Personnel dosimetry
CNE Cernavoda is responsible for ensuring radiological monitoring of the work environment of professionally exposed workers and visitors during the performance of its authorized activities.
The correct measurement and recording of the doses collected by the professionally exposed personnel of CNE Cernavoda and the contractors is a very important element of the Dosimetry Program.
The dosimetry program of CNE Cernavoda is based on the requirements of the applicable national legislation and on the most recent recommendations of the International Commission for Radiological Protection.
The dosimetry program, including the methods used and their technical justification, is developed by the Radioprotection Department.
The doses collected by the professionally exposed personnel at the Cernavoda NPP are due to the external and internal exposures characteristic of a CANDU type reactor.
External exposure is exposure to radioactive sources outside the human body.
The main source for external irradiation in a CANDU type plant is gamma radiation .
The measurement of the individual external gamma dose is done with the help of a dosimeter with thermoluminescent detectors (TLD). Wearing the dosimeter is mandatory for the entire duration of the activity carried out in the radiologically controlled area.
Thermoluminescent type dosimeters are also used to measure the dose on the extremities, the thermoluminescent pills being fixed in the areas where the irradiation is the greatest (fingers, wrists, ankles).
In a CANDU plant, neutron doses have a small contribution to external irradiation and are monitored in turn with the help of a neutron flow meter.
Internal exposure (contamination) is the process of radioactive materials entering the body through inhalation, ingestion or through the skin.
The main source for internal exposure in a CANDU-type plant is tritiated heavy water vapor .
The internal dose due to this source is determined by analyzing urine samples based on the detection technique with liquid scintillators. The frequency of measuring the samples depends on the concentration of tritium in the urine at the last measured sample. As the concentration of tritium in the urine increases, the interval between two biological sample supplies decreases, varying from monthly to daily.
Internal doses due to other sources of internal contamination are determined by direct measurement of workers at the Human Body Counter, with a frequency that depends on the nature of the activity carried out. Measurements with the human body meter are done monthly, quarterly, annually or once every three years.
Registration of doses
For the registration of doses, a registration system is established in electronic format (database type) and on paper. In addition to the record of received doses, the system also keeps records of the analytical results of all samples.
Maintaining the organization’s commitment to reducing staff exposure has led to top results regarding collected collective doses, which placed both units in the first 25% of plants evaluated by WANO.
I will believe
Internal and external dosimetry services are provided by the Center’s Individual Dosimetry Laboratory. It is accredited by CNCAN according to certificate OD 02_LDI/2020 valid until 31.12.2024. The laboratory’s accreditation is renewed once every five years.
Internal and external dosimetry services are supervised by CNCAN accredited experts.
In addition, the Individual Dosimetry Laboratory has CNCAN accreditation, according to certificate LI 01_LDI/2020 valid until 31.12.2024, for the analysis of samples of liquid and gaseous radioactive effluents.
To be compared
In order to validate the working methods according to ISO 17025 and the Norms of individual dosimetry and Radon (approved by CNCAN order No. 180/2020) and to demonstrate the credibility of dose measurements for personnel and the population, the Individual Dosimetry Laboratory participates annually in international intercomparison exercises .
For internal dosimetry measurements, the Individual Dosimetry Laboratory is a member of the French Association PROCORAD (Promotion of Quality Control in Radiotoxicological Analysis) and participates in intercomparison exercises on internal dosimetry measurements since 2001.
For external dosimetry measurements, the Individual Dosimetry Laboratory participated in an exercise organized by the IAEA in 1999, and since 2007 it has participated in intercomparison exercises (Performance tests for dosimetry systems with TLD used in CANDU power plants) organized by COG.
For radioactivity measurements in effluent samples, the Individual Dosimetry Laboratory participated between 2008 and 2013 in intercomparison exercises organized by the National Physics Laboratory (NPL) in England on gamma spectrometric measurements in high and low activity aqueous samples.
The results obtained in the intercomparison exercises between 1999 and 2021 were good and very good. It should be noted the results obtained in the category of “Tritium measurements in urine” where the dosimetry laboratory qualified as a reference laboratory in the years 2004, 2006, 2007 in the category of “C-14 measurements in urine” where it qualified in the “Top 4 ” the best performing laboratories of the PROCORAD Association in 2001, 2004, 2006, 2007, 2008, 2009 and 2010, as well as in the “H3-C14 dual-label measurements” category in 2012, 2013 and 2018.
Following the visit made by the WANO team in October 2013, the Radioprotection Department received a “strength” for the external and internal dosimetry services performed, the Dosimetry Laboratory being appreciated as a “Top” laboratory in the field of dose measurement. This assessment was supported by the results of the plant’s dosimetry program as well as the excellent results obtained at the international intercomparison exercises (COG, IAEA, PROCORAD).