The 6-th International Conference “Safety Assurance of NPP with WWER” EDO “GIDROPRESS”, Podolsk, Russia
26-29 May, 2009
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DYNAMIC BEHAVIOUR OF WWER 1000/320 REACTOR FUEL ASSEMBLIES
AND INFLUENCE OF MAIN CIRCULATING PUMP PRESSURE PULSATIONS
P.Stulík
Nuclear Research Institute, Rez, Czech Republic
Annotation: The evaluating of changes in fuel assemblies dynamic behaviour is particularly needed
and required. Self power neutron detectors installed in reactor fuel assemblies can hold important
information about vibration in spite of complex surrounding influencing signal output by many
parameters. The paper deals with the analysis of available set of self power neutron detectors to show
influence of main circulating pump excitement forces.
Key words: Reactor vibration, pressure pulsations, fuel assembly, fuel rod, self power neutron
detector, power spectral density, transfer function, time domain, frequency domain, joint time
frequency domain, beat frequencies.
1. Introduction In the past many start-up and operational measurements of pressure vessel and internals
vibrations of both VVER 1000/320 NPP Temelin reactor units have been performed. These
measurements included pressure sensors (TP), accelerometers (ACC), ex-core ionisation chambers
(XNN) and self-powered neutron detectors (INN). The measurement data sets were originated
from several diagnostic systems – operational diagnostic system RVMS (the part of in-plant
diagnostic system TDMS delivered by Westinghouse, USA ), start-up special system ANALOG
(implemented by ŠJS start-up supplier– [1], [2]) and system DMTS (developed by NRI Rez for the
distributed acquisition of large volumes of data, their relevant processing and evaluation in
the different domains primarily by means of noise diagnostics ([3]).
In [4] the accelerometers installed on the flange of reactor pressure vessel have been used
for measurement, the evaluated significant frequencies were compared with the exciting ones and
the good agreement was indicated.
The influence of the NPP Temelin reactor operational vibrations on the core barrel stability was
investigated in [5] by means of the developed 3D mathematical reactor model and evaluated
measurement results under the condition of full MCPs operation with slightly different revolving
frequencies.
Some following works were further conducted ([6] - [7]) in which the dynamic responses of NPP
Temelin reactor in full and less loop main circulating pump combinations were examined on reactor
models and experimentally verified.
With the Gidropress experience in the area of reactor internals and fuel vibration research
published in ([9], [12]) on mind, the NPP Temelin new fuel elements project ([10]) has been
initiating the solution of further investigations ([13], [14]).
The 6-th International Conference “Safety Assurance of NPP with WWER” EDO “GIDROPRESS”, Podolsk, Russia
26-29 May, 2009
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2. NPP Temelin diagnostic measurements In-plant system RVMS delivered by Westinghouse and described in [1] or [2] has being used not
only during both units commissioning tests (2000, 2002) but then primarily in the normal plant
operation. It features 12 bit amplitude resolution in six frequency ranges up to 200Hz with 0.5 Hz
frequency resolution and 1 kHz sampling frequency enabling thus measurements of 4 accelerometers
ACC on the upper reactor flange, 6 accelerometers ACC on the steam generator (Unit 1), 8 ionization
chambers XNN in upper and lower positions, 5 pressure fluctuation sensors PFT (only Unit 2) placed
on cold loops, 12 reactor output thermocouples, 256 self powered neutron detectors INN measured
in 16 groups just as it is shown in Table 1.
The Škoda system ANALOG was used during both units commissioning tests on set of specially
arranged sensors. Measurement was accomplished with 12 bit amplitude resolution, with variable
frequency domain resolution 0,1 – 0,5 Hz and 1 kHz sampling frequency.
The NRI Řež system DMTS has been applied in various stages of both units operation
by acquiring and processing extensive time records with 24 bit amplitude and selected 0,122 Hz
frequency resolution with 1kHz sampling frequency.
It is worthwhile to note in this context that there are important issues for diagnostic
investigations especially for the case of actual or anticipated operational events with known
implications but with unknown causalities
it is necessary to have a well arranged frequency domain results (APSD, CPSD, COH, PHASE etc.) with pertaining operation parameters enabling comparison of similar reactor units
the existence of sufficient time records is necessary for more detailed processing and evaluation.
Table 1
NPP Temelín RVMS sensors
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The 6-th International Conference “Safety Assurance of NPP with WWER” EDO “GIDROPRESS”, Podolsk, Russia
26-29 May, 2009
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3. Reactor vibrations There are three main types of reactor internals exciting forces – pressure pulsations generated
by main circulation pumps (MCP), pressure pulsations in turbulent boundary coolant flow layer
in the core barrel - reactor pressure vessel gap and the acoustic pressure sources in the primary circuit
coolant.
The analysis of reactor pressure vessel vibration was fulfilled in [4] and [5]. Four piezoelectric
accelerometers (0.5 – 300 Hz) installed on reactor cover had been measured at nominal 100% power
with enhanced amplitude resolution by system DMTS. The acquired signals were processed
in frequency range of 0.5 – 100 Hz. The used 3D mathematical reactor model with 137 degree of
freedom was tuned in by means of measured operational frequency 18.738 Hz.
The analysis summary is as follows
authors classified the set of frequencies 6.714, 13.57, 33.05, 53.386 Hz as the operational acoustic frequencies with the assumption that the corresponding pressure fluctuations cause
forced reactor vibrations
the frequency 9.278 Hz of reactor vertical movement depends on the coolant temperature and there is authors´ opinion that this reactor vibration is generated by tube – cavity resonance well
explained by the Helmholtz resonator theory
the frequency 18.738 Hz represent the horizontal pendulum motion of the system reactor pressure vessel – core barrel driven by turbulent pressure fluctuations appearing in the near boundary
layers of coolant flow
there are operational frequencies of 16,602, 33,204, 49,926, 66,528, 83,130, c Hz of forced reactor vibrations induced by corresponding MCP revolution frequencies.
Power spectral densities of all accelerometers A511-A514 are shown in Fig. 1 with marked MCP revolution frequencies up to 6
th harmonic one.
Fig. 1 NPP Temelín Unit 1 reactor head accelerometers A511-A514 power spectral densities
The 6-th International Conference “Safety Assurance of NPP with WWER” EDO “GIDROPRESS”, Podolsk, Russia
26-29 May, 2009
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The peak amplitudes of reactor vessel vibration induced by pressure pulsations generated by
main circulation pumps MCP revolution are given in Table 2. Their values are well below under
acceptable level of 0,1 g in frequency domain [9] but we can mark the 3 order difference
at operational 99.730 Hz which corresponds 6th
MCP harmonic. When converting values of Table 2
into Fig. 2 we can see slight curve resemblance of A511 with A512 and A513 with A514
accelerometer couples, which could indicate the similar vibration behaviour of reactor vessel
on these induced frequencies.
In the past the revolutions of main circulation pumps rotor were supposed to be constant.
The authors of [6] reported that the power spectral densities of reactor pressure vessel are not stable
in time. The operational JTFS spectrograms of A511 head reactor accelerometr presented in Fig. 3
(NPP Temelin Unit No2, 3
rd fuel cycle, Nnom=100%) demonstrate clear indication of reactor beat
vibration in 0 – 150 Hz frequency range. The different beat forms of particular MCP harmonics
from the same measurement are shown in Fig. 4 for the time interval 0 – 1200 s. Tab 3 gives the
amplitude statistics for these beat harmonics where namely frequencies of 49.926, 83.130 and 99.730
Hz are dominating by their average, standard, maximal and range values.
Table 2
NPP Temelín reactor head accelerometers PSD : frequency peak values of
vibration forced by MCP revolutions
ACC Apeak [10
-5 g]
1 2 3 4 5 6
A511 29,7 33,0 20,7 17,6 5,4 1797,4
A512 5,1 24,1 19,3 9,1 2,6 2788,9
A513 7,3 18,6 25,9 8,1 2,8 2811,6
A514 9,8 26,7 27,8 13,3 2,2 4618,6
Frequency peak values of vibration forced by MCP revolutions
1,0
10,0
100,0
1000,0
10000,0
100000,0
16,601 33,203 49,926 66,528 83,129 99,731
Operational frequency [Hz]
Ap
eak [
10
-5g
]
A514
A513
A512
A511
Fig. 2
The 6-th International Conference “Safety Assurance of NPP with WWER” EDO “GIDROPRESS”, Podolsk, Russia
26-29 May, 2009
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Fig. 4 MCP harmonics (16,6 – 99,7 Hz) with beat character from JTFS spectrogram of A511 accelerometer
0 – 150 Hz 0 – 50 Hz
Fig. 3 Operational JTFS spectrograms of A511 head reactor accelerometer (NPP Temelin Unit No2)
Table 3
A511 accelerometer statistics of operational beat harmonics forced by MCP
revolutions
MCP Beat
Harmonics
[Hz]
[dB]
Average StandDev Min Max Range
16,602 40,8 5,2 20,3 48,5 28,2
33,204 43,5 5,1 13,1 49,6 32,3
49,926 46,6 5,2 22,2 54,4 36,5
66,528 53,0 2,6 43,9 57,6 13,7
83,130 41,9 5,7 16,2 49,7 33,4
99,730 69,7 4,8 56,3 78,2 21,9
The 6-th International Conference “Safety Assurance of NPP with WWER” EDO “GIDROPRESS”, Podolsk, Russia
26-29 May, 2009
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As proved in [7] the similar beat character is observed also for exciting pressure pulsations
measured at reactor input and output. The two couples of operational JTFS pressure pulsation
spectrograms shown in Fig. 5 (NPP Temelin Unit No2, 5
th fuel cycle, Nnom=0%) demonstrate
however another feature. The noticeable change of spectrogram couples measured in two hours span
is due to changed reactor operation conditions when less loop main circulating pump combinations
were examined between the pressure pulsation measurements. It is necessary to mark that these
measurements themselves were realized in steady state within time interval 0 – 1000 s.
The common beat display of exciting pressure pulsations and reactor vibration at MCP
harmonics can be demonstrated when calculating the transfer function between signals of these
quantities. In Fig. 6 the close relationship between reactor input/output pressure pulsations TP1/TP5
and reactor vibration A511 is presented when good coherence is achieved also for the MCP
harmonics regions.
3.7.2008, 22:38 3.7.2008, 00:38
Fig. 5 JTFS spectrograms of reactor input/output pressure pulsations TP1/TP5 (NPP Temelin 2th
Unit, 5th
cycle, Nnom=0%)
REACTOR INPUT
REACTOR OUTPUT
The 6-th International Conference “Safety Assurance of NPP with WWER” EDO “GIDROPRESS”, Podolsk, Russia
26-29 May, 2009
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The developed model of forced reactor vibrations excited by pressure pulsations generated
by main circulation pumps was described in paper [8]. The vibration analysis based on this new
generalised reactor model with spatial localization of fuel assemblies, protection tubes and linear
stepper control rod drives has confirmed that the slightly different pump revolutions are sources
of the beating effects. These effects cause an vibration amplification and increase a possibility
of the contact loss in internal core barrel linkages.
4. Dynamic fuel assemblies behaviour NPP Temelín units were connected to grid in June 2002 or in April 2003 with initial VV6 fuel
load. Then there were successive changes to VV6 Phase 0, VV6 Phase 1X fuel assemblies
from WEC during 4 – 6th
fuel cycles of both units. Nowadays they have decided to change fuel
supplier to TVEL with TVSA-T fuel assemblies to be loaded in May 2010 in U1C9 cycle.
Both fuel assemblies are shown in Fig.7 ([10]). Fuel assembly mechanical, hydraulic and neutron-
physical compatibility is expected having been supported by many preparatory works including
vibration research ones.
From the operation view of point it is necessary to evaluate continually changes in fuel
assemblies dynamic behaviour. The knowledge of fuel assemblies and fuel rods natural frequencies
is then an essential step for the utilization of self power neutron detectors SPND signals. These are
composed by many source contributions including e.g. collective fuel assemblies vibration but their
signal structure is not yet fully identified for the time being. Nevertheless, the qualified information
about fuel rods fretting and fuel assembly bowing is required
As described in [11] the natural frequencies of selected reactor components were computed
by program “WWER 1000 reactor modal analysis”. This program is the part of mathematical reactor
model with 137 degrees of freedom incorporating 8 subsystems of main reactor components
(pressure vessel, core barrel, active zone with 163 VV6 fuel assemblies, etc.). The first six bending
modes of VV6 fuel assembly natural frequencies are listed in Table 4 together with
the corresponding values for UTVS and TVS-2M assemblies, which were get from the modal
experiments with hammer and shaker excitement ([12]).
Fig. 6 Transfer function of reactor input/output pressure pulsations TP1/TP5 [kPa] and A511 acceleration [g]
The 6-th International Conference “Safety Assurance of NPP with WWER” EDO “GIDROPRESS”, Podolsk, Russia
26-29 May, 2009
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The analysis of one possible reason of VV6 fuel rod integrity infringement was done for Temelin
U2C3 cycle [13]. The starting assumption was the loss of contact between rod and grid in the area
of spacer grids 2, 3, 4 and computed hydrodynamic forces acting on fuel rods were compared with
natural bending frequencies of fuel rods. The evaluation of exciting force frequency was done for the
velocities of coolant with the characteristic values for a flow around fuel rods (outer diameter of fuel
rod as characteristic dimension, Strouhal, Reynolds numbers from velocity models based on Temelin
U2C3 operation data). The pulsation of hydrodynamic forces has a frequency in the range 1 – 9 Hz
and acts primarily on the level of 1 – 4, 8, 9 spacer grid. Even if the fuel rod natural frequencies
estimation was not based on exact VV6 dimension and material data, the overall result (Tab.5)
is considered to be sufficient for the early comparison with the fuel rod exciting forces. It shows
relatively big fuel rod infringement probability in the frequency range 1 – 11 Hz.
Table 5
Bending natural frequencies of unreleased/released fuel rods
#
Spacer grid
Mode
#
Spacer grid
Mode
OK … spacer grid in contact with fuel rod, x … released fuel rod in spacer grid,
red marked numbers … 1st and 2nd modes of fuel rod natural frequencies up to 11 Hz
Kodl, Macák, 2006, [13]
Table 4
Bending natural frequencies of fuel assemblies
Mode [Hz]
VV6 1 UTVS
2 TVS-2M
2
1 3,00 4,7 5
2 6,35 10,5 10,5
3 10,82 17,7 16,5
4 16,2 25,3 23
5 21,5 34 28,5
6 31,7 - 35,5
1 Zeman, WWER1000/320 Mathematical model, 2008, [11]
2 Makarov, TVS modal analysis, 2007, [12]
The 6-th International Conference “Safety Assurance of NPP with WWER” EDO “GIDROPRESS”, Podolsk, Russia
26-29 May, 2009
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Data from 256 SPND signals are normally acquired by operational diagnostic system RVMS
at 12 bit resolution with 1 kHz sampling frequency and reduced into frequency domain results
with 0,5 Hz resolution. The more detailed measurements by system DMTS (NRI Řež, 24 bit
resolution in time domain, 0,122Hz in frequency domain) were made at Nnom=100% with all working
MCPs during Temelin U1C3 a U2C3 cycles. The acquired data of 15 min unified length were
centred, normalized to maximum value and processed in time and frequency domain.
The frequency interval 0 – 70 Hz for processing was determined with regard to above mentioned
works [11], [13]. 52 SPND from altogether 272 measured ones were chosen for further evaluation in
spectral maps. These maps are constructed as 3D graphs in XY view with arbitrary variables
(frequency and spectra serial number) and power spectral density PSD value as a dependent variable.
This layout yields overall and quick overview namely in the case when comparison between units is
required what was an original aim of the work done in [14]. There are spectral maps for both Temelin
units presented in Fig.8 and Fig.9 together with the above mentioned fuel assembly and fuel rod
natural frequencies, which are divided in two regions according of released/unreleased, state rod to
grid.
When interpreting these spectral maps the following conclusions can be made:
the peak frequencies and amplitudes occurrence of both units with the same VV6 basic design fuel in the same fuel cycle is distinctively different
the 2nd unit amplitudes are almost ten times higher with the significant occurrence number also in the region of 1 – 3
rd mode released fuel rods natural frequencies
there are however frequency individual values, smaller or larger regions where the both units behave in similar manner
the neighbourhood of 9 and 13 Hz
the revolution frequency 16,6 Hz and its harmonic 33,3 Hz
the neighbourhood of 18 Hz
the bands 25 – 30, 30 – 32, 41 – 47 and 49 – 50 Hz. It is necessary however to be aware of the fact that these conclusions are valid only for the one
of both units cycles.
In order to cover qualified detection of fuel rods infringements, more systematic approach is
required in the future.
The 6-th International Conference “Safety Assurance of NPP with WWER” EDO “GIDROPRESS”, Podolsk, Russia
26-29 May, 2009
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Fig. 8 NPP Temelin unit #1 (3th cycle) SPND power spectral density map with fuel rod and assembly natural frequencies
1-3th mode of released fuel rods
All modes of unreleased fuel rods
Kodl, Macák [13]
FR
3 6,35 10,82 16,2 21,5 31,7 Hz VV6
FA
Zeman [11]
4,7 10,5 17,7 25,3 34 Hz UTVS
FA
Makarov [12]
5 10,5 16,5 23 28,5 35,5 Hz TVSA-2M
FA
Makarov [12]
Fig. 9 NPP Temelin unit #2 (3th cycle) SPND power spectral density map with fuel rod and assembly natural frequencies
Kodl, Macák [13]
3 6,35 10,82 16,2 21,5 31,7 Hz VV6
FR
FA
Zeman [11]
4,7 10,5 17,7 25,3 34 Hz UTVS
FA
Makarov [12]
5 10,5 16,5 23 28,5 35,5 Hz TVSA-2M
FA
Makarov [12]
1-3th mode of released fuel rods
All modes of unreleased fuel rods
The 6-th International Conference “Safety Assurance of NPP with WWER” EDO “GIDROPRESS”, Podolsk, Russia
26-29 May, 2009
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5. Conclusions The paper has introduced NPP Temelin diagnostic measurements in conjunction with
the description of reactor vibration. The phenomena of vibration beats namely on main circulation
pump revolution harmonics was referred to pressure pulsations generated by main circulation pumps
with slightly differed revolutions. The amplitude statistics shows that particularly at 4th
– 6th
harmonic frequencies the beat character is dominating by average, standard, maximal and range
values. These beat phenomena represent inconsiderable component in overall reactor vibration,
which can cause contact loss of internal parts during long-term operation.
The operational data from selected self power neutron detectors of both NPP Temelin units were
processed together with modal parameters of VV6 and TVSA assemblies to show probable region
of possible fuel rod infringement.
In order to be able to detect fuel incorrect behaviour during the reactor operation it is advisable
to extend synchronous measurement and processing to other diagnostic sensors inclusive main
circulating pumps parameters.
The 6-th International Conference “Safety Assurance of NPP with WWER” EDO “GIDROPRESS”, Podolsk, Russia
26-29 May, 2009
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References
[1] Tanzer M., Mašek V., Smolík J., Macák P. : „The signal measurement evaluation and RVMS system setting-up of NPP Temelin Unit 1“, Škoda JS plc report N
o Ae 967/Dok, Plzeň,
September 2002, in Czech
[2] Smolík J.,Tanzer M., Mašek V. : „The signal measurement evaluation and RVMS system setting-up of NPP Temelin Unit 2“, Škoda JS plc report N
o Ae 11 112/Dok, Plzeň, June 2003
[3] Stulík P. : “Calibration and On-line Monitoring Methods on Czech NPP Operational Diagnostic Systems”, Technical IAEA meeting on Increasing instrument calibration interval
through on-line monitoring technologies, OECD, Halden Reactor Project Halden, Norway,
September 2004
[4] Pečínka L., Stulík P., Šípek B. : “Operating shapes vibration analysis of NPP Temelin WWER 1000/320 reactor”, Computational Mechanics 2006, 22nd Conference with International
Participation, Nečtiny, November 2006, in Czech
[5] Pečínka L., Stulík P., Zeman V. : “Influence of the operational vibrations on the WWER 1000/320 reactor of NPP Temelin core barrel stability”, 5
th International Conference “Safety
Assurance of NPP with WWER”., May 2007, Podolsk, in Russian
[6] Pečínka L., Stulík P. : “Experimental verification of WWER 1000/320 reactor dynamic response to pressure pulsations generated by the main circulating pumps”, Colloquium
Dynamics of Machines, Prague, February 2008, in Czech
[7] Stulík P., Šípek B. : “The operational dynamic responses of NPP Temelin WWER 1000/320 reactor in less loop main circulating pump combinations ”, Nuclear Research Institute Rez plc,
Report No Z 2125, February 2008, in Czech
[8] Zeman V., Hlaváč Z. : “Dynamic response of WWER 1000 type reactor excited by the main circulating pump pressure pulsations“, Colloquium Dynamics of Machines, Prague, February
2008, in Czech
[9] Dragunov J.G., Dranchenko B.N, Abramov V.V., Chairetdinov V.U. : ”Vibration studies for WWER designs”,5
th International Conference “Safety Assurance of NPP with WWER”.,
May 2007, Podolsk, in Russian
[10] Mečíř V. : ”Temelin NPP Fuel experience”, 7th International Conference on WWER Fuel Performance, May 2007, Albena
[11] Zeman V., Hlaváč Z., Pečínka L. : “Dynamic response of WWER 1000 type reactor excited by pressure pulsations generated by main circulating pumps“, West Bohemian University report
No 52 120 – 01 - 08, Plzeň, May 2008, in Czech
[12] Makarov V.V., Afanasiev A.V., Matvienko I.V. : ”Modal analysis of the WWER fuel assembly dummies during the force and kinematic vibration excitation”,5
th International
Conference “Safety Assurance of NPP with WWER”., May 2007, Podolsk, in Russian
[13] Kodl P., Macák P. : “The possible reason evaluation of fuel assemblies damage”, ŠKODA JS plc report N
o Jad-Výp/E26/06, Plzeň, October 2006, in Czech
[14] Stulík P. : “NPP Temelin in-core detectors analysis in the frequency range important from the fuel behaviour view”, Nuclear Research Institute Rez plc, Report N
o 13 010, June 2008, in
Czech
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