Presentation on theme: "Braidwood Station Alternate Post Peroxide Cleanup Methodology."— Presentation transcript:
Braidwood Station Alternate Post Peroxide Cleanup Methodology
2 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.
3 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.
4 Exelon Shutdown Chemistry Outage 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.
5 Exelon Shutdown Chemistry Outage 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 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
6 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.
7 Pre-Outage / Shutdown Dose Rates
8 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
9 Pre-Dissolution Activities Chemical Degas For the alternate template approach, RCS Hydrogen must be reduced to 1 cc/kg prior to the forced oxidation because the RCPs will be secured and LSIVs closed prior to the peroxide add.
10 Pre-Dissolution Activities Shutdown all 4 RCPs Isolates Pressurizer and associated piping from dissolution thus reducing pressurizer system dose rates.
11 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
12 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.
13 Pressurizer Isolation Top of Pressurizer normally 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.
14 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.
15 Pressurizer Isolation Pressurizer Weld Overlay Project Project estimate Rem Project challenge Rem Actual Project total – Rem 7% TLD bias – Rem Lowest Dose industry PWOL using PCI
16 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.
17 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.
21 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
23 Alternate Post Peroxide Cleanup Methodology Peak Dissolution Activity 12.8 Ci/ml Flood Up EPRI Guidelines suggests clean-up to less than 0.05 Ci/ml. Actual cleanup prior to flood up was Ci/ml. Final cleanup was Ci/ml. Clean up window is 40 hours.
24 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)
25 Alternative Post Peroxide Cleanup Methodology