FACTBOX-Japan's stalled water filtering system at Fukushima
Sept 3 (Reuters) - Japan has pledged nearly $500 million to help Tokyo Electric Power Co (Tepco), the operator of the crippled Fukushima nuclear plant, filter and contain massive amounts of radioactive water accumulating at the site.
Japan will allocate 15 billion yen ($150 million) to upgrade a stalled water treatment system co-developed by Toshiba Corp and U.S.-based EnergySolutions that can greatly reduce the amount of harmful radioactive elements in water.
Three reactors had meltdowns at the Fukushima Daiichi plant north of Tokyo after the March, 2011 earthquake and tsunami. Tepco uses a jerry-rigged cooling system to flush water over melted uranium fuel rods. That water leaks into a maze of basements and trenches beneath the reactors and mixes with groundwater flowing into the complex. Excess contaminated water is stored in hastily built tanks, at least one of which started leaking recently.
The government on Tuesday decided to install a second water filtering system, similar to ALPS, in the year from next April.
* The Advanced Liquid Processing System (ALPS) can remove 62 different types of radionuclides, including strontium and cobalt from contaminated water. It doesn't extract tritium, which is considered one of the less dangerous radioactive elements for humans.
* Radioactive materials are filtered out of contaminated water as it flows through 14 steel cylinders that contain active carbon, artificial minerals and other absorbents.
* Waste materials like the absorbent and remaining sludge are then transferred to high-integrity containers (HICs) that are transported to a temporary storage facility.
* Tepco said last year highly radioactive waste would need to be stored for around 20 years in such containers.
* The three lines of the ALPS system have the capacity to treat up to 1,500 tonnes of contaminated water every day.
* The chairman of Japan's Nuclear Regulation Authority (NRA) has said ALPS-treated water with tritium levels below international regulatory limits may have to be released into the Pacific Ocean to make more room for highly radioactive waste water accumulating at the Fukushima site.
* ALPS was installed at Fukushima in August-September last year, but did not begin "hot tests" until the end of March.
* The NRA ordered Tepco to make sure the HICs that would hold radioactive waste can withstand shock. It told the utility to run multiple drop tests with the containers.
* The NRA also said Tepco must make sure any leak of highly radioactive material from the ALPS system or any of its waste containers can be isolated in the facility and would not harm any workers.
* The International Atomic Energy Agency said in April that the system still had not "accomplished the expected result of removing some radionuclides" in tests, and noted Tepco needed to develop long-term storage plans for waste created by treating water.
* On April 4, the system shut down for an hour due to an operator error.
* On June 15, a Tepco worker found a leak at the bottom of one of the tanks in an ALPS line. Tepco halted the system again for inspections and found signs of corrosion in the stainless steel tanks.
* Tepco halted all three lines of the ALPS filtering system on Aug. 8 for further inspections.
* Japan has ordered Tepco to fix the system and begin operating ALPS as early as the middle of this month.
($1 = 99.35 Japanese yen)
(Reporting by Mari Saito, Leng Cheng and Osamu Tsukimori; Editing by Aaron Sheldrick and Ian Geoghegan)