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IFPE/SOFIT, WWER-440 Fuel Thermal Performance and Fission Gas Release

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Program name Package id Status Status date
IFPE/SOFIT NEA-1310/04 Arrived 16-JAN-2023

Machines used:

Package ID Orig. computer Test computer
NEA-1310/04 Many Computers
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The SOFIT program is described as a sub-task under the Finnish- Russian co-operation on VVER fuel research and consists of a series of irradiation tests in the MR reactor at the Kurchatov Institute, Moscow. The contracting parties are Imatran Voima Oy (IVO) and the Russian National Research Centre Kurchatov Institute (IRTM). The program is divided into three distinct phases each addressing specific objectives:

- SOFIT 1 Parametric fuel rod irradiations with basic steady state power histories up to moderate levels of burn-up as dictated by instrumentation endurance.

- SOFIT 2 Parametric studies based on irradiation of instrumented high burn-up rods.

- SOFIT 3 Irradiation testing under transient conditions.

The results of 2 assemblies of SOFIT 1 are at present available where the main objective was to obtain well qualified data on VVER-440 fuel for verifying and improving codes. In each assembly, rods of different design were irradiated with in-pile instrumentation to measure fuel centreline temperature, fuel stack and cladding elongation. PIE has been performed to obtain data on microstructural changes and measurement of fission gas release (FGR). The first series of irradiations were completed by May '92 and some destructive PIE has been performed.



Precharacterization and irradiation histories for SOFIT 1.1 rods 1-6, 7 and 12.

In-pile temperatures for rods 1-6 and PIE fgr from rods 7 and 12.



Precharacterization and irradiation histories for SOFIT 1.3 rods 1, 3, 4 and 5.

In-pile fuel and clad extension measurements for rods 1 and 3.

In-pile temperature data for rods 4 and 5.


Irradiation conditions in the MR reactor

The MR reactor is a pool type research reactor with a total power of 50 MW. The reactor contains several pressurized loops which can be connected to one or more in-pile test channels. These channels are located between blocks of beryllium which act as moderators. The reactor is operated in 30 to 40 day cycles of near constant power. At the time of the SOFIT tests, the axial form factor was 1.37 and the in-channel radial form factor was 1.2.

Rod power determination was based on the calorimetric bundle power measurements and calculations. The axial and radial power distributions were calculated using a model based on experimental data from the MR reactor. Axial power profiles were refined using signals from the 5 axially located neutron detectors by fitting a 5th order polynomial to the measurements to obtain a smooth power profile. The uncertainty in the axial power profiles is estimated at +/-5%. The in-bundle radial power profile was calculated using signals from 3 neutron detectors located on the same plane as the core central elevation. The detectors measured some azimuthal variation in power during irradiation and the uncertainty of the radial profile of +/-5% combined to provide an estimated total uncertainty of +/-10% in local linear power.


Experimental details

SOFIT 1.1 - 1.4 comprised 4 assemblies each of 18 rods arranged in hexagonal geometry around a central non fuelled tube used for instrumentation including neutron detectors and coolant temperature thermocouples. The fuel-to-clad gaps ranged between 140 and 290 microns, the fill gas, both helium and xenon were used, varied in pressure between .1 to 2 MPa. The UO2 density varied between 10.4 and 10.75 g/cc and the fabricated grain size was around 5 microns. The fuel active length was 1000 mm within a total rod length of 1200 mm. In most cases 6 of the 12 outer rods were instrumented with thermocouple hot junctions located between 300 and 500 mm above the lower end of the fuel stack and near the maximum power position.

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Package ID Status date Status
NEA-1310/04 16-JAN-2023 Masterfiled restricted
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- V Yakovlev, A Moshajev, P Strizhov, J Johansson, P Liuhto, P Hyvarinen and R Terasvirta: SOFIT: A Joint Experimental Programme Between the USSR and Finland on VVER Fuel Performance, Paper presented at IAEA International Symposium on the Utilization of Multi-purpose Research Reactors and related International Co-operation, Grenoble, France, 19-23 October, 1987.

NEA-1310/04, included references:
- P. Losonen: OECD/NEA Data Bank, SOFIT-DATA, Note (28/11/96)
- P. Losonen: Verification of Transuranus Against Temperature Data from WWER
type Test Fuel Rods from Sofit Experiments, Paper to be presented in IAEA/OECD
Data Base Training meeting in Halden, Norway, 25-27 September 1996
- V. Yakovlev, R. Strijov, V. Murashov, J. Johansson, R.P. Terasvirta, O.
Tiihonen and K. Ranta-Puska: Research carried our on WWER-440 Type Fuel Rods in
the MR Reactor IAEA-SM-288/64, Reprint from Improvements in Water Reactor Fuel
Technology and Utilization
- V. Yakovlev, R. Strijov, V. Murashov, A. Senkin, R.P. Terasvirta, P. Liuhto,
J. Moisio, O. Tiihonen, S. Kelppe and K. Ranta-Puska: Qualification and
Interpretation of MR Test Reactor Irradiation Data on VVER-440 Type Fuel Rods
for Fuel Thermal Model Validation, IEA-TC-659/1.4
- A.V. Smirnov et al.: WWER-1000 and WWER-440 Fuel Operation Experience
American Nuclear Society, Int. Topical Meeting on LWR Fuel Performance Florida,
USA, April 16-19, 1994
- Yu. Bibilashvili et al.: Toward High Burnup in Russian WWER Reactors and
Status of Water Reactor Fuel Technology, American Nuclear Society, Int. Topical
Meeting on LWR Fuel Performance Florida, USA, April 16-19, 1994
- D. Elenkov and K. Lassmann: The Development of the Transuranus-WWER Version
- Solonin M. et al.: WWER Fuel Performance and Material Development for
Extended Burnup in Russia, Proceedings of the Second International Seminar,
WWER Reactor Fuel Performance, Modelling and Experimental Support, 21-25April
1997, Sandanski, Bulgaria (Ibid. [4] pp. 48-57)
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No specified programming language
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Imatran Voima Oy (IVO)

Vantaa, Finland


Kurchatov Institute (IRTM)

Kurchatov Square

123182 MOSCOW, Russian Federation


Compilation: J.A. Turnbull

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SOFIT1.1 files:
S1-1R*.BOL   Detailed 10 zone histories for beginning of life for SOFIT 1.1 rod
1 to 6
S1-1R*.IRR   Complete 10 zone irradiation history rod 1, 4, 5, 6, 7, 12
S1-1R3L.IRR Detailed 10 zone history for SOFIT 1.1 rod 3, for lower
thermocouple position
S1-1R3U.IRR Detailed 10 zone history for SOFIT 1.1 rod 3, for upper
thermocouple position
S1-1R1_6.PC Precharacterization data rods 1-6
S1-1R7.PC    Precharacterization data for rod 7
S1-1R12.PC   Precharacterization data rod 12
S1-1R*.TF    Values of fuel temperature as recorded by thermocouples for rods
S1-1R3L.TF   Values of fuel temperature as recorded by lower thermocouple for
SOFIT 1.1 rod 3
S1-1R3U.TF   Values of fuel temperature as recorded by upper thermocouple for
SOFIT 1.1 rod 3
S1-1R*.TFB   Values of fuel temperature as recorded by thermocouples for rods
1,2,4,5,6 for beginning of life
S1-1R3U.TFB Values of fuel temperature as recorded by upper thermocouple for
rod 3 beginning of life
S1-1R3L.TFB Values of fuel temperature as recorded by lower thermocouple for
rod 3 for beginning of life
SOFIT1.3 R3 files:
S1-3R.PC     Precharacterization data for SOFIT 1.3 rods 1,3,4 & 5
S1-3R*.IRR   Complete 10 zone irradiation history for rods 1, 3, 4 and 5
S1-3R1.EX    Fuel stack & clad elongation rod 1
S1-3R3.EX    Fuel stack & clad elongation rod 3
S1-3R4.TF    Fuel temperatures rod 4
S1-3R5.TF    Fuel temperatures rod 5
SUMMARY.SOF SOFIT programme summary
README.3     Readme file
Review of SOFIT Experiments.doc
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Keywords: VVER type reactor, experimental data, fission products, fuel elements, fuel pellets, fuel rods, fuel-cladding interaction, fuel-coolant interactions, xenon.