ML101890187
| ML101890187 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 08/27/2010 |
| From: | Blount T Division of Policy and Rulemaking |
| To: | O'Brien K Division of Reactor Safety III |
| E. Bowman, DPR/PLPB,301415-2963 | |
| References | |
| TIA 2010-004 | |
| Download: ML101890187 (14) | |
Text
August 27, 2010 MEMORANDUM TO:
Kenneth G. OBrien, Deputy Director Division of Reactor Safety Region III FROM:
Thomas B. Blount, Deputy Director
/RA/
Division of Policy and Rulemaking Office of Nuclear Reactor Regulation
SUBJECT:
FINAL RESPONSE TO TASK INTERFACE AGREEMENT-SINGLE-FAILURE-PROOF DESIGN FOR REACTOR PRESSURE VESSEL HEAD STRONGBACK, DRYER/SEPARATOR STRONGBACK, AND REACTOR PRESSURE VESSEL HEAD LIFTING LUGS AT CLINTON POWER STATION (TIA 2010-004)
By letter dated February 21, 2010 (Agencywide Documents Access and Management System Accession No. ML100540404), Region III requested assistance from the Office of Nuclear Reactor Regulation in answering the following question regarding the single-failure-proof design for the reactor pressure vessel head strongback, the dryer/separator strongback, and the reactor pressure vessel head lifting lugs at the Clinton Power Station:
From a licensing basis perspective, what are the requirements for Clinton for the reactor pressure vessel (RPV) Head Strongback, Dryer/Separator Strongback, and RPV Head Lifting Lugs with respect to meeting single-failure-proof design criteria?
The NRR staffs assessment is documented in the enclosed staff evaluation.
Enclosure:
As stated CONTACT: Eric Bowman, DPR/PLPB (301) 415-2963
MEMORANDUM TO:
Kenneth G. OBrien, Deputy Director Division of Reactor Safety Region III FROM:
Thomas B. Blount, Deputy Director
/RA/
Division of Policy and Rulemaking Office of Nuclear Reactor Regulation
SUBJECT:
FINAL RESPONSE TO TASK INTERFACE AGREEMENT-SINGLE-FAILURE-PROOF DESIGN FOR REACTOR PRESSURE VESSEL HEAD STRONGBACK, DRYER/SEPARATOR STRONGBACK, AND REACTOR PRESSURE VESSEL HEAD LIFTING LUGS AT CLINTON POWER STATION (TIA 2010-004)
By letter dated February 21, 2010 (Agencywide Documents Access and Management System Accession No. ML100540404), Region III requested assistance from the Office of Nuclear Reactor Regulation in answering the following question regarding the single-failure-proof design for the reactor pressure vessel head strongback, the dryer/separator strongback, and the reactor pressure vessel head lifting lugs at the Clinton Power Station:
From a licensing basis perspective, what are the requirements for Clinton for the reactor pressure vessel (RPV) Head Strongback, Dryer/Separator Strongback, and RPV Head Lifting Lugs with respect to meeting single-failure-proof design criteria?
The NRR staffs assessment is documented in the enclosed staff evaluation.
Enclosure:
As stated CONTACT: Eric Bowman, DPR/PLPB (301) 415-2963 DISTRIBUTION:
Non-PUBLIC PLPB Reading File RidsNrrDpr John Jolicoeur RidsRgn1MailCenter RidsRgn2MailCenter RidsRgn3MailCenter RidsRgn4MailCenter RidsNrrDprPgcb RidsAcrsAcnwMailCtr RidsNrrDss RidsNrrDssSbpb RidsNrrPMClinton ADAMS ACCESSION NO: ML101890187 *No substantive change from input NRR-043 OFFICE NRR/DPR/PLPB NRR/DPR/PLPB NRR/DSS/SBPB NRR/DPR/PLPB NRR/DPR NAME EBowman EHylton GCasto*
JJolicoeur TBlount DATE 7/8/2010 7/8/10 7/6/2010 8/26/10 8/27/10 OFFICIAL RECORD COPY
ENCLOSURE FINAL RESPONSE TO TASK INTERFACE AGREEMENT 2010-004 SINGLE-FAILURE-PROOF DESIGN FOR REACTOR PRESSURE VESSEL HEAD STRONGBACK, DRYER/SEPARATOR STRONGBACK, AND REACTOR PRESSURE VESSEL HEAD LIFTING LUGS AT CLINTON POWER STATION
1.0 INTRODUCTION
While implementing Operating Experience Smart Sample (OpESS) FY2007-03, Revision 2, Crane and Heavy Lift Inspection, Supplemental Guidance for IP-71111.20, Region III inspectors reviewed licensing and design basis documents related to the design of the reactor pressure vessel (RPV) head strongback, the dryer/separator strongback, and the RPV head lifting lugs. The inspectors reviewed several applicant letters submitted in response to requests for additional information during the licensing process for Clinton. The inspectors identified several references in these letters indicating that the RPV head strongback, dryer/separator strongback, and RPV head lifting lugs were in conformance with the single-failure-proof guidelines of Section 5.1.6, Single-Failure-Proof Handling Systems, of NUREG-0612, Control of Heavy Loads at Nuclear Power Plants, 1980.
Through a Task Interface Agreement (TIA), Region III requested that the Office of Nuclear Reactor Regulation (NRR) address the following:
From a licensing basis perspective, what are the requirements for Clinton for the RPV Head Strongback, Dryer/Separator Strongback, and RPV Head Lifting Lugs with respect to meeting single-failure-proof design criteria?
2.0 REGULATORY EVALUATION
Applicable Regulations:
For the Clinton Nuclear Station, the design basis for control of heavy loads was developed during the initial operating license review and following issuance of the construction permit for the facility. Pursuant to the requirements of Title 10 of the Code of Federal Regulations, Section 50.34, Contents of applications; technical information, Paragraph (b), (10 CFR 50.34(b)) the applicant for an operating license must submit a final safety analysis report that describes the facility, presents the design basis and the limits on its operation, and presents a safety analysis of the structures, systems, and components, and the facility as a whole. This report shall include a description and analysis of the structures, systems, and components of the facility, with emphasis upon performance requirements, the bases upon which such requirements have been established, and the evaluations showing that safety functions will be accomplished.
The U. S. Nuclear Regulatory Commission (NRC) staff evaluated information provided by operating license applicants pursuant to the requirements of 10 CFR 50.40, Common Standards. For issuance of an operating license, the NRC staff considers whether the processes to be performed, the operating procedures, the facility and equipment, the use of the facility, and other technical specifications collectively provide reasonable assurance that the applicant will comply with the regulations in 10 CFR Part 50 and that the health and safety of the public will not be endangered.
Staff Guidance:
The NRC staff issued a letter dated December 22, 1980, regarding safety issue A-36, Control of Heavy Loads near Spent Fuel, to licensees of operating plants, applicants for operating licenses and holders of construction permits. The staff later identified this letter as Generic Letter (GL)80-113. In the letter, the staff requested that addressees review controls for the handling of heavy loads to determine the extent to which the guidelines of NUREG-0612, Control of Heavy Loads at Nuclear Power Plants, were satisfied at each facility and identify the changes and modifications that would be required in order to fully satisfy these guidelines. The NRC staff divided this request into two phases (Phase I and Phase II) for implementation by licensees. Phase I guidelines addressed measures for reducing the likelihood of dropping heavy loads and provided criteria for establishing safe load paths; procedures for load handling operations; training of crane operators; design, testing, inspection, and maintenance of cranes and lifting devices; and selection and use of slings. Phase II guidelines addressed alternatives to reduce further the probability of a load handling accident or to demonstrate the consequences of heavy load drops would be acceptably small.
With respect to Phase I responses regarding special lifting devices, the staff requested addressees to verify lifting devices used with reactor building handling systems conformed to the standards of ANSI/ANS N14.6 - 1978, Standard for Special Lifting Devices for Shipping Containers Weighing 10,000 pounds (4500 kg) or More for Nuclear Materials. For special lifting devices where this standard, as supplemented by the guidance of Section 5.1.1(4) of NUREG-0612, was not satisfied, the staff requested addressees demonstrate the equivalency of proposed alternative lifting devices with respect to load-handling reliability. The guidance contained in Section 5.1.1(4) of NUREG-0612 stated the following:
Special lifting devices should satisfy the guidelines of ANSI N14.6-1978, Standard for Special Lifting Devices for Shipping Containers Weighing 10,000 pounds (4500 kg) or More for Nuclear Materials. This standard should apply to all special lifting devices which carry heavy loads in areas-as defined above. For operating plants certain inspections and load tests may be accepted in lieu of certain material requirements in the standard. In addition, the stress design factor stated in Section 3.2.1.1 of ANSI N14.6 should be based on the combined maximum static and dynamic loads that could be imparted on the handling device based on characteristics of the crane which will be used. This is in lieu of the guideline in Section 3.2.1.1 of ANSI N14.6 which bases the stress design factor on only the weight (static load) of the load and of the intervening components of the special handling device.
For licensees with handling systems determined to have sufficient design features to make the likelihood of a load drop extremely small, the staff requested that the applicant provide detailed information about the handling system as part of the Phase II response. This information included an evaluation of the lifting devices and interfacing lift points associated with each single-failure-proof handling system against the guidelines of NUREG-0612, Section 5.1.6 (i.e.,
complete compliance with NUREG-0612, Section 5.1.6, or partial compliance supplemented by suitable alternative or additional design features). Section 5.1.6 of NUREG-0612 included the following guidance for special lifting devices used with single-failure-proof handling systems:
Special lifting devices that are used for heavy loads in the area where the crane is to be upgraded should meet ANSI N14.6 1978, Standard for Special Lifting Devices for Shipping Containers Weighing 10,000 Pounds (4500 kg) or More for Nuclear Materials, as specified in Section 5.1.1(4) of this report except that the handling device should also comply with Section 6 of ANSI N14.6-1978. If only a single lifting device is provided instead of dual devices, the special lifting device should have twice the design safety factor as required to satisfy the guidelines of Section 5.1.1(4). However, loads that have been evaluated and shown to satisfy the evaluation criteria of Section 5.1 need not have lifting devices that also comply with Section 6 of ANSI N14.6.
The NRC staff issued GL 85-11, Completion of Phase II of Control of Heavy Loads at Nuclear Power Plants, NUREG-0612, on June 28, 1985. In this document, the NRC staff presented its conclusion that a detailed review of the Phase II responses received from licensees was not necessary. The NRC staff based its conclusion on the improvements resulting from the review of the Phase I responses and the findings identified through a pilot of several Phase II responses. The pilot was based on Phase II responses from 20 operating reactors at 12 sites and 6 operating license applicants at 5 sites. Of those 26 reactors, all 10 boiling water reactors (BWRs) had single-failure-proof cranes; 10 pressurized water reactors (PWRs) had load-drop analyses demonstrating satisfactory outcomes; and 6 PWRs had a combination of administrative controls and limited load drop analyses demonstrating satisfactory outcomes.
Based on these reviews, the NRC staff concluded that the cost to install single-failure-proof polar cranes in PWR containment buildings was not justified on a generic basis. Nevertheless, the NRC staff encouraged licensees to determine and implement the appropriate actions to provide adequate safety.
Prior Relevant Evaluations:
On May 29, 2007, the NRC staff issued Supplement 1 to Regulatory Issue Summary (RIS) 2005-25, Clarification of NRC Guidelines for Control of Heavy Loads. The intent of the RIS was, in part, to communicate regulatory expectations associated with 10 CFR 50.59 and 10 CFR 50.71(e), as these requirements relate to operating license holders control of design basis information related to the safe handling of heavy loads. The regulatory expectations included incorporation in the licensing basis of Phase I load handling restrictions derived from completed Phase II evaluations.
Licensing Basis Information:
The staff reviewed the following letters Illinois Power Company (the applicant) submitted in response to GL 80-113 and subsequent requests for additional information:
Illinois Power Letter U-0249 L30-81 (06-19)-L to NRC,
Subject:
December 22, 1980, letter on Control of Heavy Loads; dated June 22, 1981 Illinois Power Letter U-0294 L30-81 (09-25)-L to NRC,
Subject:
Clinton Power Station Units 1 and 2 Docket Nos. 50-461 and 50-462; dated September 25, 1981 Illinois Power Letter U-0656 L30-83 (07-28)-L to NRC,
Subject:
Clinton Power Station Unit 1 Control of Heavy Loads (NUREG-0612); dated July 28, 1983 Illinois Power Letter U-06850982-L L30-83 (12-21)-L to NRC,
Subject:
Clinton Power Station Unit 1 Control of Heavy Loads (NUREG-0612); dated December 21, 1983 Illinois Power Letter U-0800 L30-85(02-21)-6 B48-85(02-21)-6 1A.120 to NRC,
Subject:
Clinton Power Station Unit 1 Control of Heavy Loads (NUREG-0612); dated February 21, 1985 The Office of Nuclear Reactor Regulation (NRR) staff reviewed these letters. The letter dated June 22, 1981, provided the applicants Phase I response, and the letter dated September 25, 1981, provided the applicants Phase II response. The remaining letters addressed staff requests for additional information, some of which were designated as Phase I or Phase II requests. As indicated in the TIA prepared by Region III staff, the applicant described design information related to the reactor pressure vessel (RPV) head strongback, dryer/separator strongback, and RPV head lifting lugs in these letters. The staff identified the following relevant information:
The letter dated June 22, 1981, identified the RPV head strongback and dryer/separator strongback used with the containment polar crane as carrying heavy loads such as the RPV head, drywell head, steam dryer, and steam separator over safety-related equipment. The applicant had evaluated the hazard of either the RPV head strongback or dryer/separator strongback dropping a heavy load over safe shutdown equipment and determined the likelihood of handling system failure for this load is extremely small (i.e., Section 5.1.6 NUREG-0612 satisfied).
The letter dated September 25, 1981, provided a detailed evaluation of the overhead handling system with respect to the feature of design, fabrication, inspection, testing, and operation as delineated in GL 80-113. The applicant provided a detailed evaluation of the reactor building polar crane demonstrating compliance with NRC guidelines for single-failure-proof cranes for nuclear power plants. The applicants response specific to requirements for the lifting devices was that the main hoist load block assembly, rope reeving system, and lifting devices are of redundant design (dual load attaching points) such that each attaching point and lifting device is capable of supporting a static load of three times the rated load without permanent deformation.
The letter dated September 25, 1981, also responded to an NRC request to provide an evaluation of the lifting devices for each single-failure-proof handling system with respect to the guidelines of NUREG-0612, Section 5.1.6. The applicants response was that the two lifting devices are currently anticipated to be used to accomplish lifts with the polar crane over the refueling floor. Both are supplied by General Electric. They are the steam separator/dryer strongback and the RPV head carousel strongback. Each strongback is provided with four lift points to the load. General Electric (GE) states that two of the four attachments are capable of supporting the load. A single failure is considered as the loss of one lift point only. The strongbacks are attached to the polar crane redundant sister hook through the use of a hook box on top of the strongbacks and through two six inch diameter link pins. General Electric terms the strongbacks single-failure-proof.
Finally, the letter dated September 25, 1981, responded to an NRC request to provide an evaluation of the interfacing lift points with respect to the guidelines of NUREG-0612, Section 5.1.6. The applicants response was that the four lifting lugs are used on the RPV head. After failing two lugs, each of the remaining two lugs would have to support 63,100 pounds. These two remaining lugs are assumed to be opposed on the head so that the head would remain level. Based on a tensile strength of 80,000 psi and a cross-sectional area of each lug of 18 inches squared, the lugs have a design factor of safety of approximately 22 based on yield strength. The cross sectional area above also applies to the steam separator and the steam dryer lugs.
In the letter dated July 28, 1983, Illinois Power Company described that two strongbacks were purchased as special lifting devices for Clinton Power Station.
One was designed for lifting either the RPV head or the drywell head. The other strongback was designed to lift the steam separator or the steam dryer, as needed. The two strongbacks were subcontracted by the General Electric Company to separate companies. The available information indicated that the strongbacks were designed to industry standards using good engineering practices. Specific design criteria discussed included:
The strongbacks were designed with a factor of 5 based on ultimate strength under static load conditions.
The design strength with a 15 percent impact allowance would then be 4.25.
The head strongback was proof tested to 125 tons (192 percent of the maximum load of 65 tons for the drywell head).
The dryer/separator strongback was tested to 55 tons (125 percent of the maximum load of 44 tons for the steam separator).
The letter dated December 21, 1983, responded to an NRC request, which stated that the dryer/separator strongbacks load test does not meet the formal requirements of a 150 percent test. The NRC staff indicated that the 125 percent load test may be acceptable; however, more information should be provided. If the applicant considered the device single-failure-proof, the NRC staff requested a description of the device and the meaning of the load test. Otherwise, the staff requested that the device description be accompanied by a discussion of potential load drop consequences. The applicants response was that the strongback will be upgraded to a factor of safety of ten in compliance with Section 5.1.6(1a), Single-Failure-Proof Handling Systems, of NUREG-0612.
The letter dated February 21, 1985, responded to an NRC request to confirm the actual number of special lifting devices and to verify that each meets ANSI N14.6-1978 and all are designed for static plus maximum dynamic loads. The applicants response was that two special lifting devices will be used at Clinton, the RPV head strongback and the dryer/separator strongback, both of which were designed and supplied by General Electric to accomplish their intended reactor vessel servicing and refueling functions. Information provided in this letter contradicted the response addressing the strongback design factor provided in the letter dated December 21, 1983. The letter included the following statements:
Both strongbacks were designed to be single-failure-proof and should adequately comply with NUREG-0612, Paragraph 5.1.1(4).
Design calculations based on estimated weights demonstrated safety factors of greater than 3 with respect to yield and greater than 5 with respect to the ultimate strength of the material, including a 15 percent dynamic load allowance.
Although the component weights estimated by the applicant are greater than those used in the design calculations, the difference is negligible considering the conservative dynamic load allowance.
Both strongbacks were load tested to 125 percent of the rated load [Note:
the dryer/separator strongback was tested to 125 percent of the suspended load, but the RPV head strongback was tested to 125 percent of the combined weight of the head and the strongback with a 15 percent dynamic allowance].
The NRR staff also reviewed NUREG-0853, Safety Evaluation Report Related to the Operation of Clinton Power Station Unit No. 1, and its supplements to help determine the basis for staff acceptance at the time of original licensing. Consistent with the Region III TIA, the NRR staff identified the following relevant excerpts:
NUREG-0853, Supplement No. 2, May 1983, Section 9.1.5, Overhead Heavy-Load Handling System, stated:
The SER stated that the applicant had committed to implement the interim actions before the final implementation of the NUREG-0612 guidelines and before the receipt of the operating license. The applicant has made two submittals dated June 22, 1981, and September 25, 1981, concerning the implementation of NUREG-0612. The NRC staffs review of the applicants submittals is continuing. However, the NRC staff will require that a condition be placed in the license requiring that, before startup after the first refueling outage, the applicant shall comply with Section 5.1.1 of NUREG-0612 (Phase I: the 6-month response to the NRC Generic Letter dated December 22, 1980).
Before startup after the second refueling outage, the applicant shall have made commitments acceptable to the NRC staff regarding the guidelines of Section 5.1.2 through Section 5.1.6 of NUREG-0612 (Phase II: 9-month responses to the NRC Generic Letter dated December 22, 1980).
NUREG-0853, Supplement No. 5, January 1986, Section 9.1.5, Overhead Heavy-Load Handling System, stated:
The staff and its consultant, the Idaho National Engineering Laboratory (INEL), have reviewed the applicants submittals for the Clinton Power Station, Unit 1. As a result of its review, EG&G has issued a Technical Evaluation Report (TER) which is contained in Appendix H to this supplement. The staff has reviewed the TER and concurs with its findings that the guidelines in NUREG-0612, Section 5.1.1 (Phase I), have been satisfied.
In Supplement No. 2 to the Clinton SER, license condition 13 regarding compliance with the criteria of Phases I and II (Section 5.1.2 through 5.1.6) of NUREG-0612 was added. On the basis of the applicant's compliance with the criteria of Phase I, and the reviews of Phase II to date, license condition 13 is no longer needed.
NUREG-0853, Supplement No. 5, January 1986, Appendix H, Control of Heavy Loads at Nuclear Power Plants - Clinton Power Station - Unit 1 (PHASE I),
stated:
The Steam Dryer/Separator Strongback is handled by the polar crane. The device was supplied by General Electric Co. who terms the strongback Single-Failure-Proof. The strongback is attached to the redundant dual hook of the crane through the use of a hook box on top of the strongback and two six inch diameter link pins. The ANSI N14.6-1978 standard as amended by NUREG-0612 Section 5.1.1(4) was used for making a thorough evaluation of the design. The information obtained supports that they were designed to industry standards. The design load was 54.5 tons, which includes a 15 percent dynamic allowance. It provides safety factors of greater than three with respect to yield and greater than five with respect to ultimate strength of the material.
Appendix H also stated:
The RPV Head strongback is rated at 100 tons. Its largest single load is the Drywell Head of 65 tons. The maximum load is the RPV Head plus the strongback, nut tray, nuts and washers of 25 tons. General Electric Co. used design estimates of 86.7 tons plus a dynamic allowance of 13 tons. Resultant safety factors were greater than three with respect to yield and greater than five with respect to ultimate strength of the material.
Finally, the NRR staff reviewed the Clinton Power Station (CPS) Updated Safety Analysis Report (USAR), which essentially provides the licensees record of the current licensing basis.
Consistent with the Region III TIA, the NRR staff identified the following relevant excerpts:
USAR Section 9.1.4.2.5.6, Dryer and Separator Strongback, Revision 11, stated:
The strongback is a cruciform shaped I beam structure which has a hook box with two hook pins in the center for engagement with the reactor service crane sister hook and it has a socket with a pneumatically operated pin on the end of each arm for engaging it to the four lift eyes on the steam dryer or shroud head.
The strongback has been designed such that one hook pin and one main beam of the cruciform will be capable of carrying the total load and so that no single component failure will cause the load to drop or swing uncontrollably out of an essentially level attitude. The safety factor of all lifting members is five or better in reference to the ultimate breaking strength of the material.
The structure is designed in accordance with The Manual of Steel Construction by AISC [American Institute of Steel Construction].
The completed assembly was proof tested at 125% of rated load.
USAR Section 9.1.4.2.5.7, Head Strongback/Carousel, Revision 11, stated:
The strongback is a box beam structure which has a hook box with two hook pins in the center for engagement with the reactor service crane sister hook. Each arm has a lift rod for engagement to the four lift lugs on the RPV head.
USAR Section 9.1.4.2.5.7 also stated:
The strongback with its lifting components is designed to meet the Crane Manufacturers Association of America, Specification No.
- 70. The design provides a 15 percent impact allowance and a safety factor of five in reference to the ultimate strength of the material used. After completion of welding and before painting, the lifting assembly is proof load tested and all load affected welds and lift pins are magnetic particle inspected.
The steel structure is designed in accordance with The Manual of Steel Construction by AISC. Aluminum structures are designed in accordance with the Aluminum Construction Manual by the Aluminum Association.
The strongback is designed in accordance with ASME, American National Standard for overhead hoists ANSI B30.16 - 1973, Paragraph 16-1.2.2.2 [which specifies a 125% load test] and such that one hook pin and two of the four arms of the structure are capable of carrying the total load, and so that no single component failure will cause the load to drop or swing uncontrollably out of an essentially level attitude.
USAR Section 9.1.4.2.10.2, Refueling Procedure, Revision 13, stated:
The polar crane and cruciform-shaped strongback will be used to handle the 96-ton load of RPV Head and attachments. The strongback is designed so that no single component failure will cause the load to drop or swing uncontrollably out of an essentially horizontal attitude.
The strongback attaches to the crane sister hook by means of an integral hook box and two hook pins. Each pin is capable of carrying the rated load. Two of the four arms of the cruciform are capable of carrying the rated load.
3.0 ISSUE EVALUATION Because the Clinton Power Station evaluated and implemented measures for control of heavy loads during the operating license review period, applicable NRC regulations required only that the applicant for an operating license include in the final safety analysis report a description and analysis of the structures, systems, and components of the facility related to control of heavy loads. In support of issuance of the operating license, the NRC staff evaluated the safety analysis report information to establish reasonable assurance that operation of the facility would comply with NRC regulations and public health and safety would not be endangered. More specific regulations (e.g., the General Design Criteria of Appendix A to 10 CFR Part 50) were not applied to the evaluation of control of heavy loads through either the CPS safety analysis report or the NRC issue evaluation guidelines included in GL 80-113. Documents referenced by GL 80-113 (e.g., NUREG-0612 and ANSI/ANS N14.6) provided guidance and design criteria acceptable to the NRC staff, but these documents did not constitute regulatory requirements.
Thus, the information in the CPS safety analysis report at the time of licensing, including any direct references, constitutes the CPS original licensing basis with respect to control of heavy loads and, more specifically, special lifting devices.
The staffs basis for finding that reasonable assurance that operation of the facility would comply with NRC regulations and public health and safety would not be endangered was documented in the Safety Evaluation Report (SER) Related to the Operation of Clinton Power Station Unit No. 1, NUREG-0853. Supplement 5 to this SER referenced the letters from Illinois Power Company listed above and one other letter dated January 26, 1985, that the NRR staff was unable to locate. The staffs basis for acceptance of the Phase I information was described in Section 9.1.5 of Supplement 5 to this SER as the Technical Evaluation Report evaluation contained in Appendix H to Supplement 5 of the SER. In the SER, the staff dismissed the need for License Condition 13 on the basis of acceptable implementation of Phase I and the review of Phase II information completed at the time. This basis is similar to the basis described in GL 85-11 for dismissing full review of Phase II for operating license holders. Although the basis for dismissal of the license condition is poorly defined in the SER, the current NRR staff concludes that the basis for not pursuing the commitments specified in the license condition was the small additional safety benefit associated with full compliance with NUREG-0612 guidelines. As with GL 85-11, the staff likely determined that information provided in the CPS Phase II submittals had demonstrated the risk from planned heavy load handling evolutions was acceptably small and no further action was necessary to further reduce risk. For CPS, this conclusion was supported by information demonstrating the polar crane was designed to have an extremely small likelihood of failure and information demonstrating that the strongbacks were suitably designed, constructed, and tested to support safe handling of the drywell head, reactor vessel head, steam separator, and steam dryer.
The NRR staff reviewed the licensing correspondence against the staff SER (NUREG-0853) and Revision 11 of the CPS USAR. The staff found that the information in the documents was generally consistent. The licensing documentation contained some information that was not incorporated in the CPS USAR. Specifically, Illinois Power Company described that the likelihood of handling system failure for loads over the reactor vessel would be extremely small (i.e., Section 5.1.6 NUREG-0612 satisfied) in the Phase I response provided by letter dated June 22, 1981, and the applicants December 21, 1983, response to a request for information stated that the dryer/separator strongback would be upgraded to a factor of safety of ten in compliance with Section 5.1.6(1a), Single-Failure-Proof Handling Systems, of NUREG-0612.
However, the NRR staff found such information to be general in nature or related to a future action that was superseded by subsequent correspondence. During the licensing review, the staff concluded that the likelihood of a load drop over the reactor vessel would be acceptably small based in part on the Phase II response (e.g., description of redundant features included in the crane design and certain features included in the design of the strongbacks). Also, the staff accepted the design of the strongbacks after correspondence provided on February 21, 1985, which stated that the strongbacks were designed to lower safety factors than those described in the correspondence dated December 21, 1983.
Information provided in the Phase II submittal (i.e., the information provided by letter dated September 25, 1981) and other information relevant to the strongbacks was incorporated in the USAR and cited in part in the staff SER. Although the Phase II request contained in GL 80-113 requested an evaluation of special lifting devices relative to the guidelines of Section 5.1.6 of NUREG-0612, the response to that specific request neither cited conformance with those guidelines nor specifically addressed individual elements of those guidelines. Instead, Illinois Power Company described the strongbacks as single failure proof in a sense that could reasonably apply only to the specific examples cited in the response. The staff SER does not include references to criteria from Section 5.1.6 of NUREG-0612 in finding the strongbacks acceptable to support reactor operation. Therefore, the NRR staff concludes that the licensing basis of the special lifting devices is adequately described in the CPS USAR and does not include the criteria contained in Section 5.1.6 of NUREG-0612.
Based on the above assessment, the NRR staff determined that the following design basis criteria apply to the CPS RPV head strongback and the dryer/separator strongback:
Two strongbacks were purchased as special lifting devices for Clinton Power Station: one was designed for lifting either the RPV head or the drywell head and the other strongback was designed to lift the steam separator or the steam dryer, as needed.
Each strongback is provided with four lift points to the load.
The strongbacks are attached to the polar crane redundant sister hook through the use of a hook box on top of the strongbacks and through two six inch diameter link pins.
The steel structures of the strongbacks were designed in accordance with the Manual of Steel Construction by the American Institute of Steel Construction (AISC).
Any aluminum structures are designed in accordance with the Aluminum Construction Manual by the Aluminum Association.
The strongbacks are designed so that no single component failure will cause the load to drop or swing uncontrollably out of an essentially horizontal attitude. One hook pin and two opposing arms of the four arms of each structure are capable of carrying the total load.
However, the licensing basis information specifies that a single-failure is a loss of one lift point only. Accordingly, a third arm of each structure may be credited with stabilizing the load attitude. Since no specific design information was described related to these load conditions, the analytical methods and acceptance criteria of the AISC Manual of Steel Construction apply to analyses of these load conditions.
Design calculations based on estimated weights demonstrated safety factors of greater than 3 with respect to yield and greater than 5 with respect to the ultimate strength of the material, including a 15 percent dynamic load allowance. The information provided in the letter dated February 21, 1985, does not specify the loading conditions where these safety factors apply, and the discussion in Appendix H to Supplement 5 of NUREG-0853 compares these safety factors to the guidelines of Section 5.1.1.(4) of NUREG-0612. Therefore, these safety factors are applicable to load conditions without component failures. Both strongbacks were proof-load tested to 125 percent of the rated load.
The licensing basis for interfacing lift points is much less complete. The staff identified only the following information regarding the RPV head, steam separator, and steam dryer:
In a letter dated September 25, 1981, responding to the Phase II information request, Illinois Power Company described that, assuming two lifting lugs failed, the remaining two lifting lugs were capable of supporting the entire 63,100 pounds weight of the RPV head. These two remaining lugs are assumed to be opposed on the head so that the head would remain level. Based on a tensile strength of 80,000 psi and a cross-sectional area of each lug of 18 inches squared, the lugs have a design factor of safety of approximately 22 based on yield strength. The cross sectional area above also applies to the steam separator and the steam dryer lugs.
The NRR staff found that the existing licensing basis of the special lifting devices and associated interfacing lift points provides a level of safety reasonably consistent with a low probability of handling system failure. The special lifting devices and interfacing lift points were constructed to industry standards and designed with reasonably large design margins. In addition, the special lifting devices were subject to proof load tests. As documented in NUREG-1774, A Survey of Crane Operating Experience at U.S. Nuclear Power Plants from 1968 through 2002, poor heavy loads program implementation and human performance errors caused most load drop events, and no load drop events resulted from structural failure of special lifting devices. Therefore, the NRR staff considers the existing licensing and design basis for the special lifting devices at CPS appropriate and acceptable.
4.0 CONCLUSION
The NRR staff found that the licensing basis of the RPV head strongback and the dryer/separator strongback was reasonably well defined in the CPS Updated Safety Analysis Report (USAR). The USAR defines specific component failures that the strongbacks are designed to withstand and associated qualitative acceptance criteria. The USAR also describes safety factors applied in evaluating the design of the strongbacks. The licensing basis with respect to interfacing lift points is minimal because the USAR does not address the design of the lift points and the NRC staff did not review the design of the lift points. The licensing basis of the special lifting devices, as documented in the USAR, complies with NRC regulations and provides reasonable assurance of protection of public health and safety with respect to the safe handling of heavy loads at the Clinton Power Station.
Principal Contributor: Steven R. Jones Date: