Development of internal dosimetry evaluation code for chronic exposure

The Fukushima Daiichi nuclear power plant accident, that occurred on March 11, 2011, resulted in a release of radionuclides to the environment and a wide range of radioactive contamination. As a result, the public concerns the internal doses for chronic exposure due to intake in daily life. To reduce some concerns, it is important to develop the evaluation method of chronic internal dose. The Japan Atomic Energy Agency (JAEA) developed the DSYS (Dose SYStem) code that calculates internal dose to the public with dose coefficients based on the International Commission of Radiation Protection's (ICRP's) respiratory tract model (Publ.66), GI-tract model (Publ.30), biokinetic models (Publ.30, 56, 67, 69, 71, 72), bladder model (Publ.67) and dosimetric model (Publ.56). The DSYS is included in the probabilistic accident consequence assessment (a Level 3 PSA) code, the OSCAAR code system developed at the JAEA. The DSYS treats dose assessment of internal exposure due to acute intake based on the ICRP's Publications. Therefore, it cannot apply to the evaluation of whole-body retention values or committed effective/equivalent dose for chronic exposure. In the present study, the authors considered the evaluation method of chronic internal dose and developed the DSYS-Chronic to evaluate chronic internal dose by incorporating into the DSYS code. This report shows the outline of the DSYS-Chronic code and the example of evaluation results. (author)