Shallow Land Burial Research Articles

Low activation structural materials for ICF reactors: differences with MCF environments

Activation calculations considering the neutron flux and spectrum of a first structural wall (FSW) in an inertial confinement fusion reactor (ICF) are performed for all stable elements, using a recently upgraded data base. Surface γ dose rate and waste disposal rating (WDR) are employed as indices to compare the merit of elements and compute the concentration limits corresponding to hands-on processing, remote recycling and shallow land burial (SLB). The performance of steels, vanadium alloys and silicon carbide, as candidate structural materials has also been explored. The materials with less waste/recycling concerns are identified, and the influence that impurities can exert in their radiological performance is analyzed. Critical radionuclides, dominant reactions, and isotopes originating critial transmutation/decay sequences are indicated. In addition, calculations for magnetic confinement fusion (MCF) conditions are made to perform ICF/MCF comparisons, finding that some important elements and materials respond very differently in the two environments.

Microstructural and mechanical characterization of new low-activation CrMn austenitic steels

Abstract On the basis of alloy design considerations, and aiming at the disposal by shallow land burial of the waste of fusion tokamak reactors (to be achieved by limiting the long-lived radioactivity of the first wall through the optimization of the composition of the conventional CrNi austenitic steels), the authors designed a series of new low-activation austenitic steels. The paper presents the results of the last stage of the development, concerning the microstructure and the tensile properties of these steels, which have been subject of extensive experimental characterization work.

Waste Disposal of Candidate Structural Materials in Fusion Reactors Utilizing Different Fuel Cycles

The management and disposal of the radioactive waste generated in any nuclear system are major safety and environmental concerns for the deployment of such a power source. In this paper the waste disposal rating is compared for four structural materials when used in deuterium-tritium, deuterium-deuterium, and D-{sup 3}He fusion reactors. The materials considered are HT-9, primary candidate alloy (PCA), Tenelon, and a modified HT-9. Generic models for the reactors are assumed such that each produces a fusion power of 10 MW/m of the axial length and has a sufficient shield/blanket to produce identical magnet damage rates. The latter is achieved by varying the material compositions and thicknesses. The results show that using the advanced fuel cycle D-{sup 3}He, with its low neutron yield, alleviates the activation problems and also allows considerable volume reduction of the radioactive waste. This cycle also permits the use of conventional alloys and at the same time satisfies the regulations criteria for shallow land burial of the low-level waste. In addition, and because of the low damage rate in the D-{sup 3}He reactors, the useful lifetimes of the materials are greatly increased.

Divertor Engineering for the ARIES-I Reactor†

The ARIES tokamak-reactor design study is a multi-institutional project investigating several different visions of the tokamak as a commercial power reactor. The ARIES-I reactor design incorporates modest extrapolation of existing physics with advanced technology in the fusion power core (FPC) design. Use of aggressive technology such as high-field magnets and low-activation silicon-carbide (SiC) composites help to make ARIES-I an attractive reactor with excellent safety characteristics. The ARIES-I reactor uses a double-null poloidal-field (PF) divertor for particle exhaust and impurity control. Control of the edge-plasma density and temperatures has reduced the energy of the incident particles at the divertor to ∼20 eV, which is below the self-sputtering threshold for the tungsten target surface material. The target is constructed of SiC composite tubes with a 2-mm-thick plasma-sprayed coating of tungsten on the plasma-facing side and a 0.5-mm chemical-vapor deposited (CVD) coating of SiC on the back. The divertor is cooled by helium at lOMPa with inlet/outlet temperatures of 350°/650°C. In removing the divertor surface heat flux of 4.5 MW/m2, a design safety factor of 1.8 is achieved. The divertor has a waste disposal rating of 0.10 (see text for definition), thus allowing Class-C shallow land burial, and a site boundary dose of 11.2 rem during an accidental release. Isotopic tailoring of the tungsten and target replacement every two years is necessary to achieve these safety characteristics.

Root Mass and Vertical Root Distribution of Five Semi-arid Plant Species

The root masses of big sagebrush, Great Basin wild rye, Russian thistle, streambank wheatgrass, and crested wheatgrass were determined at 20 cm depth increments from plants grown in high clay content soils in cylindrical containers. All species had roots in the deepest (100-120 cm) depth increment. Crested wheatgrass had the greatest average (+/- SD) total root mass (775 +/- 211 g). Results provide data for some scenarios for fate and effect models for shallow-land burial of low-level radioactive wastes in semi-arid environments.

Calibration of the CREAMS Model for Landfill Cover Designs Limiting Infiltration of Precipitation at Waste Repositories

The water balance relationships of two shallow land burial (SLB) cover configurations were studied using a hydrologic model in an attempt to design waste disposal site covers for successful long-term closure at Los Alamos. Burial site performance requirements for site closure are discussed, along with the role of hydrologic models in assessing the dynamics of the hydrology of the SLB cover. The calibration of a hydrologic model using field data from two SLB cover designs is then described, followed by evaluation of the influence of vegetation, precipitation, and runoff curve number on the design of SLB covers at Los Alamos. Future directions of field research efforts and subsequent hydrologic modeling activities are recommended in terms of their usefulness for waste management decisions to be made at Los Alamos.

Tensiometer Data Acquisition System for Hydrologic Studies Requiring High Temporal Resolution

AbstractCommercially available differential pressure transducers, tensiometers, and a data acquisition system were combined to evaluate soil water tension changes with time within two landfill cover designs used for the shallow land burial of waste materials. A typical error for the differential pressure transducers in the voltage‐pressure calibration curve was estimated to be 0.14 V at a transducer output of 4 V. Tensiometer data collected simultaneously using the data‐acquisition system and a hand‐held manual pressure‐transducer system agreed well (r2 = 0.994). The utility of the tensiometer data acquisition system to collect field data was demonstrated successfully using reference tensiometers with known hydraulic heads. Diurnal fluctuations in tensiometer data collected in the field are discussed relative to future experiments to be performed with the system. In addition, tensiometers with unknown and variable hydraulic heads were used to determine tensiometer response times of approximately 50 min.

Fusion reactor materials to minimize long-lived radioactive waste

Abstract This paper examines, in relation to the norms and practices now applied in different countries, the prospects for the storage and disposal of the radioactive wastes to be expected from future fusion power plants. There is at present no regulation in Europe that defines the treatment and the allowed concentration of the possible long-lived nuclides of waste to be disposed of in shallow land burial. There are a few sites of this type, each one having different acceptability criteria. In the USA the norms applicable are those of the Code of Federal Regulation (10CFR61) which could be logically and consistently extrapolated to fusion materials. The knowledge of the acceptability index of the elements appears to be quite useful in improving the composition of fusion reactor materials, in particular for the first wall and the breeding blanket. These indices, or waste disposal ratings, have been computed either with reference to the UK site norms, which are at present the most restrictive in Europe, or with reference to be extrapolated US norms. The conclusion is relatively optimistic in the second case and less so in the first. The state of the activation cross sections is also examined and recent progress, particularly in the data needed for long-lived radioactive nuclei, is reported.

Leaching Scale Effect for Cement-Waste Forms

The confinement ability of a waste package is one of the major safety characteristics to consider in shallow land burial. In order to determine if the confinement is acceptable, in accordance with local policy, one way is to proceed to leaching tests. The practical method, for sake of simplicity, cost and time limit, is to carry out the leaching tests on laboratory samples which are easier to prepare than full-scale blocks, but the representativity of which needs to be treated with caution; it is in this context, that one of the aspect of our work concerns what is known as the “scale effect”.This study has been conducted using blocks the volumes of which are respectively of 200, 20, 2 and 0, 2 1, and made with the same cement-waste form (13 Cs) system.

Recycling and Shallow Land Burial as Goals for Fusion Reactor Materials Development

The acceptability of each natural element as a constituent for fusion reactor materials has been determined for the purpose of limiting long-lived radioactivity, so that the material could be recycled or disposed of by near-surface burial. The results show that there is little incentive for optimizing the composition of steels for recycling. The development of a steel with an optimized composition that would allow reaching shallow land burial conditions even for the first wall is more interesting and feasible.

Representing Soil Moisture in Experimental Trench Cover Designs for Waste Burial with the CREAMS Model

ABSTRACT An agriculturally based soil water balance model called CREAMS, using recommended parameter values for application to shallow land burial in semiarid areas, was used to estimate soil water...

Processing and waste disposal needs for fusion breeder blankets systems

We evaluated the waste disposal and recycling requirements for two types of fusion breeder blanket (solid and liquid). The goal was to determine if breeder blanket waste can be disposed of in shallow land burial, the least restrictive method under U.S. Nuclear Regulatory Commission regulations. Described in this paper are the radionuclides expected in fusion blanket materials, plans for reprocessing and disposal of blanket components, and estimates for the operating costs involved in waste disposal.

放射性廃棄物浅地中埋設処分による地下水移行経路からの被曝線量の試算

To identify characteristics of radiation dose and important parameters in calculation of the dose from the pathway through groundwater in shallow land burial of radioactive waste, calculation of dose, sensitivity analysis and pathway analysis were carried out under a specific calculation condition. Following results were obtained: (1) For groundwater migration scenario, the pathway of direct drinking of groundwater is an important one. (2) The critical pathway differs with nuclides and changes with time. (3) Doses from use of river or lake water are several orders of magnitude smaller than that from use of groundwater. (4) When the disposal site is located at a coastal area, the critical pathway is ingestion of sea products and the doses are several orders of magnitude smaller than those at an inland area. (5) The groundwater velocity and the distribution coefficient are important parameters in calculation of radionuclide concentration in groundwater.

Determination of 241Pu in low-level radioactive wastes from reactors.

Plutonium-241 is unique in low-level radioactive wastes (LLW) from nuclear power plants because it is the only significant beta-emitting transuranic nuclide in LLW, has a relatively short half-life of 14.4 y, and has a fairly high allowable concentration for shallow land burial. Radiochemical separation of Pu followed by liquid scintillation analysis was used to quantitate 241Pu in a wide range of solid, semi-solid, and liquid LLW samples from two nuclear plants in Michigan. The 241Pu concentrations varied considerably by sample type and reactor operational period as did their correlation with 137Cs, 144Ce, 239Pu and 240Pu concentrations in the same sample. These patterns were also found in reported data for 241Pu in LLW from other reactors, raising the difficulty of accurately determining the inventory (or source term) in a LLW shallow land burial site and its implications for predicting and controlling the future environmental and public health impacts of such disposal.

Development of ferritic steels for reduced activation: The US program

The Cr-Mo ferritic (martensitic) steels are candidates for the structural components of fusion reactors. Irradiation of such steels in a fusion environment produces long-lived radioactive isotopes, which lead to difficult radioactive waste disposal problems once the structure is removed from service. Such problems could be reduced by using steels that contain only elements that produce radioactive isotopes that decay to low levels in a reasonable time (tens of years instead of hundreds or thousands of years). The US Department of Energy has a program to develop steels to meet the criteria for shallow land burial as opposed to deep geologic storage. A review of the alloy development programs indicates that ferritic steels that meet these criteria can be developed.

Low Level Radioactive Waste Disposal — Technology and Public Policy

The disposal of low level radioactive waste (LLRW) is becoming a political problem of the eighties. The problems with shallow land burial of LLRW in the recent past have indicated to the public that the operational technology is not adequate; therefore, studies are concentrating on the use of alternate technologies. These technologies consist of below and aboveground vaults, earth-mounded concrete bunkers, minded cavities, and augered holes. Each of these disposal concepts meet various performance criteria set for the disposal of LLRW. However, there are some performance criteria in each case, where the alternate disposal methods do not show any Improvement over shallow land burial. A trade-off is then necessary between sociopolitical acceptance and technical performance.

Reduced activation guidelines in perspective

The US Fusion Materials program recently adopted a requirement that structural alloys qualify for shallow land burial at the end of their life. In the absence of a directly applicable regulation, the activation limits currently being used are taken from a US Nuclear Regulatory Commission regulation, 10CFR61, developed to handle existing waste streams from the commercial nuclear industry. Activation calculations are characterized by many uncertainties, e.g., in nuclear data, in handling of multi-step reactions, in appropriate neutron flux-spectra, in component lifetimes, and in the viability of isotopic tailoring. These uncertainties, coupled with uncertain regulatory criteria, mean that calculated concentration limits should be viewed only as a qualitative guide in developing reduced activation materials.

Some aspects of sandwiched soil cover design for toxic waste repositories

The environmental concern favours “dry” waste management systems compared to the more common practice of shallow land burial. With the former, sandwiched soil covers are usually employed. A double barrier concept is presented and discussed for the sandwiched construction. The critical matrix potentials of the two barrier materials appear to have significant influence on the performance of the dual barrier system. Despite some practical problems, the concept appears promising.

土壌環境における多成分系破過曲線の推算 ＩＩ イオン交換平衡

A model of multicomponent ion exchange is developed in order to estimate effects of coexisting ions in groundwater such as Ca and Mg on radionuclide migration.This model well estimated following experimental results for Sr-Ca-Mg system.(1) Breaktimes of Sr are drastically reduced due to coexistence of Ca and Mg.(2) Peak height of effluent concentration of Ca reached level about 2 times larger than initial concentration of Ca. This overshoot effect is caused by additional Ca newly leached from the sand.Above phenomena are considered to be observed more or less at any soil environment which is in contact with underground water for a long time. The model of multicomponent ion exchange proposed seems to be therefore effective tool for safety assessment of shallow land burial of low level radioactive waste.

Erosion of Earth Covers Used in Shallow Land Burial at Los Alamos, New Mexico

AbstractThe Los Alamos National Laboratory and the USDA‐ARS examined soil erosion and water balance relationships for a trench cap used for the shallow land burial of low‐level radioactive wastes at Los Alamos, NM. Eight 3.05 by 10.7 m plots were installed with bare soil, tilled, and vegetated surface treatments on a 15 by 63 m trench cap constructed from soil and crushed tuff layers. A rotating boom rain simulator was used to estimate the soil erodibility and cover‐management factors of the Universal Soil Loss Equation (USLE) for this trench cap and for two undisturbed plots with natural vegetative cover. The implications of the results of this study are discussed relative to the management of infiltration and erosion processes at waste burial sites and compared with similar USDA research performed throughout the USA.