Boiling transition phenomenon in BWR fuel assemblies effect of fuel spacer shape on critical power

Yasushi Yamamoto, Shinichi Morooka, Toru Mitsutake, Seiichi Yokobori, Jiro Kimura

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


A thorough understanding of the thermal-hydraulic phenomena near fuel spacer is necessary for the accurate prediction of the critical power of BWR fuel assemblies, and is thus essential for effective developments of a new BWR fuel assembly. The main purpose of this study is to develop an accurate method for predicting the effect of spacer shapes on critical power. Tests have been conducted under actual BWR operating conditions, using an annulus flow channel consisting of a heated rod and circular-tube channel, and BWR simulated 4×4 rod bundles with heater rods unheated just upstream of spacer. The effect of spacer shapes on critical power was predicted analytically based on the droplet deposition rate estimation. The droplet deposition rate for different spacer shapes was calculated using a single-phase flow model. The prediction results were compared with the test results for the annulus flow channel using ring-type spacers. Analytical results of critical power agreed with measured critical power from point of the effects of changes in the rod-spacer clearance and the spacer thickness on critical power.

Original languageEnglish
Pages (from-to)315-323
Number of pages9
JournalNippon Genshiryoku Gakkaishi/Journal of the Atomic Energy Society of Japan
Issue number4
Publication statusPublished - 1996
Externally publishedYes


  • Analytical prediction
  • BWR type reactors
  • Critical power
  • Droplet deposition
  • Fuel assemblies
  • Rod bundles
  • Spacers
  • Subchannel code
  • Thermal-hydraulics
  • Thickness
  • Two-phase flow

ASJC Scopus subject areas

  • Nuclear Energy and Engineering


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