RPV Long Terra Operation: Open Issues
This paper presents and describes key open issues which are being debated nowadays by experts in the field, and for which clarification is essential for a safe operation of the nuclear power plants during life extension. Notably: late blooming effects in low Cu steels; effects of Cu, Ni, Mn, and P o...
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
2013
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irk-123456789-1119722020-12-17T16:08:24Z RPV Long Terra Operation: Open Issues Ballesteros, A. Altstadt, E. Научно-технический раздел This paper presents and describes key open issues which are being debated nowadays by experts in the field, and for which clarification is essential for a safe operation of the nuclear power plants during life extension. Notably: late blooming effects in low Cu steels; effects of Cu, Ni, Mn, and P on the irradiated microstructure and on hardening and embrittlement; use of material test reactor data for assessment in power reactors (including flux and spectrum effects); Master Curve versus Unified Curve and fracture toughness behavior of highly irradiated material; embrittlement in RPV zones out of the traditional beltline (“the expanding beltline”); embrittlement trend curves at high neutron fluence, where data are scarce; re-embrittlement after annealing. Описаны актуальные проблемы обеспечения безопасной работы АЭС при продлении сроков эксплуатации, которые широко обсуждаются экспертами данной отрасли. К ним, в частности, относятся: эффекты запаздывания в сталях с низким содержанием меди влияние Cu, Ni, Mn и P на микроструктуру, упрочнение и охрупчивание облученных сталей применимость результатов испытаний, полученных в исследовательском атомном реакторе, к промышленным реакторам, включая эффекты флакса и спектра сопоставление Мaster-кривой с унифицированной кривой, а также особенности разрушения высокооблученных материалов; охрупчивание материалов в зонах корпусов реакторов вне традиционных участков; построение трендовых кривых охрупчивания для высокого флюенса нейтронов при малом объеме данных; повторное охрупчивание после отжига. Описано актуальні проблеми забезпечення безпечної роботи АЕС при продовженні термінів експлуатації, які широко обговорюються експертами даної галузі. До них, зокрема відносяться: ефекти запізнювання в сталях із низьким вмістом міді; вплив Cu, Ni, Mn і P на мікроструктуру, зміцнення і окрихчування опромінених сталей; використання результатів випробувань, отриманих у дослідном атомному реакторі, до промислових реакторів, включаючи ефекти флакса і спектра; зіставлення Мaster-кривої з уніфікованою кривою, а також особливості руйнування високоопромінених матеріалів; окрихчування матеріалів у зонах корпусів реакторів поза традиційними участками побудова трендових кривих окрихчування для високого флюенса нейтронів за малого об’єму даних; повторне окрихчування після відпалу. 2013 Article RPV Long Terra Operation: Open Issues / A. Ballesteros, E. Altstadt // Проблемы прочности. — 2013. — № 4. — С. 7-13. — Бібліогр.: 13 назв. — англ. 0556-171X http://dspace.nbuv.gov.ua/handle/123456789/111972 539.4 en Проблемы прочности Інститут проблем міцності ім. Г.С. Писаренко НАН України |
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Научно-технический раздел Научно-технический раздел |
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Научно-технический раздел Научно-технический раздел Ballesteros, A. Altstadt, E. RPV Long Terra Operation: Open Issues Проблемы прочности |
| description |
This paper presents and describes key open issues which are being debated nowadays by experts in the field, and for which clarification is essential for a safe operation of the nuclear power plants during life extension. Notably: late blooming effects in low Cu steels; effects of Cu, Ni, Mn, and P on the irradiated microstructure and on hardening and embrittlement; use of material test reactor data for assessment in power reactors (including flux and spectrum effects); Master Curve versus Unified Curve and fracture toughness behavior of highly irradiated material; embrittlement in RPV zones out of the traditional beltline (“the expanding beltline”); embrittlement trend curves at high neutron fluence, where data are scarce; re-embrittlement after annealing. |
| format |
Article |
| author |
Ballesteros, A. Altstadt, E. |
| author_facet |
Ballesteros, A. Altstadt, E. |
| author_sort |
Ballesteros, A. |
| title |
RPV Long Terra Operation: Open Issues |
| title_short |
RPV Long Terra Operation: Open Issues |
| title_full |
RPV Long Terra Operation: Open Issues |
| title_fullStr |
RPV Long Terra Operation: Open Issues |
| title_full_unstemmed |
RPV Long Terra Operation: Open Issues |
| title_sort |
rpv long terra operation: open issues |
| publisher |
Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| publishDate |
2013 |
| topic_facet |
Научно-технический раздел |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/111972 |
| citation_txt |
RPV Long Terra Operation: Open Issues / A. Ballesteros, E. Altstadt // Проблемы прочности. — 2013. — № 4. — С. 7-13. — Бібліогр.: 13 назв. — англ. |
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Проблемы прочности |
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AT ballesterosa rpvlongterraoperationopenissues AT altstadte rpvlongterraoperationopenissues |
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2025-07-08T03:06:32Z |
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2025-07-08T03:06:32Z |
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1837046429362683904 |
| fulltext |
ÍÀÓ×ÍÎ-ÒÅÕÍÈ×ÅÑÊÈÉ
ÐÀÇÄÅË
UDC 539.4
RPV Long Term Operation: Open Issues
A. Ballesterosa and E. Altstadtb
a Tecnatom, Madrid, Spain
b Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany
ÓÄÊ 539.4
Àêòóàëüíûå ïðîáëåìû îáåñïå÷åíèÿ äîëãîâðåìåííîé ðàáîòû êîðïóñîâ
ÀÝÑ
À. Áàëëåñòåðîñà, Å. Àëüòøòàäòá
à Òåêíàòîì, Ìàäðèä, Èñïàíèÿ
á Äðåçäåí-Ðîññåíäîðôñêèé Ãåëüìãîëüö-öåíòð, Äðåçäåí, Ãåðìàíèÿ
Îïèñàíû àêòóàëüíûå ïðîáëåìû îáåñïå÷åíèÿ áåçîïàñíîé ðàáîòû ÀÝÑ ïðè ïðîäëåíèè ñðîêîâ
ýêñïëóàòàöèè, êîòîðûå øèðîêî îáñóæäàþòñÿ ýêñïåðòàìè äàííîé îòðàñëè. Ê íèì, â ÷àñò-
íîñòè, îòíîñÿòñÿ: ýôôåêòû çàïàçäûâàíèÿ â ñòàëÿõ ñ íèçêèì ñîäåðæàíèåì ìåäè; âëèÿíèå Cu,
Ni, Mn è P íà ìèêðîñòðóêòóðó, óïðî÷íåíèå è îõðóï÷èâàíèå îáëó÷åííûõ ñòàëåé; ïðèìåíèìîñòü
ðåçóëüòàòîâ èñïûòàíèé, ïîëó÷åííûõ â èññëåäîâàòåëüñêîì àòîìíîì ðåàêòîðå, ê ïðîìûø-
ëåííûì ðåàêòîðàì, âêëþ÷àÿ ýôôåêòû ôëàêñà è ñïåêòðà; ñîïîñòàâëåíèå Ìaster-êðèâîé ñ
óíèôèöèðîâàííîé êðèâîé, à òàêæå îñîáåííîñòè ðàçðóøåíèÿ âûñîêîîáëó÷åííûõ ìàòåðèàëîâ;
îõðóï÷èâàíèå ìàòåðèàëîâ â çîíàõ êîðïóñîâ ðåàêòîðîâ âíå òðàäèöèîííûõ ó÷àñòêîâ; ïîñòðîå-
íèå òðåíäîâûõ êðèâûõ îõðóï÷èâàíèÿ äëÿ âûñîêîãî ôëþåíñà íåéòðîíîâ ïðè ìàëîì îáúåìå
äàííûõ; ïîâòîðíîå îõðóï÷èâàíèå ïîñëå îòæèãà.
Êëþ÷åâûå ñëîâà: äîëãîâðåìåííàÿ ýêñïëóàòàöèÿ, ðåàêòîðíûé ñîñóä äàâëåíèÿ,
îáëó÷åííàÿ ñòàëü, îõðóï÷èâàíèå, Ìaster-êðèâàÿ, óíèôèöèðîâàííàÿ êðèâàÿ.
Introduction. The lack of new build of plants over the last twenty years has
resulted in a switch within the industry from design, construction and development
of new systems to the strengthening of safety systems and to the life extension, or
long term operation (LTO), of existing reactors. The most relevant component of
any nuclear power plant (NPP) is the reactor pressure vessel (RPV). This is
because currently the RPV is still considered irreplaceable or prohibitively expensive
to replace. A RPV operational life of 60 years is being considered frequently by
many utilities in their plant life management programmes. Consideration is given
also to extending that further to possibly 80 years.
© A. BALLESTEROS, E. ALTSTADT, 2013
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2013, ¹ 4 7
There are several scientific and technical open issues which are critical for a
safe plant operation to 60 years and beyond. Several of these issues are considered
old, in the sense that they have been debated by experts in the field since long time
ago. For instance, the “neutron flux effects” or the “re-embrittlement after
annealing.” Other issues are relatively more recent, since they arise directly from
the need to get a more accurate picture of the material behavior after long exposure
times. That is the case of the “expanding beltline” or the development of
“embrittlement trend curves at high fluence.”
The following sections describe in detail the relevant open issues.
1. Old Open Issues.
1.1. Chemical Composition. A more precise analysis of the nickel-manganese
effect is needed. In addition, it may be strong synergistic interactions at high fluences
between copper, nickel, manganese and phosphorus. The role of silicon should be
clarified. Its presence in clusters should indicate an increase in embrittlement with
increasing silicon concentration, but there are results indicating the opposite
influence [1].
The RPV wall material of the WWER-440 (15Kh2MFA) is alloyed with Cr,
Mo, and V. The vanadium alloying may increase the radiation resistance, but
phosphorus segregation to vanadium carbonitride interfaces has been observed [2].
1.2. Late Blooming Effects. Models suggest and increasing experimental
evidence shows that clusters rich in Ni and Mn may form in low Cu steels and may
or may not contribute to hardening and embrittlement until relatively high
fluences – called “late blooming effect” (LBE).
A late blooming effect on both the yield stress increase and the magnetic
scattering cross section of SANS data has been observed for low-Cu RPV steels
irradiated at a relatively low temperature of 255�C [3].
SANS, APT and electrical resistivity-Seebeck coefficient measurements all
show large volumes of Mn and Ni rich clusters and high hardening in two Cu-free,
high Ni steels irradiated at 270�C and intermediate flux to � �1 7 1019. n/cm2 [4].
Other investigations (e.g., [5]) indicate that there is no such late-blooming effect in
several RPV steels irradiated at relatively high fluxes in the temperature range
from 265 to 300�C.
1.3. Flux, Spectrum, and Irradiation Temperature Effects. Whether or not
the same magnitude of “damage” would be exhibited by materials irradiated under
“fast” versus “slow” fluence accumulation conditions is considered an open issue.
Early investigations of flux effects, using test reactor experiments, did not reveal a
significant influence of this exposure variable on steel property changes. In most
instances, the data bank information does not offer a 1:1 comparison for a specific
material.
A further impediment to testing for flux effects is the general tie between flux
level and neutron spectrum. Decoupling these two factors experimentally is
difficult.
Temperature irradiation effects seem to be more important for higher neutron
doses representative of long term operation conditions. Experimental data on
studies of JRQ steel under irradiation at different temperatures (265 and 300�C)
show that there is significant difference in hardening as the irradiation dose
growth. After irradiation to the dose of 5 1019� n/cm2 the difference in hardening is
A. Ballesteros and E. Altstadt
8 ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2013, ¹ 4
~ 60 ÌÐà, and at irradiation to 15 1020. � n/cm2 it is ~ 150 ÌÐà [6]. Similar result
was obtained in the modelling studies of [7].
1.4. MTR versus Power Reactor. In general, surveillance data correspond to
“low fluences.” There are insufficient surveillance data to cover service life
prolongations. Typical problems are:
(i) insufficient number of surveillance capsules initially inserted;
(ii) longer exposures needed for reinserted capsules;
(iii) insufficient lead factors in some plants.
The use of high fluence material test reactor (MTR) data is a preliminary step
to life extension, but still high controversy exists on the use of MTR data to
support life extension, in particular related to the “flux effects” issue.
1.5. Thermal Ageing. Thermal ageing is not considered, in general, a problem
for Western European RPV steels since the Ni content is relatively low. It is known
that nickel enhances thermal embrittlement as a result of activation of segregation
mechanisms.
For WWER-1000 RPV welds with high Ni the embrittlement dependency can
be determined on the basis of tests results of thermal surveillance sets. If the time
of thermal exposure is around 100,000 h, the DBTT shift amounts to approximately
20 K [8], however, a more pronounced thermal embrittlement cannot be excluded
for exposure times typical for LTO (e.g., 450,000 h).
1.6. Master Curve and Unified Curve. Currently there are two advanced
approaches of fracture toughness evaluation, the Master Curve (MC) and the
Unified Curve (UC), represented by the following equations:
K T TJc med
MC
( ) exp[ . ( )],� � �30 70 0 019 0
K
T
Jc med
UC
( ) tanh .� � �
��
�
�
�
�
�
26 1
130
105
�
The prediction of K TJc( ) curve for the RPV end of life may be non
conservative when the MC is applied. One of the main differences between the MC
and the UC is the shape of the curve. The MC is not affected by irradiation and the
shape parameter is constant and equal to 0.019/�C, while for the UC the shape is
changing with irradiation. When the degree of embrittlement increases the parameter
� decreases. According to [9], the MC can be seen as a particular case of the UC.
1.7. Re-Embrittlement after Annealing. The traditional models (lateral shift,
vertical shift, etc.) on re-embrittlement after annealing are not able to describe the
peculiar behavior of high phosphorus steels, as it is the case of WWER-440 high P
welds. More general validation of re-embrittlement models based on studies of
mechanical properties, as well as on microstructural investigations, is still needed.
A better understanding of re-embrittlement mechanisms is essential for an accurate
prediction. An attempt of integrated approach to this problem was made in [10].
Results of the PRIMAVERA project on “WWER-440 Welds Re-Embrittlement
Assessment” show that current evaluation methods for embrittlement after annealing
are adequate or conservative. Nevertheless some open issues remain: e.g., verification
of PRIMAVERA results for low flux and high fluence irradiation and possible flux
effects.
RPV Long Term Operation: Open Issues
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2013, ¹ 4 9
SANS investigations at a WWER-440 weld material revealed that re-irradiation
after annealing causes clusters in the same size range as for the original irradiation,
however, their formation strongly decelerates or saturates at a smaller volume
fraction. The new clusters differ in composition from the original ones. The
observed hardness change due to re-irradiation indicates that the obstacle strength
of the re-irradiation-induced clusters is higher than that for the original irradiation
[11].
2. New Open Issues.
2.1. Embrittlement Trend Curve at High Fluence. There is a lack of
embrittlement data at high fluence. 90% of existing data (75% of surveillance data)
are for irradiation times of less than 15 years. In addition, some well known
embrittlement trend curves, as for R.G. 1.99 Rev. 2 and 10CFR50.61a, have a
tendency to under-predict more as fluence increases, and the same outcome is valid
for test reactor irradiations.
It is not clear whether it is appropriate the direct use of high flux test reactor
data to predict �T for high fluence – low flux conditions.
On the positive side it is worth to mention the trend curve model called
“Charpy Master Curve,” which has been developed recently by EPRI using a
method of fitting raw Charpy data in a manner consistent with the Master Curve
approach [12].
The “Coordinated PWR Reactor Vessel Surveillance Programme” is in
progress in US and it intends to generate high-fluence surveillance data needed to
develop embrittlement correlation for fluences representative through 80 years of
operation.
2.2. The Expanding Beltline. For 80 years or longer operation times some
regions outside the beltline can accumulate nonnegligible neutron fluence. The
chemical content of embrittling elements (Cu, Ni, P) may be higher than in the
beltline, or unknown. In addition, materials from regions outside the traditional
beltline may not be available for irradiation and testing. Sharing of data between
plants of similar design and vendor is vital to address this issue.
Lack of material data may lead to a need to assign generic properties for
extended beltline materials, and therefore lead to more restrictive pressure–
temperature limit curves.
2.3. Monitoring Embrittlement during Life Extension. The issue of monitoring
embrittlement during life extension is directly related to the availability or non-
availability of surveillance material. The use of miniature specimens and
reconstitution techniques can help to solve or mitigate the situation. Other tools are
the use of tailored or surrogate material or the participation of the plant in an
Integrated Surveillance Programme.
Different surveillance strategies can be applied to increase the number of
surveillance data at high fluence:
(i) testing a different capsule (with higher lead factor) than planned;
(ii) irradiate the standby capsules, if available, in positions with higher lead
factor;
(iii) retain surveillance capsules in vessel for longer period of time, then
increasing the neutron fluence accumulated by the capsule;
(iv) move the surveillance capsule to higher lead factor position in vessel;
10 ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2013, ¹ 4
A. Ballesteros and E. Altstadt
(v) reinsert previously removed capsule for additional irradiation (using
specimen reconstitution if needed);
(vi) manufacture new capsule if there exists an archive material.
3. Research Needed for LTO. European coordinated research on RPV
embrittlement and LTO issues is addressed in the Euratom projects PERFORM-60
and LONGLIFE, which are key research projects of the NUGENIA Association
(www.nugenia.org). NUGENIA is an association dedicated to the research and
development of nuclear fission technologies, with a focus on Generation II and III
nuclear plants. This research is complemented with several national programmes,
as the Enhanced Surveillance Strategy (Belgium), the CARISMA and CARINA
projects (Germany), the revision of embrittlement trend curves (France), etc.
The primary motive in US for reactor pressure vessel integrity is to ensure that
plants can safely and efficiently operate through 80 years without significant
operational constraints or mitigation of RPV embrittlement. The RPV integrity
programme roadmap includes among others the following activities: late blooming
phase embrittlement testing, development of surveillance database, develop
coordinated surveillance capsule programme for PWRs, evaluate the impact of the
extended beltline, etc.
Recommendations for future research were elaborated during the general
assembly of the last IAEA-JRC specialists meeting on RPV embrittlement held in
Znojmo in October 2010 [13]. The following is a non-exhaustive list:
(i) establish the relationship of microstructural variability and fracture
toughness;
(ii) collection and analyses of the worldwide existing research and surveillance
data;
(iii) use of RPV material data from decommissioned reactors for supporting
LTO (low flux – high fluence);
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2013, ¹ 4 11
T a b l e 1
Open Issues for LTO
Issue Importance for long term operation
Low Medium High
Chemical composition �
Late blooming effects �
Flux effects �
Spectrum effects �
Irradiation temperature effects �
MTR versus power reactor �
Thermal ageing �
Master curve versus Unified curve �
Re-embrattlement after annealing �
Embrittlement trend curve at high fluence �
Expanding beltline �
Monitoring embrittlement during life extension � �
RPV Long Term Operation: Open Issues
(iv) link nano-, micro-, and mesoscales and to study initiation and propagation
of microcracks, including the mechanisms behind transgranular and intergranular
propagation;
(v) develop procedure for construction of a design fracture toughness curve
using concepts of Master Curve and Unified Curve focused on small specimens.
Table 1 lists the RPV issues discussed in the previous sections.
Conclusions. The RPV open issues are classified according to the importance
for long term operation. Ongoing research is needed to ensure that the appropriate
analytical tools and correlations are developed to analyse and model vessel
integrity for safe and efficient operation through 60 years and beyond.
Ð å ç þ ì å
Îïèñàíî àêòóàëüí³ ïðîáëåìè çàáåçïå÷åííÿ áåçïå÷íî¿ ðîáîòè ÀÅÑ ïðè ïðî-
äîâæåíí³ òåðì³í³â åêñïëóàòàö³¿, ÿê³ øèðîêî îáãîâîðþþòüñÿ åêñïåðòàìè äàíî¿
ãàëóç³. Äî íèõ, çîêðåìà â³äíîñÿòüñÿ: åôåêòè çàï³çíþâàííÿ â ñòàëÿõ ³ç íèçüêèì
âì³ñòîì ì³ä³; âïëèâ Cu, Ni, Mn ³ P íà ì³êðîñòðóêòóðó, çì³öíåííÿ ³ îêðèõ÷ó-
âàííÿ îïðîì³íåíèõ ñòàëåé; âèêîðèñòàííÿ ðåçóëüòàò³â âèïðîáóâàíü, îòðèìàíèõ
ó äîñë³äíîì àòîìíîìó ðåàêòîð³, äî ïðîìèñëîâèõ ðåàêòîð³â, âêëþ÷àþ÷è åôåê-
òè ôëàêñà ³ ñïåêòðà; ç³ñòàâëåííÿ Ìaster-êðèâî¿ ç óí³ô³êîâàíîþ êðèâîþ, à
òàêîæ îñîáëèâîñò³ ðóéíóâàííÿ âèñîêîîïðîì³íåíèõ ìàòåð³àë³â; îêðèõ÷óâàííÿ
ìàòåð³àë³â ó çîíàõ êîðïóñ³â ðåàêòîð³â ïîçà òðàäèö³éíèìè ó÷àñòêàìè; ïîáó-
äîâà òðåíäîâèõ êðèâèõ îêðèõ÷óâàííÿ äëÿ âèñîêîãî ôëþåíñà íåéòðîí³â çà
ìàëîãî îá’ºìó äàíèõ; ïîâòîðíå îêðèõ÷óâàííÿ ï³ñëÿ â³äïàëó.
1. T. J. Williams, D. Ellis, C. F. English, and J. Hyde, “A model of irradiation
damage in high nickel submerged arc welds,” Int. J. Press. Vess. Piping, 97,
649–660 (2002).
2. M. Miller and J. Kocik, “Atom probe tomography of 15KhMFT Cr–Mo–V
surveillance specimens,” in: Proc. IAEA Specialists Meeting on Irradiation
Embrittlement and Mitigation, IWG LMNPP-99 (1999), pp. 432 – 435.
3. F. Bergner, A. Ulbricht, and H. W. Viehrig, “Acceleration of irradiation
hardening of low-copper reactor pressure vessel steel observed by means of
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Received 03. 10. 2012
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RPV Long Term Operation: Open Issues
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