Information Notice No. 95-41: Degradation of Ventilation System Charcoal Resulting from Chemical Cleaning of Steam Generators
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
September 22, 1995
NRC INFORMATION NOTICE 95-41: DEGRADATION OF VENTILATION SYSTEM CHARCOAL
RESULTING FROM CHEMICAL CLEANING OF STEAM
All holders of operating licenses or construction permits for nuclear power
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to the potential degradation of ventilation system
charcoal as a result of the charcoal's exposure to chemicals during the
chemical cleaning of steam generators. It is expected that recipients will
review the information for applicability to their facilities and consider
actions, as appropriate, to avoid similar problems. However, suggestions
contained in this information notice are not NRC requirements; therefore, no
specific action or written response is required.
Description of Circumstances
On June 5, 1994, a chemical cleaning of the secondary sides of the steam
generators at Surry Unit 2 was begun. During this cleaning, containment purge
was established using train A of the auxiliary ventilation system, which
contains a safety-grade charcoal adsorber. The chemical cleaning process
involves the use of ethylene diamine tetraacetic acid (EDTA) as the cleaning
agent and of various other chemicals such as ethylenediamine (EDA), hydrazine,
ammonia, hydrogen peroxide, nitrogen, and CCl-801, a proprietary corrosion
inhibitor. During the chemical cleaning the steam generators were isolated
from the containment atmosphere and force-vented to the outdoor atmosphere
through the atmospheric steam dump relief valves. The steam generators were
rinsed to remove residual chemicals. After the rinse, the steam generators
were opened for sludge lancing of the tube sheet region.
On June 16, 1994, a strong odor of ammonia was reported in the Unit 2
containment. Concentrations were measured at 30 ppm (parts per million)
ammonia and 6 ppm hydrazine. Consequently, personnel were evacuated from the
containment. At the time of the evacuation, the chemical cleaning and rinse
had been completed on steam generators A and C and the steam generators were
vented to the containment. Because of the elevated levels of hydrazine and
ammonia in the containment, train B of the auxiliary ventilation system was
started to assist train A in reducing the airborne concentrations. Both
trains operated approximately 8 hours until chemical concentrations in the
containment were reduced.
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September 22, 1995
Page 2 of 3
As a result of the exposure of the charcoal to the chemicals, in accordance
with the technical specifications (TS), a sample of train A charcoal was taken
and a laboratory test of a sample of the sample was performed. The results of
the laboratory test showed a methyl iodide removal efficiency of 93.4 percent,
which was below the TS limit. The charcoal was replaced. A sample from
train B was tested and the results of the laboratory test of that sample
showed a methyl iodide removal efficiency of 90.7 percent. This value was
also below the TS limit, and the train B charcoal was replaced.
The failure of these samples was a surprise to the licensee. At the time the
charcoal was determined to have failed, train A had operated for 657 hours,
while the train B had operated for 360 hours. In addition, the licensee had
held discussions with the charcoal supplier during which the supplier had
indicated that exposure of the charcoal to hydrazine and ammonia in the above
noted concentrations should not have resulted in its degradation.
As a result of the experience at Unit 2, when the steam generators at Unit 1
were chemically cleaned, the licensee arranged for the containment flow to be
diverted to a non-safety-grade system containing charcoal. When the licensee
completed the cleaning operation, laboratory testing of the charcoal in the
non-safety-grade system showed that the adsorber efficiency was 3.3 percent
less than its efficiency before the chemical cleaning. On the basis of these
two experiences, the licensee concluded that discharging the air involved in
steam generator cleaning operations through systems containing charcoal was
likely to degrade the charcoal.
The licensee's laboratory tests of the charcoal were performed at 30�C [86�F]
and a relative humidity of 95 percent with a face velocity of 24.4 meters per
minute [80 feet per minute]. The laboratory tests were conducted using the
1979 version of American Society for Testing and Materials (ASTM) D3803,
"Standard Test Method for Nuclear-Grade Activated Carbon." The licensee did
not attempt to determine the chemical compound responsible for the degradation
of the charcoal. However, it and its charcoal supplier believe that the
probable culprits were EDA and EDTA.
The NRC staff held telephone conversations with charcoal suppliers and
testing laboratory representatives. Based upon these conversations, the
parties concluded that, although the ammonia did not contribute to the
degradation of the charcoal, the breakdown of hydrazine in the charcoal may
have contributed additional moisture to the charcoal resulting in its
degradation. These discussions also confirmed that both EDA and EDTA could
degrade the charcoal. The staff also noted that, had the licensee performed
the laboratory tests in accordance with the guidance in NRC Information Notice
87-32, "Deficiencies in the Testing of Nuclear-Grade Activated Charcoal,"
(Accession No. 8707070003) or in accordance with the 1989 version of ASTM
D3803, the measured degradation of the charcoal would have been greater than
that identified by the licensee.
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September 22, 1995
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Exposure of charcoal to chemical compounds can result in its degradation.
With such degradation, in the event of an accident, the charcoal may perform
at an efficiency less than that assumed in the staff's safety evaluation.
Therefore, if licensees divert air flow through charcoal adsorbers in their
ventilation systems during and/or after chemical cleaning, they may find it
appropriate to perform a laboratory test of the charcoal to ensure that the
charcoal has not degraded below its TS surveillance requirements limit.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.
/s/'d by DMCrutchfield
Dennis M. Crutchfield, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contact: John J. Hayes, NRR
1. Referenced Codes and Standards
2. List of Recently Issued NRC Information Notices
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