Technical Assistant Request, Venting of Turbine Building at Grand Gulf Nuclear Station
See the memorandum from L. J. Cunningham to E. G. Adensam dated June 23, 1993.
This RSS memo responds to a technical assistance request from Region II, dated October 22, 1992, regarding the unidentified and unmonitored release pathway for noble gases and iodine from the turbine building roof hatches of the Grand Gulf Nuclear Station. HPPOS-099 and HPPOS-254 contain related topics.
RSS provided the following responses to specific questions in the TAR from Region II.
Question 1: Was it acceptable for the turbine building roof hatches to remain open, creating an unmonitored release pathway?
The turbine building roof hatches were designed to provide additional ventilation in the turbine building in case of fire. The Grand Gulf Nuclear Station SER, Section 9.4.4, Turbine Area Ventilation System, noted that failure of the system does not compromise the operation of any essential systems and does not affect the capability to safely shutdown the plant. Although no immediate safety threat was imposed, an unmonitored release pathway was created by inadvertently leaving the turbine buildings roof hatches open. Therefore, it is not acceptable to allow them to be left open and unattended for an extended period.
Question 2: Would it have been reasonable to evaluate the extent of the radiation hazards that may be present as required by 10 CFR 20.201 [or, at present, 10 CFR 20.1501]?
The licensee said that an assessment of the potential releases from the hatches was made before they were opened. The licensee consulted information from continuous air sampling and monitoring equipment located within a reasonable distance of the hatches. The air sampling equipment included charcoal filters to monitor for radioiodine. The licensee concluded that this monitoring information represented the concentrations of radioactive material in the air that would be released through the hatches. For a controlled release of short duration, such an assessment of the potential release is an adequate survey as required by 10 CFR 20.201 [or 10 CFR 20.1501]. However, the hatches were inadvertently left open and unattended for an extended period. No conscious assessment of the potential release from the hatches for the extended period was done before the hatches were opened. In cases where the hatches are to be left open for an extended period, a quantitative method of assessing the potential release should be provided. NRC does not believe the event warrants a citation for violation of 10 CFR 20.201 [or 10 CFR 20.1501]; the major issue concerns the breakdown of administrative controls.
Question 3: Should the unplanned and unmonitored release by the turbine building roof hatches be reported in the Semiannual Effluent Release Report?
According to the Grand Gulf Technical Specifications 126.96.36.199 and 188.8.131.52, a summary of all planned and unplanned quantities of radioactive liquid and gaseous effluents from the unit must be included in the Semi-Annual Effluent Release Report. Using the continuous air sampling and monitoring information, the licensee should provide a bounding estimate of the amount of radioactive material released from the hatches and include it in the Semiannual Effluent Release Report. [Note: Effluent reports are now required annually.]
The issue of unmonitored release pathways through turbine building roof hatches is not uncommon to BWRs and the necessity of monitoring turbine building effluents has been recognized. SRP 11.5, "Process and Effluent Monitoring," GDC 64, and 10 CFR 50, Appendix I, call for such monitoring. While the activity released from the roof vents may represent a small fraction of the total activity released from the plant, experience has shown that when considering the meteorology associated with a ground level release, the ground level source can account for most of the dose commitment from a facility.
In summary, the licensee left the turbine roof hatches open and unattended over an extended period due to administrative oversight. Although the licensee conducted a reasonable survey before opening the hatches for a controlled release of short duration, it was not acceptable for the turbine building roof hatches to remain open and unattended for an extended period without a continuous quantitative method for monitoring potential releases and creating an unidentified and unmonitored release pathway.
Regulatory references: 10 CFR 20.201, 10 CFR 50, Regulatory Guide 1.21, Technical Specifications
Subject codes: 2.2, 5.0, 5.5, 7.3