carina – a programme for experimental investigation of the … · 2017. 11. 20. · experimental...

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VGB PowerTech 5 l 2013 CARINA - Experimental investigation of RPV materials

Kurzfassung

CARINA – Ein Programm zur experimentellen Untersuchung des Bestrahlungsverhaltens von deutschen Reaktordruckbehälter-Werkstoffen

Der Nachweis eines ausreichenden Sicherheits-abstandes gegen Sprödbruch des Reaktordruck-behälters (RDB) ist ein wichtiger Bestandteil der Betriebssicherheit von Kernkraftwerken. Zur sicherheitstechnischen Bewertung des RDB wird in Deutschland die KTA 3201.2 des Regel-werks des kerntechnischen Ausschusses (KTA) zugrunde gelegt. Dieses deterministische Be-wertungskonzept beruht auf dem Vergleich der Belastungskurven mit dem Materialwiderstand hinsichtlich Bruchzähigkeit. Die Bruchzähig-keitskurve kann entweder auf indirektem Weg nach dem auf Kerbschlagbiegeversuchen basier-ten RTNDT-Konzept oder direkt nach dem besser geeigneten RTT0-Konzept, welches auf einer Master-Curve-Analyse von bruchmechanischen Versuchen beruht, bestimmt werden. Mit dem Forschungsvorhaben CARINA (Characteristics

CARINA – A programme for experimental investigation of the irradiation behaviour of German reactor pressure vessel materialsHieronymus Hein, Elisabeth Keim, Eduard Bechler, Pål Efsing, Jens Ganswind, René Knobel, Günter König, Pablo Barreiro, Martin Widera and André de Jong

Introduction

The evidence of sufficient safety margin against brittle fracture of the reactor pres-sure vessel (RPV) is an important part of the operational safety of nuclear power plants since the RPV takes up a central position with respect to the management of deviations from normal operation, to maintain core cooling, and the general function as a physical barrier for fission product retention. The safety assessment procedure for reac-tor pressure vessels to be applied in Germa-ny is regulated in KTA 3201.2 [1] of the Nu-clear Safety Standard Commission (KTA). It involves a concept developed in the USA in the 1970s – the RTNDT-concept, which is based on the definition of a deterministic lower bound fracture toughness – tempera-ture curve obtained from measured values. This curve is then adjusted to the material under consideration with the help of the adjusted reference temperature RTNDTj de-termined individually for the specific mate-rial. As stipulated in the KTA standard, the position of this fracture toughness curve must be determined either indirectly ac-cording to the RTNDT-concept by compari-son of the test results from pre-irradiated and non-irradiated Charpy-V specimens, or directly according to the fracture me-

chanics concept described in KTA 3203 [2] through testing of irradiated fracture me-chanics test specimens.This new fracture mechanics concept, which is based on the so-called Master Curve or T0-concept [3], is being advanced and was already applied for safety analyses worldwide, as it is regarded as an appropri-ate method to prove the safety of reactor pressure vessels against brittle failure. The Master Curve concept represents a method that uses the measured fracture toughness KJc-values to determine a KJc,T curve. Data analysis is performed in a statistical approach that allows probabil-istic evaluation of the curve. An essential advantage of the Master Curve concept is the direct determination of the reference temperature for brittle fracture by fracture mechanical tests and therefore a more re-alistic transfer to component behaviour. In this context, it is also conceivable to apply the two concepts in parallel and with equal priority, with a view that the RTT0-concept could replace the RTNDT-concept in the long-term. For example, it is envisaged to use both concepts in parallel for lifetime management in Japanese plants and for the new generation III+ reactor EPRTM. In Ger-many, additional irradiation capsules with fracture toughness specimens were already placed in the RPV of the modern Neckar-westheim 2 and Isar 2 Konvoi plants. The objective of the CARINA programme (Characteristics of Irradiated German RPV Materials) was to extend the experimental database to reach a final comparative as-sessment of both concepts for the evidence against RPV brittle fracture for further ir-radiated German RPV materials including a larger fluence range together with special influences such as neutron flux, manufac-ture effects, and specific irradiation ef-fects such as late blooming. The analysis of materials irradiated at higher neutron fluences complements the representative-ness of the conclusions from previous stud-ies for the applicability to NPPs in Germany and some neighbouring countries in terms of “upper bound” coverage for a fluence range, which covers the NPPs lifetime (for all PWRs operated 2010 in Germany the

AuthorsHieronymus HeinElisabeth KeimAREVA GmbH Erlangen/GermanyEduard Bechler E.ON Kernkraft GmbH Hannover/GermanyPål EfsingRinghals AB Väröbacka/SwedenJens GanswindVGB PowerTech e.V. Essen/GermanyRené KnobelKraftwerk Gösgen-Däniken AG Däniken/Switzerland Günter KönigPablo BarreiroEnBW Kernkraft GmbH Neckarwestheim/Philippsburg/GermanyMartin WideraRWE Power AG Essen/GermanyAndré de JongN.V. EPZ Kerncentrale Borssele Borssele/The Netherlands

of Irradiated German RPV Materials) wurde die experimentelle Datenbasis für bestrahlte deutsche RDB-Werkstoffe durch umfangrei-che Bruchmechanikversuche erweitert. Die bis zu Neutronenfluenzen von 7.67× 1019 n/cm² (E > 1 MeV) erhaltenen Versuchsdaten wer-den insbesondere mit Bezug auf Master-Curve-Anwendungen ausgewertet und diskutiert. Die experimentellen Ergebnisse zeigen, dass opti-mierte RDB-Herstellungsspezifikationen und Reaktorauslegungen für einen langfristigen Kraftwerksbetrieb von Vorteil sind, im Ver-gleich zu weniger optimierten Werkstoffen mit niedrigerer Zähigkeit und zu Reaktorbaulinien mit wesentlich höherer Neutronenbestrahlung. Mit den gewonnenen Daten, Erfahrungen und Erkenntnissen konnte auch ein wesentlicher Beitrag zur Einarbeitung des Master-Curve-Konzepts in das deutsche Regelwerk geliefert werden. l

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CARINA - Experimental investigation of RPV materials VGB PowerTech 5 l 2013

design range for 32 EFPY is in between 5×1018 and 2×1019 n/cm2 (E > 1 MeV)). In this way CARINA makes a significant contribution in proving the safety of espe-cially German nuclear power plants and maintains the link to international proce-dures, in particular with regard to the ma-terial behaviour of reactor pressure vessels under neutron irradiation and in long-term operation. The CARINA programme lasted from 2008 to 2012 and was funded by VGB (VGB Special Committee “Plant Engineering” No. 65/07), BMWi (German Federal Min-istry of Economics and Technology, FKZ 1501357), the Gösgen (Switzerland) and Ringhals (Sweden) nuclear power plants, and Areva GmbH.

The deterministic RPV integrity approach

Reference temperatures for nil-ductility transition are used in the RPV integrity as-sessment for the adjustment of the mate-rial resistance curve (fracture toughness) which is compared to the load path curve (stress intensity) as shown in F i g u r e 1 . The fracture toughness curve is based on a so-called lower bound curve described in the ASME code [4] and depends on the reference temperature. The higher the ref-erence temperature the more the curve is shifted to the right in Figure 1. There are two essential concepts used worldwide for the adjustment of the material resistance curve:

– RTNDT-concept – Master Curve concept

The RTNDT-concept is based on drop-weight and Charpy-V tests resulting in an adjusted reference temperature RTNDTj (Reference Nil-Ductility Transition Temperature) ac-cording to Equation 1.

RTNDTj = RTNDT + ΔT41 (1)

The Master Curve is based on fracture mechanical tests resulting in a reference temperature T0 at 100 MPa m0.5 on the 50 % fractile median curve normalised to 1T (25 mm) specimens as defined in ASTM E 1921 [5]. Then a margin is applied to the T0 which is 19.4 K according to ASME code case N-629 [6] and N-631 [7], respectively resulting in a reference temperature RTT0 as shown in Equation 2.

RTT0 = T0 + 19.4 K (2)

Whereas the material resistance is gov-erned by a reference temperature defined by Equation 1 or Equation 2, the load path is governed by any loading higher than the normal operation caused by loss of cool-

ant accidents (LOCA) or other transients. In this case the emergency core cooling system is switched on and cold water is fed in the RPV at high pressure and high temperature resulting in significant higher stresses e.g. in the nozzle region and in the core beltline of the RPV, the so-called PTS (pressurised thermal shock). In a deterministic PTS analysis the follow-ing essential steps have to be performed:

– determination of critical areas and flaw postulates in the RPV,

– thermal hydraulic analyses to determine the temperature field as function of time,

– structure mechanical Finite Element analyses to determine the stress fields and the stress intensity factors in the postulated flaws (at crack tip) as func-tion of time.

Finally it has to be proven that brittle frac-ture can be excluded with sufficient safety margins in the specific RPV areas for the LOCA paths considered.

Specimen materials, irradiation facilities and experimental test programme

The RPV materials of the CARINA test ma-trix are representative for all four German PWR construction lines built by the for-mer Siemens/KWU company. Due to the similarities of the vessel steels, the Ger-man BWR type 72, which is of significantly lower fluence, is also covered. Three base materials (BM, forgings), two heat affected zones (HAZ) and three weld metals (WM) were studied in the CARINA programme as shown in Ta b l e 1 containing also the materials studied in the previous CARIS-MA programme [8]. Both RPV steels with optimised chemical composition and with

Stre

ss in

tens

ity, f

ract

ure

toug

hnes

s in

MPa

√m

Temperature in °C

Material resistance

Load path

K = s · √pas

Fig. 1. Deterministic RPV integrity assessment.

Fig. 2. Material testing cell in the Hot Cells Laboratory.

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higher susceptibility to irradiation em-brittlement by high copper or high nickel content were examined. In addition, the already available data of two high nickel welds (R3 WM with 1.58 % Ni and R4 WM with 1.66 % Ni) were considered.

The CARINA materials were irradiated in two facilities, in the VAK (Versuchsatom-kraftwerk Kahl) reactor and in a commer-cial PWR of Siemens/KWU design within a RPV irradiation surveillance programme. The surveillance specimens were irradiat-ed in standard capsules inserted in the RPV at a position of highest flux with a very low axial flux gradient near core midplane, and in so-called gradient capsules at a po-sition with lower flux due to the axial flux gradient near core edge. The VAK reactor, a small experimental boiling water reactor operated by the German utility RWE with an electrical power of approx. 15 MW, was in operation until 1985 and between 1975 and 1985 it was also used by the former company Siemens/KWU as an irradiation plant for various research and irradiation surveillance programmes. The neutron spectrum of the VAK reactor was compa-rable to that of other PWR manufactured by Siemens/KWU. For the various types of irradiation studies an irradiation tempera-ture between 265 °C and 316 °C was used. The VAK was also the main irradiation fa-cility for the CARISMA materials.

The neutron fluences applied to the tested specimen materials are in the range between 5.44×1018 n/cm2 and 7.67×1019 n/cm2 (E > 1 MeV) with a neutron flux from 2.64 × 1010 n/cm2s to 2.55 × 1012 n/cm2s.The maximum irradiation temperature of the CARINA materials irradiated in the VAK reactor was between 283 °C and 289 °C, and around 300 °C for those irradi-ated in the commercial PWR. In particular for the irradiated condition, some material data were already available from previous programmes, however for

most of the irradiated CARINA materials specimen fabrication and testing was nec-essary.

The CARINA experimental test programme consisted of tensile, Charpy impact, and crack initiation and arrest tests with the main focus on toughness tests as shown in Ta b l e 2. Altogether 399 specimens were tested including some materials of the pre-vious CARISMA programme. Whereas the crack initiation tests were performed with single edge notched bending (SE(B)) spec-imens of 10 x 10 x 55 mm size according

Tab. 1. Overview on RPV materials examined.

RPV material German PWR generation

Material code Cu [%] P [%] Ni [%]

CARINA

20MnMoNi5-5 JSW

4 (Konvoi)

P142 BM 0.06 0.005 0.8

22NiMoCr3-7 JSW

3 P150 BM 0.05 0.008 0.83

22NiMoCr3-7 JSW

3 P150 HAZ – – –

22NiMoCr3-7 Klöckner

1 to 2 P151 BM 0.09 0.006 0.96


1 to 2 P151 HAZ - - -

Molytherme Electrode Sulzer

2 P152 WM 0.02 0.014 0.09

S3NiMo1/OP41TT GHH

4 (Konvoi)

P142 WM 0.06 0.012 0.9

S3NiMo3/OP41TT Uddcomb

3 P16 WM 0.08 0.012 1.69

CARISMA

20MnMoNi5-5 JSW

4 (Konvoi)

P141 BM 0.05 0.01 0.79


1 to 2 P7 BM 0.12 0.02 0.97

22NiMoCr3-7 JSW

3 to 4 P147 BM 0.05 0.01 0.84

S3NiMo1/OP 41 TT UP, GHH

4 (Konvoi)

P141 WM 0.03 0.02 1.01

S3NiMo3/OP 41 TT UP, Uddcomb

3 P16 WM 0.08 0.012 1.69

NiCrMo1 UP/LW320, GHH

2 to 4 KS05 WM 0.05 0.01 0.91

NiCrMo1 UP(modified)/ LW320,

LW330

1 P370 WM 0.22 0.02 1.11

Tab. 2. CARINA test matrix

Material code Tensile tests Charpy-V tests SE(B) tests Crack arrest tests

P142 BM 6 9 19 8

P150 BM – – 39 –

P150 HAZ – – 32 –

P151 BM – – 74 –

P151 HAZ – – 56

P152 WM – – 64 –

P142 WM 3 12 18 6

P16 WM 3 – 11 13

P141 WM – – – 8

P370 WM – 9 –

P7 WM – – – 9

∑ 12 30 313 44

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to the test standard ASTM E-1921[5], so-called duplex crack arrest specimens were used for the crack arrest tests based on the test standard ASTM E-1221 [9]. The recon-stitution technique, at which specimens are manufactured from broken halves or from untested compact specimens, was often applied for reasons of limited avail-ability of irradiated material. All tests have been performed in the accredited Hot Cell Laboratory of the Areva GmbH in Erlangen ( F i g u r e 2 ). The duplex crack arrest specimen type was used to overcome invalid test results for some highly irradiated weld metals tested with standard compact crack arrest speci-mens. The particularity of duplex crack arrest specimen used is that two different parts of 100 mm width and 25 mm thick-ness are welded together by electron beam welding. One part consists of the crack starter material which is heat treated with a defined hardness, yield strength, elonga-tion, and microstructure. This part is weld-ed together with the second part contain-ing the real testing material. The theory behind this modification is that a fast run-ning crack with a higher crack driving force and velocity may jump through the ductile heat affected zone of the weld seam and will arrest in the material which is under investigation [10]. The neutron fluences (E > 1 MeV) accu-mulated by the specimens irradiated in the various irradiation facilities were calculat-ed for each specimen by well established neutron transport codes such as ANISN/DORT and TORT in three-dimensional form.

Results of the material testing

The main objective of the material tests was to provide toughness data for both crack initiation and crack arrest and to an-alyse them by the Master Curve approach

with the aim to determine reference tem-peratures applied for adjustment of the lower bound toughness curves up to high neutron fluences. The yield and ultimate strength data of the tensile tests confirmed the increased hard-ening caused by irradiation. Moreover the yield strength data were used to calculate limit values KJc(limit) for the fracture tough-ness according to the test standard ASTM E-1921[5].The obtained Charpy-V test results were used for the determination of the adjusted reference temperatures RTNDTj by the ΔT41 shift according to Equation 1. According to the applied standard the fracture toughness test results were re-calculated to the specimen thickness 1T (= 25.4 mm) in order to facilitate an evaluation which is independent on the specimen thickness. In F i g u r e 3 a typi-cal fracture toughness test evaluation in a KJc-T diagram with Master Curve applica-tion is shown where the fracture toughness is measured with SE(B) specimens for the

irradiated weld material P142 WM. The diagram contains the 2 %, 5 %, 95 % and 98 % percentiles, the Master-Curve (50 % median) and the T0 ± 50 K intervals. The T0 transition temperature at 100 MPa m0.5 is then used for the determination of the reference temperature RTT0=T0+19.4 K according to Equation 2.

Discussion of crack initiation results

The reference temperature of interest, the RTT0, was determined in this way for all of the CARINA materials for various irradia-tion levels. In F i g u r e 4 the reference temperatures RTT0 depending on neutron fluence are given for the CARINA materials together with the RTlimit curve of the German KTA 3203 [2]. The RTlimit curve defines an upper bound for the reference tempera-ture as a function of the neutron fluence (E > 1 MeV) and is based on measured German RPV surveillance data. The curve is valid for all German BWR and PWR pressure vessel forgings and plates (22 NiMoCr 3-7 and 20 MnMoNi 5-5 base materials), and weld materials with Cu ≤ 0.15% and Ni ≤ 1.1%. This RTlimit curve was also confirmed by U.S. and French irradiation surveillance data of ap-propriate materials under comparable irra-diation conditions [11]. The increase of T0 is a reliable indicator for the irradiation embrittlement. In spite of the relatively high fluences only a moder-ate increase of T0 is clearly seen for all ma-terials, except for the high nickel weld ma-terials P16, R3 and R4 confirming the well known effect of high nickel content on the reference temperature shift caused mainly by the radiation induced formation of man-ganese-nickel rich precipitates (MNP).

For all specimen materials where the Cu and Ni contents are in the valid range (max. 0.15 % Cu and 1.1% Ni) according to the standard, the measured RTT0 values in-dicate a comparatively low irradiation em-

160

120

80

40

0

-40

-80

-120

-160

P16 WM

R3 WM

R4 WM

P142 BM

P142 WM

P150 BM

P151 BM

P150 HAZ

P151 HAZ

P152 WM

KTA Limit curve

RTT0

(j) i

n°C

Neutron fluence F in cm-2 with E > 1 MeV

0.0E+00 2.0E+19 4.0E+19 6.0E+19 8.0E+19 1.0E+20

Fig. 4. Reference temperatures RTT0 of the CARINA materials (P16 WM, R3 WM and R4 WM are high nickel weld materials).

300

250

200

150

100

50

0

K JC(1

T) in

MPa

√m

75-150 -125 -100 -75 -50 -25 0 20 50

CARINA, P142 WM, neutron fluence 5.15 ∙ 1019 cm-2

2 % and 98 % boundary curve5 % and 95 % boundary curveMaster curveT0 ±50 °CValid values

T0 = -39 °C, σ = 7.9 °C (σexp = 4 °C)

Temperature in °C

Fig. 3. Measured KJc(1T) values and Master Curve for T0 determination for P142 WM irradiated to 5.15 × 1019 n/cm2 (E > 1 MeV).

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brittlement and are enveloped with a com-fortable safety margin by the upper bound curve RTlimit of KTA 3203. Even the refer-ence temperatures of the specimen materi-als with higher contents Ni (e.g. P16 WM) are still below the RTlimit curve for fluences of 2×1019 n/cm2 (E > 1 MeV) which is far below the RPV fluence even after 60 years of operation for PWR with high nickel RPV welds operated in Germany. It is also obvious in Figure 4 that the RTT0 of heat affected zone materials is always lower compared to the base materials. This confirms the procedure stipulated in the US-American and German set of regula-tions to omit the HAZ in RPV irradiation surveillance programmes.A further point of interest is whether the measured fracture toughness data are envel-oped by the lower bound curve of the ASME Boiler and Pressure Vessel Code [4] repre-senting conservative values based on meas-ured static initiation KI values. The meas-ured fracture toughness data for static initi-ation and normalised with RTT0(j) are shown in F i g u r e 5 together with the ASME KIc lower bound curve which was confirmed by the data from the application point of view.

The few data points, which were not envel-oped by the curve, were tested at very low temperatures and belong to materials with a low T0 as well. Since this temperature re-gion is not reached during plant operation, these values are not relevant for safety as-sessment applications. In addition, the con-cerned data points with KJc(1T) smaller than 50 MPa√m are not located within the safety relevant measurement range.

If the measured KJc(1T) data are nor-malised with RTNDT(j) as shown in F i g - u r e 6 , where the data are also enveloped by the curve, two advantages of the Master Curve/RTT0 approach are becoming clear. First, the strong inherent scatter of the data normalised with RTNDT(j) ( Figure 6 ) is significantly reduced by normalisation with RTT0(j) (Figure 5). Second, the KJc(1T) data of the base materials normalised with RTNDT(j) (Figure 6) have substantially larg-er margins to the ASME KIc lower bound curve than the weld materials data, com-pared to normalisation with RTT0(j) (Fig- ure 5). This behaviour is confirmed in F i g -u r e 7 showing the measured RTT0(j) against the fluence adjusted RTNDT(j) for both the CARINA and the CARISMA materials. For

the base materials the RTT0 approach leads to significantly lower reference tempera-tures compared to the RTNDT concept, how-ever this is not the case for the weld materi-als for which the general trend of RTNDT(j) > RTT0(j) is less or not at all pronounced. This conservative RTNDT behaviour of the base materials is caused by the “acceptance tests” at initial state by which for base ma-terials usually the drop weight test is lead-ing for the NDT temperature. The weld bead applied to the base material in the drop weight test leads to a material change and a crack arrest value is effectively meas-ured, contrary to the weld materials where less conservative NDT temperatures are measured. Thus, the high conservativity of the RTNDT-concept is particularly under-lined for base materials.

Another point of interest is the correlation between the shift of the reference tempera-ture obtained from the fracture mechanics test and shift of the T41 determined from Charpy-V test. As shown in F i g u r e 8 , the shifts ΔT0 and ΔT41 show a good correla-tion, wherewith the ΔT0 and ΔT41 can be used equivalently for the determination of the reference temperature.

K JC(1

T) in

MPa

√m

T-RTT0 (j) in K

250

200

150

100

50

0100

ASME KIC CurveP142 BMP150 BMP150 HAZP151 BMP151 HAZP142 WMP152 WMP16 WM

-200 -150 -100 -50 0 50

Fig. 5. KJc(1T) values normalised to T-RTT0(j) for CARINA materials.

K JC(1

T) in

MPa

√m

T-RTNDT int in K

250

200

150

100

50

0100-200 -150 -100 -50 0 50

ASME KIC curveP142 BMP150 BMP151 BMP142 WMP152 WMP16 WM

Fig. 6. KJc(1T) values normalised to T-RTNDT(j) for CARINA materials.

-125

-75

-25

25

75

125

175 P141 BMP7 BMP147 BMP141 WMKS05 WMP370 WMP16 WMP150 BMP151 BMP142 BMP152 WMP142 WMR3 WMR4 WM

±25 K

RTT0

in °C

RTNDTj in °C-125 -75 -25 25 75 125 175

Fig. 7. Measured RTT0(j) versus fluence adjusted RTNDT(j) values of CARINA and CARISMA materials.

ΔT 0

in K

ΔT41 in K

P141 BMP7 BMP147 BMP141 WMKS05 WMP370 WMP16 WMP150 BMP151 BMP142 BMP152 WMP142 WMR3 WMR4 WM

250

200

150

100

50

0

-50

-100-100 -150 0 50 100 150 200 250

±25 K

Fig. 8. Measured ΔT0 versus fluence adjusted ΔT41 values of CARINA and CARISMA materials.

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Special effects

In F i g u r e 9 the reference temperatures RTT0 from materials irradiated in standard (high neutron flux) and gradient (lower neutron flux) capsules are shown. The re-sults do not show any relevant flux effect for the RPV materials investigated. Again, the lower RTT0 of heat affected zone mate-rials compared to the base materials con-firms the procedure stipulated in the US-American and German set of regulations to omit the HAZ in RPV irradiation surveil-lance programmes.Late Blooming Phases (LBP) may occur for low Cu and high Ni materials at high flu-ences. No significant indications for any LBP at high fluences (>2 × 1019 n/cm2) have been found in the CARINA data base. However, final confirmation is still pending by ongoing microstructural analyses of the

material concerned within the European LONGLIFE project.

Discussion of crack arrest results

The application of the Duplex-CCA speci-men geometry (details in [10]) in CARINA led to an increase of the test temperature up to 60 °C beyond the NDT temperature (before ~20 °C) of the material and to an increase of the “testable” crack arrest toughness to 150 MPa√m to get valid test results. This enabled the testing of irradiat-ed weld materials. However, for the testing of highly irradiated weld materials, whose “test window” lies in the temperature range >70 °C, a further optimisation of the specimen fabrication process would be re-quired. Another alternative is the manufac-ture of bigger specimens or the irradiation of the specimens after the manufacture.

The measured crack arrest toughness val-ues of the non-irradiated and irradiated materials are enveloped by the RTNDT(j) as well as by RTTKIa and TKIa indexed “lower bound” ASME KIR-curve. This confirms the applicability of both the RTNDT and the Master Curve concept for crack arrest. However, the alternative use of RTT0 for indexation of the KIa fracture toughness curve described in ASME Code Case N-629 [6] is not confirmed by the measured data ( F i g u r e 10 ).Finally, the experimental data confirmed the correlations known from the literature between the crack arrest transition temper-ature TKIa (determined by the Master Curve approach), the TFA4kN (determined by the instrumented Charpy impact test) and the TNDT (from drop-weight test). Thus, the correlations concerned are a promising alternative to costly crack arrest tests.

Summary

A fracture mechanical database was ex-tended which is representative for all German PWR construction lines includ-ing the German BWR type 72 and a good technical base for long term operation far beyond 32 EFPY. The neutron fluences applied to the specimen materials are in the range between 5.44 × 1018 n/cm2 and 7.67 × 1019 n/cm2 (E > 1 MeV) with a neutron flux from 2.64 × 1010 n/cm2s to 2.55 × 1012 n/cm2s.The “lower bound” ASME KIc-curve for crack initiation (brittle failure) could be confirmed by the measured fracture toughness values. Herewith considerable progress in terms of the usage of fracture toughness curves in combination with structures for the RPV safety assessment could be achieved. The irradiation reac-tion (increasing ductile to brittle transition

P152 WM standardP152 WM gradientP151 BM standardP151 BM gradientP151 HAZ standardP151 HAZ gradient

0.0E+00 1.0E+19 2.0E+19 3.0E+19 4.0E+19 5.0E+19 6.0E+19 7.0E+19 8.0E+19

0

-20

-40

-60

-80

-100

-120

-140

-160

-180

RTT0

(j) in

°C

Neutron fluence with E > 1 MeV in cm-2

WM

BM

HAZ

2.18E+112.64E+10

4.41E+109.13E+10 1.06E+11

2.15E+11 2.69E+10

2.35E+11

4.40E+10

2.37E+11

6.87E+10 8.35E+10

2.18E+11

2.65E+10 2.29E+11 5.80E+10

7.11E+10

Fig. 9. Measured reference temperatures RTT0(j) for CARINA materials irradiated with different neutron fluxes (neutron flux numbers in cm–2s–1, E > 1 MeV).

KIR lower boundP7 BMP7 BM (3.89E+19)P141 BM (6.87E+18)P147 BMP147 BM (1.17E+19)P142 BM (3.78E+19)P370 WMP141 WM (8.39E+18)P16 WM (7.41E+18)P142 WM (4,28E+19)

KIR lower boundKIC lower boundP7 BMP7 BM (3.89E+19)P141 BM (6.87E+18)P147 BMP147 GW (1.17E+19)P370 BMP142 BM (3.78E+19)P370 WMP141 WM (8.39E+18)P16 WM (7.41E+18)P142 WM (4.28E+19)

T-RTTKIa in °CT-RTT0 in °C

0

50

100

150

200

250

250

200

150

100

50

0-100 -50 0 50 100 -200 -150 -100 -50 0 50 100

K Ia

in M

Pa√m

K Ia

in M

Pa√m

Fig. 10. Measured crack arrest toughness data indexed with RTT0 and RTTKIa.

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temperature) of the tested RPV materials is relatively low, even at higher fluences. The high nickel materials form an excep-tion for which the irradiation reaction is higher, but starting from a very high initial toughness.

For a 60 years operation comfortable safety margins to the KTA-limit curve have been determined with both the RTNDT- and the RTT0-concept, which demonstrates a good applicability of both concepts for all ma-terials tested. For the high nickel welds (Ni > 1.1 %) all measured reference tem-peratures have also been covered by the KTA limit curve to a fluence which would not be exceeded by the German PWRs con-cerned even after 60 years of operation.

The fracture toughness results do not show any relevant flux effect for the RPV materials investigated and any occurrence of Late Blooming Phases at high fluences (>2 × 1019 n/cm2) was not found.

The RTT0-concept compared to the RTNDT-concept led to lower reference tempera-tures for the base materials. For the weld materials the general trend of RTNDT > RTT0 is less or not at all pronounced. A reason for that could be “acceptance tests” (drop-weight tests) which lead to less con-servative TNDT-results for the weld materi-als. Moreover, it was found that ΔT0 and ΔT41 show a good correlation, wherewith the ΔT0 and ΔT41 can be used equivalently in determination of the reference tempera-ture.

The lower RTT0 of heat affected zone ma-terials compared to the base materials con-firms the procedure stipulated in the US-American and German set of regulations to omit the HAZ in RPV irradiation surveil-lance programmes.

The application of the Duplex-CCA speci-men geometry led to a general improve-ment in test temperature range and to an increase of the “testable” crack arrest

toughness to 150 MPa√m to get valid test data. Nevertheless, further optimisation of the specimen manufacture would be re-quired for testing highly irradiated materi-als. The measured crack arrest toughness values of the non-irradiated and irradiated materials are enveloped by the RTNDT(j) as well as by RTTKIa and TKIa indexed “lower bound” ASME KIa-curve. This confirms the applicability of both the RTNDT and the Master Curve concept for crack arrest. However, the alternative use of RTT0 for indexation of the KIa fracture toughness curve described in ASME Code Case N-629 is not confirmed by the measured data. The correlations between the crack arrest tran-sition temperatures TKIa, TFa4kN and TNDT confirm the correlations obtained from literature. The correlations concerned are a promising alternative to costly crack ar-rest tests.

Moreover, the experimental results show that optimised RPV manufacturing speci-fications and reactor designs are advan-tageous for a long term plant operation in comparison to less optimised materi-als with lower toughness and to reactor designs with substantial higher neutron design fluences. With the obtained data, experiences and insights an essential con-tribution was made to the integration of the Master Curve concept in the German standard KTA 3201.2 [1].

References[ 1] Sicherheitstechnische Regel des KTA

„Komponenten des Primärkreises von Leichtwasserreaktoren, Teil 2: Ausle-gung, Konstruktion und Berechnung“ KTA 3201.2, Fassung 6/96.

[ 2] Sicherheitstechnische Regel des KTA ”Überwachung des Bestrahlungsverhal-tens von Werkstoffen der Reaktordruck-behälter von Leichtwasserreaktoren“ KTA 3203, Fassung 06/01.

[ 3] Wallin, K.: Recommendations for the Ap-plication of Fracture Toughness Data for

Structural Integrity Assessments, Proceed-ings of the Joint IAEA/CSNI Specialists Meeting on Fracture Mechanics Verifica-tion by Large-Scale Testing, NUREG/CP-0131 (ORNL/TM-12413), October 1993.

[ 4] ASME Boiler and Pressure Vessel Code, Section XI, Division 1, Appendix A Article A-4000 Material Properties, 2007 Edition.

[ 5] ASTM E 1921 – 13, Standard Test Method for Determination of Reference Tempera-ture, T0, for Ferritic Steels in the Transition Range.

[ 6] ASME Boiler and Pressure Vessel Code, Section XI, Rules for In-service Inspection of Nuclear Power Plant Components, Code Case N-629, 1998 Edition.

[ 7] ASME Boiler and Pressure Vessel Code, Section III, Requirements for Design & Manufacture of Nuclear Power Plant Com-ponents, Code Case N-631, 1999 Edition.

[ 8] Hein, H., Keim, E., Schnabel, H., Seibert, T., and Gundermann, A.: Final Results from the Crack Initiation and Arrest of Irradi-ated Steel Materials Project on Fracture Mechanical Assessments of Pre-Irradiated RPV Steels Used in German PWR. Journal of ASTM International, STP1513, Effects of Radiation on Nuclear Materials and the Nuclear Fuel Cycle: 24th Volume.

[ 9] ASTM E 1221 - 12, Standard Test Method for Determining Plane-Strain Crack-Arrest Fracture Toughness, KIa, of Ferritic Steels.

[10] Gundermann, A., Keim, E., and Obermeier, F.: Further development of duplex speci-mens for measuring plane strain crack arrest fracture toughness. 18th European Conference on Fracture, ECF18-441, Sep-tember 2010.

[11] Bartsch, R., Langer, R., and Nagel, G.: New German KTA Rule for Irradiation Surveil-lance, Evaluation and Application in the Safety Assessment of RPV. Fontevraud 5, 23-27 September, 2002.

[12] Altstadt, E., Bergner, F., and Hein, H.: Irradiation Damage and Embrittlement in RPV Steels under the aspect of Long Term Operation – Overview of the FP 7 Project LONGLIFE. Proceedings of ICONE 2010 International Conference on Nuclear En-gineering, May 17-21, 2010, Xi’an, China. l

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