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Fukushima Nuclear Daiichi Plant

Overview of Current Status of the Accidents

 

Overview

 

Reactor #1

#2

#3

#4

(3/11) ECCS malfunctioned

(3/11) ECCS malfunctioned

(3/11) ECCS malfunctioned

No fuel in reactor core

ECCS not required

(3/11) Sea water injection into the reactor core; Steam release by vent valve; The core exposed at least partially; Hydrogen explosion in the top portion of the reactor building (its cause not reported).

(3/14) ECCS stopped; Sea water injection into the reactor core; the entire length of the fuel rods exposed, duration of the exposure unknown; steam release through the vent valve.

(3/15) Steam release to atmosphere from the reactor containment; An explosion in the pressure suppression chamber in the reactor containment.

(3/13) ECCS stopped; A part of fuel rods exposed, Steam release through the vent valve; Injection of sea water into the reactor core.

(3/14) Hydrogen explosion damaging the top of the reactor building.

(3/16) White smoke observed from the damaged top of the reactor building.

(3/17~18) Sprinkling of sea water into the damaged top of the reactor building by fire fighters and Japanese self defense army.

At the time of earthquake and tsunami, the reactor was under a major maintenance so there was no fuel in the core.

(3/15) Hydrogen explosion in the top area of the reactor building; the top of the reactor building was severely damaged; a highly radioactive leak. (3/16) Another fire in the same location, with a highly radioactive leak.

Number of fuel assemblies in the spent fuel pool=

292

587

514

1331

Heat generation rate (spent fuel pool) Kcal/hr

60,000

400,000

200,000

2,000,000

Condition of the spent fuel

(3/19)Unknown

(3/19)Unknown

(3/19)Severe damage likely

(3/15)Severe damage likely

(3/15) Release of radiation.

(3/16) Fire broke again in the same area

(3/16) Release of radio activity.

 

Condition of the reactor containment

(3/19) Believed to be intact

(3/15) The pressure suppression equipment was damaged. Condition of concrete structure unknown

(3/19) Believed to be intact

(3/19) Believed to be intact

Condition of the reactor building above the reactor containment

(3/11) Damaged

(3/19) Believed to be intact

(3/14) Damaged

(3/15) Hydrogen explosion in the top portion of the reactor building damaged that portion of the building.

Release of radio activity

(3/12) Radio active steam released

(3/14) Radio active steam released

(3/15) High level radioactivity released

(3/13) Radio active steam released

(3/15)

 

 

 

 

Major references:

http://www.asahi.com/photonews/gallery/infographics/npp001.htm

http://www.asahi.com/photonews/gallery/infographics/npp003.html

 

 

 

 

 

 

 

Editorís view of what are not reported (3/19)

 

In the past few days, the water sprinkling by the fire fighters and Japanese Defense Army has been reported frequently but no significant reports have been released on the conditions of the reactor cores that have been damaged. Also, no reports have been made regarding the spent fuels in No1 and No.2 reactors.

 

The editorís view on these issues are as follows:

 

In Reactor No.1, the fuel rods were exposed without water for some period of time. Since fuel rods cannot sustain for long when no cooling is available, some portion of the fuel rods should have been damaged.Damage of the fuel rods means that zirconium alloy cladding of the fuel rods are broken and consequently the fuel pellets (uranium oxide of approximately 1 cm diameter and 1 cm high) are no longer contained in the cladding tubes but fell toward the bottom of the reactor core or possibly to the bottom of the pressure vessel.

 

In reactor No.2, an explosion in the pressure suppression pool was reported on 3/15.The cause of the explosion must be burning of the hydrogen gas generated inside the reactor core, that is, the zirconium alloy cladding reacted with water under the condition that no water covered the fuel rods.This must be a severe damage of the fuel rods.A significant fraction of the core, possible the almost entire fuel rods, collapsed and fell downward in the form of pellets. The fuel pellets may be stuck in the middle of the control rods assembly or have fallen to the bottom of the pressure vessel.The only mechanism to prevent from melt-down of the uranium oxide is the cooling effect of the water in the bottom of the pressure vessel.This condition is very dire, as the core material can melt forming a molten mass that can penetrate the pressure vessel bottom.

 

In Reactor No.3, the fuel rods were exposed without water for some period of time. The condition inside the reactor core seems to be similar to that of No.1.Damage of the fuel rods means that zirconium alloy cladding of the fuel rods are broken and consequently the fuel pellets are no longer contained in a rod form but fell toward the bottom of the reactor core or possibly to the bottom of the pressure vessel.

 

Spent fuel pool of No.1 reactor.When the hydrogen explosion at the top portion of the reactor building occurred, where the hydrogen came from was not known, or at least not reported.However the explosions at No3. reactor and No.4 reactor are very similar to that of No.1 reactor. Therefore, we must conclude that the spent fuels were overheated and generated hydrogen gas that ignited in No.1 plant. Therefore the spent fuels are in a similar condition as in No.3 and No.4 although no effort to supply water to the spent fuel storage pool has been made.

 

The condition of the spent fuel pool of No.2 reactor is not known. No effort to supply water to the spent fuel pool has been made.However, we must concern about it.††