Download - Concentration of Tritium in Liquid Samples by Electrolysis problem solved HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS 17 th Annual RETS – REMP Workshop.

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]