News Navigator: How are radioactive materials in discharged Fukushima water measured?

The Mainichi Shimbun answers some common questions readers may have about radioactive materials in treated water from the disaster-stricken Fukushima Daiichi nuclear plant.

Question: Does the treated water from Tokyo Electric Power Company Holdings Inc. (TEPCO)’s Fukushima Daiichi Nuclear Power Station contain radioactive materials?

Answer: ALPS, or multi-nuclide removal equipment, can remove radioactive materials from the treated water to nearly below regulated standard values, but tritium, which is difficult to separate from water, remains.

TEPCO diluted the treated water with seawater to reduce the tritium concentration to less than one-fortieth of the national standard and began discharging it into the sea in August. Since then, the company has been measuring eight types of radioactive materials, including tritium, to check for any abnormalities in water quality.

Q: How are they measured?

A: TEPCO samples seawater and fish from the area around the nuclear plant for measurement. Seawater is distilled to remove impurities, then subjected to a special measuring device. Fish are measured for the concentration of radioactive substances in their muscles, or analyzed via water extracted after freeze-drying.

Q: What kind of analysis are they doing?

A: Radioactive materials emit various kinds of radiation, and different analysis methods are applied to each type of radiation. Since beta rays emitted by tritium are weak, a special technique is used in which a chemical is added that glows in response to the rays before the amount of light emitted is measured. On the other hand, for substances such as cesium that emit gamma rays or other strong radiation, water that has been filtered of impurities can be directly measured by applying it to a detector.

Q: How long will it take to see the results?

A: For tritium, analysis using seawater takes from one week to around one month. More detailed results can be obtained by increasing the time spent in the measuring device or by adding a procedure called electrolytic enrichment, which increases the concentration of the substance in water. It is also possible to conduct an analysis that provides results in about one day to detect abnormalities in water quality as quickly as possible. For fish analysis, it takes about a month and a half because of the time required for pretreatment.

(Japanese original by Yui Takahashi, Lifestyle, Science & Environment News Department)