Mixing it up

Due to the nature of its nuclear programme, which includes reprocessing, Japan has a variety of waste streams – and a myriad of organisations responsible for these wastes.

Against this complex backdrop, the country’s deep geological repository programme is underway. But much work is needed before a final repository can be built – not least to find a community that wants to host the repository.

In Japan, radioactive waste other than high-level waste (HLW) is usually called low-level waste (LLW). Therefore, LLW includes items ranging from very low activity waste from hospitals and universities up to highly active waste such as ion exchange resins, irradiated reactor core components and some LLW containing transuranic nuclides (TRU waste), the latter of which is to be disposed of geologically.

LLW is sub-classified according to origin (differing radionuclide composition) and level of radioactivity.

Japanese waste policy, defined in the Specified Radioactive Waste Final Disposal Act 2000, is that HLW should be disposed of in a stable geological formation at a depth of more than 300m. The vitrified waste in canisters is to be encapsulated in metal containers (overpacks) and, once emplaced in a repository, surrounded by a clay buffer material. This multibarrier system used for waste disposal is a combination of engineered and natural barriers.

Research and development on the multibarrier system is continuing in Japan with a view to “building confidence” in the concept, according to the Nuclear Waste Management Organisation of Japan (NUMO). NUMO was set up in 2000 by the private sector and has responsibility for the repository programme.

NUMO’s forward programme includes research and development to promote public understanding, for example building geological disposal demonstration facilities and using them for public relations purposes. It also wants to develop an approach to explaining the long-term safety of geological disposal.

NUMO feels that to build public credibility, work supporting the disposal programme should not only be aimed at building a strong safety case, but also communicating this to stakeholders. NUMO is also linking with international partners to learn from other countries’ experiences, such as Sweden and Finland.

The cost of disposing of a set figure of 40,000 canisters of HLW was estimated to be approximately JPY3 trillion ($31 billion) but this may change over time and does not include any compensation paid to affected communities. The 40,000 canister figure is the estimated total volume of waste arising from the start of operation of the country’s nuclear power plants up to the year 2020.

Waste producers are required to make payments into a fund which will cover future disposal costs. These payments are reflected in the price of electricity paid by the consumer and amount to JPY0.2/kWh. Funds are administered by the Radioactive Waste Management Funding and Research Center.

The repository is scheduled to be open for business from around 2035. In the meantime, a HLW interim store is used. In 1995, the country’s first HLW interim store was opened at the Rokkasho suite of nuclear facilities, owned and run by Japan Nuclear Fuels Ltd (JNFL). The first load of vitrified HLW from Europe, which was a result of reprocessing Japanese fuel, arrived that year.

The HLW has arisen from 2940t of spent fuel owned by ten Japanese power companies which was shipped to France for reprocessing between 1969–90. Some 4100t of fuel was shipped to the UK for reprocessing.

Reprocessing of fuel in France ended in 2004 and all the HLW produced has now been shipped back to Rokkasho for interim storage of 30 to 50 years prior to long-term disposal.

Waste shipments from the UK are scheduled for completion by 2016 and are subject to waste substitution arrangements in which the UK sends back proportionately more HLW than it received, but returns less LLW.

Japan Atomic Energy Agency (JAEA) has a small reprocessing plant at Tokai, in conjunction with the Monju fast reactor.

JNFL also has a commercial-scale reprocessing plant at Rokkasho that is due to start operations later this year.

Inventory

As of the end of March 2008, waste stored at nuclear power reactor facilities included about 630,000 200L drums in solid waste storage facilities, 29 used steam generators in steam generator storage facilities, used control rods, disused channel boxes and spent resin in spent fuel pools and other facilities.

At sites other than nuclear power plants, HLW of approximately 1600 vitrified packages and approximately 400m³ liquid HLW are stored in fuel reprocessing facilities, and LLW of approximately 590,000 200L drums and about 5400m³ liquid LLW are stored in fuel reprocessing facilities, fuel fabrication facilities, laboratories, university research reactor facilities, and Japan Radioisotopes Association stores.

Further storage capacity for spent fuel was announced in 2005, when Tokyo Electric Power Company and Japan Atomic Power Company said a 5000t-capacity spent fuel store would be built in Mutsu, Aomori, and would operate from 2010. This store is to provide interim storage for up to 50 years prior to reprocessing.

In March 2008, preparatory construction began. Firstly, a 3000t store will be built, followed by a second store.

In February 2009, the Japanese media reported that a project costing over JPY14 billion ($146 million) was to take place at Rokkasho’s vitrification plant. The government is to provide about half the money, which is to be spent on work up to 2013 to alleviate technical problems at the plant. Work will be carried out to improve the structure of the melting furnace to prevent platinum-group metals from accumulating on its floor.

The vitrification plant conditions waste for final disposal by setting it in glass, and is equipped with compression, incineration, melting, solidification and sorting processes. Some of the relevant processes are:

• Liquid LLW is dried and made into pellets then stored in drums.

• Spent solvent is treated by pyrolysis (chemical decomposition of a condensed substance by heating) and hydrothermal solidification then stored in drums.

• Relatively low-level beta/gamma inflammable waste is incinerated and solidified hydrothermally then stored in drums.

• Hulls and end pieces are stored in a bespoke facility.

• Channel boxes and burnable poisons are cut up then loaded in drums and stored at a special treatment facility.

• Other wastes are stored in their original shapes at the intermediate storage facility.

LLW?disposal

A portion of LLW stored at commercial reactors, which has a comparatively low concentration of radionuclides, has been transported to JNFL’s Low-Level Radioactive Waste Disposal Center since 1992 (the near-surface Disposal Facility One). This large LLW disposal site at Rokkasho is Japan’s central LLW disposal facility. Commercial operations at Number Two facility began in 2000.

Credit: JNFL

The JNFL LLW disposal site at Rokkasho.

Following on-site storage, LLW is shipped here from individual nuclear power plants throughout the country. It is comprised of the two facilities with a total disposal capacity of 80,000m³ (400,000 200L drums). The final business scope is to dispose of 600,000m³. The JNFL disposal facility at Rokkasho had disposed of about 210,000 drums of waste, as of the end of April 2009.

Number one disposal facility includes homogenous waste including condensed liquid waste and spent resin which have been solidified in cement, asphalt or plastics. Number two disposal facility is for solid waste encapsulated in mortar, such as contaminated metal and plastics.

The disposal sites consist of dozens of concrete pits containing cells, the majority of which can hold 320 drums each. They are transported to Mutsu-ogawara port by a specialised ship Seiei-maru from nuclear plants in Japan and then taken by road to the pits at the disposal site.

Meanwhile, at the disposal facility belonging to Tokai Research and Development Center, Nuclear Science Research Institute (part of JAEA), about 1670t of very-low-level waste resulting from dismantling of the Japan Power Demonstration Reactor were disposed of (see table). The facility operated for a year from 1995-6.

At a plenary session of Japan’s Upper House on 28 May 2008, unanimous approval was given to revise the Japan Atomic Energy Agency Law, giving JAEA responsibility for promoting the disposal of radioisotopes and other radioactive waste from its research facilities and other sites.

A framework was set up for the disposal of this waste, which stood at about 550,000 200L drums at the end of 2007.

Siting process

The siting process for a HLW repository in Japan consists of three steps, which are outlined in the Specified Radioactive Waste Final Disposal Act. These are: selection of preliminary investigation areas (PIAs), selection of detailed investigation areas, and selection of a repository construction site.

NUMO is working on the disposal process, including site selection, demonstration of technology, licensing, construction, operation, monitored retrievable storage for 50 years and closure of the repository.

On 19 December 2002, NUMO officially announced the start of a request for volunteer areas for preliminary investigation for a HLW repository. The approach was based on the need for local community support in conducting a geological disposal programme, and all municipalities in Japan were eligible.

A communication programme was carried out, which included public meetings, public relations activities at a national level and community activities to improve understanding amongst potential host regions.

Information packs were issued containing: an introduction into the request for volunteer areas, instructions for the application, repository concepts, siting factors for PIA selection, and the approach for the outreach scheme.

NUMO has stated that the flexibility required by the siting process dictates use of a procedure which tailors repository designs, safety cases and site characterisation processes to the volunteer areas – this is described as the NUMO “structured approach”.

In contrast to the idealised generic studies from the past, NUMO says its current studies are based on practicality and what it calls “adaptive staging” – tailoring the different stages of the repository concept to site characteristics. There is also a focus on future operational safety in the repository and processes associated with repository closure.

Sites which may be suitable are scheduled to undergo detailed investigation from 2012. NUMO hopes that a third phase to 2030 will end with site selection.

In January 2007, Toyo town in Kochi prefecture applied to take part in the process. Before conducting a literature survey, NUMO said it would initiate an internal procedure that included confirming the geological conditions in the volunteer area.

However, on 23 April 2007, Toyo decided to withdraw from the process after a mayor was elected who opposed the waste disposal facility being sited there.

TRU waste

On 2 April 2008, NUMO announced that it had been approved by the Ministry of Economy, Trade and Industry as the implementing organisation for final disposal of ‘second class’ specified radioactive waste, in line with the Specified Radioactive Waste Final Disposal Act.

In accordance with a revision to this act in June 2007, low-exothermic radioactive waste with long half-lives (TRU waste) is classified as LLW and is the ‘second class’ of two specified radioactive wastes requiring geological disposal. The ‘first class’ requiring geological disposal is HLW.

TRU waste is generated by reprocessing and in MOX fuel fabrication plants, and includes spent fuel cladding tubes and filters containing radioactive iodine.

The organisation is also revisiting designs and investigating whether it would be beneficial to bury TRU waste at the same site as a HLW repository, bearing in mind that TRU waste is predicted to give rise to higher doses.

Recently, NUMO has said efforts are needed to bring the TRU waste disposal safety case to a level equivalent to the safety case for HLW disposal. Key points include improving the technical basis for TRU waste disposal, looking at alternative technology for conditioning problematic waste streams, and improvement of safety evaluation methodology – particularly for co-location of the wastes.

One of its main aims now, though, is to gain volunteer communities.

Underground lab work

Researchers are currently working on underground rock laboratories at Mizunami (crystalline rock), in Gifu, and Honorobe (sedimentary rock), in Hokkaido. Surface investigations have been completed, whilst the drilling of shafts and drifts is ongoing.

The labs’ work is planned in phases with the current phase being the use of gathered data to verify results from surface investigations, and find out how the geology will change during excavation of the facility. Afterwards investigation of the underground sites will shape the focus of ongoing work.

In terms of geological stability, Japan’s active faults mean that it is extremely important to assess geology for the resulting repository safety case.

Possible problems could result from hidden active faults, magma and high temperature fluids at depth. Assessment of uplift and erosion are also important.

JAEA has also carried out research at the Engineering Scale Test and Research Facility and the Quantitative Assessment of Radionuclide Migration Experimentation, which are both at Tokai.

Some of the topics studied include the corrosion lifetime of the carbon steel overpack, a thermodynamic and sorption database, and a computer matrix (FepMatrix) which is designed to help understand relationships between different scenarios in rock engineering systems.