Issue Number:CWM-102
Phase: Preparation
Decommissioning Process Contaminated Water Management
Investigation Subject Understanding current status
Issue Understanding current status of underground and buildings

Needs

① Understanding the behavior and overall picture of groundwater

Desired state and reasons for it

At present, contaminated water is increasing due to groundwater flowing from the mountain side to the sea side into the reactor building, etc. and mixing with water containing radioactive materials retained in the building, etc. A multilayered contaminated water management is being implemented to control groundwater stably in accordance with the three basic policies of “removing” the contamination sources, “keeping away” the water from the contamination sources, and “not leaking” the contaminated water.
It is desirable to understand the behaviors and the overall picture of the groundwater, because, by understanding them, it is possible to promote the multilayered contaminated water management more effectively, based on the three basic policies.

Current state against ideal

Although the relationship between the rainfall, etc. (IN-side) and an increase in the amount of contaminated water (OUT-side) is grasped, the details of the process (including the amount of groundwater, the amount of inflow into the building, the amount not inflowing into the building, the amount of bypassing groundwater, the amount of subdrain, and the path of groundwater, etc.) are not known.

Issues to be resolved

In order to deal with groundwater and contaminated water in a rational and systematic manner, it is necessary to understand their behaviors as a whole.
In order to evaluate the migration of radionuclides contained in the soil around the building, it is necessary to understand the groundwater behavior around the building.
Furthermore, in order to maintain the effectiveness of contaminated water countermeasures over the medium to long term, it is necessary to ensure the periodic inspection and renewal of each facility, including the land-side impermeable wall and sub-drain facilities.
② Understanding locations of inflow into the building

Desired state and reasons for it

At present, contaminated water is increasing due to groundwater flowing from the mountain side to the sea side into the reactor building and mixing with water containing radioactive materials retained in the building, etc. It is desirable to be able to understand the location of the inflow into the building.

Current state against ideal

Although it has been confirmed that contaminated water has been flowing into the building from the torus room, it is not easy to investigate where because of the high radiation dose around the reactor building. In particular, the specific location and amount of inflow have not been known. Even if a robot is inserted into the torus room for investigation, the location of inflow has not yet been identified.
In addition to rainwater inflow countermeasures by facing around Units 1-4, it is being investigated on water stoppage measures(filling, ground improvement, etc.) for building penetrations (piping, etc.) and gap ends between buildings as local water stoppage measure for Unit 3.

Issues to be resolved

In order to prevent the inflow of groundwater into the building, it is necessary to identify location of the inflow points and the inflow volume and clarify the form of the inflow points and the state of the area surrounding them. (It is necessary to understand the preconditions for investigating a method of full water stoppage.)
A long period of time is required to complete fuel debris retrieval. In addition to selecting a method to further expand the scale of fuel debris retrieval, which is currently underway, it is necessary to take a fresh overview at the current contaminated water countermeasures and investigate more stable contaminated water countermeasures and more appropriate maintenance and management of each facility, with a view to the mid- to long-term future.
③ Implementing sea-water monitoring

Desired state and reasons for it

Seawater monitoring is important because the presence or absence of leakage of contaminated water can ultimately be confirmed detecting the leakage to the ocean.
In addition, investigation are underway to discharge ALPS treated water into the ocean. To analyze the impact of the discharge of ALPS treated water into the ocean, it is important to understand the concentration of nuclides in seawater before, during, and after discharge.

Current state against ideal

In December 2021, "Application for Approval of Changes to the Implementation Plan for Specific Nuclear Facilities for Installation of ALPS Treated Water Dilution and Discharge System and Related Facilities" was submitted to the Nuclear Regulatory Commission and review for the offshore discharge system and its operation method, safety during offshore discharge, etc was made and then, approval was granted in July 2022.
At the government's Monitoring Coordination Meeting held on March 30, 2022, a plan was presented to strengthen and expand monitoring of the marine environment to be conducted by the government (Ministry of the Environment, Nuclear Regulation Commission, etc.), TEPCO, and Fukushima Prefecture and the monitoring began in April 2022. TEPCO is proactively conducting monitoring in cooperation with the national government and local governments.

Issues to be resolved

It is necessary to implement seawater monitoring in and out of ports quickly, easily and systematically.
In particular, since a certain period of time is required to measure tritium concentrations before discharge, it is desirable to have a technology for shortening the measurement period.

Relevant Issues

References

Please note that this English text is a provisional translation of the Japanese original.