Publications

Abstract not provided.

There has only been one naturally occurring reactor region (Oklo) identified historically. There has to have been other factors that prevented uncontrolled nuclear criticality events. There are higher concentration uranium depositions in the earth's crust than the Oklo region, that did not go critical based on uranium enrichment. There are many papers on the Oklo phenomena which do not address why the uranium did not reach criticality prior to the historical point of 2 billion years ago, nor do they specifically address the lack of radiogenic lead in any of the uranium deposits. Consideration of the lack of lead as a potential indicator of the age of the earth as being a possible factor. Reports which address the leaching effect could consider the reactivity effect of moderation associated with higher enrichment uranium. The lack of radiogenic lead associated with the uranium may or may not be due to leaching. Also, the higher concentration uranium deposits (>15%) were discovered in the 1990s, and reevaluation of the overall effect on a natural reactor criticality were not considered. The high reactivity levels and the low quantity of radiogenic lead identified in uranium tailings, tends to favor a significantly shorter time period or a highly efficient naturally occurring leaching process. A shorter time period would reduce uranium mass and enrichment. Given even a small quantity of moderator would allow an uncontrolled nuclear criticality for high concentration uranium deposits for enrichment between 3 and 8 percent 235 U. The evaluation and analysis of the nuclear criticality safety factors should be evaluated further to document the actual uranium ore grade, and Pb constituents. Identification of the macro-scale quantity (PPM) of radiogenic lead coupled with the NCS factors could be a more useful tool for determining the age of the earth. Further calculations could be considered to determine the impact of different rock formations and materials where uranium is located, and evaluation of the natural leaching of uranium and its decay by-products to associate the effect of radiogenic lead or other materials.

Abstract not provided.

The process nuclear criticality accident that occurred at the Mayak Production Association (Chelyabinsk-40) on January 2, 1958 involving a vessel of uranyl nitrate solution claimed the lives of three workers and left a fourth worker with continuing health problems. There are a myriad of uncertain parameters involved with this accident: What was the molarity of the solution? How much solution was in the vessel at the time of the accident? In what position was the vessel and the solution when it went critical? How important was the impact of reflection due to the workers and/or the floor? These uncertain parameters have made this accident particularly difficult to analyze in the past. This work aims to lower the uncertainty on some of these parameters. A most-probable solution composition is determined by comparing literature on the physical properties of uranyl nitrate solutions to those presented in LA-13638 [1], which describes the accident in question. Using this most-probable solution, the main contributions to the reactivity of the system and hence the eventual accident, are identified through Serpent 2 and OpenFOAM analyses. Serpent 2, a Monte Carlo software tool, is used to perform calculations of the reactivity effects of lowering the vessel toward the floor and the reactivity added by the close proximity of workers. OpenFOAM, a C++ partial differential equation solver toolkit, is used to simulate the fluid inside the vessel as the vessel is tipped. This is done by treating the solution and air inside the vessel as two incompressible, isothermal, and immiscible fluids using a volume of fluid (VoF) approach. The goal of this approach is simply to track the interface between the two fluids, and hence give an accurate description of the geometrical structure of the solution as the vessel is tipped. These two unique tools are then coupled to provide a time-dependent flow simulation to study the effect that the changing geometrical structure had on the criticality of the system, which is novel to the criticality safety field. This work provides a more accurate picture of the accident going forward. Key Words: Serpent 2, OpenFOAM, multi-physics, prompt neutron excursion, nuclear criticality safety accident, process condition change.

Abstract not provided.

Sandia National Laboratories (SNL) has limited inventories of, and activities with, fissile-material. Personnel who perform nuclear criticality safety (NCS) assignments do so on a part-time basis. Sandia's "tailored approach" to training and qualification of these personnel can serve as a model for others with "small" NCS programs. SNL uses a single set of qualification cards for qualifying nuclear criticality safety engineers (NCSE). Provision is made for: (1) training and mentoring of new NCSE with testing or other verification of their skills and knowledge and (2) "qualification by documentation" for staff who historically have been performing NCSE-like duties. Key areas for evaluation include previous formal education and training; demonstrated success in writing Criticality Safety Assessments (CSA) and related documents; interaction with the SNL criticality safety committees; and overall knowledge (e.g., as judged against the objectives in DOE-STD-1135). Gaps of knowledge are filled through self-study, training, or mentoring. Candidate mastery of topics is confirmed primarily by evaluation of work products and interviews. Completion is approved by the Criticality Safety Officer (CSO) - the closest SNL comes to having an NCS manager - and then management. In applying the tailored approach, NCSE candidates are not required to be subject-matter experts for all NCS-related facilities and activities at SNL at the time of qualification. Familiarity with each of the facilities and activities is expected, along with the ability to "self-train" when needed (e.g., analogous just-in-time [JIT] procurement). The latter is supported by identification of applicable SNL-wide fissile-material facilities and activities along with resource organizations and personnel in NCS, safety analysis, accountability, etc. The capstone is a discussion with the CSO, or other experienced NCSE, demonstrating the ability to explain in some detail how a specific NCS assignment would be tackled (e.g., options for gaining facility/activity knowledge, performing analyses, using resource personnel, and traversing the required peer- and committee-review processes).

Abstract not provided.

Abstract not provided.

This Safety Analysis Report (SAR) is prepared in compliance with the requirements of DOE Order 5480.23, Nuclear Safety Analysis Reports, and has been written to the format and content guide of DOE-STD-3009-94 Preparation Guide for U. S. Department of Energy Nonreactor Nuclear Safety Analysis Reports. The Hot Cell Facility is a Hazard Category 2 nonreactor nuclear facility, and is operated by Sandia National Laboratories for the Department of Energy. This SAR provides a description of the HCF and its operations, an assessment of the hazards and potential accidents which may occur in the facility. The potential consequences and likelihood of these accidents are analyzed and described. Using the process and criteria described in DOE-STD-3009-94, safety-related structures, systems and components are identified, and the important safety functions of each SSC are described. Additionally, information which describes the safety management programs at SNL are described in ancillary chapters of the SAR.