Modeling the uncertain impacts of climate change

Human and earth systems are extremely complex processes. The modeling of these systems to assess the effects of climate change is an activity fraught with uncertainty. System models typically involve the linking of a series of computer codes, each of which is a detailed model of some physical or social process in its own right. In such system models, the output from one process model is the input to another. Traditional methods for dealing with uncertainty are inadequate because of the sheer complexity of the modeling effort: Monte Carlo methods and the exhaustive evaluation of what if '' scenarios estimate sensitivities fail because of the heavy computational burden. More efficient methods are required for learning about system models that are constructed from a collection of computer codes. A two-tiered modeling approach is being developed to estimate the distribution of outcomes from a series of nested models. The basic strategy is to develop a simplified executive, or simplified system code (SSC), that is analogous to the more complex underlying code. An essential feature of the SSC is that it uses information abstracted from the detailed underlying process codes in a manner that preserves their essential features and interactions among them. Of course, to be useful, the SSC must be much faster to run than its complex counterpart. The success of the SSC modeling strategy depends on the methods used to extract essential features of the complex underlying codes

Analysis of Tank 241-AN-106 characterization and grout performance criteria

This report provides an assessment of how well we can resolve the following issues concerning Tank 241-AN-106 at the Hanford Reservation, given the current state of information: How well we can characterize the contents of 241-AN-106; whether the degree of characterization is sufficient to use 241-AN-106 wastes to develop tests of grout adequacy. The wastes must be characterized not only to ensure grout adequacy but also to provide assurance that the wastes can be successfully and safely transferred. In this report, we evaluate the adequacy of characterization for transfer and tests of grout adequacy, and we evaluate the current status of acceptance criteria and grout formulation experiments

Uncertainty and sampling issues in tank characterization

A defensible characterization strategy must recognize that uncertainties are inherent in any measurement or estimate of interest and must employ statistical methods for quantifying and managing those uncertainties. Estimates of risk and therefore key decisions must incorporate knowledge about uncertainty. This report focuses statistical methods that should be employed to ensure confident decision making and appropriate management of uncertainty. Sampling is a major source of uncertainty that deserves special consideration in the tank characterization strategy. The question of whether sampling will ever provide the reliable information needed to resolve safety issues is explored. The issue of sample representativeness must be resolved before sample information is reliable. Representativeness is a relative term but can be defined in terms of bias and precision. Currently, precision can be quantified and managed through an effective sampling and statistical analysis program. Quantifying bias is more difficult and is not being addressed under the current sampling strategies. Bias could be bounded by (1) employing new sampling methods that can obtain samples from other areas in the tanks, (2) putting in new risers on some worst case tanks and comparing the results from existing risers with new risers, or (3) sampling tanks through risers under which no disturbance or activity has previously occurred. With some bound on bias and estimates of precision, various sampling strategies could be determined and shown to be either cost-effective or infeasible

Characterization report for the ferrocyanide safety issue

Recently PNNL was tasked by DOE to develop and demonstrate a risk-based strategic approach to characterizing Hanford`s Nuclear Waste Tanks. This strategic approach was documented in a report entitled ``A Risk-Based Focused Decision-Management Approach for Justifying Characterization of Hanford Tank Waste``. In support of the general approach, a specific strategy for addressing each of the several safety issues associated with the tanks was developed. This report documents the approach for the Ferrocyanide Safety Issue. The purpose of this report is to describe a structured logic diagram (SLD) for determining the risk associated with the ferrocyanide tank safety issue and provide the supporting information for the SLD. The SLD addresses the resolution of risks resulting from the presence of ferrocyanide layers within the Hanford tanks. The informational requirements for determining risk from any reaction stemming from ferrocyanide are outlined in the SLD. This report will describe the potential paths to a successful resolution of the ferrocyanide safety issue. Complete development of the intervention pathway is outside the scope of this current activity. General descriptions of the approach, key components of the SLD, and conclusions are provided in the body of this report. The complete SLD, descriptions of each box shown in the SLD, a discussion on how to fill data needs, and a list of contributors is provided in the appendices

Comparison of NDA and DA measurement techniques for excess plutonium powders at the Hanford Site: Statistical design and heterogeneity testing

Quantitative physical measurements are a n component of the International Atomic Energy Agency (IAEA) nuclear material m&guards verification regime. In December 1994, LA.FA safeguards were initiated on an inventory of excess plutonium powder items at the Plutonium Finishing Plant, Vault 3, on the US Department of Energy`s Hanford Site. The material originl from the US nuclear weapons complex. The diversity of the chemical form and the heterogenous physical form of this inventory were anticipated to challenge the precision and accuracy of quantitative destructive analytical techniques. A sampling design was used to estimate the degree of heterogeneity of the plutonium content of a variety of inventory items. Plutonium concentration, the item net weight, and the {sup 240}Pu content were among the variables considered in the design. Samples were obtained from randomly selected location within each item. Each sample was divided into aliquots and analyzed chemically. Operator measurements by calorimetry and IAEA measurements by coincident neutron nondestructive analysis also were performed for the initial physical inventory verification materials and similar items not yet under IAEA safeguards. The heterogeneity testing has confirmed that part of the material is indeed significantly heterogeneous; this means that precautionary measures must be taken to obtain representative samples for destructive analysis. In addition, the sampling variability due to material heterogeneity was found to be comparable with, or greater than, the variability of the operator`s calorimetric measurements

Discovering the relation between project-factors and project success in post-mortem evaluations

Post-mortem project reviews often yield useful lessons learned. These project reviews are mostly recorded in plain text. This makes it difficult to derive useful overall findings from a set of such post-mortem reviews, for example to monitor and guide a software process improvement program. We have developed a five-step method to transform the qualitative, natural language type information present in those reports into quantitative information. This quantitative information can be analyzed statistically and related to other types of quantitative projectspecific information. In this paper we discuss the method, and show the results of applying it in the setting of a large industrustrial software process improvement initiative

Human experiments in trust dynamics

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Measuring serial dependence in categorical time series

Categorical time series, Serial association, Weak stationarity, Discrete ARMA processes,