A new radiochemical method for determining deuterium-tritium (DT) fuel and plastic ablator (CH) areal densities (ρR) in high-convergence, cryogenic inertial confinement fusion implosions at the National Ignition Facility is described. It is based on measuring the (198)Au/(196)Au activation ratio using the collected post-shot debris of the Au hohlraum. The Au ratio combined with the independently measured neutron down scatter ratio uniquely determines the areal densities ρR(DT) and ρR(CH) during burn in the context of a simple 1-dimensional capsule model. The results show larger than expected ρR(CH) values, hinting at the presence of cold fuel-ablator mix.

We describe a radiochemical measurement of the ratio of isotope concentrations produced in a gold hohlraum surrounding an Inertial Confinement Fusion capsule at the National Ignition Facility (NIF). We relate the ratio of the concentrations of (n,γ) and (n,2n) products in the gold hohlraum matrix to the down-scatter of neutrons in the compressed fuel and, consequently, to the fuel's areal density. The observed ratio of the concentrations of (198m+g)Au and (196g)Au is a performance signature of ablator areal density and the fuel assembly confinement time. We identify the measurement of nuclear cross sections of astrophysical importance as a potential application of the neutrons generated at the NIF.

XANES (X-ray Absorption Near Edge Spectroscopy) has been employed to evaluate the efficacy of a process designed to encapsulate and reduce TcO 4 - in cement matrices, thereby immobilizing Tc. The oxidation state of Se following bioremediation of Se by bacteria has also been determined by XANES. The XANES measurements were performed at the Stanford Synchrotron Radiation Laboratory (SSRL) and the National Synchrotron Light Source (NSLS) at the respective K edges of Tc (21.0 keV) and Se (12.7 keV). Comparison of the XANES spectra of Tc in untreated cement to Tc in slag treated cement and to the chemical shifts of reference materials, shows that the oxidation state of Tc is the same in both cements. Thus, the addition of a reducing agent to the cement formulation does not significantly reduce the TcO 4 - . The common soil bacterium, Bacillus subtilis , is known to incorporate Se on or within the cell wall when exposed to a Se(IV) solution. The Se XANES spectra of B. subtilis , as well as bacillus isolated from selenium rich soil, show that the organisms reduce selenite to the red allotrope of elemental Se.

The offshore production of oil and gas leads to naturally occurring Ra-226,Ra-228 being brought to the surface along with produced water. Assessment of potential environmental exposures, if any, requires accurate, precise and practical methods for the measurement of low concentrations of Ra-226,Ra-228. A method for the simultaneous measurement of Ra-226,Ra-228 in marine sediments, biota and produced water at a sensitivity of 0.01 pCi/g using high-sensitivity, high-resolution gamma-spectrometry was subjected to an interlaboratory exercise using U.S. commercial laboratories to validate its accuracy, precision, robustness, and sample throughput. The prescribed method involves direct counting for solid samples and a simple Pb(Ba-133,Ra)SO4 co-precipitation procedure for water samples followed by gamma-counting. Analytical results received from the participating laboratories were subjected to data analysis and statistical evaluation to validate the overall performance of the prescribed method. Relatively good precision and high accuracy of data were achieved when the participating laboratories followed the prescribed procedure closely. The consistency of results among laboratories was not correlated to the Ra-226,Ra-228 concentrations in the samples. Most of the results that failed the acceptance criteria were either due to the absence of geometric and secular equilibrium between Ra-226 and its signature decay daughters, or due to insufficient counting statistics when laboratories are working close to their detection limits. No significant bias or systematic errors were observed, except for produced water samples where results were biased high compared to the known values.

The offshore production of oil and gas leads to naturally occurring 226,228Ra being brought to the surface along with produced water. Assessment of potential environmental exposures, if any, requires accurate, precise and practical methods for the measurement of low concentrations of 226,228Ra. A method for the simultaneous measurement of 226,228Ra in marine sediments, biota and produced water at a sensitivity of 0.01 pCi/g using high-sensitivity, high-resolution gamma-spectrometry was subjected to an interlaboratory exercise using U.S. commercial laboratories to validate its accuracy, precision, robustness, and sample throughput. The prescribed method involves direct counting for solid samples and a simple Pb(133Ba,Ra)SO4 co-precipitation procedure for water samples followed by gamma-counting. Analytical results received from the participating laboratories were subjected to data analysis and statistical evaluation to validate the overall performance of the prescribed method. Relatively good precision and high accuracy of data were achieved when the participating laboratories followed the prescribed procedure closely. The consistency of results among laboratories was not correlated to the 226,228Ra concentrations in the samples. Most of the results that failed the acceptance criteria were either due to the absence of geometric and secular equilibrium between 226Ra and its signature decay daughters, or due to insufficient counting statistics when laboratories are working close to their detection limits. No significant bias or systematic errors were observed, except for produced water samples where results were biased high compared to the known values.

In a high level waste repository in which temperatures are elevated due to waste decay, concrete structures will be subjected to hydrothermal conditions that will alter their physical and chemical properties. Virtually no studies have examined the interaction of hydrothermally altered concrete with radionuclides. We present the results of experiments in which soluble and colloid-associated U and Np, were eluted into a fractured, hydrothermally altered concrete core. Although the fluid residence time in the fracture was estimated to be on the order of 1 minute, U and Np in the effluent from the core were below detection (10-9 - 10-8 M), for both soluble and colloid-associated species. Inorganic colloids and latex microspheres were similarly immobilized within the core. Post-test analysis of the core identified the immobilized U and Np at or near the fracture surface, with a spatial distribution similar to that of the latex microspheres. Because hydrothermal alteration followed fracturing, the growth of crystalline calcium silicate hydrate and clay mineral alteration products on, and possibly across the fracture, resulted in a highly reactive fracture that was effective at capturing both soluble and colloidal radionuclides. Comparison of results from batch experiments [1] with these experiments indicate that partitioning of U and Np to the solid phase, and equilibration of the incoming fluid with the concrete, occurs rapidly in the fractured system. Transport of U through the concrete may be solubility and/or sorption limited; transport of Np appears to be limited primarily by sorption.

The primary rationale for studying the transport behavior of radionuclides through the Engineered Barrier system / Near Field Environment (EBS/NFE) is to ascertain whether the material properties of the introduced and altered host rock can significantly affect the transport of radionuclides from the waste container to the far field. The intent of this report is to present data and modeling results that can be used to assess the importance of canister corrosion products and cementitious materials to transport of radionuclides to the far field.

The solubility of Np(V) and Np(VI) has been measured in three synthetic Na-K-Mg-Cl brines in the presence of C02(g). Experiments were prepared from oversaturation by adding an excess of NpOJ or NpOj" to the brines and allowing the neptunium solids to precipitate. Vessels were maintained in contact with fixed C02(g) partial pressures at constant pH and 24 ±1 °C. Dissolved Np(V) concentrations decreased several orders of magnitude within the first 100 days of the experiment, while dissolved Np(VI) concentrations decreased initially but then remained relatively constant for more than 400 days. The solid phases formed in all experiments were identified by X-ray powder diffraction as KNp02C0, · XH20(S). Steady state concentrations for Np(V) are similar to those observed for Pu(V) in the same brines under the same conditions, where Pu occurs predominantly as Pu(V). Similarly, steady state concentrations for Np(VI), which was not reduced over a two year period, compare well with measured Pu(VI) concentrations in the same brines before the Pu(VI) was reduced to Pu(V).

The solubility of Np(V) was measured in NaCl solutions ranging from 0.30 to 5.6 molal at room temperature ({approximately}21 {plus_minus} 2{degrees}C). Experiments were conducted from undersaturation and allowed to equilibrate in a CO{sub 2}-free environment for 37 days. The apparent solubility products varied with NaCl concentration and were between 10{sup -9} and 10{sup -8} mol{sup 2}{sm_bullet}L{sup -2}. Using the specific ion interaction theory (SIT), the log of the solubility product of NpO{sub 2}OH(am) at infinite dilution was found to be - 8.79 {plus_minus} 0.12. The interaction coefficient, {epsilon}(NpO{sub 2}{sup +} - Cl{sup -}), was found to be (0.08 {plus_minus} 0.05).

Solubility and speciation are important in understanding aqueous radionuclide transport through the geosphere. They define the source term for transport retardation processes such as sorption and colloid formation. Solubility and speciation data are useful in verifying the validity of geochemical codes that are a part of predictive transport models. Solubility experiments will approach solution equilibrium from both oversaturation and undersaturation. In these experiments, we have approached the solubility equilibrium from oversaturation, Results are given for solubility and speciation experiments from oversaturation of {sup 237} NpO{sub 2}{sup +} {sup 239}Pu{sup 4+}, and {sup 241}Am{sup 3+}/Nd{sup 3+} in a neutral electrolyte containing a total carbonate concentration similar to groundwater from the Yucca Mountain region, Nevada, which is being investigated as a potential high-level nuclear waste disposal site, at 25{degrees}C and three pH values. In these experiments, the solubilitycontrolling steady-state solids were identified and the speciation and/or oxidation states present in the supernatant solutions were determined.