NSD-NRC-98-5624, Forwards W Response to RAI 640.185 Re Comments on Passive Containment Cooling Sys in Rev 3 of AP600 Certified Design Matl,As Requested in Ltr from Staff

Forwards W Response to RAI 640.185 Re Comments on Passive Containment Cooling Sys in Rev 3 of AP600 Certified Design Matl,As Requested in Ltr from Staff

ML20217D307
Person / Time
Site:	05200003
Issue date:	03/18/1998
From:	Mcintyre B WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:	Quay T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NSD-NRC-98-5624, NUDOCS 9803270374
Download: ML20217D307 (6)

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6 Wistinghouse Energy Systems gg,34, ,3 3 3 ,33 Electric Corporation DCP/NRC1304 NSD-NRC-98-5624 Docket No.: 52-003

- March 18,1998 Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION: T. R. QUAY

SUBJECT:

RESPONSES TO STAFF REQUESTS REGARDING TIIE AP600 INSPECTIONS, TESTS, ANALYSES, AND ACCEPTANCE CRITERIA (ITAAC)- PCS

Dear Mr. Quay:

Enclosed are three copies of Westinghouse's response to RAI 640.185 related to comments on the Passive Containment Cooling System (PCS)in Revision 3 of the AP600 Certified Design Material as requested in a letter from the staff dated March 6,1998.

This submittal closes, from Westinghouse's perspective, open item 6639. As a result, the Westinghouse status column will be changed to "Cor. firm W" in the Open item Tracking System (OITS). The NRC should review this response and inform Westinghouse of the status of the open item to be designated in the "NRC Status" column of the OITS.

Please contact Mr. Eugene J. Piplica at (412) 374-5310 if you have any questions concerning this transmittal.

A/ -

Ilrian A. McIntyre, Manager

' Advanced Plant Safety and Licensing jml Enclosures j cc: J. N. Wilson, NRC (1L. IE)

N. J. Liparuto, Westinghouse (w/o Enclosures)

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NRC FSER OPEN ITEM --

J Questior : 640.185 (OITS 6639)

Your response to RAI 640.168 requires clarification. You committed to add item 1.f to ITAAC 3.3,

" Buildings," in your revised response to RAI 640.140, dated December 19,1997 that will verify certain dimensions of the Nuclear Island. You also committed to add a different item 1.f to ITAAC 3.3 in you response to RAI 640.168, dated January 30,1998, to verify the above deck region of the AP600 containment volume. If both design Commitments are included in the AP600 ITAAC, they will satisfy a portion of the NRC staff's concern. However, ITAAC 3.3 does not verify the volumes and flow paths to the level of detail assumed in the Containment Evaluation Model (WCAP-14407, Section 4). Also, your response refers to " structures" and " major equipment," as important heat sinks within the containment, but it does not demonstrate thai the heat sinks identified in reference 640.168-1 are verified by ITAAC nor does it indicate what fraction of these heat sinks are verified by ITAAC. Because the design basis analyses for AP600 show little, or no, difference between the calculated pressure and the design pressure, it is important to demonstrate that the assumptions used in the design basis analyses are verified. Also, because the coatings below the operating deck are not safety-related, it is important to assure that the heat transfer characterization of these coatings are covered in the design basis analyses used to support design certification. Therefore:

(a) Identify the fraction of the heat sinks that are captured in your ITAAC. What is the minimum set necessary to assure that the assumptions in the design basis analyses that support design certification will not result in an unacceptable evaluation?

(b) Explain how the proposed ITAAC demonstrate that the heat transfer characterizations of the heat sinks are verified to a level of detail described in the AP600 Containment Evaluation Model.

(c) Provide an ITAAC that verifies the heat sinks, volumes, and flow paths to a level of detail described in WCAP-14407, Section 4.

Response

The purpose of ITAAC is to verify that the as-built facility conforms to the approved plant design and the regulations. The scope of the ITAAC is limited to, but must be consistent with, the systems, structures, and components (SSCs) that are in the certified design. However, the level of detail specified in the ITAAC should be commensurate with the safety significance of the functions and bases for that SSC. Where plant safety performance is dependent on the approved plant design features, e.g., the physical parameters of the plant, the ITAAC ensures that the fundamental integrity of the safety analyses used to demonstrate plant safety is preserved in the as-built facility referencing the design.

Westinghouse *s approach to meet regulatory requirements for the AP600 containment is to develop and apply a bounding methodology and associated containment Evaluation Model for predicting a resulting containment pressure response to postulated mass and energy release events. The containment pressure response is driven by three functions; volume of the containment, heat and mass sources, and heat and mass sinks. Westinghouse's objective is to demonstrate that the AP600 containment Evaluation Model used to predict containment pressure conservatively treats model inputs related to volume, sources, and sinks.

640.185-1

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Items (a), (b), and (c), above primarily concern the treatment and verification of heat sinks in the j evaluation model. The following discussion provides a basis for defining the relative importance of plant parameters related to their use in the treatment of heat sinks in the AP600 containment Evaluation Model. He "important" parameters related to the treatment of heat sinks are determined by an evaluation of the conservative methodology used to treat heat sinks. The conservative methodology described below, supports an ITAAC approach that verifies the existence of "important" equipment heat sinks.

The conservative treatment of heat sinks includes:

. Heat & Mass Transfer Multipliers (Reference 640.185-1, Section 4.4)

Reference 640.185-1 describes the clime noding used in the AP600 containment Evaluation Model.

The following biases to heat and mass transfer correlations are identified in that description; Location Phenomena Blas Multiplier Shell Outside Surface Heat and Mass Transfer 0.84 Shell Inside Surface Heat and Mass Transfer 0.73 The use of the bias multipliers assures a lower bound on heat and mass transfer calculated for the M' GOTHIC AP600 containment Evaluation Model. This results in a calculation that predicts a conservatively high peak containment pressure.

2, Neglect Forced Convection on inside Surface of Containment (Reference 640.185-2. Section 2.3)

Heat is transferred from the containment atmosphere to the inner surface of the containment shell by condensation, radiation and convection. The AP600 containment Evaluation Model calculation assumes condensation and convective heat transfer takes place at the surface of a thin liquid film that develops on the inside surface of the containment vessel. He inside surface of the containment shell is expected to experience hyh velocity steam and air flow during the blowdown portion of the large break loss of coolant accideat (LOCA) event and the mass and energy release duration of a main steamline break (MSLB) event as the jet-like flow from the break location vigorously circulates the containment atmosphere. Heat transfer during this time period would be turbulent forced or mixed convection. For the LOCA, the duration of blowdown is approximately 30 seconds. For the limiting MSLB event, the duration of mass and energy release is about 600 seconds. However, the heat transfer on the inside surface of the containment is conservatively modeled as turbulent free convection throughout all phases of the postulated LOCA and MSLB events.

640.185 2 3 Westinghouse

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3. Neglect Heat Sinks in Dead-Ended Compartments (Reference 640.185-2. Section 9.3.2)

Dead-ended compartments are those compartments below the operating deck that have only one opening for flow to either enter or exit. During the blowdown portion of a transient, these compartments pressurize along with the rest of containment. Additional flow into the compartments following the initial blowdown is driven by the condensation occurring within the compartments, and pressurization due to post-blowdown releases. The AP600 containment Evaluation Model conservatively neglects the heat sinks in dead-ended compartments for the LOCA and MSLB events after 30 seconds. For LOCA and MSLB transients, the IRWST, CVS compartrnent, and accumulator compartments are considered dead-ended.

4. Neglect Decks On Operating Deck and in Below-Deck Compartments (Reference 640.185-1.

Section 9.3.1.1 and Section 9.3.1.3)

The effect of potential steam concentration gradients on the utilization of heat sinks was bounded in a study that assumed extreme stratification gradients (Reference 640.185-1 Section 9). A simple bias of removing the upward facing horizontal surfaces is included as a conservative treatment of heat sinks in the AP600 containment Evaluation Model.

5. Conservative Treatment of Concrete-Steel Gap (Reference 640.185 3)

Reference 640.185-3 demonstrated the maximum gap size predicted for the jacketed concrete heat sinks of the AP600 to be 0.014 inches, with an average gap of 0.008 inches. The AP600 containment Evaluation Model uses an assumed gap of 0.020 inches for all steel jacketed concrete heat sinks. A smaller gap will facilitate heat transfer into the concrete, increasing the effectiveness of those structures as heat sinks. Based on sensitivity calculations, modeling the gap as 0.008 inches rather than 0.020 inches would result in a reduction of about 0.15 psi in calculated peak pressure for the postulated large LOCA.

As an additional conservatism, the AP600 containment Evaluation Model treats the steel jacket as a single layer of steel. The actual design contains trusses and welded studs that penetrate into the concrete substrate. These studs and trusses will facilitate the transfer of heat through the plate and into the base concrete. This effect has been conservatively neglected in the AP600 containment Evaluation Model.

6. Delay PCS Water Coverage (Reference 640.1851, Section 7.2.4)

The AP600 PCS design has an initial PCS flow of 440 gpm. At this flow, the time to establish steady state coverage is conservatively estimated to be 337 seconds. The AP600 containment Evaluation Model takes no credit for PCS flow applied to the containment shell before 337 seconds after PCS actuation. Heat transfer from the containment shell to the environment during this time is assumed to be by either convection or radiation; no evaporative mass transfer is credited until fully developed PCS flow is predicted to occur. This is conservative as the water 640.185-3

e NRC FSER OPEN ITEM distribution bucket is calculated to fill and begin spilling within 36 seconds after initiation of PCS flow. Neglecting cooling at the outside surface of the containment shell until PCS flow is calculated to reach steady-flow conditions neglects 300 seconds in which there is water on the dome that is not credited in the containment pressure calculation.

7. Conductance Penalty Applied to Safety-Grade Zinc-coated Shell Surfaces A factor of four penalty is applied to the conductance value for the safety-grade zinc coating applied to the inside and outside shell surfaces. This penalty is included in the AP600 cont..inment Evaluation Model as a conservative treatment of the shell heat sink to account for effects of oxidation of the zinc coating.

All of the items described above contribute to the conservative treatment of heat sinks in the AP600 containment Evaluation Model. As noted above, sensitivities have been performed to confirm that the conservatism in the model inputs results in a conservative calculation of containment pressure.

Based on the overall conservative treatment of heat sinks in the AP600 containment Evaluation Model, the level of detail required to demonstrate the fundamental integrity of the containment analyses are the overall dimensions of the physical plant. These dimensions include the containment shell inside diameter and containment height above the operating deck. Verification of these dimensions is sufficient to confirm containment free volume and heat transfer surface of the containment shell. For the volumes, surface areas and heat sinks below the operating deck, verification of the overall dimensions of the plant is sufficient. Column-to-column line distances, building elevations, and wall and floor / ceiling thicknesses are verified in the Nuclear Island non-System ITAAC, Section 3.3, of the AP600 Certified Design Material. These physical parameters are considered to be important parameters for input to the plant structural and seismic analysis. 'Ihey also represent a sufficient level of detail for verification of the important dimensions used as input to the containment analyses.

The AP600 Certified Design Material also contains ITAAC for the systems located inside containment.

These systems have a specific ITAAC to inspect the functional arrangement and the location of the major equipment contained in these systems. These ITAAC verify the existence of the major components that are modeled as metal heat sinks. For example, the Passive Core Cooling System contains the Core Makeup Tanks (CMTs), which are two large heat sinks modeled in the DECLG LOCA WGOTHIC calculation. The ITAAC for the CMTs are included in the AP600 CDM Section 2.2.3, Figure 2.2.3-1 (Functional Arrangement) and in Table 2.2.3-4, item 8.c (Volume). Another example is the Fuel Handling and Refueling System (CDM Section 2.1.1) which confirms the existence of the refueling machine and the Mechanical Handling System (CDM Section 2.3.5) which confirms the existence of the containment polar crane.

Westinghouse performed a sensitivity calculation using the AP600 containment Evaluation Model to assess the effect of non-uniform coating thickness on heat sinks inside containment. The sensitivity calculation increased the thickness of all nonsafety-related epoxy coating on heat sinks inside containment by 50%. The sensitivity calculation resulted in an increase in calectated peak 640.185-4 3 W85tingh00S8

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NRC FSER OPEN ITEM c'ontainment pressure of about 0.06 psi compared to the limiting LOCA and MSLB SSAR cases. The lack of sensitivity of containment pressure to changes in epoxy thickness is due to the epoxy thermal resistance accounting for less than 10% of the resistance from the bulk gas to the underlying heat sink material. Therefore, the effect of potential non-uniform application of nonsafety-related coating to heat sinks inside containment is insignificant. As a result, no ITAAC related to the treatment of heat sink coatings is warranted.

Westinghouse's response to RAI 640.168 proposed the verification of certain dimensions of the Nuclear Island commensurate with their importance in the overall treatment of heat sinks in the evaluation model. Based on the discussion above, the ITAAC proposed in our response to RAI 640.168 is consistent with how the equipment and stnicture heat sinks are treated as part of the conservative methodology used to model heat sinks.

References:

640.185-1 WCAP-14407, "WGOTHIC Application to AP600," Revision 1 dated July 25,1997 640.185-2 WCAP-14326 " Experimental Basis for the AP600 Containment Vessel Heat and Mass Transfer Correlations," Revision 1, dated May 5,1997 640.185-3 Westinghouse Response to RAI 640.155, transmitted via Letter DCP/NRCl252, dated 2/10/98.

SSAR Revision: None ITAAC Revision: See response to 640.168 g 640.185-5