IAEA Coordinated Research Project on the Establishment of a Material
Properties Database for Irradiated Core Structural Components for
Continued Safe Operation and Lifetime Extension of Ageing Research
Reactors
B. van der Schaaf 1, Y. Barnea1, A. Zeman3, A. Borio di Tigliole1,
P. Adelfang1, E. Bradley1, A. Shokr2
(1) Research Reactor Section – NEFW
(2) Research Reactor Safety Section – NSNI
(3) Physics Section – NAPC
International Atomic Energy Agency (IAEA)
VIC, PO Box 100, Vienna, Austria
Corresponding Author: A.Borio@iaea.org
ABSTRACT
Today, more than 50% of the operating Research Reactors (RRs) are over 45 years
old. Thus, ageing management is one of the most important issues to face in order to
ensure availability (including life extension), reliability and safe operation of these
facilities for the future. Management of the ageing process requires, amongst others,
the predictions for the behavior of structural materials of major components subjected
to irradiation such as reactor vessel and core support structures, many of which are
difficult to replace. In fact, age-related material degradation mechanisms can result in
unplanned outages as well as lengthy shutdowns and the need for additional
regulatory activity, which could have been prevented by utilizing available data for
the implementation of appropriate maintenance and surveillance programs. The
proposed IAEA Coordinated Research Project (CRP) will provide a forum for input
and discussion of relevant materials data and operating experience with RRs leading
to the establishment of a “Research Reactor Irradiated Structural Components and
Materials Properties Database” to be used by RRs Operators and Regulators to help to
predict ageing related degradation.
In order to collect information on the needs and types of activities considering the
prediction of ageing related degradation of core components, a questionnaire was
submitted to Member States. The analysis of the preliminary responses of the
questionnaire is presented in this work.
1. Introduction
Today about 55% of operating Research Reactors (RRs) are over 40 years old and about 75%
are over 30 years old [1]. Thus, ageing management is one of the most important issues to
face in order to ensure availability (including life extension), reliability and safe operation of
these facilities for the future. Ageing management is defined as a comprehensive effort of
engineering, operations and maintenance actions to control, within acceptable limits, the
ageing effects that could impair the ability of a structure, system or component (SSC) to
function within its acceptance criteria (ageing degradation) [2] [3]. Management of the
ageing process requires, amongst others, the predictions for the behavior of structural
materials of major components subjected to irradiation such as reactor vessel and core
support structures, many of which are difficult to replace [4]. In fact, age-related material
degradation mechanisms can result in unplanned outages as well as lengthy shutdowns and
the need for additional regulatory activity, which could have been prevented by utilizing
available data for the implementation of appropriate maintenance and surveillance programs.
The proposed IAEA Coordinated Research Project (CRP) will provide a forum for input and
discussion of relevant materials data and operating experience with RRs leading to the
establishment of a “Research Reactor Irradiated Structural Components and Materials
Properties Database” to be used by RRs Operators and Regulators to help to predict ageing
related degradation [5]. Moreover, the CRP will specify further activities needed to address
the identified data gaps of the Database for potential follow-up activities.
In order to collect information on the needs and types of activities considering the prediction
of ageing related degradation of core components, a questionnaire was made available to
Member States (MS) operating RRs through the IAEA website. The analysis of the
preliminary responses of the questionnaire is presented in this work.
2. CRP Specific Research Objectives and Expected Outcome
The Specific Research Objectives (SRO) identified for the proposed CRP are the following:
1) to obtain relevant data and operating experience from research reactors, including
materials data through comprehensive literature reviews, and evaluate data gaps; 2) to
compile an evaluated, reviewed and assessed Database that can be used for sharing relevant
information among interested MS, that will establish a rational basis for research reactor
material evaluation, and that will provide a structure for future incorporation of new data as
they become available; 3) to specify further activities needed to address the identified data
gaps of the Database for potential follow-on activities by the IAEA, and to produce an IAEA
publication that provides relevant information to users of the Database.
The expected Outcome of the CRP should be the transfer of know-how in the area of research
reactor data analysis, maintenance, surveillance techniques, safety analysis, operation,
enhancing safety and better operational performances of research reactors in the participating
organizations.
3. The CRP Questionnaire
In order to evaluate the interest in the CRP and to collect preliminary information on the data
needs and types of activities considering the prediction of ageing related degradation of core
components, the IAEA has made available to Member States (in RRS/NEFW web-page) a
questionnaire containing the following five questions:
1) What are the components and materials affected by ageing in your facility?
2) What information is available to you for those materials?
3) What information is not available that you would like to have?
4) What form of Database would be most useful to you?
5) What specific monitoring and surveillance programs are implemented at your facility
to address ageing of core components and materials?
In order to facilitate and harmonize the responses, a list of the data needed for the evaluation
of material capability to perform its safety function and a list of research reactor core
components and materials were attached, as appendices, to the questionnaire. The two lists
are reported in the following Tab. 1 and Tab.2.
TAB.1- Data needed for the evaluation of material capability to perform its safety function
Environment:
• Definition of fast and thermal neutron energies
• Fast to thermal ratio for each test
• Fluxes
• Irradiation and test temperatures
• Coolant chemistry (e.g. for water: pH, conductivity; for NaK: mass ratio; for He: impurities)
Sample:
• Definition of un-irradiated specimen material (certificated composition and thermal-mechanical
treatment, material properties, residual stresses etc.)
• Standard used for specimen manufacture
Measurements and calculations:
• Composition changes (chemical and isotopic) (calculated or measured?)
• Displacements per atom (with method of determination)
• Formation of loops and dislocation density (m-2)
• Voids and bubble density and composition (1H, 3H, He) (% volume or m-2)
• Swelling (volume %)
• Corrosion rate (dimensional, mass changes)
• Changes in resistance to Stress Corrosion Cracking (SSR test, ECP-diagram)
• Changes in UTS, yield strength, 2% yield (MPa)
• Changes in ductility (uniform and total elongation) (%)
• Changes in fracture toughness (MPa.m½ )
• Changes in stress and strain driven fatigue properties (threshold stress; N f with definition)
• Changes in fatigue crack growth rate (da/dn)
Additional parameters should be provided, as appropriate, for materials with special applications. Some (nonexhaustive) examples follow:
• Epoxy resins and glues: initial curing conditions and subsequent bond degradation with neutron and
gamma fluence
• Fastening and joining aspects: bolting (relaxation, galvanic), welding (heat affected zone, galvanic),
compatibility of materials
• Graphite: Swelling, accumulation of Wigner energy
• Zirconium: Growth, directionality of properties
• Concrete: density, compression strength
• Cable insulation: Insulation degradation
TAB.2 - Listing of typical research reactor core components and structures and the most
common materials used. Components that are generally fixed and difficult to replace are
indicated by (1) and those that are more readily replaced are indicated by (2). The ease of
replacement of components is determined by the research reactor design and the indications
given may not be accurate for all designs.
Components
Materials
Components
Pressure(Tank) vessel + connecting pipes
Pressurized vessel (1)
Low pressure tank (1)
Low alloy steel
Aluminium alloys
Stainless steel
Aluminium alloys
Stainless steel
Zirconium
Materials
Reflector Devices/Systems
Heavy Water tank &
accessories (1)
Aluminium alloys
Zirconium
Metallic sealing rings
Beryllium (1/2)
Beryllium
Aluminium-Be alloy
Graphite (2)
Graphite
Connecting pipes (1/2)
Aluminium alloys
Stainless steel
Beam ports/nozzles (1)
Aluminium alloys
Low alloy steels
Zirconium
Poolside irradiation facility (1)
Aluminium alloys
Stainless steel
Cold source
Zirconium
Aluminium alloys
Liners (Pool type RR) (1)
Aluminium alloys
Stainless steels
Epoxy resins
Ceramic tiles
Thermal column
Zirconium
Aluminium alloys
Neutron guide tubes
Aluminium alloys
Stainless steels
Core support structure components
Core support grid (1/2)
Other structural and internal
support structures
Core box/vessel (1/2)
Aluminium alloys
Stainless steels
Low alloy steels
Aluminium alloys
Stainless steels
Low alloy steels
Aluminium alloys
Stainless steels
Low alloy steels
Guide Tubes (2) for:
Control devices
Fuel elements
Experimental facilities
Isotope production
Aluminium alloys
Stainless steels
Inconel
Zirconium
Aluminium alloys
Zirconium
Aluminium alloys
Stainless steels
Inconel
Zirconium
Aluminium alloys
Stainless steels
Zirconium
Beam related devices, highly irradiated portion (2)
Shielding structures
Concrete (1/2)
High density concrete
Structural concrete
Lead (2)
Lead types
Tungsten (2)
Tungsten alloys
Other
Cables
Organic insulation
4. Analysis of the Responses to the CRP Questionnaire
At the time of this work, 14 Member States have provided answers in 18 filled out
questionnaires. The analysis of the responses is presented below [6].
4.1 Components and Materials Affected by Ageing
The contributing MS have indicated the highest priority (i.e. named by more than half of the
respondents) to the following components:
• Core basket and grid (plate support) structure
• Reactor vessel (tank)
• Irradiation facilities
The intermediate categories, mentioned by 6 to 8 respondents, are:
• Control rod absorbers, followers, guide tubes safety
• Reflector (elements)
• Pool cooling piping and support
Other subjects that were mentioned from 1 to 3 times are:
• Beam ports/nozzles
• Cooling piping and support
• Pool liners
• Shields thermal (carbon steel)
Some of them are not satisfying the definition Irradiated Core Structural Components exactly.
The remaining items are worthwhile considering, but their priority is limited in comparison
with the items in the high and intermediate section of subjects.
The answers on materials show that the highest on the list (i.e. named by more than half of
the respondents) are:
• Stainless steel (AISI 304L, 316, 316L, 347)
• Aluminum AISI 6061 (T6), alloys, high purity
Beryllium is indicated 5 times, while Concrete and Graphite are brought up 3 times each and
take a lower position in the materials responses. The remaining materials are: Carbon steel
(twice) and Boron carbide, Coating, unspecified (once).
The two materials with the higher response: aluminium alloys and stainless steel are not
really materials, but two classes of alloys: one on the basis of aluminium and one on the basis
of iron, chromium and nickel. Because of their composition differences, though within the
limits given for a particular alloy, they cover quite a wide range of materials and
consequently properties.
4.2 Available Information on Materials
The responses on available materials information allow categorizing the answers into five
information domains:
• Materials properties
• Neutron transport analysis and measurements
• Operational information
• Visual records and geometrical data
• Documentation
The details in these domains show that some information is rather specific for the particular
research reactor. For example the videos of core components in the Visual records domain
and the manuals and historical manufacturing data indicated in the Documentation domain
have a highly reactor specific character that is not easy to translate for other RRs. The
information domains on Materials properties and Neutron transport analysis and
measurements have highly useful elements for wider application, but to be sure more details
of the content and presentation of the available information is necessary. More details needed
are: the temperature domain and the accumulated radiation dose/neutron fluence the materials
were exposed to. In addition it is useful to know the measurement and the analysis technique
for the determination of the radiation doses. The other data might have significance for
others, but the information needs transformation for the specific condition for the user.
Some of the detailed information might be useful for application elsewhere, but the three
latter information domains do not lend themselves easily for use in other research reactors. In
general the information is not ready for direct use for others. Though the three latter
information domains do not include data generally applicable, the methodologies used have
certainly value for others. It might be useful to investigate the value of these methods for
others than the owner of the research reactor. This activity is not the primary goal of the
identification of inputs and urgent needs, but it might be useful to investigate the value of the
indicated methods for other research reactor owners.
4.3 Lacking Information that is needed
More than half of the respondents’ reactions on lacking information have to do with radiation
effects data. The MS identified seven detail areas related to the effect of neutron radiation on
mechanical properties. With the exception of Hafnium absorbers all identified materials are
included in the listing of typical research reactor core components and structures (see Tab.2).
The detail areas identified are within the scope of the data base. In addition five detailed areas
are related to the domain of Radiation effects on corrosion. Also in this case the identified
items are in the scope of data needed for evaluation of material capability to perform its
safety function.
The MS identified the need for reference corrosion data in part parallel to the areas for the
radiation effects, expressed in three sub-domains. Since corrosion properties have been
extensively treated in recent IAEA publications (as ex. [7] [8] [9]), they are beyond the scope
of the present CRP, and will not be followed up in this CRP.
The Dimensional stability domain comprises three elements. Two have to do with the
geometry of the core structures. The remaining one indicates the need for verification of the
design details in–situ, which goes further than dimensional checks: material composition
verification is also recommended.
The domain of Optical examination holds the item for the video recording of core structures
allowing the logging of eventual changes in the surface appearance and shape of the
structures.
Dimensional stability and Optical examination results are strongly tied to the design of the
research reactor. The intended data base can thus not address this need.
Two of the items in the miscellaneous domain contain two items that are highly linked to the
availability of data on a particular reactor such as availability of spare parts and
manufacturing characterization data. The third item on leaking liners data is not defined in
terms of materials properties or processes. Their inclusion within the scope of the intended
Database is useful starting with descriptions of existing cases of liner leakage, followed by
analyses revealing the basic mechanisms for leakage providing guidance for RR Operators to
prevent, and or mitigate their occurrence.
The list of needed details provided by the MS does not include surprise materials or
processes. Aluminium alloys, stainless steel 316, and Zircaloy-4 are prominently mentioned
as could be expected. The properties needed, mechanical as well as growth are in line with
the expected data needed.
The identification underlines the need for data for determining the safe life of core structures.
The MS made clear that they need mechanical data on neutron irradiation effects to support
the analyses of the core structures.
4.4 Preferences for Database Form
Twelve Member States indicated at least MS Excel, seven mentioned at least MS Access, and
SQL was mentioned three times. The preference of the Member States for MS Excel as
Database form is evident. The RR Operators have wide experience with the use of Excel
sheets with its simple handling and short training time for the user. MS Access needs more
knowledge and experience to handle properly. SQL requires professional levels of knowledge
and experience to use it effectively, which raises barriers for immediate deployment for most
of the RR Operators. In return SQL offers more safeguards for the integrity of the Databases.
4.5 Implemented Monitoring and Surveillance Programs
The contributing MS identified the Visual Inspection domain as the largest category out of
the major five (13 responses). This domain is not within the Database scope. The importance
and significance of visual inspection is nevertheless high. Exchange of methodologies,
standardization and benchmark problems definition in any case will be highly valuable for
research reactor safety, but since it is out of scope of the Database it needs to be treated
elsewhere (an IAEA NE Series Report on “RR Primary System Inspection Technologies and
Techniques” is planned).
The domain Measurements (with 8 responses) includes three answers referring to
measurement of radiation embrittlement of structural alloys. Another three answers concern
water chemistry measurements, which are out of the scope of this CRP. The remaining two
answers address measurements of safety rod dropping, and NDT inspection. The
measurements domain has thus a rather wide range, where only the three measurements of
radiation embrittlement fall within the scope of the data base collection and building.
The Dimension measurements have been gathered in a dedicated domain resulting in eight
items. These are of high importance for the support of safe research reactor operation, but
with exception of the swelling measurement of control rod materials not useful for the
Database. Blistering data might be added to the Database, if their measurement results allow
quantitative inclusion in the data base.
The domains Neutron transport and Data collection & analyses hold respectively three and
two reactions of MS. These are not contributing directly to the data base, though the final
item on “Development of appropriate ageing indicators for each group of components to
detect and predict its degradation” is valuable for the application of the data base.
The Monitoring and surveillance department of the questionnaire provides thus elements in
principle valuable for the data base in the domains of :
•
•
•
Measurement of radiation embrittlement of structural alloys
Swelling measurement of control rod materials
Development of appropriate ageing indicators.
5. Conclusions
The population of research reactors was covered in a satisfying power range above 1 MW.
The number of received questionnaires, 18 from 14 MS, does not allow quantitative reliable
statistics. Though not all the responses of the MS are strictly within the scope of the
questionnaire, the results are highly valuable for the identification of items relevant for the
establishment of a material properties Database for irradiated core structural components for
continued safe operation and lifetime extension of ageing RR’s.
The respondents considered the core basket and grid (plate support) structure, reactor vessel
and some irradiation facilities as the most important components affected by ageing. Control
rod related structures, reflectors and pool related structures were mentioned less frequently.
As the major materials affected by ageing were identified stainless steel and aluminum alloys,
followed by Beryllium, carbon steel, Zircaloy and boron carbide.
The information on materials properties and neutron transport analysis and measurements
have highly useful elements for wider application into the Database. Regarding the other
domains the respondents indicate that they are too specific for inclusion into the Database.
The most important lacking information that the respondents indicate as needed, concerns
irradiation effects on mechanical properties. The identified materials and components are in
the listing of typical research reactor core components and structures.
For what concern the Database form, the respondents’ majority shows a preference for MS
Excel environment.
The monitoring and surveillance programmes implemented by the respondents are focused on
visual inspections and measurements. Many of those are highly specific, and the resulting
data are only usable for other RR Operators after transformation of the information into
quantities lending themselves to inclusion in the Database.
The measurement results of radiation embrittlement of structural alloys, swelling
measurement of control rod materials, and development of appropriate ageing indicators are
items that might be included in the data base useful for a much wider community.
6. References
[1]
[2]
[3]
[4]
[5]
IAEA NUCLEUS - Research Reactor Data Base
IAEA Safety Glossary, ed. 2007
SSG-10 “Ageing management for research reactors” IAEA, 2010.
“Research reactor application for materials under high neutron fluence”, IAEA
TECDOC-1659, 2011.
Y. Barnea, A. Zeman, E. Bradley Jr., P. Adelfang, “IAEA Recent Activities to Create a
Database on Assessment, Monitoring and Surveillance of Research Reactors’ Core
Structural Materials Ageing” Proceedings of the SMiRT 21 (Structural Mechanics in
Reactor Technology), 6-11 November, 2011, New Delhi, India.
[6]
[7]
[8]
[9]
Bob van der Schaaf , “Analysis of the questionnaires for potential CRP participants
Identification of inputs and urgent needs - Status Report”, private communication,
August 2012.
“Corrosion of Research Reactor Aluminium Clad Spent Fuel in Water”, IAEA
TECDOC-1637, 2010.
“Data Processing Technologies and Diagnostics for Water Chemistry and Corrosion
Control in Nuclear Power Plants (DAWAC)”, IAEA TECDOC-1505, 2006.
“Development of protocols for corrosion and deposits evaluation in pipes by
radiography”, IAEA-TECDOC-1445, 2005.