Presentation on theme: "Causes of Tritium Effluent Releases and Strategies for Reducing Releases Clay R. Madden Columbia Generating Station Chemistry Department TRITIUM MANAGEMENT."— Presentation transcript:
Causes of Tritium Effluent Releases and Strategies for Reducing Releases Clay R. Madden Columbia Generating Station Chemistry Department TRITIUM MANAGEMENT
Presentation Outline How Does CGS Compare With the BWR Fleet With Respect to Effluents Perspective of CGS and Effluent Limits Tritium and Boron Sampling Tritium and Boron Sources –Activation, Fuel, CRB, SLC, CJW, ISFSI, HWC, Recycle Tritium Releases –Liquids, Evaporation of SFP, Steam Leaks, etc Considerations to Reducing Releases
Liquid Effluents Gallons per Month Columbia vs. BWR Fleet Trends
Liquid Effluents Fission and Activation Products
Columbia vs. BWR Fleet Trends Liquid Effluents - Tritium
Gaseous Effluents I-131 and Particulates Columbia vs. BWR Fleet Trends
Gaseous Effluents - Noble Gases
Columbia vs. BWR Fleet Trends Gaseous Effluents - Tritium
Perspective on ODCM Limits 131 I, 133 I, 3 H, & Particulates (>8d T ½ ) 10CFR50 Appendix I Design Objective –Organ Dose Limit:15 mrem during year –Actual Release in 2003:0.01 mrem –% of Guide: 0.067% 10CFR20-Based Limit: – Organ Dose Limit: 1500 mrem/year –% of organ dose limit: %
50-Mile Offsite Dose 50-Mile population organ dose =.251 p-rem –Maximum organ = lung –44% is from inhalation pathway 98.3% of this is from H-3 –36% is from vegetable pathway 100% of this is from H-3 –In total, 99% of this dose is from H-3 Average individual dose = millirem
2003 Columbia Releases NuclideCuries Iodine Iodine Strontium Strontium Cobalt Cobalt Manganese Zinc Hydrogen I, 133 I, 3 H, & Particulates (>8d T ½ )
Turbine Bldg Tritium Releases Year Curies Released
Reactor Water Tritium
Tritium Sampling Routine Tritium Grab Sampling –Monthly from Turbine and Radwaste Buildings –Weekly from Reactor Building Non Routine Sampling and Considerations –Sampling building intakes –Weekly from Turbine Building to test variance –Exploring inline humidity monitors
Boron Sampling Historic Boron Sampling –Semiannual from Demineralized Water Storage Tank (DWST) and Condensate Storage Tanks (CST) Changes to Boron Sampling –Monthly from CST –Weekly from SFP –Weekly from Reactor Water
Tritium Production In a Boiling Water Reactor (BWR), tritium is produced by three principal methods: –Activation of naturally occurring deuterium in the primary coolant, –Ternary fission of UO 2 fuel, and –Neutron reactions with boron in control rods 10 B(n,2 ) 3 H – barns 10 B(n, ) 7 Li – 3838 barns; 7 Li(n,n ) 3 H – barns FSAR production rate = 1.7E-4 Ci/sec/MWt = 18.7 Curies/yr
Tritium Production Sources of Deuterium –Water (Coolant) and Hydrogen Water Chemistry (minor) Sources of Boron-10 –Leaking Control Rod Blades –Standby Liquid Control –Air Compressor Jacket Water (borated corrosion inhibitor) –Diesel Generator Cooling Jacket Water –Independent Spent Fuel Storage Installation (ISFSI) MPCs Sources of Tritium –Leaking Fuel Rods and Control Rod Blades –Heating, Ventilation, and Air Conditioning (HVAC) Intake from Building Wake Effects
Leaking Control Rod Blades Three types of GE Control Rod Blades (CRB) at Columbia –Original Equipment - GE SIL 157 (1981) –Duralife GE SIL 654 (2004) –Marathon CRB Locations: –Reactor Vessel –Spent Fuel Pool (SFP)
R14 R15 R16 Tritium and Boron Changes
Coolant Boron Coolant Tritium Reactor Power Leaking Control Rod Blades Reactor Power (%)Coolant Boron (ppb) Coolant Tritium ( Ci/ml)
Standby Liquid Control At Columbia, loss of boron from Standby Liquid Control (SLC) was ruled out based on the isolation valve type, limited testing of the system, and precautions taken to keep it out of radwaste. Operations performs a surveillance on the SLC system periodically which produces barrels of water that has been in contact with the SLC system. Years ago, after the barrels were sampled by chemistry personnel, the water was dumped down the storm drain piping. It was found that the vent piping for the storm drain piping in the reactor building was cross connected to the Reactor bldg. sump vent exhaust system. This allowed (due to air flow and condensation) boric acid to be present in the reactor building sumps. The boric acid in the sumps was not removed by resins when the water was reprocessed and it subsequently ended up the the reactor.
SLC Boron Level Changes
Compressor Jacket Water Borated corrosion inhibitor leaked from the CJW surge tank to the floor drain following corrective maintenance. Loss of the borated corrosion inhibitor (Nalco 2100) to the Floor Drain System means it will end up in Radwaste for processing. Radwaste water treatment is not very effective at removing boron and some of the boron can make it to the reactor.
ISFSI MPCs ppb
Increases in Boron not seen in other metals or nuclides.
ISFSI MPCs Grams of Boron released to SFP per ISFSI cask loaded –Based on ~35 ppb increase in the pool for each cask and a pool volume of 356,700 gallons Hydrostatic pressure on lowering into SFP
ISFSI MPCs Alloy Aluminum Boral: B4C and Al Alloy Steel Basket Wall Stainless Steel Alloy Aluminum Boral What is Boral?
ISFSI MPCs Boron Migration/Dilution/Concentration –Letdown of SFP to CST is 5,000 gallons/cask –Makeup from Evaporation is 1,000 gallons/day –Boron in the spent fuel pool can make its way into radwaste when the filter/demineralizers are backwashed and ultimately end up in the CSTs. –Water in the vessel, Suppression Pool, SFP, and CST commingles during refueling operations.
Tritium Release Essentially all tritium in the primary coolant is eventually released to the environment –Liquid Effluents Columbia’s last release was September 1998 –Offgas contains HT and HTO. Evaporation of Spent Fuel Pool, Sumps, Tanks Turbine Building Steam Leaks –Solids Dewatered Spent Resin
Evaporation of Spent Fuel Pool Total curies released from Reactor building –1.6 curies per month (2003) –1.2 curie per month (2004). Evaporation rate based on curies released –44,000 gallons per month (2003) –30,000 gallons per month (2004).
Turbine Building Steam Leaks Developed a calculation to estimate steam leak rate using the increase in tritium concentration in the outlet air. Ran test cases from 1998 to 2003 to estimate leak rate. Spot checked results against water balance data for selected periods Results agreed surprisingly well. Indications are that the average leak rate has not changed over several years
Turbine Building Steam Leaks The average non-outage Turbine building leak rate (gallons/min) 5.56 The total Turbine building H-3 released (Curies)1281 The average condensate H-3 concentration (microcuries/ml) 1.88E E-03 A quantitative analysis of the extent of steam leaks was attempted for 1998 (low tritium effluents) and for 2003 for comparison and calculation validation. The leak rate has been fairly constant. However, both the curies released and the condensate tritium concentration have increased by a factor of 6.8 and 5.1 respectively.
Station Dose to Reduce Steam Leaks YearPerson-Rem *2.226 * to date – 6/2004
Actions to Reduce Releases Reduce the primary system tritium concentration: Release water to the river. Pro –May be able to decrease Primary system concentration sooner. Con –This again will require about 2 million gallons of release and would require about 6 months to complete. During this time the liquid effluent release indicators would degrade to third or forth quartile. Erodes public confidence and trust.
Actions to Reduce Releases Reduce the primary system tritium concentration: Allow make-up for steam leaks and SFP evaporation to slowly dilute the tritium to the baseline value. Pro –Little or no work is involved. We will gradually move to improved quartiles as this occurs. Relies on limited boron introduction. Con –This will require a loss of about 2 million gallons of water and 8 – 10 months at our current leak rate
Actions to Reduce Releases Reduce the primary system tritium and boron concentration: Quickly reposition leaking CRBs out of the active core. Pro –Boron and tritium begin to decline. Con –This reactive approach doesn’t prevent the initial tritium and boron intrusion and reduction is slow.
Actions to Reduce Releases Reduce tritium gaseous effluent release rate: Repair steam leaks in TG bldg. Pro –The leak rate reduction will provide a directly proportional reduction in the release rate. The reactor bldg. release from the fuel pool is around 1 Ci/month at the current tritium concentration. That means that the TG bldg. leaks would need to be near zero to achieve first quartile. Con –This will “bottle up” the existing tritium and extend the time we are susceptible to high releases with any new leaks. –Repair of leaks is high dose work even at reduced power compared to offsite dose from tritium release.
Actions to Reduce Releases Remove potential sources of tritium and boron in the plant: Replace Control Rod Blades prior to end of life. Pro –This proactive position will reduce the likelihood of future boron and tritium intrusions. Con –The CRBs cost $85,000 each. The total cost of the 27 blades that will reach end of life next cycle is $2.3M. The disposal cost could reach $13M.
Conclusions for Columbia Quickly identify leaking CRBs and reposition or move them out of the active core. Reduce Turbine Building steam leaks to prevent equipment degradation, not for effluent control. Proactively prevent/mitigate boron intrusion into radwaste systems from borated corrosion inhibitors. Consider methods to reduce ISFSI MPC boron impurity levels.
For Consideration Is the BWR fleet comparing apples to apples? –Sampling and analysis similar? –LLD low enough? –Dilution air interference? If your coolant tritium concentration is stable or trending down, you ARE releasing. –Is your monitoring program detecting it? –Does your effluent report reflect it?
LLD and Curies H-3 LLDCuries H-3 1E E-070 1E E E E Columbia ODCM required LLD 2 Current Columbia LLD for H-3