April 2017
At the Fukushima Daiichi Nuclear Power Station we are enlisting
the cooperation
of a great many people in order to move forward
with countermeasures for contaminated water that was generated
in conjunction with the accident and contained high concentrations of radioactive substances.
Through this portal site we shall explain the current situation and give you data/information on treated water while also showing how we have removed the radioactive substances from contaminated water and reduced risks.
At the Fukushima Daiichi Nuclear Power Station, the radioactive substances in contaminated water are removed using a multi-nuclide removal equipment (ALPS) and the resulting treated water is stored in tanks on site along with Cesium/Strontium-treated water. There are 962 tanks on site. 768 storage tanks are being used for water treated with ALPS, 170 storage tanks are being used for Cesium/Strontium-treated water, and 24 tanks are being used for other purposes (as of February 21, 2019).
※In accordance with construction plans, the total tank capacity will be approximately 1.37 million m³ built by the end of 2020.
ALPS etc. treated water
Cesium/Strontium-treated water
At current time, water treated with multi-nuclide removal equipment (ALPS) is being stored in tanks after removing most radionuclides, with the exception of tritium.
ALPS has the ability to remove radionuclides (with the exception of tritium) to levels below “concentrations required by law,” which is the Japanese government’s regulatory standard used when discharging contaminated water/treated water into the environment.
However, as a result of malfunctionsthat occurred when the equipment was put into operation and differing operating objectives that have changed with time, the amount of water being stored at current time is as shown in the diagram on the right that breaks down the amounts by the sums of the ratios of the concentrations required by law.
Cesium/Strontium-treated water
The Japanese government’s standard for storing treated water at the Fukushima Daiichi Nuclear Power Station stipulates that “the effective dose at site borders must be under 1mSv/year.” Since FY2013 we have been purifying contaminated water with multi-nuclide removal equipment (ALPS) and as of the end of FY2015 had achieved our goal of reducing the effective do.se rate at site borders to below 1mSv/year. After achieving this goal, ALPS continued to be operated with the intention of reducing risks at the power station.
The site border dose rate during 2013, when highly radioactive contaminated water from which only cesium had been removed was being stored in tanks on site, was 9.76mSv/year, thereby greatly exceeding the “effective dose at site borders of 1mSv/year or less,” which was the standard stipulated by the government.
The multi-nuclide removal equipment (ALPS) was put into operation in 2013 and equipment operation rate was increased to purify contaminated water and quickly reach the objective of reducing effective dose rates at site borders to below 1 mSv/year.
As a result of purifying contaminated water with the ALPS, the effective dose rates at site borders was reduced to below 1 mSv/year by the end of FY2015. However, due to nonconformances with the ALPS equipment, concentrations of radionuclides that required by were exceeded.
※１ Percentage of times that of the concentrations required by law was exceeded based on the number of samples and broken down for each radionuclide.
※２ Total amount treated by existing ALPS, additionally installed ALPS, high-performance ALPS
The multi-nuclide removal equipment (ALPS) enabled much progress to be made with contaminated water treatment thereby causing the amount of treated water to exceed the storage capacity of constructed tanks and we started to run out of tanks to store treated water.
In addition to accelerating the construction of tanks to store the treated water, the purification capacity of ALPS was leveraged and equipment operated while keeping in mind the concentrations required by law for each type of radionuclide.
As a result of leveraging ALPS purification capacity, in comparison to FY2013~FY2015, the percentage of cases where the concentrations of radionuclides required by law were exceeded decreased.
※１ Percentage of times that of the concentrations required by law was exceeded based on the number of samples and broken down for each radionuclide.
※２ Total amount treated by existing ALPS, additionally installed ALPS, high-performance ALPS
Water being stored in bolt-tightened flanged tanks, which pose a high risk of leaking, will be treated as quickly as possible.
All water stored in flanged tanks shall be treated with the multi-nuclide removal equipment (ALPS) by the end of FY2018 while maintaining effective dose rates at site borders at below 1 mSv/year and increasing the operation rate of ALPS in an effort to reduce risk.
The operation rate of ALPS was increased while keep in mind the objective of reducing risks associated with water stored in flanged tanks. As a result, while the treatment of all the Cesium/Strontium-treated water (water that had yet to be treated with ALPS) stored in flanged tanks was completed in November 2018, the percentage of cases where the concentrations of radionuclides required by public noticewere exceeded increased compared to FY2016.
※１ Percentage of times that of the concentrations required by law was exceeded based on the number of samples and broken down for each radionuclide.
※２ Total amount treated by existing ALPS, additionally installed ALPS, high-performance ALPS
Inside the reactors of Fukushima Daiichi Nuclear Power Station Units 1~3, there is fuel that melted and solidified during the accident (fuel debris). This fuel debris is being kept cool by continuously spraying it with water, but when this water comes in contact with the fuel debris it is exposed to the highly concentrated radioactive substances and becomes “contaminated water.” This “contaminated water” that contains highly concentrated radioactive substances accumulates inside the reactor buildings and when it mixes with groundwater or rainwater flowing into the buildings even more “contaminated water” is produced.
This “contaminated water” is being treated/purified to reduce the concentrations of radioactive substances using multiple types of equipment. After risk has been sufficiently reduced in this manner , it is stored in tanks on site as “treatead water”.
The ALPS is one of the pieces of equipment used to purify contaminated water at the Fukushima Daiichi Nuclear Power Station. Radioactive substances are removed by passing the contaminated water through adsorption towers that are filled with adsorbents thereby enabling this equipment to remove the most of radionuclides with the exception of tritium.
The government has stipulated two different regulatory standards for contaminated water. The first are regulations for contaminated water if it is to be stored in tanks. And, the second are regulations for contaminated water if it is to be discharged into the environment. Preventing impact on the surrounding environment has been our first priority, so contaminated water has been purified/treated using the ALPS etc. while adhering to the regulations for storing contaminated water in tanks. Therefore, at current time, all of the water that has been processed with the ALPS meets the regulations for tank storage, however more than 80% of it does not yet meet the regulations for environmental discharge.
If TEPCO decides to dispose of the water treated with the ALPS by discharging it into the environment the water will first be purified again (secondary treatment) in order to reduce the amount of radioactive substances in the water as much as possible (with the exception of tritium) and ensure that it meets the regulations for environmental discharge.
Tritium is hydrogen with two extra neutrons (hydrogen-3) and it has the same characteristics as hydrogen.
Tritium is a radionuclide that emits beta radiation but the amount of energy emitted is weak and can be blocked with a sheet of paper.
Tritium is generated when cosmic radiation from space mixes with the Earth’s atmosphere. In the atmosphere the tritium bonds with oxygen instead of hydrogen which is why it exists in the form of water in the water vapor and rain in the atmosphere, as well as in the oceans, etc.
We ingest tritium through the water we drink in our daily lives but our metabolism prevents it from accumulating/concentrating in our bodies and it is immediately excreted.
Tritium is generated through the process of nuclear fission in nuclear power facilities both in Japan and overseas (nuclear power stations and reprocessing facilities), and each country has regulations for discharging tritium into the oceans and atmosphere in a controlled manner.
One of the systems used to purify contaminated water that has been generated at the Fukushima Daiichi Nuclear Power Station. With the exception of tritium, this equipment can remove most of the radionuclides present in contaminated water.
Click here for details
Contaminated water from the Fukushima Daiichi Nuclear Power Station that has been purified and is being stored in tanks at the power station site. There are two types of treated water. “Cesium/Strontium-treated water” is water from which cesium (Cs) and strontium (Sr) have been removed, and “ Multi-nuclide removal equipment (ALPS) etc. treated water” is Cesium/Strontium-treated water from which most radionuclides, except for tritium, have been removed.
Click here for details
Water from which most radionuclides, with the exception of tritium, have been removed using the multi-nuclide removal equipment (ALPS), which is equipment used for purifying contaminated water generated at the Fukushima Daiichi Nuclear Power Station.
Click here for more details on the ALPS
The Japanese government has two regulatory standards for contaminated water:
1.Standards for water that is to be stored in tanks
(effective dose rate at site borders)
2.Standards for discharging water into the environment
(concentrations required by law)
Japanese laws and regulations stipulate the radioactive concentration limits for each radionuclide (concentrations required by law) if radioactive substances are to be discharged into the environment. Since the concentrations required by law differ for each radionuclide, when discharging multiple radioactive substances the ratios of the concentrations required by law are calculated for each radionuclide and the total is referred to as the "sum of the rations of the concentrations required by law”
※Public notice of Requirements for the Safety of the TEPCO Fukushima Daiichi Nuclear Power Station and the Protection of Specific Nuclear Fuel Material
How to handle ALPS etc. treated water stored in tanks as we move forward into the future is being discussed by a government subcommittee. Based on these discussions, TEPCO will listen to the opinions of all stakeholders, including the local community, and decide on an appropriate course of action while employing a careful decision-making process. If ALPS etc. treated water is to be discharged into the environment, government regulations require that the sum of the ratios of the concentrations required by law be less than 1. If TEPCO decides to dispose of ALPS etc. treated water by discharging it into the environment, before it is discharged the water will be once again subjected to purification (secondary treatment) in order to reduce the amounts of radioactive substances (with the exception of tritium) as much as possible and fulfill the regulatory requirements mentioned above.
Concept drawing of the secondary treatment of ALPS etc. treated water
National laws and regulations※ that stipulate the radioactive concentration limits for each radionuclide if radioactive substances from the Fukushima Daiichi Nuclear Power Station are to be discharged into the environment.
※Public Notification of Requirements for the Safety of the TEPCO Fukushima Daiichi Nuclear Power Station and the Protection of Specific Nuclear Fuel Material
The Nuclear Regulation Authority requires that additional doses (additional doses newly given off by the power station facility that exclude naturally occurring radiation) posed on site borders from rubble and contaminated water stored at the power station site must be under 1mSv/year. This “effective dose at site borders” is used as a safety management standard when storing contaminated water in tanks on site.
Multi-nuclide removal equipment (ALPS) etc. treated water is stored in tanks on site. In order to reduce the risks associated with leaks, bolt-tightened flanged tanks are being gradually replaced with welded tanks. Furthermore, double layers of dikes has been erected around the tank areas to prevent water from leaking outside of the area in the event that a tank does leak. The tank areas are also patrolled and water levels continually monitored in order to prepare for risks associated with leaks.
Upon realizing the necessity to not only examine scientific safety, but also deliberate methods for disposing of multi-nuclide removal equipment (ALPS) etc. treated water that take into consideration social impact, the government established the Subcommittee on the Handling of ALPS etc. treated water. The subcommittee comprises experts from various fields that comprehensively discuss not only technical issues, but also social impact, such as damage to reputation.
