Analysis of LaSalle-2 Neutron Flux Oscillation Event with RETRAN Code

Fumimasa Araya, Masashi Hirano, Kazuo Yoshida, Kiyoshi Matsumoto, Masao Yokobayashi, Atsuo Kohsaka

Research output: Contribution to journalArticlepeer-review


A series of calculations were performed with a transient thermal-hydraulic calculation code RETRAN on the neutron flux oscillation event at LaSalle County Station Unit 2 on March 9, 1988, with the objectives to clarify the causes of the oscillation and effects of the power distribution on stability which were pointed out as a major difference between LaSalle-2 and typical BWRs in view of BWR stability. A method to determine instability threshold developed by the authors was used in the calculations. In order to clarify the causes of the oscillation, the event was simulated and a stability map under the conditions of the event was produced. By drawing the calculated locus of the event on the instability map, it was clarified that the neutron flux oscillation was caused by increase in core inlet subcooling during natural circulation condition due to recirculation pumps trip. In order to clarify effects of power distributions on the stability, sensitivity calculations were performed on the transient behaviors with the LaSalle-2 scenario changing the feedwater temperature transients. Also, the sensitivity calculations on the instability map assuming extremely stable power distributions were perfomed. Based on the calculated results it was concluded that the power distribution had large effects on the stability. It was pointed out that, in the extremely stable case, a neutron flux oscillation would not occur during a transient with the LaSalle-2 scenario and a margine in core inlet subcooling would be 10K until oscillation would occur.

Original languageEnglish
Pages (from-to)565-575
Number of pages11
JournalNippon Genshiryoku Gakkaishi/Journal of the Atomic Energy Society of Japan
Issue number6
Publication statusPublished - 1992
Externally publishedYes


  • BWR type reactors
  • computerized simulation
  • instability map
  • neutron flux oscillatins
  • power distribution
  • reactor stability
  • RETRAN code
  • sensitivity analysis

ASJC Scopus subject areas

  • Nuclear Energy and Engineering


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