Sitakanta Mohanty

System-View International, LLC · Environmental and Energy

Permeability is an important bulk physical property used for determining fluid flow and transport in materials such as buffer, backfill, crushed zone, or packing materials that serve as a transport barrier and as a settlement barrier for overlying rock. The paper presents the development of a permeability model using material properties, at the por...

Simulations that combine flow modeling with radionuclide transport modeling provide insights into the potential performance of a hypothetical geologic repository for intermediate level long-lived (ILLLW) and high-level (HLW) radioactive waste. Key parameters to performance can be identified and quantified using probabilistic sampling of the model p...

This paper examines selected sensitivity analysis approaches, compares these methods using results from MC-MELODIE, a probabilistic hydrologic flow and contaminant transport code, and highlights experience gained from using these methods in the context of deep geologic disposal of intermediate long-lived and high-level wastes in France. The paper c...

The Swedish Nuclear Fuel and Waste Management Company (SKB) included analysis of a range of scenarios in its SR-Site report. SKB grouped these scenarios into two categories—main and residual. The main scenario included a likely scenario (corrosion failure) and a less probable scenario (seismicity-induced shear failure). The residual scenario includ...

The Nuclear Regulatory Commission (NRC) Total-system Performance Assessment (TPA) code is a tool to independently evaluate the long-term performance of the proposed Yucca Mountain (YM) high-level radioactive waste (HLW) repository by modeling processes such as the dissolution of the spentnuclear fuel (SNF) and the subsequent transport through unsat...

Estimated parameter distributions in groundwater models may contain significant uncertainties because of data insufficiency. Therefore, adaptive uncertainty reduction strategies are needed to continuously improve model accuracy by fusing new observations. In recent years, various ensemble Kalman filters have been introduced as viable tools for upda...

Groundwater models are critical decision support tools for water resources management and environmental remediation. However, limitations in site characterization data and conceptual models can adversely affect the reliability of groundwater models. Therefore, there is a strong need for continuous model uncertainty reduction. Ensemble filters have...

A grid-based, cluster ensemble Kalman filter (GCEnKF) is developed for updating multimodal heterogeneous hydrogeologic parameter distributions via dynamic data assimilation. Significant model and data uncertainties may exist when groundwater models are built on preliminary site characterization data. Therefore, adaptive strategies are needed to con...

This paper presents a methodology for screening insignificant random variables and ranking significant important random variables using sensitivity measures including two cumulative distribution function (CDF)-based and two mean-response based measures. The methodology features (1) using random samples to compute sensitivities and (2) using accepta...

The Regionalized Sensitivity Analysis (RSA) procedure is applied to a complex total-system performance assessment model of a geologic high-level radioactive waste repository. The analysis is designed to identify the constituent model parameters that influence the discrimination between model outputs above and below prescribed thresholds. The RSA pr...

Geological repositories designed to isolate high-level radioactive waste need natural and engineered barriers that prevent or slow the release of radioactive elements into the accessible environment to acceptable regulatory limits. Under the U.S. Nuclear Regulatory Commission's (NRC's) regulations, a barrier is any material, structure, or feature t...

A generic performance assessment model to study the feasibility of a deep disposal system of high-level radioactive waste in Japan was published in the H12 Report.1) This report concluded that such a repository was feasible without compromising public safety. In this paper, an independent performance assessment model is discussed, and results assum...

The key findings from a suite of independent analyses of the performance of the proposed repository at Yucca Mountain, conducted by the Center for Nuclear Waste Regulatory Analyses (CNWRA) and the U.S. Nuclear Regulatory Commission (NRC), are summarized. The analyses are geared toward obtaining risk insights from deterministic and probabilistic cal...

As part of its preparation to review a potential license application from the U.S. Department of Energy (DOE), the U.S. Nuclear Regulatory Commission (NRC) is examining the performance of the proposed Yucca Mountain nuclear waste repository. In this regard, we evaluated postclosure repository performance using Monte Carlo analyses with an NRC-devel...

This paper presents a sensitivity analysis method that provides a powerful tool for understanding the behavior of large and complex systems. This method produces easy-to-understand results that can explain the performance of a system clearly at the component level rather than parameter by parameter. A system model for the proposed disposal of high-...

In quantitative performance assessment (PA) for nuclear waste repositories, probabilistic (e.g., Monte Carlo) calculations are frequently used to estimate dose and risk [1], Each Monte Carlo realization represents the uncertain estimate of the future effect of the repository. There are at least two ways to interpret the model output; (1) take the p...

The complexity of the safety case for a high-level nuclear waste repository makes it imperative that deliberate and significant effort be made to incorporate in it a high level of transparency and traceability. Diverse audiences, from interested members of the public to highly trained subject matter experts, make this task difficult. A systematic s...

The U.S. Nuclear Regulatory Commission (NRC) is developing regulatory perspectives for a potential high-level waste repository at Yucca Mountain, Nevada, USA that would be constructed by the U.S. Department of Energy (DOE). The proposed regulations on which a potential license would be granted are "risk-informed and performance-based". It is necess...

A cumulative distribution function (CDF)-based method has been used to perform sensitivity analysis on a computer model that conducts total system performance assessment of the proposed high-level nuclear waste repository at Yucca Mountain, and to identify the most influential input parameters affecting the output of the model. The performance asse...

The Fourier Amplitude Sensitivity Test (FAST) method has been used to perform a sensitivity analysis of a computer model developed for conducting total system performance assessment of the proposed high-level nuclear waste repository at Yucca Mountain, Nevada, USA. The computer model has a large number of random input parameters with assigned proba...

Both the pre-and post-closure safety cases for high-level nuclear waste repositories rely to a significant extent on analyses based on mathematical models and use a large amount of data. Such analyses called integrated safety analysis (ISA) and performance assessment (PA), respectively, are usually quite complex. An ISA and a PA contain system desc...

A description is presented of the various models (i.e. thermal, chemical environment, humid-air and aqueous corrosion) used in the engineered barrier system performance assessment code (EBSPAC) to represent processes that govern the failure of waste packages (WPs) and, ultimately, the release of radionuclides from the engineered barrier system (EBS...

This paper is the second in a series describing the models used in the Engineered Barrier System Performance Assessment Code (EBSPAC) to represent processes that govern the failure of waste packages (WPs) and the release of radionuclides from the engineered barrier system (EBS). These models are specifically adapted to the US Department of Energy (...

The U.S. Department of Energy (DOE) has released a Viability Assessment (VA) of the proposed high-level waste (HLW) repository at Yucca Mountain (YM), Nevada. The proposed standard for the repository requires the evaluation of the predicted - over 10,000 yr - performance of the system. In the VA, it is argued that long waste package (WP) lifetimes...

This paper presents a method for calculating the effective stagnant thermal conductivity of consolidated porous media with multiphase fluid saturation. The method takes into account the pore-level heterogeneity in the rock and uses a realistic distribution of multiphase fluids in the pores. Unlike the relationships developed in the past, the propos...

The U.S. Department of Energy (DOE) has released a Viability Assessment (VA) of the proposed high-level waste (HLW) repository at Yucca Mountain (YM), Nevada. The proposed standard for the repository requires the evaluation of the predicted —over 10,000 yr— performance of the system. In the VA, it is argued that long waste package (WP) lifetimes ar...

A study of elemental transport at the Akrotiri archeological site on the island of Santorini, Greece, has been conducted to evaluate the use of natural analog data in support of long-term predictive modeling of the performance of a proposed geologic repository for nuclear waste at Yucca Mountain, Nevada. Akrotiri and Yucca Mountain have many analog...

A comprehensive summary of the coupled mechanical hydraulic (MH) behavior of natural rock joints as investigated in two different laboratory experiments (test cases) under the international cooperative project DECOVALEX is presented. The first test case experiment (TC1) was conducted by the Norwegian Geotechnical Institute (NGI) using their coupled...

Steamflood performance often suffers from channelling and gravity segregation, resulting in poor sweep efficiency. Alkaline additives may be used with steam for certain types of crude oils to improve steamflood performance. In this paper, an experimental study is presented to evaluate the effectiveness of sodium hydroxide, sodium metasilicate and s...

This report consists of an extensive, yet not exhaustive, literature review on the subjects of effective property calculations, fracture network generation with stochastic approaches, and modeling approaches for fluid flow simulation in fractured rock. It also presents visualization, statistical, and connectivity analyses of realistic networks at t...

This paper describes the development of a transient technique to measure thermal diffusivily and conductivity of porous samples. The method uses the film heat sensor to probe heat flux. Temperature and heat flux are measured dynamically allowing conditions to vary in time at the point of measurement. The data are then treated by a deconvolution alg...

A real space renormalization group method for the percolation problem in isotropically and anisotropically correlated systems is proposed. The macroscopic conductive properties at all volume fractions of the conducting phase are computed. It is demonstrated that the anisotropy in the correlation structure of the original lattice has a major effect...

SPE Members Abstract A method is proposed for obtaining effective permeabilities of heterogeneous porous media at many length permeabilities of heterogeneous porous media at many length scales. The real space renormalization group method (RSRG) has been modified to determine the effective properties of both uncorrelated and correlated permeability...

Progress by the U.S. Nuclear Regulatory Commission (NRC) is presented in developing licensing requirements and technical agreements with the U.S. Department of Energy (DOE) relating to multiple barriers for the proposed Yucca Mountain high-level waste repository. Natural and engineered barriers are required to prevent or substantially delay movemen...

On February 22, 1999, U.S. Nuclear Regulatory Commission (NRC) made available, for public comment, its proposed licensing requirements (10 CFR Part 63) for disposal of high-level radioactive waste (HLW) in the proposed geologic repository at Yucca Mountain, Nevada. During the public comment period (February 22, 1999 through June 30, 1999), we held...

The US Nuclear Regulatory Commission and the Center for Nuclear Waste Regulatory Analyses recently developed a general computer model for conducting total-system performance assessment for the proposed high-level-waste geologic repository at Yucca Mountain, Nevada. The computer model, referred to as the total-system performance assessment (TPA) cod...