Water leak prevention technology to be tested on mock nuke reactor soon

24 October 2016

The International Research Institute for Nuclear Decommissioning (IRID), a government-business think tank charged with studying ways of decommissioning the crippled Fukushima Daiichi nuclear power station, is set to launch a test as soon as November to verify technology for preventing water leakage from the damaged containment vessels of nuclear reactors at the Tokyo Electric Power Co. plant. The technology is regarded as an important element in developing the “submersion method” of filling containment vessels with water and retrieving melted nuclear fuel debris. The test will use a mock-up reactor at the Japan Atomic Energy Agency’s Naraha Remote Technology Development Center in Naraha village, Fukushima Prefecture.

The method is one of the processes suggested by the government-funded Nuclear Damage Compensation and Decommissioning Facilitation Corp. (NDF) as choices under its “strategic plan” to substantiate the technological feasibility of decommissioning work. The NDF views the method as “the best process if realized” from the outset because water can shield radiation and at the same time prevent dust, including highly concentrated radioactive substances, from spreading.

But the containment vessels of the Fukushima reactors have multiple damaged portions, possibly leaking water contaminated with radioactivity when it is poured into them. These portions will be repaired before starting the planned decommissioning work under the method.

The upcoming test is designed to confirm if the technology to be used will prevent water from leaking from “vent tubes” that let out pressure inside containment vessels and from “pressure suppression chambers” below vent tubes. In the test, a special auxiliary material that swells up like a balloon will be inserted into a vent tube and any aperture will be filled by mortar and other waterproof agents. Concrete and other materials will be poured into a pressure suppression chamber, and its supporting legs will be reinforced.

All work in the test, including hole drilling and insertion of waterproof agents associated with a vent tube and a pressure suppression chamber, will be conducted by remote control in an attempt to explore safer and swifter methods. The test will also look into the quality and amount of waterproof agents and concrete necessary to ensure no water linkage in case of rapid moisture and temperature changes.

(Translated by Kyodo News)