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DOE OSTI2017

Moderation Control Challenges in a Shutdown Facility

On October 27, 2015, an Occurrence Reporting and Processing System (ORPS) Significance Category 1 nuclear criticality safety (NCS) event was discovered at the Paducah Gaseous Diffusion Plant (PGDP) located near Paducah, Kentucky. The NCS violation was a result of the failure to obtain semi-annual moisture samples on sections of large (greater than or equal to 14-inch inside diameter) cascade piping. The event was reported in ORPS EM-PPPOFPDPPGDP- DEAC-2015-0020 under reporting criterion 3C(2) which states, 'A condition in which no documented controls are available to prevent a criticality accident. An accident has not occurred due to other, non-documented barriers or controls.' The purpose of this paper is to present the challenges the site encountered maintaining atmospheric moderation control after the enrichment operation ended, the oversight activities in response to the event and the need to evaluate the changed conditions impact on the Nuclear Criticality Safety Evaluation (NCSE)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2016

C-400 and C-409 Criticality Incredible Road Map

Many guides and standards describe a process for evaluating process operations with known quantities of fissile material. The accepted industry guides and standards for performing criticality evaluations for fissile material operations are not well suited for operating systems that may contain residual fissile material. The Paducah Site deactivation activities includes large process components that have unfavorable geometries for the {sup 235}U enrichment levels present. The fissile material holdup in these components can range from negligible residual quantities to significant deposits weighing several hundred pounds. The purpose of this white paper is to outline a methodology that can be used to declare a facility as criticality incredible (CI). For the purpose of this paper, criticality incredible means that the inventory and its form and distribution within the facility does not need Nuclear Criticality Safety Evaluation (NCSE) type (e.g., administrative or engineered) controls. This assumes of course that certain project assumptions are maintained. For example in the facilities that will be discussed within this paper, wet decontamination is not part of the planned demolition and disposal operations. The proposed methodology for deactivation of a facility to the point that criticality incredible can be declared will be applied to the C-400 Chemical Cleaning Building and to the C-409 Decontamination Facility at the Paducah Gaseous Diffusion Plant (PGDP). The purpose and intent of the CI declaration is to release a facility from Nuclear Criticality Safety (NCS) requirements and simplify the demolition of the facility. In practical terms, this means the facility can be re-categorized as < a Hazard Category 3 facility per DOE-STD-1027-92 Hazard Categorization and Accident Analysis Techniques for compliance with DOE Order 5480.23, Nuclear Safety Analysis Reports, NCS controls are not needed, and the Criticality Accident Alarm Systems (CAAS) can be removed from service. The only involvement from the site NCS program following the declaration would be to ensure that the underlying assumptions are not violated through discovered conditions or project changes. This includes the institutional control of preventing new fissile material from being introduced into the facility. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗