition, the inspectors noted that the PM records did not include or document any additional activities performed after the first Allied Wagner NCH-20 grappler head assembly shaft failure in January 1995.

I Following the cylinder drop on September 18,1997, the inspectors observed the j grappler shaft and housing. The inspectors noted that ample amounts of lubricant were present at the time of the shaft failure which indicated that current lubrication efforts were adequate.

Conci" alans The inspectors determined that the current preventive maintenance program for the cylinder haulers appeared adequate. However, only limited vendor guidance was available to direct preventive maintenance for the grappler. In addition, documentation of preventive maintenance activities, including changes made in response to equipment failures, was weak.

4.2 I a==nns I anmed Pronram The inspectors reviewed past maintenance activities to determine if previously identified failures for a specific cylinder hauler had been evaluated for the other cylinder haulers.

Through discussions and a review of the Allied Wagner NCH-35 mobile cranes' maintenance records, the inspectors determined that Allied Wagner NCH-35 mobile 7

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cranes had, in the past, experienced two different component failures. The component failures involved a transmission declutch switch and the telescoping boom wear pads.

The first failure resulted in the cylinder hauler striking a telephone pole during routine cylinder movement activities. The second failure was manifested through boom sticking, during telescoping activities. Following each of the failures, the certificatee took proper action to apply the lessons leamed from one cylinder hauler to the other onsite cylinder haulers.

During further discussion of the failures with maintenance staff, the inspectors were informed that for each of the component failures, the vendor had previously identified the problems and implemented generic corrective actions. However, the certificatee did not appear to be proactive in identifying changes to the cylinder haulers made by the vendor to correct generic design or performance problems.

Following the September 18,1997, cylinder drop event, the inspectors noted that plant operations and maintenance staff communicated the particulars of the event to their counterparts at the Portsmouth Gaseous Diffusion Plant. Timely discussions between the two plants resulted in the Portsmouth plant taking similar actions to identify and correct potential problems with the routine use of cylinder haulers.

Conclusions The inspectors concluded that the certificatee took appropriate actions to ensure the generic aspects of component failures were properly addressed for similar onsite equipment. However, the certificatee did not appear to be proactive in identifying changes to the cylinder haulers made by the vendors to correct generic design or performance problems.

4.3 Quality inspection Proaram The inspectors reviewed various phases of the quality inspection program for the cylinder haulers. Through a review of procedures and discussions with quality inspection staff, the inspectors determined that, for quality inspection purposes, some cylinder haulers were classified as fork-lifts, while others were classified as mobile l' cranes. The Allied Wagner NCH-20, the cylinder hauler involved in the event, was classified and inspected as a fork-lift. The Allied Wagner NCH-35 mobile cranes, the cylinder haulers used primarily to move full cylinders of uranium hexafluoride, were classified as mobile cranes.

During discussions with quality inspection (Ql) staff, the inspectors were informed that the Allied Wagner NCH-20 cylinder hauler was last inspected just before the January 1995 grappler shaft failure. The QI staff indicated that changes in the inspection l program for fork-lifts, implemented in 1996, effectively ended routine inspections of the l cylinder haulers classified as fork-lifts. The QI staff further explained that current j inspection practices would not have identified a failing grappler shaft.

The Ql manager indicated that the Allied Wagner NCH-35 mobile cranes were inspected and tested in accordance with plant Procedure CP4-TO-Ol1087, " Inspection and Testing of Mobile Cranes." The inspectors noted that the procedure provided checklists for the i performance of periodic and interim inspections. However, the checklists included only )

limited inspection guidance. For example, the inspection guidance for structural defects was limited to an instruction to check for cracks, severe nicks or gouges. The procedure i

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l did not specify critical structural locations requiring inspection or how to characterize i identified structural defects.

During a review of past quality inspection reports for the Allied Wagner NCH-35 mobile cranes, the inspectors determined that load tests, required by plant procedures and national standards for mobile cranes, had not been performed following recent j modifications to the Allied Wagner NCH-35 mobile crane booms. The certificatee also I identified that the initial load tests, performed at the factory by the vendor, were not in j accordance with the equipment purchase engineering specifications. As a result of these load testing inadequacies, the certificatee declared the equipment inoperable and performed load tests on the two Allied Wagner NCH-35 mobile cranes. One of the Allied Wagner NCH-35 mobile cranes failed the load test, in part, due to an incorrect hydraulic system relief valve setting. The setting was last adjusted by the vendor at the factory. Following adjustment of the relief valve setting, the Allied Wagner NCH-35 mobile cranes both passed the required load tests.

The irispectors noted that over the past three years, engineering staff had significantly increased their involvement and oversight in the design and testing of safety-related components. However, these efforts had not yet been fully extended to include equipment not classified as safety-related, such as the cylinder haulers and mobile cranes. The historical lack of effective oversight of both the design and maintenance of the cylinder haulers appeared to contribute to: 1) the failure which led to the event, and;

2) the inadequate initial and post-modification testing.

Conclusions j

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The inspectors concluded that the quality inspection program for the mobile cranes and cylinder haulers was inconsistent and included several weaknesses. The weaknesses ,

involved a lack of detailed guidance to ensure consistent inspections and a lack of engineering involvement in the specification of inspection requirements following modification activities. Because safety-related activities were not involved, the faliure to perform an adequate post-modification test for the Allied Wagner NCH-35 mobile cranes is not a violation of NRC requirements. j l

5.0 Design and Modification Control [ Charter item No. 3)

The inspectors reviewed the design adequacy of and modification control for the cylinder haulers and mobile cranes used to transport cylinders containing uranium hexafluoride.

5.1 Shaft Failure Exam The inspectors examined the Allied Wagner NCH-20 cylinder hauler grappler shaft '

failure surface to ascertain the break mechanism. The examination revealed that a reverse bending fatigue failure occurred. The symmetrical failure pattern indicated that the force that fatigued the shaft was perpendicular to the cylinder and each side of the shaft was subject to approximately the same number of load applications. The grappler was designed to allow the shaft to rotate in the head, so the orientation of the boom to j the failure could have varied. However, the cylinder was generally carried perpendicular j to the boom during transport. At the time of the event, the grappler and cylinder were perpendicular to the boom.

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The shaft failed below the threaded portion, on the thread relief undercut. No initiation flaw was evident. A circumferential crack was also evident at the next reduction in the shaft diameter. There were also cracks located at the weldment of the shaft to the cylinder grappler attachment plate.

Conclusions Through examination of the failed shaft, the inspectors concluded that the failure occurred due to fatigue caused by a significant bending moment in excess of the design -

that was continuously applied in various directions.

5.2 Shaft History The inspectors reviewed the history of the Allied Wagner NCH-20 cylinder hauler. The Allied Wagner NCH-20 cylinder hauler was purchased in February 1994. The grappler design was changed from an initial design to its present form; however, the inspectors could not determine the basis for the design change. On January 5,1995, the grappler shaft failed at approximately the same location as the current failure. At the time of the January 1995 failure, the cylinder hauler had been used for approximately 220 service hours.

The grappler was retumed to the vendor to be redesigned or repaired. At the time, the vendor indicated that the failure occurred as a result of defective material. However, neither the vendor nor the certificatee staff could locate records of an analysis to support the determination. Following the January 1995 failure, the vendor redesigned the shaft making it longer, doubling the bearing area around the shaft, adding a second thrust bushing, and adding radii at all shaft notches. Once repairs to the grappler shaft were complete, the grappler was retumed to the certificatee and used at both the Paducah and Oak Ridge Gaseous Diffusion Plants. At the time of the September 1997 event, the cylinder hauler had been used for 871 service hours.

During review of grappler design documents, the inspectors determined that the original design incorporated head tilt stops to prevent rotation to approximately 15 degrees perpendicular and 10 degrees parallel to the cylinder. The inspectors noted that the presence of the stops could introduce a significant impact shock to and bending mornent on the shaft. The shock and bending moment could occur when the cylinder was swung causing the grappler to contact the stops. During inspection of the grappler following the September 1997 event, the inspectors observed that modifications had been made to the original stop design to further restrict cylinder sway. With the modifications, the head was restricted in movement to approximately 5 degrees perpendicular and 8 degrees parallel to the cylinder.

Previous inspection of the failed shaft surface indicated that the perpendicular direction appeared to be the orientation of highest stress. The inspectors also noted that a head rotational stop had been added to the grappler which restricted the grappler rotation to slightly less than 180 degrees. The stops were observed to have impact marks. The inspectors could not determine when the observed changes to the original design for the stops had been made. The certificatee could not locate engineering calculations that assessed the impact of the design changes.

' Following the dropped cylinder event at Paducah, Portsmouth Gaseous Diffusion Plant management directed the inspection of an Allied Wagner NCH-20 cylinder hauler used 10

at that facility. Disassembly of the grappler and inspection of the shaft revealed cracks at the same shaft locations as observed on the failed Paducah cylinder hauler grappler shaft. At the time of the Portsmouth inspections, the Portsmouth cylinder hauler had been used for approximately 500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br /> of service. However, no modifications had been made to the grappler rotational and tilt stops.

Conclusions Modifications of the grappler, to include additinnal rotational and tilt stops, appeared to reduce the time to failure of the Paducah Allied Wagner NCH-20 cylinder hauler grappler shaft. Also, a lack of adequate root cause evaluation of the 1995 grappler shaft failure contributed to the current failure.

5.3 Grapoler Design The inspectors attempted to analyze the design of the grappler shaft to gain an understanding of why the failure occurred. During discussions with the certificatee, the inspector was informed that plant engineering staff had not performed detailed engineering evaluations for the cylinder hauler or the grappler. Instead, the certificatee procured the mobile cranes and cylinder haulers as standard industrial systems, developed for used in other commercial heavy lifting applications. The inspectors review of the purchase specifications for the Allied Wagner NCH-20 and NCH-35 confirmed these statements.

The inspectors determined that an absence of detailed engineering calculations for the mobile cranes and cylinder haulers tended to limit the plant staff's ability to independently determine if certain operational uses of the equipment were acceptable I

and to assess the appropriateness of proposed design changes. For example, the inspectors noted that during initial operation of the Allied Wagner NCH-20 cylinder hauler at the Portsmouth site, Portsmouth plant staff identified that the load chart, located in the operator's cab, did not authorize the lifting of loads as heavy as those j normally involved in cylinder movements. To address the finding, Portsmouth and Paducah staff collaborated with the vendor's engineering staff to re-calculate the load limits for the range of boom extensions and angles. However, the engineering work was not performed or documented in a rigorous manner, as demonstrated by a lack of documented calculations to support the final conclusions and a failure to incorporate the revised load limits into the load chart displayed in the Paducah Allied Wagner NCH-20 operator cab.

The inspectors also noted that changes to the stops incorporated into the grappler for the Paducah Allied Wagner NCH-20 cylinder hauler were made without the benefit of engineering evaluations. Similar changes were not made to the Portsmouth cylinder l

hauler grappler stops. A post-failure review of the shafts from the Paducah and Portsmouth cylinder haulers appeared to indicate that the modifications made to the stops decreased the time-to-failure of the shaft. Engineering assessment of the change may have identified the significant impact of the system modification prior to the impact being self-revealed through the shaft failure.

During discussions with the current engineering staff, the inspectors were informed that I several significant changes had been made, within the past two years, to the engineering processes used at Paducah. Many of the changes were implemented specifically to increase the rigor and detail of engineering oversight and calculations.

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Although these changes were focused on engineering activities involving safety-related 4 activities, the engineering manager indicated that nonsafety-related engineering activities, such as design and modification of the cylinder haulers, would also have been improved as a result of the changes. The inspectors noted that other NRC inspection  ;

reports, issued within the past two years, indicated improvements have been observed in the overall engineering processes.

Conclusions The inspector determined that the cylinder hauler grappler shaft failures were caused, in part, by a previous lack of a rigorous engineering evaluation of the initial and modified j system designs. Because safety-related activities were not involved, the failure to use j rigorous engineering processes for the initial or modified designs of the cylinder haulers is not a violation of NRC requirements.

l 5.4 Generic Imolications of Engineering Design Issues to Other Cvlinder Haulers The inspectors performed physical inspections of other cylinder haulers to determine if failure modes, similar to those that contributed to the current event, existed for the other cylinder haulers. Three other types of cylinder haulers, in addition to the Allied Wagner NCH-20 involved in the September 1997 event, were currently available for use. The other cylinders haulers were: two ATPs; one Gradall Model 554, and; two Allied-Wager NCH-35 mobile cranes.

The inspectors performed a visualinspection of the ATPs and observed that the lifting head was similar in design to the Allied Wagner NCH-20 cylinder hauler grappler. In addition, the ATP had cracked welds on the grappler support assembly. The ATPs were purchased in 1988 and were used primarily to move full uranium hexafluoride cylinders, until replaced, in 1993, by the Allied Wagner NCH-35 mobile cranes. Though not currently in use, the staff indicated that the ATPs could be used to move cylinders following the completion of a required periodic inspection of the equipment. At the time of the inspectors' review of the idle equipment, the ATPs were not tagged out-of-service.

Plant staff tagged the ATPs out-of-service, in accordance with plant procedures, shortly after the inspectors' review of the equipment.

The inspectors reviewed records of previous periodic inspections of the ATPs and discussed the periodic inspection results with the quality inspection (Ol) staff responsible for the inspections. The QI staff indicated that previous inspections had identified the grappler support assemM ' structural cracks and that the findings had been referred to engineering for evaluation and repair, as necessary. The QI staff indicated that the equipment was not taken out-of-service following their previous identification of the cracks. The Ql staff were not aware if an engineering evaluation of the cracks was performed or if the required repairs had been made. Although the cracks had existed for some time according to the QI staff, the inspectors noted that the inspection records did not consistently record the findings.

At the time of the September 1997 event, the one Gradall Model 554 cylinder hauler was out-of-service for routine maintenance. The Gradall Model 554 was purchased in 1988 and had logged 5489 hours0.0635 days <br />1.525 hours <br />0.00908 weeks <br />0.00209 months <br /> of service according to the cylinder hauler engine meter. The certificatee had not experienced any previous grappler failures with this cylinder hauler.

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The inspectors performed a physicalinspection of the Gradall Model 554 grappler and observed that the grappler was similar in design to the Allied Wagner NCH-20 assembly.

However, due to the presence of a large amount of grease, a detailed inspection of the grappler, for visible cracks, was not performed. The inspectors noted that the assembly did not include mechanical stops that could cause impact loads, similar to those experienced by the Allied Wagner NCH-20 cylinder hauler during operations. During discussions with certificatee staff, the inspectors were informed that an engineering inspection and evaluation of the Gradall Model 554 head assembly would be conducted prior to returning the cylinder hauler to service.

In 1993, the certificatee purchased two Allied Wagner NCH-35 mobile cranes to support the timely movement of full cylinders of uranium hexafluoride, a task previously performed using the ATPs. The inspectors could not perform a complete visual inspection of the grapplers due to visual obstructions. However, a review of the vendor's specifications for the grapplers indicated that sufficient load carrying margin was incorporated into the design, if appropriate maintenance was performed. The inspectors noted that the grapplers utilized limit switches to prevent cylinder sway during either lifting or travel versus mechanical stops; thus minimizing the potential for significant bending moments due to impacts with the mechanical stops.

Conclusions The inspectors determined that other cylinder haulers appeared to have design weaknesses similar to those that contributed to the Allied Wagner NCH-20 cylinder hauler grappler shaft failure. The ATP cylinder grappler was observed to have weld cracks indicating previous problems with structural adequacy for loads lifted, l

6.0 Root Cause and Corrective Actions (Charter item No. 4] l Through personnel interviews and reviews of documentation associated with the 1995 ,

cylinder hauler grappler shaft failure , the inspectors determined that the plant staff did not perform a root cause evaluation of the event. Corrective actions to the event were implemented by returning the cylinder hauler to the vendor for warranty repair or replacement. Following return of the cylinder hauler grappler to the vendor, the plant staff were informed that the shaft failed as a result of material defect. However, no specific engineering analysis or paperwork was provided by the vendor to substantiate this conclusion. No other corrective actions were implemented by the plant staff.

The inspectors also observed the major portions of the plant staff's investigation and evaluation of the current failure. The inspectors noted that the current investigation efforts were conducted in accordance with a revised corrective action system that was designed to ensure that both direct and indirect issues were identified and evaluated.

The inspectors noted that the investigation process was initiated shortly after the initial event; however, the staff did not appear to immediately identify some issues that could have had generic impacts, including training and the inadequacy of past engineering evaluations. As a result, inadequately trained operators continued to perform cylinder i movements and other cylinder haulers remained in service with operational uncertainties l requiring engineering evaluation. The inspectors also observed that the investigation j team did not include an individual that possessed a detailed knowledge of mobile crane design or operations. In spite of the observed weaknessns, the overallinvestigation j process and results were noted to be adequate.

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Condusions The plant staff failed to aggressively pursue a documented root cause evaluation of the 1995 failure of the cylinder hauler vertical shaft and to implement appropnate corrective actions. Some weaknesses were identified in the plant staff's investigation to the September 1997 event; however, the overall process and results _were noted to be adequate.

7.0 Event Response, Classification, and Reporting [ Charter item No. 5]

The inspectors reviewed the immediate actions taken by the certificatee in response to -

the event. The review consisted of interviews with personnel directly involved in the cylinder movements and management personnel involved in the initial response to the dropped cylinder. In addition, the inspectors observed actions taken to both control and later clear the event scene.

Immediately following the event, plant personnel in the vicinity of the dropped cylinder halted all activities and contacted the plant shift superintendent. Initial assessments were made at the scene to determine if the cylinder had been breached and to ensure that non-essential personnel were excluded from the area. No action was taken to either upright or move the cylinder. Shortly after the event, the plant shift superintendent suspended plant staff use of other cylinder haulers. The Department of Energy and Portsmouth management took similar actions following a briefing on the event.

The inspectors discussed the event, classification of the occurrence using the site emergency plan, and the applicable reporting requirements with the plant shift superintendent. Based upon the discussions and a review of the applicable procedures, the inspectors determined that the plant shift superintendent had property concluded that the event did not meet any classification criteria and was not reportable to the NRC.

Conclusions The inspectors determined that the plant staff and management's immediate response to and evaluation of the event for classification and reporting was appropriate and consistent with the site emergency response plan and current reporting requirements.

8.0 Exit interview The lead inspector met with plant management and staff on February 16,1998, and summarized the purpose of the special inspection, the special inspection charter items, and the inspection findings. The plant staff acknowledged the findings presented. The inspector asked the plant staff whether any materials examined during the inspection should be considerec proprietary. No proprietary information was identified.

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Attachment:

Special inspection Charter it c .

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PARTIAL LIST OF PERSONS CONTACTED Licensea

• J. A. Labarraque, Safety, Safeguards and Quality Manager Lockheed Martin Utility Services

'S. A. Polston, General Manager

• H. Pulley, Enrichment Plant Manager

• L. L. Jackson, Nuclear Regulatory Affairs Manager

• S. R. Penrod, Operations Manager

• V. J. Shanks, Production Support Manager

• R. Chambers, Engineering Manager

• J. H. Thomas, Investigation Team Leader Department of Energy G. A. Bazzell, Site Safety Representative

• Denotes those present at the February 16,1998 exit meeting.

Other members of the plant staff were also contacted during the inspection period.

LIST OF ACRONYMS USED NRC Nuclear Regulatory Commission PM Preventive Maintenance QI Quality inspection 15 1

Paducah Gaseous Diffusion Plant hardal Inanardinri Chartar hrdamhar 18.1997 Cvlinelar Dron A. Background On September 18,1997, at approximately 8:45 a.m. (CST), an empty 10-ton cylinder used to transport uranium hexafluonde was dropped by a mechanical cylinder hauler just south of Building C-400. Various types of cylinder haulers (front-end loaders with hydraulically operated clamshell arms for grasping cylinders) are used onsite to transport cylinders containing either solid uranium hexafluoride or heel material (the 50 pound or less of uranium-bearing material remaining in a cylinder after it is fed into the cascade). Initial observations at the scene indicated that the linchpin, which connect the clamshell arms to the boom of the cylinder hauler, has sheared causing the cylinder to drop approximately 2 feet. The cylinder did not appear to have been breached. The area was quarantined by the certificatee while a root cause investigation was initiated.

' B. Scopa Determine and evaluate the root causes for the event, generic implications of the root causes to other site activities, and the certificatee's investigation efforts of this event through a focused assessment of the following areas:

1. Definition and implementation of operational controls for the movement of cylinders containing uranium hexafluoride using mobile cranes including:

a) training; b) equipment and task operating procedures, and; c) management controls.

2. Definition, application, and implementation of preventive, routine, and corrective maintenance programs, and of program for material /part replacement for mobile cranes used to transport cylinders containing uranium hexafluoride.

3. Design adequacy and modification control of the mobile cranes used to transport cylinders containing uranium hexafluoride.

4. Adequacy and implementation of corrective actions to a 1995 failure of the Allied Wagner cylinder hauler.

5. Certificatee's response to the event, including classification and reporting.

Attachment

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