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Title: A Calibration to Predict Concentrations of Impurities in Plutonium Oxide by Prompt Gamma Analysis

Abstract

Prompt gamma (PG) analysis has been used to identify the presence of certain impurities in plutonium oxide, which has been stored in 3013 containers. A regression analysis was used to evaluate the trends between the count rates obtained from PG analysis and the concentration of the impurities in plutonium oxide samples measured by analytical chemistry techniques. The results of the analysis were used to obtain calibration curves, which may be used to predict the concentration of Al, Be, Cl, F, Mg, and Na in the 3013 containers. The scatter observed in the data resulted from several factors including sample geometry, error in sampling for chemical assay, statistical counting error, and intimacy of mixing of impurities and plutonium. Standards prepared by mixing plutonium oxide with CaF{sub 2}, NaCl, and KCl show that intimacy mixing and sampling error have the largest influence on the results. Although these factors are difficult to control, the calibrations are expected to yield semiquantitative results that are sufficient for the purpose of ordering or ranking.

Authors:
; ;
Publication Date:
Research Org.:
Office of Scientific and Technical Information, Oak Ridge, TN; Los Alamos National Laboratory (LANL), Los Alamos, NM
Sponsoring Org.:
USDOE
OSTI Identifier:
861382
Report Number(s):
LA-14258
TRN: US0600302
DOE Contract Number:
W-7405-ENG-36
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY; CALIBRATION; CONTAINERS; IMPURITIES; PLUTONIUM OXIDES; REGRESSION ANALYSIS; SAMPLING; PROMPT GAMMA RADIATION; MULTI-ELEMENT ANALYSIS; CALIBRATION STANDARDS

Citation Formats

J.E. Narlesky, E.J. Kelly, and L.A. Foster. A Calibration to Predict Concentrations of Impurities in Plutonium Oxide by Prompt Gamma Analysis. United States: N. p., 2005. Web. doi:10.2172/861382.
J.E. Narlesky, E.J. Kelly, & L.A. Foster. A Calibration to Predict Concentrations of Impurities in Plutonium Oxide by Prompt Gamma Analysis. United States. doi:10.2172/861382.
J.E. Narlesky, E.J. Kelly, and L.A. Foster. Tue . "A Calibration to Predict Concentrations of Impurities in Plutonium Oxide by Prompt Gamma Analysis". United States. doi:10.2172/861382. https://www.osti.gov/servlets/purl/861382.
@article{osti_861382,
title = {A Calibration to Predict Concentrations of Impurities in Plutonium Oxide by Prompt Gamma Analysis},
author = {J.E. Narlesky and E.J. Kelly and L.A. Foster},
abstractNote = {Prompt gamma (PG) analysis has been used to identify the presence of certain impurities in plutonium oxide, which has been stored in 3013 containers. A regression analysis was used to evaluate the trends between the count rates obtained from PG analysis and the concentration of the impurities in plutonium oxide samples measured by analytical chemistry techniques. The results of the analysis were used to obtain calibration curves, which may be used to predict the concentration of Al, Be, Cl, F, Mg, and Na in the 3013 containers. The scatter observed in the data resulted from several factors including sample geometry, error in sampling for chemical assay, statistical counting error, and intimacy of mixing of impurities and plutonium. Standards prepared by mixing plutonium oxide with CaF{sub 2}, NaCl, and KCl show that intimacy mixing and sampling error have the largest influence on the results. Although these factors are difficult to control, the calibrations are expected to yield semiquantitative results that are sufficient for the purpose of ordering or ranking.},
doi = {10.2172/861382},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Dec 13 00:00:00 EST 2005},
month = {Tue Dec 13 00:00:00 EST 2005}
}

Technical Report:

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  • Over 5,500 containers of excess plutonium-bearing materials have been packaged for long-term storage following the requirements of DOE-STD- 3013. Knowledge of the chemical impurities in the packaged materials is important because certain impurities, such as chloride salts, affect the behavior of the material in storage leading to gas generation and corrosion when sufficient moisture also is present. In most cases, the packaged materials are not well characterized, and information about the chemical impurities is limited to knowledge of the material’s processing history. The alpha-particle activity from the plutonium and americium isotopes provides a method of nondestructive self-interrogation to identify certainmore » light elements through the characteristic, prompt gamma rays that are emitted from alpha-particle-induced reactions with these elements. Gamma-ray spectra are obtained for each 3013 container using a highresolution, coaxial high-purity germanium detector. These gamma-ray spectra are scanned from 800 to 5,000 keV for characteristic, prompt gamma rays from the detectable elements, which include lithium, beryllium, boron, nitrogen, oxygen, fluorine, sodium, magnesium, aluminum, silicon, phosphorus, chlorine, and potassium. The lower limits of detection for these elements in a plutonium-oxide matrix increase with atomic number and range from 100 or 200 ppm for the lightest elements such as lithium and beryllium, to 19,000 ppm for potassium. The peak areas from the characteristic, prompt gamma rays can be used to estimate the concentration of the light-element impurities detected in the material on a semiquantitative basis. The use of prompt gamma analysis to assess impurity concentrations avoids the expense and the risks generally associated with performing chemical analysis on radioactive materials. The analyzed containers are grouped by impurity content, which helps to identify high-risk containers for surveillance and in sorting materials before packaging.« less
  • This report documents the new PG calibration regression equation. These calibration equations incorporate new data that have become available since revision 1 of “A Calibration to Predict the Concentrations of Impurities in Plutonium Oxide by Prompt Gamma Analysis” was issued [3] The calibration equations are based on a weighted least squares (WLS) approach for the regression. The WLS method gives each data point its proper amount of influence over the parameter estimates. This gives two big advantages, more precise parameter estimates and better and more defensible estimates of uncertainties. The WLS approach makes sense both statistically and experimentally because themore » variances increase with concentration, and there are physical reasons that the higher measurements are less reliable and should be less influential. The new magnesium calibration includes a correction for sodium and separate calibration equation for items with and without chlorine. These additional calibration equations allow for better predictions and smaller uncertainties for sodium in materials with and without chlorine. Chlorine and sodium have separate equations for RICH materials. Again, these equations give better predictions and smaller uncertainties chlorine and sodium for RICH materials.« less
  • Prompt gamma-ray analysis is being implemented at the Plutonium Finishing Plant (PFP) to screen impure plutonium oxide inventory items, received in the mid-1980s from the Rocky Flats Plant, for the presence of sodium chloride and potassium chloride salts from the electrorefining process. A large fraction of these items are suspected to contain electrorefining salts. Because the salts evaporate at the=950C stabilization temperature mandated for long-term storage under the U.S. Department of Energy plutonium oxide stabilization and storage criteria to plug and corrode process equipment, items found to have these salts qualify for thermal stabilization at 750C. The prompt gamma raymore » energies characteristic of sodium, potassium, chlorine, and other low atomic weight elements arise from the interaction the light elements with alpha radiation from plutonium and americium radioactive decay. High-resolution gamma ray spectrometers designed to detect energies up to {approx}4.5 MeV are used to gather the high-energy prompt gamma spectra.Observation of the presence of the high-energy gamma peaks representing the natural chlorine-35, sodium-23, and potassium-39 isotopes and the sodium-to-chlorine peak area ratios in the range for plutonium oxide materials known to contain the electrorefining salts give the evidence needed to identify plutonium oxide materials at the PFP that qualify for the lower-temperature processing. Conversely, the absence of these telltale signals in the prompt gamma analysis provides evidence that the materials do not contain the electrorefining salts. Furthermore, based on calibrations using known assayed items, semiquantitative measurement of the quantity of chlorine present in materials containing electrorefining salt also can be performed by using the count rates observed for the chlorine peak, the plutonium quantity present in the measured item, and the plutonium- and chlorine-specific response of the gamma detection system. The origin and characteristics of the impure plutonium oxide, the process impacts of the electrorefining salts, and the background and technical bases of application of prompt gamma-ray analysis to identify electrorefining salt-bearing plutonium oxide at the PFP are described.« less
  • Equipment has been assembled at the National Bureau of Standards (NBS) reactor by the University of Maryland group in cooperation with the NBS staff in order to initiate studies of a new analytical technique, neutron-capture prompt ..gamma..-ray activation analysis. According to this technique one observes prompt ..gamma..-rays while the sample is under neutron bombardment, rather than observing ..gamma.. rays from decay of radioactive species produced. It is expected that this technique will make possible the non-destructive determination of a number of elements in several classes of samples that cannot be measured by present analytical methods. A beam thimble has beenmore » built for insertion into the reactor. A beam stop and target holder have been designed and are under construction. The detection system has been designed and is on order. The pulse-height analyzer system has been obtained and debugged and most of the software needed has been written.« less
  • S>The relative effectiveness in prompt-gamma neutron activation analysis of two Pu-Be isotopic neutron sources and an Am - Be neutron source is compared. Thermal neutron levels and the associated gamma radiation produced by these sources in a standard moderating system are normalized to the nominal neutron emission rate. The methods of measurement include a BF/sub 3/ neutron detector, a Geiger-Mueller gamma detection tube, and an NaI scintillation crystal. The normalized thermal neutron level for both sources is the same. The Am source has a higher gamma radiation level than the Pu source of the same neutron emission rate. The highermore » gamma radintion level is primartly the result of the higher energy gamma ray emitted in the decay of Am/sup 214/. (auth)« less