1. 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.

2. 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.

3. 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.

4. 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.

5. 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

6. 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.

7. 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.

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

9. 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 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.

10. 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.

11. 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

12. 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.

13. 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

14. 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.

15. 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.

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

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

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

19. 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

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

21. 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.

22. Mitigating Adverse Radiological Impacts of Steam Generator Replacement Through Source Term Reduction
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