The emplacement of nuclear waste in the proposed geologic repository must satisfy relevant regulatory requirements with respect to criticality, 10CFR60. I31 (h) (Ref. 25). The waste packages for the various waste forms will be designed to preclude criticality (typically by the inclusion of neutron absorbers) even if the waste package becomes filled with water. Criticality may, however, be possible if the contents of the waste package become degraded in such a way that the fissile material can be separated from the neutron absorbers, while sufficient moderator is retained.

The Nuclear Waste Policy Act of 1982, as amended (NWPA), establishes a process for the siting, construction and operation of one or more national repositories for permanent disposal of the Nation’s spent nuclear fuel (SNF) and high-level radioactive waste (HLW). In 1987, after the Department of Energy (the Department or DOE) had conducted studies of nine potential repository sites located throughout the United States, Congress amended the NWPA and selected the Yucca Mountain site in Nye County, Nevada as the only site for further study for the first national repository.

As part of the plutonium waste form development and down-select process, repository analyses have been conducted to evaluate the long-term performance of these forms for repository acceptance. Intact and degraded mode criticality analysis of the mixed oxide (MOX) spent fuel is presented in Volume I, while Volume II presents the evaluations of the waste form containing plutonium immobilized in a ceramic matrix.

The purpose of this engineering calculation is to document the MCNP4B2LVevaluations of Laboratory Critical Experiments (LCEs) performed as part of the Disposal Criticality Analysis Methodology program. LCE evaluations documented in this report were performed for 22 different cases with varied design parameters. Some of these LCEs (10) are documented in existing references (Ref. 7.1 and 7.2), but were re-run for this calculation file using more neutron histories.

The Office of Civilian Radioactive Waste Management (OCRWM) is responsible for all spent fuels and high-level wastes (HLW) that will eventually be disposed of in a geologic repository. The purpose of this document, and the information contained in the associated computerized data bases and supporting technical reports, is to provide the technical characteristics of the radioactive waste materials that will (or may) be accepted by DOE for interim storage in an MRS or emplacement in a repository as developed under the Nuclear Waste Policy Act Amendment of 1987.

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.

At the request of the staff to the Blue Ribbon Commission on America’s Nuclear Future (“BRC”), we have reviewed the following questions:
1. Is there legal authority for DOE or any other entity to undertake to site a repository for “co-mingled” nuclear materials (i.e., civilian and defense spent nuclear fuel (SNF) and high-level radioactive waste (HLW)) at any site other than Yucca Mountain?

The purpose of this calculation is to document the Crystal River Unit 3 pressurized waste reactor (PWR) reactivity calculations performed as part of the commercial reactor critical (CRC) evaluation program. CRC evaluation reactivity calculations are performed at a number of statepoints, representing reactor start-up critical conditions at either beginning of life (BOL), beginning of cycle (BOC), or mid-cycle when the reactor resumed operation after a shutdown.

This model report documents the abstraction of drift seepage, conducted to provide seepage relevant parameters and their probability distributions for use in Total System Performance Assessment for License Application (TSPA-LA). Drift seepage refers to the flow of liquid water into waste emplacement drifts.