Rokkasho plant yields troubling nuke surprise

Kyodo News

Some of the highly radioactive vitrified nuclear waste being churned out by the fuel reprocessing plant in the village of Rokkasho, Aomori Prefecture, has been found to contain unexpected highly soluble chemical compounds that are escaping the vitrification process as liquids, Japan Nuclear Fuel Ltd. said Thursday.

A permanent disposal site for the accumulating waste hasn’t been chosen yet, but JNF, which runs the plant, said it was confident the waste will not have any unfavorable effects on the environment.

But it has also asked the Atomic Energy Society of Japan to conduct an environmental assessment when it is stored underground.

Antinuclear groups said they are concerned about what will happen if the unexpected radioactive liquids, found in more than half the storage vessels produced so far, enter the water supply after the vitrified waste is buried.

The facility reprocesses spent nuclear fuel discarded by nuclear power plants from across Japan. The reprocessing method, however, produces plutonium, uranium and highly radioactive liquid waste. These byproducts are mixed with raw glass material in a furnace, vitrified into a more solid state, and placed into stainless-steel vessels for long-term storage.

But liquid waste with lower viscosities than expected started emerging after JNF first began vitrification at the plant last November.

The fluid wastes contain compounds mainly made up of molybdenum, sulfur and sodium and are heavier than glass. A vessel filled with vitrified nuclear waste weighs about 500 kg. The liquid waste accounts for about 0.1 percent of that.

Earlier this month, the liquid waste was found in 35 of the 60 vessels produced. But engineers have altered the operating process for the melting furnace and no more liquid waste is being produced, JNF said.

Hiroyuki Nakamura, who heads JNF’s reprocessing department, said no one has been able to determine whether the low-viscous liquids are mixed in with the glass material.

The unexpected liquid waste might have been produced by a flaw in the furnace’s thermal management, Nakamura said.

Japan Nuclear Fuel was founded in 1992 by the nation’s power utilities to set up a commercial-based nuclear fuel cycle. The fuel reprocessing plant in Rokkasho is currently in the middle of testing.

The state-backed Nuclear Waste Management Organization of Japan started looking for a permanent disposal site for the high-level nuclear waste six years ago. If it finds a spot, Japan plans to bury about 40,000 vessels stuffed with vitrified nuclear waste there.