ML20067B709
| ML20067B709 | |
| Person / Time | |
|---|---|
| Site: | 05000605 |
| Issue date: | 02/05/1991 |
| From: | Dua S GENERAL ELECTRIC CO. |
| To: | Chris Miller NRC, NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| EEN-9109, MFN-011-91, MFN-11-91, NUDOCS 9102110001 | |
| Download: ML20067B709 (3) | |
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GE Nuclear Energy
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vs cunn. m u e a ms February 5,1991 MFN No.01191 Docket No. STN 50 605 -
EEN.9109 l
Document Control Desk U.S. Nuclear Regulatory Commission i
Washington, D.C. 205$5 Attention:
Charles L. Miller, Director i
Standardization and Non Power Reactor Project Directorate l
Subject:
GE-Response to Discussion Item 1 of January 1,1991 GE/NRC Conference Call Pertaining to Seismic Review Portion of AllWR SSAR Enclosed are thirty four-(34) copies of the GE response to Discussion item 1 (The Impact of i
Changes in the Seismic flazard Function on the ABWR Seismic Screening Procedure) of the-subject conference call, it is intended that GE will amend the SSAR, where appropriate, with this response in a future -
[
amendment.
Sincerely, add tot m
- Si am S. Dua, Acting Manager latory and Analysis Services
. M C 382, (408) 925 6948 '
F. A. Ross ]tiDOE) -
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D. C. Scalet (NRC).
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- V.M. McCree (NRC)
D. R. Wilkins - (GE) -
J; F. Oultk (GE) '
)N mo2nox1 9102
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Jhe Impact of Changes in the Seismic Hazard Function on the ABWR Seismic Screening-Procedure In~ performing.the AWBR seirmic PRA, the procedure started with the consideration of seismic.nitiated accident sequences, and the construction of accident event trees.
A preliminary screening analysis indicated that-the dominant accident sequences as a result of the earthquake would all be sequences initiated by the loss of offsite
-power, and that other sequences.(sequences where offsite power was not lost) would be relatively-insignificant.
One reason for this is that the. fragility of ceramic insulators in the switchyard-is very much lowoc than the fragility of other components and structures.
The next consideration in the screening process was the effect-of
- structural failures with the conservative assumption that structural
-failure would be sufficiently complete to render inoperative all equipment within the structure.
Therefore, structural failure was taken_to result directly in core damage.
As'a result of the two considerations above, it was found that in cases where there is no structural failure and offsite power is not lost, the Efrequency of core-damaging accidents is negligible.
Since all cases of
- structural: failure result directly in core damage, the only remaining accident sequences to be analyzed are for cases ofino structural
' failure,.but with loss of offsite power.
(Increases in1the magnitude of the seismic hazard function would rosult in a' higher probabillty of core damage due to building failure, but would not affect the above screening rationale.)
LWhen there is no structural failure, but offsite power is lost because of the seismic event, the most important concern is whether or not emergencympower and service water are available, since the loss of either support function presents the most serious challenge to the 4
plant.1 Thus, it is important to evaluate accident' sequences involving those losses.
The vital safety. equipment involved-in these accident sequences' includes the ACJand DC emergency power systems, service' water systems,_RCIC, RHR,_and'AC-independent water makeup.
All_of these
- systems require treatment in the seismic analysis of these accident
-sequences.
If:neither. emergency power or service water are lost, there are still
- potentially significant accident sequences involving other functions -
and' equipment.
The first concern is whether-or not there is a successful scram or alternate rod insertion.
The RPS, CRD, and'ARI systems are-all involved in-successful scram, but these systems need-notLbe analyzed if the failure of the control rods to insert is dominated'by the relatively low seismic fragility of the fuel assemblies and control rod guide tubes.and housings.
If it is not possibic_to insert control rods, SLC can be used to effect shutdown.
Failure of the;SLC system is dominated by failure of the pumps and boron supply tank.
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Given successful-scram with emergency power and service water available, the remaining vital functions-needed to prevent core damage are the maintenance of the inventory of water in the reactor and the removal of decay heat from the reactor and containment.
The additional Lsystems required to perform these functions are the HPCF, ADS, and
'LPFL.
(Changes in the shape or magnitude of the seismic hazard function should not affect any of the above screening criteria.)
The systems that need to be included in the seismic analysis are the emergency power systems, the service water systems, RCIC, RHR, firewater,-SLC, HPCF, and LPFL.
Additionally, consideration of seismic effects must be given to structures, reactor depressurization, and alternate means of injecting boron.
Within~the systems and functions identified for inclusion in the seismic analysis, the components selected for inclusion are those components that perform an active safety function and whose operation could be affected by an_ earthquake.
Passive components also included in the analysis are pipes, ducts, electrical buses, cable trays, heat exchangers, tanks, and battery racks.
~(Since-all vital components within the screened systems were included in the analysis,. increases in the magnitude of the seismic hazard function would not affect the selection of components to be analyzed.)-
1 Systems and equipment which require offsite power, such as feedwater and condensate systems, are not modeled since offsite power is assumed to-not be available.
RPS, ARI, RPT, and CRD are not modeled since failure of control rods to insert is-caused predominantly by changes in core geometry ~due to the earthquake.
All other important systems are L
included in the analysis.
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