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Monju reactor fuel removal faces delays as monitoring cameras fog up in tests

A special lane used to remove nuclear fuel during decommissioning work is seen in Tsuruga, Fukui Prefecture. (Mainichi)

Fogged monitoring camera lenses could set back plans to remove fuel from the Japan Atomic Energy Agency (JAEA)'s Monju fast-breeder reactor, part of decommissioning work slated to start as soon as August.

The removal of fuel from the prototype reactor in Fukui Prefecture must be carried out remotely, because there are some areas that human workers cannot enter. Fuel rods will be removed from the reactor vessel and from a spent fuel pool, both filled with sodium -- a material that is difficult to handle because it reacts with water and air -- using special equipment.

Before extracting the fuel, staff tested their removal technique up until July 26 by attempting to take control rods out of the spent fuel pool. However, two cameras near a special receptacle for the rods and at an enclosed intermediate monitoring area fogged up, preventing workers from properly checking the work, the agency said.

The temperature of the sodium in the pool is about 200 degrees Celsius, and the control rods were hot when they were removed and shifted to the intermediate area. The rods had to be cooled at the intermediate monitoring area, and a large amount of steam was produced when water was put in.

The Nuclear Regulation Authority has emphasized that the cameras remain the only way for the agency to check on the state of removed fuel. It pointed out that checks were insufficient and instructed the agency to clarify the problems.

To solve the problem, the humidity level in the enclosed intermediate area has to be decreased, like removing steamy air from a bathroom. The agency is considering blowing air into the space to prevent steam from building up, but this remains a difficult task, and there may be delays before the agency can move onto the next step in the decommissioning process.

Problems with equipment also surfaced during an earlier preparation stage, prompting the agency to push back the start of full-scale decommissioning operations from the end of July until August.

(Japanese original by Toshiyuki Sato, Science & Environment News Department)

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