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Analytical Challenges with Tritium and the new NEI/ANI guidelines. IPEC S. Sandike 6/08
Before setting up an analyzer • Liquid Phase or Gel Phase – Ratio of cocktail to sample • • Glass or plastic vials Determine count time for desired LLD Dark adaption to lower bkgd count rate Tritium channel 0 -19 kev – Setting up other channels to enhance your chances of evaluating or identifying problems.
Distillation • Check for obvious turbidity (quench) • Evaluate need for quench curves • Distill most if not all samples – Not just a function of isotopic carryover – Other interferences • Biological Activity • Chemical Activity • Combinations
Prior to Distillation • Several chemicals are typically added • An oxidizer (KMn. O 4) can be added for samples with organics (sewage, etc) • Neutralization may be required – Acid or caustic to bring p. H = 4 to 9 – 1 M Sodium Hydroxide typically used – A cation filter may also work – Hydrophilic PVDF Membrane – TORAY filter for ion-exchange
Micro Distillation • Many advantages – Reduces cross contamination – Pre-packaged chemical treatment available – Filtering incorporated • Disadvantage? – At first, some cost, but long term, cost is recovered in fewer “re-analyses”.
NEI / ANI new requirements • Just about any fluid on site needs to be analyzed for tritium • 80 -10, possible effluent, in particular • Secondary fluid in PWR, will of course, have 1000 -10, 000 p. Ci/L of H-3. • Groundwater could be turbid, and full of just about any kind of chemical • NEI/ANI guidance adds Sewage Effluent
Sewage “Effluent” for H-3 ANI 07 -01, March 2007, Section 9. 0: – Identify inputs that could be radioactive – Perform a pathway analysis – EITHER clarified water to environment, OR raw sewage to a publicly owned treatment works (POTW) is to be tested for gamma spec and tritium – Clarified water for H-3 is straightforward, but raw sewage for H-3 is not widely performed.
IPEC sewage is pumped to local municipality’s plant Local village input Clean Areas: Gen Support, Training, etc IPEC RM Village Plant RM IPEC Sample Points Unit 2 Unit 3 RM 3 adjacent to line Radiation Monitors in use, shielded Na. I
ASTM: not much help • No direct ASTM for Tritium in Raw Sewage • Several labs offered sound approaches • IPEC chose from many available Ø Using micro-distillation Ø Sodium Hydroxide (1 M) Ø Potassium Permanganate (5%) • These preparations did not INITIALLY involve any specific determination of individual adjustments that may be necessary due to variation in level of organics, or generation of ammonia, etc.
Method adopted for raw sewage • • Micro-distillation selected. Approx 6 mls of sample in tube Add 1 drop of 1 M Na. OH to raise p. H Add 1 drop of 5% KMn. O 4 • With these preps in place, the first few analyses in Aug 2007 indicated no H-3.
Trace positive H-3 in sewage? • In Sep, 2007, only a few months after analyses were initiated, some positives started to show up. • Re-analysis was often below Lc, but investigation began nonetheless • Exhaustive search for possible ingress of plant fluid into plant sewage.
Chemiluminescence Suspected • Despite following established lab practices, we inspected the spectrum for signs of chemiluminescence. • Found most spectra normal, but positives indicated chemiluminescence, despite the chemicals added.
Normal Spectrum for Sewage H-3
False positive approx 1100 p. Ci/L We didn’t yet know what this was, but we KNEW it wasn’t TRITIUM !
Chemiluminescence • Generation of electromagnetic radiation (light) by release of chemical energy • Three types: – Chemical : generally involves oxidized species – Living Organisms: “bio”- luminescent (fireflies) – Electro-chemiluminescence: from current • Here, it appeared we were experiencing Chemical, from perhaps an imbalance of oxidizer and the p. H additive.
Chemistry behind reaction • Fragmentation of bonds (oxidation) causes energy (light) to be emitted. • More pronounced at elevated p. H (> 9) • The cocktail helps transfer the energy to the photomultiplier tubes at very low energies, DISPROPORTIONAL to the standard Poisson Distribution of Tritium. • Must look at beta spectra to see clearly.
Correction • If false positive is suspected: – Look at spectra for Poisson distribution – Use special p. H test strip to determine if a sample’s p. H is outside the ban (4 – 9) • Place a few drops on the strip • Adjust p. H if needed • With varying degrees of anaerobic digestion, the chemicals identified in procedure, when added to raw sewage, may produce a solution of too high a p. H and promote chemiluminescence.
Looking back at sample prep • Adding chemicals in a sewage sample with plenty of “bugs” generally had an expected result of p. H=8, and a good spectrum indicating no Tritium activity. • But if the original sample was “light” with regard to sewage activity, the chemicals drove the p. H above 9 (the permanganate had little to oxidize).
Solution • After speaking with some of the labs from whom we “borrowed” analysis procedures: – When false positives are discovered, re-test raw water with chemicals for p. H. – Adjust p. H 4 -9, and re-analyze – Don’t adjust the overall analysis procedure, false positives are not that frequent.
Verification of this correction Ø“Robust” sewage samples seemed to behave with a certain buffering, and p. H was never a problem. No false positives. Ø“Light” sewage samples were the only ones identified as false positives. ØEach false positive had a peak that quickly descended to baseline, well before 19 kev.
Other Verifications • Spike tests were run in house and sent to vendor with excellent comparisons, once p. H was verified 4 -9. • Engineering determined no viable ingress of primary fluid into sanitary sewage. • Rad monitors and routine grab samples would have seen other isotopes (gamma emitters). • Secondary fluid would have had to be nearly completely UNDILUTED to reach levels identified in the false positives.