Albert S. Aloy

PRETREATMENT OF TC-CONTAINING WASTE AND ITS EFFECT ON 99 TC LEACHING FROM GROUTS

A salt solution (doped with Tc-99), that simulates the salt waste stream to be processed at the Saltstone Production Facility, was immobilized in grout waste forms with and without (1) ground granulated blast furnace slag and (2) pretreatment with iron salts. The degree of immobilization of Tc-99 was measured through monolithic and crushed grout leaching tests. Although Fe (+2) was shown to be effective in reducing Tc-99 to the +4 state, the strong reducing nature of the blast furnace slag present in the grout formulation dominated the reduction of Tc-99 in the cured grouts. An effective diffusion coefficient of 4.75 x 10{sup -12} (Leach Index of 11.4) was measured using the ANSI/ANS-16.1 protocol. The leaching results show that, even in the presence of a concentrated salt solution, blast furnace slag can effectively reduce pertechnetate to the immobile +4 oxidation state. The measured diffusivity was introduced into a flow and transport model (PORFLOW) to calculate the release of Tc-99 from a Saltstone Vault as a function of hydraulic conductivity of the matrix.

Effect of Synthesis Conditions on Phase Composition of Pyrochlore-Brannerite Ceramics

Three melted samples of pyrochlore-brannerite-based ceramics produced under different redox conditions were examined. Two of the samples were produced using cold crucible melting at ~1600 C. The third sample was obtained via melting in a microwave oven at 1700-1800 C. All the samples are composed of major pyrochlore and brannerite phases, and minor rutile and UO 2 -based solid solution or pseudobrookite phases. Pyrochlore-structured phases predominate in all three samples and account for 50-60% of the total bulk. Two pyrochlore varieties – Ca-pyrochlore (predominant) and Ba-pyrochlore have been found in these samples. The latter phase is more stable at high temperatures than the Ba-hollandite present in sintered pyrochlore-rich Synroc-F ceramics. Decomposition of the Ba-hollandite results in rutile formation in the melted samples.

Evaluation of Durability of Mortars and Concretes Used in Ancient Structures

The data on historic mortars and concretes provide qualitative and quantitative information to evaluate long-term behavior of cement materials in repositories and to understand processes that may occur in repositories (e.g., interaction with other materials and radionuclide transfer). Beyond that, such information is important to demonstrate safety aspects of the repositories to the public and stakeholders. A number of reports have been devoted to study of historical mortars and concretes used in the Western countries. The purpose of this paper is to review studies on compositions and structures of analogs, located mainly over the former Soviet Unions territory.

Glass Waste Form Performance for Disposal of the Cesium and Strontium Concentrate Resulting From the Partitioning of HLW

The recent advances in HLW partitioning indicate that cesium–137 and strontium–90 can be separated in the form of a pure concentrate. Based on this concentrate the glass RT2–1 containing 4.7 wt.% Cs 2 O and 2.7 wt.% SrO was selected for more intensive and wider studies to predict long-term performance of this waste form under repository conditions. Leach tests were made in distilled and mineralized water before and after crystallization at 20, 90 and 130°C. Fully devitrified glass contained only one crystalline phase corresponding to the pollucite structure.

Separation of 137Cs from Acidic Nuclear Waste Simulant via an Engineered Inorganic Ion Exchanger

An engineered ion exchange material has been prepared for the specific purpose of removing radioactive cesium from acidic waste. Separating the fission product 137 Cs from the bulk of the nuclear waste stream is often advantageous because, after typical cooling times, this isotope is usually the primary source of gamma radiation dose. The engineered ion exchanger was prepared using ammonium molybdophosphate impregnated into hollow glass crystalline microspheres. The microspheres or cenospheres, are refractory compounds of silica and alumina that are derived from the fly ash produced in coal combustion. This paper describes equilibrium experiments that were conducted with the engineered ion exchanger and a simulated acidic waste solution. These tests indicate that the new material has a high capacity and selectivity for cesium in these matrices.

Radiolytic Gas Generation in Chemically-bonded Iron Phosphate Ceramic Forms used for Immobilization of Plutonium Ash Residues

Iron phosphate ceramic (IPC) samples were prepared with plutonium-238, and radiolytic gas generation was detennined for exposure times of up to 195 days. The specific activity of the synthesized IPC samples was 1.91 mCi/g. The composition of the generated gases was determined to contain mainly H, and lower amounts of O 2 , CO 2 and CO. The molecular hydrogen G value (molecules of H 2 per 100 eV absorbed dose) depended on the sample preparation methodology, ranging from 0.07 at 79 days for sample IPC-2 to 0.34 at 119 days for sample IPC-1. This difference could be due to different total amount (wt.%) of free water resulting in sample preparation. The leach rate data for radioactive and non-radioactive IPC samples obtained by the ANSI/ANS 16.1 procedure resulted in Leachability Indexes of 13.7 for Pu and 15.4 for Ce, above the NRC LLW acceptance minimum index of 6.

Porous Alumina Silicate Matrix Gubka for Solidification of {sup 137}Cs Strip Product

Separated liquid high-level radioactive waste (HLW) fractions, in particular, about 100 liters of a {sup 137}Cs strip product with activity up to {approx} 100 Ci/l (3.7 TBq/l) have been produced during the development and testing of partitioning technology and temporarily stored at V.G. Khlopin Radium Institute (KRI) (Saint-Petersburg, Russia). The bench-scale experimental unit designed for operation in the hot cell was developed for {sup 137}Cs strip product solidification using an alumina silicate porous inorganic material (PIM) called Gubka. Conditions of saturation, drying, and calcinations of the salts into Gubka pores were optimized, and the operations under a remote control regime were executed during tests using a simulated strip product doped with {sup 137}Cs. The volume reduction coefficients were equal by a factor of 3.2-3.9 and a {sup 137}Cs discharge into an off-gas system was not detected. {sup 137}Cs leach rates from Gubka blocks after calcination at 800 deg. C were 1.0-1.5.10{sup -3} g/m{sup 2}.per day. (authors)

Immobilization of Pu-containing solution using a porous crystalline (Gubka) matrix

This paper describes the results of a joint research program of the Russian institutes at St. Petersburg, Krasnoyarsk and the Idaho National Engineering and Environmental Laboratory, which tested the stabilization/immobilization of surrogate actinide solutions containing tracer americium and plutonium using the Gubka matrix.