1. Richard L. Doty PPL Susquehanna, LLC
Very Low Exposure Rates: The Culmination of a Series of Source Term Reduction Efforts
Richard L. Doty
PPL Susquehanna, LLC

2. But Really, A Story Of Challenges Management Commitment
Strategic Dose Reduction Planning
Execution of the Plan
Results

3. Challenges in the 1990s High insoluble iron levels in feedwater
Plan to implement hydrogen injection to reduce susceptibility to stress corrosion cracking of reactor vessel internals
Recognition that while Susquehanna was improving dose-control performance, other plants appeared to be improving faster
The high insoluble iron levels prevented Susquehanna from economically using depleted zinc injection. The cost of zinc would have been much too high. That of course meant that means to reduce insoluble iron levels would need to be considered in the planning process.
The injection of hydrogen to reduce susceptibility to stress corrosion cracking (SCC) was considered in terms of repairs to the recirculation piping, but it was the potential for cracking of, and the need to repair, vessel internals that led to a decision to implement hydrogen injection.
Standards at operating nuclear power plants continue to be set at higher levels, and performance at the plants continues to improve, sometimes at dramatic rates. If Susquehanna did not accelerate its rate of improvement, then Susquehanna performance would drop from the top (first) quartile into the second and potentially even the third quartile.

4. Management Expectation
Develop a plan to meet the strategic goals for the station (top quartile or better)
Base that plan on industry experience and good forecasting
Address both outage and operational periods
Implement that plan, recognizing that full implementation may take several years
In the plants it is really easy to get caught up by what is happening today, or will happen in the next outage, and those tasks do need to be dealt with in the best possible way. However, someone on staff should be looking at where the station needs to be 5 or 10 years down the line, and making suggestions as to how to ensure that the station can get there.
In the mid-1990s, the “strategic thinkers” thought that by 2005 the best quartile performance would probably be less than 1.0 person-Sievert per reactor per year in the U.S. At that time, such performance looked to be virtually unachievable at Susquehanna. Reduction of dose to below current levels became an interim milestone toward future reductions.
Susquehanna staff paid a lot of attention to the experiences of others and tried to analyze those experiences to their advantage. Then they tried to make the best possible business case to station management to obtain approvals to take on projects that they knew would involve a substantial number of dollars.

5. Expected Dose Reduction with CFS and One Chem Decon per Reactor Unit
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Actual
With HWC
With HWC & CFS
Chem Decon
Pre-HWC
Post-HWC
(PERSON-SV)
This graph shows the anticipated effects of implementing a hydrogen water chemistry regime at Susquehanna. The dose consequences were expected to be up to an additional 3 person-Sv per year. By also implementing a new condensate filtration system (mechanical filtration) to reduce iron and other contaminant levels in feedwater, those adverse dose consequences could be reduced substantially (cut in half). Also, Susquehanna needed to consider chemical decontamination of the reactor recirculation system and the in-containment portion of the reactor water clean-up system. The graph depicts the initial forecasts of the changes in collective dose performance given one chemical decontamination of each reactor.
A chemical decontamination means manpower resources used in preparation and execution, a challenge to nuclear safety which must be effectively dealt with, dollars for implementing the process itself, and critical path implications for the outage. On the plus side, expected reductions of more than 1 person-Sv per year were anticipated. As it turns out, the chemical decontamination factors exceeded expectations, and consequently the dose savings exceeded expectations.

6. Susquehanna Unit 2 Milestones
Condensate Filtration /99
FW Iron Injection /99
HWC /99
Chemical Decon /01
GEZIP (DZO) /02
Chemical Decon /03
Rick chose to focus on Unit 2 in this presentation. That is because the last completed outage for Susquehanna was on Unit 2 in the spring of 2005, so the data are perhaps a little more complete for that unit.
Susquehanna is on a 24-month cycle for each unit. So, HWC was implemented after the spring 1999 outage, meaning that the spring 2001 outage was the first Unit 2 outage after HWC implementation on that unit.
In case you are wondering, I am told that Unit 1 projects and results look very much the same, maybe even better in terms of results. Unit 1 is in outage in March 2006, with pre-outage results suggesting that Unit 1 may continue to be slightly better than Unit 2.

7. SSES U2 Average BRAC Rick wanted to point out two items on this graph.
First, Susquehanna expected, and unfortunately observed, a large increase in recirc system piping exposure rates at the first outage after implementation of HWC on unit 2. The increase was in line with, but near the upper end of, their forecasts. That forecast was a major contributor to the decision to prepare for a chem decon on unit 2 during that outage.
Second, they anticipated the need to do a chem decon on unit 2 during its outage in spring They did not want to continue doing chem decons. They did want to initiate depleted zinc injection. Their analysis concluded that zinc injection needed to be initiated at least 3-4 months ahead of the refueling outage, to pre-condition the fuel and the feedwater piping with zinc going into the outage. The intent was to ensure that zinc injected coming out of the outage did its “magic” in replacing cobalt deposition onto recirc and other downstream piping, not get taken up on the feedwater side of the flow path.

8. Unit 2 Cycle 12 Chemistry and Operational Data 3/03-3/05
Pre-Decon BRAC 3/ mSv/hr
Post-Decon BRAC 3/ mSv/hr
Median FW Zn(S) ppb
Median FW Fe(I) ppb
Median RCS Zn(S) ppb
Median RCS Co-60(S) Bq/ml
Median RCS Co-60(I) Bq/ml
You will note on this graph, a decon factor for the 2003 outage of over 30.
Feedwater and Reactor Coolant System zinc levels are near those considered to be optimal for this cycle.

9. Unit 2 Cycle 12 Chemistry and Operational Data 3/03-3/05
Median Co-60(S)/Zn(S) E-02 Bq/ml-ppb
HWC ppm
Estimated DZO kg cycle 11
66 cycle 12
Cycle Run days
End of Cycle Coast-down with semi-soft shutdown
2005 BRAC mSv/hr
You will note on this graph that the cobalt-to-zinc ratio is on the order of E-2.
You may also note that Susquehanna uses a relatively high hydrogen injection rate to maintain protection for the vessel internals. One implication is that they need to do good analyses when work needs to be done on-line in steam-affected areas, where exposure rates are relatively high because of the relatively high hydrogen injection rate. Susquehanna Health Physics technicians developed a model to forecast exposure rates in certain plant areas as a function of reactor power and hydrogen injection rate, to be able to better decide what changes to hydrogen injection may be needed and what doses may be expected to do certain tasks in steam-affected areas.

10. These data show recirc system exposure rates for a set of BWRs as of summer (I am sure that Dennis Hussey and other EPRI personnel would be pleased to discuss with you, how the measurements program operates.)
Susquehanna’s two units have among the lowest exposure rates for the BWRs. (Numbers 1 and 4 as Rick recalls) They anticipate the units’ remaining in the top few positions over the near term.
Not obvious from this graph is the trend in median value. On this graph the median value is about 1.3 mSv/hour, whereas if you look at this graph for a time period not too long ago, you would have seen a median value of closer to 2.0 mSv/hour. The point – the standard has been raised, performance is improving. If you are where you were several years ago, your position relative to your sister stations has declined.

11. Other Susquehanna Unit 2 Project Milestones
Permanent Drywell Shielding /05
Feedwater Heater Bay Shielding 3/05
Equipment Reliability Enhancements
Example: redesign of MSIVs
In anticipation of some level of degradation in exposure-rate control for materials within the pipes, and to otherwise reduce dose rates, Susquehanna has added and is planning to add additional permanent shielding with the drywell. This reduces the effective dose in the primary areas of work in the drywell (where up to 70% of outage dose is accrued).
To reduce dose rates in hallways where considerable numbers of personnel are in transit, Susquehanna added shielding on the floors under (and some selected shielding around hot spots around) the feedwater heaters. The change is less than 5 uSv/hour, but that adds to a considerable collective dose when tens of thousands of people traverse the hallways of interest.
The MSIVs were redesigned, not specifically for exposure reduction purposes but for equipment reliability purposes. Simply put, the less frequent the work on a piece of equipment, and the less intrusive the work on that equipment, the less dose the station will accrue.

12. Examples of Other Source-Term Reduction Program Elements
Hydrolazing
Hot Spot Flushes
Stellite Reduction
- Enhanced “Clean-up” Post-maintenance
- Design Changes for Components to
eliminate stellite

13. Examples of Time/Distance/Shielding Program Elements
Remote audio, video, and dosimetric monitoring
Virtual tours
Robotics
HWC flow reduction modeling
Risk-based ISI
Work management improvements
Example: 360-degree reactor cavity work platform
Remote monitoring has been a significant contributor to dose reduction for the station. Its biggest impact to date has been in reducing the dose to HP Technicians who otherwise would have had to accompany workers into higher radiation areas.
Virtual tours using video and photographic data have reduced the time needed for plant walk-downs and other preparatory work.
The 360-degree reactor cavity work platform is mentioned not because it is inherently a dose reduction tool. Its primary purpose is critical path (time) savings. Indirectly, dose is saved. Absent very good work management, numbers of tasks will tend to increase as the time available to perform tasks increases. Constraining the time available, in conjunction with doing the right work and only the right work, will lead to dose reduction.
INPO recently gave Susquehanna a strength for its HWC flow reduction modeling capabilities. They were stated as being unique to U.S. BWRs and are used effectively for dose control purposes.

14. Health Physics Technician Drywell Dose Compared to Prior Outages
As a direct result of reductions in drywell dose rates and increases in the use of remote monitoring technologies, the dose to Health Physics staff has decreased. As the years progress (brown to purple to blue to magenta lines) the dose to drywell Technicians decreases. The difference between 2002 and 2005 is almost 90 person-mSv per outage.

15. Susquehanna vs. U.S. BWRs WANO/INPO PI data through 3Q05
BWR Single Fuel Cycle CRE
Best Quartile person-Sv
SSES person-Sv
BWR 12-Month Collective Dose
Best Quartile person-Sv
SSES person-Sv
There are three messages in this graph.
First, Susquehanna is a top-quartile plant in the U.S. regarding control of collective dose. That validates the conduct of much of the work planned and executed over the past decade.
Second, Rick says there is a message to Susquehanna staff. Susquehanna has work to do. If Susquehanna is the plant with virtually the lowest recirc system dose rates in outages, then why are they not the best-performing plant, as opposed to being top-quartile (and maybe even top-decile) for annual collective dose? Susquehanna is, so far, neither the top performer in terms of on-line dose control nor outage dose control. Rick says that the answer may lie in the need to further improve their work management practices, an element of current dose-control emphasis.
Third, this graph says nothing about control of dose to the individual. As we progress into what may become a lower annual dose limit to the individual, where is Susquehanna? In reasonable shape, in that there have been no individuals receiving more than 20 mSv/year at Susquehanna recently. Rick expects that you will begin to see a higher percentage of graphs at future meetings that deal with dose to the individual.

16. Susquehanna vs. BWRs Worldwide
Average collective dose per reactor (person-Sv), using available data for 2004
European BWRs
Japanese BWRs
SSES –
This is another graph that keeps Susquehanna staff from complacency. Compared to European stations, Susquehanna is just average. Average is not the position to which the Susquehanna staff aspires.
Another message to Susquehanna staff (and the rest of the audience) – let’s go see what good things are happening elsewhere. There are good ideas available for use “at home”.
You might note the Japanese numbers. Regarding the point just made, you may be aware that Japan sent teams of people to visit several European and U.S. plants in January-February of this year, to learn what ideas can be effectively applied in Japan.

17. This graph speaks for itself and shows a substantial level of success for Susquehanna.
In 2006, they anticipate a 1.0 person-Sv refueling outage and a 1.7 person-Sv total accumulated annual dose for the two units. That would again put Susquehanna at about the 0.85 person-Sv mark for each reactor unit and is expected to mean that Susquehanna would continue to be a top-quartile performer among US plants.
But where does this graph go after 2006? Rick mentioned that last year at this time, Willie Harris (the RPM at the Limerick station), suggested that top quartile may in the not-too-distant future lie in the range of 0.6 person-Sv per US BWR unit. (He recalled that Willie suggested an annual outage dose of 0.8 person-Sv and an on-line dose of about 0.4 person-Sv for two units.)
Susquehanna is thinking along those lines as the place to be. Susquehanna is planning to achieve dose reductions so that those levels would be achievable. What about your expectations for cumulative dose reduction at your station?

18. Summary from Chemistry Control Perspective
Implementation of chemistry modifications along with excellent chemical decontaminations has been a success
Condensate filtration system with iron addition has been run effectively.
Pre-conditioning the fuel and FW piping to DZO prior to the refueling outage and an excellent chemical decontamination reduced impact of recontamination rates.

19. Summary from Chemistry Control Perspective, continued
The SSES U2 Co-60(s)/RCS Zn(s) ratio is about a factor of 6-10 less than the current EPRI recommendation for NMCA plants.
The Co-60(s)/RCS Zn(s) ratio appears to work for moderate HWC plants
Minimizing this ratio is important. Maintaining FW and RCS Zn (s) at desired levels is also important.

20. Summary from Dose Control Perspective
Results: Top quartile plant - collective dose
Result: INPO strengths – management commitment and dose modeling techniques
Recognition: Techniques Susquehanna used were not especially unusual, except perhaps in their timing
Recognition: You’re only as good as your latest results

21. Summary, continued
Recognition: Continuing improvements are required – higher standards, better results
Recognition: Importance of planning the work and working the plan
Recognition: One team, one commitment – there is success only by that approach
Re. bulldot #3 – HP is not an island. Dose control and dose reduction are station issues, and success can be achieved only with the cooperation of everyone on-site.