Document: NRC Regulatory Guide
Document ID: de79d411-4fc9-456e-a5a0-f4a910ca4c9a
Document Type: regulatory_guide
Title: Assumptions Used for Evaluating a Control Rod Ejection Accident for Pressurized Water Reactors (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2111/ML21119A157.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.77
CFR Part: 
CFR Title: 

Content:
tability evaluation called HABIT. HABIT is an integrated set of computer codes that the NRC uses to evaluate CR habitability and estimate the control room personnel’s exposure to a chemical release. Revision 1 of RG 1.78 endorsed an earlier version of HABIT, which is described in NUREG/CR-6210, Supplement 1, “Computer Codes for Evaluation of Control Room Habitability (HABIT V1.1),” issued October 1998 (Ref. 9). More recently, the NRC staff endorsed a newer version of HABIT in NUREG-2244, “HABIT 2.2: Description of Models and Methods,” issued May 2021 (Ref. 10). This latest version of HABIT is available at the Radiation Protection Computer Code Analysis and Maintenance Program Web site, https://ramp.nrc-gateway.gov/. Background GDC 19 requires operating reactor licensees to provide a CR from which actions can be taken to maintain the nuclear power unit in a safe condition under accident conditions including protecting the CR from hazardous chemicals that may be discharged as a result of equipment failures, human errors, or events and conditions outside the control of the NPP. Based on NUREG/CR-6624, “Recommendations for Revision of Regulatory Guide 1.78,” (Ref. 11), the NRC issued RG 1.78, Revision 1 in 2001. It updated the two guidance tables (i.e., Table C-1 and Table C-2) with the latest IDLH values and established the connection of CR habitability and hazardous chemicals from mobile (e.g., tank trucks, railroad cars, and barges) and stationary (e.g., storage tanks, pipelines, fire-fighting equipment) sources which in turn provided the segue for further validating the criteria and for developing the procedures used in CR habitability evaluations. Further, NUREG/CR-6624 also affirmed that all nuclear reactor CR operators should be trained and expected to don personal protection equipment (PPE) such as respirators and protective clothing within 2 minutes, so that they will not be subjected to risk from prolonged exposure more than two minutes at the