Data: Japan’s Separated Plutonium Inventory (as at 2004)

The government has published details of Japan’s plutonium inventory for 2004. Click on the links below for relevant tables and analysis.

2004 plutonium inventory plus overview of long term trends – article in Nuke Info Tokyo 109 (Nov./Dec. 2005)

Material unnaccounted for in 2004.

Material Unaccounted For (MUF)
Details on MUF for 2004 have been obtained by CNIC. (See two tables below.)

MUF refers to the quantity of plutonium (or other material of concern) which cannot be accounted for in the end of year material balance accounts.

In processes where large amounts of plutonium are handled it is inevitable that inputs and outputs will not balance precisely. This is of particular concern when the error is large enough to be of signficance from the point of view of nuclear proliferation. In the case of plutonium the International Atomic Energy Agency (IAEA) has specified that 8kg represents a “Significant Quantity” (SQ). This quantity is considered to be enough to make one nuclear weapon (though in fact a nuclear weapon can be made with less than this).

Details of relevance to MUF were published with the 2004 plutonium inventory data. For the first time an appendix was included with a materials flow chart showing the “increase/decrease in plutonium inventory”. Of particular interest was a category entitled “increase/decrease in plutonium inventory resulting from internal processes including transfer to retained waste, etc”. The figures for this category were as follows:

Total: decrease of 13kg
Tokai Reprocessing Facility: decrease of 4kg
Fuel Fabrication Facility: decrease of 9kg

Unfortunately, these figures were not very meaningful in the form provided. Clearly some of the decrease could be classified as “material unaccounted for”, but how much was unclear. CNIC sought clarification and eventually the Japan Atomic Energy Agency provided the information below in response to inquiries by Diet Member Nobuto Hosaka.

Readers will note from the tables below that the amount classified as MUF is less than 1 SQ. There are three important points to remember in this regard.

First, the key issue is the error that can be expected in the end of year materials balance accounts. Some years outputs will appear to be less than inputs, while in other years ouputs might even appear be greater than inputs. The point is that precise accounting is not possible, which means that in theory material could be diverted to military use without being noticed.

Second, though MUF in any one year might be less than 1 SQ, added up over several years, it might exceed 1 SQ.

Third and most important, when the Rokkasho reprocessing plant begins operating a much larger quantity of plutonium will be separated each year than has been separated at Tokai. Only 259 kilograms were separated at Tokai in 2004, whereas about 3.5 tons will be separated during the planned active tests at Rokkasho. One would therefore expect larger figures for MUF. (Click here for more on this topic.)

The Japanese government points out that materials balances are not the only safeguards. Other measures include surveillance and seals. However, materials balances remain the core component of IAEA safeguards.

Tokai Reprocessing Facility

Fuel Fabrication Facility

*1. Retained waste refers to the high- and low-level liquid wastes generated when nuclear materials are recovered from dissolved spent nuclear fuel.

*2. This refers to material recovered when waste which had been transferred to retained waste is processed to reduce the volume.

*3. Most of the MUF generated in 2004 came from nuclear material which over time had become stuck to instruments in glove boxes during fuel fabrication. Measuring instruments had become available and based on discussions between Japan and the IAEA, the material was measured and added to the account for the new period. Based on discussions between Japan and the IAEA, this nuclear material was transfered to retained waste.

*4. Plutonium which had been stored for a long period of time was supplied as raw material to the manufacturing process. The nuclear loss was reported as at the date of supply.