24 May (NucNet): Relatively stable cooling of fuel and fuel debris in the reactors and spent fuel pools has been established at Fukushima-Daiichi, but there are still “several challenges” to be met before “a sustainable situation” is achieved at the plant, the International Atomic Energy Agency has said.
In a report released yesterday, the IAEA said the continuing accumulation of contaminated water at the site is influencing the stability of the situation and must be resolved in the near term before other recovery and decommissioning steps can begin.
The report also warned that “a high degree” of uncertainty is influencing some of the key aspects which form the basis for progress at the nuclear site.
The most important is the “unknown detailed radiological and physical situation” inside the reactor pressure vessels and the integrity of the units’ primary containment vessels.
The status and the location of the fuel debris, the extent of the structural damage and the loss of integrity of the structures and components, as well as the magnitude of the contamination are not well known, the report said.
The condition and the location of the fuel debris have to be determined in order to plan for its removal and to develop adequate technologies. The removal of the debris is a prerequisite for decommissioning.
For ensuring the long term stability of the fuel and fuel debris cooling, efforts must continue to improve the reliability of essential systems, to assess the structural integrity of the site facilities and to improve protection against external hazards, the report said.
Considering the magnitude of the accident consequences, achievement of an “end state” for Fukushima-Daiichi will present a challenging task for several decades, the report concluded.
In the report, the IAEA said whether all the radiation-contaminated material at the plant will be removed, some structures including waste facilities will be left, or the site will be used for power generation in the future is of “crucial” importance to waste management strategy.
The decommissioning will require deployment of “very large human and financial resources” and will involve generation and management of huge amounts of waste, including retrieval of the waste from the existing temporary waste storage sites and its proper disposal.
The report said adequate waste disposal facilities or long-term storage sites with adequate capacity will have to be made available in time to support a programme of such magnitude.
The report acknowledges Japanese accomplishment and provides advice on a range of issues, including overall strategy and planning, stakeholder involvement, and the management of reactor fuel.
The report follows an invitation by Japan for the IAEA to carry out an independent peer review of decommissioning plans for Fukushima-Daiichi units 1 to 4.
The review has been organised in two steps, with the first part carried out in Japan from 15 to 22 April 2013.
The decommissioning roadmap was released in December 2011 by the Ministry of Economy, Trade and Industry (METI).
It calls for the four Fukushima-Daiichi units to be decommissioned in three phases with the final phase taking up to 40 years. However, this phase might not begin for another 10 years, allowing time for the removal of spent fuel and other debris.
Phase one will last two years and involve starting the removal of spent fuel from the spent fuel pools.
Units 1, 2 and 3 at the six-unit plant were in commercial operation at the time of the March 2011 accident and all suffered reactor core and fuel damage.
Unit 4 was offline and was not loaded with fuel, but the reactor building was severely damaged by a hydrogen explosion.
The IAEA report is online:
www.iaea.org/newscenter/focus/fukushima/missionreport230513.pdf
