Analysis of reactor water level measurements during the Fukushima unit 3 accident

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientificpeer-review

Abstract

The reactor water level measurement in the Fukushima reactors was based on measuring the pressure difference between two water-filled pipes that were connected to the reactor at different elevations. The measurements were distorted by boiling of the water in the measurement system during the accident, and the indicated water level became much higher than the actual level. This phenomenon can give clues about the events that occurred during the accident.
The water level measurement system of Fukushima unit 3 was added to VTT's MELCOR model of the accident. Various assumptions were tested to find out what could have caused the boiling of the water in the measurement system 42.2 h after the earthquake. It was found that there was probably a leak of superheated steam from the reactor to the drywell at this time. The best match to the measurements was obtained by assuming a 20 cm2 leak from the steam line to the drywell at the same time when the Automatic Depressurization System actuated. However, the calculations could not rule out a steam line failure as a reason for the reactor depressurization.
Original languageEnglish
Title of host publication19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19)
PublisherAmerican Nuclear Society (ANS)
Publication statusPublished - 2022
MoE publication typeA4 Article in a conference publication
Event19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics - Virtual conference
Duration: 6 Mar 202211 Mar 2022

Conference

Conference19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics
Abbreviated titleNURETH-19
Period6/03/2211/03/22

Keywords

  • Severe accidents
  • Fukushima
  • MELCOR
  • Water level measurement

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