Nuclear Waste Repository In Basalt Research Articles

Exploratory shafts for the nuclear waste repository in basalt : Schmidt, B Proc 1987 Rapid Excavation and Tunnelling Conference, New Orleans, 14-17 June 1987 V2, P1051–1071. Publ Littleton: Society of Mining Engineers, 1987

Exploratory shafts for the nuclear waste repository in basalt : Schmidt, B Proc 1987 Rapid Excavation and Tunnelling Conference, New Orleans, 14-17 June 1987 V2, P1051–1071. Publ Littleton: Society of Mining Engineers, 1987

Characterization of the state of in situ stress by hydraulic fracturing for a nuclear waste repository in basalt : Kim, K; Dischler, S A; Aggson, J R; Hardy, M P Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, 1–3 Sept 1986P657–667. Publ Lulea: Centek, 1986

Hydraulic fracturing tests designed to characterize the state of in situ stress were conducted in four deep boreholes. These tests are part of a site investigation program to assess the feasibility of constructing a nuclear waste repository in a basalt formation underneath the Hanford Site in southeastern Washington State. The results of these tests are examined in light of stress indicator data, which include core disking, borehole wall spalling, and fault plane solution data obtained at the site.

Nuclear waste elements slip through hydrothermally altered basalt

Basalt that is altered hydrothermally in the laboratory does not bind the elements Pu, Np, U, Eu and Ba (and, by implications, Am, Sr and Ra) from flowing water as well as does freshly fractured basalt. The results suggest that the ability of a nuclear waste repository in basalt to retain disposed radioactivity will not be as great as measured for freshly-fractured basalt. Safety assessments of a repository in basalt must consider the enhanced mobility of many radioelements that now can be expected of rock surfaces in prolonged contact with water. The dominant secondary minerals of a tholeiitic basalt altered hydrothermally in the laboratory are stevensite, α-quartz and calcite. Gypsum, sericite, several zeolites and scapolite are also formed. Before the rock is hydrothermally altered, calcite, stevensite and minor amounts of quartz are identified on recent fracture surfaces of the rock as the products of natural alteration. The hydrothermally altered surfaces of the rock are more compatible, chemically, with groundwater sampled from the basalt than are surfaces of recent fissures, suggesting that the laboratory-altered surfaces approximate, chemically, old fracture surfaces of the rock that are now in contact with the groundwater.

Experimental Interaction of Basalt, Bentonite, and Water: Implications for Groundwater Chemistry in Waste Package Packing Material in a Nuclear Waste Repository

AbstractExperiments have been conducted by the Basalt Waste Isolation Project (BWIP) to assess changes in solution chemistry in the near-field environment of a nuclear waste repository in basalt. These Dickson autoclave experiments were carried out using Grande Ronde basalt ± bentonite and synthetic groundwater or deionized water at 300°C, 30 MPa, and solution-to-solid mass ratio of 10 for up to two years. Groundwater solution changes during reaction of the basalt and basalt/bentonite included initial decreases in pH and sodium concentration presumably due to smectite formation. This initial trend subsequently reversed in the basalt system with pH rising to ca. 7.5 and sodium increasing to the starting value. Steady state pH values for the basalt/bentonite system were ca. 6.4. The basalt + deionized water test exhibited a constant rise in pH to ca. 7.9 and release of sodium to solution in response to basalt dissolution. Slightly oxidizing conditions characterized the early part of all of the experiments followed by a decrease in fO2 to 10−31 to 10−32 These results are consistent with other work at similar and lower temperatures, suggesting that the packing material will react in the waste package environment to produce slightly alkaline, reducing conditions.

Corrosion of Candidate Container Materials in Air-Steam Mixtures

AbstractThe environment during the operating period of a high-level nuclear waste repository in basalt is expected to be air saturated with steam. Liquid groundwater is not expected to be in contact with the container surface during that time.The report presents corrosion findings from tests conducted for one to twenty-five months in an air-steam environment. Tests were carried out with bare metal specimens exposed to an air atmosphere containing 12% moisture in chambers maintained at temperatures between 150°C and 300°C. Cast carbon steel exhibited total penetrations less than 0.002 mm for exposures up to 25 months. A ferritic alloy steel, Fe9CrlMo, showed corrosion results very similar to cast carbon steel. Unalloyed copper materials showed essentially linear corrosion rates, with total penetrations between 0.002 mm at 150°C and 0.14 mm at 300°C in 25 months. Cupronickel 90−10 exhibited total penetrations between 0.001 mm at 150°C and 0.05 mm at 300°C in 25 months. There was a tendency for the corrosion rate to increase with time for cupronickel at 250°C and 300°C possibly because of a mid-test change in the corrosion mechanism. Limited testing of specimens surrounded with bentonite/basalt packing material indicated that the presence of packing has no strong effect on the corrosion of iron-base materials; however, copper-base and cupronickel materials corroded at higher rates in the presence of packing, with a possible shift towards the lower bare specimen corrosion rates with increasing time.

Probabilistic Modeling of Radionuclide Release at the Waste Package Subsystem Boundary of a Repository in Basalt

Estimation of potential radionuclide releases from the waste package subsystem of a nuclear waste repository is required for two reasons: (1) to judge whether the engineered barrier system complies with the performance regulations prescribed by the US Nuclear Regulatory Commission; and (2) to provide radionuclide source terms needed to predict the isolation performance of the natural barriers (i.e., geologic medium) which must be compared with the US Environmental Protection Agency safety standard. In this paper, a probabilistic approach developed at the Basalt Waste Isolation Project (BWIP), for the estimation of radionuclide releases from a proposed nuclear waste repository in basalt is presented. The central idea of this approach is that uncertainties in both the radionuclide transport parameters and the random nature of container failures impact the estimation of release rates. Details of the method are provided which account for both sources of uncertainty. Sample applications are presented that are based on preliminary data. Briefly, the BWIP methodology consists of (1) a container corrosion model, (2) a model describing the random sequence of container failures in time, (3) a stochastic transport model to obtain the probability distribution of releases from a single container failing at a specified time, and (4) amore » model to integrate the releases from the randomly failing containers in the repository.« less

Solids Characterization from Hydrothermal Tests with Spent Fuel

AbstractReacted solids from 200°C, 25 MPa tests with spent light water reactor fuel and other component materials of a high-level nuclear waste repository in basalt were analyzed by scanning electron microscopy, X-ray powder diffractometry, transmission electron diffraction, Auger electron spectrome- try, and microautoradiography. The work complements solutions analysis from the same tests conducted in Dickson-type rocking autoclaves for the Basalt Waste Isolation Project. Spent fuel reacted very slowly in fuel/water tests, exhibiting noticeable grain boundary etching and uranium silicate formation only after six months. Particle abrasion in the rocking autoclave produced fuel fines that remained apparently unaltered. In spent fuel tests with basalt or basalt and steel, iron smectite clay formed at the expense of mesostasis phases in the basalt. Low concentrations of β-emitters, probably Cs and Tc released from grain boundaries in the fuel, were incorporated in the clay. Steel corroded very slowly under the low-oxygen conditions of the tests, forming minor amounts of magnetite, hematite and wustite. The sluggishness of spent fuel/water and steel/water reactions is attributed to limited availability of oxygen under the test conditions.

Effects of Gamma Radiolysis on Waste Package Components

AbstractPreliminary short-term experiments to study the effect of gamma radiation on the waste package materials interactions in the environment of a nuclear waste repository in basalt were completed. Experimental parameters were similar to those expected during the saturated post- closure period of the repository, i.e., a temperature of 200°C and a hydrostatic pressure of ≤70 bar. The test components included various combinations of synthetic groundwater (GR4), low carbon steel coupons, CH4, basalt, and basalt/bentonite mixtures (packing). The tests were run in low carbon steel pressure vessels.It was found that gamma radiation at a dose rate of 104rad/hr for a duration of one and two months increased the H2 yield in all tests. Increases in the organic carbon yield, the sulfate ion concentration, and the corrosion rate of the coupon were observed in some of the tests. These latter results varied with the combination of waste package components included in the tests. Evidence for the quench effect was observed in tests which included basalt.

Assessment of required flow thickness for structural integrity of repository rooms

The method presented herein for selecting an acceptable flow-flowtop layer thickness for the satisfactory structural performance of a nuclear waste repository in basalt is the result of a parametric finite element study of layered geologic material. The layer thicknesses and the material properties of the layers were varied, and the stresses were calculated for representative thermal and in situ loading. The relation between repository room peak stress and roof thickness was established for average material parameters.

Experimental Studies of Packing Material Stability

ABSTRACTThe Basalt Waste Isolation Project is conducting experiments to assess the stability of bentonite (sodium montmorillonite)and crushed basalt as waste package packing materials in a nuclear waste repository in basalt. The experiments are designed to identify changes in physical, chemical, and mineralogical properties that these materials could undergo in the repository environment. A series of bentonite dehy-dration experiments showed that after 1 year at 370°C the clay's structural and swelling properties were preserved and only reversible dehydration occurred. At 440°C, however, irreversible dehydration, collapse of the clay structure, and loss of swelling ability took place. Hydrothermal tests using bentonite, or an equal mixture of bentonite and basalt, along with synthetic groundwater, were also conducted. Abentonite + water experiment showed negligible structural alteration at 200°C, although some iron enrichment of the clay occurred. At 300°C, partial conversion of the mont-morillonite to an iron- and potassium-rich smectite occurred, along with the formation of secondary quartz and albite. An experiment in the basalt + bentonite + water system at 150°C resulted in partial etching of the basalt grains, but no detectable change in rock or clay mineralogy. At 300°C, the basalt was strongly etched. Furthermore, iron- and potassium-rich smectite apparently replaced montmorillonite as the dominant clay, and secondary silica, zeolites, and minor feldspar were formed. These mineral assemblages are thought to be metastable at 300°C, based on natural analogs. The kinetics and reaction paths of further transformations of packing materials are important areas for continued study.