Nuclear criticality safety for fissile materials outside reactor - Nuclear criticality safety based on limiting and controlling moderators
1 Scope
This part specifies the methods and requirements for ensuring the nuclear criticality safety of fissile materials by limiting and controlling moderators in a moderator control area.
This part applies to limiting and controlling moderators to achieve criticality safety in operations with fissile materials in a moderator control area.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this standard. For dated references, subsequent amendments (excluding corrections) to, or revisions of, any of these publications do not apply to this standard. However parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies.
GB 15146.1 Nuclear criticality safety for fissile materials outside reactors - Administrative regulation for nuclear criticality safety
GB 15146.2 Nuclear criticality safety for fissile materials outside reactor - Basic technical criteria and subcritical limits for handling, processing and operations of fissile materials
EJ/T 1074 Criteria for nuclear criticality safety training
3 Terms and definitions
For the purposes of this part, the following terms and definitions apply.
3.1
moderation
process of decreasing the energy of neutrons through successive collisions with moderator nuclei without appreciable capture
3.2
moderator
material that reduces neutron energy by scattering without appreciable capture )
3.3
moderator control area
area defined by the process evaluation in which moderators are limited and controlled for nuclear criticality safety
3.4
moderator control engineered barrier
physical feature of a system specifically identified and used to limit or control the introduction of moderators for nuclear criticality safety )
3.5
process evaluation
document that identifies and defines all known criticality safety concerns; documents criticality safety assumptions, requirements, limits, and controls; and demonstrates subcriticality. The process evaluation is often referred to as a Nuclear Criticality Safety Evaluation (NCSE)
4 Nuclear criticality safety practices
4.1 Administrative practices for limitation and control of moderators
4.1.1 Written procedures shall be prepared and shall include the nuclear criticality safety limits and controls for operation. These procedures should address any step to be taken if a moderator control fails.
4.1.2 Written procedures shall be provided for monitoring, testing, and maintenance to ensure that the limits and controls specified in process evaluations are maintained.
4.1.3 Written procedures shall be provided for moderator sampling and analysis as required by the process evaluation.
4.1.4 Moderator control areas shall be identified to personnel in accordance with facility-specific practices.
4.1.5 Appropriate limits and other means for moderator control shall be posted.
4.1.6 Moderator control requirements shall be included in the fire-fighting plans.
4.1.7 Combustible materials in moderator control areas should be minimized.
4.1.8 Training in understanding and complying with moderator limits and controls shall be provided to appropriate personnel as part of nuclear criticality safety training. Additional guidance can be found in EJ/T 1074.
4.1.9 Additional guidance for administrative practices can be found in GB 15146.1.
4.2 Process evaluations for limitation and control of moderators
4.2.1 The process evaluation shall define the moderator control area.
4.2.2 The process evaluation shall demonstrate that the operation will be subcritical under both normal and credible abnormal conditions.
4.2.3 The process evaluation shall explicitly identify the limits, controls, and engineered barriers for moderator control areas. The limits shall be based on experimental data or derived through the use of calculational methods which are validated as required by GB 15146.2.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Nuclear criticality safety practices
5 Engineered practices for moderator control areas
Annex A (Informative) Typical moderating materials
Annex B (Informative) Potential sources of moderators
Annex C (Informative) Moderator content measurements
Annex D (Informative) Examples of engineered barriers to control moderators
