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GEORGIA POWER COMPANY..

HATCH NUCLEAR PLANT

PROCEDURE.

Determination of the Extent j

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Of Core Damage Under Accident Conditions |PROCEDURE TITLE j

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HNP-4848PROCEDURE NUMBER

LabRESPONSIBLE SECTION

SArt:.i Y RELATED ( X) NON-SAFETY RELATED ( )|

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APPROVED APPROVEDREV. DESCRIPTION DEPT. PLANT - DATE

HEAD MANAGER .. ____-. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ..____ _-_______ _.. _ _ _ _ _ _ _ _ _ . _ _ ..________

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Q.: .

DETERMINATION OF THE EXTENTOF CORE DAMAGE UNDER ACCIDENT CONDITIONS

_

A. PURPOSE

To provide instructions for determining the extent of core. damageunder accidant conditions.

B. REFERENCES

NEDO-22215 " Procedures for the Determination of the Extent ofCore Damage Under Accident Conditions" by C. C. Lin

C. SAFETY

Observe good radiation protection practices when handling samples,

to minimize personnel exposure.,

D. PROCEDURE^ ~ '

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Obtain a reactor water sample and a drywell atmosphere sample byusing the installed Post Accident Sampling System (PASS).

{/ Determine the corrected activity concentration in micro-curies',

per gm (uCi/gm) decay corrected back to time of reactorshutdown. This correction can be done by entering the time ofthe reactor shutdown into the computer for the sampling time.

Determine the corrected concentrations of the indicator isotopesI-131, Cs-137, Xe-133, and Kr-85. Multiply the concentrations ofI-131 and Cs-137 that are in the reactor water by 1.22. Multiplythe Xe-133 and Kr-85 in the drywell atmosphere sample by 0.786for Unit I and 0.795 for Unit II. After multiplication, theresulting concentrations are the normalized concentrations andcan be compared to the charts developed by General Electric andincluded in this procedure as Figures 1 through 4. Any damage tothe fuel in the core can be determined directly from the graphsby reading pe,rcent of damage versus corrected concentration inuCi/am or uCi/cc.

E. OTHER FACTORS

For further refinement of the core damage estimate, consult thereference in Section B. Some other factors that may be useful indetermining core damage are summarized as follows.

1. Containment Radiation Levels

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Containment radiation level provides a measure of core(. damage, because it is an indication of the inventory of

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airborne fission products (i.e., noble gases, a fraction ofthe halogens, and a much smaller fraction of the'particulates) released from the fuel to the containment.Containment hydrogen levels, which are measurable by thePASS or the containment gas analyzers, provide a measure ofthe extent of metal-water reaction which, in turn, can beused to estimate the degree of clad damage.

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2. Reactor Vessel Water Level;

Another significant parameter for the estimation of core i

damage is reactor vessel water level. This parameter isused to establish if there has been an interruption ofadequate core cooling. Significant periods of coreuncovery, as evidenced by reactor vessel water levelreadings, would be an indicator of a situation where coredamage is likely. Water level measurement would b'eparticularly useful in distinguishing between bulk core .damage situations caused by loss of adequate cooling to the -

entire core and localized core damage situations caused by aflow blockage in some portion of the core.

3. Main Steam Line Monitors,

There are other parameters which may provide an indicationthat a core damage event has occurred. These are main steamline radiation level and reactor vessel pressure. Theusef lness of main steam line radiation measurement islimited because the main steam line radiation monitors aredownstream of the main steam isolation valves (MSIVs) andwould be unavailable fol' awing vessel isolation.

4. Reactor Vessel Pressure Measurement

Reactor vessel pressure measurement would provide anambiguous indication of core damage, because, although ahigh reactor vessel pressure may oe indicative of a coredamage event, there are many non-degraded core events wcichcould also result in high reactor vessel pressure.

5. Detection of the Less Volatile Fission Products

There are other measurements besides radionuclidemeasurements which are obtainable using the PASS which wouldfurther aid in estimating core damage. Detection of suchelements in the reactor coolant as Sr, Ba, La, and Ru isevidence of fuel melting. These indications could befactored into the final core damage estimate.

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6. Metal-Water Reaction of Hydrogen in the Containment1

The extent of fuel clad damage as evidenced by the extent ofmetal-water reaction can be estimated by determination ofthe hydrogen concentration in the containment. Thatconcentration is measurable by either the containmenthydrogen monitor or by the post accident sampling system. l

|A correlation has been developed which relates containment '

hydrogen concentration to the percent metal-water reactionfor Mark I type containments. That correlation is shown inthe curve below. Steps 1 and 2 below indicate the method bywhich Plant Hatch can use the correlation to determine theextent of clad damage.

Step 1: Obtain containment hydrogen monitor reading, (H),in %.

Step 2: Using the curve below, determine the metal-waterreaction for the reference plant, MW ref .

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. METAL-WATER REACTION OF HYDROGEN CURVE

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7. Containment Radiation Level Readings

-An' indication of the extend of core damage is thecontainment radiation level which is a measure of theinventory of fission products released to the containment.The purpose of this step is to present that correlation andprovide a method whereby Plant Hatch can use the corr-elationto determine the degree of core damage.

The procedure for determination of fraction of fuelinventory released to the containment is as follows:

Step 1: Obtain containment radiation monitor reading, (R),| in Rem /hr.'

Step 2: Determine elapsed time from plant shutdown to thecontainment radiation monitor reading (t) in hours.,

*Step 3: Using the. curves below, determine the fuel

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inventory release of airborne radioactivity to thecontainment in percent.

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PERCENT OF FUEL INVENTORY AIRBORNE IN THE CON TAINMEN _ CURVE

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8. Application of Other Significant Parameters to Core DamageEstimate

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As noted previously, procedures have already been developedWhich provide an estimate of core damage based onradionuclide measurements. Based on these procedures, aninitial assessment of core damage is made. Based on.aclarification provided by the NRC, that assessment wouldappear in a matrix as follows:

Degree of ' Minor Intermediate Major )Degradation (C10%) (10% - 50%) (>50%)

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No fuel damage t-----------l-----------3Cladding failure 2 3 4Fuel Overheat 5 6 7Fuel Melt 8 9 10

As recommended by the NRC, there are four jeneral classes ofdamage and three degrees of damage within each of the*

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{ descriptive of the condition where between 10 and 50 percentof the fuel cladding has failed. Note that the conditionsof more than one category could exist simultaneously. Theobjective of the final core damage assessment procedure isto narrow down to the maximum extent possible thosecategories which apply to the actual inplant situation.

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