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Tritium in The Demin Water System -- An IE Bulletin 80-10 Challenge

Tritium in The Demin Water System -- An IE Bulletin 80-10 Challenge. Ken Sejkora Entergy Nuclear Northeast – Pilgrim Station Presented at the 12 th Annual RETS-REMP Workshop Atlantic City, NJ: 24-26 Jun 2002. Problem Identification.

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Tritium in The Demin Water System -- An IE Bulletin 80-10 Challenge

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  1. Tritium in The Demin Water System -- An IE Bulletin 80-10 Challenge Ken Sejkora Entergy Nuclear Northeast – Pilgrim Station Presented at the 12th Annual RETS-REMP Workshop Atlantic City, NJ: 24-26 Jun 2002

  2. Problem Identification • Detected tritium in October sample from station heating system: 3E-6 uCi/mL • Previous samples historically showed NDA; follow-up sampling indicated upward trend • Response delayed by lack of on-site H-3 analysis capabilities… delays through vendor lab • Initiated IE80-10 sampling of interfacing systems

  3. Problem Scoping • IE80-10 sampling detected H-3 in demineralized water system: 9E-6 uCi/mL • DW system analyzed monthly for gamma; no previous H-3 analysis • Follow-up sampling indicated upward trend • Initially suspected backflow from interfacing system; extensive sampling in various legs of DW system yielded ~ equal concentrations… no smoking gun!!

  4. Problem Assessment • DW used as makeup to clean systems (diesel generators, stator cooling); top off lead-acid batteries (mixed waste?); mix chemical standards for clean-area use • Lack of previous H-3 sampling of DW system gave us nothing to compare to… i.e., had the problem existed before, or was it “new”? • Review of system design revealed shared vent line with condensate storage tanks… could we exchange activity through a vent line? H-3…YES! • PNPS has had an eight-fold increase in reactor coolant boron and tritium in past 2 years from control blade leakage… coincidence?

  5. Diagram of Tank Ventilation Cross-connection Condensate Storage Tank (one of two) Demin Water Storage Tank El. 40’6” 275,000 gal. El. 22’2” 12” Vent Pipe Internal to CST 50,000 gal. 4” Vent Pipe Internal to DWST 16” Underground Ventilation Header to Radwaste Building

  6. Condensate Storage Tanks • Two tanks at 275,000 gal each • Tritium Concentration = 7E-2 uCi/mL, total H-3 inventory in CST = 146 Ci • Average daily water flux = 33,000 gal/d, 4,400 cu.ft/day • Nominal temperature at 80 deg.F, airborne H-3 = 1.8E-6 uCi/cc air • Daily airborne tritium flux = 220 uCi/day

  7. Demin Water Storage Tank • One tank at 50,000 gal • Tritium Concentration = 2E-5 uCi/mL, total H-3 inventory in DWST = 0.0038 Ci • Average daily makeup = 2,300 gal/day, 308 cu.ft/day • Nominal temperature ~ outside ambient (45 deg. F in winter) • DWST is heat sink compared to 80 deg. CSTs… effective condensation trap!!

  8. Air Exchange From CSTs

  9. Tritium Exchange From CSTs

  10. Proposed Solution • Remove source term to DWST by removing ventilation cross-tie • Maintain venting of CSTs to radwaste building, capture as monitored release • Vent DWST to atmosphere, as radiological concerns disappear following modification • Cannot effectively remove H-3 through treatment… dilution, bleed & feed • Radiological concerns following mod?

  11. Modified Tank Ventilation Scheme Condensate Storage Tank (one of two) Demin Water Storage Tank El. 40’6” 275,000 gal. El. 22’2” 12” Vent Pipe Internal to CST 50,000 gal. 4” Vent Pipe Internal to DWST Capped End DWST Vent open to Underground Valve Pit 16” Underground Ventilation Header to Radwaste Building

  12. Projected Dose Consequences • Catastrophic failure of DWST, entire volume released in 20 min as liquid effluent release: 7E-6 mrem to maximum-exposed individual • Evaporation of tank volume released as airborne effluent following vent modification: 6E-6 mrem to maximum-exposed individual

  13. Questions Raised: IE80-10 • Do we control station heat and demin systems as ‘contaminated’ systems… negligible dose impact, impossible to measure activity by normal survey methods; posting requirements? • What LLDs do we need to achieve to call the system “clean”? Effluent? Environmental? • ALARA considerations… negligible dose consequences to leave as is (DWST concentration is at EPA drinking water standard); real dose is incurred to fix the “problem”

  14. Summary • Don’t overlook the obvious! • Tritium can pose special concerns • What other systems could have similar cross-ties? • Which LLDs does one use to declare victory and call a IE80-10 system “clean”? • How much time, effort, money, and REAL DOSE should be expended to fix a problem that has no dose impact?

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