1. 10 years of experience with Westinghouse
fuel
at NPP Temelin
Daniel Ernst & Luka Milisdorfer
VVER 2010
Prague, November 1-3, 2010

2. 2VVER 2010
History
Contract with Westinghouse was signed in 1993
First fuel assembly (FA) VVANTAGE-6 - was loaded into the reactor of Unit 1 in July,
2000 .
..and first criticality was achieved 3 months later
8 cycles at Unit 1 (Cycle 5 was divided on Cycle 5 and 5A) and 7 cycles at Unit 2
These 15 cycles represent 960 FAs 490 FAs (U1) + 470 FAs (U2)
Average burnup of unloaded F/As was 37.800 MWd/tU and maximum average burnup of
F/A was app. 44.500 MWd/tU
67 leaking FAs, 27 FAs were repaired and reused

3. 3VVER 2010
Content
History
Core Design, Safety Evaluation and Core Monitoring
Fuel Problems
Post Irradiation Inspection Program
Conclusion

4. 4VVER 2010
Core Design and Safety Evaluation
Transfer of computational software and methodology (NRC
licensed). Computational aids were modified by Westinghouse for
usage with hexagonal core (ANC-H; PHOENIX-H, etc.)
Set of core design trainings for EZ personnel several of them
as on-job-trainings important know-how transfer allows CEZ
to perform its own core design-related calculations
Close WEC- EZ joint cooperation in loading pattern search the
preliminary patterns (with brief safety evaluation) were found by
EZ and then fully evaluated by Westinghouse and delivered as a
final core design.
Over time the participation of the CEZ personnel in core design
process becomes more and more significant

5. Core Design and Safety Evaluation
Complicated core design:
Real cycle lengths significantly departs from the scheduled ones
Core Design constraints caused by IRI and grid-to-rod fretting
Common core design limitations and efforts: safety aspects,
reactor vessel fluency minimalization; economical aspects.
In despite of the above-mentioned limits the safe, operation-
friendly and reasonable cost-effective loading patterns were found
Low leakage cores reactor vessel fluency minimalization
Cores which helps to mitigate the IRI issue.
Cores with sufficient and comfortable margins to operational
limits (peaking factors)
Cores with minimalized sixth asymmetry forcing function, etc.
5VVER 2010

6. Core Design and Safety Evaluation
During IRI and grid-to-rod fretting problems detailed core design
guideline was created to mitigate/eliminate the above-mentioned
issues.
Since the irreparable leakage of the fuel, which were several times
determined during outages the Contingency Plans was always
created before each fuel reload helps with quick redesign
The core redesign were often performed in challenging time range
days/few weeks
6VVER 2010

7. Core Design and Safety Evaluation
The flexible fuel assemblies design was the main presumptions for
successful core design:
Fuel enrichment according to core designer requests
(restricted only by range 0.7 5.0 % w/o)
Axial and primarily radial profiled fuel assemblies
Fine tuning of burnable absorbers using integrated fuel burnable
absorbers (IFBA) rods from 0 to 84 IFBA rods per assembly
The loading pattern proposals safety evaluation:
Using the bounding principle
Performed for reasonable cycle burn-up window
- mostly ± 20 EFPD
Safety margins sufficient for safe and comfortable operation
7VVER 2010

8. Core Monitoring
The Westinghouse core monitoring system BEACON based on
Rhodium self-powered incore detectors was modified for use for
hexagonal core
BEACON TSM (Technical Specification Monitoring) used at
Temelin
For the first cycles the version BEACON 2.0.1 were used the
core monitoring model development was fully performed by
Westinghouse
The modified De-coupled version BEACON 6 was fully
applied in 2008. The preceding system tuning and test opartion
was performed in close WEC-CEZ cooperation
8VVER 2010

9. Core Monitoring
The BEACON Model Development Training was performed in
2009
The training was performed as a on-job-training (U2C7)
The BEACON models were than develop by CEZ personnel and
verified by Westinghouse.
In 2010 the training for determining self powered detectors
cross-section constants for using with fuel containing gadolinium
It allows CEZ to develop the core monitoring system model for
the cores with new type of fuel supplied by JSC TVEL
9VVER 2010

10. 10VVER 2010
Fuel Problems
Problems with RCCAs (Rod Control Cluster Assembly) during
operation Incomplete Rod Insertion (IRI)
Fuel Assembly (FA) / Fuel Rod (FR) Bow
Excessive FA Growth
Leaking FRs

11. 11VVER 2010
Fuel Problems - IRI
Description
Some RCCAs (on both Units) do not drop fully to the bottom position (IRI
Incomplete Rod Insertion) - root cause was changes in FA geometry
Worst case - Unit 1, June 2 test showed two RCCAs stopped above the level of the
hydraulic dashpot, in other words they failed to meet the Limit Condition
unscheduled outage for refueling
Since the problem became known, the function of RCCAs dropping has been
repeatedly tested at intervals specified by SUJB
The interval for tests was 30 days (in 2005) and is 150 days (in 2010)
Based on previous tests fuel vendor:
provides prediction of number of IRI for upcoming test we were/are better
prepared for given situation
performs a safety assessment

12. 12VVER 2010
Fuel Problems IRI (cont.)
Corrective actions
BCO (Bases for Continuous Operation)
Non fuel modification was done in 2005 - control rod drive shaft connecting bars were
modified (drilled holes, increased weight the similar way as on the other VVER1000
units)
FA design modifications (2006-2007)
tube-in-tube dashpot design and top nozzle modifications (Phase 0)
fuel rod loading equipment alignments
a new structural materials of FR cladding and other FA components (Phase 1X)
A methodology for core design with bowed and twisted FAs has been developed

13. 13VVER 2010
Fuel Problems IRI (cont.)
Odstran ni IRI na ETE modifikaci paliva Westinghouse
0
5
10
15
20
25
30
35
40
45
50
55
1.8.2004
9.11.2004
17.2.2005
28.5.2005
5.9.2005
14.12.2005
24.3.2006
2.7.2006
10.10.2006
18.1.2007
28.4.2007
6.8.2007
14.11.2007
22.2.2008
1.6.2008
9.9.2008
18.12.2008
28.3.2009
6.7.2009
14.10.2009
22.1.2010
PoetIRI
U2EOC2
U1EOC3
U1EOC4
U1EOC5
U1EOC5AU2EOC3
U2EOC4
U1EOC6 U1EOC7
U2EOC5 U2EOC6

14. 14VVER 2010
Fuel Problems FA/FR Bow
Description
The mechanical deformations of FR and FA, i.e. the deviations from their ideal
geometric shapes and the elongation of fuel assemblies (radiation growth), come as a
natural phenomenon accompanying the production of energy inside the cores of
nuclear reactors
FAs prone to geometry changes due mostly to the radiation growth of FRs and FA
skeleton. The changes translate themselves into FA bow and twist
The first cores in the Temelin NPP have been designed to tolerate the flow area
reductions by as many as 51%. All subsequent core designs were calculated with the
conservative assumption that the FRs could touch each other
FA bow has affected refueling of core, reshuffling sequence of FAs was changed, the
special dummy assemblies have been used to load bowed and twisted FAs
However, FA bow and twist is not a safety problem, it is an usual phenomenon in all
reactors in the world

15. 15VVER 2010
Fuel Problems FA/FR Bow (cont.)

16. 16VVER 2010
Fuel Problems FA/FR Bow (cont.)

17. 17VVER 2010
Fuel Problems Excessive FA Growth
Comparison of three different designs of VVANTAGE-6 fuel
0
2
4
6
8
10
12
14
16
0.0 2.0 4.0 6.0 8.0 10.0
Fast Neutron Fluence, (x 1E21 NVT)
FuelAssemblyGrowth,mm
T1 Growth Updated Best Estimate Curve
Updated Upper Limit Curve T2 Growth
Phase 1X Growth
T1 design:
- original design
- loaded to Unit 1, first core
only
- Zircaloy-4
T2 design
- loaded to Unit 2, first core
and all reloads for both Units
till 2006
- Zircaloy-4
Phase 0
- loaded to both Units in 2006
- Zircaloy-4
Phase 1X design
- all reloads from 2007 till now
- ZIRLO

18. 18VVER 2010
Fuel Problems Excessive FA Growth (cont.)
F/A Growth vs. WEC database
Zr-4 Fuel Assembly Growth Data Base
0.000
0.050
0.100
0.150
0.200
0.250
0.300
0.350
0.400
0.450
0.500
0.00 2.00 4.00 6.00 8.00 10.00 12.00
Fast Fluence (1e21 nvt)
FuelAssemblyGrowth(%)
Zr-4 Fuel Assembly Growth Data Base
Temelin 1 EOC 1 and 2 Data
Temelin 2 EOC 2 Data
Temelin 1 EOC 3 Data
Temelin 1 EOC 4 Data
Temelin 2 EOC 3 Data
Temelin 1 EC 5A Data - ZIRLO

19. 19VVER 2010
Fuel Problems Leaking FRs
Description
The nuclear reactor installed at the Temelin NPP contains 163 fuel assemblies and each
assembly holds 312 fuel rods. All nuclear power plants are designed on assumption that a
certain number of the rods develop leaks
The number of fuel rods supposed to become leaky is determined with reliance on safety
analyses and detailed in Technical Specifications in the form of Safety Limits & Conditions - at
the Temelin NPP the fuel rods are checked for tightness through monitoring the specific
activity in the primary circuit the overall specific activity limit of 3,7x109 Bq/l
Summary of maximum activities found in the primary circuit coolant on both Units (Bq/l):
2003 2004 2005 2006 2007 2008 2009 2010
Unit 1 5,9x10
6
2,4x10
6
3,6x10
6
6,3x10
6
7,9x10
6
7,1x10
6
6,3x10
6
4,3x10
6
Unit 2 2,7x10
6
7,0x10
6
3,3x10
6
6,4x10
6
8,5x10
6
5,8x10
6
6,3x10
6
6,6x10
6

20. 20VVER 2010
Fuel Problems Leaking FRs (cont.)
FRI faktor
FRI ETE 2005 - 2010
0
20
40
60
80
100
120
140
160
leden05
bezen05
kvten05
ervenec05
zai05
listopad05
leden06
bezen06
kvten06
ervenec06
zai06
listopad06
leden07
bezen07
kvten07
ervenec07
zai07
listopad07
leden08
bezen08
kvten08
ervenec08
zai08
listopad08
leden09
bezen09
kvten09
ervenec09
zai09
listopad09
leden10
bezen10
kvten10
as [m s]
FRI
[Bq/g]
HVB 1 HVB 2

21. 21VVER 2010
Fuel Problems Leaking FRs (cont.)
Sipping systems are used to search the leakers:
On-line Sipping - the system applies a gas method of continuous changes in the
Xe 133 concentration
Off-line sipping - the system used to conduct qualitative measurements of a FA
found damaged in an attempt to reveal the scope of damage done
Fuel Inspection & Repair Equipment a system used to identify and repair leakers:
mobile equipment (for both Units) designed and manufactured by Westinghouse
during outage is FRIE assembled on the floor of the Reactor Hall and than is
transported into the fresh fuel cask pit next to spent fuel pool
the refueling machine moves fuel assemblies in and out of the FRIE
the fuel assembly rests on a turntable which allows it to be rotated 360 degrees
during
the inspection process
is designed to provide complete fuel inspection for entire FA
the fuel assembly UT inspection system is used to locate leaking fuel rods
the failed fuel rod storage basket (FFRSB) provides storage for the failed fuel rods
leakers are replaced with dummy rods.

22. 22VVER 2010
Fuel Problems Leaking FRs (cont.)
Unit 1
End of Cycle # of Leakers # of Repaired Leakers # of Leaked F/Rs
2 1 0 0
3 5 1 1
4 6 1 1
5 6 6 8
5A 4 2 3
6 7 7 10
7 3 1 1
8 0 0 0
Unit 2
End of Cycle # of Leakers # of Repaired Leakers # of Leaked F/Rs
2 3 2 5
3 10 2 4
4 5 2 2
5 7 2 3
6 5 0 0
7 5 1 2
An overview of leaks disclosed in fuel at the Temelin NPP

23. 23VVER 2010
Fuel Problems Leaking FRs (cont.)
Root cause of leaking FRs is grid-to-rod fretting that means vibration of FRs in spacer
grids
Fuel Rod Fuel Rod with fretting marks

24. 24VVER 2010
Fuel Problems Leaking FRs (cont.)

25. 25VVER 2010
Fuel Problems Leaking FRs (cont.)
FR separation event at Unit 2
Fuel reconstitution was being performed on assembly BE24
One leaking fuel rod was to be removed and replaced by a stainless steel rod
After withdrawing about 150 cm of the fuel rod, the rod jerked suddenly and fractured
Visual examination of the fracture location indicated the separation was caused by
secondary hydriding (there had been no indications of significant hydriding from the
visuals)
Extensive through-wall grid-to-rod fretting was found
Visual examinations of the fractured ends on both rod segments showed intact fuel
pellets with no empty area, indicating that no fuel pellets were lost during the fracture
event.

26. 26VVER 2010
Fuel Problems Leaking FRs (cont.)

27. 27VVER 2010
Post Irradiation Inspection Program (PIIP)
Post Irradiation Inspection Program (PIIP)
substituted the Lead Test Assembly program for new fuel design
program was structured to meet requirements of the Czech Regulatory Body (SUJB)
additional proof of material compatibility, analytical methods support and verification,
overall thermomechanical performance demonstration
8 selected FAs (these 8 FAs were pre-characterized )
The inspection program included:
FA measurements
Visual Examination
FA Bow, Twist and Overall FA Length Measurement
Peripheral FR Corrosion Measurements
Single FR measurements
Visual Examination
Corrosion Measurements
Profilometry Measurements
RCCA inspections
Measurements of Total Wear of the Tube Cross Section

28. 28VVER 2010
Post Irradiation Inspection Program (PIIP) cont.
PIIP results
Positive:
visual examinations revealed little or no corrosion on the cladding
surfaces confirmation of compatibility of Zircaloy alloy with the VVER
water chemistry
there was no wear of any RCCA rodlet (criterion is wear less than10%)

29. 29VVER 2010
Post Irradiation Inspection Program (PIIP) cont.
PIIP results
Negative:
FA twist, bow and length measurements showed an unexpected
behavior
FR visuals of leaking FRs indicated GRF

30. 30VVER 2010
Conclusion
During first decade of the Temelin NPP operation, formidable
mission of implementing and development program of a new fuel
system has been accomplished. Indeed, it raised more or less
serious problems which all were solved together with the fuel vendor
and we can say they are under the control.
Today, we are standing at the beginning of new era, waiting what
will be brought by the future.