ML19344D480
| ML19344D480 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 03/04/1980 |
| From: | Groce R Maine Yankee |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19344D481 | List: |
| References | |
| WMY-80-41, NUDOCS 8003120463 | |
| Download: ML19344D480 (4) | |
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%.y e B.3 2.1 WMY 80-41 March 4,1980 United States Nuclear Regulatory Commission Washington, D.C.
20555 Attention: Office of Nuclear Reactor Regulation
References:
License No. DPR-36 (Docket No. 50-309).
(a)
(b) " Summary of Meeting with MYAPC on October 18 to Discuss Their Asymmetric LOCA Loads Evaluation in Bethesda, Maryland" from S. B. Hosford to L. S. Shao.
(c) MYAPC Letter to USNRC, WMY 79-107, dated 9/27/79.
(d) MYAPC Letter to USNRC, WMY 80-1, dated 1/7/80.
(e) USNRC Letter to PWR Licensees dated 1/25/78.
Subject:
Resolution of Asymmetric LOCA Loads
Dear Sir:
On February 7,1980 the NRC staf f and EG&G Idaho met with technical staff members of Yankee Atomic Electric Company Nuclear Services Division to discuss As the resolution of the Asymmetric LOCA Load Issue at Maine Yankee.
requested at that meeting and subsequently reiterated via telecon (February 12, 1980), this letter is written to outline Maine Yankee's current status regarding evaluation of asymmetric LOCA loads.
in the Maine Yankee. is the first operating Combustion Engineering plant United States to have installed retrofit pipe rupture restraints specifically designed to limit pipe break blowdown area and thereby greatly diminish maximum asymmetric loads on the primary support system due to a hypothetical Loss of Coolant Accident (LOCA).
Taking credit for the load reduction af forded by pipe rupture restraints, Maine Yankee has quantitatively characterized maximum loadings on affected Safety Class I components, supports and structures.
In direct combination with normal operating and previously considered transient loadings, maximum stresses due to asymmetric LOCA, including thrust load, are within original, conservative FSAR design limits. Therefore, the structural integrity of the reactor coolant system (RCS), supports and associated structures is not compromised due to additional asymmetric loads imposed by a hypothetical LOCA, and the original plant licensing bases are not violated.
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March 4,1980
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U.S. Nucloor R3gulctory Commission Pcgs 2 4
Attention Office of Nuclear Reactor Rsgulation W
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Pipe Rupture Restraints As noted in References (b) and (c), Maine Yankee elected to install pipe i l rupture restraints to limit the pipe break area resulting from a hypothet caMai rupture of reactor coolant system piping.that given an extensive, ex d the j
elastic / plastic, detailed dynamic analysis, eventual system adequacy an LOCA-mitigating ability of the RCS and ECCS could ultimately be shown withou However, this approach was not considered cost effective, added restraints.
nor could it have been~ completed in the required time frame.
l Pipe rupture restraints have been installed at each of six nozzle locations, outside the primary shield wall surrounding the reactor pressure The vessel and inside piping penetrations through the prima In conjunction with pipe motion axial direction of the ruptured pipe.
supports, tc'st blowdown areas restraint afforded by existing component designs are approximately equal to those of currently licensed plant (Reactor c Maine Yankee were originally designed to withstand LOCA thrust loads together achieved.
with normal operating and SSE seismic loads, maintaining elastic stress level s).
The pipe rupture restraints are designed to accommodate dynamic loads applied through a gapped interface while maintaining elastic stress levers.
Therefore, during normal operating conditions and transients other than pipe i
rupture, there is no effect on reactor coolant system riping due to restra nt Design loads transmitted through the pipe rupture restraints into existing subcompartment walls were quantified and the integrity of installation.
existing structures was analytically assured.
Potential adverse effects on existing concrete walls due to the f
restraints' becoming a thermal conduction path, and loss of ability to per orm inservice inspection due to pipe rupture restraint installation wereThe thermal-identified as critical design constraints.
The pipe rupture restraint such that concrete overheating will not occur.
design has been reviewed by the Yankee Atomic Electric Company ISIinsta Pipe rupture restraint Coordinator.
the ability to perform inservice inspection.
Structural Eva1uation Report A preliminary draf t of " Evaluation of LOCA-Related Loadings on the Reactor Coolant System Components, Supports and Piping at Maine Yankee",
Enclosure (A), is provided for your information in order to assist inThis ve expediting review of the final report.
contains detailed descriptions of methodologies and analytical models used to define components cf the asymmetric LOCA loads and their application to structural model for subsequent analysis.
for assessing the effects of total applied loads are described for each reactor coolant system component support and for ECCS and branch piping..
Detailed analyses are undergoing internal review in accordance with Yankee Atomic Electric Company Operational Quality Assurance procedures, and However, results of analyses are therefore are not presented at this time.
e 4
March 4,1980 4
U.S. Nuclear. Regulatory Commission Page 3 4
Attention Office of Nuclear Reactor Regulation f
i available to the extent that applied loading and resulting sa ety marg nTherefore, 1
magnitudes are qualitatively assessed.
l integrity..
a high degree of confidence is used in concluding structura Evaluation As previously discussed, (Reference (b) and (d)), original design f applicability to analysis methods and results, together with determination o i l Maine Yankee of results' obtained for similar plants s i
This basis for concluding system structural adequacy at Maine Yankee.
l additional approach was successfully utilized to determine that sm li from i
postulated breaks outside the primary shield wall do not comprom sestructura components', supports' or subcompartment wall s'
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definition for reactor coolant system components a i
accomplished using more detailed analytical investigations.
Classical thermal hydraulic and structural analysis techniques were t reaction employed to conservatively predict upper bound RCS c Analytical models ana analysis cethodology, described in t
Enclosure (A), have been presented to the NRC staf f and EG&G Idaho at a loops.
site.
meeting held at the Maine Yankee plantdynamic analyses indic 3
ithin original operating, maximum seismic and total asymmetric LOCA loads i
f pipe rupture restraints as well as an indication of the high degree o FSAR limits.
i Further, reactor conservatism employed in the original design analyses. inter l
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There is no detailed dynamic structural analyses performed for Maine Yankee.
j lting increase in reactor pressure vessel displacements reintive to those res l.
from original design LOCA loads.
lies due to reactor to ECCS and RCS branch piping; and control elem2nt assemb i
motion is unchanged.
l Conclusion Maine Yankee has evaluated the consequences of a hypothetical reacto the coolant pipe rupture as requested in Reference (e).
Based upon
' calculations and studies performed, Maine Yankee concludes that-
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t no loss in structural integrity of essential components and suppor s due to the accident considered is anticipated, 1.-
f the the ability of safety systems to mitigate the consequences oFSAR accident under consideration as defined in the Maine Yank 2.
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remains unchanged.
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March 4,1980.
U.S.. Nuclear Rzgulatory Commission Page 4 Attention Office of Nuclear Reactor Regulation l demonstrated Maine Yankee concludes that plant safety has been adequate yily resolved.
if and considers the issues identified in Reference (e) sat s i letter, please feel free to call.
Very truly yours, MAINE YANKEE ATOMIC POWER COMPANY h
Robert H.'Groce Senior Engineer - Licensing AVR/kaf d
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