Ludovt Kupca: Irradiation Embrittlement Monitoring Programmes in Slovak Republic

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IRRADIATION EMBRITTLEMENT MONITORING
PROGRAMMES IN SLOVAK NUCLEAR POWER PLANTS
Author Ludovít Kupca VÚJE Trnava, Inc.-
Engineering, Design and Research
Organization Okruná 5, 918 64 Trnava, Slovak
Republic
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1. STANDARD SURVEILLANCE SPECIMEN
PROGRAMME (SSSP) RESULTS ANALYSIS
SSSP programs were applied in NPP V-2
WWER-440/213 type RPVs for irradiation
embrittlement monitoring.
1.1 EXPERIMENTAL MATERIAL OF THE SURVEILLANCE
SPECIMENS
Surveillance specimens were prepared from
the base metal (BM) - steel 15CH2MFA - a core
region, samples of weld metal (WM) and heat
affected zones (HAZ) from R-weld, six twin
chains were prepared for each RPV, set of
samples for the initial conditions properties
testing - so called zero or initial condition
material properties.
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1.2 NEUTRON FLUX MONITORING AND CALCULATIONS
Fe, Cu, Nb and Co foils detectors placed in the
six capsules along the reactor core.
Calculation for energy En gt 0,5 MeV and
En gt 0,1 MeV. The accuracy of the
neutron fluence estimation was lt 20.
Fig.No.1 Fluence values for the units 3 and 4
NPP V-2 after 5 and 10 years of irradiation
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1.3 IRRADIATION TEMPERATURE MONITORING
Based on the diamond lattice parameters changes
due to the irradiation. The mean values of
irradiation temperatures were following Unit
3 Tirr 288 18 oC Unit 4 Tirr 272 19
oC. The results of these measurements
were not satisfactory.
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1.4 STATIC TENSILE TEST

• Sub-size tensile specimen were used
• Irradiation hardening coefficients were
  calculated by formula
• BF dRp0,2. (F. 10-22)-1/3

1.5 CHARPY TEST

• main evaluation criterion is the TKCV 50 J/cm2
• the lateral expansion (dB 0,9 mm)
• share of ductile/brittle fracture surface (50)
  as supplementary
  methods were used

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1.6 COD TEST

• The samples with side grooves and fatigue cracks
  starting from the V-notch (1 mm)
• The trend curves creation by formula
• Kic, Kcj, K0,2
  KminLHa0LH.exp(a1LH.T)
• Calculation of the irradiation embrittlement
  coefficient by formula
• AfLH ?TT100LH . (F. 10-22)-1/3

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1.7 TRANSITION TEMPERATURES TRENDS FOR BM AND WM
OF BOHUNICE UNITS 3 AND 4

• Tkf for BM is evaluated for the maximum
  of neutron fluence in the internal surface
  of RPV
• in the position of WM No.4 by formula
• Tkfi Tkf0 AfKCV10 .(i . F10. 10-22)1/3

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1.8 CONCLUSIONS FROM SSSP

• After 10 years of irradiation, we observed the
  significant growth of strengths
  and decrease of ductility.
• Transition temperature shifts of WM calculated
  from the Charpy-V and fracture toughness tests
  results are in the range of prediction after 10
  years of irradiation.
• Higher WM irradiation embrittlement coefficients
  values of unit 3 are possible to explain due to
  the lower precision of fluence for this unit.
• From the SSSP tests results and calculations of
  RPVs materials embrittlement trends after ten
  years of irradiation follow that the real
  embrittlement of both reactors NPP V-2 till
  planed EOL will be acceptable.

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2. EXTENDED SURVEILLANCE SPECIMEN PROGRAMME
(ESSP)
This program was prepared on the base of
critical analysis of SSSP.
2.1 EXPERIMENTAL MATERIAL
The main problem was the limited amount of
original RPVs material. After SSSP
applications were available for ESSP the rest
from sets of first set un-irradiated specimens
only.
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2.2 SPECIMENS FOR IRRADIATION
In ESSP were prepared several types of specimens
for irradiation base and weld metal Charpy
V, COD, special samples for transmission
electron microscopy, Mössbauer spectroscopy and
electron-positron annihilation measurement.
In one irradiation capsule are 12 specimens which
enables to create the Charpy-V notch versus
temperature and J-R curves too.
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The main goals of irradiation condition
monitoring in ESSP were value of lead
factor in the range 3-5, higher accuracy of
neutron dosimetry, fixed samples orientation
to the reactor core, dose rate effect
evaluation.
Six chains by VÚJE design were prepared for each
unit NPP V-2.
This approach of ESSP enables the irradiation
embrittlement of RPV materials monitoring
according the international standards,
validation of SSSP results, prediction of Tkf
and Tka values.
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2.3 ESSP NEUTRON DOSIMETRY
Improved ESSP neutron dosimetry is based on
new sets of activation foils and wires for each
irradiation capsule (Nb93, Fe54, Cu63,
Ni58, Ti46, Mn55), improved symmetry of
monitors inserted in irradiation capsules,
fixed orientation of irradiation capsules to the
reactor core, neutron fluence monitoring
opposite the irradiation capsules on the outside
surface of RPV.
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2.4 IRRADIATION TEMPERATURE MEASUREMENT
In ESSP are used two methods of irradiation
temperature measurement thermocouples (one set
of ESSP capsules), melting monitors (all
irradiation capsules).
Application of thermocouples measurement method
is rather complicated and expensive for power
reactors, but has best accuracy. Melting monitors
are not so precise, but widely used because of
its simplicity.
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In ESSP are used following melting monitors
for temperature range 271-305C
pure Bi with Tmelt 271 C PbAg2Sb4
with Tmelt 284 C PbAg2Sb2 with Tmelt
296 C PbAg2,5 with Tmelt 305 C.
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2.5 ESSP SUPPLEMENTARY METHODS
All applied methods transmission electron
microscopy (TEM), Mössbauer spectroscopy
(MS), and electron-positron annihilation
(EPA), are used for estimation of the density and
type of irradiation induced defects of the RPV
steel crystal lattice as the function of
irradiation environment.
2.6 ESSP REALIZATION SCHEDULE
ESSP program started in the year 1994 and is
scheduled till 2005. ESSP program was prepared
and is managed by VÚJE institute.
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2.7 ESSP PRELIMINARY RESULTS
Till this time were realized following activities
from ESSP program analysis of the first four
sets of samples (KCV, COD) from the units 3 and
4, analysis of activation foils and special
samples by - Mössbauer spectroscopy
and electron-positron measurement, -
neutron dosimetry measurement, -
transmission electron microscopy. melting
monitor evaluation was finished and documented,
the computer database preparation for
processing and archiving all ESSP results and
relevant data. Fourth stage of ESSP evaluation
will be finished in this year.
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Fig. 8 Melting monitors from the capsule No.445
ESSP unit 4 NPP V-2
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3. MODERN SURVEILLANCE SPECIMEN PROGRAMME (MSSP)
APPLICATION FOR MOCHOVCE NPP
3.1 INTRODUCTION

• In the year 1996 start of completely new
  surveillance specimen program preparation for the
  Mochovce RPVs unit-1 and 2.
• VÚJE institute prepared MSSP with completely new
  philosophy for monitoring of RPV irradiation
  embrittlement.
• MSSP great advantage complete sets of RPVs
  specimen from the Standard Surveillance Program.
• This project was included to the range of the
  Mochovce NPP safety improvements SI CI-01
  Irradiation embrittlement monitoring.

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Nuclear Power Plants Research Institute (VÚJE
)Trnava, Inc. - Engineering, Design and Research
Organization
3.2 MSSP CHARACTERIZATION

• MSSP concept is derived from
• the fundamental postulate - to provide the
  irradiation embrittlement monitoring till unit
  EOL,
• the time delay of NPP Mochovce operation enabled
  the essential upgrading of the RPVs surveillance
  program,
• the critical analysis of SSSP results for
  WWER-440 type V-213 reactors,
• approved concept and experience from the
  implementation of ESSP at NPP V-2,
• recommendations after the evaluation of the first
  set of irradiated specimens from ESSP.

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• The main goals of the new surveillance program
  for NPP Mochovce were
• to perform mechanical tests on unirradiated
  specimens,
• to prepare specimens for the first six MSSP
  chains for NPP EMO unit 1 and 2 from the
  specimens after the tests of unirradiated set,
• to save the rest of other SSSP chains for the
  irradiation embrittlement monitoring till EOL.

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3.3 TYPE OF SPECIMENS

• For transition temperature shift evaluation, we
  are using
• Charpy test,
• COD test.
• MSSP also used inserts 10x10x11mm, from which
  Charpy-V and COD specimens are reconstituted by
  electron beam welding.
• The set of 12 specimens are used for
  determination of the transition temperature Tkf
  from the Charpy test.
• Other 12 specimens are used for determination of
  the J-integral and J-R curve from the COD test.
• All set for one curve is in one irradiation
  capsule.

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3.4 MSSP MATERIALS

• Main attention is paid to WM and BM.
• The tests on HAZ are not considered in this
  program, because of
• large dispersion of the measured results,
• problems with exact positioning of the notch into
  center of HAZ,
• irregular fracture path through HAZ samples.

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3.5 IRRADIATION TEMPERATURE MEASUREMENT

• All irradiation capsules are equipped with
  melting monitors covering the temperature range
  from 270 to 300oC.
• Chain No.4 is equipped with thermocouples for a
  continuous measurement.
• Except this MSSP is equipped by
• temperature measurement on the RPV outer surface
  around the weld No. 4,
• optimization of number and types of the melting
  monitors.

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3.6 FLUENCE MEASUREMENT

• The fluence measurement in the MSSP program is
  improved by
• extended set of the neutron flux monitors in the
  capsules and in the reactor shaft with the
  fissile monitors,
• improved design for placing the neutron monitors
  outside RPV,
• fluence monitoring outside RPV in correlation to
  the measurements in the irradiation capsules,
• adaptation of the existing monitoring system to
  enable data recording and archiving.

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3.7 COMPLEMENTARY MEASUREMENTS
MSSP concept design considers application of the
following methods

• transmission electron microscopy (TEM),
• Mösbauers spectroscopy (MS),
• electron -positron annihilation (EPA).

WM, BM, and HAZ foils are irradiated in the
selected irradiation capsules.
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3.8 IRRADIATION CHAINS DESIGN
For the first stage of MSSP is the design of the
irradiation chain similar as in ESSP, with
several modifications based on the experience
gained within this program.

• Such a solution provides for
• compatibility with internal construction of
  Mochovce RPV,
• fixed orientation of the capsules towards the
  reactor core center,
• reliable and operationally proved construction of
  the thermocouple leads out of the reactor,
• variable length of the irradiation chains,
• proper placement of the irradiation capsules
  along the reactor core (lead factor).

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3.9 CONCLUSIONS
Present situation is following
1. The project of MSSP was prepared at the end of
the year 1996 and is realized now on the both
operated Mochovce NPP units. 2. The mechanical
testing from the first of MSSP irradiation sets
of Mochovce 1st and 2nd units are
finished. 3. The MSSP program will continue by
the schedule presented in the table 1.
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Figure 9 Complete set of irradiations chains for
NPP Mochovce unit 1
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Fig. 12 The trends of TkfWM shift for the RPV
unit 1 NPP EMO
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Fig. 13 The trends of TkfWM shift for the RPV
unit 2 NPP EMO
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4. NEW SURVEILLANCE SPECIMEN PROGRAMME FOR THE
NPP V-1 RPV VVER-440/230 TYPE
Main goals of NSSP Validation of material
properties values used for RPV integrity
assessment according to 1. annealing recovery
efficiency 2. re-embrittlement rate.
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• MANDATORY EXPERIMENTAL PROGRAM
• (R) reference material as received conditions
• (I) irradiation embrittlement - chain N-1
• (IA) recovery after annealing - chain N-2
• (IAI) re-embrittlement after annealing - chain
  N-3

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OPTIONAL EXTENDED PROGRAM

• (IAIA) recovery after double annealing - chain
  N-4
• (IAIAI) re-embrittlement after double annealing -
  chain N-5

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According to the schedule of NSSP were till this
time realized mechanical properties
evaluation in as received conditions, mechanical
properties measurement of N-1 chain after one
year of irradiation and N-4 chain after double
annealing, annealing of N-2 and N-3 chains,
double anealing of N-4 and N-5 chains,
insertion of annealed N-3 chain for
re-irradiation by NSSP schedule,
disassembling of N-2 and N-5 chains in the
Re laboratories, mechanical properties
measurement from N-2 and N-5 chains, till
september 2003,
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4.1 COMPARISON OF STANDARD MECHANICAL PROPERTIES
WITH SP TESTS RESULTS FROM NSSP CHAIN N1 AFTER
ONE YEAR OF IRRADIATION
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4.2 PREDICTION OF Tkf SHIFT
F1/4,WM 3,61E22 during 16th campaign of
unit 3 Faverage 2,91E22
For NPP V-1 unit 1
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4.3 PLANNED ACTIVITIES DURING THE YEAR 2003
standard mechanical properties measurement of
WM RPV samples from the N-2 and N-5 chains,
base mechanical properties measurement on the
samples from BM, WM a HAZ by small punch
test, pull out the N-3 chain, disassembling
of N-3 chain in hot Re laboratories.