Izvestiya vuzov. Yadernaya Energetika

The peer-reviewed scientific and technology journal. ISSN: 0204-3327

Model of Gas Pressure under the Cladding of WWER-1000 Fuel Rods after Operation

3/18/2024 2024 - #01 Modelling processes at nuclear facilities

Bokov A.A. Pavlov S.V. Ilyin P.A. Teplov V.G.

DOI: https://doi.org/10.26583/npe.2024.1.12

UDC: 621.039.548

The paper summarizes and analyses the results of post-irradiation examinations of under-cladding gas pressure and composition in more than 300 fuel rods of different designs from 26 fuel assemblies of the VVER-1000 reactors operated at different nuclear power plants. In their design (the diameter of the fuel pellet, its central hole, and the cladding wall thickness), all the fuel rods fall into three groups. The fuel burnup in the fuel rods under study varied from 16 to 72 MW·day/kgU. Each group showed a growth of gas pressure under cladding with an increase of the fuel burnup and was well approximated by linear dependencies within the burnup range considered. The pressure increase rate for the fuel rods with thinner cladding and a fuel pellet 7.8 mm in diameter without a central hole (group 1) was higher than for the fuel rods with standard cladding and pellets with a central hole (groups 2 and 3). A phenomenological model of under-cladding gas pressure in spent fuel rods was developed. The model’s fundamental principle is Dalton’s law for gas mixtures and empirical dependencies of changes in the free volume of the fuel rods and changes in the quantity of krypton and xenon under cladding on the fuel burnup. For each group of fuel rods, the quantity of gaseous fission products (xenon and krypton) released under the cladding was well described by the exponential burning-up function corresponding to the specific group of fuel rods. The gas pressure calculations by the phenomenological model showed that for each group of fuel rods the rate of pressure rise inside the fuel rods started to increase with a growth of burnup beginning from ~ 55 MW·day/kgU. An experimental verification of this phenomenon requires an additional study of the fuel rods with increased fuel burnup. The phenomenological model developed can be used for the verification of the computer codes describing the behavior of the VVER-1000 fuel rods during normal operation in the reactor and long-term «wet» and «dry» storage of spent fuel assemblies.


  1. Federal norms and rules in the field of the use of atomic energy «Basic requirements for the justification of the strength and thermomechanical behavior of fuel assemblies and fuel elements in the core of power water reactors» (NP-094-15). Moscow, 2016 (in Russian).
  2. Fadin S.Y., Murashov V.N., Yakovlev V.V. Experimental study of pressure in fuel elements of container type with uranium dioxide fuel. Preprint Institut atomnoj energii-4133/4. Moscow. 1985, 15 p. (in Russian).
  3. Plyasov A.A. Mechanisms of water-cooled reactor cladding properties degradation during dry storage of spent nuclear fuel. VANT. Ser. Materialovedenie i novye materialy. 2019, iss. 4 (100), pp. 144 – 159.Available at: https://www.elibrary.ru/download/elibrary_44630380_16352517.pdf/ (accessed Jul. 01, 2023) (in Russian).
  4. Likhanskii V.V., Aliev T.N., Kolesnik M.Yu., Khoruzhiy O.V., Zborovsky V.G., EvdokimovI.A., Sorokin A.A., Ulybyshev K.E., Gurovich B.A., Zabusov O.O., Zhurko D.A., Frolov A.S., Zvir E.A., Ilyin P.A. Modeling of fuel claddings mechanical properties under dry storage conditions. XI conference on reactor material science, dedicated to the 55th Anniversary of the JSC SSC RIAR Material Testing Complex. Dimitrovgrad, 2019, pp. 94 – 95.
  5. Bratton R.N., Jessee M.A., Wieselquist W.A. Rod Internal Pressure Quantification and Distribution Analysis Using FRAPCON. Oak Ridge National Laboratory, Report No. ORNL/TM-2015/557, 2015, 61 p.
  6. Feria F., Herranz L.E. Internal pressure of spent PWR fuel rod at high burnup: prediction enhancement through FRAPCON-3.5 uncertainty analysis. Top Fuel conference proceeding, part 2. 2015, pp. 194 – 203.
  7. Demyanov P.G., Kuznetsov V.I., Novikov V.V., Zvir E.A., Zhitelev V.A. UO2 and UO2-Gd2O3 Fuel Rods of VVER-1000 Size Change Modeling. Proceedings of the 13th International Conference on WWER Fuel Performance, Modelling and Experimental Support. Nesebar, Bulgaria. 15 – 21 September 2019, pp. 326–332.
  8. Shcheglov A.S. Development of methods, models and engineering programs for calculating the thermophysical parameters of the WWER fuel element. Cand. Sci. (Engineering) Diss. Abstr. Moscow, 2008, 27 p. (in Russian).
  9. Passage G., Stefanova S., Shcheglov A.S., Proselkov V.N. Comparison of the results of calculations and post-reactor investigations of VVER-1000 fuel elements with burnup 49 MW·days/kg. Atomic Energy. 2006, vol. 101, iss. 6, pp. 869 – 875. DOI: https://doi.org/10.1007/s10512-006-0183-4
  10. The procedure for conducting an examination of programs for electronic calculating machines used to build calculation models of processes that affect the safety of nuclear facilities and (or) types of activities in the field of nuclear energy use. Rostekhnadzor, July 30, 2018, No. 325 (reg. with the Ministry of Justice of Russia on November 12, 2018 No. 52650) (in Russian).
  11. Bogdan S.N., Zhylmaganbetov N.M., Kozlova N.A., Ponizov A.V., Sharafutdinov R.B., Shevchenko R.A., Shevchenko S.A., Yashnikov D.A. Current issues of review of computer codes used for safety analysis of nuclear facilities. Yadernaya i radiatsionnaya bezopasnost’. 2022, iss 2 (104), pp. 31 – 49. DOI: 10.26277/SECNRS.2022.104.2.002 (in Russian).
  12. Kileen J.C., Turnbull J.A., Sartori E. Fuel Modelling at Extended Burnup: IAEA Coordinated Research Project FUMEX-II. Proceeding of the 2007 International LWR Fuel Performance Meeting. San Francisco, California, September 30 – October 3, 2007. Paper 1102.
  13. Bokov A.A., Pavlov S.V., Teplov V.G. Features of changing of the free volume of WWER-1000 fuel rods depending on fuel burnup. VANT. Ser. Yadernye i Reaktornye Konstanty. 2023, iss. 1, pp. 159 – 169. Available at: https://vant.ippe.ru/images/pdf/2023/issue2023-1-159-169.pdf/ (accessed Jul. 01, 2023) (in Russian).
  14. Pimonov Yu.I., Bulygin V.A., Dvoretsky V.G. Methodological aspects of measuring the amount and composition of gas under the cladding of irradiated fuel elements. Proceedings of JSC “SSC RIAR”. 1998, no. 1, pp. 37 – 41 (in Russian).
  15. Gurov K.P. Phenomenological thermodynamics of irreversible processes (physical foundations). Moscow, Nauka Publ., 1978, 128 p. (in Russian).
  16. Dmitriev D.V., Gonchar N.I., Jilkin A.S. Modeling of the yield and distribution of stable gaseos fission products in a sealed fuel rod of container type. VANT. Ser. Yadernye i Reaktornye Konstanty. 2022, iss. 2, pp. 53 – 60. Available at: https://vant.ippe.ru/images/pdf/2022/issue2022-2-53-60.pdf/ (accessed Jul. 01, 2023) (in Russian).
  17. Struzik C., Garcia Ph., Noirot L. A comparative study of fission gas behaviour in UO2 and MOX fuels using the meteor fuel performance code. Fission Gas Behaviour in Water Reactor Fuels Seminar Proceeding. Cadarache, France. 2000, pp. 511 – 522.
  18. Noirot J., Desgranges L., Marimbeau P. Contribution of the RIM to the overall fission gas release: what do isotopic analyses reveal? Fission Gas Behaviour in Water Reactor Fuels Seminar Proceeding. Cadarache, France. 2000, pp. 223 – 234.
  19. Bernard L.C., Jacoud J.L., Vesco P. Framatone analysis of fission gas release and related topics. Fission Gas Behaviour in Water Reactor Fuels Seminar Proceeding. Cadarache, France. 2000, pp. 463 – 478.
  20. Bibilashvili Yu.K., Medvedev A.V., Khvostov G.A., Bogatyr S.M., Korystine L.V. Development of the fission gas behaviour model in the START-3 code and its experimental support. Fission Gas Behaviour in Water Reactor Fuels Seminar Proceeding. Cadarache, France. 2000, pp. 407 – 431.

fuel rod burnup nuclear fuel water-water power reactor gas pressure model

Link for citing the article: Bokov A.A., Pavlov S.V., Ilyin P.A., Teplov V.G. Model of Gas Pressure under the Cladding of WWER-1000 Fuel Rods after Operation. Izvestiya vuzov. Yadernaya Energetika. 2024, no. 1, pp. 147-158; DOI: https://doi.org/10.26583/npe.2024.1.12 (in Russian).