TEPCO begins critical work unloading Fukushima Daiichi Unit 4 spent fuel pool

Author: 4 Comments Share:

Unit 4 Spent Fuel Pool Cask

On Monday at 15:18, TEPCO workers began work removing spent fuel from the crippled Fukushima Daiichi Unit 4 spent fuel pool, which holds 1,533 assemblies.  Of the 1,533 assemblies, 1,311 are spent fuel, the other 222 are unused.

This project has been labeled by some as one of the most dangerous nuclear operations in human history.  Experts all agree that the engineering challenges are on a scale unseen to date.

Workers are removing the unused assemblies first, as they do not emit as much radiation and heat as the spent fuel assemblies.

Each spent fuel assembly is made up of about 80 fuel rods, which by assembly can contain up to 7,500 trillion becquerels of radioactivity and around 1% plutonium by weight.

The 2013 World Nuclear Industry Status Report claims that the “full release from the Unit-4 spent fuel pool, without any containment or control, could cause by far the most serious radiological disaster to date.”

Work will be challenging, due to the amount of debris in the spent fuel pool from the March 2011 explosion, which ripped the building asunder.

Workers will discover new damage to fuel units they were unaware of previously.  The pieces of debris from the explosion were ejected with enough force to potentially damage fuel rods or jam multiple assemblies together.

The assemblies could also be moved too close together.  The spent fuel rods could break, or be exposed to air and potentially ignite; both scenarios would potentially release a massive amount of radiation, which could necessitate the evacuation of workers from the plant.

According to Bloomberg, if the rods were to overheat or break, a self-sustained nuclear chain reaction similar to the meltdowns in the crippled reactors could be prompted.

The spent fuel assemblies are gripped by a huge remote-controlled crane and transferred into dry cask storage containers which each can hold up to 22 assemblies.  Moving the first assembly into the cask took workers more than an hour.

Once the storage cask is full, workers will lift the container out, load it onto a trailer, and move it to the central repository.  Work is largely carried out at a slow crawl.   The movement of one cast out of the pool takes 12 hours over a 48-hour period, and 8 to 10 days to complete transfer to the new storage pool.

Tokyo Electric plans to finish removing all the spent fuel from the Unit 4 reactor building by the end of 2014.

Many experts have brought to light their concerns related to another major earthquake striking Japan near the Fukushima Daiichi site while workers are conducting removal work.

Source: TEPCO

Source: NHK

Source: Bloomberg

Previous Article

Public meeting tonight in St. Louis to discuss radioactive waste at public landfill

Next Article

Leaks confirmed in Fukushima Daiichi Unit 1 containment vessel

4 Comments

  1. Fukushima fallout damaged thyroid glands of California babies
    19th November 2013 The Ecologist
    Confirmed cases of hypothyroidism, defined as those with Thyroid Stimulating Hormone level greater than 29 units increased by 21% in the group of babies that were exposed to excess radioactive Iodine in the womb. The same group of children had a 27% increase in ‘borderline cases’.
    Our paper reports 44 confirmed thyroid cancer cases in 0-18 year olds in Fukushima in the last six months (a figure that has since risen to 53). In the hypothyroidism paper we discuss the 44 cases relative to the population and calculate that this represents an 80-fold excess based on national data prior to the Fukushima Iodine releases.

  2. The danger of handling the Fukushima fuel assemblies has been exaggerated. They have had three years for the most active fission products to be consumed. Each assembly has a steel envelope encasing the fuel rods, and the assemblies have been held in steel racks. Any assembly that resists removal will be left in place until the end of the removal operation.

    Dismantling the TMI core offered far more engineering challenges. New tools and procedures had to be developed for that operation.

Leave a Reply