Groundwater works intensify at Fukushima

Thursday, 15 August 2013

Efforts to pump, control, store and otherwise manage groundwater at the Fukushima Daiichi site stepped up today with the addition of a new borehole and pumping station.

Measurements taken at the end of May showed significant contamination in groundwater between the reactor buildings, with this expected to follow the known natural flow to the sea, but routine seawater monitoring at the seafront by the Nuclear Regulation Authority (NRA) has so far shown no notable increase in radioactivity.

Today a new borehole was drilled and pumping plant installed between units 1 and 2 for the extraction of groundwater. It comes one day after the approval of site work plans by the Nuclear Regulation Authority (NRA), which included the order to act on the issue 'as soon as possible'.

The cooling of the reactor cores damaged in March 2011 still requires a constant flow of water, which circulates through the power plant basements before treatment and storage. The basements were never designed to be fully watertight and it is thought that groundwater is entering and thereby increasing the volumes of water to be managed. Another aspect could be the potential escape of contaminated water from the basements to the surrounding soil.

The main contaminating substance is tritium, a form of hydrogen that poses very little threat to the environment due to its constant movement in water. It does not concentrate in the bodies of living creatures and its beta radiation is easily blocked by surrounding water.

Tritium

Tritium is produced during the operation of water cooled reactors and its usual disposal route is a monitored outflow to a large body of water. During normal operation the Fukushima Daiichi plant was licenced to dispose of 22 TBq of tritium to the sea each year, and Tepco estimated that the groundwater may have taken 40 TBq to sea since the accident 28 months ago.

Despite a lack of measured environmental impact, public and political opinion demand that the groundwater issue is tackled as a priority. It is hoped that the extraction of groundwater from specific points will reduce the local flow rate and alleviate the issues while another possible option could be the large scale freezing of the ground in a grand attempt to control the groundwater, but this is not part of currently published plans.

To date Tepco has drilled several boreholes near the reactor buildings to monitor contamination levels and constructed an underground barrier in an attempt to stop the groundwater flow, but the apparent result was the welling up of water towards the surface as a route around the barrier. Tepco was not permitted to control flow by extracting groundwater before the point of contamination and discharging to sea.

Tepco is not permitted to release any water to sea, even if cleaned to drinking water standards, leading to a major challenge in storing vast and ever-increasing volumes of water. This may be exacerbated by NRA's insistence yesterday that extracted groundwater must also be stored. Tepco has also faced intense criticism from senior regulators and politicians over the evolving issue, spurred on by the company's perceived failure in waiting until mid-June to release the groundwater measurements taken at the end of May.

Researched and written
by World Nuclear News