The prevention of criticality accidents is of paramount importance to NFI. We establish a variety of controls and restrictions for each process involving the handling of nuclear fuel material (uranium) to assure a criticality never occurs. We also periodically inspect the safety features of equipment. Additionally, we periodically train employe to keep everyone current and mindful of criticality safety control.
Examples of restrictions that prevent criticality accidents
- Mass control
The design is such that criticality is precluded even if the nominal maximum handling volume is doubled (e.g., this is applied for the power mixing process)
- Geometric control (diameter control and thickness control)
Nuclear fuel materials (uranium) will be prevented from accumulating and being configured in a critical mass or critical shape (e.g., this is applied at the molding process and the sintering process)
- Control of the number of rods and assemblies
At the inspection process for fuel rods and at the assembly process for the fuel assemblies, the numbers of rods and fuel assemblies and the distances between these rods and assemblies are controlled. This assures the numbers and distances between the rods, which contain nuclear fuel material (uranium), and the fuel assemblies, which have an array of the rods, are always limited such that criticality is precluded.
For the safety and health of operators who handle radioactive materials, we observe the radiation control laws and company regulations as well as conduct training regarding radiation safety.
When handling radioactive materials, operators wear the designated work clothes and protective equipment to reduce exposure, and also wear a glass dosimeter to monitor exposure dose.
When an operator exits the radiation-controlled area, the radiation dose is always measured with instruments to confirm the safety of the worker.
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We installed monitoring posts in the Works, from which we continuously measure the dose equivalent rate of gamma rays at the boundary of the supervised area around the Works.
In the very unlikely event that the measured dose equivalent rate (measured as µGy/h or µSv/h) exceeds the established value, an alert is issued.
The nominally expected value during normal operations is about 0.03 to 0.12 (µGy/h or µSv/h).
| Note: | When it rains, radioactive materials (such as radon) in the natural world aggregate on the ground surface and a higher high value can temporarily registered. |
We continuously monitor the radioactive concentration (Bq/cc air) in exhaust air released from Works to the environment. In the unlikely event that the measured radioactive concentration exceeds the setting value, an alert is issued.
We always monitor the radioactive concentration and amount of liquid effluent from the Works, and after confirming that the drainage is normal, we discharge it. The amount of radioactivity is calculated by multiplying the measured radioactive concentration (Bq/cc) in the liquid effluent by the volume of this liquid.
We reduce the volume of radioactive solid waste and store it in the appropriate designated place according to the safety policy and the environmental policy of each works so that the waste does not affect living environment.
To continuously improve the employee’s working environment, we conduct risk assessment, Learn-from-Close-Calls activity, and risk prediction training.
Our risk assessment program includes risk evaluation of the working environment, and continuous improvement Learn-from-Close-Calls activities, and safety and health activities that record and analyze close calls and near misses, to preclude their recurrence.
- Japan Nuclear Technology Institute
To further promote nuclear safety, the NS Network was established in December 1999. The objective of the NS Network is to improve the safety culture by sharing experience among nuclear operators. In April 2005, the NS Network transferred its operations to the NS Network Division of the Japan Nuclear Technology Institute. This division promotes safety culture through seminars and other meetings and conducts peer reviews in which members mutually evaluate the efforts of their fellow companies with regard to nuclear safety. The Tokai Works and Kumatori Works underwent peer reviews by the NS Network in May 2000 and January 2004, respectively. The safety culture at both sites was confirmed.
- International Network for Safety Assurance of Fuel Cycle Industries (INSAF)
INSAF was established in April 2000 to promote a safety culture, to foster successful safety programs, and to share and exchange safety information among the world's nuclear fuel cycle industries. It recognizes that safety must be the most important theme at these industries throughout the world , including fuel fabrication companies and research institutions for fuel fabrication.
