The National Dose Registry (NDR) is a centralized record keeping system for occupational doses of all radiation workers in a country. It contains the dose records of individuals who are monitored for occupational exposures to ionizing radiation. The International Atomic Energy Agency (IAEA) highly recommends that all Member States establishes NDR to serves as the largest national occupational radiation exposure database in a country. To promote the establishment of NDR by Member States, the IAEA has organized technical meetings to promote the establishment of NDR in non-established Member States which includes Nigeria.
The Objectives of the NDR are:
i. Contribute to health research and to the scientific knowledge on risks from occupational exposure to ionizing radiation
ii. Assessment of dose trends and statistical analysis and evaluations
iii. Provide dose histories to individual radiation workers and organization for use in radiation exposure work planning and also for use in compensation and litigation cases
iv. Useful in Epidemiological studies for short and long term effects of radiation
v. Assist Regulatory Authority in the control of occupational exposures from ionizing radiation by notifying cases of over exposures within particular practices.
The Occupational exposure monitoring is a systematic process of evaluating the potential/real risk (occupational or dose) associated with working in any activities involving radiation. Occupational dose are dose received by an individual in a controlled area while performing assigned duties that entails exposure to radiation sources. However, members of public who are not in a controlled area or involved in exposure to radiation sources are not included as part of occupational dose. Workers in both radiological and nuclear facilities such as fuel cycle facilities, diagnostic radiology, nuclear medicine, industrial radiography, well logging, gamma irradiation facilities and nuclear power plants etc are always exposed to radiation. During the course of employment, they are capable of receiving both internal and external dose of ionizing radiation in varying amounts of radiation, depending on their jobs and the sources with which they are involved with.
The Authority is been saddled with the responsibility of establishment and enforcement of requirements for the monitoring, recording and control of occupational exposures in exposure situations in all nuclear and radiological facilities and activities. In order to fully achieve the above, the Authority has established guides and regulations which require employers of radiation workers, Registrant or Licensee engage the services of an accredited Dosimetry Service Provider (DSP) by the NNRA to monitor, keep and submit occupational dose of radiation workers quarterly and annual basis with an approved template for submission. The DSPs are to make and maintain pursuant to the arrangements a copy thereof until the person to whom the records relates has or would have attained the age of 75 years or for at least 50 years from when they were made, whichever is earlier. The dose records submitted by the DSPs are evaluated by the Radiological Monitoring and Technical Services Unit of Radiological Safety Department of NNRA to establish annual effective doses of individual radiation workers, average doses of specific practices and collective doses for each year.
Five (5) DSPs have been accredited by NNRA, utilizing Thermo Luminescence Dosimeter and Instadose Dosimeter for monitoring. The Authority has put in place standards that provides procedure for testing the performance of Dosimetry systems used to monitor personnel exposure to ionizing radiation otherwise known as proficiency testing. The aim of the Proficiency is for standardization and credibility of dose records from the DSPs, a standard instituted by the International Atomic Energy Agency (IAEA), which are conducted to ascertain important criteria like reproducibility, linearity etc of dosimeters use for occupational dose monitoring. This standard applies first time entrants, existing renewals and introduction of new models of dosimeters. The proficiency testing summary conducted so far which gives permissible limits of approval or rejection of the DSPs is graphically presented below.
Figure 1: Graphical presentation of the proficiency testing summary report from DSPs
The occupational dose records submitted by authorized DSP to the Authority on quarterly/yearly basis are evaluated through a process of:
i. Doses of individual radiation workers collated and analyzed to form cumulative dose for the year;
ii. Cumulative Doses from facilities collated and averaged for each practice to form average dose for occupational groups
iii. Total numbers of radiation workers for the year was derived.
iv. Average Doses from different occupational groups was averaged and multiplied by total number of radiation workers to arrive at the annual collective dose (manSieverts).
These Dose records collated, analyzed and evaluated from year 2012 to 2017 are graphically presented below:
Figure 2: Graphical presentation of dose ranges within practices for 2017.
Figure 3: Graphical presentation Average Dose of Radiation Workers 2012-2017
Based on the importance and benefits of storing these records from radiological facilities in the country, to provide dose histories to individual radiation workers and organization as empowered in the Authority’s Regulations, manual collection, collation, analysis and evaluation of these records has shown to be cumbersome. Hence, the NNRA is moving from manual operations to a well developed online software system well supported by IAEA and African Alara Network (AFAN – htpp://African-alara.net) which Nigeria is a member . This online system enables:
i. All activities regarding dose submission, collation, analysis, storage etc from the accredited DSPs to the Authority to be carried out digitally (online).
ii. Eliminates manual errors of inputting and retrieving of data
iii. Reduces down time of exchange of data between the facility, DSPs and the NNRA
iv. Prompt evaluation of life time dose of each radiation worker of specific practice
The NDR in Nigeria with assistance of IAEA and AFAN is expected to be deployed online before the end of 2019.