The UN’s nuclear watchdog on Wednesday delivered a preliminary report on their review of Japan’s efforts to plan and implement the decommissioning of the Fukushima Daiichi Nuclear Power Station that suffered a meltdown during the Great East Japan Earthquake and tsunami of 2011.

Following a 10-day visit, a 19-member team of experts praised Japan for making progress on shutting down the crippled plant, but warned that the situation there remained “very complex”. The International Atomic Energy Agency (IAEA) team also acknowledged that processed water now kept on site would probably have to be dumped in the ocean.

“We are still at the beginning of a lengthy process but Japan is gaining a better understanding of the situation, an understanding that is critical to address the challenges,” said team leader Juan Carlos Lentijo, Director of Nuclear Fuel Cycle and Waste Technology at the IAEA. “The situation, however, remains very complex, and there will continue to be very challenging issues that must be resolved to ensure the plant’s long-term stability.”

The visit and report spring from the IAEA’s Action Plan on Nuclear Safety — endorsed by all IAEA Member States in September 2011 and meant to strengthen worldwide nuclear safety — that encourages the use of peer review missions to take full advantage of global experience.

Within that framework, the Japanese government invited the IAEA to conduct an independent review of their “Mid-and-Long-Term Roadmap towards the Decommissioning of TEPCO’s Fukushima Daiichi Nuclear Power Station Units 1–4” with two main objectives:

• To improve the decommissioning planning and the implementation of pre-decommissioning activities; and
• To share the good practices and lessons learned by the review with the international community

The latest visit was the second — an April 2013 initial review of the Roadmap included assessments of decommissioning strategy, planning and timing of decommissioning phases and a review of several specific short-term issues and challenges.

During the 25 November to 4 December 2013 visit, the team examined a variety of decommissioning issues, focusing particularly on TEPCO’s removal of fuel assemblies from Reactor Unit 4’s spent fuel pool and on contaminated water management issues. The experts also looked at Japan’s efforts to monitor radiation conditions in the marine environment, including seawater, sediment, and biota.

The Preliminary Summary Report highlights “19 areas of important progress (acknowledgments) to date and offers 19 advisory points where the team felt that current practices could be improved”.

But its overall tone seems to be one of encouragement. The report states that though the decommissioning “is a very challenging task that requires the allocation of enormous resources, as well as the development and use of innovative technologies to deal with the most difficult activities” the government and TEPCO have taken a more proactive approach since the April mission. “Japan has achieved good progress in improving its strategy and the associated plans, as well as in allocating the necessary resources towards the safe decommissioning.”

“The team also notes that the current situation is very complex, and that there are still some very challenging issues (e.g., contaminated water management, nuclear fuel removal, and fuel debris removal) that must be resolved to ensure the long-term sustainability of the plant’s stable condition.”

And all the encouraging praise aside, those challenging issues are indeed thorny. The recently begun work on removing fuel assemblies from the spent fuel pool in Reactor No. 4 means the removal of 1,533 fuel assemblies — a huge and sensitive task, well described by The Guardian. The job will take until the end of 2014.

The management of contaminated water that has been used to cool reactor cores also is a multi-faceted undertaking. Because groundwater from nearby mountains has been flowing onto the site and into the reactor buildings, 400 metric tons of radioactive water is produced daily. Japan’s Roadmap states that construction of a groundwater bypass to reroute that mountain water is underway and that the frozen underground walls planned for Building Units 1 to 4 are in the conceptual design phase and preparatory work was to commence in mid-November.

Meanwhile, 400,000 tons of water are stored at the site in about 1,000 tanks. The “Advanced Liquid Processing System” (ALPS) is capable of removing all radioactive materials except tritium (“one of the least dangerous of radionuclides” according the the US Environmental Protection Agency). And the IAEA preliminary report puts much emphasis on its “consistent and high performance”. Sadly, the system is trouble-prone and was shut down again last weekend, just prior to the report’s launch.

So it remains to be seen what will emerge from the experts’ advice on the topic:

“TEPCO should bolster its efforts to treat this water and then examine all options for its further management, including the possibility of resuming controlled discharges [to the sea] in compliance with authorized limits. To pursue this option, TEPCO should prepare appropriate safety and environmental impact assessments and submit them for regulatory review.”

The IAEA team will produce their final report on their inspection by the end of January. Overall, the government’s Roadmap for decommissioning the Fukushima plant envisages a process that is expected to last three or four decades.