Mitigating Adverse Radiological Impacts of Steam Generator Replacement Through Source Term Reduction Startup and Shutdown Operating and Chemistry Strategies to Promote Source Term Reduction and Control Dose Rates What we are about to talk about is not intended to be particularly innovative representing new incites into dose rate control but a rather simple / straight forward approach to understanding corrosion product behavior and how they ultimately contribute to radiation fields.

Current Radiological Conditions Steam Generator Replacement Performed at End of a Three Year Shutdown Replaced with B&W Model 51R in Fall of 2000 Plant Dose Rates Decayed to Low Levels Anticipated Dramatic Increases Due to Replacement S/G’s Co 58 contribution to dose radiation fields was essentially non-existent. From Industry OE it was clear that there were some challenges ahead.

Power History Following Steam Generator Replacement One Mid-cycle Outage During First Cycle Following Replacement Service Water System Silt Ingress – 32 days Two Mid-cycle Outages During Second Cycle Following Replacement Main Transformer Fire - 20 days Fish Intrusion (est. 1.2 million fish) – 34 days Did not have smooth sailing following the 3 year S/D. While in Cycle 17 had a cold shutdown right in middle of cycle. Cycle 18 worked through 2 cold S/D forced outages Main transformer fire at midpoint of cycle Fish intrusion 10 weeks following return to power.

Industry Experience First and Second Cycle Following Replacement Elevated Post Hydrogen Peroxide Addition Co 58 Peaks Elevated CRUD Levels Elevated Dose Rates Had the Advantage of knowing what to expect from replacement S/G’s from OE’s. Already begun revising site source term reduction program Planned additional actions to address the conditions that were anticipated.

Developed Options to Mitigate New Radiological Challenges Increased Letdown Flow rate to 200 GPM Following Peroxide Addition to Improve Cleanup Performance Proposed Changes to Operating Activities and Chemistry Shutdown / Startup Program Primary Effort to Increase Letdown Flowrate to prevent an extension of cleanup time. Split letdown flow through two demineralizers – normal letdown demin and a deborating demineralizer Took steps necessary to employ PRC-01 due to likely increase in Corrosion product inventory

Startup Chemistry Strategies Performed stoichiometric additions of hydrazine to the RCS and pressurizer. Performed RCS lithium additions immediately following de-coupling of RHR from the RCS to establish an alkaline environment prior to heat-up. Beginning with Startup Chemistry Changes: DO NOT move core deposit inventory around prior to power operation. PREVENT ACID REDUCING CONDITIONS Get out of acid chemistry ASAP Stay away from reducing chemistry until late in heat-up.

Startup Chemistry Strategies Delayed dissolved hydrogen controls until late stages of heat-up. Minimized coolant boron dilutions during heat-up prior to establishing a minimal dissolved hydrogen inventory.

Startup Chemistry Strategies Established RCS lithium controls prior to entering Mode 2. Stabilize the pH that the core deposit will see during power operation.

Power Operation Chemistry Source Term Reduction Strategies Maintained tight lithium controls during initial power ascension by performing a series of lithium additions. Controlled dissolved hydrogen in upper half of 25-50 cc/kg range while at power. Adjusted coolant lithium concentrations following any power excursions in order to meet the pH(t) objective. Additions based on boron projections during power escalation from Nuclear Engineering. Tight Lithium controls during normal power operation. Adjust coolant lithium concentration as a function of RCS T(ave) to maintain a constant pHt.

Shutdown Chemistry Source Term Reduction Strategies Reduced RCS lithium concentration to 6.5 pH(t) during downpower to optimize acid reducing environment. Employed ultra filtration ion exchange media (PRC-01) to improve particulate removal in letdown stream. During SD, many revision of the program were made. Aggressively work toward creating coolant chemistry that will promote source term reduction. Aggressive Lithium removal helps to create acid early in cooldown.

Shutdown Chemistry Source Term Reduction Strategies Coordinated the removal of dissolved hydrogen during cooldown as a function of coolant temperature. Performed RHR train flushes prior to placing in service. Performed a hydrogen peroxide addition in Mode 5. To promote nickel ferrrite decomposition Eliminate oxygen in RHR Standard procedure – cleanup to < 0.05 uCi/g

Reactor Coolant Radiochemistry End of Cycle 17 Source Term Reduction 8 uCi/gram 58Co peak 3,536 Ci 58Co Removed 4.4 Kg Nickel Removed Highest peak on record at the station and most inventory removed on record.

Reactor Coolant Radiochemistry Cycle 18 Source Term Reduction 1st Mid-cycle 0.89 uCi/g 58Co peak 2,088 Ci 58Co Removed 3.1 Kg Nickel Removed 2nd Mid-cycle 377 Ci 58Co Removed 1.38 Kg Nickel Removed Cycle 18 Refueling Outage 1.27 uCi/g 58Co peak 637 Ci 58 Co Removed First indication that something significant had changed. Transformer fire cold S/D (20 days) performed standard S/D chemistry program including forced oxidation. Completely unexpected response to peroxide addition – only 0.89 uCi/g peak Had advertised a 10 uCi/g peak based on second cycle OE. Delayed response to inventory removed in previous outage – use of PRC-01. Note sequential decrease in inventory

Reactor Coolant Radiochemistry Cycle 17 Average Reactor Coolant 58Co Activity 1st Half of Cycle 6.9E-05 uCi/g Service Water Silt Outage 2nd Half of Cycle 9.04E-05 uCi/g Failed to perform any source term reduction actions. Expected short outage ended up 32 days. Maintained coolant alkalinity throughout shutdown No significant corrosion product inventory reduction. Lost opportunity Note increase in average coolant radio cobalt activity after returning to power following outage.

Reactor Coolant Radiochemistry Cycle 18 Average Reactor Coolant 58Co Activity 1st Segment of Cycle 7.6E-05 uCi/g Transformer Fire Outage 2nd Segment of Cycle 1.7E-04 uCi/g Fish Intrusion 3rd Segment of Cycle 8.6E-05 uCi/g Coolant activity was relatively low on return to power (slightly below the activity at the end of the previous cycle. Anomaly - S/U Crud burst Note coolant activity on return to power.

Refuel Outage Dose Rate Data Best overall depiction of dose rate reduction S/G Hotleg # 14 S/G only generator opened last refueling outage

Refuel Outage Dose Rate Data S/G Cold Leg Same story

Dose Rate Profile During Cobalt Cleanup Depiction of cleanup Blanks are missing data. Approximately 32 hours between peak and return to baseline.

Refuel Outage Dose Rate Data RTD Lines ~ 30-50% Lower than U1C18 PZR Deck ~ 30% Lower than U1C18 Regen Hx ~ 200% Lower than U1C18 S/G #14 ~ 30-50% Lower than U1C18 Additional Dose rate data

Final Results Successful Mitigation of Potentially Difficult Radiological Conditions Outage Exposure Goal of 125 Person-Rem Lowered to 90 Actual Outage Exposure - 78.82 Person-Rem Despite Significant Re-work and a 5 Day Outage Extension A 47% Reduction in Personnel Contamination Events

Conclusions Took Full Advantage of Mid-Cycle Outages to Promote Source Term Reduction Ultra-Filtration of Letdown Flow (PRC-01) During Refueling Outages A Combination of Many Chemistry and Operating Strategies We believe: Source term reduction (corrosion product reduction) translates into dose rate reduction. Radiological changes were driven by source term reduction as a direct result of plant operation and revised operating and chemistry practices. Unable to determine if all changes contributed to overall result. Will continue these programs and continue to gain better understanding of corrosion product chemistry.

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