1. 1 Braidwood Low Inventory Shutdown Experience Harry Bush ALARA Section Braidwood Nuclear Station 2009 ISOE ALARA Symposium & EPRI Radiation Protection Conference January 14, 2009 Ft. Lauderdale, Florida, USA

2. 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. 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. 4 Exelon Shutdown Chemistry Outage Readiness On-Line Chemistry - Maintained constant elevated pH of 7.2 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.

5. 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

6. 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. 7 Pre-Outage / Shutdown Dose Rates

8. 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. 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. 10 Pre-Dissolution Activities Shutdown all 4 RCPs Immediately after RCS Hydrogen < 5 cc/kg the last RCP is secured, RCS is de-pressurized. Isolates Pressurizer and associated piping from dissolution thus reducing pressurizer system dose rates.

11. 11 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. 377’ IMB General Area dose rates also reduced.

12. 12 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 (1CV8119) set point adjusted to increase flow/pressure. Engineering design change increased set point from 230 psi to 265 psi. Will increase flow to >180 gpm

13. 13 Dissolution With the pressurizer at 95% level, peroxide was added for forced oxidation (e.g. introduce oxygen to the coolant). Immediately after reaching the radionuclide peak, charging flow was realigned to the top of the pressurizer and the RCS drain to the flange was commenced. Even though the peak was twice as large as would have been the case using the old method of forced oxidation with RCP’s in operation (due to dissolving the same inventory into ~ ½ the system volume), the cleanup duration was not impacted

14. 14 Dissolution In addition to normal charging the entire volume of the pressurizer served as a source of cleanup water as the RCS was drained to the flange. This unique approach: 1.allowed cleanup to be performed in the same amount of time, 2.limited the amount of RCS and connected systems subjected to the forced oxidation to ~ ½ of the volume of the old method, and 3.permitted draining the RCS to the flange 6 hours earlier

15. 15 Alternate Post Peroxide Cleanup Pressurizer Isolation Results 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.

16. 16 Alternate Post Peroxide Cleanup Pressurizer Isolation Results 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.

17. 17 Alternate Post Peroxide Cleanup Pressurizer Isolation Results Pressurizer Weld Overlay Project Project estimate 20.963 Rem Project challenge 16.940 Rem Actual Project total – 13.641 Rem 6.44 % TLD bias – 12.686 Rem Lowest Dose industry PWOL using PCI

18. 18 Alternate Post Peroxide Cleanup Pressurizer Isolation Results RY Platform RY Platform general area dose rates are normally 150 – 500 mrem/hr. A1R13 general area dose rates were 50 – 200 mrem/hr.

19. 19 Alternate Post Peroxide Cleanup Letdown Isolation Results 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 – 100 mrem/hr. A1R13 contact dose rate were 100 –150 mrem/hr.

20. 20 Standard Radiation Measurement Program

21. 21 Alternate Post Peroxide Cleanup S/G Isolation Results 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

22. 22 Base Point Surveys

23. 23 Outage Maintenance Second largest scope is 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 - 91 Rem actual

24. 24 Historical Outage Exposure A1R13 = 91.25 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)

25. 25 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 0.028  Ci/ml. Final cleanup was 0.015  Ci/ml.

26. 26 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)

27. 27 Alternative Post Peroxide Cleanup Methodology

28. 28 Transferability This improved shutdown methodology is applicable to all PWRs, regardless of NSSS vendor and specific design. It is not necessary to have loop stop isolation valves to benefit from this new shutdown method: any plant that has no flow in the primary loops after securing the last reactor coolant pump can benefit from this approach. EPRI Primary Guidelines are being revised to accommodate this methodology.