Ned E. Bibler

Leaching Tc-99 from SRP glass in simulated tuff and salt groundwaters

Results of leach tests with Tc-99 doped SRP borosilicate waste glass are presented. The glass was prepared by melting a mixture of SRP 165 powdered frit doped with a carrier free solution of Tc-99 at 1150{sup 0}C. Dissolution of portions of the resulting glass indicated that the Tc-99 was distributed homogeneously throughout the glass. Static leach tests up to 90 days were performed at 90{sup 0}C in J-13 tuff groundwater or WIPP brine A at a SA/V of 100m{sup -1}. Normalized mass losses were calculated for Tc-99 as well as all the major elements in the glass. Results indicated that under ambient oxidizing conditions Tc-99 leached no faster than the glass-forming elements of the glass. In J-13 water, Tc-99 leached congruently with B. In WIPP brine A, it leached congruently with Si. Leach rates for Li were higher in both groundwaters, probably due to a contribution from an ion exchange mechanism. Leach tests were performed under reducing conditions in J-13 water by adding Zn/Hg amalgam to the leachate. In these tests the pH increased significantly, probably because of the reaction of the amalgam with the water. In a 21-day test, the pH increased to 13 and leach rates for the glass were very high. Even though there was signifcant dissolution of the glass, the normalized mass loss based on Tc-99 was only 0.02g/m{sup 2}. This result and the fact that reducing conditions at normal pH values do not significantly affect the dissolution of the glass, indicate that the low concentrations for Tc-99 obtained under reducing conditions are due to is solubility and not due to an increased durability of the glass. 14 refs., 2 figs., 5 tabs.

GAMMA AND ALPHA RADIOLYSIS OF AQUEOUS SOLUTIONS OF DIETHYLENETRIAMINEPENTAACETIC ACID.

Abstract The radiolytic destruction of diethylenetriaminepentaacetic acid (DTPA), an eluting agent for the purification of 244 Cm by cation exchange chromatography, was studied in H 2 SO 4 and HNO 3 solutions. In 0·4 M H 2 SO 4 , DTPA is effectively destroyed by both H atoms and OH radicals. For γ radiation, G (-DTPA) = G H + G OH ; and for a radiation, G (-DTPA) = G H + G OH + G HO 2 . At doses > 10 21 eV/g in solutions less than 4 M acid, lanthanide and actinide oxalates precipitate. In ∼ 4 M HNO 3 solutions containing > 1 g/l. 244 Cm eluted from cation exchange columns, the DTPA must be completely destroyed by α-radiolysis before the 244 Cm can be concentrated by precipitation with 1 M NaOH. At high pH values and in the presence of metal cations that are complexed by DTPA, G (-DTPA) is lowered significantly. Competition studies with various solutes established that OH radicals destroy DTPA effectively (k = 2 × 10 9 M −1 sec −1 ). Failure of excess Br − ions to lower G (-DTPA) suggests that DTPA can react by a charge transfer mechanism in addition to H atom abstraction.

Radiolytic Gas Generation in Concrete Made with Incinerator Ash Containing Transuranium Nuclides

The effects of various factors on H2 generation by alpha radiolysis of concrete containing TRU incinerator ash were studied. Methods for reducing H2 generation were investigated. Samples of portland and high-alumina cement containing up to 30% calcined ash (dry basis) were doped with 238PuO2. Gas pressures were measured as a function of radiation dose; gas compositions were determined. Gas yields were calculated in terms of G values (molecules produced per 100 eV of alpha energy absorbed). These yields were used to estimate pressures in containers of radioactive concrete waste during storage.

Effects of Alpha, Gamma, and Alpha-Recoil Radiation on Borosilicate Glass Containing Savannah River Plant Defense High-Level Nuclear Waste

At the Savannah River Plant, the reference process for the immobilization of defense high-level waste (DHLW) for geologic storage is vitrification into borosilicate glass. During geologic storage for 10 6 y, the glass would be exposed to ∼3 × 10 10 rad of β radiation, ∼10 10 rad of γ radiation, and 10 18 particles/g glass for both α and α-recoil radiation. This paper discusses tests of the effect of these radiations on the leachability and density of the glass. No effect of the radiations was detected that reduced the effectiveness of the glass for long-term storage of DHLW even at doses corresponding to 10 6 years storage for the actual glass. For the tests, glass containing simulated DHLW was prepared from frit of the reference composition. Three methods were used to irradiate the glass: external irradiations with beams of ∼200 keV or Pb ions, internal irradiations with Cm–244 doped glass, and external irradiations with Co–60 γ rays. Results with both Xe and Pb ions indicate that a dose of 3 × 10 13 ions/cm 2 (simulating >10 6 years storage) does not significantly increase the leachability of the glass in deionized water. Tests with Cm–244 doped glass show no increase in leach rate in deionized water up to a dose of 1.3 × 10 18 α and α-recoils/g glass. The density of the Cm–244 doped glass has decreased by 1% at a dose of 10 18 particles/g glass. With γ-radiation, the density has changed by 10 rad. Results of leach tests in deionized water and brine indicated that this very large dose of γ-radiation increased the leach rate by only 20%. Also, the leach rates are 3 to 4 times lower in brine.

Materials interactions relating to long-term geologic disposal of nuclear waste glass

In the geologic disposal of nuclear waste glass, the glass will eventually interact with groundwater in the repository system. Interactions can also occur between the glass and other waste package materials that are present. These include the steel canister that holds the glass, the metal overpack over the canister, backfill materials that may be used, and the repository host rock. This review paper systematizes the additional interactions that materials in the waste package will impose on the borosilicate glass waste form-groundwater interactions. The repository geologies reviewed are tuff, salt, basalt, and granite. The interactions emphasized are those appropriate to conditions expected after repository closure, e.g. oxic vs anoxic conditions. Whenever possible, the effect of radiation from the waste form on the interactions is examined. The interactions are evaluated based on their effect on the release and speciation of various elements including radionuclides from the glass. It is noted when further tests of repository interactions are needed before long-term predictions can be made. 63 references, 1 table.

The Role of Groundwater Oxidation Potential and Radiolysis on Waste Glass Performance in Crystalline Repository Environments

Laboratory experiments have shown that groundwater conditions in a granite repository will be as reducing as those in a basalt repository. Chemical analysis of the reduced groundwaters confirmed that the Fe/sup 2 +//Fe/sup 3 +/ couple controls the oxidation potential (Eh). The reducing groundwater conditions were found to decrease the time-dependent release of soluble elements (Li and B) from the waste glass. However, due to the lower solubility of multivalent elements released from the glass when the groundwaters are reducing, these elements have significantly lower concentrations in the leachates. Gamma radiolysis reduced the oxidation potential of both granitic and basaltic groundwater in the absence of both waste glass and oxygen. This occurred in tests at atmospheric pressure where H/sub 2/ could have escaped from the solution. The mechanism for this decrease in Eh is under investigation but appears related to the reactive amorphous precipitate in both groundwaters. The results of these tests suggest that radiolysis may not cause the groundwaters to become oxidizing in a crystalline repository when abundant Fe/sup 2 +/ species are present.

Characterization of Borosilicate Glass Containing Savannah River Plant Radioactive Waste

Vitrification is the reference process for immobilization of radioactive waste from the Savannah River Plant. The waste, consisting mostly of hydrous oxides of Fe, Al, and Mn contaminated with fission products and alphemitting radionuclides, is mixed with glass-forming chemicals and melted at 1150°C to produce a durable borosilicate glass. In this paper, the results of studies characterizing glass containing actual radioactive waste are presented. The glass was produced in a small-scale joule-heated melter in a shielded facility at the Savannah River Laboratory. Feed for the melter was a mixture of 35 wt % waste (primarily Fe2O3 and Al2O3) and 65 wt % frit (primarily SiO2, Na2O, and B2O3). The melt was poured into 600-cc stainless steel beakers and allowed to cool. The glass was intensely radioactive. Dose rates at the surface of the glass were approximately 106 rad/hr. Specific activities (dpm/g glass) of the principal radionuclides were: 1.2 x 1010 for Cs-137, 7.9 x 109 for Sr-90, and 1.0 x 108 for alpha activity (primarily Pu-238 and Cm-244). Examination by optical and electron microscopy indicated the presence of 1–5 wt % spinel crystals — primarily NiFe2O4. Leach tests indicated good durability in deionized water, brine, and silicate water. These latter two leachants simulate groundwater from possible geologic repositories. Release rates at 40°C based on gamma, beta, and alpha activity in a 28-day test were approximately 0.01 g glass/ m2-day. This result agrees with results of tests with glass containing simulated waste and indicates that the borosilicate glass effectively immobilizes SRP radioactive waste. Also, during the leach tests, the pH of the leachates did not decrease even though they were exposed to the intense gamma, beta, and alpha radiation from this glass.

Radiation Effects in Silicate Glasses - A Review

The study of radiation effects in complex silicate glasses has received renewed attention because of their use in special applications such as immobilization of high level nuclear wastes and fiber optics. Radiation may change the properties of these glasses by altering their electronic and atomic configurations. Electronic defects may cause absorption centers that limit their optical uses and also cause microscopic phase changes and dilatations. Atomic dislocations induced in the already disordered structure of the glasses may affect their use where heavy radiations such as alpha particles, alpha recoils, fission fragments, or accelerated ions are present. Large changes (up to 1%) in density may be caused. In some cases the radiation damage may be severe enough to affect the durability of the glass in aqueous solutions.