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Suppls 860930 Submittal Documenting Results of Analysis Performed in Support of Resolution of Issues Re Control of Combustible Gas in containment.In-depth Discussion of Each Accident Transient Analyzed Encl
	ML20214A046
Person / Time
Site:	Mcguire, Catawba, McGuire, 05000000
Issue date:	11/14/1986
From:	Tucker H; DUKE POWER CO.
To:	Harold Denton, Youngblood B; Office of Nuclear Reactor Regulation
References
	NUDOCS 8611190175
	Download: ML20214A046 (31)
	v • d • e

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s DUKE POWER GOMPANY P.O. DOX 33189 CHARLOTTE, N.C. 28242 HAL D. TL*CKER TELEPHONE (704) 373-4531 vu.m reassomwr mm.

-r November 14, 1986 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C.

20555 Attention:

Mr. B. J. Youngblood, Project Director PWR Project Directorate No. 4 Re: Catawba Nuclear Station Docket Nos. 50-413 and 50-414 McGuire Nuclear Station Docket Nos. 50-369 and 50-370

Dear Sir:

By letter dated September 30, 1986, Duke Power Company (Duke) submitted for NRC review a set of graphs documenting the results of analysis performed in support of the resolution of issues concerning control of combustible gas in containment.

Subsequent discussions between Duke and the NRC staff established that these graphical results did not contain sufficient information for the staff to perform the necessary reviews. Accordingly, Duke has prepared the attached document which briefly describes each one of the accident transients which was analyzed. This discussion includes a description of significant assumptions and sequences which clarifies the course of events for each analysis.

Very truly yours, 44

/

Hal B. Tucker ROS/32/ sib Attachment xc:

Dr. J. Nelson Grace, Regional Administrator U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 NRC Resident Inspector Catawba Nuclear Station g0k 861119017S 861114 Mr. W. T. Orders PDR ADOCK 05000413

'g '\\

P PDR NRC Resident Inspector McGuire Nuclear Station

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i ATTACHMENT 1 MCGUIRE/ CATAWBA NUCLEAR STATIONS DISCUSSION OF MAAP ANALYSES As part of the plan for resolving issues concerning control of combustible gases in containment, Duke Power Company agreed to provide release rates of mass and energy into containment for several accident sequences. The information contained herein provides additional information concerning those sequences.

MAAP, Version 2.0 B was used to analyze four degraded core sequences. MAAP is a computer code developed by the Industry Degraded Core Rulemaking Program (IDCOR).

It is designed to provide realistic thermal-hydraulic assessments for severe core damage accident sequences.

The model divides the primary system into ten nodes as shown in Figure 1.

Nodes exist for the core region, upper plenum, downconer, broken loop cold leg, broken loop hot leg, unbroken loop cold leg, unbroken loop hot leg, pressurizer, and both the broken and unbroken loop steam generator secondary sides.

This primary system nodalization permits a detailed accounting of the water which is available for cooling the core and for reacting with the zircaloy fuel cladding.

In addition, this scheme allows the user to track hydrogen and fission products through the primary system and thereby calculate release rates to the containment.

The safety systems considered in this analysis include the charging pumps (NV),

safety injection pumps (NI), low pressure injection pumps (ND), cold leg accumulators, auxiliary feedwater, containment sprays, ice and containment fans.

These are shown in Figure 2 along with other systems important to accident progression such as the pressurizer and steam generator safety and power operated relief valves. In order to model individual accident sequences, all these systems can be enabled or disabled by the user through the use of MAAP " event codes".

MAAP differs from the NRC code MARCH, in that it is not possible to specify the cut off value for zircaloy oxidation. In order to achieve the desired amount of oxidation, several runs for each sequence were performed using various times for recovering core cooling. Then the run nearest the desired target value of 75% clad oxidation was chosen. Additionally, co achieve oxidation values as high as 75%,

the IDCOR core blockage model was overridden. This allowed steam to reach core nodes even if they were above the zircaloy melting temperature of 2098 degrees K.

1 l

The four sequences analyzed are discussed below:

S D Sequence 2

i 1

The first sequence analyzed (S D) was a small (2-inch diameter) break on the hot 2

i leg, followed by failure of the emergency core cooling system (ECCS) (Figures 3 l

through 9).

The auxiliary feedwater system was assumed to function properly and provided secondary side heat removal. The loss of primary system inventory through the 2-inch diameter break eventually lead to the core being uncovered and a loss of l

decay heat removal (0.75 hours8.680556e-4 days 0.0208 hours 1.240079e-4 weeks 2.85375e-5 months ).

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The core continued to heat up and oxidation of the zircaloy cladding began at 1.0 hour0 days 0 hours 0 weeks 0 months . By 1.20 hours2.314815e-4 days 0.00556 hours 3.306878e-5 weeks 7.61e-6 months the hottest core node had reached the UO melting temperature 2

of 3113 degrees K.

ECCS was recovered at 1.25 hours2.893519e-4 days 0.00694 hours 4.133598e-5 weeks 9.5125e-6 months with all NI and NV pumps available. The core was essentially cooled, and all H Production is stopped by 1.32 hours3.703704e-4 days 0.00889 hours 5.291005e-5 weeks 1.2176e-5 months . However, the 2

core was not completely covered until 1.6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months . H2 gas c ntinued to be expelled through the break until 2.75 hours8.680556e-4 days 0.0208 hours 1.240079e-4 weeks 2.85375e-5 months .

The total fraction of the clad oxidized was 0.81.

S H Sequence 2

This S H sequence was modeled as a 2-inch diameter break on the hot leg with 2

successful ECCS injection but failure of ECCS to operate in the recirculation mode (Figures 10 through 16).

The sequence began with a 2-inch diameter break on the hot leg.

By 28.1 seconds the primary system pressure had dropped to the ECCS set point of 1860 psia, and all high head pumps began injection of cooling water into the primary system.

Containment sprays were initiated automatically at 83 seconds causing rapid depletion of refueling water storage tank (RWST) inventory. At 0.94 hours0.00109 days 0.0261 hours 1.554233e-4 weeks 3.5767e-5 months the RWST was empty, and ECCS failed to switch over to the recirculation mode of core cooling.

The loss of primary inventory resulted in the core being uncovered at 1.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months .

H Production from zircaloy water reaction began at 1.6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months . By 1.8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months the 2

hottest core node had reached the UO melting temperature.

2 ECCS was restored at 2.0 hours0 days 0 hours 0 weeks 0 months with all NI and NV pumps operating in the recirculation mode. The core was rapidly covered by reflood at 2.3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months halting all H Production. By 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months all H release from the primary system was complete.

2 2

The total fraction of the clad oxidized was 0.73.

S D Sequence g

The S D sequence was modeled as a 6-inch diameter break on the hot leg followed by g

failure of the ECCS injection (Figures 17 through 23). Auxiliary feedwater was assumed to operate during this sequence.

The 6-inch diameter break rapidly depressurized the primary system. The core uncovered at 1.2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months , and H Production began at 1.4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months .

By 1.6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months the 2

hottest core node had reached the UO Production and release from the primary 2

system was halted.

At 1.8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months ECCS was returned to service and injection of RWST water into the primary system began. However, to achieve the high levels of oxidation desired, only the high head pumps were used to recover this sequence.

By 2.2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months the core was covered, and all H Production and release from the primary system was halted.

2 The total fraction of the clad oxidized was 0.791.

2

TMLU Sequence The TMLU sequence was modeled as a station blackout (Figures 24 through 27). As the result of loss of power, main feedwater failed, ECCS failed, and the MSIVs closed.

It was also assumed that the auxiliary feedwater system and the pressurizer PORVs failed.

Initially, the decay heat from the core was removed by boiling of the water remaining in the steam generators. However, as the secondary side inventory was depleted, heat transfer from the primary system to the secondary system decreased, and at 1.1 hours1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months the pressurizer safety valves lifted relieving pressure to the Pressurizer Relief Tank (PRT). At 1.27 hours3.125e-4 days 0.0075 hours 4.464286e-5 weeks 1.02735e-5 months the PRT rupture disk blew out and began the release of steam to containment.

By 1.36 hours4.166667e-4 days 0.01 hours 5.952381e-5 weeks 1.3698e-5 months the steam generators had boiled completely dry.

At approximately 1.9 hours1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months , the core began to uncover, and at 2.4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months the hottest core node had reached the UO B*lting temperature. At 2.25 hours2.893519e-4 days 0.00694 hours 4.133598e-5 weeks 9.5125e-6 months the ECCS was 2

restored, and the high head pumps provided cooling water by pumping against the high primary system pressure.

By 2.6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months the core was cooled preventing further clad oxidation.

The total fraction of the clad oxidized was 0.71.

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Dear Sir:

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