Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 85-30
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
April 19, 1985
Information Notice No. 85-30: MICROBIOLOGICALLY INDUCED CORROSION OF
CONTAINMENT SERVICE WATER SYSTEM
Addressees:
All holders of a nuclear power reactor operating license (OL) or
construction permit (CP).
Purpose:
This information notice is provided to alert recipients of significant
corrosion pitting due to microbiologically induced corrosion identified in
stainless steel piping sections of a service water system after an extended
plant outage. It is expected that recipients will review the information for
applicability to their facilities and consider actions, if appropriate, to
preclude similar problems occurring at their facilities. However,
suggestions contained in this information notice do not constitute NRC
requirements; therefore, no specific action or written response is required.
Description of Circumstances:
On January 26, 1984, H. B. Robinson Unit 2 was shut down and remained shut
down throughout the year to replace the lower assemblies of the steam gener-
ator and perform other maintenance work.
On November 19, 1984, Carolina Power and Light Company (CP&L) reported that
minor pinhole leaks were found in the heat affected zones of circumferential
welds joining 6-inch diameter, Schedule 10, 304 stainless steel piping that
provides service water to the four containment chilling units. Visual
inspection of the entire system revealed minor leakage at a total of 54 weld
joints, 32 inside and 22 outside containment. Further radiographic
examination revealed evidence of localized corrosion pitting on the inside
surface at many other austenitic piping weld joints of the system. Numerous
sleeve assemblies were required to restore integrity of the welds degraded
by the corrosion attack.
Discussion:
The licensee's investigation determined that the root cause of the problem
was the result of microbiologically induced corrosion (MIC). This is repre-
sentative of several similar incidents reported in construction and
operating plants in past years. A very recent example may be a large number
of leaking welds in
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IN 85-30
April 19, 1985
Page 2 of 3
the Essential Spray Pond Piping system at Palo Verde Unit 2. The licensee's
evaluation is currently underway, but their preliminary conclusion is the
problem is caused by MIC.
MIC is a form of corrosive action that occurs as a direct, or indirect, re-
sult of living organisms in contact with the materials of construction.
Microorganisms have been observed in a variety of environments including
soils, sediment, natural fresh water (e.g., wells, rivers, lakes), brackish
and sea water, as well as oil and other natural petroleum products. Many
species may form synergistic cross feeding support systems with other bac-
teria, fungi, algaes and the like to enhance survival under the most adverse
conditions. They have been known to tolerate a wide-range of temperatures
(-10 to 90C), pH values of 0 to 10.5, oxygen concentrations from zero
to almost 100 percent O2 and extreme hydrostatic pressure. There are six
different classifications of microorganisms containing over 30 species that
can be a problem, depending on the geographic location and the environmental
conditions.
The metabolic processes of organisms are sustained by chemical reactions.
These processes can significantly influence the corrosion behavior of mater-
ials by (1) destruction of protective surface films, (2) creating corrosive
deposits, and/or (3) altering anodic and cathodic reactions depending on the
environment and organism(s) involved.
Several general methods for inhibiting MIC have been employed with varied
degrees of success in recirculation systems. Among these methods were an
application of protective coatings in conjunction with cathodic protection,
corrosion inhibitors, or water chemical treatment such as periodic shock
chlorination. However, it is important to correctly diagnose the presence of
MIC and the organisms involved before attempting such corrective measures to
ensure that no products are formed that themselves have a detrimental effect
on the materials. Moreover, if water chemical treatment is used, it is
important to ensure that residual chemical levels are maintained within the
permissible range of applicable EPA requirements.
Where the above measures are not practical, it has been observed that rela-
tively rapid fluid flow tends to prevent attachment of organisms whereas low
flow rates or stagnant conditions favor biofouling and concentration cell
corrosion. Thus, cleaning and dry lay up, or periodic recirculation
flushing, during extended outages to mitigate know biological activity would
appear to be prudent alternatives.
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IN 85-30
April 19, 1985
Page 3 of 3
No specific action or written response is required by this information
notice. If you have any questions about this matter, please contact the
Regional Administrator of the appropriate NRC regional office or the
technical contact listed below.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: William J. Collins, IE
(301) 492-9630
Attachment: List of Recently Issued IE Information Notices
