Qualified Coatings in Nuclear Power Plants. Commercial products

40ª Reunión Anual de la SNE
Valencia, España, 1-3 octubre 2014
Qualified Coatings in Nuclear Power Plants. Commercial products.
(Pinturas homologadas en centrales nucleares. Productos comerciales)
Javier Bárcena (1) / Borja Nuñez (1) / Mariluz Romero (1) / Marta Baladía (2)
(1) Empresarios Agrupados / (2) CNAT
[email protected] / [email protected] / [email protected] / [email protected]
Abstract
Recently, the supplier of paints that were qualified for use in nuclear applications as
protective coatings have ceased to supply in Spain the paints that was used in areas or
components with special requirements for nuclear power plants (NPPs). This lack of
the common commercial products called for the search for and homologation of other
products.
A study was performed on the current status of the homologation of commercial
products for NPPs and on the codes and standards governing them. The criteria to be
met have been defined and the results of the tests performed on the selected paints
have been compared against the established criteria so as to allow the homologation of
the paints.
Resumen
Recientemente, el fabricante de pinturas homologadas para aplicaciones nucleares ha
dejado de suministrar en España las pinturas que se venían aplicando como
recubrimiento en las centrales nucleares (CC.NN.) en zonas o componentes con
requisitos especiales. La falta de los productos comerciales habituales ha forzado la
búsqueda y homologación de otros productos.
Se ha realizado un trabajo sobre el estado de homologación actual de los productos
comerciales para CC.NN. y sobre las regulaciones y normas que rigen este tema
aplicables a cada Central (Almaraz y Trillo), definiendo los criterios que deben cumplir
y comparando los resultados de los ensayos realizados en las pinturas seleccionadas
con los criterios establecidos, lo que permite su homologación.
1. INTRODUCTION
This paper presents the work being conducted to qualify protective coatings (paints)
for use in Almaraz and Trillo NPPs.
Such paints are mainly used in existing NPPs for maintenance purposes (repairing or
patching) of Systems, Structures or Components (SSCs) as well as for painting of new
installed SSCs inside the controlled area. Maintenance of coatings implies, in some cases,
the application of new paints on already coated substrates.
The need for new qualified coatings arises because the supplier has stopped
providing NPPs in Spain with the qualified coatings that had been being used until recently
in nuclear applications. Thus, new ones have had to be qualified.
To do this, the requirements for coatings of NPPs were first identified. Then, a set of
criteria was established for each NPP and Service Level according to their technology, the
40ª Reunión Anual de la SNE
Valencia, España, 1-3 octubre 2014
legislation and licensing commitments. Lastly, the market was explored and available
products were matched with the established criteria.
In addition, adherence tests have been carried out to analyse the performance of the
qualified coatings when they are applied on the existing ones.
Among the problems encountered for homologation were that the legislation and
licensing commitments were unclear or poorly defined; moreover, few manufacturers could
prove compliance with strict nuclear requirements.
2. OBJECTIVE
Protective coatings are used throughout NPPs in different areas and on a wide range
of SSCs. They are applied either inside the Reactor Containment (RC) or in controlled or
conventional areas, on top of safety-related SSCs or non safety-related ones and on steel
or concrete substrates. This work focuses mainly on maintenance coatings applied in
controlled areas (including the RC) and on safety-related SSCs of existing NPPs (Service
Levels I, II and III, defined below).
The aim of the work is to identify the requirements demanded to the different
coatings depending on their Service Level at the nuclear plant, and to find commercial
coatings that can be used in existing NPPs during maintenance operations in order to
qualify them.
3. REQUIREMENTS FOR PROTECTIVE COATINGS
Protective coatings used for these purposes have two main objectives: to prevent
corrosion and to ease decontamination of surfaces. Additionally, it can be used for marking
or colouring. However, as SSCs thus coated may be affected by accident, the coatings
used are required to meet specific requirements so as not to interfere with the performance
of the safety systems.
Requirements should be defined based on applicable legislation, codes and
standards. U.S. codes and standards have been followed to set out requirements, in
particular, Regulatory Guide 1.54 [1] and Standard ASTM D5144 [2].
Figure 1. Service Levels and relation to safety.
40ª Reunión Anual de la SNE
Valencia, España, 1-3 octubre 2014
In them, the requirements that coating systems must meet according to the Service
Level are set out, along with the definition of the test methods to be followed. Coatings are
classified according to their service level as follows (See Figure 1):

Nuclear Service Level I: used in areas inside the RC

Nuclear Service Level II: used in areas outside RC subject to radiation or
contamination. Not safety related.

Nuclear Service Level III: used in areas outside the RC and not exposed to irradiation
and/or contamination where failure could adversely affect the safety function of a
safety-related Systems, Structure or Component
An important requirement derived from GL 98-04 [3] is that coating debris inside
the RC not be produced during a Loss Of Coolant Accident (LOCA) in order to avoid sump
blockage and/or malfunction of the Emergency Cooling Systems.
Therefore, the fact that some coatings may be subjected to a Design Basis Accident
(DBA) or irradiation conditions implies the need to have special performance and that
defects such as flaking, peeling, delamination or blistering not be produced. Other defects
such as decolouration or little blistering (without rupture) are accepted. In other words,
coatings must remain firmly adhered under operation and accident conditions.
Moreover, the fact that each Plant has its own DBA and irradiation conditions means
that the requirements have to be adapted for each plant (See Figure 2). This situation
implies that each coating must be evaluated for each Plant as the DBA or irradiation
conditions may differ from one plant to another.
Figure 2. Comparison of temperature curves during accident.
40ª Reunión Anual de la SNE
Valencia, España, 1-3 octubre 2014
In some cases, coatings are tested following standards of the country of origin which
differ from those established in a particular Plant. As tests, for example DBA, are not easy
to carry out and/or resources consuming, when this happens, the conditions and
requirements set out in the Standards have to be compared with those established in the
Plant and evaluated to determine whether the results obtained through those standards are
valid.
3. QUALIFIED COATING SYSTEMS
As mention above, the maintenance of protective coatings of existing NPPs includes
the painting of existing SSCs as well as the newly-installed SSCs derived from design
modifications or changes.
The application of protective coatings on new SSC, where the substrate is intact,
makes it easier to select and test potential coatings based on the supplier’s technical
datasheets. Suppliers define the type of substrate and surface preparation for each type of
coating system and test the coating systems considering these conditions. Results can be
used directly.
However, when it comes to repairs in coatings that have suffered deterioration over
time or patching, sometimes it is necessary to apply protective coatings over already
painted SSCs. In this case, it is necessary to analyse the performance of potential coatings
on these coated substrates. New tests shall be done to verify compliance with requirements
under these conditions and to analyse the performance of the whole coating system.
Qualified coating systems are those that fully meet the requirements established by
codes and standards (See Table 1). To meet Quality Assurance requirements, the fulfilment
of a criterion must be recorded in a report signed by a competent testing laboratory or
company.
During the qualification stage, nuclear coatings already existing on the market were
sought first. Several suppliers were consulted to obtain all the documentation related to the
specific requirements that should be met. The information provided was then evaluated.
Coatings were sought for both steel substrates or for concrete structures and for being
applicable for the three service levels.
The final analysis concluded that only a few coating systems can currently be fully
qualified for use in these Spanish NPPs, although potential ones are pending to be qualified
due to the lack of test reports.
This lack of test reports meant NPPs carried out their own analyses following the
defined standards. Until now these tests have mainly focused on the application of coatings
on existing and already coated SSCs. For maintenance purposes it is important to know the
performance of new coatings when they are applied over old ones and the compliance with
the requirements. These tests are out of the scope of the suppliers and are normally not
provided.
Lastly, a qualified system is deemed valid if the manufacturer certifies its production in
the same way and with the same raw material, or the legislation/requirements do not
change.
40ª Reunión Anual de la SNE
Valencia, España, 1-3 octubre 2014
Table 1. Requirement for protective coatings as a function of service level.
REQUIREMENT
LEVEL I
LEVEL II
LEVEL III
A
DBA
YES
NO
NO
B
Decontamination (only for
top coat)
YES
YES
NO
C
Radiation resistance
YES
YES
NO
D
Flame spread (Class 1E)
YES
YES
YES
E
Thermal conductivity
YES
NO
NO
F
Temperature
YES
YES
YES
G
Adherence
YES
YES
YES
H
Repainted (maintenance)
YES
YES
YES
I
Gloss
YES
YES
NO
J
Colour
YES
YES
YES
K
Abrasion (only for floors)
YES
YES
YES
L
Chemical Resistance
YES
YES
YES
M
Outdoors
NO
NO
YES
4. ENVIRONMENTAL QUALIFICATION
Although the mandatory nuclear codes and standards do not contemplate the
environmental qualification of coatings, it is a fact that the products with recently formulated
compositions are environmentally friendlier: they have lower volatile organic compound
(VOC) content than their predecessors and some of them use water as a solvent.
5. CONCLUSIONS
Protective coatings must be evaluated and qualified. Some requirements are
general, but others must be defined for each NPP based on its technology and licensing
documentation.
The nuclear market in most countries is small, which means manufacturers do not
invest many resources in nuclear coating applications. Associating several plants may
make it possible to run tests together and thus share costs.
It is also important to mention that Spanish NPPs have created a work group led by
UNESA with the goal of finding new commercial products qualified for use in its NPPs.
This paper also shows that, from an environmental point of view, the coatings used
should be upgraded so as to make greater use of commercially available products that
contain fewer solvents.
Adherence tests carried out by Trillo and Almaraz NPPs have obtained positive
results. It is possible to use new paints, usually top coatings, on already existing ones in
good conditions. This can be done, for now, only outside the Reactor Containment, where
the DBA test is a must.
40ª Reunión Anual de la SNE
Valencia, España, 1-3 octubre 2014
REFERENCES
[1] Regulatory Guide 1.54, Service Level I, II and III Protective Coatings Applied to
NPP
[2] ASTM D5144-08, Standard Guide for Use of Protective Coatings Standards in
NPP
[3] NRC Generic letter GL 98-04, Potential for degradation of the Emergency Core
Cooling System and the Containment Spray System after a Loss-Of-Coolant
Accident because of construction and protective coating deficiencies and foreign
material in containment.