【国外标准】 Standard Practice for Sampling Gaseous Uranium Hexafluoride Using Zeolite in Single-Use Destructive Assay Sampler

5.1 Facility operators and safeguards inspectors routinely collect UF6 samples from processing lines, isotopic enrichment cascades or storage cylinders to determine uranium isotopic composition. The isotope ratio n(235U)/n(238U) is particularly important since it is used to calculate the amount of fissile 235U in the sample.5.2 Conventional sampling practices (such as Practices C1052 and C1703) collect samples of UF6, usually in quantities greater than one gram. Due to the chemical hazards of UF6 (and in some cases the high collection mass), an increasing number of air transport operators are unwilling to transport such samples. In contrast, SUDA samples are expected to be transported as excepted quantities (for example, under UN 2910 (3)), as the conversion to a less hazardous, more stable chemical species avoids the chemical hazards of UF6 similar to Practice C1880. Additionally, the decreased shipping requirement and small collection mass of SUDA samplers (less than Practice C1880) allow for multiple SUDA samples to be transported in the same shipment.5.3 For safeguards applications, isotopic measurements that fall within the 2010 International Target Value (ITV) ranges (5) have been demonstrated (1).5.4 This practice provides the following qualities:5.4.1 Fitness for purpose in verifying nuclear material declarations.5.4.2 A safe, simple and fast procedure for the sample collector that minimizes sample handling and potential for cross-contamination.5.4.3 Flexibility for use in a wide variety of facilities.5.4.4 Robustness to adapt to minor changes in facility operating parameters.5.4.5 Confidentiality for the operating facility from which the sample is collected.5.4.6 Safety in sample handling and transport since the sample is a less hazardous, more stable form (specifically, UO2F2 is more stable and less volatile than UF6 gas).5.4.7 Ease of sample preparation in the laboratory with reduced processing hazards during recovery of the uranium content (1).5.5 Samples collected using this practice are suitable for determination of uranium isotopic composition, as described in 4.5, for safeguards applications. Care must be taken to ensure cleanliness of the sampling tap to be used for SUDA samples, as any UF6 holdup in the sampling tap from previous sample collection could affect sample collection and isotopic measurements (see Section 9 for further details regarding this issue). Other applications of this practice are possible but require validation prior to use.1.1 This practice is applicable to sampling gaseous uranium hexafluoride (UF6) from processing facilities, isotope enrichment cascades or storage cylinders, using the sorbent properties of zeolite in a single-use destructive assay (SUDA) sampler.1.2 This practice is based on the SUDA method developed at Pacific Northwest National Laboratory (1)2 for collection of samples of UF6 for determination of uranium isotopic content for nuclear material safeguards and other applications.1.3 The UF6 collected is converted to uranyl fluoride (UO2F2), allowing samples to be handled and categorized for transport under less stringent conditions than are required for UF6.1.4 This practice can be used to collect samples for safeguards measurements. Safeguards samples collected with this practice have been shown to provide suitable isotopic measurements (1).1.5 This practice has not been demonstrated for suitability for compliance with Specifications C787 and C996. Practices C1052 or C1703 can be used to collect samples for compliance with these specifications.1.6 The scope of this practice does not include provisions for preventing criticality.1.7 Units—The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.