ISO 13168:2015 水質—トリチウムと炭素14の活性の同時測定—液体シンチレーションカウンティングを使用したテスト方法 | ページ 2

Foreword

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The committee responsible for this document is ISO/TC 147, Water quality, Subcommittee SC3 Radioactivity measurements.

This corrected version of ISO 13168:2015 incorporates the following correction:

• —8.2, Formula (3): r_st has been replaced by r_sc.

Introduction

Radioactivity from several naturally-occurring and anthropogenic sources is present throughout the environment. Thus, water bodies (e.g. surface waters, ground waters, sea waters) can contain radionuclides of natural, human-made, or both origins:

• natural radionuclides, including potassium 40, tritium, carbon 14, and those originating from the thorium and uranium decay series, in particular radium 226, radium 228, uranium 234, uranium 238, lead 210, can be found in water for natural reasons (e.g. desorption from the soil and wash-off by rain water) or can be released from technological processes involving naturally occurring radioactive materials (e.g. the mining and processing of mineral sands or phosphate fertilizer production and use);
• human-made radionuclides, such as transuranium elements (americium, plutonium, neptunium, curium), tritium, carbon 14, strontium 90 and gamma emitting radionuclides can also be found in natural waters as a result of authorized routine releases into the environment in small quantities in the effluent discharged from nuclear fuel cycle facilities. They are also released into the environment following their use in unsealed form for medical and industrial applications. They are also found in the water as a result of past fallout contamination resulting from the explosion in the atmosphere of nuclear devices and accidents such as those that occurred in Chernobyl and Fukushima.

Drinking-water may thus contain radionuclides at activity concentrations which could present a risk to human health. In order to assess the quality of drinking-water (including mineral waters and spring waters) with respect to its radionuclide content and to provide guidance on reducing health risks by taking measures to decrease radionuclide activity concentrations, water resources (groundwater, river, lake, sea, etc.) and drinking water are monitored for their radioactivity content as recommended by the World Health Organization [WHO] and may be required by some national authorities.

An international standard on a test method of simultaneous measurement of tritium and carbon 14 concentrations in water samples is justified for test laboratory carrying out these measurements, required sometimes by national authorities, as laboratories may have to obtain a specific accreditation for radionuclide measurement in drinking water samples. Such standard is to be used as a screening method, until the interference of other beta emitters in the test portion is considered negligible.

Tritium and carbon 14 natural activity concentration can vary according to local geological and climatic characteristics, at a level below 5 Bq/l and below 0,1 Bq/l respectively. These radioactivity levels can be locally enhanced by nuclear installation authorized discharges of low level radioactive effluent into the environment. The guidance level for tritium and carbon 14 in drinking water as recommended by WHO is 10 000 and 100 Bq/l respectively.^[4]

This International Standard is one of a set of International Standards on test methods dealing with the measurement of the activity concentration of radionuclides in water samples.

1 Scope

This International Standard describes a test method for the simultaneous measurement of tritium and carbon-14 in water samples by liquid scintillation counting of a source obtained by mixing the water sample with a hydrophilic scintillation cocktail.

This is considered a screening method because of the potential presence of interfering nuclides in the test sample.

The method can be used for any type of environmental study or monitoring.

This International Standard is applicable to all types of waters having an activity concentration ranging from 5 Bq/l to 10⁶ Bq/l (upper limit of the liquid scintillation counters for direct counting). For higher activity concentrations, the sample can be diluted to obtain a test sample within this range.

2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

Bibliography