ML20206P555

Forwards Analysis Re SER Confirmatory Item 9 Main Steam Line Break Outside Containment for Superheat Condition.Encl Proposed FSAR Changes Will Be Incorporated in Amend 25, Scheduled for Sept 1986

ML20206P555
Person / Time
Site:	Vogtle
Issue date:	06/25/1986
From:	Bailey J GEORGIA POWER CO.
To:	Youngblood B Office of Nuclear Reactor Regulation
Shared Package
ML20206P559	List: ML20206P555 ML20206P575
References
GN-963, NUDOCS 8607020155
Download: ML20206P555 (28)

Text

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, Georgia Power Company Rout 3 2, Box 299A Waynesboro, Georgia 30830 Telephone 404 554-9961 404 724-8114 Southern Company Services, Inc.

Post Office Box 2625 Birmingham, Alabama 35202 Telephone 205 870-6011 Vogtle Proj.ect June 25, 1986 Director of Nuclear Reactor Regulation File: X7BC35 Attention: Mr. B. J. Youngblood Log: GN-963 PWR Project Directorate #4 Division of PWR Licensing A U. S. Nuclear Regulatory Commission Washington, D.C. 20555 NRC DOCKET NUMBERS 50-424 AND 50-425 CONSTRUCTION PERMIT NUMBERS CPPR-108 AND CPPR-109 V0GTLE ELECTRIC GENERATING PIANT - UNITS 1 AND 2 SER CONFIRMATORY ITEM 9: MAIN STEAMIlNE BREAK (MSLB)

OUTSIDE CONTAINMENT

Dear Mr. Denton:

Attached for your staff's review is the VECP specific analysis of the MSLB outside containment for superheat condition. This submittal contains the following:

Attachment 1 - VEGP Evaluation of Main Steamline Break with Superheat -

Blowdown Outside Containment Attachment 2 - Thermal Analysis of Safety Related Valves Exposed to VEGP Control and Auxiliary Building Steamline Breaks Attachment 3 - FSAR changes to incorporate the above analysis The proposed FSAR changes will be incorporated in Amendment 25 presently scheduled for September 1986.

If your staff requires any additional information, please do not hesitate to contact me.

S' cerely, J. A. Bailey Project Licensing Manager JAB /sm e607020155 860625 PDR ADOCK 05000424 E PDR I D

~ Director of Nuclear Reactor Regulation File: X7BC35 June 25, 1986 Log: GN-963 Page 2 Attachment xc: R. E. Conway R. A. Thomas J. E. Joiner, Esquire

.B. W. Churchill, Esquire M. A. Miller (2)

B. Jones, Esquire G. Bockhold, Jr.

NRC Regional Administrator NRC Resident Inspector D. C. Teper W. C. Ramsey L. T. Gucwa C. W. Hayes Vogtle Project File 0561V t

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I ATTACHMENT 1 r

VEGP EVALUATION OF MAIN STEAM LINE BREAK WITH SUPERHEATED BLOWDOWN OUTSIDE CONTAINMENT l

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I JUNE 1986 l

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BACKGROUND In December 1984, the Nuclear Regulatory Commission (NRC) 1ssued Inspection and Enforcement (IE) Information Notice 84-90 (Main Steam Line Break Effect on Environmental Qualification of Equipment) requesting all licensees to review their main steam line break (MSLB) analyses with regard to steam l superheating during steam generator tube bundle uncovery as a result of postulated main steam line breaks and subsequent release to compartments.

Superheated steam being expelled from a MSLB would result in higher temperature conditions for the area of the plant containing and communicating with the break. This could possibly preclude safety-related components in the area from performing their intended safety function.

The Vogtle Electric Generating Plant (VEGP) Units 1 and 2 have four main steam lines for each unit. Two of the main steam lines (loops 2 and 3) are routed in the control building main steam isolation valve (MSIV) compartment directly north of the containment and the other two (loops 1 and 4) are routed in the aux 111ary building MSIV compartment directly south of the containment. (See figure 1.) The MSIV compartments are physically separate from other areas of the power block, and all penetrations (e.g.,

piping, instrumentation, and electrical condult) into other areas are physically sealed to prevent pressurization of these areas. The main steam piping in the MSIV compartments consists of straight piping runs extending from the containment penetrations to the five-way restraints mounted in the auxiliary building and control building walls through which these lines enter the main steam tunnel. There is a partial wall between the two main steam lines in each MSIV compartment that provides additional separation in each MSIV compartment. The MSIVs, MSIV bypass valves, main feedwater isolation valves, main feedwater bypass isolation valves, main steam safety i valves, atmospheric relief valves, and auxiliary feedwater discharge valves are located in these compartments. The VEGP design has separated the essential equipment such that the valves associated with steam generators 2 l and 3 are in the control building MSIV compartment and the valves

associated with steam generators 1 and 4 are in the auxiliary building MSIV compartment. Because a MSLB in one MSIV compartment does not impact the j equipment in the other MSIV compartment, there are two unaffected loops available to achieve safe shutdown.

In addition, the main steam piping in the MSIV compartments is designed to the break exclusion (superpipe) criteria of Branch Technical Position MEB 3-1 Item B.I.b for the portions of piping passing through the primary containment and extending to the first five-way restraint past the MSIVs.

The superpipe design meets the following conditions:

e The superpipe design maintains low stress and fatigue usage factors which are attributable in part to the use of good geometry; e The superpipe design uses seamless pipe to minimize circumferential and longitudinal welds; 5379t I

e The superpipe design avoids attachment welds to the superpipe surface except where detailed stress analyses or tests are performed to demonstrate that the maximum stresses do not exceed the limits defined in Branch Technical Position MEB 3-1 B.I.b(1) e The superpipe nominal wall thickness is 2 1/16 inches and 2 13/16 inches for the 28-inch and 29.5-inch forgings, respectively.

e The superpipe is examined through 100 percent volumetric inspection of all welds during each inspection interval.

The superpipe design reduces the probability of a MSLB in this portion of piping, so a single active failure is not considered concurrent with a MSLB in the superpipe.

SCENARIOS EVALUATED The environmental effects of superheated steam exiting from a MSLB in the MSIV compartment have been evaluated for the following scenarios:

e In the superpipe region, MSLBs up to one square foot were evaluated without a single active failure; e Downstream of the superpipe region, the largest MSLB that resulted in j

superheated steam being released in the compartment prior to the MSIVs i isolating the blowdown was considered with a single active failure; and l e The largest main steam branch line break was considered with a single active failure.

DEVEl.0PMENT OF MASS AND ENERGY RELEASE DATA As active members in the Westinghouse Owners Group (HOG), VEGP participated in the H0G Subgroup for High Energy Line Break /Superheated Blowdowns Outside Containment (HELB/SBOC). The purpose of the program was to provide members with steamitne break mass and energy releases necessary to address l

equipment qualification outside containment (NCAP-10961-P).

l The generic analyses were performed to include all member plants. VEGP was grouped with other IK)G members categorized by the following criteria: the number of loops, power rating, and the type of steamline break protection logic. The mass and energy releases of the original NOG analyses were I

l evaluated to determine the temperature profiles in the MSIV compartments l outside containment for VEGP. Several cases were reanalyzed as described in this report using a VEGP specific model and input.

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Analysis The assumptions used in the WOG analyses were utilized in the VEGP analysis with the exceptforas t'olow:

A. A VEGP specific NSSS model was used. This included piping volumes, RCS loop pressure drops, and steam generator type (Model F).

B. The initial conditions representative of VEGP were also used.

This included initial temperature, pressure, steam generator mass, power rating, RCS flow, and fuel data.

C. The VEGP protection system was modeled with allowances for system errors. Plant specific setpoints for over temperature delta T (OTDT), over power delta T (OPDT), low-low level steam generator water level, high neutron flux, low pressuri7er pressure, and low steamline pressure were used with nominal errors since none of the sensors experience the adverse environment.

D The VEGP auxillary feedwater system was modeled. This was reflected primarily in the flowrates assumed in the analysis.

Methods The LOFTRAN code used to model the superheated steamline break mass and energy releases is identical to the code used in the WOG analyses. LOFTRAN is a digital computer code that simulates transient behavior in a multi--locp, pressurized water reactor system. The code simulates the neutron kinetics, thermal-hydraulic conditions, pressurizer, steam generators, reactor coolant pumps, and control and protection system

operation.

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! The purpose of this analysis is to generate a more detailed evaluation l Incorporating the VEGP specific aspects of the NSSS design. The difference between initial steam generator level and the low level setpoint was reduced for VEGP (the difference primarily being the relatively higher low level setpoint for VEGP and a different steam generator model). This impacts the relative mass and energy released before the low steam generator level setpoint is reached. The low steamline pressure safety injection setpoint was increased since no adverse environmental error was required. VEGP steamilne pressure transmitters are not located in the compartments that would experience or communicate with the break.

Consequently, a low steamline pressure setpoint for similar conditions was reached earlier in the transient than the WOG subgroup study. The low pressurizer pressure safety injection setpoint was increased which actuated SI sooner. Two trains of safety injection pumps were also used.

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i Auxiliary feedwater For breaks in superpipe, a single failure does not have to be taken into account. This impacts the amount of auxiliary feedwater available.

Normally, for a given single failure, the turbine-driven AFH pump is assumed to fall since it possesses the largest single flowrate. However, for the superpipe break cases in this analysis, it was assumed to be available. The mass and energy blowdown data was calculated both with and without the turbine-driven pump operating to address breaks that do not occur in the superpipe.

The modeling of the auxiliary feedwater system is complex. The conditions under which the water is pumped to the steam generators varies significantly with pressure. Prior to steamline isolation, all four steam generators depressurize equally. Once steamline isolation occurs, the intact steam generators begin to repressurize rapidly to a steady-state pressure (this steady-state pressure varies with power level). The faulted steam generator quickly blows down to atmospheric pressure. When the assumption of turbine-driven pump availability is changed, it also impacts the flow. For the cases analyzed, auxiliary feed flow was modeled as a function of pressure.

The logic for AFW pump actuation is consistent with the H0G subgroup study and VEGP. Any one steam generator low-low level signal will start the motor-driven pumps. Low-low level signals are needed in two steam generators to start the turbine-driven pump.

VEGP specific cases f Two power levels were assumed: 102% and 70%

Four break sizes were assumed: 1.0, 0.7, 0.5, and 0.4 ft' These break sizes represent the following:

1. 1.0 ft' is the largest postulated break in superpipe,

2. 0.7 ft' is the largest break downstream of the MSIV where the temperature envelope is exceeded prior to protection actuation.

3. 0.5 ft' is the largest branch 11ne break,

4. 0.4 ft' is the smallest break that occurs with the resulting compartment temperature exceeding 320*F (the current specified qualification temperature).

DEVELOPMENT OF MSIV COMPARTMENT TEMPERATURE PROFILES The analyses of the environmental response of each MSIV compartment to MSLBs with superheated steam blowdown is consistent with the requirements of NUREG-0588. These analyses were completed using the Bechtel computer code "FLUD". FLUD is a multi-node, one-dimensional, thermal-hydraulic code 5379t 4

which takes credit for heat transfer to the surrounding concrete structures. The FLUD code provides a calculation of the long-term subcompartment pressures and temperatures as a function of time following the pipe break.

The auxiliary building and control building MSIV compartments are modelled into various control volumes with interconnecting flow paths. The nodal boundaries are taken at significant restrictions such as at walls, gratings or major pipes. The aux 111ary building MSIV compartment is modeled into 12 nodes (see figure 2), and the control building MSIV compartment is modelled into 8 nodes (see figure 3).

The centerline of the superpipe portion of the main steam lines is at elevation 229'-6" and forms the boundary between nodes 1 and 2 and between nodes 5 and 8 in the auxiliary building, and between nodes 1 and 2 and between nodes 4 and 5 in the control building. The portion of the main '

steam line (nonsuperpipe) downstream of the five-way restraint is in nodes 9 and 10 in the auxillary building MSIV compartment and in node 8 of the control building MSIV compartment. The main steam line branch lines are in nodes 1, 2, 5, 8, 9 and 10 of the aux 111ary building MSIV compartment and in nodes 1, 2, 4, 5 and 7 of the control building MSIV compartment. The MSLBs in the superpipe region and the branchline breaks are taken in node 5 of the auxiliary building and in node 1 of the control building because it has been shown that taking breaks in these nodes give conservatively high temperatures in the break node and the surrounding nodes. MSLBs in the nonsuperpipe are taken in node 9 in the auxiliary building and node 8 of the control building MSIV compartment. MSLBs are not considered in node 10 of the auxiliary building MSIV compartment because there is no safety-related equipment located in this area and the temperatures in the other nodes are less than for a break in node 5.

MSLBs with superheated steam blowdown were considered in both the auxillary building and control building MSIV compartments, but the environmental response of the control building MSIV compartment was the worst. This is mainly due to the smaller break node volume and flow areas to the '

i surrounding nodes in the control building than in the auxillary building.

• The calculated maximun peak teirperature is 422*F in the break node (node 1 of the control building MSIV compartment) and is of short duration. The worst case for each of the four break sizes considered is summarized in table 1.

Summary of Facility Response and Evaluation of Eautement Qualification A facility response evaluation was performed for the safety-related -

equipment located in the MSIV compartments. The facility response evaluation considered the following questions to determine if the equipment ,

was essential for a MSLB in the area. ,

e Is the equipment required to mitigate the effects of the H5LB?

e Is the equipment required to function for post-accident monitoring?

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e Is the equipment required to function for post-accident recovery?

e Will consequential actuation have an adverse impact on the event?

If the equipment was determined to be essential for a MSLB in the area, the environmental qualification test reports for the equipment were reviewed to ensure that the equipment is quallfled for the MSLB event.

For four components (MSIVs, MSIV bypass valves, steam generator atmospheric relief valves and auxiliary feedwater discharge valves) the maximum environmental temperatures achieved during the qualification tests did not envelope the maximum MSLB environmental temperature profiles considering superheat (limiting profiles are shown in figures 4 through 8) developed for the control building and auxiliary building MSIV compartments. A thermal lag analysis was performed on these components to demonstrate that the actual safety-related component temperature achieved under the VEGP MSLB conditions is less than the component temperature reached in the qualification testing program.

The thermal response of a component exposed to an MSLB is characterized by the heat transfer mechanism occurring at a given point in time. The component temperature will rise rapidly to the saturation temperature and remain at this temperature until the water which condenses on the valve changes state from saturated 11guld to saturated vapor. After " drying off" the component temperature will rise based on the forced convection heat transfer mechanism. Attachment 1 provides a sumary of the thermal lag methodology used in the evaluation of these coteponents. This methodology is consistent with NUREG-0588 requirements for thermal lag analyses.

CONCLUSIONS The essential equipment for an MSLB in the auxiliary and control building MSIV ccmpartments has successfully completed environmental qualification test programs which, in conjunction with thermal lag analysis, demonstrate that the equipment is quallfled for the maximum MSLB environmental temperature postulated in these compartments. It is concluded that no l

required .afety components are precluded from performing their safety

function in the event of an MSLB in either of the MS1V compartments.

l Therefore, no safety implications exist to prevent safe shutdown of the l VEGP.

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. TABLE 1

. MSIV COMPARTMENT BREAK NODE TEMPERATURES Peak Time above Break Size Temperature 320*F*

2 Break location (ft ) (*F) (sec)

Control Building Node 1 1.0 422 100

- 0.7 397 250 0.5 374 400 1

0.4 358 600 i

Control Building Node 8 0.7 144** NA -

Auxiliary Building Node 5"* 1.0 333 20 i

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• 320*F is the current specified environmental qualification temperature requirement.

• • 8ecause there is no essential equipment located in the break node, tha peak temperature is for node 1 rather than the break node.

• • • For all the other cases analyzed for the auxiliary building MSIV compartment the temperature is less than 320*F.

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