ISO 24390:2023

INTERNATIONAL ISO
STANDARD 24390
First edition
2023-11
Nuclear energy — Nuclear fuel
technology — Methodologies for
radioactivity characterization of very
low-level waste (VLLW) generated by
nuclear facilities
Énergie nucléaire — Technologie du combustible nucléaire —
Méthodologies pour l'évaluation de la radioactivité des déchets de
Très Faibles Activité (TFA) produits par les installations nucléaires
Reference number
© ISO 2023
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Waste acceptance criteria (WAC) for VLLW . 3
5 Radioactivity characterization . 4
5.1 Principle of radioactivity characterization of VLLW. 4
5.1.1 Requirements and limits . 4
5.1.2 Measurement methodology . 4
5.2 Process for radioactivity characterization of VLLW . 5
5.2.1 General . 5
5.2.2 Step 1: Investigation of waste characteristics . 6
5.2.3 Step 2: Surface scanning . 8
5.2.4 Step 3: Gamma activity measurement . 9
5.2.5 Step 4: Destructive analysis . 10
5.3 Decision thresholds . 10
5.4 Correlation of measurement methods . 11
5.5 Scaling factor method .12
5.6 Radionuclide vector method . 13
6 Sampling .13
6.1 General .13
6.2 Homogeneous waste . . 14
6.3 Heterogeneous waste . 14
6.4 Sampling uncertainty . 14
7 Data quality objectives (DQO) .15
8 Quality assurance .15
8.1 General . 15
8.2 Laboratory . 15
8.3 Measuring instruments .15
8.4 Personnel . 16
8.5 Documentation and procedures . 16
Annex A (informative) Typical application of characterization procedure to three different
waste streams .17
Bibliography .19
iii
Foreword
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iv
Introduction
The activity concentration of very low-level waste (VLLW) is generally below a few becquerels per gram
(Bq/g), which is still greater than the allowable limits for clearance waste (often 10 times to 100 times
greater). It is generally accepted that due to the low levels of activity associated with this type of waste,
VLLW does not require a high level of containment and isolation, as is the case for low and intermediate
level waste.
To take full advantage of opportunities for directing waste to alternative waste management routes
that are more advantageous, the waste should be appropriately characterized and classified. Accurate
waste characterization is also crucial for the protection of people and the environment, given the lower
levels of isolation or containment barriers at VLLW disposal sites (generally in ordinary landfills).
Additionally, proper characterization may allow waste classification for reuse or recycling.
Although the process for radioactively characterizing waste as low-level waste (LLW), VLLW and
clearance generally follows common principles, it is appropriate to establish a specific document to
assist in identifying low-level waste against waste acceptance criteria on VLLW.
This document describes the methodologies and procedures for the identification of waste that can be
categorized as VLLW.
v
INTERNATIONAL STANDARD ISO 24390:2023(E)
Nuclear energy — Nuclear fuel technology —
Methodologies for radioactivity characterization of very
low-level waste (VLLW) generated by nuclear facilities
1 Scope
This document describes methodologies for radioactivity characterization of very low-level waste
(VLLW) generated from the operation or decommissioning of nuclear facilities. The purpose is to
differentiate VLLW from low-level radioactive solid waste and waste below clearance levels. The aim is
to effectively characterize and to demonstrate that it satisfies the criteria for VLLW.
This document focuses specifically on characterization methods of radioactive solid waste. Clearance
and exemption monitoring are not covered within this document. Additionally, the characterization of
liquid and gaseous wastes is also excluded from this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 12749-3, Nuclear energy, nuclear technologies, and radiological protection — Vocabulary — Part 3:
Nuclear fuel cycle
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 12749-3 and the following
apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
very low-level waste
VLLW
radioactive waste that does not necessarily meet the criteria of exempt waste, but that does not need
a high level of containment and isolation and, therefore, is suitable for disposal in landfill type near
surface repositories with limited regulatory control
Note 1 to entry: Such landfill type near surface repositories may also contain other hazardous waste. Typical
waste in this class includes soil and rubble with low levels of activity concentration. Concentrations of longer-
lived radionuclides in VLLW are generally very limited.
[SOURCE: IAEA Safety Glossary: 2022 edition]
3.2
waste acceptance criteria
WAC
quantitative or qualitative criteria specified for the waste form and waste package to be accepted by
the operator of a waste management facility
[SOURCE: IAEA Safety Glossary: 2022 edition, modified — Definition revised.]
3.3
data quality objective
DQO
process used to establish performance or acceptance criteria, which serve as the basis for designing a
plan for collecting data of sufficient quality and quantity to support the goals of a study
[SOURCE: ISO 18557:2017, 3.8]
3.4
difficult-to-measure radionuclide
DTM radionuclide
radionuclide whose radioactivity is difficult to measure directly from the outside of the waste packages
by non-destructive assay means
[SOURCE: ISO 21238:2007, 2.1, modified — Examples removed.]
3.5
key radionuclide
gamma-emitting radionuclide whose radioactivity is correlated with that of difficult-to-measure
radionuclides (3.4) and can be readily measured directly by non-destructive assay means
Note 1 to entry: Also called “easy-to-measure radionuclide” or “marker radionuclide”.
[SOURCE: ISO 21238:2007, 2.2, modified — Example removed.]
3.6
scaling factor
factor or parameter derived from the mathematical relationship used in calculating the radioactivity
of difficult-to-measure radionuclides (3.4) from that of key radionuclide (3.5) determined from sampling
and analysis data
[SOURCE: ISO 21238:2007, 2.3]
3.7
nuclide vector
fingerprint
used to infer and quantify the presence of other key nuclides
Note 1 to entry: Applying correlation factors enables estimations of difficult-to-measure radionuclides (3.4).
Note 2 to entry: It is a method which involves measurements of key radionuclides (3.5) (usually gamma emitters,
137 60
e.g. Cs, Co) to quantify difficult-to-measure nuclides.
[SOURCE: ISO 18557:2017, 3.12]
3.8
heterogeneous waste
radioactive waste that does not meet the definition of homogeneous waste (3.9), including solid
components and mixtures of solid components
EXAMPLE Cartridge filters, contaminated tools or instruments.
[SOURCE: ISO 21238:2007, 2.13, modified — Part of definition used to create EXAMPLES.]
3.9
homogeneous waste
radioactive waste that shows an essentially uniform distribution of activity and physical contents
EXAMPLE Flowable wastes such as concentrates, solidified liquids and spent resins.
[SOURCE: ISO 21238:2007, 2.12, modified — EXAMPLES revised.]
3.10
destructive analysis
analytical techniques of radioactive and chemical materials using methods which involve the destruction
of a sample, for example chemical and radiochemical analysis, ICP-MS or alpha spectrometry
[SOURCE: ISO 18557:2017, 3.9, modified — Definition revised.]
3.11
non-destructive analysis
NDA
analytical techniques that allow measurement of specific properties without physical destruction of
the media or item
Note 1 to entry: Generally used for in situ measurements.
[SOURCE: ISO 18557:2017, 3.20]
4 Waste acceptance criteria (WAC) for VLLW
Waste acceptance criteria (WAC) are quantitative or qualitative criteria which state the conditions by
which waste can be accepted by the operator of facilities that process, store or dispose of VLLW.
WAC specify the radiological, mechanical, physical, chemical and biological characteristics of the waste
packages or unpackaged waste which may be accepted into the facility.
WAC are important because they:
— ensure compliance with safety and environmental requirements;
— are designed to assist with the selection of appropriate processing and packaging options;
— prevent technological problems during processing;
— standardize waste management operations;
— ensure waste tracking.
WAC are developed so as to be relevant, concise, measurable and verifiable, provide some flexibility, and
be appropriate to each waste stream. WAC ensure that the interfaces between all parties and facilities
associated with the management and disposal of VLLW are clearly understood.
Waste characterization requirements are typically developed from disposal safety and/or performance
assessment, and the waste acceptance criteria for disposal are derived at the same time.
The radioactivity characterization of VLLW should address the requirements of WAC and should ensure
that the requirements for each stage associated with waste management and disposal are considered.
It is good practice to develop and justify the requirements of WAC using a robust process, such as data
quality objectives (DQO).
The requirements for radioactivity characterization should be interpreted and confirmed, and sufficient
characterization should be accomplished to satisfy the requirements of the WAC.
5 Radioactivity characterization
5.1 Principle of radioactivity characterization of VLLW
5.1.1 Requirements and limits
The main purpose of VLLW characterization is to identify conveniently this waste stream from higher-
level radioactive waste (LLW) and lower-level radioactive waste (clearance waste). The general
measurement methods used for the characterization of LLW and clearance waste are also applicable to
VLLW. The selection of characterization methods for VLLW mainly depends on:
— regulatory requirements, including activity limits or dose rate limits;
— monitoring purpose, such as reuse, recycling or landfill disposal;
— limitations on measurement possibilities.
Activity limits can be expressed in terms of surface activity or mass activity and can be fixed for a
single radionuclide or a group of radionuclides (e.g. alpha emitters, beta-gamma emitters, pure beta
emitters).
The limits of dose rate of gamma emitters can be derived from activity limits and are recommended to
identify and determine the classification of radioactive waste (as seen in 5.3).
5.1.2 Measurement methodology
During the radioactivity measurement of VLLW, the following considerations should be taken into
account:
— surface activity measurement, i.e. in situ direct measurement, consists mostly of beta and gamma
measurement;
— results of in situ direct measurement can be used to show the preliminary distribution of the
contamination and confirm “active spots”;
— surface activity measurements can guide targeted sampling and associated gamma spectrometry
or destructive analysis;
— alpha particle, soft beta radiation as well as low energy gamma radiation are difficult to detect by in
situ direct measurement;
— measurement of alpha particles and soft beta radiation typically requires radio-chemical analysis
or spectroscopic analysis to define the composition of mixed radionuclides;
— radio-chemical analysis of low activity requires sufficient samples to facilitate easier measurement
and to improve the accuracy of specific activities;
— alpha contamination measurement of VLLW from reactors is usually unnecessary unless cladding
ruptures have occurred;
— for mixtures of radionuclides, easily detectable radionuclides (e.g. Co) can be used as contamination
indicators to determine quickly the activity level of radioactive waste;
— selection of measurement apparatus should be based on the activity limits and characteristics of
the apparatus;
— the apparatus should be calibrated following the standards of various energies; the detection
thresholds and background levels should be regularly checked to prevent any major error;
— the uncertainty should be carefully considered during the sampling and measurement.
5.2 Process for radioactivity characterization of VLLW
5.2.1 General
The following steps are considered good practice for identification of waste that may be categorized as
VLLW:
— investigation of waste properties;
— surface scanning, dose rate assessment;
— theoretical calculation and measurement of waste activity;
— activity measurement by means of destructive analysis.
The process is shown in Figure 1.
The steps in the process are further described in 5.2.2 to 5.2.5.
Key
L activity limit, in becquerels
A
L dose rate limit, in grays per hour
D
Figure 1 — VLLW radioactivity characterization process
5.2.2 Step 1: Investigation of waste characteristics
The objective of the first step is to obtain as much information as possible about the properties of the
waste. This involves collecting, reviewing and analysis of all available data, guided by the DQO process.
The aim is to define the waste characterization objectives and associated sampling and analysis
strategy against the appropriate waste acceptance criteria. Typically, the following information, at a
minimum, should be considered based on the specific waste stream:
— basic information, including:
— the process by which the waste was generated;
— the location of the waste;
— the radiological history of the waste;
— the processing technology and storage conditions;
— physical properties, including:
— waste volume or weight;
— quantity of waste;
— form of waste;
— material composition;
— geometry;
— moisture content;
— containment, if any;
— chemical properties, including:
— pH;
— oxidation reducibility;
— thermal stability;
— presence of organic and inorganic compounds;
— radiation characteristics, including:
— distribution of radioactivity (i.e. homogenous or heterogeneous);
— surface activity;
— radionuclides present;
— radionuclide concentrations;
— surface dose rates;
— results from any previous measurements or characterization campaigns, including surface
scans.
VLLW can be generated from various processes at nuclear facilities, and the radiation characteristics
of waste from different sources can vary significantly. The characteristics of the waste are likely to be
different from those of other radioactive sources, depending on the source of contamination.
The radiation properties of waste generated from uranium enrichment, conversion and fuel fabrication
are relatively well-defined, simple and stable. The radioactive contamination in such waste is mainly
uranium and its daughter nuclides. Waste generated from nuclear power plants (NPPs) has relatively
clear and stable radiation properties, but it is more complex. This waste could be contaminated
with alpha, beta and gamma-emitting radionuclides. A large number of different radionuclides are
generated as a result of fission, activation and decay. The radiation properties of VLLW generated
from reprocessing of spent fuel are very complex. Radiation sources in such waste include fission and
activation products.
The application example for the characterization process of the three different waste streams is
presented in Annex A.
During the investigation of waste properties, the integrity and reliability of the waste characterization
information should be assessed and updated regularly. This information will be used to establish the
scaling factors or ratios between different radionuclides. Depending on the specific radionuclides
present in the waste, verification can also be achieved through destructive sampling analysis.
5.2.3 Step 2: Surface scanning
5.2.3.1 General
Surface scanning is typically performed using portable instruments to detect surface dose rates and
measure surface contamination. Portable instruments are commonly used for this purpose. During
the operation of these instruments, several factors should be considered, including the environmental
background level, instrument resolution, detection limit and range and alarm threshold.
5.2.3.2 Surface dose rate detection
The surface dose rate detection is used to:
— prevent unnecessary radiation exposure during radioactivity measurement;
— identify hot spots inside the waste;
— measure the surface dose rate and determine the radioactivity level of waste following Formula (1)
and Formula (2) as specified in 5.3. As shown in Figure 1, if the measured result exceeds L or L ,
D A
the radioactive waste cannot be classified as VLLW.
The uncertainty of surface scanning results from the uncertainty in instrument calibration and the
measurement process. For the dose rate detector, the uncertainty of calibration includes:
— the choice of primary or secondary standard instrument;
— the distance of the instrument from radiation source;
— the uniformity of the radiation beam;
— the variation of background dose rate;
— variation of environmental conditions.
The uncertainty of dose rate detection includes:
— variations of environmental conditions during detection (such as background, temperature,
humidity, etc.);
— the characteristics of apparatus (such as background, efficiency, detection limit, stability, etc.);
— method of measurement, including speed of probe movement, distance to the surface of contamination
and position of counts reading.
5.2.3.3 Surface contamination measurement
Before conditioning and treatment of radioactive waste, surface contamination measurement is
usually used to initially estimate the characteristics of radioactive contaminants. The purpose of
surface contamination measurement is to prevent unnecessary contamination during radioactivity
measurement and to decrease the radioactive level through decontamination.
The principles, wipe test method and apparatus calibration of surface contamination measurement are
given in ISO 7503-1, ISO 7503-2, ISO 7503-3, respectively.
5.2.4 Step 3: Gamma activity measurement
Given the potential waste stream generators identified in 5.2.2, gamma activity measurement can
usually be achieved through direct measurement. The objectives of gamma measurement include:
— obtain the γ spectra;
— identify possible γ radionuclides in the waste;
— identify easily measurable key radionuclides;
— provide input for the calculation of scaling factors between difficult-to-measure radionuclides and
key radionuclides;
— provide input for the calculation of ratios between dose rate and activity concentration;
— verify the relevant parameters of radiation characteristics obtained in the first step, such as
radiation contamination type, possible radionuclide type and previous surface scans.
It is good practice to measure gamma activity through non-destructive analysis (NDA) means, ideally
through use of a system capable of acquiring a gamma spectrum and suitable for the measurement of
60 137 51 54
waste containing high energy γ radionuclides (e.g. Co, Cs, Cr, Mn).
The measurement results may be given in units of total activity or activity concentration. For VLLW,
it is recommended that the minimum detectable activity (MDA) is selected based on the activity
measurement that is most advantageous in differentiating VLLW from other categories of waste.
Gamma activity measurement can be performed using different techniques, such as segment gamma
spectrum, rotating gamma scanning or tomographic gamma scanning. The i
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