On-line Drying of Augmented Offgas Charcoal Ken Sejkora, B rad Barrus, Charles Minott, Phil Harizi, Paul McNulty Entergy Nuclear Northeast – Pilgrim Station Presented at the 12 th Annual RETS-REMP Workshop Atlantic City, NJ: Jun 2002

Offgas Treatment System Diagram Air Ejector 30-min Holdup Main Stack Recombiner 30-min Holdup Cooler Condenser & Moisture Separator Charcoal Adsorbers Augmented System Offgas Condenser

PNPS AOG Charcoal System Design Two trains of six series beds each; configurable as series or parallel operation; 12 beds total 3 tons charcoal/bed; 36 tons total Nominal flow rate = 12 scfm Design retention = 29 hours for Kr, 525 hours (22 days) for Xe; Activity Reduction Factor = 185 Permanent fixture… not designed for removal or replacement of charcoal, no sample ports, minimal instrumentation/monitoring

Charcoal Retention Behavior Lower is better! Lower humidity/moisture content yields more available adsorption sites Lower flow rate yields more contact time, longer retention time; inverse relationship… flow*2 = retention*0.5 Lower temperature yields better dynamics for retention on available sites

Noble Gas Retention Efficiency vs. Humidity

Charcoal Moisture Content vs. Humidity

Noble Gas Retention Efficiency vs. Charcoal Moisture Content

Observed AOG Retention

AOG Inlet/Outlet Comparison 04-Sep-2000 Data, Flow = 37 scfm Nuclide Inlet uCi/cc Outlet uCi/cc DF Number of Halflives Holdup hours Percent of Design Kr-85m 3.70E-42.41E % Kr E-35.66E % Kr E-37.20E % Xe E-49.35E % Xe E-31.35E % Xe E-2NDA--

PNPS CHALLENGES High moisture content: charcoal in vessels was 22% moisture by weight… saturated!! High air inleakage: scfm vs. design value of 12 scfm Perception: tight fuel meant noble gas releases were low… belief by some that AOG wasn’t needed for ALARA, as doses were already well below 10CFR50 Appendix I objectives

Challenges: Moisture Poorly instrumented lines… most points were local readout only, no recording of flow, temperature, dew point, etc. Charcoal was saturated, 22% moisture content… 15,800 lbs = 1,900 gal water High dew point (50+ deg.F), high humidity (70+%) air into charcoal… kept charcoal saturated Automatic cooler condenser drain valve was not functioning, would not allow condenser to drain; poor condenser performance, plus carryover of liquid water into charcoal vessels

Challenges: Moisture (continued) Opening cooler condenser drain valve improved condenser performance… reduced dew point from 50+ deg.F to <28 deg.F Objective: Now that we had dry air going into charcoal, how do we remove existing 2,100 gallons of water in vessels? Engineering solution: On-line drying, by heating room to 100+ deg.F, to raise temperature of beds… low dew point air flowing through beds will remove water

On-line Drying: HVAC Approach Detailed engineering and 10CFR50.59 evaluation Concern for potential combustion of charcoal… limited room temperature to maximum of 125 deg.F High room temperature raised charcoal temperature from ~77 deg.F to ~89 deg.F Concern that higher temperature would reduce retention times by affecting dynamics… determined benefit of drying outweighed risk of poorer dynamics Increased noble gas sampling from once/month to once/week to monitor for degraded dynamics… none seen Commenced drying Sep 2000, secured drying in Nov 2001

Challenges: Inleakage Turnover of system engineers… lack of continuity Poorly instrumented lines… most points were local readout only, no recording of flow, temperature, dew point, etc. High dose rates in areas where leakage was suspected… downpower evolution, past efforts inconclusive Air purge valve seat leakage: scfm 2nd point feedwater heaters: 30 scfm; very inaccessible, hard to locate Current air inleakage: scfm

AOG Inlet/Outlet Comparison 29-Apr-2002 Data, Flow = 16 scfm Nuclide Inlet uCi/cc Outlet uCi/cc DF Number of Halflives Holdup hours Percent of Design Kr-85m 9.21E-4NDA-- Kr E-3NDA-- Kr E-3NDA-- Xe E-4 MDC = 5.25E % Xe E-3NDA-- Xe E-2NDA--

Post-treatment Process Radiation Monitor Response

Challenges: Perception Even with diminished AOG performance, maximum offsite noble gas dose was <5% of 10CFR50 Appendix I ALARA objectives Education process… convey that AOG is not for ‘normal’ operations, but meant for minimizing dose impact in the event of fuel failure “Sell” from standpoint of INPO comparisons for noble gas releases; increased failed fuel operating margin; increased NRC & INPO concern… it’s the right thing to do!

Challenges: Perception (continued) Activity reduction factor vs. dose reduction factor Substandard retention can provide an ‘acceptable’ DF for short-lived noble gases which have low dose impact… activity reduction may look good, but minimal impact on dose Reduction Activity Reduction = 8.4; Dose Reduction = 8.2 Reduction Activity Reduction = 190; Dose Reduction = 1,560

Summary Key to success was interdisciplinary team approach… Engineering, Operations, Chemistry, Maintenance, etc. -- everyone contributed! Think outside the box… On-line drying?? You’ve got to be kidding! Attack all the problems, not just one or two Older plants with degradation of ancillary systems… drain pots, loop seals, condenser cooler performance, etc.

Summary (continued) Importance of recording instrumentation to aid in diagnosing performance, problems, and success of solutions… need to retrofit? Dose reduction vs. activity reduction… what are you really going after? How do you measure success?