ASTM C1855-2018 Standard Test Method for Determination of Uranium and Plutonium Concentration in Aqueous Solutions Using Hybrid K-Edge Densitometry and X-Ray Fluorescence.pdf

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1、Designation: C1855 18Standard Test Method forDetermination of Uranium and Plutonium Concentration inAqueous Solutions Using Hybrid K-Edge Densitometry andX-Ray Fluorescence1This standard is issued under the fixed designation C1855; the number immediately following the designation indicates the year

2、oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method specifies the determination of thevolume

3、tric uranium and plutonium concentrations, typically, innitric acid solutions through the combination of K-Edgeabsorption Densitometry (KED) and K X-Ray fluorescence(XRF) using an X-Ray generator. It is known as the “HybridK-Edge” (HKED) technique whose original implementation isdescribed in Ref (1)

4、.2The method is applicable to dissolver(input) solutions and product solutions. The test method alsospecifies the determination of low concentrations (50 g/L and 1 %for plutonium in typical U-Pu solutions for a typical measure-ment time of 3 1000 s (3 replicates, 1000 s live time each)(1).5.3 For pu

5、re plutonium only product solutions, the KEDtechnique can achieve measurement precisions better than0.3 % for plutonium concentrations 50 g/L for a typicalmeasurement time of 3 1000 s.5.4 For pure uranium only solutions, precisions of betterthan 0.3 % can be achieved using the KED technique forurani

6、um concentrations 50 g/L, for a typical measurementtime of 3 3600 s.5.5 For uranium only or plutonium only solutions of con-centrations approximately 1 g/L, assayed using XRF, a mea-surement precision of 1.0 % has been achieved (1). Forsolutions of concentration approximately 50 g/L, assayed usingXR

7、F, measurement precisions of 0.2 % or better have beenachieved. The typical measurement time for stand-alone XRFassay is 3 3000 s.5.6 Quality Control (QC) samples are assayed for a typicalmeasurement time of 3 3000 s.5.7 It is applicable when solutions to be measured arehomogeneous with respect to c

8、hemical composition.5.8 Results are typically used for fuel fabrication, processcontrol, quality control, material control and accountancy, andsafeguards in nuclear fuel reprocessing plants. Each applica-tion can have its own data quality objectives (Guide C1068).5.9 The HKED instrument may use a si

9、ngle cylindrical vialfor both the KED and XRF measurements, or separate samplecontainers for KED and XRF. The typical values for the pathlength of the rectangular cuvette and the inner diameter of thecylindrical vial are given in 7.8.5.10 The transfer of the sample into the HKED system canbe accompl

10、ished either horizontally by means of a suitablydesigned sample conveyor system coupled to a shieldedglovebox or hot cell facility or vertically through a pneumaticsample transfer system.5.11 The U and Pu concentrations measured by HKED aredependent on the sample temperature. The analysis softwarein

11、cludes a normalization of the measured concentration at theambient room temperature to a reference temperature of 25 C.The ambient room temperature is input into the analysissoftware. HKED has been employed as a rapid alternative todestructive chemical analyses, such as Isotope Dilution MassSpectros

12、copy (IDMS) or titration, because there is minimalsample preparation, and precision of HKED is comparable tothe precision of such chemical analyses. This is especiallyuseful when high sample throughput is important.5.12 For the three modes of operation that are possibly,namely, K-Edge only, Hybrid K

13、-Edge/XRF, and Stand-aloneXRF, the uncertainty levels that can be achieved for U andU/Pu samples have been established for routine safeguardsmeasurements are described in the ITV (2).6. Interferences6.1 K-Edge MeasurementIn the energy region of interest,the intensity of the transmitted X-Ray beam fo

14、r KED is aboutthree orders of magnitude higher than that obtained from theself-radiation of typical input solutions. In view of this, theKED measurement is insensitive to self-radiation from inputsolutions. This is true for fuels with relatively short coolingtimes (1).6.2 If the system is calibrated

15、 for samples in a limited rangeof U:Pu ratios, for example 100:1, in a given mass range, (50g/L to 400 g/L), but a sample with a much higher U:Pu ratio ismeasured, the attenuation of the bremsstrahlung by the minoractinide (Pu) will cause a bias on the KED results from themajor actinide (U). The hyb

16、rid XRF measurement of sampleswith U and Pu may be subject to the following types ofinterferences.6.2.1 The UK1and the PuK2peaks overlap and interferewith each other. In the current region of interest (ROI) basedapproach, a correction is applied for this interference.6.2.2 The UK2and UK3peaks overla

17、p, and so do UK1and UK3. An ROI that includes UK2and UK3, and anotherROI that includes UK1and UK3are set up and used duringcalibration as well as sample analysis. Therefore no bias resultsfrom interferences in these cases.6.2.3 TheAmK1ROI is used to provide a correction for thepresence of AmK2X-Rays

18、 in the PuK1background ROI.6.2.4 Dissolver solutions (or “input” solutions) from spentnuclear fuels are chemically complex and highly radioactive.The spectrum from a dissolver solution is dominated bygamma rays from a few longer lived fission products such as137Cs,144Ce,154Eu, and155Eu. The gamma ra

19、ys from fissionproducts cause the excitation of uranium and plutonium in thesample and result in the emission of their characteristicX-Rays. This is termed “self-radiation.”6.2.4.1 To correct for self-radiation effects, a separate pas-sive spectrum can be acquired by turning off the X-Rays.Alternati

20、vely, an empirical derived correction factor can beused by relating the additional counts due to fission products inthe energy range 125 keV to 131 keV, to the passive count ratesin the ROIs for the evaluation of the net X-Ray peak counts (1).6.2.5 Besides self-radiation, the downscattering of the f

21、is-sion product gamma rays increases the continuum levels,degrading the precision of the measurements.7. Apparatus7.1 Standard equipment for high resolution gamma rayspectroscopy, including two high resolution high-purity germa-nium detectors each with electronics for fast pulse processing,a multich

22、annel analyzer and a dedicated software package areused for spectrum acquisition and evaluation. ElectronicsC1855 183should be capable of handling a count rate of at least 50 000counts per second (cps).7.2 Planar HPGe detectors with an active area of 100 mm2to 200 mm2and a thickness of 10 mm are gen

23、erally used.7.3 The energy resolution is demonstrated using109Cd and57Co by measurement of the FWHM of the gamma ray peaksfor these two isotopes with the same electronics configurationas used under routine measurement conditions. During systeminstallation and set up, the energy resolution (FWHM) of

24、theKED and XRF detectors is demonstrated using a57Co sourceand is typically 570 eV or better at 122 keV at a shaping timeof 2.0 microseconds. During operation, the energy resolution ismonitored using the FWHM at the 88 keV gamma ray peakfrom109Cd and is typically 520 eV or better at a count rate ofa

25、pproximately 50 000 cps.7.4 Some instruments use a sample changer. The position ofthe samples must be controlled to within 0.3 mm to control themisalignment from causing more than 0.1 % bias.7.5109Cd source is typically affixed near the detectors forenergy calibration and gain stabilization. The typ

26、ical countrates from the109Cd source are 2000 cps (peak/backgroundratio of 2:1).7.6 X-Ray equipment consisting of a cooled X-Ray tube,high voltage power supply, and operation console. An X-Raytube with a window diameter not exceeding 50 mm isrecommended.7.7 The X-Ray tube is nominally run at 150 kV

27、and 5 mAto 15 mA. Stability of the high voltage supply should be lessthan 0.1 % with adjustable high-voltage and current controls.7.8 Sample Containers:7.8.1 Either a single cylindrical vial or a combination ofrectangular cuvette and cylindrical vial are typical. In a systemthat uses two sample cont

28、ainers (see Fig.A1.1, AnnexA1), thetypical path length of the X-Rays through the rectangularcuvette is 2.0 cm, and the typical inner diameter of thecylindrical vial is 0.9 cm. In a system where the samplecontained in a single cylindrical vial is used for KED and XRF,the typical inner diameter of the

29、 vial is 1.4 cm. These pathlengths are dependent on the areal density of the samples andmust be selected appropriately. For example, a measurementprecision of 0.23 % can be achieved in a KED assay of a 150g/L uranium solution contained in a cuvette of path lengthequal to 2.0 cm (1). This corresponds

30、 to an areal density of 0.3g/cm2. To achieve a similar precision for a 100 g/L uraniumsolution, one will need to use a cuvette of path length equal to3.0 cm (areal density = 0.3 g/cm2). Refer to 13.3 for additionalguidelines on areal densities of samples.7.9 The K-Edge measurement depends on the eff

31、ective pathlength of the X-Ray beam through the solution. For meetingthe ITVs this geometrical parameter must be carefullycontrolled, because its fractional uncertainty propagates di-rectly into the fractional uncertainty of the uranium or pluto-nium concentration measurement. The uncertainty on the

32、 pathlength in this case must be small compared to other sources ofuncertainty (0.01 % typically). The preferred type of samplevials are spectroscopy cells whose thickness is known to aprecision less than 0.01 %.7.10 In HKED systems that use a single cylindrical vial forboth KED and XRF, the uncerta

33、inty in the KED measurementsdue to uncertainty in the pathlength is 0.07 % typically. Thepoorer uncertainty is because of the curvature of the cylindricalcontainer. The uncertainty in sample positioning is typically0.1 %.7.11 The vial wall thickness should be as acceptably thin aspossible in order t

34、o manage the intensity of scattered radiationfrom the X-Ray beam while maintaining structural integrityand safe containment of the solutions.7.12 If secondary containment is required for the samplecontainer (for example, to prevent contamination of thesystem), it should allow for transmission of the

35、 X-Rays fromthe generator and the sample with minimal interference. Aschematic drawing of the HKED system geometry is shown inFig. A1.2 in Annex A1. The drawing shows the configurationwith a composite sample container consisting of a quartzcuvette for the KED measurement and a polyethylene vial forX

36、RF.8. Hazards8.1 Safety Hazards:8.1.1 The high voltage supply for the X-Ray generator hassufficient power to be a lethal hazard. Appropriate precautionsshould be taken when performing maintenance or during initialsystem set up. The HV generator must be properly grounded.8.1.2 The X-Ray generator cre

37、ates a high level of ionizingradiation when energized, that can result in a lethal dose in ashort period of time (on the order of minutes). Appropriateprecautions should be taken when performing maintenance orduring initial system set up.8.1.3 High resolution gamma-ray detectors operate at volt-ages

38、 as high as 5 kV. Appropriate precautions should be takenwhen using, assembling, and disassembling these systems.8.1.4 Some detectors have beryllium windows which arefragile and considered hazardous due to oxidation and inhala-tion hazard due to BeO.8.1.5 Collimators and shielding may use materials

39、(forexample, lead and cadmium) which are considered toxic, andcan be physically heavy and difficult to maneuver. Proper carein their use and disposal are required.8.1.6 Uranium-, plutonium-, and fission-product-bearingmaterials present both chemical and radiological hazards. Theanalyst should be awa

40、re of these hazards and take appropriateprecautions.8.1.7 The solutions are typically highly acidic (for example,nitric or hydrofluoric acid). Proper care must be taken in thepreparation and handling of these solutions.8.1.8 The X-Ray system is connected to a three phaseexternal power supply of 220/

41、230/240 volts. Proper proceduremust be followed in energizing or de-energizing the X-Raytube to prevent arcing.8.1.9 The operator must be cognizant of the possibility ofliquid leaking from the cooler or the generator, leading to aslippery condition or electrocution.C1855 1848.1.10 Proper maintenance

42、 of high voltage cable in theX-Ray system is necessary to prevent arcing in the X-Raysystem.8.1.11 The high voltage generator must be grounded to theearth to minimize the potential for arcing of the system.8.1.12 Sealed calibration standards stored for an extendedperiod of time pose a hazard due to

43、build-up of pressure whichcould result in the seals cracking, leading to spread ofcontamination.8.2 Technical Hazards:8.2.1 Personnel operating the HKED system must have theappropriate qualifications and training, in accordance withrecommendations found in Guides C1297 and C1490.8.2.2 The detector a

44、nd the signal processing electronicsmust be properly grounded to eliminate ground loops.8.2.3 Electromagnetic interference, vibrations, and couplingto a hot cell (mechanical or electrical, or both) can alsointroduce noise artifacts and must be mitigated.8.2.4 Inhomogeneity of the sample solution due

45、 to residues/sedimentation or precipitation will impact the correlation of thetransmission of the X-Rays to the concentration of U and Pu inthe solution.8.2.5 If the sample contained in the vial is not usedimmediately after being prepared, and instead stored, evapo-ration will occur. The evaporation

46、 rate could be as much as0.2 % per hour and will result in an overestimation of the U orPu concentration in the container the sample was drawn from.The rate of evaporation depends on the temperature, humidityand the fill height of the solution in the vial.8.2.6 The fill height of the solution inside

47、 the container mustbe high enough in order to envelope the X-Ray beam passingthrough it.8.2.7 The activity of the109Cd source must be high enoughto ensure that the 88 keV peak is detected above the continuumand can be reliably used for gain stabilization and small enoughto avoid random coincidence s

48、umming between the 22 keVX-Ray and the 88 keV gamma ray lines.8.2.8 The matrix of the reference (blank) solution must bethe same as the matrix of the sample.8.2.9 The high voltage generator and the X-Ray tube mustbe cooled to a consistent temperature; otherwise the outputcould vary.8.2.10 Solutions

49、with high concentrations of uranium orplutonium can cause radiolysis in the matrix, leading to theformation of bubbles. The rate of radiolysis on the HKEDresults depends on the isotopic composition of uranium orplutonium in the sample. The impact on the results is notpredictable. Shorter lived isotopes can cause higher radiolysis(241Pu,238Pu,240Pu) than longer lived isotopes such as239Pu.8.2.11 Partial warm-up of Ge detectors can lead to gain shiftand degradation in energy resolution, and resulting in incorrectresults.8.2.12 Sample temperature is required as an