Unit 1 Decommissioning

info soon

Unit 1 Spent Fuel Removal: Second half of FY2017
Unit 1 Reactor Fuel Removal: First half of FY2020

Unit 1 status as of July 2014 (METI)

Building dimensions
1. approx.40m
2. approx.45m
3. approx.0.5-1.5m
Concrete

Containment Structure
1. approx.32m
2. approx.10m
3. approx.18m
4. approx.8m
5. approx.2m
6. min.15mm
Carbon steel liner

Reactor Vessel
1. approx.19m
2. approx.4.8m
3. approx.16cm
4, approx.18.4m
Carbon steel (with stainless steel lining)
Weight of UO2: 77t

Temperature at the bottom of RPV: latest data
Temperature in PCV: latest data
Temperature in reactor building As of 11/14, 2013: 13.3℃ (reference) Outdoor air temperature 12.0℃
Temperature of accumulated water in torus room: 32.4-32.6℃ (As of 9.20,2012)
Humidity in PCV: 100%(the form of a mist as of 10,2012)
Humidity in RPV: Unidentified
Flow rate of nitrogen injection: latest here
Hydrogen concentration in PCV: latest here
Pressure in PCV: latest here
Dose rate in PCV: approx. 11.1Sv/h (As of 10.10,2012)
Dose rate in RPV: Unidentified
Dose rate in the building: Most recent survey 2013
Dose rate in torus room: 200-2400mSv/h (As of 5.30,2013)
Radioactive concentration: latest here
Water level of accumulated water in PCV: Approx. 2.8m from bottom part (As of 10.10,2012)
Water level of accumulated water in torus room: OP3700mm (As of 2.20,2013)
Water level of accumulated water in triangle corner: OP3910-4420mm (As of 9.20,2012)
Mass of fuel debris: Unidentified
Distribution of fuel debris (assumption): Most of the fuel has fallen down into the PCV
Fuel debris MCCI products: Unidentified
Fuel debris dose rate: Unidentified
Fuel debris hardness: Unidentified
Fuel debris density: Unidentified (experiments to estimate fuel debris density here)
Weight ratio of fuel debris remaining in RPV: 0%
Percentage of fuel debris not in the RPV: 100%
Diagram of reactor vessel internal structures along with weights and dimensions located here: reactor_internals_id09_e.

Unit 1 Building Cover Removal & Refueling Floor Demolition:

TEPCO has announced their plan to remove the cover of unit 1 so that debris on the refueling floor can be cleaned off. This work will enable viewing of the spent fuel pool and the condition of the reactor well. The work has come under increased scrutiny after it was discovered that similar demolition work at unit 3 had caused contamination up to 50km from the plant due to the wind blowing radioactive building dust.

TEPCO’s plan for dismantling the mess on the refueling floor hopes to cut down on releases to the environment. They challenge may be that the releases from unit 3, even though they were considerable didn’t cause readings at the site boundary or nearby that caused anyone to take notice. Only an in plant reading near a bus stop caused an alarm, along with two contaminated workers.

The plan will involve first removing portions of the roof cover building. Upper sides will be removed but the lower sides near the first floor will be left on. A wind break type sheeting will be installed around the refueling floor as can be seen in the illustration below as the green band on the building.

During the dismantling process for the cover building fixative will be sprayed to attempt to hold down dust.

Prior to the removal of the cover building an inflatable plug was installed in the equipment shaft to attempt to prevent contamination from leaving the building through that structure.

A combination of a vacuum system, the fixative sprayer and a water spray unit will be used during demolition to try to keep dust down. TEPCO did not explain where they water will run off to or how much water they anticipate using during the process.

Graphic by TEPCO outlining their plan for debris removal at unit 1.

TEPCO cited their monitoring post system as a feature for tracking releases. The system appears to be the same one in place during the unit 3 demolition work. TEPCO does plan to reaccess the tactics for demolishing of the top of unit 1 during the process to see if adjustments are needed.

IRID cites the current nitrogen injection system as the starting point for plans to be developed to manage hydrogen gasses during decommissioning and fuel debris retrieval.