Resolution of Generic Safety Issues: Issue 83: Control Room Habitability (Rev. 3) ( NUREG-0933, Main Report with Supplements 1–34 )
On August 18, 1982, the ACRS issued a letter671 to the Commission which: (1) identified deficiencies in the maintenance and testing of engineered safety features designed to maintain control room habitability; (2) provided examples of design and installation errors, including inadvertent degradation of control room leak tightness; and (3) cited a shortage of NRC and licensee personnel knowledgeable about HVAC systems and nuclear air-cleaning technology. These ACRS concerns encompassed both plant licensing review and operations/inspection activities. In January 1983, the staff responded436 to the ACRS concerns and recommended increased training of NRC and licensee personnel in inspection and testing of control room habitability systems. The staff also provided a profile of control room HVAC system component failures based on an analysis of LERs from 1977 through mid-1982. On April 28, 1983, NRR and OIE representatives met with the ACRS Subcommittee on Reactor Radiological Effects to discuss the staff response.
In May 1983, the ACRS issued a letter673 to the EDO which expressed continuing concerns about control room habitability and provided both general and specific comments and recommendations for further staff evaluation. In July 1983, NRR transmitted to the EDO a joint NRR/OIE proposal674 for evaluating the ACRS comments and recommendations and the adequacy of the control room habitability licensing review process and criteria. In August 1983, the EDO indicated agreement675 with the proposal and directed NRR to coordinate with OIE and the NRC Regional Offices to complete the program and submit a report to the EDO by June 1, 1984. In September 1983, NRR established676 a Control Room Habitability Working Group and a Steering Group for conducting and guiding the proposed review. Other generic issues that addressed related concerns were B-36, B-66, and III.D.3.4.
Loss of control room habitability following an accident release of external airborne toxic or radioactive material or smoke can impair or cause loss of the control room operators' capability to safely control the reactor and could lead to a core-damage accident. Use of the remote shutdown station outside the control room following such events is unreliable since this station has no emergency habitability or radiation protection provisions similar to the control room.
The Control Room Habitability Work Group was expected to identify any recommended actions that would correct significant deficiencies in control room habitability design, installation, test, or maintenance.
In June 1984, NRR provided a report678 to the EDO along with its plans for implementing the recommendations of the report, including a survey of several operating plants. Based on the ongoing staff work, it was concluded that a solution had been identified and a schedule679 for the resolution of the issue was developed by DSI/NRR.
PNL completed a report677 entitled "A Probabilistic Examination of Nuclear Power Plant Control Room Habitability During Various Accident Scenarios," and the findings of the survey of operating plants were published in NUREG/CR-4960.1371 As a result of these studies, it was recognized that the methodology used to evaluate control room habitability system design needed improvement. Accordingly, the staff initiated activities to develop: (1) improved methods for calculating control room dose and exposure levels; (2) improved meteorological models for use in control room habitability calculations; and (3) revised exposure limits to toxic gases for control room operators.
The results of the improved methods were documented in NUREG/CR-5669247 and NUREG/CR-6210249 and the HABIT Code was developed to provide an integrated code package for evaluating control room habitability. NUREG-1465,1465 published with the resolution of Issue 155.1, will provide updated source term information for the evaluation of control room designs. As recommended296 by the ACRS, the staff was expected to consider NIOSH recommendations for toxic chemicals in its revision of Regulatory Guide 1.78.1373 Thus, this issue was RESOLVED with no new requirements.335 Consideration of a license renewal period of 20 years would not have changed this conclusion.
However, in June 2003, NRC Generic Letter 2003-011812 was issued to address findings at U.S. nuclear power plants which suggested that licensees may not have been meeting the control room licensing and design bases, and applicable regulatory requirements, and existing TS surveillance requirements may not have been adequate. The affected licensees were requested to submit information demonstrating that their control rooms complied with existing licensing and design bases, and applicable regulatory requirements, and that suitable design, maintenance, and testing control measures were in place.