The radionuclide characteristics of light-water-reactor (LWR) spent fuel play key roles in the design and licensing activities for radioactive waste transportation systems, interim storage facilities, and the final repository site.

The purpose of this calculation is to evaluate the transient behavior and consequences of a worstcase criticality event involving intact pressurized water reactor (PWR) mixed-oxide (MOX) spent nuclear fuel (SNF) in a degraded basket configuration inside a 21 PWR waste package (WP). This calculation will provide information necessary for demonstrating that the consequences of a worst-case criticality event involving intact PWR MOX SNF are insignificant in their effect on the overall radioisotopic inventory and on the integrity of the repository.

The purpose of this analysis is to evaluate the transient behavior and consequences of a worst case criticality event involving intact pressurized water reactor (PWR) spent nuclear fuel (SNF) in a degraded basket configuration inside a 21 PWR assembly waste package (WP). The objective of this analysis is to demonstrate that the consequences of a worst case criticality event involving intact PWR SNF are insignificant in their effect on the overall radioisotopic inventory in a WP.

The objective of this calculation is to perform intact and degraded mode criticality evaluations of the US Department of Energy's (DOE) Advanced Test Reactor (ATR) Spent Nuclear Fuel (SNF) placed in the DOE standardized SNF canister. This analysis evaluates the codisposal of the DOE SNF canister containing the ATR SNF in a 5-Defense High-Level Waste (%-DHLW) Short Waste Package (WP) (Bechtel SAIC Company, LLC [BSC] 2004a), which is to be placed in a monitored geologic repository (MGR).

The responsible use of calculational methods in nuclear criticality safety includes a determination of bias and bias uncertainty that may exist between the calculated results and reality. Such biases exist due to approximations used to model the real world, uncertainties in nuclear data, and approximations associated with the calculational method (e.g., Monte Carlo method). The bias and bias uncertainty are typically determined by using the modeling approximations, nuclear data, and calculational method to model well-known, usually critical, systems.

The OECD/NEA “Burn-up Credit Criticality Benchmark” working group has studied the effect of axial burn-up profile on the criticality of a realistic PWR spent fuel transport cask (Phase II-B). The final results of this benchmark are presented and analysed in this report. Nine basic cases and two additional accident configurations were considered with the following varying parameters: burn-up (0 GWd/t for fresh fuel, 30 and 50 GWd/t), fuel composition (actinides only and actinides with fifteen fission products), axial burn-up discretisation (1 or 9 zones).

The Nuclear Regulatory Commission (NRC) Office of Regulatory Research (RES) has initiated a program to support effective implementation of burnup credit in the criticality safety assessment of transport and dry storage casks. The goal is to develop technical bases that can be used to provide criteria and guidance for use in licensing activities. The program is being conducted in a phased approach, with the initial focus on unresolved issues related to the use of actinide-only bumupcredit in transport and dry storage casks designed for spent fuel from pressurized-water reaciors (PWRs).

The effects of radiation on the corrosion of various metals and alloys, particularly with respect to in-reactor processes, has been discussed by a number of authors (Shoesmith and King 1998, p. 2). Shoesmith and King (1998) additionally discuss the effects of radiation on the proposed Monitored Geologic Repository (MGR) Waste Package (WP) materials. Radiation effects on the corrosion of metals and alloys include, among other things, radiolysis of the local gaseous and aqueous environment to produce both oxidizing and reducing radicals.

The objective of these calculations is to perform intact and degraded mode criticality evaluations of the Department of Energy’s (DOE) Three Mile Island – Unit 2 (TMI-2) spent nuclear fuel (SNF) in canisters. This analysis evaluates codisposal in a 5-Defense High-Level Waste (5-DHLW/DOE SNF) Long Waste Package (Civilian Radioactive Waste Management System Management and Operating Contractor [CRWMS M&O] 2000b, Attachment V), which is to be placed in a potential monitored geologic repository (MGR).

The requirements of ANSI/ANS 8.1 specify that calculational methods for away-from-reactor criticality safety analyses be validated against experimental measurements. If credit for the negative reactivity of the depleted (or spent) fuel isotopics is desired, it is necessary to benchmark computational methods against spent fuel critical configurations.

This analysis is prepared by the Mined Geologic Disposal System (MGDS) Waste Package Development (WPD) department to provide a probabilistic evaluation of the potential for criticality of fissile material which has been transported from a geologic repository containing breached waste packages of commercial spent nuclear fuel (SNF). This analysis is part of a continuing investigation of the probability of criticality resulting from the emplacement of spent nuclear fuel in a geologic repository.

The Radioactive Waste Management Directorate (RWMD) is responsible for implementing geological disposal of the UK’s higher-activity radioactive wastes. RWMD’s research into geological disposal considers safety during waste transport to a disposal facility, during waste disposal operations, and once the facility has been closed. The wastes for disposal comprise a wide range of materials and include some fissile radionuclides.

The Disposal Criticality Analysis Methodology Topical Report, YMP/TR-0004Q (DOE 1998b) described a risk-informed methodology for postclosure criticality analyses in the potential repository at Yucca Mountain, Nevada. Various models contained in the methodology were described and a process for validating these models was presented. The topical report also committed to following this process in validating the models used for License Application.

The purpose of this analysis report is to evaluate the features, events, and processes (FEPs) associated with criticality and document the screening decision for either inclusion or exclusion of criticality in the Total System Performance Assessment for License Application (TSPA-LA). The FEPs associated with criticality address scenarios that include initiators of sequences of events or processes that could lead to configurations that have potential for criticality in the repository.