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U.S. NRC Nuclear Regulatory Commission

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Facilities & Safety

NRC oversees the safety of nuclear reactors, materials, and waste facilities nationwide.
Reactors, Facilities, Sites
Safety & Security
Radiation & Waste
Protection
- Radiation Protection
- Fire Protection
Regulations & Legislation

Covers the laws establishing the NRC, its 10 CFR regulations, and the rulemaking process, including petitions, public comment, and Federal Register notices.
Regulations
- How We Regulate
- Regulations (NRC, 10 CFR)
Legislation
Rulemaking
Guidance
- Regulatory Guides (by Division)
Documents & Reports

Access NRC reports, ADAMS documents, Commission communications, data and research tools, plus forms, public submissions, and comment periods.
Reports
Communications
- Congressional Documents
- Generic Communications
Data & Tools
Forms & Submissions
- Forms (NRC)
- Petition for Rulemaking Dockets
Documents
Search ADAMS NRC's public document library
Licensing & Applications

Covers NRC's licensing process for facilities, materials, and reactor operators, plus tools for tracking, submitting, and reviewing applications.
Facility Licensing
Operator Licensing
Materials Licensing
- Licensing
- Materials License Process
Tools
Education & Regulatory Research

Explore NRC's regulatory research programs, staff training and apprenticeship pathways, and public education resources on nuclear science.
Regulatory Research
- Research Activities
Training & Development
- Nuclear Regulator Apprenticeship Network
- Technical Training
Education
Public Meetings & Hearings

Find NRC's public meeting schedules, adjudicatory hearings, meeting archives, and conferences such as the RIC and RAMP events.
Meetings
Conferences
- Conferences & Symposia
About NRC

Learn about NRC's leadership, priorities, and news, how to work with or contact the agency, and key legal and privacy resources.
About NRC
Get Involved
Resources

- Facilities & Safety
  
  NRC oversees the safety of nuclear reactors, materials, and waste facilities nationwide.
- Reactors, Facilities, Sites
- Safety & Security
- Radiation & Waste
- Protection
  - Radiation Protection
  - Fire Protection
- Documents & Reports
  
  Access NRC reports, ADAMS documents, Commission communications, data and research tools, plus forms, public submissions, and comment periods.
- Reports
- Communications
  - Congressional Documents
  - Generic Communications
- Data & Tools
- Forms & Submissions
  - Forms (NRC)
  - Petition for Rulemaking Dockets
- Documents
  Search ADAMS NRC's public document library
- Education & Regulatory Research
  
  Explore NRC's regulatory research programs, staff training and apprenticeship pathways, and public education resources on nuclear science.
- Regulatory Research
  - Research Activities
- Training & Development
  - Nuclear Regulator Apprenticeship Network
  - Technical Training
- Education

Breadcrumb

Home
Education & Regulatory Research
Glossary
Critical mass

Critical mass

Glossary
Critical mass

The smallest mass of fissionable material that will support a self-sustaining chain reaction.

Page Last Reviewed/Updated Monday, September 14, 2026

Nuclear Regulatory Commission

Contact Us

301-415-7000

OPA.resource@nrc.gov

To report a safety concern, call 301-816-5100

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