IE Circular No. 80-03, Protection from Toxic Gas Hazards
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
IE Circular No. 80-03
Date: March 6, 1980
PROTECTION FROM TOXIC GAS HAZARDS
Chlorine gas releases have been reported at two different reactor
facilities in the past two years.
At Millstone, in March 1978, a leak of about 100 standard cubic feet of
chlorine (about a gallon of liquid) occurred over a ten minute period.
resulting in the hospitalization of 15 people. The ventilation system
carried the chlorine into the plant buildings, where personnel distress
was noted. No injuries occurred in the buildings due to the small size
of the release.
At Browns Ferry, in June 1979, a small leak from a diaphragm on a
chlorine reducing valve resulted in the hospitalization of 5 people,
including a control room operator.
Chlorine is highly toxic, producing symptoms after several hours exposure
in concentrations of only one ppm. Concentrations of 50 ppm are dangerous
for even short exposures and 1000 ppm is fatal for brief exposures.
Chlorine, used at some power stations to control organisms in the
circulating water, is normally supplied in one ton containers or in tank
cars of up to 90 tons capacity.
Other potential sources of toxic gas that have been identified at nuclear
power plants include:
Nearby industrial facilities. At Waterford, in July 1979, construction
forces had to be evacuated for two and a half hours due to a chlorine
gas release from a nearby chemical plant.
Chlorine transportation on adjacent highways, railways and rivers.
Large tanks of aqueous ammonia stored near plant buildings
Both acid and caustic storage tanks located in a common building near
the control room. At the Dresden site, in August 1977. accidental mixing
of acid and caustic solutions resulted in toxic fumes that entered the
control room via the ventilation system.
Criterion 19 of Appendix A to 10 CFR 50 requires a control room for which
action can be taken to maintain the reactor in a safe condition under
accident conditions. The control room designs in current license
applications are reviewed for operator protection from toxic gases (as
well as radiation), in accordance with Standard Review Plan (SRP) 6.4
(NUREG 75/087 dated 11/24/75). Related information on the identification
of potential hazards and the evaluation of potential accidents can be
found in SRP sections 2.2.1-2.2.2 and 2.2.3, respectively. The SRP
references Regulatory Guide 1.78 (dated June 1974) on control room
habitability during chemical releases. It also references Regulatory Guide
1.95 on requirements for protection against chlorine releases
The majority of the plants currently operating, however, were built and
licensed prior to the development and implementation of this guidance. A
review of some older plants, with respect to toxic gas hazards indicates
that they do not have the degree of protection that would be required for
present day plants. Evaluation of the protection of control rooms from
toxic gas releases is part of the systematic evaluation program currently
being carried out on certain older plants. Also, as older facilities
submit requests for significant license amendments, their design features
(continued next page)
and controls for protection of control rooms are reviewed and, if
appropriate, are required to be changed. However, the recent history of
frequent toxic gas release incidents appears to warrant a more rapid
implementation of the newer toxic gas protection policies.
For the above reasons, it is strongly recommended that:
You evaluate your plant(s) against section 6.4 and applicable parts of
sections 2.2.1-2.2.2 and 2.2.3 of the SRP with respect to toxic gas
Where the degree of protection against toxic gas hazards is found to be
significantly less than that specified in the SRP, provide the controls
or propose the design changes necessary to achieve an equivalent level
No written response to this circular is required. If you desire additional
information regarding this matter, contact the Director of the appropriate
NRC Regional Office.
Sections 2.2.1-2.2.2 - 2.2.3 and
6.4 of NUREG 75/087
Page Last Reviewed/Updated Thursday, March 25, 2021