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.
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 language | English |
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Title of host publication | Proceedings of the 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-19 |
Publisher | American Nuclear Society (ANS) |
ISBN (Electronic) | 978-90-76971-26-1 |
Publication status | Published - 2022 |
MoE publication type | A4 Article in a conference publication |
Event | 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics - Virtual conference Duration: 6 Mar 2022 → 11 Mar 2022 |
Conference
Conference | 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics |
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Abbreviated title | NURETH-19 |
Period | 6/03/22 → 11/03/22 |
Keywords
- Severe accidents
- Fukushima
- MELCOR
- Water level measurement