ML17312A763

Calculation Summary of Radiological Doses for SG Tube Rupture W/Loss of Offsite Power & Stuck Open Adv

ML17312A763
Person / Time
Site:	Palo Verde
Issue date:	05/08/1996
From:	Golbabi M ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:
Shared Package
ML17312A761	List: ML17312A763
References
NUDOCS 9605210182
Download: ML17312A763 (11)

Text

Enclosure to ST-96%287 Page 1of9 Enclosure to ST-96-0287 Calculation Summary ofRadiological Doses for Steam Generator Tube Rupture with Loss ofOffsite Power and Stuck Open ADV Prepared By ehran lbabai NamelSignaturtJD ate VERIFICATIONSTATUS'OMPLETE The Safety-Related design information contained in this document has been verified to bc correct by means ofDesign Rcvicw using the Other Design Document Checklist of QPM 101.

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Enclosure to ST-96-0287 Page 2 of9

Subject:

Calculation ofthe Radiological Doses for the Steam Generator Tube Rupture with LOSS OF OFFSITE POWER and Stuck Open ADV event at 2% Stretch Power

SUMMARY

The following discussion summarizes selected methods and assumptions used in calculation ofthe radiological releases for the Steam Generator Tube Rupture with LOSS OF OFFSITE POWER and Stuck open ADVat 2% stretch power. In summary:

1)

The 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> primary to secondary leakages and secondary steam releases remain the same as the original calculation.

The primary to secondary leakage is a function ofthe RCS and steam generators pressures which are mostly controlled by the operator during the event and are not impacted by the 2% power increase or lower AFAS setpoint.

For the erst two hours, the secondary steam releases are driven by the stuck open ADV on the affected steam generator which removes much more heat than the core generates as decay heat.

For the 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> period, the total integrated decay heat generated by the stretch power core using the 1979 ANS decay heat curve is less than that assumed in the original analysis.

2)

The additional radiological doses are due to the increased period oftube uncovery during the event.

The assumed period of uncovery was increased

&om 887 seconds in the original calculation to 1230 seconds (effectively assuming a tube uncovery period &om 460 seconds to 1690 seconds) for the stretch power analysis.

3)

A copy ofthe chronology ofthe event was marked up and is attached.

The only markup is the time that the level in the faulted steam generator rises above the top ofthe U-tubes.

This value has been increased &om 1385 seconds (in the copy) to 1690 seconds.

Even though the changes considered in the stretch power calculation would slightly impact the timing of the event, the increase in time of level recovery above the U-tubes is the only change needed to represent the conservative approach used for radiological dose calculation.

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DISCUSSION Enclosure to ST-96-0287 Page 3 of9 The radiological doses for this event are primarily due to the releases &om the stuck open ADVon the affected steam generator.

Most ofthe releases occur between the time that the affected steam generator ADV becomes stuck and the time that the level in the affected steam generator rises above the top ofthe tubes.

During this period, the entire primary to secondary leakage is assumed to flash immediately and be released to atmosphere with a DF of 1.0. The original calculation ofthis event established this time to be &om 460 seconds to 1347 seconds, for a total of887 seconds (14.8 minutes).

The 2%

stretch power calculation increased this time period to 1230 seconds (20.5 minutes),

effectively assuming a tube uncovery period from 460 seconds to 1690 seconds.

The additional 343 seconds are due to the followingconsiderations:

1) 212 seconds resulting &om reduction of the AFW rate &om 750 GPM to 650 GPM.

2) 60 seconds to account for lower steam generator masses at initiation ofthe event and the time ofAFAS initiation.

3) 71 seconds resulting &om the reduction ofAFAS initiation analytical setpoint &om 25% to 21% ofwide range span.

The 2% higher power does not affect the two hour or 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> steam releases and radiological doses. For the first two hours, the secondary steam releases are driven by the stuck open ADVon the affected steam generator which removes much more heat than the core generates as decay heat.

For the 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> period, the total integrated decay heat generated by the stretch power core using the 1979 ANS decay heat curve is less than that assumed in the original analysis.

Based on the above discussion, the two hour and 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> PIS and GIS radiological doses were calculated as follows:

2 Hour PIS From the original calculation, the radiological doses during the tube uncovery period (460 to 1347 seconds) were 185.2 REM.

The total two hour radiological doses were 206.6 REM.

The two hour PIS doses for stretch power are calculated by ratioing the original dose release in proportion to the increased time oftube uncov'ery, as follows:

K20.5/14.8)

• 185.2] + (206.6-185.2) = 278 REM.

Enclosure to ST-96-0287 Page 4 of9 The radiological doses were conservatively increased by another 5% to account for the expanded MSSV setpoint tolerances &om 1% to 3%. This brings the 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> PIS dose to 292 REM (rounded up).

2 Hour GIS From the original calculation, the radiological doses between 1337 and 1690 seconds (the additional period oftube uncoveiy for stretch power) were recalculated, assuming that the entire primary to secondary leakage Qashes immediately and becomes airborne with a DF of 1.0, The additional doses during this period were calculated to be 30.6 REM.

The additional doses during this period were added to the 40.4 REM, the 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> doses &om the original calculation. This resulted in a two hour GIS dose of71 REM.

The increased MSSV tolerances do not significantly impact the overall GIS doses since the GIS spiking is small during the MSSV opening this period.

8 Hour PIS and GIS The additional dose increases determined above for two hour PIS and GIS, resulting &om the increased tube uncovery period for stretch power were subsequently recalculated using the 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> to two hour dispersion factor ratio and then added to the respective 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> PIS and GIS doses ofthe original calculation.

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. Enclosure to ST-96-0287 Page 5 of9 Table 15.6.3-6 DECREASE IN REACTOR COOLANT INVENTORY SEQUENCE OF EVENTS FOR A STEAM GENERATOR TUBE RUPTURE WITH A LOSS OF OFFSITE POWER AND FULLY STUCK OPEN ADV (Sheet 1 of 5)

Time (sec)

Event Setpoint or Value Success Path or Comment 0.0 Tube rupture occurs 40 40 47 Third charging pump

started, feet'below program level Letdown control valve throttled back to minimum flow, feet below pxogram level CPC hot leg saturation trip signal generated

-0.75

-0.75 Primary system integrity Primary system integrity Reactivity control 47.15 Trip breakers open Reactivity control 51 Turbine/generator trip Loss of offsite power Secondary system integrity 52 52 56 LH main steam safety valves open, psia RH main steam safety valves

open, psia Maximum steam generator pressures both steam generators, psia

1) 265 1,265 1,330 Secondary system integrity Secondary system integrity March 1990 15.6-40 (1)

Revision 2

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Enclosure to ST-96-0287 Page6of9 PVNGS UPDATED FSAR Table 15.6.3-6 DECREASE IN REACTOR COOLANT INVENTORY SEQUENCE OF EVENTS FOR A STEAM GENERATOR TUBE RUPTURE WITH A LOSS OF OFFSITE POWER AND FULIY STUCK OPEN ADV (Sh'eet 2 of 5)

Time (sec)

Event Setpoint or Value Success Path or Comment 121 Steam generator water level reaches auxiliary feedwater actuation signal (AFAS) analysis setpoint.in unaffected generator, percent wide range level 122 AFAS generated 131 Steam generator water level reaches AFAS analysis setpoint in the affected generator, percent wide range level 25+

25+

Secondary system integrity Primary system integrity 132 AFAS generated 167. 0 177. 0 Auxiliary feedwater initiated to unaffected steam generator Auxiliary feedwater initiated to affected steam generator Secondary system integrity Secondary system integrity (1)

Revision 2

• The analysis used a setpoint of 21%. Even though this change would slightly impact the timing of the event, the only change needed to represent the conservative approach of the analysis is the time of L

level recovery above the u-tubes.

March 1990

15. 6-41

Enclosure to ST-96-0287 Page7of9 Table 15.6.3-6 CREASE IN REACTOR COOLANT INVENTORY SEQUENCE OF EVENTS FOR A STEAM GENERATOR TUBE RUPTURE WITH A LOSS OF OFFSITE POWER AND FUI LY STUCK OPEN ADV (Sheet 3 of 5)

Time (sec)

Event Setpoint or Value Success Path.

or Comment 460 484 Operator initiates plant cooldown by opening one ADV on each SG ADV of the affected SG instantane-ously opens fully Pressurizer empties Reactor heat removal 513 MSIS actuation secondary pressure.

psia 535 Automated isolation of AFW to affected SG, hP

SGs, psi 919 185 Secondary system integrity Secondary system integrity 581 581 Pressurizer pressure reaches safety injection actuation signal (SIAS) analysis

setpoint, psia Safety injection actuation signal generated 1, 578 Reactivity control March 1990 15.6-42 (1)

Revision 2

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4 Enclosure to ST-96-02&7 Page 8 of9 Table 15.6.3-6 CREASE IN REACTOR COOLANT INVENTORY SEQUENCE OF EVENTS FOR A STEAM GENERATOR TUBE RUPTURE WITH A LOSS OF OFFSITE POWER AND FULLY STUCK OPEN ADV (Sheet 4 of 5)

Time (sec)

Event Setpoint or Value Success Path or Comment 581 655 Safety injection flow initiated Operator overrides the AFW isolation signal and starts feeding the affected SG with AFW Reactivity control 16 fg 775 895 1015 Operator takes manual control of the AFW

system, feeds affected SG with both AFW pumps Operator shuts the ADV of the unaffected steam generator Operator initiates auxiliary spray to the pressurizer Level in the affected SG above the top of U-tubes, percent wide range

71. 5 March 1990 15.6-43 (1)

Revision 2

Enclosure to ST-96-0287 Page 9 of9 Table 15.6.3-6 CREASE IN REACTOR COOLANT INVENTORY SEQUENCE OF EVENTS FOR A STEAM GENERATOR TUBE RUPTURE WITH A LOSS OF OFFSITE POWER AND FULLY STUCK OPEN ADV (Sheet 5 of 5)

Time (sec)

Event Setpoint or Value Success Path or Comment 2040 2400 28.800 28,800 Pressurizer

level, percent Operator controls HPSI flow, backup pressur-izer heater

output, and auxiliary spray flow to control RCS pressure and subcooling, F

Shutdown cooling entry conditions are reached; RCS pressure, psia/

temp.

F Operator activates shutdown cooling system 50 20 400/350 March 1990 15.6-44 (1)

Revision 2