ML20196E313
| ML20196E313 | |
| Person / Time | |
|---|---|
| Site: | Paducah Gaseous Diffusion Plant |
| Issue date: | 11/25/1998 |
| From: | Toelle S UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | Paperiello C NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| GDP-98-0198, GDP-98-198, NUDOCS 9812030117 | |
| Download: ML20196E313 (11) | |
Text
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J o USEC A Global Energy Company November 25,1998 GDP 98-0198 Dr. Carl J. Paperiello Director, Office of Nuclear Material Safety and Safeguards Attention: Document Control Desk United States Nuclear Regulatory Commission Washington, D.C. 20555-0001 Paducah Gaseous Diffusion Plant I
Docket No 70-7001 Notification of Changes in Regulatory Commitments - Compliance Plan Issue 36 - Seismic Upgrades to Buildings C-331 and C-335
Dear Dr. Paperiello:
The purpose of this letter is to notify the Nuclear Regulatory Commission (NRC) of changes to two regulatory commitments regarding the construction sequence for performing the seismic upgrades to Buildings C-331 and C-335 that are required by Issue 36 of DOE /ORO-2026, " Plan for Achieving Compliance with NRC Regulations at the Paducah Gaseous Diffusion. Plant," (the Compliance Plan).
The specifics of the commitment changes are provided in Enclosure 1.
As described in Enclosure 1, the physical constmetion activities to complete the seismic upgrades are proving to be more difficult than originally anticipated and are proceeding slower than originally planned. The delays are due, in part, to several of the restrictions that were imposed on the construction activities in order to resolve one of the originally identified unreviewed safety questions associated with the project. The constmetion sequence changes described in Enclosure 1 will reduce I
i unnecessary conservatisms associated with these restrictions so as to facilitate the construction I
activities and improve schedule progress during the latter phases of steel removal and replacement.
Should you have any questions related to this subject, please contact Steve Routh at (301) 564-3251.
/Y The revised construction sequence commitments are identified in Enclosure 2.
1 Sincerely, S.D. M h.D Steven A. Toelle Nuclear Resmlatory Assurance and Policy Manager 9812030117 981125 PDR ADOCK 07007001 yo., swuucuge drive, Bethesda, MD 208i7 i818 93C009 Teierhone 3oi.364 3200 rax 30i s64 320i http://
uscc.com OfBces in Uvermore CA Paducah, KY Portsmouth, OH Washington, DC
[' '
Dr. Carl J. Paperiello November 25,1998 GDP 98-0198, Page 2 L
Enclosures:
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Buildings C-331 and C-335 Seismic Upgrades - Description of Changes in i
l Commitments l
2.
Commitments Contained in this Submittal l
cc:
Mr. Robert C. Pierson, NRC l
NRC Region III Office NRC Resident Inspector, PGDP NILC Resident Inspector, PORTS t
Mr. Randall M. DeVault, DOE i
I i
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f i
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GDP 98-0198 Page1of8 Buildings C-331 and C-335 Seismic Upgrades Description of Changes in Commitments
1.0 Background
In letters GDP 97-0062, dated April 23,1997, and GDP 97-0136, dated July 31,1997 (References 1 and 2, respectively), USEC identified three unreviewed safety questions (USQs) associated with performing the seismic upgrades to Buildings C-331 and C-335 as required by Issue 36 of DOE /OR-2026, " Plan for Achieving Compliance with NRC Regulations at the Paducah Gaseous Diffusion Plant,"(Compliance Plan). These USQs were subsequently reviewed and approved by the NRC in Amendment 15 to Certificate ofCompliance GDP-1 (Reference 3). One of the three USQs identified that the process ofinstalling the new structural steel in Buildings C-331 and C-335 may temporarily make the buildings and contained equipment more susceptible to seismically-induced failure as the existing structural frames are altered and/or replaced.
In a letter dated August 20,1997 (Reference 4), the NRC requested additional information regarding the subject USQ. In particular, the NRC asked:
"How will interferences encountered during steel installation be cleared? Will the interferences be " field relocated" or will engineering assistance always be required?
How will you assure that these relocations are reflected in the drawings?"
The NRC also requested that USEC:
"[p]rovide a description of the construction sequence to be used to install the structural modifications. Describe how this sequence minimizes the time that the structure is in a degraded state from what currently exists. How long will the structure be in a degraded condition from what currently exists?"
i USEC's response to the August 20,1997 request for additionalinformation was submitted to the NRC by letter GDP 97-0166, dated September 19,1997 (Reference 5). Commitments pertaining to the physical relocation ofinterferences and the construction sequence to be followed were identified in Enclosure 2 to GDP 97-0166. These commitments were referenced in the NRC's Certificate Evaluation Report issued in support of Amendment 15 to Certificate of Compliance GDP-1 (Reference 6).
As discussed in the following sections, the referenced commitments have been changed to facilitate the construction activities and to expedite the completion of the seismic upgrades to Buildings C-331 and C-335.
GDP 98-0198 Page 2 of 8 Buildings C-331 and C-335 Seismic Upgrades 1
Description of Changes in Commitments 2.0 Change in Commitment for Physical Relocation ofInterferences 2.1 Statement of Current Commitment f
The current commitment (from Enclosure 2, Item 13, ofletter GDP 97-0166) reads as follows:
i "The physical relocation of interferences is performed by PGDP maintenance personnel.
PGDP design engineering provides final approval of interference relocations.
If the steel installation is found to interfere with existing systems, structures, or components, the steel installation will be stopped and engineering assistance will be l
requested. Modifications to the plant will be documented in accordance with the existing design process."
l 2.2 Statement of Revised Commitment The revised commitment is as follows:
i "The physical relocation ofinterferences is performed by qualified personnel. PGDP design engineering provides final approval ofinterference relocations.
If the steel installation is found to interfere with existing systems, structures, or components, the steel installation will be stopped and engineering assistance will be requested. Modifications to the plant will be documented in accordance with the j
existing design process."
2.3 Justification for Revised Commitment In order to facilitate the relocation ofinterferences, qualified subcontractor personnel will be used in addition to qualified PGDP maintenance personnel. PGDP design engineering will continue to provide final approval of all interference relocations, and all interference relocations will be performed in accordance with the requirements of the USEC Quality Assurance Program Description.
USEC has reviewed this change in commitment in accordance with the requirements of 10 CFR 76 and has determined that prior NRC approval of the change is not required.
1 i
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GDP 98-0198 Page 3 of 8 Buildings C-331 and C-335 Seismic Upgrades Description of Changes in Commitments 3.0 Change in Commitment for Construction Sequence 3.1 Statement of Current Commitment The current commitment (from Enclosure 2, Item 1, ofletter GDP 97-0166) is as follows:
"The constmetion sequence presented in Letter GDP 97-0166 (Enclosure 1, Table 1) is for the building section bounded by Column Lines A,17, Mx, & 9x. The construction sequence is typical for all four of the small footprint building sections bounded by Column Lines A, 34, Mx, & 1. The construction sequence for the remainder of the large footprint building sections of the cell floor will follow a similar pattern, i.e., demolition of existing bracing in a single " story" of a bay followed by installation of structural elements having larger cross sections in the same bay. Each story of the bay will be worked sequentially until bracing installation is completed.
Work typically will begin in a centrally located bay with respect to the building section in plan and proceed outward towards the perimeter of the building section. The construction sequence for the ground floor will be conducted in a similar fashion.
A comparison of the planned demolition / erection schedule presented in Table I with the bracing layout shown for the cell floor in Drawing S5E-19484-A03, Revision 3, (provided to the NRC by Reference 2) shows that construction will occur one bay at a time. Demolition will only occur in a single bay between adjacent braced elevations, e.g., from elevation 405'-6" to elevation 417'-l1" (braced elevations are generalized approximations for purposes of this discussion), Erection of replacement steel will immediately follow demolition. The next higher set of bracing in the same bay will then be demolished and replaced. Simultaneous demolition in a bay from cell floor to building roof will not be permitted. Construction crews will commence work on the cell floor in the building section bounded by Column Lines A,9, Mx, & l.
Construction will progress clockwise around the building from section to section until the work is complete on the cell floor. The construction plan ensures that no more than three bays bounded by adjacent braced elevations are in a degraded configuration at the same time.
.After preparatory work is completed, existing bracing will be removed and the new bracing temporarily installed on the day shift Final welding and bolt-up will be completed on the night shift
GDP 98-0198 Page 4 of 8 i
Buildings C-331 and C-335 Seismic Upgrades Description of Changes in Commitments i
The ground floor installation will proceed in the same fashion as for the cell floor but commencement ofwork on the ground floor will not begin until work on the cell floor is complete. In addition, replacement of existing bracing on the ground floor will not commence until installation of new ground floor bracing is complete.
Construction will proceed from the center of the structure towards its perimeter so i
as not to aggravate torsional effects that may be induced by potential wind activity during construction.
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i 4
The intent is to follow this constmetion sequence. This sequence may be modified due to unanticipated field conditions which may delay the demolition or installation at a particular bay. This flexibility will be utilized to maximize the efliciency of the work force while minimizing the overall construction duration."
3.2 Statement of Revised Commitment l
The revised commitment is as follows:
" Steel installation may proceed on both the ground floor and the cell floor concurrently. Work on both floors will typically begin in a centrally located bay with respect to the building section in plan and proceed outward toward the perimeter of the building section.
In order to ensure that adequate structural capacity of the buildings is maintained, proposed construction sequences will be modeled using the GTSTRUDL structural analysis program:
Computer models of each building will be loaded statically with anticipated dead, live, and wind loadings. The wind loading used will be based on a wind speed of 70 mph. The acceptance criteria will be to show that member stresses do not exceed the allowables specified in the American Institute of Steel Construction (AISC) Manual of Steel Construction, 8th Edition.
The stiffness of the buildings as measured by the lateral load-deflection ratio of selected building model control points relative to the original as-found condition will also be evaluated. Prior to achievement of the structures'
" lateral stiffness threshold" (i.e., the point at which the lateral stiffness of the building is greater than or equal to that of the original as-found config-
GDP 98-0198 Page 5 of 8 Buildings C-331 and C-335 Seismic Upgrades Description of Changes in Commitments uration), no more than three bays will be demolished simultaneously and no steel will be removed from any ground floor location, although new steel may be added to ground floor locations which do not require steel removal. After achievement of the lateral stiffness threshold, any number of bays may be demolished simultaneously, provided the resultant structural configuration exhibits a lateral stiffness equal to, or greater than, that exhibited by the as-found structural configuration."
3.3 Justification for Revised Commitment Steel demolition and re-installation is currently underway. Experience during the initial stages of construction has revealed several problems with the current restrictions on the construction sequence:
The removal of existing steel and the subsequent installation of replacement steel in an individual bay cannot be accomplished in two shifts as originally estimated.
High temperatures with the risk of heat stress severely curtail the amount of time that heavy labor can be performed. In addition, demolition of the existing bracing and gusset plates without damaging the remaining structure is more diflicult than originally anticipated.
Also, the current construction restrictions require that work on the cell floor be completed before commencing work on the ground floor. This sequencing was based on the original schedule for fabricating the new steel braces. That schedule called for completing fabrication of the cell floor steel before beginning production of the ground floor steel. Subsequent changes in the fabrication and installation schedules have resulted in ground floor bracing being available for installation concurrently with cell floor bracing. There is no structural reason why installation of new steel on the ground floor in locations which do not require removal of existing steel could not begin at any time, as this will only serve to increase the stiffness of the buildings.
As noted in the NRC's Compliance Evaluation Report approving the original USQs (Reference 6):
"The installation sequence that one should employ is not clear-cut. One would like to minimize both the time that the structure is degraded and the amount of degradation since risk is directly proportional to these parameters. Installing the stmetural modifications, however, is a trade-off between minimizing the time that the structure is in a weakened state, both during construction and the total time that the structure is below its required capacity; and minimizing the degradation to the structure during construction."
GDP 98-0198 Page 6 of 8 Buildings C-331 and C-335 Seismic Upgrades Description of Changes in Commitments To minimize the time that each building is below its desired upgraded capacity, and also below its as-found capacity, the construction sequence has been revised as described below.
Steel installation will proceed on both the ground floor and the cell floor concurrently. Work on both floors will typically begin in a centrally located bay with respect to the building section in plan and j
proceed outward towards the perimeter of the building section.
During the initial stages of the construction process, existing steel cannot be removed without degrading the as-found structural capacity of the buildings. Although the vertical stiffness of the structure is essentially unchanged by the demolition and installation of cross-bracing, the as-found lateral stiffness of the structure can be reduced by the planned construction activities. To limit the degradation of the as-found lateral stiffness, the current construction sequence restrictions allow only i
three bays to be demolished simultaneously.
However, as the modification process proceeds with the installation of the upgraded cross-bracing, the lateral stiffness of the building will be continually increased. At some point during the construction process, a " lateral stiffness threshold" equivalent to the as-found configuration of the building (i.e., the configuration of the building as it existed before the start of the seismic upgrades) will be achieved.
In order to ensure that adequate structural capacity of the buildings is maintained, the impact of proposed construction sequences will be evaluated using the GTSTRUDL stmetural analysis program based on three-dimensional models of the subject building frames:
The building models will be loaded statically with anticipated dead, live, and wind loadings.
The wind loading used will be based on a 70 mph wind speed. The 70 mph wind speed is the current evaluation basis wind speed as described in SAR Section 4.6.2 and Reference 7. [A 70 mph wind speed has also been established as the evaluation basis wind speed for a 250-year return period event in Section 2.7.3 of the Safety Analysis Report Update (SARUP) submittal (Reference 8).] The acceptance criteria will be to show that member stresses do not exceed the allowables specified in the American Institute of Steel Construction (AISC)
Manual of Steel Construction, 8th Edition.
The stiffness of the buildings as measured by the lateral load-deflection ratio of selected building model control points relative to the original as-found condition will also be evaluated.
Prior to achievement of the stmetures' " lateral stiffness threshold" (i.e., the point at which the lateral stiffness of the building is greater than or equal to that of the original as-found configuration), no more than three bays will be demolished simultaneously and no steel will
GDP 98-0198 Page 7 of 8 Buildings C-331 and C-335 Seismic Upgrades Description of Changes in Commitments be removed from any ground floor location, although new steel may be added to ground floor locations which do not require steel removal. After achievement of the lateral stiffness threshold, any number of bays may be demolished simultaneously, provided the resultant i
stmetural configuration exhibits a lateral stiffness equal to, or greater than, that exhibited by l
the as-found structural configuration.
As described above, during the early phases of construction, the stmetural capacity of the buildings I
will be degraded from their as-found capacity for limited periods of time while some of the existing j
steelis removed and before the replacement steel is reinstalled. To minimize this time, every effort will be made to ensure that work at any location will not be interrupted from the time removal of the 4
~
existing steel begins until final welding and bolt-up of the replacement steel is completed, with the exception of shift turnover periods and any required evacuations for personnel safety. (For example, 1
in the case of CAAS LCOs being entered, constmction personnel are classified as essential personnel and will be allowed to return to their work area after receiving personal alarming dosimeters.) Until the " lateral stiffness threshold" described above is achieved, no more than three bays will be in a degraded configuration at the same time, and no steel will be removed from any ground floor location, although new steel may be added to ground floor locations which do not require steel removal. (Note that with three bays in a degraded condition, there is no adverse impact on the buildings' ability to withstand the evaluation basis wind speed of 70 mph.)
The revised commitment will allow construction to proceed at a more rapid pace that will also accelerate as the structural capacity of the buildings is improved due to the addition of new bracing.
It is anticipated that the total time that each building will experience less than as-found structural capacity will remain in the range of 30 to 90 days, in spite of the increased demolition and restoration time experienced at any given location. The GTSTRUDL computer model will be used to ensure that, as additional bays are demolished simultaneously, the buildings will continue to exhibit a lateral stiffness equal to or greater than the stiffness of the original as-found configuration. At the same time, USEC expects the accelerated schedule during the latter phase will allow for significant schedule recovery.
USEC has reviewed this change in commitment in accordance with the requirements of 10 CFR 76 and has determined that prior NRC approval of the change is not required.
J l
i Stiffness as used here means the lateral load-deflection ratio of building model control 8
points. The lateral stiffness threshold used here is the collective lateral stiffness that the subject stmeture exhibits in its as-found configuration. Control points typically will consist of model nodes experiencing maximum deflection when the as-found structural configuration is subjected to unit lateral loading.
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GDP 98-0198 Page 8 of 8 Buildings C-331 and C-335 Seismic Upgrades Description of Changes in Commitments References 1.
Letter from James H. Miller (USEC) to Dr. Carl J. Paperiello (NRC), " Certificate Amendment Request - Buildings C-331 and C-335 Seismic Upgrades," Letter No. GDP 97-0062, April 23,1997.
2.
Letter from Steven A. Toelle (USEC) to Dr. Carl Paperiello (NRC), " Certificate Amendment Request - Buildings C-331 and C-335 Seismic Upgrades," Paducah Gaseous Diffusion Plant, Letter No. GDP 97-0136, July 31,1997.
3.
Amendment 15 to Certificate of Compliance GDP-1, transmitted by letter from Carl J.
Paperiello (NRC) to Mr. James H. Miller (USEC), "Paducah Certificate Amendment Request
- Buildings C-331 and C-335 Seismic Upgrades (TAC NO. L32028)," March 20,1998.
4.
Letter from Robert C. Pierson (NRC) to Mr. James H. Miller (USEC), " Request for Additional Information Concerning Seismic Upgrade USQs (TAC No. L32028)," dated August 20,1997.
5.
Letter from James H. Miller (USEC) to Mr. Robert C. Pierson (NRC), " Response to NRC Request for Additional Information Concerning Seismic Upgrade USQs (TAC No. L32028),"
Paducah Gaseous Diffusion Plant, Letter No. GDP 97-0166, September 19,1997.
6.
Letter from Merri Horn (NRC) to Mr. James H. Miller (USEC), "Paducah Cenificate Amendment Request - Buildings C-331 and C-335 Seismic Upgrades (TAC No. L32028),"
dated December 8,1997.
7.
Letter from Robert C. Pierson (NRC) to Mr. Steven A. Toelle (USEC), November 20,1998.
8.
Letter from James H. Miller (USEC) to Dr. Carl J. Paperiello (NRC), " Certificate Amendment Request - Update the Application Safety Analysis Report," Paducah Gaseous Diffusion Plant, Letter No. GDP 97-0188, October 31,1997.
(
%, to GDP 98-0198 Page1 ofI Commitments Contained in this Submittal The following revised commitments conceming the seismic upgrades to Buildings C-331 and C-335 are contained in this submittal:
1.
The physical relocation ofinterferences is performed by qualified personnel. PGDP design engineering provides final approval ofinterference relocations.
If the steel installation is found to interfere with existing systems, structures, or components, the steelinstallation will be stopped and engineering assistance will be requested. Modifications to the plant will be documented in accordance with the existing design process.
2.
Steel installation may proceed on both the ground floor and the cell floor concurrently. Work on both floors will typically begin in a centrally located bay with respect to the building section in plan and proceed outward toward the perimeter of the building section.
In order to ensure that adequate structural capacity of the buildings is maintained, proposed construction sequences will be modeled using the GTSTRUDL structural analysis program:
Computer models of each building will be loaded statically with anticipated dead, live, and wind loadings. The wind loading used will be based on a wind speed of 70 mph. The acceptance criteria will be to show that member stresses do not exceed the allowables specified in the American Institute of Steel Construction (AISC) Manual of Steel Construction, 8th Edition.
The stiffness of the buildings as measured by the lateral load-deflection ratio of selected building model control points relative to the original as-found condition will also be evaluated. Prior to achievement of the structures'
" lateral stiffness threshold" (i.e., the point at which the lateral stiffness of the building is greater than or equal to that of the original as-found configuration), no more than three bays will be demolished simultaneously and no steel will be removed from any ground floor location, although new steel may be added to ground floor locations which do not require steel removal.
After achievement of the lateral stiffness threshold, any number of bays may be demolished simultaneously, provided the resultant stmetural configuration exhibits a lateral stiffness equal to, or greater than, that exhibited by the as-found structural configuration.
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