Nuclear Engineering Seibersdorf GmbH - UB · NUCLEAR ENGINEERING SEIBERSDORF GMBH 1 Nuclear Engineering Seibersdorf GmbH TDCR-LSC and TDCR-Cerenkov-Counting in a Radwaste Treatment

NUCLEAR ENGINEERING SEIBERSDORF GMBH

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Nuclear Engineering Seibersdorf GmbH

TDCR-LSC and TDCR-Cerenkov-Counting in a

Radwaste Treatment Facility

Andreas Vesely

Mile Djuricic, Wolfgang Jaiczay


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•AIT is Austria‘s largest non-university research group

•NES is a 100% affiliate of AIT with specific tasks - Austrian

organization for radioactive waste management

•Handling all radioactive waste arising in Austria (collection,

processing and storage)

•Decommissioning of former nuclear research and industrial

installations

NES as Part of AIT (Austrian Institute of Technology)


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Analysis (chemical, radiological) of different types of samples: •Solids:

•construction waste •metals/alloys •soil •ashes •etc.

•Liquids: • waste water • liquid waste

•Gases: •off-gases

Analytical Work - Chemical and Radiological


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•Wide range of activity concentrations •Very different sample composition •This work

•Monitoring of 3H-emissions from a radioactive waste incinerator (flue gas, waste water from scrubber) by LSC •Screening measurements for 90Sr on samples (concrete, plaster, digested with nitric acid) obtained during decommissioning of a hot cell facility, by Cerenkov counting •Comparison of a conventional counter (2 PMTs) with commercially available TDCR-counter

Analytical Work - Radiological


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•Perkin Elmer Quantulus 1220 •External standard (152Eu source) for quench determination based on the energy distribution of Compton electrons •Very low blank count rates

•Hidex 300SL

•TDCR method •Basic model, NOT metrological, NOT low level…

Instrumentation


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TDCR LSC

bs

D

T

sTBCACABD

ABCT

rrA)(

r

rTDCR)(

rrrrrr)(

rr)(

4

3

22

1

For beta emitters:

•Simplified model: Counting efficiency equals triple to

double coincidence ratio (TDCR)

•„Absolute“ method for betas

r – count rate

A, B, C – PMTs

D – double coincidence

T – triple coincidence

- efficiency

s – sample

b – blank

A - activity


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TDCR LSC – 3H, 63Ni, 14C, 90Sr/Y

3H

63Ni

14C 90Sr


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TDCR LSC – quenched 3H standards


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Monitoring of effluents from a radwaste incinerator

•Sampling of flue gas for the determination of 3H and 14C:

•Aspiration of gas sample (200 ml/min)

•Catalytic oxidation of CO, CHx etc. (Catalyst PGM,

450°C)

•Adsorption of water vapour on silica gel

•Absorption of CO2 in aq. NaOH

•Sampling period: 1 week

•Sampling of waste water from scrubber

•Daily sampling


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Sampling of flue gas

CO, CHx, H2 →CO2 + H2O

Adsorption of H2O

NaOH

Absorption of CO2

Catalyst 450°C

STACK

Silicagel


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Sampling of flue gas


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•Determination of 3H

•From flue gas: thermal desorption of water from silica

gel (150°C, ca. 20 mbar abs.), condensation in a LN2-

cooled trap; mixing with cocktail, LSC

•From waste water: filtration, mixing with cocktail, LSC

•Flue gas scrubber operated at constant temperature →

good correlation of concentrations of 3H in gas and liquid

•Liquid can be sampled more frequently → better real time

monitoring


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Desorption apparatus for 3H analysis


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3H in liquid and gaseous effluents


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3H in off-gas


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•Determination of 3H by LSC

•With Quantulus: determination of efficiency with

external standard and quench curve

•With Hidex 300SL: efficiency = TDCR

•At low count rates, unreasonable high TDCR values


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TDCR for 3H vs. count rate


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TDCR-LSC at low count rates

corr

bs

bs

bbsscorr

TDCR

rrA)(

rr

TDCRrTDCRrTDCR)(

6

5

•Correction with TDCR

of blank

•Excellent agreement of

the results obtained

with two different

instruments

r – count rate

s –sample

b - blank


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3H – LSC with two methods


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•Samples (concrete, plaster) obtained during decommissioning of a hot cell facility

•Leaching of solid sample with boiling 8N nitric acid, filtration, Cerenkov counting (20 ml)

•Gamma spectrometry: no sign of high energy beta emitters, low content of K (40K) → Cerenkov count rate fully assigned to 90Sr/Y

•Robust method, compatible with high concentrations of salts and acid, only colour quench (Fe3+) to be taken into account

Cerenkov Counting for 90Sr


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•Counting efficiency by standard addition

•Applied on both Quantulus and Hidex instruments

•Addition of a small amount of standard with high specific activity (e. g. 50 mg with 200Bq 90Sr/Y → insignificant change of sample colour)

•Straightforward method, but 2 measurements

Cerenkov Counting – Standard Addition

st

samplestsample

A

rr


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•TDCR-Cerenkov recently introduced by PTB; complex algorithm

based on various inputs

•This work: simple empirical correlations of efficiency vs. TDCR

•Radionuclides: 90Sr/Y, 234mPa(238U), secTh, 40K(natK)

•Colour quench (addition of FeCl3)

•Linear correlation in a narrow range of , slope ≠ 1, intercept ≠ 0

•2nd order polynomial approximation for higher range of

•No good fit for secTh, Cerenkov counts from 3 high energy betas

(228Ac, 214Bi, 208Tl), perturbance of equilibrium during sample

preparation?

TDCR-Cerenkov Counting


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TDCR-Cerenkov Counting – Empirical Correlations


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• by standard addition vs. TDCR → extended range, 2nd order polynomial fit

TDCR-Cerenkov Counting for 90Sr


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•Calculation of and activity from TDCR, comparison with results from Quantulus/standard addition → good correlation at high count rates, worse at low rates

•Many samples with low count rates, correction of TDCR (see method for 3H), recalculation of and activity from TDCRcorr → correlation still not satisfactory

TDCR-Cerenkov Counting for 90Sr


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TDCR vs. count rate

rb+3srb


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90Sr comparison of results from Quantulus and TDCR


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90Sr comparison of results from Quantulus and TDCR


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•Good performance with beta-LSC; at low count rates, correction of TDCR with blank

values → good results, even with non-low level instrumentation

•Cerenkov: use of empirical correlation of efficiency vs. TDCR → good performance

at high count rates and mo

•derate color quench; not satisfactory at low count rates and high quench levels

•Needs: low–level instrumentation, more sophisticated algorithms?

Application of TDCR-LSC and TDCR-Cerenkov-Counting

for Radwaste Analysis - Conclusions

Documents

Nuclear Engineering Seibersdorf GmbH - UB · NUCLEAR ENGINEERING SEIBERSDORF GMBH 1 Nuclear Engineering Seibersdorf GmbH TDCR-LSC and TDCR-Cerenkov-Counting in a Radwaste Treatment