United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

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

Page Last Reviewed/Updated Thursday, March 29, 2012