ML20129E908

Hydrogen Deflagration Pressure Effects on Equipment

ML20129E908
Person / Time
Site:	River Bend
Issue date:	07/31/1985
From:	GULF STATES UTILITIES CO.
To:
Shared Package
ML20129E901	List: ML20129E908 RBG-21457, Forwards Hydrogen Deflagration Pressure Effects on Equipment, Providing Further Evidence to Support Interim Operation at Full Power Until Final Analysis Completed
References
NUDOCS 8507170108
Download: ML20129E908 (17)

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%wm Deflagration Pressure Effects on Dquipnent July, 1985 Gulf States Utilities Capany River Bend Station - Unit 1 4

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INTRODUCTION In the unlikely event of a degraded core accident occurring at River Bend Station - Unit 1 (RBS), equipnent located in the containment may be exposed to a harsh environment resulting frcm the release of reactor coolant and hydrogen. The hydrogen is produced by reaction of core cladding with reactor coolant. Hydrogen, once released to the containment, may undergo burning which will result in increased tmperatures and pressures in the containment. This report assesses the effect of the pressure increases on equignent required to survive a hydrogen burn (essential equiput) . The tmperature effect on essential equipnent has been addresses in Reference 1.

BURN ENVIRONENT w o degraded core accident scenarios have been postulated to occur.

Briefly, these can be described as a stuck open relief valve (SORV) accident and a pipe break in the drywell (DWB) . These accidents have been assumed to occur with a coincident loss of all mergency core cooling systms. After an appropriate period of time, it is assumed that a core cooling injection systs is restored and core reflood occurs. Further description of the accident sequences can be found in References 2 and 3.

Wo distinct hydrogen burn phenmena are considered to occur. One type of hydrogen burning, diffusion burning, is characterized by the presence of a continuous, standing flame generally occurring at the site of the hydrogen release into the containment. Diffusion burning results in locally high tmperatures and a gradual increase in global tmperature and pressure. Because the pressure rise resulting fran diffusion burning is gradual, and since the total pressure rise is expected to be less than the containment design pressure, the pressure effects of diffusion burning are not a threat to the containment or essential equipnent.

The second type of hydrogen burning is deflagration burning which is modeled in CLASIX-3 as rapid burning throughout an entire subvolume.

The CLASIX-3 cmputer program has been used to predict the tmperature and pressure response of RBS to this type of burning (References 2 and

3) . Figure 1 shows the nodal arrangment used in the BBS CLASIX-3 analysis. Figures 2 through 9 show the calculated pressure response for the SORV and DWB accidents for the various nodes. The pressure responses show periodic spikes which are less than the drywell and containment design pressure. Note that the results presented include a single pressure spike which is due to an arbitrary forced burn occurring past the end of the hydrogen release. This burn was forced to occur concurrently in the wetwell, intennediate volume and upper containment and for this reason is considered artificial. The artificial pressure spike is less than the ultimate capacities of the drywell and containment structures (References 4 and 5) . This artificial pressure response is not considered in the evaluation of equipnent response to hydrogen deflagration burning.

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Table 1 provides a cmparison of the design pressures and the pressures predicted by the RBS CLASIX-3 analysis (References 2 and 3) .

mui OF PRESSURE ON ESSENTIAL EQUIPMENT The list of essential equipnent provided in Reference 1 has been reviewed to identify equipnent that may be affected by rapid pressure increases resulting fran deflagration burns. As a result of this review, equipnent was determined to be either not affected by pressure transients or potentially susceptible to the transients.

Equipnent determined not to be affected by the pressure transients predicted by CLASIX-3 includes equipnent that fonns a portion of the primary containnent boundary e.g. , the airlocks, hatches and containment penetration assenblies. These were evaluated in the analysis of the ultimate pressure capability (References 4 and 5) and found to be able to withstand pressures exceeding those predicted by CLASIX-3. Other essential equipnent considered to be unaffected by pressure transients includes valves and cables. Containnent isolation valves have '

previously been shown (References 4 and 5) to be capable of withstanding pressures predicted by CLASIX-3. Other valves (e.g., LPCI injection valves) would not be affected until the pressure significantly exceeds the design pressure of the valve, which does not occur. Electrical cables are not affected by the external pressure transients.

Mditionally, the hydrogen mixing system fans are unaffected by these pressure transients since they will not be operating at the time of hydrogen burning and are not expected to be operated until the core has been recovered. Operator direction concerning the hydrogen mixing systen is included in the station operating procedure. Electric motors, such as those used for motor-operated valves, are of sturdy construction and can withstand the effects of post-IOCA pressurization. Because of their construction, electrical motors are not considered to be susceptible to the pressure transients predicted by CLASIX-3.

Functioning of air-operated ADS valves is unaffected, since predicted containment pressures ranain well below the design air pressure.

The renainder of the essential equipnent is considered to be potentially susceptible to pressure transients. Equipnent which may be susceptible to pressure transients includes the hydrogen recanbiners, containment unit coolers and sealed equignent such as hydrogen igniters. The types of failures considered include binding of moving parts due to ,

deformation, loss of function due to major defonnation, and failure of integrity of seals. Deformation-related failures would only result fran very rapid pressure transients exceeding design values. Slower pressurizations for unsealed equipnent would result in low differential pressures with limited potential for deformations. Therefore, unsealed equipnent will not be considered further due to the respectively slow pressurization predicted by CLASIX-3. However, sealed itens such;as hydrogen igniters may be susceptible to high absolute pressures.

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The RBS hydrogen recmbiners are located in the upper contaiment volume. During operation, flow is provided by a draft induced by the heaters located within the unit. The r - hiners have no moving parts and have large openings cmmunicating with the local at2nosphere.

Because of these large openings, the recmbiners are insensitive to increases in pressure. Examination of the predicted pressure response in Table 1 and on Figures 5 and 9 show that the recmbiners would be exposed to a pressure spike of approximately 8 psi, with a rise time of more than 50 sec. Although the magnitude of the pressure spike exceeds the pressurization spike resulting frm a IDCA (Peference 6), the rise time was significantly longer, such that the rate of pressure rise is less than that associated with a IOCA. W erefore, deformation of the s unit is not expected to occur.

RBS contaiment unit coolers are located in the intermediate volume as defined in the GASIX-3 analysis. The unit coolers have large inlets drawing frm the local atanosphere. The normal discharge of the unit coolers is through a duct system which distributes flow throughout the contaiment. The duct system is not designed to withstand large differential pressures. We unit cooler heat removal function is therefore protected by a relief damper designed to open on the occurrence of a pressure pulse. Once the relief damper is opened, a flow path for the processed air is ensured, regardless of deformation of the rmainder of the duct systs. Because the unit coolers are open, they are insensitive to increases in absolute pressure. Examination of Table 1 and Figures 4 and 8 shows that the unit coolers are exposed to a pressure time-history very similar to that seen by the hydrogen reembiner. We conclusions reached for the reembiners apply equally to the unit coolers.

Equipnent which consists, at least in part, of sealed cmponents is potentially susceptible to high absolute pressures. Included in the list of sealed equignent are the hydrogen igniters and terminal boxes.

Again examining Table 1 and Figures 2 through 9, it is observed that the maxim m calculated pressures do not exceed the contaiment design pressures. Werefore, all sealed cmponents will survive the pressure transients predicted by GASIX-3.

SUM @RY Essential equipnent in the RBS contalment may be exposed to pressure transients due to deflagration type hydrogen burns that are slightly more severe than those predicted for a LOCA. The number of pressure spikes and the magnitude of the spikes, as predicted to occur by the CLASIX-3 analysis, are greater than those predicted for the RBS design basis IOCA. However, it is noted that the pressurization rate for hydrogen deflagration pressure spikes is significantly less and, therefore, less severe.

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l c Equipnent response to the predicted deflagration pressure spikes is varied. See equipnent such as unit coolers, reembiners and other '

unsealed equipnent are ' virtually insensitive to pressure spikes resulting frm the series of deflagration burns. In addition, sealed equipnent even though more sensitive to pressure is expected to withstand the pressure excursions since these pressures are below con +a4 ==nt design pressures. In conclusion, since the predicted deflagration burn pressures are below the contaiment design pressure, equipnent failures are not expected.

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REFERENCES

1. RBG-21,423 dated July 1, 1985 fran J. E. Booker to H. R. Denton,

" Preliminary Equipnent Survivability Report".

2. RBG-21,218 dated June 7, 1985 fr m J. E. Booker to H. R. Denton, "Contalment Pressure and Teperature Response to Hydrogen Canbustion".

3. RBG-21,454 dated July 5, 1985 fr m J. E. Booker to H. R. Denton,

" Revised Drywell Break Base Case Analysis".

4. RBG-16,085 dated September 30, 1983 frm J. E. Booker to T. M. Novak

5. RBG-18,089 dated June 25, 1984 frm J. E. Booker to H. R. Denton

6. River Bend Station Final Safety Analysis Report, Figure 6.2-4 Page 6

TABIE 1 CAICUIATED PRESSURE, DESIGN PRESSURE, psig VOIINE psig- SORV DWB Drywell 25 3.3 (12.3) 12.0 (22.4)

Wetwell 15 7.3 (24.3) 12.7 (34.7)

Inta M iate 15 6.3 (24.3) 10.5 (34.7)

Upper Contairunent 15 6.3 (24.3) 10.0 (34.6)

( ) - Values due to forced burn past end of hydrogen release.

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TABLE 1 CAICUIATED PRESSURE, DESIGN PRESSURE, psig NOLINE psig SORV DWB 3.3 (12.3) 12.0 (22.4)

Drywell 25 Wetwell 15 7.3 (24.3) 12.7 (34.7)

Intennediate 15 6.3 (24.3) 10.5 (34.7)

Upper Containment 15 6.3 (24.3) 10.0 (34.6)

( ) - Values due to forced burn past end of hydrogen release.

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