ML17252A627
| ML17252A627 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 08/23/1990 |
| From: | Siegel B Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17202U798 | List: |
| References | |
| TASK-03-07.B, TASK-3-7.B, TASK-RR NUDOCS 9008280362 | |
| Download: ML17252A627 (6) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION INTEGRATED PLANT SAFETY ASSESSMENT REPORT (IPSAR)
SECTION 4.10 DESIGN CODES, DESIGN CRITERIA, AND LOAD COMBINATIONS.
1.0 INTRODUCTION
DRESDEN UNIT 2 DOCKET NO. 50-237 Current design criteria for nuclear power plant structures contain r'equirements that were not in effect when older plants were designed and licensed *.
Consequently, one aspect (designated Topic llI-7.B) of the implementation of NRC's Systematic Evaluation Program (SEP) required licensees to review changes that have occurred in structural design criteria since their plant was built
- and also to review the loads and load combinations used for plant structures.by comparing them with the loads and load combinations now specified for current construction. The licensee for Dresden 2, Commonwealth Edison Company {CECo),
was requested to assess the impact that these changes may have on margins*of safety for Dresden 2 structures as they were ori gi na l ly perceived and as they would be perceived under current criteria.
By letter dated August *2.,* 1982 (Reference 1) CECo provided information.*
regarding the applicability of the identified code changes to the Dresden 2 plant and an assessment of the as-built safety margins. Although the NRC staff reviewed CECo's assessment the findings were not *reported in Section 4.10 of the Integrated Plant Safety Assessment Report (IPSAR) for Dresden 2, NUREG-0823, February 1983 (Reference 2).
The staff, with assistance from*the Franklin Research Center (FRC), further
~eviewed the design code changes and more specific load combination issues for
'Dresden 2.
CECo responded to NRC/FRC requests in a letter dated July 11,
'1984 (Reference 3)~ FRC issued a Technical Evaluation Report (TER-C5506-425) dated June 3, 1986, that summarized the findings and the unresolved issues for Dresde.n 2 (Reference 4).
CECo subsequently responded to these concerns in a letter dated.August 30~ 1989 (Reference 5).
Th~ ~taff has reviewed all infor-mation provided to date on the outstanding issues concerning design codes, design criteria, loads and load combinations for Dresden 2. This Safety
- Evaluation Report resol~es and close~ all the remaining issues.
2.0. DISCUSSION In a letter dated August 2, 1982 (Reference 1), CECo provided the following information related to Dresden 2.
~*-
A list of ~tructural elements examined as a result of changes in design codes and criterion to assess the safety margins, with conunents by Sargent and Lundy engineers.
- b.
A comparison of loading combination criteria for various major structures including the reactor building, spent fuel pool, intake and discharge structure, and diesel generator portions of the turbine building. The tables of comparison were prepared by the Franklin Research Center in TER-C5257-321 and there are conunents by Sargent and Lundy engineers.
- c.
A. summary of results from the draft report (dated May 14, 1982) by NCT Engineering which reviewed the structural integrity of the drywell containment when subjected to the combination of dead weight, SSE seismic loads, accident and temperature due to LOCA, and main steam _line break, with comments by Sargent and Lundy engineers.
In *a letter dated July 11, 1984, (Reference 3) CECo responded to NRC *requests based on ~he FRC draft Te~hnical Evaluation Report (TER-C5506-425) dated November 15, 1983 *.
The response included discussions in the following areas:
- 1. Reassessment Activities
- 2.
AISC Code Requirements
- 3.
ACI Code Requirements
- 4.
ASME Code Requirements
- 5.
Load and Load Combinations (Draft TER~C5506-425, Section 5.2)
- Based on the review of the information provided by CECo, the staff concurred with FRC's findings addressed :in the final supplementary report, "Review of
- Licensee Responses to SEP Topic III-7.B. Design Codes, Design Criteria, and.
Loading Combinations," TER-C5506-425, dated June 3, 1986 (Reference 4). This report identified several issues that required additional information from
.CECo that were requested by the staff in a letter dated July' 26, 1989.
In a letter dated Au~ust 30, 1989, CECo submitted a report that resppnded.to the staff's request for additional information concerning the unresolved issues
- addressed in th_e 1986 Technical Evaluation Report by the FRC.
This response (Reference 5) which addressed all the remaining issues, permitted the staff to complete its, review and to close SEP Topic IIl-7~8 for Dresden 2.
3.0 EVALUATION The staff concurs with its consultant's findings stated in FRC's final.
supplementary report TER-C5506-425 dated June 3, 1986 (Reference 4).
Form sheets summarizing the review findings concerning technical aspects.of the implementation of SEP Topic 111-7.B and impact of design code changes have been provided in FRC's Report.
CECo's previous submittals (References 1 and 3) were
- revi.ewed and based on the assurances provided therein, many of the issues of concern relating to SEP Topic III-7.B.were considered resolved.
However, the submittals did not provide sufficient info~mation to fully resolve all issues.
The issues still remaining open were:
- a.
Code changes:
AISC 1.5.1.2.2 - Coped beam connections AISC il.15.7 - Walls subject to punching shear {SEP load combinations)
- ACI. 7.10.3 - Column splices where stress.reversal may occur AC! Appendix A - Transient thermal loads
'AC! Appendix B ~ Design of Embedments *
- b.. Loads and Load Combinations:
Accident load cases requiring simultaneous cons1.deration of SSE and LOCA Extre.me *environmental snow loads on roof On August 30, 1989, CECo, in response to the staff's request for additional information, responded to the above open issues by submitting a report entitJed, "SEP Topic I II-7.B Response to Nuclear Regulatory Commis_sion/FrankHn Research Center Requests of TER-C5506-425 dated June 3, 1986," with attached drawings.
The licensee's responses co~cerning the open* iSs*ues are evaluated as follows:
- a.
Code Changes (1)
{2)
(3)
Coae Beams - In t.he Dresden Drywell Steel Evaluation* for Units *2 an 3, a* total of 1341 connections were assessed. Of this total, 25
.required modification to bring them within FSAR allowables and have been installed. Of these 25 connections only a very small percentage required modification~ based on AISC 1980 Section 1.5.1.2.2 cope.
criteria. Considering that the design criteria including the analysis,methods used to define the loads are conservative,,the few discrepancies identified ~re judged as acceptable. Therefore, the requirements of AISC 1980 Section 1.5.1.2.2 are considered satisfied.
Walls Subject to Punching Shear - During the course of review ~f additional loading imposed on various structures, a punching shear*
- check had been performed for the vast majority of the loads considered as part of the review of structural integrity. Further-*
more, the loads to be checked for punching shear were commonly applied to the wall through an expansion anchor plate or through a concrete embedment.
In the vast majority of cases, the attachment plate would be the critical design item and the punching shear check would not control the.design. Since the design codes and design criteria are generally conservative, the few cases of discrepancy.are considered as acceptable. Therefore, the provisions *of ACI 349-76 Section 11.15.7 are satisfied.
Embedment Plates - The scope of several reassessment programs for embedment plates was quite extensive. These assessment programs involved approximately 1000 baseplates, 2000 pipe supports, 150 pieces of equipment, 1100 embedments and 1857 attachments. The
,*, number Df items requiring modification to remain within FSAR require-ments were small in comparison with the number of embedded items considered. Since the design codes and criteria are basically conservative, the few cases of inconsistency are judged as acceptable-.
Based on the, results of these programs and the results of other ongoing work at the Dresden Station, the requirements of ACI 349-76 Appendix B are considered as satisfied.
(4)
Adequacy of Spliced Reinforced Columns - The staff's concern is the capacity of columns to resist stress reversals during a,strong earthquake or severe wind. loadings. The licensee contends that since the vertical seismic acceleration is small and since lateral loads ar~ carried by the shear wa 11 system, the possible stress reversa 1 in the colu,mn should not occur.
In addition, tensile splice capacity is not required for overall structural stability since all lateral loads, are carried* by the shear wall system. Forty-eight column splices in the Dresden Unit 2 Reactor Building had been evaluated using the requirements of the ACI 349-76 Code.* Only 3 of the 48 splices had interaction factors greater than 1 and less than 1.6. Potential overstresses of column splices are, therefore, considered as of secondary importance. Considering that the design criteria, including the analysis methods used to define the loads, are conser-vative, the few discrepancies identified are judged to be acceptable.
(5)
Adequacy of'Concrete Regions Subject to Accident Temperatures and Thermal Transients - The staff is concerned about the potential effects of* accident conditions and the thermal transients associated with them.
The design basis accident temperature for Dresden is approximately 350°F.
Two fires occurred at Dresden Unit 3 on January 20, 1986 and on June 4, i988. A temperature of 450°F was recorded during the first fire.
An evaluation of the effects of each fire on the structure was performed by CECo and no detrimental effects to the integrity of the Dresden structure was demonstrated.
The high temperature and transient nature of these two fires.were similar to thermal loadings during accident conditions. Therefore, the staff has concluded that the structure can withstand thermal stresses from accident events.
- b.
Loads and,Load Combinations (1) Extreme Environmental Snow Load - The Reactor B~ilding, Turbine Building, and Crib House roof parapets ~t Dresden have been modified to reduce the amount of water that.can be retained on the roof. The attached drawings to the response submittal (Reference 5) show the roof details and parapet modifications.
Summer probable maximum precipitation has been considered in design.
Based on the review of this information the staff concludes that the modification is acceptable.
(2) *'
- The Dresden Updated FSAR, Section
- 12.1.2.3,.contains the required loading combination for Class 1
- structures. The primary containment. (including penetrations) is designed for simultaneous SSE and LOCA, including LOCA pressure and LOCA thermal load~ *. ThiS load combination is in compliance with the staff positton and i~, therefore; acceptable.
Du~in~ the cotirse of review.of *various loading conditions the staff has looked
- .. i.nto the cases that involved--wind lOads*. Specifically, the pipe reaction loads
... ~nd therma 1 1 oa~s *were cons ide.red. in ~combination with wind loads.(including
'tornadoes a_nd tornado. missiles) under Topic III-7.B. This load combination is acceptab.le because it provides reasonable assurance *that structural integrity is* maintained and that the structure.me~ts the *interrt of current _design criteria.
It th~refore form~ the basis of:acteptance of SEP Topic III-2, Wind and Tornado.
Loadings. See SER tri*IPSAR, Section 4.3. Wind and To~nado Loadings for Dresden*2
. *(Ref ere nee
- 6) *.
~.-.
. ** 4.a* CO.NCLUSION
- As-discussed ab~v~, the remaining unresolved *i~sues ~ere mainly due tb incom-.
plete responses to previous staff requests for additional information and clarification.
- S~nte th~n, full ~~sponses and clarifications have be~n pro-vided and.all open..issues*have been adequately addressed.
Ba_sed on the results o~.revi~w, '.the staff finds tha~CECots explanation jnd clarification of load
. and load combinations a.re acceptable, and, therefore,';Con*siders that all, issues associat~.d with'.SEP Topic IU~7.B,ar~'resolv.ed *. :....
.~..
Principal' Reviewer:. Sa i Chan pat.ed::~* *:,August 23,.1990
'~..
- 1.
- 2.
- 3.
References Letter from Rausch (CECo) to O'Connor (NRC),
Subject:
Dresden 2 SEP*
Topic:
III-7.B, Design Codes, Design Criteria, and Loading Combinations, dated August 2, 1982.
NUREG-0823, "Integrated Plant Safety Assessment, Systematic Evaluation Program, Dresden Nuclear Power Station, Unit 2 11 Final Report, U.S. NRC February 1983..
Letter from Rybak ( CECo) to Gilbert (NRC),
Subject:
Dresden Station Unit 2, Systematic Evalu.ation Program, IPSAR Section 4.10, Topic III-7.B, Design Codes, Design Criteria, and Load Combinations, dated July 11, 1984.
4 *. *Franklin Research Center, Technical Evaluation Report (TER~C5506-425),
."Final Supplementary Report, Review of Licensee Responses to SEP Topic III-7.B, Design Codes, Design Criteria and Loading C~mbinations. Dresden Nuclear Power Station Unit 2, 11 June 3, 1986.
- 5.
Letter from Silady (CECo) to Murley (NRC), transmitting a report entitled, "SEP Topic III-7.B Response to Nuclear Regulatory Coll'lllission/Franklin Research Center Requests of TER-C5506~425 dated June 3, 1986, 11 dated August 30, 1989.
- 6 *.
- Memorandum from Bagchi (NRC) to Craig (NRC),
Subject:
Integrated Plant Safety Assessment Report (IPSAR), NUREG-0823, Sections 4.3, Wind and.
Tornado Loadings, and 4.5 Tornado. Missiles - Dresden Unit.2 (TAC 49363)
(enc 1 os i ng SER}, dated September* 13, 1989.
. *.