Modelling design basis accidents LOCA and RIA from the perspective of single fuel rods

Asko Arkoma

Research output: ThesisDoctoral ThesisCollection of Articles


When designing a nuclear power plant and its fuel, certain accidents are postulated to occur with a predetermined low frequency. The consequences of these accidents are mitigated by various passive and active safety features, and an adequate safety level is implemented by the regulatory authority in the safety requirements. The dissertation considers computational modelling of two main design basis accidents in current light water reactors: loss-of-coolant accident (abbreviated LOCA) and reactivity initiated accident (RIA). The applied computer programmes are designed for modelling the behaviour of a single fuel rod in transient and accident conditions. LOCA modelling is focused on developing a statistical analysis methodology for the evaluation of fuel failures in LOCA. The statistical system is applied to a large break LOCA in an EPR type reactor, and fulfilment of the regulations included in the Regulatory Guides on nuclear safety set by the Finnish nuclear safety authority STUK is studied. In order to determine the underlying factors affecting the fuel rod failures, a sensitivity analysis is performed. A systematic multistage procedure is developed for the sensitivity analysis. RIA modelling focuses on adaptation of the single rod RIA modelling code SCANAIR for boiling water reactor (BWR) conditions. The SCANAIR code, developed by the French research organisation Institut de Radioprotection et de Sûreté Nucléaire (IRSN), is specifically designed for modelling RIAs in pressurized water reactors (PWRs). In this dissertation, the code is adapted to take into account BWR specific properties and conditions.
Translated title of the contributionSuunnitteluperusteisten onnettomuuksien (LOCA ja RIA) mallinnus yksittäisten polttoainesauvojen näkökulmasta
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Tuomisto, Filip, Supervising Professor
  • Hämäläinen, Anitta, Thesis Advisor
Print ISBNs978-952-60-7846-5, 978-951-38-8617-2
Electronic ISBNs978-952-60-7847-2, 978-951-38-8616-5
Publication statusPublished - 2018
MoE publication typeG5 Doctoral dissertation (article)


  • loss-of-coolant accident
  • reactivity initiated accident
  • fuel rod modelling

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