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Refuel Outage Shutdown Chemistry • Proper shutdown chemistry is necessary in order to ensure: • Primary system dose rates and smearable contamination levels are maintained ALARA to the extent that shutdown activities influence these parameters. • The coolant is prepared for head lift (fully oxygenated and purified to within EPRI guideline endpoints). • Plant effluents are minimized to the extent possible, and managed within station effluent limits. • Water movement is managed to minimize liquid radwaste effluents and tritium releases.
Exelon Refueling Outage Shutdown Template The Exelon Refueling Outage Shutdown Template is a tool to prepare for refueling outage shutdown. This “Alternate” template was developed for A1R13 to establish a different approach to shutdown that allows the LSIV’s to be closed prior to forced oxidation so that other outage work can be accommodated.
Exelon Shutdown ChemistryOutage Readiness • On-Line Chemistry - Maintained RCS at constant elevated pH • U2 pH is maintained at 7.2 during fuel cycle. • U1 pH is maintained at 7.35 (first time) during fuel cycle. • RWST is placed on recirculation cleanup with an FC Demineralizer 3 months prior to the start of the outage to reduce soluble iron and radionuclides. • Prepare Both CV Demins and both FC Demins with fresh HOH resin underlay and macro-porous resin overlay. • Plans for Orthoporous in one Letdown Demin use during A1R14.
Exelon Shutdown ChemistryOutage Readiness • Assess the condition (dose and differential pressure) of the reactor coolant filter approximately one week prior to shutdown to determine filter size / change out frequency. • Normal use of 0.1 micron PAL filters • U1 installing 0.05 micron filter – November 2008. • Increase to 0.45 micron filters - if change out periodicity is less than 2 hours • Increase to 1 micron filters - if change out periodicity is less than 1 hour
Exelon Shutdown Chemistry • Shutdown Chemistry – End of Cycle (EOC) Boron. • Determine the refueling boron concentration target for the shutdown. • Exelon data shows that refueling outage dose rates increase significantly when EOC boron is allowed to reach zero ppm. • Since implementation of EOC Boron at 10 ppm, ~10% dose rate reduction on S/G tubesheets. • Deboration is controlled through the Demins rather than through dilution to avoid oxygenated water.
Alternate Post Peroxide Cleanup Methodology • Reduced volume of water for post peroxide clean up from 107,000 gallons to 62,000 gallons or 58% of original inventory. • Isolated Pressurizer • Isolated Steam Generators • Isolated some CV / Letdown areas
Pre-Dissolution Activities • Chemical Degas • For the alternate template approach, RCS Hydrogen must be reduced to < 5 cc/kg but maintained >1 cc/kg prior to the forced oxidation because the RCPs will be secured and LSIVs closed prior to the peroxide add.
Pre-Dissolution Activities • Shutdown all 4 RCPs • Isolates Pressurizer and associated piping from dissolution thus reducing pressurizer system dose rates.
Pre-Dissolution Activities • Start-up Letdown Booster Pump • Cleanup flow at 160 gpm • Utilizing Two CV Demin Beds • Increased clean-up flow to 175 gpm • Letdown Relief Valve set point adjusted to adjusted to increase flow/pressure. • Engineering design change increased set point from 205 psi to 230 psi. • Will increase flow to >180 gpm if using two Letdown Demins
Pre-Dissolution Activities • Isolation of Steam Generators via Loop Stop Isolation Valves (LSIVs). • Less opportunity for particulates to plate out on S/G tube sheet or piping surfaces resulting with reduced dose rates on S/G platforms. • Activity of water drained to RF sump is reduced. (less dose to clean sump) • Activity of water transferred to RCDT reduced (and dose rates of components near tank). • 377’ IMB General Area dose rates also reduced.
Pressurizer Isolation • Top of Pressurizer normally 25 - 35 mrem/hr general area with 350 – 450 mrem/hr contact dose rate on RY Spray line (post dissolution & flush) • A1R13 (isolation & flush) was 15 – 20 mrem/hr general area with 150 – 170 mrem contact on RY Spray line.
Pressurizer Isolation • Bottom of Pressurizer normally 100 – 150 general area with 700 – 900 mrem/hr contact dose rate on RY Surge line (post dissolution & flush) • A1R13 (isolation & flush) was 50 mrem/hr general area with 180 mrem/hr contact on RY Spray line. • A2R13 (second cycle zinc) saw increased dose rates due to increased RCS activity and low flow area.
Pressurizer Isolation • Pressurizer Weld Overlay Project • Project estimate 20.963 Rem • Project challenge 16.940 Rem • Actual Project total – 13.641 Rem • 7% TLD bias – 12.686 Rem • Lowest Dose industry PWOL using PCI
Pressurizer Isolation • RY Platform • RY Platform general area dose rates are normally 150 – 500 mrem/hr. • A1R13 general area dose rates were 50 – 200 mrem/hr.
CV / Letdown Isolation • CV / Letdown Isolation • Only in Containment after depressurization • CV / Letdown general area dose rate normally 50 – 350 mrem/hr. • CV / Letdown contact dose rate normally 300 – 600 mrem/hr. • A1R13 general area dose rate were 20 – 150 mrem/hr. • A1R13 contact dose rate were 100 –150 mrem/hr.
Steam Generator Maintenance • Lowest dose U1 Steam Generator Maintenance in station history. • A1R13 = 19.379 person-rem • A1R12 = 27.951 person-rem • A1R11 = 23.213 person-rem • A1R10 = 39.080 person-rem • A1R08 = 24.960 person-rem • A1R06 = 44.413 person-rem • A1R05 = 34.600 person-rem • A1R04 = 33.920 person-rem • A1R03 = 47.600 person-rem • A1R02 = 63.990 person-rem
Outage Maintenance • A1R13 was second largest scope in station history (SGRP was largest) • Included PWOL, ECCS Strainer, and S/G Insulation replacement, Split Pin, Core Barrel, Ex-Core Dosimetry and Barton Transmitters. • Major Modifications accounted for 30 Rem • 109 Rem goal - 92 Rem actual
Historical Outage Exposure • A1R13 = 92 person-rem • A1R12 = 98 person-rem • A1R11 = 81.8 person-rem • A1R10 = 134.8 person-rem • A1R09 = 79.7 person-rem • A1R08 = 96.8 person-rem • A1R07 = 221 person-rem (SGRP)
Alternate Post Peroxide Cleanup Methodology • Peak Dissolution Activity • 12.8 mCi/ml • Flood Up • EPRI Guidelines suggests clean-up to less than 0.05 mCi/ml. • Actual cleanup prior to flood up was 0.028 mCi/ml. • Final cleanup was 0.015 mCi/ml. • Clean up window is 40 hours.
Alternate Post Peroxide Cleanup Methodology • Both FC Demins put into service. • Outage unit provides cavity – cavity cleanup capabilities. • Operating unit provides spent fuel pool – cavity cleanup. • Use of 1 micron PAL filters in both Tri-Nukes (600 & 240)