Concentration of Tritium in Liquid Samples by Electrolysis problem solved HELPING OUR CLIENTS SOLVE...

Concentration of Tritium in Liquid Samples by Electrolysis

problem solved

HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS

17th Annual RETS – REMP

Workshop

Stan Morton, Ph.D.

June 27, 2007

Philadelphia, PA June 27, 2007

Tritium

problem solved


• Heavy Isotope of Hydrogen

• 12.3 year half-life

• Beta Decays to Stable He-3

• Low-energy Beta Particle– 18.6 keV beta-max– 5.7 keV beta-avg

• Hydrogen and Tritium interchangeable

Tritium Unit (TU)

problem solved


TU ≡ 0.118 Bq/L ≡ 3.19 pCi/L

Or

1 Bq/L ≡ 8.47 TU

1TU ≡ Concentration of 10-18

Sources of Tritium

problem solved


• Cosmogenic• Nuclear Weapons – Atmospheric detonation

• By-Product Nuclear Power Reactors

– Boron

– Lithium

• Fission Process

Cosmogenic

problem solved


• Spallation – Cosmic-rays interact with atomic nitrogen:

14N (n, 3H) → 12C

• Reaction altitude from 11 to 16 km

• Adds to Precipitation Level

Nuclear Weapons - Atmospheric

problem solved


• Testing 1940s through 1970s

• Precipitation Levels peaked in 1963

• Additional 52 X 1018 Bq to Global Inventory

• Estimated remnant of 100 – 400 pCi/L in precipitation

Precipitation Concentrations

problem solved


Tritium Production from Boron

problem solved


• Boron-10 (19.9%) high thermal neutron cross section – 3835 barns

• Control rods for BWRs and PWRs

• Chemical shim and reactivity control in PWRs

10B(n,2α) → 3H10B(n,α) → 7Li(n,nα) → 3H

Tritium Production from Lithium

problem solved


• Most acceptable hydroxide for pH control in some PWR primary coolant

• 6Li (7.5%) 940 barns

• Principle reactions:7Li(n,nα) → 3H8Li(n,α) → 3H

Tritium from Fission

problem solved


• Lesser extent from fission

• Fission yield for 235U is ~0.01%

Tritium Inventory

problem solved


• Estimated normal releases 0.02 x 1018 Bq/year• Estimated off-normal releases 0.001 x 1018

Bq/year• Steady-state buildup 0.4 x 1018 Bq globally• Legacy release 0.4 x 1018 Bq/year• Steady-state buildup 7.4 x 1018 Bq globally

Tritium Global Inventory

problem solved


• Atmospheric detonations 50s & 60s:

185 to 240 X 1018 Bq

• Legacy today:

52 X 1018 Bq

• Combined natural and anthropogenic global inventory of approximately:

53 X 1018 Bq or ~ 10 Bq/L

Regulatory Limits

problem solved


• Weak beta and rapid elimination produce a minor constituent in dose evaluation

• EPA 1976 Drinking Water Standard is 4 mrem/yr = 20,000 pCi/L

• 1991 4 mrem/yr = 60,900; retained 1976 limit.

Dose Considerations

problem solved


• Human retention studies provide three-component half-lives– 6 to 12 days – turnover of pool of body water– 10 to 34 days – involved in carbon-tritium

chemistry– 130 to 550 days – organic molecules with

slow turnover rates

Perception vs. Risk

problem solved


• Braidwood – 1600 pCi/L ≡ 0.3 mrem/yr; Exelon Corporation bought the farm

• Decatur Daily headline: …TVA, NRC are ‘flippant’ over tritium leaks

• Morris Daily Herald: Dresden leak levels 25 times the allowable drinking water limits

• Arizona Republic: Palo Verde’s tritium leak may impact the groundwater.

• Harford Courant: Haddam a few gallons a day of tritium contaminated water breaches 6-foot thick concrete wall.

Concentration of Tritium by Electrolysis

problem solved


• 2006, GEL Labs recognized need

• Quantitative below 150 – 200 pCi/L

• Reliable method

• Well defined turn-around-times

• Quality driven

• Customer service

Concentration of Tritium by Electrolysis

problem solved


• Exploits slight differences in physical properties between hydrogen and tritium

• Molecule of water containing hydrogen more likely to dissociate by electrolysis than molecule of water containing tritium.

Overview

problem solved


• Aliquant of 500 mL sample screened for ‘high’ levels of tritium and extraneous emitters

• Shipped to Richland Service Center (RSC) in Richland, Washington

• Enrichment process

• Returned in closed vial for LSC

Ambient and Environmental Considerations

problem solved


• All commercial analytical labs evaporate hundreds of liters of tritium laden water

• May produce elevated levels of ambient tritium

• Environmental concentrations vary by region– Eastern and Southern states highest levels– Mid-west and Western States lowest levels

Richland Service Center

problem solved


Electrolysis Instrumentation

problem solved


Electrolysis Cold-Water Bath

problem solved


RSC Tritium Laboratory

problem solved


Procedure

problem solved


• 300 mL distilled

• 250 mL concentrated by electrolysis for maximum sensitivity

• Batch size– 12 samples– 2 background– LCS containing NIST traceable tritium

standard

Procedure (cont’d)

problem solved


• Cold water bath (~ 5°C)

• Constant current until 25 mL remaining

• Reduce current until 12 – 15 ml

• Volume reduction and enrichment requires 12 – 14 days

• Vacuum distillation to remove NaOH

Procedure (cont’d)

problem solved


• Volume determined by weight

X = Vi / Vf

• Enrichment determined from LCSs

Y = Cf / Ci

• Transferred to LSC vial

• Returned to Charleston for beta counting

MARLAP Approach

problem solved


• Multi-Agency Radiological Laboratory Analytical Protocols (MARLAP) Manual

• Nationally consistent approach to producing analytical data

• Performance-based approach for selecting analytical protocol

• Project specific criteria

MARLAP Method Validation

problem solved


Validation Level

Applications Sample Type1

Acceptance Criteria2

Levels3 (Concentrations)

Replicates No. of Analyses

A Without

Additional Validation

Existing Validated Method

____ Method

Previously Validated B thru E

____ ____ ____

B

Same or similar Matrix

Internal PT

Measured Value Within ±2.8μMR or ±2.8φMR Known Value

3 3 9

C Similar Matrix/

New Application

Internal or

external PT


3 3 15

D

Newly Developed or

Adapted Method

Internal or

external PT


3 3 21

E

Newly Developed or

Adapted Method

MVRM* Samples


3 3 21

Newly Developed Methods

problem solved


• Newly developed use Level D or E

• Increased number of replicates

• Best estimate of precision and bias

• Unique matrix

Determination of Uncertainty

problem solved


• Method validation determines method uncertainty

• Sample uncertainty menu includes– Method uncertainty– Liquid-scintillation counting statistics– Background subtraction– NIST standards, decay time, half-life, etc.

Uncertainty Considerations

problem solved


• Uncertainty increases as activity approaches detection limit

• Because of such effects, as analyte concentrations drop, the relative uncertainty associated with the result tends to increase, first to a substantial fraction of the result and finally to the point where the (symmetric) uncertainty interval includes zero. This region is typically associated with the practical limit of detection for a given method.

Questions & Contact Information

problem solved


Contact Information:

Stan Morton, Manager, Radiobioassay Programs 303.349.8345 [email protected]

Bob Wills, Manager, Nuclear Programs 843.556.8171 [email protected]

Concentration of Tritium in Liquid Samples by Electrolysis problem solved HELPING OUR CLIENTS SOLVE...

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