Neutron Embrittlement of WWER Reactors: EC-Supported Projects
Results of the implementation of programs on the evaluation of service life of reactor pressure vessels of NPP are considered with the account of neutron embrittlement. Data on strength of WWER-440 reactor pressure vessels with a high and moderate content of detrimental impurities (copper and...
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
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irk-123456789-470552013-07-09T16:16:47Z Neutron Embrittlement of WWER Reactors: EC-Supported Projects Ahlstrand, R. Bieth, M. Rieg, C. Научно-технический раздел Results of the implementation of programs on the evaluation of service life of reactor pressure vessels of NPP are considered with the account of neutron embrittlement. Data on strength of WWER-440 reactor pressure vessels with a high and moderate content of detrimental impurities (copper and phosphor) have been analyzed. For the welds of WWER-1000 reactor, drawbacks in the manufacture, dosimetry, and test procedures of surveillance specimens are shown. To ensure safe operations of reactor pressure vessels, new projects have been undertaken, focusing on the effect of neutron embrittlement of steel on the integrity of structures and advanced experimental methods of studying material strength. Представлены результаты исследований по определению ресурса корпусных сталей АЭС с учетом радиационного охрупчивания. Проанализированы данные по изучению прочности корпусов реакторов ВВЭР-440 с высоким и умеренным содержанием вредных примесей (медь и фосфор) в стали. Для сварных соединений отмечены недостатки процедуры испытаний образцов-свидетелей, технологии их изготовления, нейтронной дозиметрии. С целью обеспечения надежной эксплуатации корпусов реакторов разработаны новые проекты, направленные на изучение влияния радиационного охрупчивания сталей на структурную целостность и усовершенствование экспериментальных методов оценки прочности материалов. Представлено результати досліджень щодо визначення ресурсу корпусних сталей AEC з урахуванням радіаційного окрихчення. Проаналізовано дані про міцність корпусів реакторів BBEP-440 із високим і помірним вмістом шкідливих домішок (мідь і фарфор) у сталі. Для зварних з ’єднань відмічено недоліки процедури випробувань зразків-свідків, технології їх виготовлення, нейтронної дозиметрії. Із метою забезпечення надійної експлуатації корпусів реакторів розроблено нові проекти, що направлені на вивчення впливу радіаційного окрихчування сталей на структурну цілісність та удосконалення експериментальних методів оцінки міцності матеріалів. 2004 Article Neutron Embrittlement of WWER Reactors: EC-Supported Projects / R. Ahlstrand, M. Bieth, C. Rieg // Проблемы прочности. — 2004. — № 1. — С. 7-14. — Бібліогр.: 19 назв. — англ. 0556-171X http://dspace.nbuv.gov.ua/handle/123456789/47055 539.4 en Проблемы прочности Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
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English |
| topic |
Научно-технический раздел Научно-технический раздел |
| spellingShingle |
Научно-технический раздел Научно-технический раздел Ahlstrand, R. Bieth, M. Rieg, C. Neutron Embrittlement of WWER Reactors: EC-Supported Projects Проблемы прочности |
| description |
Results of the implementation of programs on the
evaluation of service life of reactor pressure vessels
of NPP are considered with the account of neutron
embrittlement. Data on strength of
WWER-440 reactor pressure vessels with a high
and moderate content of detrimental impurities
(copper and phosphor) have been analyzed. For
the welds of WWER-1000 reactor, drawbacks in
the manufacture, dosimetry, and test procedures of
surveillance specimens are shown. To ensure safe
operations of reactor pressure vessels, new projects
have been undertaken, focusing on the effect
of neutron embrittlement of steel on the integrity
of structures and advanced experimental methods
of studying material strength. |
| format |
Article |
| author |
Ahlstrand, R. Bieth, M. Rieg, C. |
| author_facet |
Ahlstrand, R. Bieth, M. Rieg, C. |
| author_sort |
Ahlstrand, R. |
| title |
Neutron Embrittlement of WWER Reactors: EC-Supported Projects |
| title_short |
Neutron Embrittlement of WWER Reactors: EC-Supported Projects |
| title_full |
Neutron Embrittlement of WWER Reactors: EC-Supported Projects |
| title_fullStr |
Neutron Embrittlement of WWER Reactors: EC-Supported Projects |
| title_full_unstemmed |
Neutron Embrittlement of WWER Reactors: EC-Supported Projects |
| title_sort |
neutron embrittlement of wwer reactors: ec-supported projects |
| publisher |
Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| publishDate |
2004 |
| topic_facet |
Научно-технический раздел |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/47055 |
| citation_txt |
Neutron Embrittlement of WWER Reactors: EC-Supported Projects / R. Ahlstrand, M. Bieth, C. Rieg // Проблемы прочности. — 2004. — № 1. — С. 7-14. — Бібліогр.: 19 назв. — англ. |
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Проблемы прочности |
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| fulltext |
НАУЧНО-ТЕХНИЧЕСКИЙ
РАЗДЕЛ
UDC 539.4
Neutron Embrittlement of WWER Reactors: EC-Supported Projects
R. A hlstrand, M. Bieth, and C. Rieg
Joint Research Centre of the European Commission, Institute for Energy, Petten, the
Netherlands
УДК 539.4
Радиационное охрупчивание корпусов реакторов ВВЭР: проекты
Европейской комиссии
Р. Альстранд, М. Биет, С. Риг
Объединенный исследовательский центр Европейской комиссии, Энергетический
институт, Петтен, Нидерланды
Представлены результаты исследований по определению ресурса корпусных сталей АЭС с
учетом радиационного охрупчивания. Проанализированы данные по изучению прочности
корпусов реакторов ВВЭР-440 с высоким и умеренным содержанием вредных примесей
(медь и фосфор) в стали. Для сварных соединений отмечены недостатки процедуры
испытаний образцов-свидетелей, технологии их изготовления, нейтронной дозиметрии. С
целью обеспечения надежной эксплуатации корпусов реакторов разработаны новые проек
ты, направленные на изучение влияния радиационного охрупчивания сталей на структурную
целостность и усовершенствование экспериментальных методов оценки прочности мате
риалов.
Ключевые слова : радиационное охрупчивание, целостность корпусной реак
торной стали, сварной шов в активной зоне реактора, программа образцов-
свидетелей.
Introduction. Neutron embrittlement of the WWER-440 NPP core weld was
recognized to be much higher than expected when the first surveillance specimens
of the Loviisa 1 reactor were tested in 1980 after 3 years of plant operation [1].
The shift in the transition temperature of the weld metal of the surveillance
program was almost 3 times higher than that defined in design specification and
other Russian documentation. Due to the cubic root shape of the embrittlement
function, the embrittlement of the core weld in Loviisa 1 in 3 years of operation
reached the level that was expected only at the EOL (End of Life = 40 years for
the RPV). Several mitigations were implemented in Loviisa NPP in order to
ensure safe operation. Measures like reduction of the core, implementation of the
© R. AHLSTRAND, M. BIETH, C. RIEG, 2004
ISSN 0556-171X. Проблемы прочности, 2004, № 1 7
R. Ahlstrand, M. Bieth, C. Rieg
low leakage core management, heating of the ECCS (Emergency Core Cooling
System) water, adjusting the capacity of high pressure emergency pumps, etc.
were taken to reduce the embrittlement rate and to make a hypothetical PTS
(Pressurized Thermal Shock) softer in order to ensure acceptable safety margins.
Similar measures were implemented also in other operating WWER-440 plants.
In 1987, the first annealing of the RPV core weld was implemented in Russia at
Novovoronezh Unit 3. Later on annealing was performed in all WWER-440 units
of the old plant of type 230 and in 1996 the first WWER-440 of the new plant of
type 213 was annealed at Loviisa 1 NPP
In WWER-1000 NPP units with a high Ni content in the RPV core welds,
neutron embrittlement also exhibited a higher rate than initially expected and
specified. However, the surpassing is much smaller in relation to what was than
observed in the WWER-440 NPP. The neutron dose rate is also much lower, and
accordingly, the embrittlement is not so pronounced in the WWER-1000 plants.
Some shortcomings have been observed in the surveillance capsules, which still
need to be properly addressed. The current temperature monitoring in the
surveillance capsules is not reliable, and there is a big gradient in the neutron flux
within one set of surveillance specimens. As a result, mitigation measures have
already been implemented in some of the WWER-1000 NPPs. The temperature of
the ECCS has been increased in order to soften possible PTS transients.
Furthermore, the surveillance program was upgraded and improved in some
plants in order to reduce the neutron fluence gradient in surveillance capsules.
Since 1991, the European Commission has financed a number of TACIS,
PHARE, and EURATOM R&D projects in order to support and ensure safe
operation of WWER plants [2-18]. In these projects and actions, main attention
and support were focused on the problem of WWER-440/230 and WWER-1000
RPV embrittlement and integrity assessment. This paper summarizes the results
already obtained in the projects financed by the European Commission and
introduces the necessary actions and tasks that should still be considered in order
to cope with remaining open issues.
W W ER-440/230 RPV Issues. Historically, concern was first with the
WWER-440/230 units. The lack of representative material data from the
manufacturing stage, as well as the absence of a surveillance program, has led to a
systematic direct characterization of non-clad operating units. High content of
phosphorus along with moderate or even high content of copper in the welds lead
to high embrittlement rates and to early development and implementation of
thermal annealing technology. In the TACIS and PHARE projects mentioned,
main efforts were concentrated on direct characterization of the core weld
material by sampling RPVs. Thin, so-called “boat samples” were cut out from the
core region of Novovoronezh 3 and 4 and Kozloduy 1 and 2 RPVs [2, 5, 10, 11,
12]. Tensile and impact toughness (for mini specimens) as well as chemical
analysis were the main characteristics studied. Neutron fluence was evaluated
based on activity measurements of cut out samples. From the shut down reactor
Novovoronezh 2, trepans were removed and through-wall material characteristics
were studied. This unit is a predecessor to the WWER-440 NPP with somewhat
different operation characteristics, so the results from these studies cannot be
applied directly to operating WWER-440 plants. Based on the test results from
8 ISSN 0556-171X. npo6n.eubi npounocmu, 2004, № 1
Neutron Embrittlement o f WWER Reactors: EC-Supported Projects
mini specimens, the fracture toughness of the studied material was evaluated
through correlation procedures. The reliability of the correlation methods was not
very good due to a large scatter of test results. Some improvements would still be
recommended in order to assure a proper use and implementation of the method.
Annealing and re-embrittlement characteristics were one of the main
objectives of the aforementioned projects. There were also efforts to determine
the condition of the original material by conducting selected heat treatments of
the material. No reliable and validated heat treatment procedures were found for
that purpose. Some of cut out mini specimens were annealed and placed back in a
host reactor for re-irradiation [5]. The results from re-embrittlement studies were
quite incoherent. It was concluded, however, that the “lateral model” for
re-irradiation kinetics could be acceptable for a limited application. Further
studies would urgently be needed in order to ensure reliable re-embrittlement
behavior of the core weld as long as annealed WWER-440 NPPs are in operation.
In [8] preliminary plans for cutting of material blocks from the decommissioned
RPVs in Greifswald in Germany including a comprehensive test plan have been
elaborated. A significant effort has been dedicated to support the justification of
further operation of those plants after annealing, but it is considered that the
limited amount of representative material will be an obstacle for further
justification of their safe operation.
Some of the Russian WWER-440/230 plants have reached or are
approaching their EOL (30 years). The policy of REA is to extend the operational
life of these plants (PLEX). The Russian nuclear authority has approved the
extension of the operation of Novovoronezh Unit 3 for 5 years. The REA
application was for 15 years. At the moment, the EC gives no support to these old
plants of the so-called “first generation.”
W W ER-440/213 RPV Issues. WWER-440/213 RPVs have been considered
as well designed and characterized and less sensitive to neutron irradiation effects
mainly due to the use of materials with smaller amounts of detrimental
components such as copper and phosphorus. Furthermore, these plants are
provided with excellent surveillance programs including archive material with
test specimens for direct fracture toughness determination. A shortcoming in the
surveillance program is the relatively high lead factor, which is about 17 for weld
specimens. The high EOL neutron dose and a non-conservative anticipation factor
of the surveillance make the case quite specific. In-depth justification for
long-term operation will be a concern for the future. Further validation of the
surveillance results and possible reduction of the related uncertainties are still
questions to be clarified, since they are partly subjected to discussions. According
to current understanding, the standard reference dependencies specified for
irradiation embrittlement in the Russian Guide [19] are not conservative.
Important issues are, therefore, to develop new reference curves for irradiation
embrittlement. Pre-fatigue cracks of fracture toughness specimens of the
surveillance programs were produced quite a long time ago during the
construction stage of NPPs. Testing of those specimens revealed that pre-fatigue
cracks were not always properly made, and therefore, it is necessary to process
the test results more globally and make an adjusted analysis of them. It is also
necessary to make reconstruction of test specimens in order to evaluate the
quality of the test results.
ISSN 0556-171X. npoôëeMbi npounocmu, 2004, № 1 9
R. Ahlstrand, M. Bieth, C. Rieg
The irradiation temperature of the surveillance specimens is an important
parameter when evaluating test results. I f the temperature of the surveillance
specimens during irradiation is higher than the temperature of the down-comer
water, the test results will be optimistic and non-conservative. The original
temperature measurement methods are not reliable, and a more sophisticated
monitoring was seen as an urgent issue. A specific shared cost action, the COBRA
Project [14], was dedicated to the direct online measurement of the surveillance
specimen irradiation temperature by using thermocouples. Thermocouples were
installed in an ordinary surveillance capsule in Kola NPP Unit 3, which is
operating with full core loading of fuel. The irradiation and monitoring took place
during one year of operation from September 2001 to August 2002. The
measurements showed that the temperature of the surveillance specimens during
operation is close to the down-comer temperature (AT ~ 5°C). The standard
requirement is AT < 15°C. Similar direct online temperature measurement was
carried out in Loviisa NPP 20 years ago. This unit was operating with a reduced
core loading and, accordingly, with less y-heating. The results in Loviisa NPP
showed the same temperature difference as was found in Kola Unit 3.
Thermocouple temperature monitoring in Bohunice in Slovakia also confirmed
similar irradiation temperature with full core loading of fuel.
W W ER-1000 RPV Issues. WWER-1000 units are the most recently
developed ones. They are contributing quite significantly to the current electricity
production, especially in Ukraine. Two TACIS projects assessing the influence of
neutron embrittlement on the RPV integrity were implemented in the -94 and -95
plans [2, 3]. For a few selected scenarios, fracture mechanics calculations were
carried out in order to assess the stability of postulated cracks in the core weld.
The results are shown in Fig.1 with the K ic and the calculated K i blow-down
curves in a SBLOCA (Small Break Loss of Coolant Accident). It can be seen in
the figure, that a 20.6 mm deep circumferential crack would be initiated in this
scenario without heating of the ECCS (“w” in Fig. 1). With a heated ECCS (“hw”
Weld 4
— *— 20.6hwcl
— 20. 6hwc2
20.6WC1
...o... 20.6WC2
---1--- 20.6
€ 20 4 0 60 80 100 120 140 160 180
Temperature (°C)
Fig. 1. Calculated stress intensity factor for circumferential (c) cracks in weld 4 by the western
approach. Crack depth is 20.6 mm and the crack aspect ratios are 1/3 (c2) and 2/3 (c1). The fracture
toughness curve is also shown. The results are shown with (hw) and without (w) pre-heating of the
ECCS [3].
in Fig. 1), crack initiation can be avoided.
10 ISSN 0556-171X. npo6n.eubi npounocmu, 2004, № 1
Neutron Embrittlement o f WWER Reactors: EC-Supported Projects
The shortcomings regarding the surveillance program of the WWER-1000
NPP was additionally recognized as a problem when collecting material
properties and, especially, when determining the fracture toughness of the core
weld. Accordingly, specified upper bound properties were used in the above
integrity analyses. The shortcomings of the surveillance program are relateed to
the positioning of the specimen capsules on the top of the core barrel with a
significant neutron flux gradient between the specimens. Only about half of the
specimens (6) in one set can be used for determining a toughness curve. The
standard requirement is 12 specimens with a fuence deviation of <15%. The
temperature of the specimens was also doubtful due to poor monitoring and
positioning above the core.
The problem regarding the neutron flux and temperature of surveillance
specimens was dealt with in the projects TACIS R2.06/96 and SRR2/95/6 and 7/,
which have been completed recently. In the framework of the TACIS R2.06/96
project, two experimental surveillance sets were designed and manufactured
including advanced temperature monitors (melting alloys) and variety of
dosimeters (iron, nickel, cobalt, titanium, copper, and niobium) from different
manufacturers. They were irradiated during one operating cycle in Balakovo unit
1 in available standard surveillance locations.
The test results showed that the irradiation temperature of the surveillance
specimens did not exceed 300°C during one operation cycle. This result is
extremely important, since it confirms that the temperature of the surveillance
specimens is close to the temperature of the RPV down-comer during plant
operation. The difference is less than 10°C, which allows assessment of the results
without the application of a temperature correction factor according to the
Russian standards.
The activity measurements showed good consistency of the results but some
differences were observed on RRCKI dosimeters, especially on copper. The
activity measurements on ring pieces cut from specimen capsules confirmed the
existence of significant fluence gradients. It is recommended to measure the
activity of each capsule in order to confirm the exact positioning direction. It was
also recommended for future fluence evaluations to use cycle-by-cycle power
distribution from the closest fuel elements instead of the average one as being
used so far. Furthermore, it was recommended to include Nb dosimeters in
neutron dosimetry due to the representative threshold energy level of 1 MeV. In
the new, advanced WWER-1000 plants, surveillance specimens will be located in
boxes at the inner wall of the RPV. This solution will definitely exclude all the
above shortcomings.
It has been recently recognized that the embrittlement of the core weld of
WWER-1000 RPV is higher than expected just as was recognized earlier for the
WWER-440 plant. This was especially observed for welds with the nickel content
above 1.5%, which is still well below the specified upper value of 1.9%. The
majority of the WWER RPV welds have nickel content above 1.5%, so the
problem can be considered quite generic. In the TACIS project R2.06/96, this was
confirmed when making reconstitution of toughness specimens from broken
surveillance specimens from Kalinin unit 1 with a welding machine provided in
the project. As a conclusion it was noted that the present Russian trend curves are
non-conservative and need to be upgraded, especially for welds with a high nickel
ISSN 0556-171X. npoôëeMbi npounocmu, 2004, № 1 11
R. Ahlstrand, M. Bieth, C. Rieg
content. However, it was addressed that since the initial toughness properties of
the welds are below the specified initial upper bound in general, the absolute
transition temperature of the core weld of the WWER-1000 RPVs will stay below
the “specified” value at EOL.
New Projects. Two new TAREG projects have been under preparation under
TACIS year 2000 budget (TAREG 2.01/00 and 2.02/00). They will be
implemented simultaneously in Russia and Ukraine in a very close cooperation,
since the results of the latter project shall be integrated in the final assessment of
the former one.
The aim of the 2.01 project is to generate the conditions for an extensive
understanding of the situation regarding the RPV integrity assessment, with a
particular concern on the material embrittlement aspects. This project includes
validation of the global program on the basis of a consistent state-of-the-art
evaluation of the current knowledge, including a comprehensive identification of
the most critical and urgent open safety issues in the topic. This task will be
carried out within an international group (Senior Advisory Group) specifically set
up for the purpose. Furthermore, this project will define the conditions for
improving the results of the WWER-1000 & 440/213 RPV surveillance projects,
the corresponding experimental program being implemented in the twin project
and made available later. The evaluation of these results and their consistency
with others shall be performed with the aim to conclude on specific aspects such
as validation or re-assessment of the neutron embrittlement prediction laws, the
“quality” of the surveillance programs, further assessment of spectrum and flux
effects on neutron embrittlement, and direct measurement of fracture toughness in
comparison with the application of the codified Charpy-V/K ic correlation. This
project also includes the preparation of the technical syntheses needed for
performing EOL RPV integrity assessments with the aim to assess the most
sensitive events. The Institute for Energy of the Joint Research Center from the
European Commission is appointed to be the Main contractor for this project.
The 2.02 project shall be seen as an experimental “support project”. It
includes the performance of in-depth analyses, as well as complementary
investigations and tests, which are being considered as necessary for upgrading
the available surveillance results. A significant number of reconstituted standard
and pre-cracked Charpy-V surveillance specimens will be prepared according to
the needs defined in TAREG 2.01/00 project. Impact tests and fracture toughness
measurements according to the “Master Curve” approach are also performed in
the framework of this project. Specific consideration is given to the
implementation of the reconstitution technique in Ukraine and qualification of
Ukrainian specialists for the corresponding techniques. Further tests for justifying
advanced methods for the evaluation of the fracture toughness are also proposed.
They are partly dedicated to further validation of the “local approach,” but they
also provide for complementary assessment of the shape of the fracture toughness
temperature dependence curve. No additional reference irradiation is proposed at
that stage of programming, since it has been considered more efficient to rely on
upgraded surveillance results. The detailed program will not be in force until
approved by the Senior Advisory Group. The results of this project will later be
included in the final stage of the 2.01 project. A tender is foreseen, which is
intended to identify the most appropriate industrial Western main Contractor.
12 ISSN 0556-171X. Проблемы прочности, 2004, № 1
Neutron Embrittlement o f WWER Reactors: EC-Supported Projects
Conclusions. The EC and other sources have been used since 1991 for
improving knowledge in neutron embrittlement of WWER RPVs. Most of the
above mentioned and described support projects have been successful and have
contributed to ensuring RPV integrity and safe operation of the plants. It is clear
that there is still a need for further clarification of material issues relating to the
RPV integrity. For this purpose, two new TAREG projects are being launched.
The beneficiaries REA and Energoatom have already approved the 2.01 project
and the administrative arrangement between AIDCO and IE/JRC is foreseen very
soon. The 2.02 project is expected to be launched within one year.
Р е з ю м е
Представлено результати досліджень щодо визначення ресурсу корпусних
сталей AEC з урахуванням радіаційного окрихчення. Проаналізовано дані
про міцність корпусів реакторів BBEP-440 із високим і помірним вмістом
шкідливих домішок (мідь і фарфор) у сталі. Для зварних з ’єднань відмічено
недоліки процедури випробувань зразків-свідків, технології їх виготовлен
ня, нейтронної дозиметрії. Із метою забезпечення надійної експлуатації
корпусів реакторів розроблено нові проекти, що направлені на вивчення
впливу радіаційного окрихчування сталей на структурну цілісність та
удосконалення експериментальних методів оцінки міцності матеріалів.
1. R. Ahlstrand, B. Вдте, K. Torronen, and M. Valo, “Surveillance programs
and irradiation embrittlement research of the Loviisa NPP,” in: ASTM STP
909 (1986).
2. TACIS R 1.1/91, Reactor Vessel Embrittlement (WWER-440) (1991).
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4. TACIS R 2.09/94, Integrity Assessment o f WWER-1000 RPVs Including
Embrittlement Aspects (WWER-1000) (1994).
5. TACIS R 2.02/95, Reactor Pressure Vessel Integrity Assessment (WWER-
440) (1995).
6. TACIS SRR 2/95, Development o f Advanced Method fo r the Evaluation o f
Irradiation Embrittlement o f WWER-1000/320-type RPVs (WWER-1000)
(1995).
7. TACIS R 2.06/96, Surveillance Program fo r WWER-1000 RPV (1996).
8. TACIS R 6.01/96, Aging o f RPV. Embrittlement Analysis at the WWER-440
Greifswald RPVs (1996).
9. TACIS R/TS0/WWER01C, Licensing Related Assessment fo r Design and
Operational Safety o f WWER-Subtask C Reactor Embrittlement (2001).
10. PH/91, RPV Embrittlement o f Units 1-4 and RPV Sampling on Unit 2
(Kozloduy) (1991).
11. PH/92, Kozloduy Unit 1 RPV Assessment, PTS on Unit 1 and Spectroscopy
Analysis on Unit 1 (1992).
ISSN 0556-171X. Проблеми прочности, 2004, № 1 13
R. Ahlstrand, M. Bieth, C. Rieg
12. PH/93, Kozloduy RPV 1 Assessment: Testing (1993).
13. PH/2.01/95, Integrity Assessment o f WWER-440/213 RPVs, Implementation
o f Dynamic Fracture Mechanics Properties and Criteria (WWER-440)
(1995).
14. COBRA, WWER-440/213 Surveillance Specimen Temperature Measurements.
15. FRAME, Validation o f Fracture Toughness Trend Curve fo r RPV Materials.
16. GRETE, Round Robin Exercise on Nondestructive Techniques to Assess
and/or Monitor Material Properties Degradation.
17. MODEL ALLOYS, Phosphorus, Copper, Nickel Effects on Embrittlement.
18. PISA, Phosphorus Role on Embrittlement Effects and Development o f a
Physically Based Model.
19. Regulatory Document, PNAE G-7-002-86, Strength Analaysis Standards fo r
Equipment and Piping at NPPs [in Russian], Moscow, Energoatomizdat,
(1989).
Received 26. 05. 2003
14 ISSN 0556-171X. npo6neMbi npouHocmu, 2004, № 1
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