ML20058F899

Forwards GE Position That Isolation Condenser Testing Not Needed for Std BWR Certification

ML20058F899
Person / Time
Site:	05200004
Issue date:	11/30/1993
From:	Leatherman J GENERAL ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
References
MFN-216-93, NUDOCS 9312090039
Download: ML20058F899 (5)

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GE Nuclear Energy o .

1 Genew necmc cwwy 175 canner Avenue, San J=,e. r4 9512$

November 30,1993 '

MFN No. 216-93 i Docket STN 52-004  ;

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Document Control Desk i U.S. Nuclear Regulatory Commission -l Washington DC 20555 >

Attention: Jerry N. Wilson, Director Standardization Project Directorate l

Subject:

GE Nuclear Energy Position that Isolation Condenser Testing is not f needed for SBWR Certification l At the request of the USNRC Staff, we hereby submit the GE Nuclear Energy position  :

that Isolation Condenser Testing is not needed for SBWR Certification.

Sincerely,

_' n~

J. E. Ixatherman SBWR Certification Manager MC-781, (408)925-2023 .

cc: M. Malloy, Project Manager (NRC) (2 attachments) .

F. W. Ilasselberg, Project Manager (NRC) (1 attachment) l l

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- MFN No. 216-93 i GE NUCLEAR ENERGY l

. POSITION TIIAT ISOLATION CONDENSER TESTING IS NOT NEEDED FOR SBWR CERTIFICATION j i

It is the position of GE Nuclear Energy that testing of the Isolation Condenser (IC)is not required for certification of the SBWR. The following discussion documents the i basis for this position.

In the SBWR, the IC System (ICS) is designated as a Safety Related system, but only  ;

because it forms part of the primary system pressure boundary and, hence, is required to be Safety Related. The ICS is not an Engineered Safety Feature (ESF) that is required  ;

to operate to tridgate the consequences of an accident. Its function is to maintain i sufficient coolant in the reactor vessel, following an isolation event, without feedwater  :

availability from nr.nnal sources, to prevent actuation of the Automatic Depressurization System (ADS) and subsequent cooling of the reactor by the Gravity Drain Cooling j System (GDCS) and Passive Containment Cooling System (PCCS). The (ADS), GDCS, and PCCS are Engineered Safety Features.  !

The SBWR can be cooled successfully, including appropriate accounting for single  ;

failures, without the ICS. No credit is taken for accident mitigation by the ICS in the  ;

SSAR. Ilowever, the ICS does mitigate the consequences of several postulated accident scenarios without challenge to the ESF Emergency Core Cooling Systems.

The requirements 10 CFR 52.47(b)(2)(i)(A) require that: 4 (1) The performance of each safety feature of the design has been demonstrated through either analysis, appropriate test programs, experience, or a combination

- thereof; (2) Interdependent effects among the safety features of the design have been found I acceptable by analysis, appropriate test programs, experience, or a combination thereof; and i

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(3) Sufficient data exist on the safety features of the design to assess the analytical  ;

tools used for safety analysis over a sufficient range of operating conditions,  !

transient conditions, and specified accident sequences, including equilibrium core f conditions.

l As noted in the previous paragraph, the ICS is not an ESF so the above requirements do f

NOT apply. This statement notwithstanding, GENE believes that the ICS meets the i i

above requirements, as detailed below: I i

(1) Isolation condensers have been used in early BWR designs (BWR1's,2's, and 3's)  !

I and most continue in operation today after nearly 25 years and over 150 combined plant operating years of service. While the details of the heat l t

exchanger design for the SBWR differ from those in current plants, the system i design is substantially the same. This experience constitutes a sufficient data base l

to meet the requirements of(1). s (2) In those scenarios in which the ICS comes into operation, no other systems are in use and, therefore, system interactions are not an issue. (See responses to RAI .

1 SRXB.30.) Since the system designs are similar in the SBWR and the operating  !

plants having ICs, the operating plant ICs perform under the same general l conditions and for the same scenarios as will occur in the SBWR, No report of a. +

system interaction effect on operating plant performance has been received by  ;

1 GENE. Thus, again, it is the GENE position that the operating plant data base is 3

,. sufficient to meet requirements (2) and (3).

-l (3) Isolation condenser performance has been predicted with the TRACG computer program which GENE is using to predict overall SBWR plant performance.

) TRACG has been qualified over a wide range of reactor conditions, including temperatures and pressures where the ICs are expected to operate. The TRACG analyses add to the confidence that the ICS will perform as expected and reinforce the GENE position that the requirements of (1), (2) and (3) have been met.

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i The design of the heat exchanger is not specified in the SSAR. Only the design requirements of the unit are given. A requirement for hardware testing is not appropriate under the certification program. Since the SBWR-specific hardware design differs from that currently in use, GENE does believe that testing before application of a specific heat exchanger design in a plant should be planned. Testing of prototype hardware, from both a heat transfer and mechanical and structural adequacy standpoint,

is planned prior to commercialization of the SBWR design.  ;

For any SBWR constructed,: t .cformance will be demonstrated. Overall testing of the heat rejection capability of the ICs is planned as part of the startup test program. No j SBWR plant will be licensed to operate until tests confirm that each IC meets the performance requirement.

With regard to the structural adequacy, it is noted that only one tube rupture has occurred in GENE's operating BWR fleet. That failure was the delayed result of an er.rlier salt water intrusion causing Intergranular Stress Corrosa. ' Cracking (IGSCC).  ;

Otherwise, the ICS has proven itself as a reliable reactor decay heat removal system. ,

Operating plant critical path unavailability caused by the ICS has been 0.5%, the major j part of which was due to problems with sensitized stainiess steel piping at one plant. Of 1

the total plant critical path unavailability, piping contributed almost 0.4%, with 0.1% l attributable to other causes. This reliability informatio" is based on the results of a I search of two data bases that contain IC data. The searches were for operating BWR 1

data relating to failures of IC systems and components.

Finally, the following design improvements have been incorporated in the SBWR ICS design to further reduce the plant critical unavailability due to the ICS:

(a) Use of carbon steel supply piping,Inconel tubing with butt-welded end attachments, and low-carbon or nuclear grade stainless steel condensate return piping which is resistant to IGSCC.

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(b) The condensate return lines are continuously sloped downward from the IC to an 1

elevation below reactor water level to avoid the trapping and collapse of steam in the drain piping.

(c) The water quality of the makeup to the IC pools is such that pool boil-off to l atmosphere and the surroundings should not require cleanup. -

(d) Three IC loops are provided. One loop will allow reactor operation at 80% of full j nower and two or more loops will allow reactor operation at 100% or higher  !

,. .ser. This enables plant availability goals to be met should problems develop with IC valve open/close cycling during periodic operational readiness testing during reactor power operation. .j 4

For the above reasons it is the position of GE Nuclear Energy that testing of the IC is  !

not required for certification of the SBWR.

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