NRC SFST ISG-19: Moderator Exclusion under Hypothetical Accident Conditions and Demonstrating Subcriticality of Spent Fuel under the Requirements of 10 CFR 71.55(e)
This Interim Staff Guidance (ISG) provides review guidance for meeting the fissile material
package standards in 10 CFR 71.55(e). The provisions of 71.55(e) require that a fissile
material package be subcritical under hypothetical accident conditions assuming that the fissile
material is in the most reactive credible configuration consistent with the damaged condition of
the package and the chemical and physical form of the contents, and water moderation occurs
to the most reactive credible extent consistent with the damaged condition of the package and
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