CONTROL ROOM HABITABILITY 

TAC No. MC0021 Final Update: 04/07/09 

 Lead NRR Division: 

 DSS Supporting Division: 

 DORL 

 CTL: N/A 

 GSI No.: N/A 

MILESTONE DATE (T/C) 

Staff review of NEI 99-03 and redline and strikeout version provided 

to NEI Control Room Habitability task force 

04/17/01 (C) 

Staff will prepare Generic Letter and develop draft Regulatory 

Guides on Control Room Habitability at Nuclear Power Reactors 

(DG-1114), Demonstrating Control Room Envelope Integrity at 

Nuclear Power Reactors (DG-1115), Methods and Assumptions for 

Evaluating Radiological Consequences of Design Basis Accidents at 

Light Water Nuclear Power Reactors (DG-1113), and Atmospheric 

Relative Concentrations for Control Room Radiological Habitability 

Assessments at Nuclear Power Plants (DG-1111)

07/01/01 (C) 

Office review of draft Regulatory Guides DG-1111 and DG-1113 12 /31/01 (C) 

Office review of draft Regulatory Guides DG-1114 and DG-1115 and 

draft Generic Letter

 03/01/02 (C) 

Brief CRGR on draft Regulatory Guides DG-1111 and DG-1113 12/31/01 (C)

Brief CRGR on draft Regulatory Guides DG-1114 and DG-1115 and 

draft Generic Letter draft

GENERIC LETTER: 04/29/02 

(C) DG-1114, DG-1115: 

03/11/02 (C)

Issue draft Regulatory Guides DG-1111, DG-1113, DG-1114, and 

DG-1115 and draft Generic Letter for public comment draft

GENERIC LETTER: 

05/09/02 (C) 

DG-1111: 12/31/01 (C) 

DG-1113: 01/31/02 (C) 

DG-1114: 03/28/02 (C) 

DG-1115: 03/28/02 (C) 

Public meeting on draft Regulatory Guides DG-1111, DG-1113, DG1114, and DG-1115 and draft Generic LetterRI: 07/11/02 (C) 

RII: 07/16/02 (C) 

RIII: 08/06/02 (C) 

RIV: 07/18/02 (C)

Resolve public comments on draft Regulatory Guides DG-1111, DG1113, DG-1114, and DG-1115 12/30/03* 

Office review and concurrence of final Regulatory Guides and 

Generic Letter 

DG-1111, DG-1113: 

01/31/03 (C) 

DG1114, DG-1115, and 

GENERIC LETTER 2003-01: 

03/24/03 (C)

Brief ACRS on final Regulatory Guides and Generic Letter 04/10/03 (C) 

MILESTONE DATE (T/C) 

Brief CRGR on final Regulatory Guides and Generic Letter 04/22/03 (C) 

Commission Information Paper on Generic Letter 06/03 (C) 

Issue final Regulatory Guides and Generic Letter 06/03 (C) 

Review 60 days responses to Generic Letter 12/30/03 (C) 
Develop replacement technical specification for Attachment B to 

Regulatory Guide 1.196 

1/24/05 (C)* 

Develop response to TSTF letter of 3/8/04 1/24/05 (C) 

Transmit staff proposal for revision to TSTF-448 1/24/05 (C)

Provide final NRC position on TSTF 448 Rev 2 in a letter to TSTF 

working group. Conduct public meeting April 2006. Update STS 

May 2006. 

12/28/05 (C) & 3/10/06 (C) 

04/20/06 (C) Meeting 

05/12/06 (C) STS

Complete review of Generic Letter response and to determine if 

additional action is warranted

12/17/2007 (C) 

Closeout Of Multi-plant Action 

MPA-L301 GENERIC LETTER 

(GL) 2003-01 

Package ML073460498

Description: In its review of license amendment submittals over the past several years, the staff has 

identified numerous problems associated with the assessment of control room habitability. These 

problems have included the overall integrity of the control room envelope and the manner in which 

licensees have demonstrated the ability of their control room designs to meet GDC-19. Licensees have 

failed to: 

1. Assess the impact of proposed changes to plant design, operation, and performance on control 

room habitability, 

2. Identify the limiting accident, 

3. Appropriately credit the performance of control room isolation and emergency ventilation systems 

in a manner consistent with system design and operation, and 

4. Substantiate assumptions regarding control room unfiltered inleakage. 

In response to Item 4 above, several utilities performed testing of their control room envelope (CRE) to 

determine unfiltered inleakage using methods from ASTM E741-93, "Standard Test Methods for 

Determining Air Change in a Single Zone by Means of a Tracer Gas Dilution." As of May 2003, about 

30 percent of the operating plants’ control rooms had been tested. At that time, all of the control rooms 

except one measured unfiltered inleakage which exceeded the design basis analysis assumptions. In 

several cases, the measured inleakage exceeded the design basis value by over an order of magnitude. 

In most of the cases to date, licensees have been able to ultimately demonstrate compliance to GDC-19 

through corrective action and retesting or by re-analysis. The nearly 100 percent failure rate of such a 

large fraction of the operating plant control rooms created a large uncertainty in the ability of the 

remaining untested facilities to meet control room habitability requirements. These control room 

habitability issues adversely affected the timely review of many license amendment requests. Licensee 

and staff expended significant resources to resolve differences regarding licensing and design basis 

issues and weaknesses in analysis assumptions, inputs and methods. While the capability of untested 

control rooms to meet their design basis was in question, the staff has reasonable assurance that 

continued operation was safe since compensatory measures; e.g., use of self-contained breathing 

apparatus and potassium iodide were established by licensees. 

Background: General Design Criterion (GDC-19), "Control Room," of Appendix A, "General Design 

Criteria for Nuclear Power Plants," to 10 CFR Part 50, establishes criteria for a control room. It requires 

that a control room be provided which allows operators to take actions under normal conditions to operate 

the reactor safely and to maintain the reactor in a safe condition under accident conditions. GDC-19 also 

requires that equipment be provided at locations outside the control room with the design capability for 

hot shutdown of the reactor, including the necessary instrumentation and controls that both maintain the 

reactor in a safe condition during hot shutdown and possess the capability for the cold shutdown of the 

reactor through the use of suitable procedures. GDC-19 also requires that adequate radiation protection 

be provided to permit access and occupancy of the control room under accident conditions without 

personnel receiving radiation exposures more than 5 rem whole body, or its equivalent to any part of the 

body, for the duration of the accident. Applicants to build or license a new plant under Part 50 after 

January 10, 1997, applicants for design certification under Part 52 after January 10, 1997, applicants to 
build a new plant under Part 52 who don’t reference a standard design certification, or current licensees 

who want to use an alternative source term as allowed by 50.67, are required by GDC-19 to use as the 

control room dose criterion 0.05 Sv (5 rem) total effective dose equivalent (TEDE). In March 1998, the 

staff briefed the Office of Nuclear Reactor Regulation Executive Team (ET) on its concerns related to the 

infiltration testing results and other aspects of control room habitability. The ET directed the staff to work 

with the Nuclear Energy Institute (NEI) to resolve the issues. Pursuant to this direction, the staff cohosted, with NEI and the Nuclear Heating Ventilation and Air Conditioning Users Group (NHUG), a 

workshop on control room habitability in July 1998. Following that workshop, NEI agreed to form a task 

force to address control room habitability. In August 1999, NEI submitted for staff review and comment a 

draft of a proposed NEI document intended to address this issue. This document, NEI 99-03, entitled, 

"Control Room Habitability Assessment Guidance," did not adequately address the staff’s concerns. In 

response to the staff concerns, NEI agreed in December 1999 to restructure NEI 99-03. During the 

period January through June 2000, the NEI task force met with the NRC staff in a series of public 

meetings to resolve outstanding issues and to discuss the content of NEI 99-03. A revision to NEI 99-03 

revision was sent to the staff on October 13, 2000. The staff reviewed the October 13, 2000, revision and 

determined that, while there was much agreement on positions taken in the document, areas remained 

where the staff and industry were in disagreement. The staff determined, and NEI agreed, that the staff 

should reflect its position in formal regulatory guidance with outstanding issues resolved through the 

public comment process. 

In June 2001, NEI issued Revision 0 of NEI 99-03, "Control Room Habitability Assessment Guidance." 

This version was substantially the same as the October 13, 2000, draft reviewed by the NRC staff. 

The NRC staff pursued a solution to the control room habitability issues with the NEI task force. The staff 

indicated its willingness to incorporate up-to-date information into its assessment of radiological analyses, 

consider possible changes in the radiological dose acceptance criteria and possible reductions in the 

conservatisms in control room habitability analyses. 

NEI did not commit to making this industry initiative binding on individual utilities. The staff believed that a 

voluntary approach would not adequately resolve its concerns and that some generic approach would be 

needed. A Generic Letter would request licensees to take action to evaluate, in light of the ASTM E741 

testing results to date, how licensees meet the requirements of GDC-19 with respect to unfiltered 

inleakage to their control room envelopes. 

During staff interactions with the NEI issue task force, many issues were discussed. The staff believed 

that additional regulatory guidance was necessary in order that control room habitability issues were 

addressed in a complete and thorough manner. In addition, it was the staff’s opinion that the regulatory 

information associated with control room habitability needed to be updated to reflect current knowledge. 

In meetings with the NEI Task Force on Control Room Habitability, changes to design basis accident 

radiological analysis assumptions were discussed. For those facilities whose licensing basis is based 

upon the TID-14844 source term, the staff and industry believed that it was necessary to consolidate 

existing information and to reflect current knowledge into one regulatory guide. For those licensees that 

implement an alternative source term as allowed by 10 CFR 50.67, Regulatory Guide 1.183, "Alternative 

Radiological Source Terms for Evaluating Design Basis Accidents at Nuclear Power Reactors," provided 

guidance for performing control room radiological analyses. These regulatory guides provided the 

industry and public more realistic assumptions for performing radiological analyses. 

The staff also believed that creating regulatory guidance on meteorology for control room habitability 

assessments was necessary and appropriate. It had been almost 20 years since the staff updated its 

information on control room habitability. Various staff and industry studies had been conducted in those 

20 years. These studies had identified issues which were addressed to only a limited extent in the 

previous guidance on control room habitability. A regulatory guide on control room habitability would 

assist licensees in their determination of the present state of the integrity of their control room envelope. 

Along with the control room habitability regulatory guide, an additional regulatory guide on control room 

envelope integrity testing would provide guidance to the industry on how plants may determine control 

room envelope integrity and continually demonstrate that integrity. Such regulatory guidance would 

utilize the information obtained from the testing that had already been conducted on 30 percent of the 
control room envelopes. Therefore, control room habitability would be addressed through a Generic 

Letter and new Regulatory Guides on: 

1. Control room habitability, 

2. Control room envelope integrity testing, 

3. Meteorology for control room habitability assessments, and 

4. Design basis accident radiological analyses. 

Additionally, to support licensees that begin testing the integrity of the control room envelope by 

measuring unfiltered inleakage, the staff proposed to the Technical Specifications Task Force (TSTF) 

changes to standard technical specifications on control room emergency ventilation systems. The staff 

discussed these changes with the NEI control room habitability task force. The staff considered 

resolution of this issue supportive of the NRR pillars of maintaining safety, increasing public confidence 

(both by restoring control room integrity to the level assumed in the facility’s licensing basis), increasing 

effectiveness and efficiency of key NRC processes (via a generic approach to resolution rather than the 

current plant-by-plant approach), and reducing unnecessary regulatory burden and increasing realism 

(due to possible relaxation in certain analysis assumptions and acceptance criteria, based on current 

information). 

Four draft regulatory guides, numbered DG-1111, DG-1113, DG-1114 and DG-1115, were issued for 

public comment. Proposed Generic Letter 2002- XX, "Control Room Envelope Habitability," (ADAMS 

accession number ML021430317) was published on May 9, 2002, at 67 FR 31385. The staff completed 

review and disposition of comments received during the public comment period and completed making 

necessary revisions to the draft guides and generic letter. Regulatory Guide 1.194, Atmospheric Relative 

Concentrations for Control Room Radiological Habitability Assessments at Nuclear Power Plants, 

formerly DG-1111 was issued in June 2003. Regulatory Guide 1.195, Methods and Assumptions for 

Evaluating Radiological Consequences of Design Basis Accidents at Light-Water Nuclear Power 

Reactors, formerly DG-1113, Regulatory Guide 1.196, Control Room Habitability at Light-Water Nuclear 

Power Plants, formerly DG-1114; and Regulatory Guide 1.197, Demonstrating Control Room Envelope 

Integrity at Nuclear Power Reactors, formerly DG-115, were issued in May 2003. Generic Letter 2003-01 

was issued on June 12, 2003. The staff’s proposed changes to technical specifications for control room 

emergency ventilation systems were included in Appendix B of Regulatory Guide 1.196. 

During the finalization of the Regulatory Guides and the Generic Letter, NEI provided Revision 1 to NEI 

99-03, "Control Room Habitability Assessment Guidance," March 11, 2003. The Generic Letter and 

Regulatory Guides referred to Revision 0 of NEI 99-03. Staff assessed the impact of Revision 1 and 

determined that revisions to the Generic Letter and Regulatory Guides were not necessary. 

On December 30, 2002, NEI provided the Industry/ TSTF Standard Technical Specification Change 

Traveler TSTF-448, "Control Room Habitability," to the NRC for consideration. On July 1, 2003, the staff 

transmitted to NEI comments on Rev. 0 of TSTF-448. The staff held a meeting with the TSTF/NEI on 

July 11, 2003, to discuss its comments on Rev. 0. On August 19, 2003, Technical Specifications Task 

Force (TSTF) transmitted to the staff Rev. 1 to TSTF-448. On December 16, 2003, the staff provided 

comments and a request for additional information on Rev. 1. In a March 8, 2004, letter, the TSTF 

responded to the staff ’s comments. In that letter the TSTF also identified what they considered to be 

beneficial revisions to TSTF-448. The TSTF indicated that if the staff agreed with these proposed 

revisions a formal revision to TSTF-448 would be provided. 

Originating Document: None. 

Regulatory Assessment: The staff believes that the potential deficiencies in the control room habitability 

designs, operations, and analyses represent safety issues that warrant resolution. It is important to 

recognize that the objective of control room habitability requirements, such as those in GDC-19, is not to 

minimize operator exposure for the purposes of ALARA (which is controlled under 10 CFR Part 20), but to 

provide a habitable environment in which to take action to operate the reactor safely under normal 

conditions and to maintain it in a safe condition under accident conditions. The dose criterion of 5 rem 

whole body was selected as it was believed that operations personnel would not be distracted from 
necessary plant operations and would not unnecessarily evacuate the controls area due to concerns for 

their personal safety. Protection against smoke and other toxic gases is also necessary since these 

hazards could cause, in some cases, immediate physical impairment or incapacitation of control room 

operators. While toxic gases are considered in control room habitability analyses in accordance with the 

guidance in Regulatory Guide 1.78, the potentially toxic byproducts of fires and their impacts on control 

room habitability were not considered a problem in the past because of the presumed integrity of the 

control room envelope. In the past, a fire outside the control room was considered to have no impact 

upon the operators because smoke and toxic fire gases were never presumed to enter the control room 

envelope. If a fire occurred in the control room, the operators had the remote shutdown areas for 

controlling the reactor. Testing of the control room envelope’s integrity has demonstrated that the 

perceived integrity does not exist. Consequently, some portions of the smoke issue may be covered 

under this action plan while other aspects may not. The staff considered the risk impacts of control room 

habitability and made a preliminary determination that control room habitability has not been addressed in 

current PRAs because: 

1. It has been assumed that the design basis was being met, and 

2. Quantification of the risk associated with failure to meet the design basis for control room 

habitability is not addressed by current metrics, methods, and risk experience data. 

Current Status: 

On December 17, 2007, the NRC issued a memo (Accession No. ML072670328) that closed out MultiPlant Action L301 GL 2003-01 “Control Room Habitability.” All plant specific licensing activities 

associated with GL 2003-01 were closed, as well as, this action plan. 

Contacts: 

NRR Lead PM: Jay Robinson, PGCB/DRL, 415-2878 

NRR Technical Contacts: R. L. Dennig, SCVB/DSS, 415-1156 

H. Walker, SCVB/DSS, 415-2827 

References: 

USNRC, Title 10 Code of Federal Regulations Part 50, Appendix A. 

USNRC, "Clarification of TMI Action Plan Requirements," NUREG-0737, 1980. 

USNRC, "Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power 

Plants,"NUREG-0800. 

L. Soffer, et al, "Accident Source terms for Light Water Nuclear Power Plants," NUREG-1465, 1995. 

Murphy, K. G. and Campe, K. W., "Nuclear Power Plant Control Room Ventilation System Design for 

Meeting General Criterion 19, " published in proceedings of 13th AEC Air Cleaning Conference. 

Driscoll, J. W., "Control Room Habitability Survey of Licensed Commercial Nuclear Power Generating 

Stations," NUREG/CONTROL ROOM-4960, 1988. 

DiNunno, et al, "Calculation of Distance Factors for Power and Test Reactor Sites," Technical Information 

Document TID-14844, USAEC, 1962. 

USNRC, Regulatory Guide 1.183, "Alternative Radiological Source Terms for Evaluating Design Basis 

Accidents at Nuclear Power Reactors," 2000. 

American Society for Testing and Materials ASTM E741, "Standard Test Methods for Determining Air 

Change in a Single Zone by Means of a Tracer Gas Dilution," 1993.