Stephen F. Wolf

Ten-year results from unsaturated drip tests with UO2 at 90°C: implications for the corrosion of spent nuclear fuel

Alteration phases may influence both the dissolution of nuclear waste forms and release of radionuclides from the waste package environment. In the present study, UO2 pellets serve as surrogates for commercial spent nuclear fuel, with the pellets being exposed to periodic drops of simulated groundwater at 90°C. Uranium release was very rapid between one and two years, resulting from grain boundary corrosion and spallation of micrometer-sized UO2+x particles from the sample surface. The development of a dense mat of alteration phases after two years apparently trapped loose particles, resulting in reduced rates of uranium release. The paragenetic sequence of alteration phases is similar to that observed in surficial weathering zones of natural uraninite deposits, with alkali and alkaline earth uranyl silicates being the long-term solubility-limiting phases for uranium. Results from this study and comparisons with natural analogue deposits suggest that the migration of fission products from altered spent fuel may be retarded by their incorporation in secondary uranium phases.

Chemical studies of H chondrites: 5. Temporal variations of sources

We report 36Cl (301-kyr half-life) data obtained by accelerator mass spectrometry allowing nominal terrestrial ages to be determined for 39 Antarctic H4–6 chondrites for which contents of volatile trace elements are known. The compositional difference between these Antarctic meteorites and 58 non-Antarctic falls increases with terrestrial age and, using multivariate statistical techniques, becomes highly significant for Antarctic samples with ages >50 kyr. The compositional difference is inconsistent with trivial causes such as weathering and seems to reflect differences in thermal histories of parent sources. Temporal source variations for the H chondrite flux on Earth thus exist not only on a short-term, 40 years, basis (Dodd et al., 1993) but also on a long-term, >50 kyr, basis.

Chemical studies of H chondrites: 4. New data and comparison of Antarctic suites

We report data for the trace elements Au, Co, Sb, Ga, Rb, Ag, Se, Cs, Te, Zn, Cd, Bi, Tl, and In (ordered by putative volatility during nebular condensation and accretion) determined by neutron activation analysis in 13 H5 chondriles from Victoria Land and 20 H4–6 chondrites from Queen Maud Land, Antarctica. These and earlier results provide Antarctic sample suites of 34 chondrites from Victoria Land and 25 from Queen Maud Land. Treatment of data for the most volatile 10 elements (Rb → In) in these suites by multivariate statistical techniques more robust, as well as more conservative, than conventional linear discriminant analysis and logistic regression demonstrates that compositions differ at marginally significant levels. This difference cannot be explained by trivial (terrestrial) causes and becomes more significant, despite the smaller size of the database, when comparisons are limited to data from a single analyst and when all upper limits arc eliminated from consideration. The Victoria Land and Queen Maud Land suites have different mean terrestrial ages (∼300 kyr and ∼100 kyr, respectively) and age distributions, suggesting that a time-dependent variation of chondritic sources with different thermal histories is responsible. As a result, these two Antarctic suites are, on average, chemically distinguishable from each other. Since H chondrites serve as a paradigm for other meteorite classes, these results indicate that the near-Earth populations of planetary materials varied with time on the 105-year timescale.

Chemical studies of H chondrites: 6. Antarctic/non‐Antarctic compositional differences revisited

We report data for the trace elements Au, Co, Sb, Ga, Rb, Ag, Se, Cs, Te, Zn, Cd, Bi, T1, and In (ordered by putative volatility during nebular condensation and accretion) determined by radiochemical neutron activation analysis of 14 additional H5 and H6 chondrite falls. Data for the 10 most volatile elements (Rb to In) treated by the multivariate techniques of linear discriminant analysis and logistic regression in these and 44 other falls are compared with those of 59 H4-6 chondrites from Antarctica. Various populations are tested by the multivariate techniques, using the previously developed method of randomization-simulation to assess significance levels. An earlier conclusion, based on fewer examples, that H4-6 chondrite falls are compositionally distinguishable from the Antarctic suite is verified by the additional data. This distinctiveness is highly significant because of the presence of samples from Victoria Land in the Antarctic population, which differ compositionally from falls beyond any reasonable doubt. However, it cannot be proven unequivocally that falls and Antarctic samples from Queen Maud Land are compositionally distinguishable. Trivial causes (e.g., analyst bias, weathering) cannot explain the Victoria Land (Antarctic)/non-Antarctic compositional difference for paradigmatic H4-6 chondrites. This seems to reflect a time-dependent variation of near-Earth meteoroid source regions differing in average thermal history.

An H chondrite stream - Identification and confirmation

Fall data indicate that a significant, elongate cluster of co-orbital H chondrite falls in May between 1855 and 1895 (H Cluster 1) records encounters with two or three closely spaced and probably related meteoroid stream components, each of which was met near its perihelion. Although meteorites included in the Cluster vary widely in petrographic type (3–6), shock facies (a-d), and 21Ne exposure age (<5 to 50 Ma), they have a distinct labile trace element signature that confirms a common thermal history and, thus, a common source region within an H chondrite parent body. Hence, meteorites selected by one criterion (fall parameters) as distinguishable from all other H chondrites, are distinguished from them by another completely different criterion (contents of labile trace elements).

An interlaboratory study of a standard glass for acceptance testing of low-activity waste glass

An interlaboratory study was conducted to determine the precision with which the composition and chemical durability of a borosilicate glass could be measured and to generate a data base of expected values for that glass. The study was conducted with a low-activity reference material (LRM) glass that was developed for use as a standard material for acceptance testing of immobilized low-activity waste (ILAW) products, including those to be made with Hanford tank wastes. The study provided nine independent measurements of the LRM glass composition and eight independent sets of triplicate product consistency tests (PCTs) at 40°C and 90°C. Statistical analysis of these data indicates that LRM glass is suitable for use as a composition and test standard. The results from this study can be used to evaluate the accuracy of composition analyses and PCTs conducted with LRM glass at other laboratories in conjunction with acceptance tests conducted with ILAW products.

Chemical studies of H chondrites 8. On contemporary meteoroid streams

Using date and time of fall and petrographic classification as criteria, many equilibrated H chondrites that fell during September and October from 1812 to the present form four significant clusters, denoted as Cluster 2 through Cluster 5, on day-year plots. Using radiochemical neutron activation analysis, we determined 15 trace elements, U, Au, Co, Sb, Ga, Rb, Ag, Se, Cs, Te, Zn, Cd, Bi, Tl, and In (ordered by increasing putative volatility during nebular condensation), in 27 members of these four clusters. We used model-dependent and model-independent multivariate statistical techniques to compare contents of the 10 most volatile elements separately in the four clusters with those of a 33-member suite of random H chondrite falls (from 1773 to 1970). The Clusters 2 and 5 suites (that fell in September 1880–1991 and October, 1919–1984, respectively), each of which is represented by 10 H chondrite falls, are not compositionally distinguishable from the suite of random falls. However, the 17-member combined suite of Clusters 3 and 4 chondrites (that fell during September–October, 1812–1992) proves compositionally distinguishable from random falls at moderate to strong significance levels of 0.01–0.001. This 17-member suite is less readily distinguished from random falls than are the previously reported suite of Cluster 1 falls (May 1855–1895), or Antarctic H chondrites with nominal terrestrial ages >50 kyr, each of which is highly significant at <0.001 levels. All suites are genomict and exhibit a range of cosmic ray exposure ages with a plurality having 6–8 Ma ages. Inconclusive results are obtained in the cases of Clusters 2 and 5. However, three H chondrite suites (Clusters 1,3, and 4) distinguishable from the random background by one property (time of fall) are also distinguishable by another (contents of volatile trace elements or thermal history). Temporal change of H chondrite sources sampled by Earth are indicated by these data.

Trace Analysis of Actinides in Geological, Environmental, and Biological Matrices

Actinide elements are ubiquitous in nature. Uranium and thorium are present in the Earth’s crust with average concentrations of 1–10 μg g-1, making them more abundant than Ag, Sb, Cd, or Hg. While U and Th can even be found as major or minor mineral constituents in a variety of geochemical environments, typically they are highly dispersed and present only at trace or ultra–trace concentrations in most natural materials. Because 238U, 235U, and 232Th are the parents of the three naturally occurring non–extinct radioactive decay chains, they are always accompanied by lower concentrations of their radioactive progeny, many of which are also actinides (Table 30.1).

Determination of 11 major and minor elements in chondritic meteorites by inductively coupled plasma mass spectrometry

We have developed a new method for the quantification of 11 major and minor elements (Na, Mg, Al, P, S, K, Ca, Cr, Mn, Fe, and Ni) in chondritic meteorites by ICPMS using external calibration with a matrix-matched standard prepared from the Allende Standard Reference Meteorite. We have demonstrated the methods accuracy and assessed three different measures of precision by performing replicate dissolutions and analyses of 0.10-g samples of a homogenized samples of the CM2 meteorite Murchison and compared our results to literature values. We subsequently applied this method to the analysis of a set of four chondritic meteorites possessing a relatively wide range of chondritic compositions with results in accord with previously published values. Because our method is designed to use the same instrumentation and can use samples and standards prepared according to methods previously validated for the determination of a comprehensive suite of minor, trace, moderately and highly volatile trace elements (i.e., Li, Sc, Ti, V, Mn, Co, Cu, Zn, Ga, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Ru, Pd, Ag, Cd, In, Sn, Sb, Te, Cs, Ba, all 14 naturally occurring lanthanoids, Hf, W, Re, Ir, Pt, Tl, Bi, Th, and U) it complements these methods and allows a single laboratory to determine the concentrations of 60 elements in semimicroscopic amounts of chondritic material.

Application of instrumental radioanalytical techniques to nuclear waste testing and characterization

This paper describes the validation of a multi-technique analytical methodology that uses inductively coupled plasma-mass spectrometry, α-spectrometry, and γ-spectrometry for the routine analysis of samples containing transuranic radionuclides. This methodology is capable of the determination of concentrations of both238Pu and241Pu in the presence of238U and241Am without the need for chemical separations. The relative merits of these three techniques were evaluated as they are applied in a nuclear waste material and spent nuclear fuel testing program by analytical (1) standards and (2) solutions prepared from the dissolution of glasses doped with237Np,239Pu, and241Am. The uncertainty associated with technique was within ±4% for standards and ±10% for doped nuclear waste glasses. The methodology was then used to analyze three fully radioactive waste glasses.