ML17255A678

Rev 0 to Procedure PC-25.4, Guidance for Interpreting Post-Accident Sampling Results to Estimate Reactor Core Damage.

ML17255A678
Person / Time
Site:	Ginna
Issue date:	03/16/1983
From:	ROCHESTER GAS & ELECTRIC CORP.
To:
Shared Package
ML17255A675	List: ML17255A673 ML17255A678 ML17255A679 ML17255A680 ML17309A324
References
RTR-NUREG-0737, RTR-NUREG-737 PC-25.4, NUDOCS 8402100256
Download: ML17255A678 (15)

Text

'HBRIIATIl)lftjifj'Y GlthNA STATION)

UNIT P3 COMi~lF; ':-D DATE: ~

ROC HESTF R GI'S A"fD ELECTRIC CORPORATION Tl)AE: ~

GING, STATION CONTROLLED COPY'NUMBER PROCFDURE RO. PC-25.4 RSJJ. NO. 0 GUIDELINFS FOR INTERPRETIt'IG POST-A CIDE"!1T SAXPLI'AG RESULTS TO EST INATF. REACTOR CORE DA?J1AGE TECHVICAL REVI F?3

. PORC RFVIE?'7 DATE OC REVI EW PLANT 8 PERI! EN~. DE~1T M~R 22 tg83 EFFECTIVE DATE OJ! ~'ON-OJ! CATEGORY 1.0 RFVIEWED ?3Y:

TRIS PROC SO!JRS CONTJ!INS 8 PJJ 8 S402i'00256 840206?,J "

",PDR(~',

05000244' PDR ADOCK, P " '

PC-25.4:1 PC-25-4 GUIDELINES FOR INTERPRETING POST-ACCIDENT SAMPLING RESULTS TO ESTIMATE REACTOR CORE DAMAGE PURPOSE:

This procedure provides guidelines for the preliminary assessment of reactor core damage based upon post-accident sampling results or other radiological indications. melting' 1 ~ 2 Certain reactor transients could result in fuel cladding damage, fuel overheating or potential fuel . One or more of these conditions would involve the release of radionuclides into the primary coolant, followed by possible transfer to auxiliary systems and the containment atmospheres 1..3 . By examining the magnitude of radioactivity increases in a post-accident condition, as well as confirming the presence or absence of certain groups of radionuclides, an early assessment of core damage can be performed.

REFERENCES =

Procedure PC-23-1, PC-23.2, PC-25.2, PC-4, PC-5 2.2 Procedure P-9 2 ' Procedure S-14.2, S-14.3 2.4 Procedure SC-188 2.5 NUREG-8737, II 'E 3 2 ' Westinghouse Mitigating Core Damage Training Manual F 7 Rogovin Report, Part 2, Volume II, pp 524 527 2 ' WASH-1488 Appendix VII 3~8 PRINCIPLE=

s

~ ~

~

C

~

'C-25.4:2

'ross indicators of radioactivity concentration (letdown monitor, containment area and airborne monitors) will provide early information on the severity of core damage following a transient. When later primary coolant and containment samples are collected and analyzed, measured concentrations of radionuclides can be examined to determine the extent of total available activity that. has been released to the RCS Auxiliary systems. Certain radionuclides will tend not to be released unless fuel overheating or melting the absence of these species will bound the maximum occurs'hus extent of core damage. The determination of certain isotope ratios may also help distinguish whether released activity originated in the gap or from overheated fuel.

PREREQUISITES AND NEEDED EQUIPMENT:

4.1 Isotopic analysis of primary liquids.

4' Data from plant radiation monitors.

4' Plant operational status including pertinent core data.

Isotopic analysis of containment atmosphere.

PRECAUTIONS AND LIMIT VALUES:

5.1 Care should be taken to avoid defining too precisely the extent of core damage based upon initial sampling results.

Other plant indicators will also be available (such as incore temperature indication, containment hydrogen monitors, etc.)

which should also be considered in arriving at a more refined est,imate.

5 ' The time of sampling relative to the suspected transient or core degradation sequence must, be considered. The effects of isotope decay, sampling equilibrium and progre'ssing core degradation may tend to confound sample interpretation.

5'3 Reactor power history is to be considered in determining whether certain key radionuclides have reached equilibrium.

5.4 Measured concentration of radioactivity may need to be adjusted to account for system dilution (e.g. accumulators, safety injection water) prior to estimating fuel damage.

6.6 INSTRUCTIONS

6~1 Indication of RCS Abnormal Conditions

~

~

~

'C-25.4:3 g

~

q ~

)

6~1~1 There are various instruments which will indicate to the plant operator if abnormal conditions exist. in the RCS which could contribute to 'fuel failure. This instrumentation would include indication of coolant temperature, and water inventory (if available). Plant operating pressure,'ubcooling and emergency procedures provide detailed instruction on how the instrumentation is to be used. ~ /

6.,1 2 Post,-accident analysis 'of- these parameters should determine whether voiding of the RCS occurred, or'ore specifically,

~

whether any part of the core was uncovered at any time.

Special attention'hould be *paid to core exit the rmocouple temperatures and core water level indications. If the core remained covered, fuel damage should be limited to gap releases from cladding defects. However, it if the core was uncovered, becomes more probable that extensive cladding oxidation could have occurred leading to cladding and fuel pellet fragmentation.

6.2 Gross Radioactivity Indications 6~2~1 Letdown Monitor R-9 6~2~1~1 If letdown has not been isolated, monitor R-9 will provide a gross indication of current. primary coolant activity.

P Refer to procedures P-9 and SC-188. A reading of 2888 mR/hr on monitor R-9 will correspond to approximately 1% fuel rod cladding defects. The monitor's upper range, 18,888 mR/hr, may therefore be assumed to correspond to about 5%

cladding defects. 1 6~2~1 2 ~ Containment Airborne Monitors R-ll, R-12 8 ~

4 ~

6-2.1 ~ 2~1 Pz'imary coolan)t system leakage results in the release of noble gas and radioactive particulates into the containment atmosphere. An increase in primary coolant activity and/or system leakage will be indicated on containment monitors R-ll and R-12. Refer to procedures P-9 and S-14.2.

Vy~ g 6 ' ' Containment Area Monitors R-2, R-29 and R-38 II l 6~2~2~1 An increase in the direct radiation readings of the containment area monitors will also indicate abnormal primary coolant activity and/or leakage conditions in the containment building.

Refer to procedures P-9 and S-14. 3. Procedure S-14. 3 provides a series of curves showing monitor dose rate versus time

~ ~

PC-25.4:4 6 '.2.1

~ ~ ~ (Cont'd) a fter shutdown. The curves have been calculated for various accident categories including postulated gap activity release, coolant release, and fuel inventory release. The procedure also provides tables of estimated isotopic activities which correspond to the accident categories considered.

6~2~3 Primary Coolant and Containment Atmosphere Samples 6 '.3 ' The previous indications may show that a substantial release of radioactivity has occurred from an accident condition.

Undiluted samples may read several orders of magnitude higher than under normal conditions. Extreme precautions are required in -sample collection, handling and analysis to minimize potentially severe radiological hazards that may exist.

6 ' Release of Fuel Rod Gap Activity 6~3 1 ~ Table 1 provides escape fractions (EF) for various categories of radionuclides which may be assumed in determining the degree of ruptured fuel rod damage. The table also indicates the associated uncertainties for each radionuclide category.

6 ' ' Table 2 gives the calculated reactor core inventories (NI) of various radionuclides based upon 1528 NWT.

6 ' ' The following equation is used to estimate the failed fuel rod fraction based upon the measured sample concentration of a given category of radionuclide:

FF = '(CA) (V)

(NI)'EF)

Where: CA = callant activity (uci/g(

V = coolant mass (1.18 x 18 g)

NI = nuclide inventory (Table 2)

EF = escape fraction (Table 1)

,6 ~ 3 ~ 4 Analytical results indicating only noble gas, iodines and cesium isotopes will suggest that only a release of gap activity has occurred. Radionuclides such as strontium, barium and tellerium would not be significant contributors to coolant'ctivity in this situation because of much lower escape fractions.

6 ' ' For a given fraction of failed fuel (e g. 18%), the initial degassed activity will be mainly comprised of radioiodines (at T=8 hr). The initial activity contribution due to cesium may be small compared to the iodine activity.

~ ~

1 PC-25.4:5 For perspective, assuming 18~ failed fuel defects, the initial gas and degassed activities are calculated to be approximately 18, times higher than normal activity levels. Activity -

levels will drop substantially (factor of 2 to 3) during the first day due to the decay of short-lived noble gas and iodine isotopes. II O 1 II " ll 4

Evidence of Fuel Overheating 6~4~1 Potential fuel overheating may be suggested primary coolant activity cannot be accounted for by assuming if the actual 188% release of gap activity; or,.if certain radionuclides are detected which are indicators of fuel pellet overheating.

6 ' ' Under conditions of fuel overheating, radionuclides such as strontium, barium and tellerium would be released from the fuel to a greater extent, than predicted from the escape fractions given in Table l.

Evidence of Fuel Melting II ~ II 1, I ~ lf Post-accident samples which display extremely high activity or a greater presence of normally less volatile radionuclides, may indicate that partial fuel melting has occurred in addition to clad damage.

'<<0 ~ III 6' '

~ ~ Table 3 provides estimated escape fraction for various radio-nuclide categories, assuming fuel melting conditions. 'The percent of fuel melted can then be estimated using the same equation given in step 6.2.3. c 6 ' ' For a given fraction of melted fuel (e g. 18%) the initial degassed activity will be largely due to radioiodine. However, the presence of strontium activity is likely to be detected following radioiodine decay, and is calculated to be more predominant than cesium activity under fuel melt conditions.

(A, .').a For perspective, assuming 18% melted fuel, the initial gross 14 ~

6 ' '

gas is calculated to increase approximately a factor of 18 over normal levels. The gross degassed activity may increase as much as 18 to 186.

6~5~5 Detailed sample isotopic analysis may also indicate the presence of noble metals (Ru, Rh, Pd, Mo, Tc), rare earths and actinides (U, Pu) and other refractory materials which would also confirm extensive fuel damage.

e 0

a a'.

~ I PC-25.4:6 TABLE' GAP RELEASE COMPONENT VALUES Fission Gap Gap Total Gap Product Release Escape Release/Escape Species Fraction Fraction Value Xe, Kr 8 83(a) e.es(a) 1 1/3(c) 8 '3 I-Br 8.817 Cs, Rb e.ls(b) 1/3(c) 8 85

~

Ba 'r,"

e.el(a) 18-4(d) 8.888881 Te, Se, Sb e.le(a) 18-3(d) 8.8881 Others Negligible(

(a) Values can be higher or lower by a factor of 4 (b) Values can be higher by a factor of 2 or lower by a factor of 4

(c) Values can be higher or lower by a factor of 3 (d) Values can be higher or lower by a factor of 188 (e) While no numerical value was developed. for these various species, the number should not exceed that used for strontium-barium.

Reference:

WASH-1488, Appendix VXX

PC-25 ':7 TABLE 2 TOTAL INVENTORY OF SELECTED RADIONUCLIDES IN THE NUCLEAR REACTOR CORE AT THE TIME OF THE HYPOTHETICAL ACCIDENT RADIOACTIVE INVENTORY RADIONUCLIDE SOURCE (curies) HALF-'LIFE (da s)

Cobalt-58 3-7 x 185 71 '

Cobalt-68 1 ~4 x 185 1, 928 Krypton-85* 2 ~ ", X~ 185 3, 958 Krypton-85m 1~2 x 187 8 '83 Krypton-87 2' x 187 8.8528 Krypton-88 3' x 187 )8 ~ 117 Rubidium-86 1 ~3 x 184 18 '

Strontium-89 4 ' x 187 52 '

Strontium-98*

Strontium-91 1 8 x 186 5'

~

x 187 ll, 838 8.483 Yttrium-98 1-8 x 186 "2 ~ 67 Yttrium-91 5' 187 59 '

Zirconium-95 7' x 187 65 '

Nobium-95 7' x 187 35 '

Molybdenum-99* 7' x 187 2 '

Technetium-99m Ruthenium-183 6'

5' 187 x 187 8 '5 39 '

Ruthenium-186 F 2 x 187 366 Tellurium-127 2 8 x 186

~ 8.391 Te 1lur ium-12 7m 5' x 185 189 Tellurium-129 1 5 x 187

~ '8. 848 Tellurium-129m 2' x 186 8.348 Tellurium-131m .6- 3,x 186 1 25 Tellurium-132 Iodine-131*,

5.8 x 187 4.8 x 187 3 '5

~

8 '5 Iodine-132 5.8 x 187 8.8958 Iodine-133* 7 ' x 187 8.875 Iodine-134 F 9 x 187 8.8366 Iodine-135 7' x 187 8.288 Xenon-133*

Xenon-135 7' x 187 1.6 x 187 5 '8 8.384 Cesium-134* 3' x 186- 758 Cesium-136 1 4 x 186-

~ 13*8 Cesium-137* 2' x 186"'87 11,888 Barium-148 7' x 12 '

Lanthanum-148 7' x 187 1 ~ 67 Cerium-141 7' x 187 32 '

Cerium-143 6' x 187 1 38

~

Cerium-144 4.8 x 187 284 Praseodymium-143 6.3 x 187 13 '

• These are the most significant nuclides.

t PC-25.4:8 TABLE 3 MELTDOWN ESCAPE FRACTION VALUES ELEMENTS RELEASE RANGE BEST ESTIMATE (percent) (percent)

Xe, Kr 58-188 I, Br 58-188 Cs, Rb ~ 48-98 88 Te(a) 5-25 15 Ba, Sr 2-28 Noble Metals( 1-18 3 Rare Earths( ~ 81-1 8' Zr, Nb .81-1 8 '

Reference:

NASH-1488, Appendix VII

• ~

lP I

I"