FNPP1 reactor parameters
Quick jumps to graphs
- Core Water Level
- RPV temperature
- RPV pressure
- PCV temperature
- PCV pressure
- CAMS containment radioact monitoring system
- NISA and METI press releases
- TEPCO’s own website (EN, JP),
- All data and graphics are available online at the following online Excel workbook, which I update more frequently than the graphs bellow. Most NISA/METI PRs can be downloaded here.
- [04/14] Added “under investigation” tags to the graphs following NISA press releases. According to TEPCO they are simply not sure all indicators are working properly, and they are closely following a number of “suspect” ones.
- [04/18] Added several new sensors as provided by TEPCO/NISA (noteworthy are those with PCV temperature info); Hope the graphs are still relatively easy to read, but I’m open for any suggestion so please don’t hesitate to comment.
- [05/11] After gaining access to #1 Reactor Building and correcting RPV water level gauge A, TEPCO estimates the whole core had melted on the early stages of the accident. As of 6/27 a similar scenario is not ruled out on #2 and #3
- [05/22] Added “water injection rate” graphs to help understanding other params evol.
- [06/04] TEPCO installed a new temporary pressure measuring system on #1 RPV (details).
- [06/21] Facing continuous problems with radioactive water purification facility, TEPCO decided to lower water injection on all 3 reactors in a bid to reduce storage filling pace.
- [06/24] TEPCO gained access to #2 and installed pressure meas syst, corrected water level.
TEPCO’s recovery roadmap evolution
Core Water Level
- A and B are two different instrumentations
- Core height is approximately 4.5m (here are the actual specs).
- At the very beginning of the accident all 3 units spent some hours without any water on the core after losing their cooling systems. You can see more details on the evolution of the accident early stages in this PPT from Areva’s Dr Braun .
- Since then all cores remain above half filled with water, which was sea-water at the beginning then progressively changed for fresh water. An early NRC report (thx Joe Wein) suggested half filled cores would indicate likely failure from recirculation pump seals, but as you can see most sensors are closer to 66% (normal value estimated by NRC) than 50%, so I wonder if that early assessment was accurate.
- [5/11] After gaining access to the interior of n1, TEPCO operators said to have “corrected” #1-A gauge, which was found to be “down-scale” (i.e. core empty). Since temperature is low all over the reactor the fuel is assumed to have completely melted down and reached the bottom of the RPV where it’s kept cool. As of 6/27 TEPCO keeps on repporting #1-B (half filled core) as well.
- [6/06] Tepco is closely investigating the evolution of all water level gauges (except #1-A)
- [6/22] Tepco gained access to #2 reactor building and tried to correct gauge level; corrected level [6/24] remains about 1/2 filled core, but TEPCO is still not sure of their ”new calibration”.
- Properly cooled down reactor RPV temperature is ~ 20 to 30ºC.
- “Cool shut down” is considered ~ bellow boiling point (100ºC at atm pres)
- [6/09] After checking it, TEPCO has determined #3 FW-Nozzle is reliable again
- [6/15] TEPCO believes all temperature readings are now reliable.
- Gauge pressure = Absolute Pressure – Atmospheric Pressure (atm pressure ~ 0.1MPa)
- Properly cooled down reactor RPV pressure is ~ 0 to 0.1 MPa gauge
- RPV normal operating pressure is ~ 7MPa, max. design pressure ~ 8.7 MPa
- [06/04] TEPCO installed a new temporary measuring system on #1 RPV (details), showing a low pressure level, similar to that in #2 and #3. I removed previous data because it was obviously wrong; you can still find it here if you feel like it.
- [06/24] TEPCO installed on #2 a temporary measuring system ~ #1.
- Data for PCV temperature started on 4/17 ; You can see the respective locations of each sensor here:
- HVH: Heating Ventilating Handling Unit: ~ bottom part
- Bellow Seal: ~ upper part
- Maximum DW design pressure is .528 MPa abs ;
- Properly cooled down reactor PCV (DW or SC) pressure is just above atm pressure (~ 0.1 MPa abs)
- Whenever pressure approaches design max. TEPCO is forced to “vent” to prevent any risk of containment failure.
- Rise observed on #1 D/W after 4/7 is due to N2 injection to reduce the risk of H2 explosion within the PCV in case of RPV leak (IAEA, NISA). After a few days it seems pressure has been distributed between DW and SC
CAMS absorbed dose monitoring
- Containment Atmospheric Monitoring System (CAMS) measures H2 and O2 concentration, as well as gamma radioactivity, within the Dry Well (D/W) and Suppression Chamber (S/C).
- You read it right, these are “Sieverts/h“, no “mili”, nor “micro”; keep in mind CAMS measures radioactivity within the containment: that is no place for people to go around
- [04/08] Unit1 CAMS sudden increase happened just before instrument malfunction and it remains unclear whether it was part of such problem or an actual reading.
- [04/17] TEPCO added many new sensors, but most of them have dubious readings (A & B are two different instrumentations measuring the same thing).
- [06/09] TEPCO checked #2 SC(B) sensor and determined it was broken (→ removed from graphs; you can still see its pre-check evolution here if you want).
- [06/15] TEPCO believes all SC sensors but #2-B are now reliable.
Here are some schematic drawings showing the relevant parts to understand the measurement points of the graphs bellow.
You can find more details on the reactor building parts in this figure at wikipedia; I stripped it to show only the relevant parts for the graphs.