A STUDY ON THE TRITIUM DISTRIBUTION CHARACTERISTICS IN THE ENVIRONMENT

2006. 6. 27

Goung-Jin Lee, Hee-Geun Kim

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Introduction Measurement Procedure Measurement of

Environmental Tritium Activity Level

Conclusions

Topics for Presentation

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Nuclear Power Plants in Operation in Korea

INTRODUCTION

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INTRODUCTION

Nuclear Power Plants under Construction or Planning in Korea

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Multiple Nuclear Power Plants in Each Site

Can cause much environmental impacts to the environment

Calculated Maximum Individual Doses may exceed the limiting value required by Regulatory Body

Public concerns can be increased

Make it difficult to construct or operate NPPs

INTRODUCTION

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INTRODUCTION

Maximum Individual Dose Calculation Procedures

MEASURE the amount of annually released radioactive effluents

CALCULATE Dilution Factor using weather data : Gaussian Plume Model

CALCULATE Air Concentration and Ground Deposition of radioactive isotopes• Exposure from Inhalation, Plume Shine, Ground Shine Pathway

Transfer Model to Food Chain• Exposure from Ingestion Pathway

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INTRODUCTION

Conservatisms included in the Calculated Individual Dose

In our experiences, the calculate Maximum Individual Doses

are very high compared to the measured Actual Doses

because of the Conservatism included in

• Dilution Factor or x/Q calculation

• Transfer model to Food Chain

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INTRODUCTION

The Purposes of This Paper Is

by measuring the tritium radioactivity around a nuclear power

plant

to quantitatively investigate the conservatism included in the

Calculated Dilution Factor

to suggest new approach of maximum dose calculation based

on the measured data

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INTRODUCTION

Why Tritium Is Selected ?

In Korean NPPs, 60~90% of total off-site Maximum Individual

Doses are due to the gaseous tritium release

Tritium is easy to measure in the points of

• Activity Level

• Simple pre-treatment process of samples

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The Measurement Procedures

The Measurement System

• a low background Quantulus 1220TM LSC

• Optiphase HisafeTM 3 Scintillant

The Measurement Procedures

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The Selection of an Effective Window

The Measurement Procedures

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The Selection of an Effective Window

Lose 10% of tritium counts in each tail

Greatly reduce background counts

61~165 channel minimizes MDA

about 1.5 Bq/L MDA was obtained by using 61~165 channel, with

480min detection time

EVT

BMDA

2/1466

The Measurement Procedures

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The Calculation of a Sample Activity

Comparison of total counting rates in an effective window between the sample and the standard source

ASMPL = (CPMSMPL - CPMBKG) / CPMSTD × ASTD

• ASMPL = the calculated activity of sample(Bq/L)

• ASTD = the activity of standard source(Bq/L)

• CPM = the counting rate in the window(61~165)

The Measurement Procedures

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The Calculation of a Sample Activity

Weighting by tritium spectrum

CPM SMPL,i = the counting rate of sample at channel i

CPM BKG, i = the counting rate of background sample at channel i

CPM STD, i = the counting rate of standard source sample at

channel i

STD

iiSTD

iiSTDiBKGiSMPL

SMPL ACPM

CPMCMPCPMA

165

61

2,.

165

61,,, )(

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The measured Background Spectrum

The Measured Spectrum of 5 Bq/L Tritiated Water Sample

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TABLE.1 The Relative Errors of Three Spectrum Analysis Method

Analysis

Sample

1~200 ChTotal Counts

61~165 ChTotal Counts

61~165 ChWeighting Method

5 Bq/L 12.8 % 4.5 % 1.7 %

10 Bq/L -5.7 % -2.1 % -0.9 %

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Sample Selection

HTO in the water, river, ground water, underground water

: very low Specific Activity due to dilution

HTO in the rain : much fluctuations due to the variations of the weather conditions

HTO in the air : comparatively high Specific Activity and

gives stable value

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Sampling Method

HTO in the air was Condensed, by using commercially available electric dehumidifier

Relative humidity and the Temperature were measured to determine the Absolute Humidity

4 measuring points, 2 seasons, eight samples in each season

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TABLE 2. The Location of Sampling Points

Direction Distances(Km) Name

Point A NE 2.1 Hongnong

Point B SSE 6.0 Bupsung

Point C SSE 16.7 YongGwang

Point D ESE 44.0 Gwangju

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TABLE 3. The Measured Average Specific Activity of Atmospheric Tritium

Aug.2005

(Bq/Kg)

Feb.2005

(Bq/Kg)

Annual Average

(Bq/Kg)

Point A 2.67 6.39 4.53

Point B <1.35 <0.89 <1.12

Point C <1.73 <1.12 <1.43

Point D <1.27 <0.98 <1.13

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Comparison of the Tritium Concentration in the Air

= tritium concentration in the air(Bq/m3) = measured tritium specific activity (Bq/kg) = absolute humidity in the air (kg/m3).

= average tritium release rate(Bq/sec)

Measurement of The Environmental Tritium Activity Level

absSMPLSMPL HA

SMPLSMPLAabsH

elHel QQ modmod )/(3

3HQ

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TABLE 5. The Comparison of the xSMPL and xmodel

Measurement of The Environmental Tritium Activity Level

Xmodel

(Bq/m3)

xSMPL (Bq/m3)

Xmodel /X SMPL

Aug.2005 Feb.2005

Point A 1.32 0.0672 0.0317 19.7~41.6

Point B 0.49 0.0159 0.0064 30.8~76.6

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We developed measurement procedures for environmental tritium(HTO) in the air

Within about 2.0 Km from the NPPs, there is measurable

tritium level increases compared with the natural backguound

Results show that the presently used DF of gaseous effluents are overestimated more than 20 times.

Conclusions