Difficult clean-up operations at Fukushima Daiichi Nuclear Power Station Nuke Info Tokyo No. 144
The struggle with highly radioactive water continues
Tokyo Electric Power Co. (TEPCO) announced on August 29 that the amount of highly radioactive water processed by the decontamination system at Fukushima Daiichi Nuclear Power Station (FDNPS) in the one week from August 24 through 30 totaled 10,970 m3, the highest volume since the system became operational. TEPCO also said the system’s operation rate was 89 percent.
At the same time, the plant operator said a total of 32 problems had occurred in the decontamination system during the period June 1-August 13, including water leaks, sudden rises in radiation levels and breakdowns of the system. Various other types of problems that had been unexpected at the start of operations also occurred, including operational errors, troubles caused by inappropriately established work procedures and improper installment of equipment by inexperienced workers.
On August 29, TEPCO announced that two of its workers had been irradiated with more than 15 millisieverts (mSv) of beta radiation while replacing filters on a system for decontaminating radioactive water. They are in their 20’s and allegedly absorbed doses of 23.4 and 17.1mSv respectively.
On the morning of August 31, two TEPCO subcontractor workers were sprayed with highly radioactive water. They were handling parts of the decontaminating system produced by Kurion, a U.S.-based nuclear waste management company. One of the workers wearing non-waterproof protective gear called Tyvek suffered a radiation exposure of 0.16mSv, and the other, wearing a waterproof parka, suffered a 0.14mSv exposure. They were using a hose in an attempt to drain radioactive water from a vessel designed to absorb cesium. They removed the hose from the vessel, believing that the valve of the vessel was closed, but the valve was still open, and they were thus sprayed with contaminated water.
Later in the day, it was reported that highly radioactive water was leaking near the device for separating mud and slime from processed water in the decontamination facility installed by the French company, Areva, and the clothes of a TEPCO subcontractor worker became wet. The worker was not wearing waterproof gear for protection against radiation exposure at the time.
The Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry has concluded that TEPCO’s measures to protect its workers from radiation exposure were insufficient and has ordered the firm to improve its measures. TEPCO said the workers had been engaged in work to depressurize the container, which they had used in the facility, before putting it in storage. At the time, contaminated water leaking from the pipe fell on their arms. According to TEPCO, the water did not penetrate through their clothes and their arms did not become wet. As a result, the workers simply suffered an external exposure of 0.89mSv. In Areva’s decontamination facility, where mud and slime are separated in two stages, the water leak occurred in the second stage. The radiation level of the processed water was relatively low at that stage because most of the mud and slime had already been separated and removed.
High radiation levels above 10Sv detected at piping connected to an exhaust tower
TEPCO announced on August 1 that extremely high radiation levels of at least 10Sv/hr, or 10,000mSv/hr, the detection limit of the measuring equipment, were detected near the surface of piping connected to an exhaust tower located to the west of the Units 1 and 2 buildings.
On August 2, TEPCO also announced that it had found another high-radiation spot nearby, where a radiation level exceeding 10Sv/hr was detected. Moreover, the utility said a radiation level above 5Sv/hr was recorded inside the Unit 1 building, which was connected by the same piping to the two spots where the radiation levels over 10Sv/hr were registered. The radiation levels exceeding 5Sv/hr were the highest ever recorded inside a building on the plant grounds.
The three workers who measured the radiation levels were exposed to up to 4mSv of radiation, TEPCO said.
A possible cause of the high radiation spot cited by TEPCO was that gas containing highly radioactive materials still remained inside the piping following venting conducted on March 12. The vent was carried out to reduce the pressure within the containment vessel of Unit 1 in order to protect the vessel from destruction. Another possible cause was that highly radioactive particles might have stuck to the outside of the piping during the venting process, the utility said.
TEPCO has limited access to the highly contaminated areas and has said the findings would not affect restoration work at the plant. However, if the workers carry out work in areas very close to the highly contaminated spots, their total radiation exposure would reach the lethal level of 7Sv within 40 minutes.
An increasing number of areas with extremely high levels of radiation will probably be found in the future, especially in or near Unit 3. The reactor was using the mixed oxide (MOX) fuel that contains a large amount of plutonium, and its air dose rate is higher than that of Unit 1. A full-scale search for such high-radiation spots around Unit 3 has yet to be conducted and there still remains great concern over heavy radiation exposure for the plant workers. (Table 1)
|Table 1: Total value of external and internal exposure levels of emergencyworkers at Fukushima Daiichi NPP.|
|(Based on TEPCO report of Aug. 31)|
A desirable system of long-term health management for plant workers
Of the workers who began working at FDNPS in or after April, three have already received more than 50mSv radiation doses from external and internal exposure. This indicates that there is a need to promptly repeal the 250mSv radiation exposure limit for the plant workers engaged in emergency operations.
In June, the Ministry of Health, Labor and Welfare summoned a committee on long-term health management for workers at TEPCO’s FDNPS. Since then, the ministry has been working on the issue, following the “Temporary approach policy for measures for people affected by the nuclear accident” announced by its Nuclear Disaster Countermeasures Headquarters on May 17. This policy calls for the creation of a database that enables long-term tracking of radiation doses absorbed by all plant workers engaged in emergency operations even after they change jobs, and provision of long-term health management for the workers. On August 3, the ministry made public its “grand design for long-term health management for workers at TEPCO’s Fukushima Daiichi Nuclear Power Station,” which was formulated on the results of discussions at the committee meetings in June and July.
In the third meeting of the committee, on August 9, the ministry presented a draft plan for long-term health management to be provided for plant workers in proportion to the amount of radiation doses absorbed. The plan calls on the employers of workers engaged in emergency operations to provide workers with ordinary health management. For workers exposed to radiation totaling 50mSv or more, the plan calls for a regular eye checkup once a year, and for workers exposed to a total of 100mSv or more, examinations of the thyroid, stomach, large intestine and lung for cancer once a year, in addition to the eye checkup.
The grand design says that workers exceeding a certain level of radiation exposure will be eligible for these medical checkups. This probably means that only those who have absorbed more than 100mSv or 50mSv radiation are allowed to take the periodic checkups. Among workers engaged in emergency operations, there are some who have no data on their cumulative radiation exposure doses, or who have no accurate data on exposures. Moreover, the majority of the plant workers will not be eligible for regular heath checkups provided by the state after they leave their current job. We must not allow the government to draw the line between workers with cumulative radiation exposure doses of more than 100mSv or 50mSv and workers who have absorbed lower levels of radiation. Since workers are carrying out emergency operations in an extremely dangerous environment created by the disastrous accident, it is necessary for the government to have a strong sense of responsibility in providing all workers with life-long health management and compensation for damage to their health. It is also necessary to launch a system in which all the plant workers obtain a health-record book that will entitle them to receive periodical medical checkups, including those for cancer, even after they leave their current jobs.
Mikiko Watanabe (CNIC)