Significance and Use
5.1 The HKED technique is highly element specific and depends upon a well-known controlled geometry.
5.2 The HKED technique can provide concentration measurements of actinides in solutions with precision typically better than 0.3 % for uranium concentrations >50 g/L and 1 % for plutonium in typical U-Pu solutions for a typical measurement time of 3 × 1000 s (3 replicates, 1000 s live time each) (1).
5.3 For pure plutonium only product solutions, the KED technique can achieve measurement precisions better than 0.3 % for plutonium concentrations >50 g/L for a typical measurement time of 3 × 1000 s.
5.4 For pure uranium only solutions, precisions of better than 0.3 % can be achieved using the KED technique for uranium concentrations >50 g/L, for a typical measurement time of 3 × 3600 s.
5.5 For uranium only or plutonium only solutions of concentrations approximately 1 g/L, assayed using XRF, a measurement precision of 1.0 % has been achieved (1). For solutions of concentration approximately 50 g/L, assayed using XRF, measurement precisions of 0.2 % or better have been achieved. The typical measurement time for stand-alone XRF assay is 3 × 3000 s.
5.6 Quality Control (QC) samples are assayed for a typical measurement time of 3 × 3000 s.
5.7 It is applicable when solutions to be measured are homogeneous with respect to chemical composition.
5.8 Results are typically used for fuel fabrication, process control, quality control, material control and accountancy, and safeguards in nuclear fuel reprocessing plants. Each application can have its own data quality objectives (Guide C1068).
5.9 The HKED instrument may use a single cylindrical vial for both the KED and XRF measurements, or separate sample containers for KED and XRF. The typical values for the path length of the rectangular cuvette and the inner diameter of the cylindrical vial are given in 7.8.
5.10 The transfer of the sample into the HKED system can be accomplished either horizontally by means of a suitably designed sample conveyor system coupled to a shielded glovebox or hot cell facility or vertically through a pneumatic sample transfer system.
5.11 The U and Pu concentrations measured by HKED are dependent on the sample temperature. The analysis software includes a normalization of the measured concentration at the ambient room temperature to a reference temperature of 25 °C. The ambient room temperature is input into the analysis software. HKED has been employed as a rapid alternative to destructive chemical analyses, such as Isotope Dilution Mass Spectroscopy (IDMS) or titration, because there is minimal sample preparation, and precision of HKED is comparable to the precision of such chemical analyses. This is especially useful when high sample throughput is important.
5.12 For the three modes of operation that are possibly, namely, K-Edge only, Hybrid K-Edge/XRF, and Stand-alone XRF, the uncertainty levels that can be achieved for U and U/Pu samples have been established for routine safeguards measurements are described in the ITV (2).
Scope
1.1 This test method specifies the determination of the volumetric uranium and plutonium concentrations, typically, in nitric acid solutions through the combination of K-Edge absorption Densitometry (KED) and K X-Ray fluorescence (XRF) using an X-Ray generator. It is known as the “Hybrid K-Edge” (HKED) technique whose original implementation is described in Ref (1).2 The method is applicable to dissolver (input) solutions and product solutions. The test method also specifies the determination of low concentrations (<50 g/L) of U and Pu using XRF measurements alone (the “stand-alone XRF” mode). Using the XRF measurement in the stand-alone mode, solutions in the 0.2 g/L to 50 g/L range of Pu with or without U and solutions in the 0.2 g/L to 50 g/L range of U with or without Pu are commonly measured.
1.2 This test method is applicable to the following common-use conditions:
1.2.1 Spent nuclear fuel reprocessing and fuel production.
1.2.2 Homogeneous aqueous solutions contained in cylindrical vials or cuvettes. HKED systems may use two separate sample containers, namely a rectangular cuvette for KED and a cylindrical vial for XRF. Alternatively, there are HKED systems that use a sample contained in a single cylindrical vial, for both K-Edge and XRF.
1.2.3 The results produced by the two sample configuration (a rectangular cuvette for K-Edge densitometry and a cylindrical vial for XRF) are compliant with the International Target Values (ITV) (1).
1.2.4 The precision results produced by the single cylindrical vial configuration are degraded in comparison to the two container system.
1.2.5 This test method is applicable to facilities that do not adopt the ITVs, but have their own Data Quality Objectives (DQO).
1.2.6 Solutions which contain uranium and plutonium with uranium concentration of 150 to 250 g/L and a U:Pu ratio of 100:1 typically, in the presence of fission products with β, γ, activity of up to 10 TBq/L.
1.2.6.1 This test method is not applicable to samples where a minor element such as U needs to be quantified in which Pu is the major element.
1.2.6.2 This test method is applicable for common use process control applications for quantifying Pu in the 5 g/L to 30 g/L range using XRF only in the presence of up to ~10 % (~100 000 ppm) of transuranic impurities (predominantly U and Am). In this application, the impurity concentration in the Pu samples is not quantified. Additional uncertainties must be estimated and factored in the Pu concentration results.
1.2.7 Solutions containing 50 g/L to 400 g/L of uranium alone.
1.2.8 Solutions containing 50 g/L to 400 g/L of plutonium alone.
1.2.9 Solutions with low concentrations of U and Pu, typically in the 0.2 g/L to 50 g/L range.
1.2.10 The concentration ranges given in 1.2.6 – 1.2.9 are application of the HKED technique for Materials Control and Accountancy (MC&A) purposes. For process control applications where precision requirements are less stringent, KED method can be used to assay samples with lower concentrations of U or Pu (down to 30 g/L).
1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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.
1.5 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.
