Technical Assistant Request, Venting of Turbine Building at Grand Gulf Nuclear Station
HPPOS-326 PDR-9308260262
Title: 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
6.9.1.8 and 6.9.1.9, 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
Applicability: Reactors