NUCLEAR
The following extracts are
from an article
written by Don A. Hill, PE
of the Washington Public Power Supply System
and published in the
November 1996 issue of the
"Journal of Protective Coatings and
Linings"
Developing a
Maintenance Program for a
Nuclear Power
Plant
A comprehensive maintenance painting
program
begun in 1991 has improved the facility,
raised morale, and saved money
at a
Washington nuclear power plant.
In February 1980, Washington Public Power Supply System made a
commitment to follow U.S. Regulatory Guide 1.54, Quality Assurance
Requirements for Protective Coatings Applied to Water-Cooled Nuclear Power
Plants. At the time of committing to this government guide, Washington
Public Power was constructing Washington Nuclear Plant-2 (WNP-2). The
Guide requires that coatings used in the primary radiation containment of
nuclear plants be manufactured and applied in accordance with ANSI N101.4,
Quality Assurance for Protective Coatings Applied to Nuclear
Facilities.
By 1984, WNP-2 was in the final construction phase, and
costs were running high. Despite the commitment to Regulatory Guide 1.54,
Washington Power made the painful decision to eliminate all painting
activity except that which was considered critical. Items such as primed
steel, equipment, piping, and weld areas throughout the plant, as well as
exposed bare steel above the water line in the wet well, were left for
future paint crews.
Except for plant modifications, the steel
surfaces were left to rust. No painting was done from 1984 until 1991. By
1991, morale was down and costs were higher than normal for
decontamination of floors and equipment. Radiation dose was high; due to
the condition of the plant and roughness of the various surfaces,
radiation contamination was difficult to remove. The US Nuclear Regulatory
Commission (NRC) asked for a painting program to improve ease of
decontamination. Management saw the need to begin a catch-up program for
the maintenance of the plant. A consultant was contracted to advise WNP-2
where and how to start this maintenance effort.
his article
describes the maintenance program that was begun in 1991.
BACKGROUND
WNP-2 is a Boiling Water
Reactor (BWR) plant. Two of its main components are the dry well and the
wet well.
The dry well is a steel pressure vessel designed for a
BWR type nuclear power plant. The dry well is usually shielded with
reinforced concrete shield plugs and double entry doors. It contains
piping, pumps, valves, and vital equipment for operation of the plant. The
dry well is situated above the wet well and is not occupied during plant
operations unless required. It has a very humid, warm and high radiation
radiation environment.
The wet well is a steel pressure vessel that
is below the reactor. It stores a large volume of water and has a
connecting vent system to the dry well. The water and vent system cool the
steam in the event of an accident. Both wells are part of the plant's
primary containment area, where risks of severe radiation exposure are
highest.
According to ANSI N101.4, the dry well and wet well are
considered Quality Class 1 areas.
As part of the licensing
procedure for operating a nuclear power facility, WNP-2 prepared a
Preliminary Safety Analysis Report (SAR) during construction.
ANSI
N101.4 outlines the quality assurance requirements for coatings that are
tested under ANSI N101.2. The objective is to have control and
traceability from the manufacturing phase through application and final
inspection.
ANSI N101.2 is a testing standard that is acknowledged
by the NRC as a means for qualification of coatings (paints) used within
Level 1 areas of a nuclear power facility. It outlines typical Design
Basis Accident (DBA) conditions of time, temperature and pressure testing
curves for both types of nuclear power plants. (DBA analysis is intended
to identify the most severe design conditions that could occur.) Radiation
exposure is outlined as well as thermal conductivity.
SURVEY OF THE PLANT
A complete coating
survey was scheduled for the fall of 1991 and during the refueling outage
of March 1992. Its objective was to answer several questions.
* What is
the condition of the coatings and overall condition of the plant?
*
What areas or items have priority for painting and why?
* What is the
condition of Quality Class 1 areas?
The condition survey was
completed by a three-person team using 3 tools.
* Video camera: A
video camera with a 30-to-1 lens, with numbered indexed frames, was used
to document the conditions of the plant. Since videotaping allows
simultaneous picture and sound, comments were made by the coatings
engineer about the condition of each item shown; the environment of the
item (e.g., damp, dry, hot, humid, high radiation area ); the type of
surface preparation that would be needed; and the type of coating that
would be required (e.g., epoxy, alkyd, epoxy ester, acrylic, etc.).
Twenty-two VCR tapes at standard speed were require for this audio-visual
plant survey.
* Computer printout: All of the data gathered by the
team, including that given on the videotapes, were compiled and presented
in a spreadsheet showing when the item should be coated based upon the
following factors:
* the area within the plant;
* its condition
overall (integrity);
* the radiological dose on the area and the ease
of the surface to be decontaminated (decon factor);
* corrosion
activity in the area (humidity; dry);
* how often the area is visited
during operations (traffic);
* the difficulty in physically getting to
the item to make the needed coating repairs or rework (difficulty); and
* the cosmetics in the area, e.g., how it looks overall and whether
the various coating colors make the area unsightly (cosmetics).
OBSTACLES TO BE CONSIDERED
From the time of
construction to the time of the survey, the state of the art changed
drastically within the coating industry to meet the needs of imposed
environmental regulations, both state and federal. Coating materials
mentioned for Level 1 areas and also within the plant's Design
Specifications formulated for 1976 through the 1980s were no longer
suitable. Therefore, a new direction and coating philosophy were suggested
that would benefit WNP-2 in both cost savings and control of radiation
exposure. The goal for radiation exposure was to control it to the lowest
level possible, known as ALARA. As Low As Reasonably Achievable; however,
many question specific to nuclear facilities had to be addressed before
products or methods could be changed.
* What changes, if any, needed to
be made in the Technical Specifications?
* What changes, if any, needed
to be made in the Design Specifications?
* Would a 10 CFR 50-59 review
be needed?
TESTING
PROGRAMS
For Level 1 areas (work within the dry well and wet
well), WNP-2 had to comply with its commitment to Regulatory Guide 1.54.
Thus, WNP-2 began an extensive testing program to qualify coatings for use
within the plant's Level 1 area. In the process, WNP-2 took advantage of
the latest coating technology for both the dry well and wet well.
A
product search began. The research involved gathering product data from as
many sources as possible. Thirty-five technical data sheets were reviewed.
Material safety data sheets were then requested for those materials that
appeared to be promising. These data sheets were also reviewed by safety
and plant chemistry personnel as well as the coatings engineer. Liquid
samples of candidate materials were requested for application screening
tests. This allowed WNP-2 to compare each material according to physical
characteristics, such as hiding power, odor, film build, sag point, and
gloss; and compatibility with and adhesion to coating systems used during
construction.
An experienced applicator was used to perform test
applications and gather information about application properties such as
ease of use. The coating engineer reviewed the test applications from a
technical viewpoint and performed adhesion tests in accordance with ASTM D
4541, Method for Pull-Off Strength of Coatings Using Portable Adhesion
Testers[5]. These screening procedures allowed the utility to determine
the most promising coating materials from the standpoints of engineering
properties and application.
DBA testing was the next part of the
testing program. There are, according to ASTM D 3911 (and earlier ANSI
N101.2), 2 phases of DBA testing. One is DBA without radiation exposure,
and the other is DBA with radiation exposure. In many cases, exposure to
radiation increases the success for such coatings to pass a DBA. Radiation
does not take within the autoclave of the DBA test but instead is
performed separately at a lab qualified to expose such panels to radiation
prior to the DBA test.
Testing for surface tolerance was also part
of the evaluation program. Surface tolerance at WNP-2 is defined as
capable of adhering to a surface prepared to SSPC-SP 3. Power Tool
Cleaning, with mill scale previously removed in prior years by blasting.
Some rust (tight) can remain on the surface. All prepared surfaces were
documented by photography before being coated for testing.
After
screening, the choice for DBA and radiation testing was narrowed down to 9
candidate materials tested. Fifty panels, each measuring 2 x 4 x 1/4 in.
(5 x 10 x 0.6 cm) were prepared according to Section 4 requirements of
ASTM D 5139. Specification for Sample Preparation for Qualification
Testing of Coatings To Be Used in Nuclear Power Plants. Of these 18 were
radiated and DBA tested; 18 were non-irradiated and DBA tested; 5 were
used to determine decontamination removal; and 9 were kept for control
purposes.
The time, temperature, and pressure curve selected for
DBA testing using an autoclave was the 340-degree BWR curve of ASTM D
3911, Method for Evaluating Coatings Used in Light-Water Nuclear Power
Plants at Simulated Design Basis Accident (DBA) Conditions [7]. (There are
2 curves within this ASTM standard. the 340-degree is the BWR - Boiling
Water Reactor - curve. The 307-degree curve in D 3911 is the PWR -
Pressurized Water Reactor - curve.) Radiation was performed in a pool with
the panels inserted within canisters having a nitrogen atmosphere. The
dose rate was 3 milarads per hour (1.1 x 10 to the power of 9) radiation
total, and the pool temperature was 85 degrees F (29 degrees C) or less.
For DBA testing, all coatings, both radiated and non-irradiated, were
evaluated 2 hours after removal from the autoclave and again after 1 week.
Acceptance criteria were those of ASTM D 3911, which states that no
flaking, delamination, peeling, or chalking is permitted. Blisters, if
present, are to be unbroken.
