Izvestiya vuzov. Yadernaya Energetika

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

«Cliff Edge Effects» in Safety Justification and Operation of NPP Units

1/20/2022 2022 - #01 Global safety, reliability and diagnostics of nuclear power installations

Makhin V.M. Podshibyakin A.K.

DOI: https://doi.org/10.26583/npe.2022.1.08

UDC: 621.039.58

The authors consider phenomena that have signs of «cliff edge effects» according to the definitions of the IAEA and NP7001715: (1) degradation of the protective barrier (fuel rod claddings in surface boiling mode with the deposition of impurities and borates on their surface and heating of the claddings) and (2) departure from nucleate boiling (DNB) on the fuel rod claddings. Despite the fact that the first phenomenon was previously unknown, the safety of the power unit is ensured by the decisions adopted in the project.

The DNB was studied and measures were taken in the project to prevent it under normal operating conditions and anticipated operational occurrences. The protection against the DNB is also obviously ensured by reducing the reactor power due to the control systems and reactor scram. These phenomena do not reach the state of «cliff edge effects» (according to the terminology of the IAEA and federal NPs of the Russian Federation) and are prevented at the initial stages. For a small7size reactor using dispersive fuel, it is possible to provide self7protection against the DNB, namely, due to partial washout of the fuel with the insertion of negative reactivity, followed by a decrease in power and termination of the crisis.


  1. Safety of Nuclear Power Plants: Design. IAEA, Vienna,.2016, STI/PUB/1715.
  2. NP-001-15. General Safety Provisions for Nuclear Power Plants. Moscow. The Federal Service for Ecological, Technological and Nuclear Supervision Publ., 2015, 74 p. (in Russian).
  3. Reshetnikov F.G., Bibilashvili Yu.K., Golovnin I.S. et al. Development, Production and Operation of Fuel Elements of Power Reactors. Book 1. Moscow. Energoatomizdat Publ., 1995, 320 p.
  4. Kritsky V.G., Rodionov Yu.A., Berezina I.G., Gavrilov A.V. Influence of Operational and Water-Chemical Parameters on the Deposition of Corrosion Products on the Surfaces of Fuel Elements. Proc. of the ISTC «Safety of VVER», Podolsk, 2011. Available at: http://www.gidropress.podolsk.ru/files/proceedings/mntk2011/documents/mntk2011-068.pdf (accessed Dec. 24, 2021) (in Russian).
  5. Optimization of Water Chemistry to Ensure Reliable Water Reactor Fuel Performance at High Burnup and in Ageing Plant (FUWAC). Vienna: IAEA, 2011. 8.7. AOA and CIPS, pp. 93-97
  6. Kritsky V.G., Rodionov Yu.A., Berezina I.G., Gavrilov A.V. Problems of Mass Transfer and Formation of Corrosion Products on VVER-1200 Fuel Elements. Proc. of the VIII ISTC «Water1Chemical Regime of NPP», October 23-25, 2012, Moscow, VNIIAES JSC (in Russian).
  7. Bennett P., Beverskog B., Suther R. Halden In-Reactor Test to Exhibit PWR Axial Offset Anomaly. Available at: https://www.osti.gov/servlets/purl/837201 (accessed Dec. 24, 2021); DOI: https://doi.org/10.2172/837201 .
  8. Henshaw Jim, McGuire John C., Sims Howard E. et al. The Chemistry of Fuel Crud Deposits and Its Effect on AOA in PWR Plants, BNFL, AEA Technology, + EPRI , 2006 (picture from Byers A. and Deshon J. Structure and Chemistry of PWR CRUD, paper 7.5. Proc. of the Int. Conf. on Water Chemistry of Nuclear Reactor Systems, San Francisco, October 2004). Available at: https://pdfs.semanticscholar.org (accessed Dec. 24, 2021).
  9. Zabelin A.I., Gordienko N.I., Svyatysheva T.S. Influence of boric acid on the hardness of the boiling water reactor coolant. Symposium CMEA «Water Modes of Pressurized Water Reactors, Radiation Monitoring of Coolants and Means of Reducing the Radiation Hazard of Coolants», GDR Gera, November 10-16, 1968, p. 90-94.
  10. Zenkevich B.A., Kozlov V.Ya., Kochetkov L.A., Peskov O.L. Heat transfer Crisis in a Reactor. Atomnaya Energiya, 1969, v. 27, iss. 5, pp. 391-396 (in Russian).
  11. Bobrov S.N. Methods and Results of Reactor Studies of Fuel Elements to Substantiate the Safety of Operation of the SM12 Research Reactor. Abstract of Diss. Cand. Sci. (Engineering). Nizhny Novgorod, 2004, p. 24 (in Russian).
  12. Bobrov S.N., Grachev A.F., Makhin V.M., Spiridonov Yu.G. et al. Experience of Operation and Serviceability of Fuel Elements of the High-Flux Reactor SM-2. Proc. of the Vth Interbranch Conference on Reactor Materials Science, Dimitrovgrad, September 8-12, 1997. Vol. 1, part 2. Fuel, Fuel Elements and Absorbing Materials), Dimitrovgrad: SSC RF NIIAR, 1998, pp. 10-19 (in Russian).
  13. Bobrov S.N., Grachev A.F., Makhin V.M., Spiridonov Yu.G. Study of the Behavior of SM Reactor Fuel Elements in the Heat Transfer Crisis Mode. Proc. of the Int. Conf. «Thermal and Physical Aspects of VVER Safety (Thermophysics198)». Obninsk. IPPE Publ., 1998, v. 1, pp. 411-417 (in Russian).
  14. Bobrov S.N., Alekseev A.V., Makhin V.M., Svyatkin M.N. On the Characteristics of the Fuel Elements of the SM Research Reactor in Regimes with a Heat Exchange Crisis. Proc. of the SSC RF NIIAR FSUE. Dimitrovgrad, 2004, iss. 2, pp. 22-26 (in Russian).
  15. Kirillov P.L. Modern Ways of Development of the Theory of the Crisis of Heat Transfer during Boiling in Channels. Proc. of the Institute of Physics and Power Engineering. Moscow. Atomizdat Publ., 1974, pp. 242-262 (in Russian).
  16. Isachenko V.P., Osipova V.A., Sukomel A.S. Heat Transfer. Moscow. Energiya Publ., 1975, pp. 322-328 (in Russian).
  17. Averyanov S.V., Kutyin L.N., Trusov B.A., Shcherbakov A.P. Features of supercritical heat transfer in multi-rod beams. Proc. of the Interbranch conference «Thermophysics1 89», November 21-23, 1989, Obninsk, 1992, pp. 90-94 (in Russian).
  18. Guidance for the Application of an Assessment Methodology for innovative Nuclear Energy Systems. IAEA-TECDOC-1575, Rev. 1, 2008.
  19. Kochetkov L.A. First Beloyarskie. ATOMINFO.RU, 22.04.2014. Available at: http://www.atominfo.ru/newsh/o0800.htm (accessed Dec. 24, 2021) (in Russian).
  20. Kochetkov L.A. On the History of the first stage of the Beloyarsk NPP. In: History of the Atomic Energy of the Soviet Union and Russia. Iss. 1. Moscow. IzdAt Publ., 2001, pp. 117-133 (in Russian).
  21. Considerations on the Application of the IAEA Safety Requirements for the Design of Nuclear Power Plants. IAEA-TECDOC-1791, Vienna , 2016. Available at: https://www-pub.iaea.org/MTCD/Publications/PDF/TE-1791_web.pdf (accessed Dec. 24, 2021).

cliff edge effects safety

Link for citing the article: Makhin V.M., Podshibyakin A.K. «Cliff Edge Effects» in Safety Justification and Operation of NPP Units. Izvestiya vuzov. Yadernaya Energetika. 2022, no. 1, pp. 90-106; DOI: https://doi.org/10.26583/npe.2022.1.08 (in Russian).