ML18030A975

Safety Evaluation Diesel Generators Not Seismic.

ML18030A975
Person / Time
Site:	Browns Ferry
Issue date:	09/27/1985
From:	TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML18030A974	List: ML18030A973 ML18030A975
References
NUDOCS 8601030300
Download: ML18030A975 (10)

Text

Tennessee Valley Authority Browns Ferry Nuclear Plant Safety Evaluation Diesel Generators Not Seismic Prepared by:

Submitted by:

Date Reviewed by PORC Chairman 8601OSOSOO 85L2i8>59 PDR ADOCK 0500 9

Safety Evaluation Diesel Generators Not Seismic On September 24, 1985, the battery racks for the 125v diesel control power for all diesel generators were found to be unqualified for earthquake loadings. This is due to unqualified material being used as bolting studs which hold the racks onto an embedded steel baseplate. Each diesel generator has its own 125v battery. It is unlikely that all eight diesel generator batteries would fail upon a seismic event. The probability of an earthquake is 4 X 10 per day for a mild operating basis earthquake, and therefore the pro)ability of loss of all AC power after an earthquake is less than 4 X 10 per day.

The cons'equenses of total loss of AC power are mild for the present plant, configuration and the sequence of events is slow moving. The worst case scenario is described in the following section.

Scenario for Secondary Containment Upon loss of all AC power, secondary containment integrity would be lost due to loss of Standby Gas Treatment System. Secondary Containment function would noh. be required, however, as long as fuel cooling can be maintained as per the fuel cooling scenario and fuel movement is not taking place thus eliminating the chance of fuel damage.

Scenario for RCS Integrity The RCS integrity is not directly affected by loss of,AC power. All connections capable of draining the RCS or a fuel pool: are seismically qualified, and the potential for LOCA is generally considered negligible I

for a Class system that is not, under pr essure. Therefore, the ability of the fuel pool and reactor vessel/cavity systems to contain fuel cooling water is not of concern..

Scenario for Reactivity Control Reactivity control for all units is by full-in control rods or fuel rack configuration. None are affected by a seismic event or a loss of AC power as they are seismically qualified and do not depend on electric power.

Scenario for Primary Containment Primary containment is open on units 1 and 2 and closed on unit 3. Because the reactor vessels cannot pressurize on units 1 and 2, primary containment is not needed to contain. energy released during a LOCA. On unit 3, the potential exists, upon loss of all AC power, for the vessel to pressurize.

Therefore, the primary containment may serve some purpose on unit 3 and should remain closed.

II' Scenario for Fuel Cooling All eight diesel generators fail after a seismic event at T = 0 All non-seismic equipment fails at T = 0 Unit is in refueling mode with core partially unloaded and pool 1 gates open, cavity flooded.

Unit 2 is in refueling mode with core completely unloaded and pool gates closed, cavity flooded.

'Unit 3 is in cold shutdown with the vessel in tact and the primary containment established.

In this condition,- it is assumed that in the worst case, no AC power would be available after a postulated earthquake. Each unit is assumed to be left with no makeup and no conventional decay heat removal. Cooling of fuel would be through heatup and later boil off of existing water inventories.

alai!~

'he decay heat load of unit 1 is approximately 2HM divided between the fuel pool and the reactor. Since the pool gates are open, the combination of pool and reactor cavity will be treated as one volume.

The fuel pool contains 51 340 ft3 of pater and is initially about 0 100 F.

Conservatively, 51,340 ft = 3.2 X 10 ibm. For an initial temprature of 112 F, 3.2 X 10 BTU is required to reach boiling.

3.2 X 10 8

BTU = 93.8 MW - hrs.

With a heat load of 2 MW, about 47 hours5.439815e-4 days <br />0.0131 hours <br />7.771164e-5 weeks <br />1.78835e-5 months <br /> are required to reach boiling. No credit is taken for reactor cavity water heatup during this phase.

The fuel pool- water would begin to boil off after reaching 212 F. Mith h

fg

= 970 btu/ibm, 7037 ibm/hr will boil off. This is equal to 14 gpm.

The fuel pool contains 10,470 gal/ft alone which results in a maximum pool level drop rate of less than 2 ft/day after the initial 47 hours5.439815e-4 days <br />0.0131 hours <br />7.771164e-5 weeks <br />1.78835e-5 months <br />. The cavity and equipment pit water would cut this rate by approximately 1/2.

Scenario for Fuel Cooling (Continued) 3lni!~

The case for unit 2 is similar to unit 1 analysis but has about 1/2 the heat load (1.1 mw) and's not: connected to the reactor cavity. Using the same assumptions, unit 2 would be bounded by the unit 1 case with 45$

margin..

Time to boil = 85 hours9.837963e-4 days <br />0.0236 hours <br />1.405423e-4 weeks <br />3.23425e-5 months <br /> Boil off rate = 7,7 gpm Drop rate = 1.1 ft/day Unit 3 pool is similar to the unit 2 case but has less decay heat load.

(.34 W)

Time to boil = 276 hours0.00319 days <br />0.0767 hours <br />4.563492e-4 weeks <br />1.05018e-4 months <br /> Boil off rate = 2;38 gpm Drop rate = .34 ft/day Unit 3 reactor is closed and assumed to be in cold shutdown at 180 F. The vessel level is assumed to be normal. At t = 0, decay heat removal would stop and the containment would isolate. The reactor vessel and coolant would heat up to boiling.

Decay heat = 0.6646 MMt Time to boil = 17.8 hrs.

After reaching boiling, heat would be transferred to the suppression pool by steaming through relief valves. Air for relief valves would come from the six ADS accumulators, which would eventually be emptied. Subsequently, the reactor vessel would be allowed to pressurize to 1105 psig and then continue to relieve. At boil off phase, 137 hours0.00159 days <br />0.0381 hours <br />2.265212e-4 weeks <br />5.21285e-5 months <br /> would be required to boil down to TAF. A total of 154 hrs. is available to establish some makeup.

Conclusions and Recommendations

1. The amount of time available for recovery of some AC power for open vessels and fuel pools for the most limiting case is on the order of 12 days. This is ample time to re-establish some sort of AC power or makeup water.

2. The amount of time available for recovery for the closed unit 3 vessel is on the or der of 150 hrs." After'this time, some vessel makeup water would be required. HPCI, which is seismically qualified and independent of AC power, could be run for short periods of time by allowing the vessel pressure to increase when water is needed. In order to accomplish this, the HPCI inboarded steam isolation valve, which is AC powered, would have to be opened initially. It is recommended that this lineup be considered as a compensatory measure.

3. The probability of adverse effects on public health and safety due to the condition of the diesel battery racks is acceptable for the existing plant configuration and the short time for which the condition will exist.

4. The low probability of occurrence of an earthquake during the short time that the condition is expected tb exist and the time and paths available for recovery do not warrant special procedures or equipment for recovery at this time.

(