Evaluation of Migration Radiological Equivalence for Dual Component Nuclear Waste in a Deep Geological Repository.

ABSTRACT: The paper is concerned with the issue of achieving the radiological equivalence (the equivalence of radiation risks) of radioactive waste of nuclear reactors and corresponding mass of natural uranium, taking into account the different migration ability of radionuclides in geological formations and soil. This migration radiological equivalence is being investigated for the deep burial of radioactive waste in the case of the development of a two-component nuclear power system with the concurrent use of thermal neutron reactors and fast neutron reactors. Calculations were performed of radiation doses and radiation risks of cancer death arising from consumption of drinking water from a well above a disposal site. The radiation risk relating to a two-component nuclear power system is lower than that from natural uranium; i.e., after reaching the radiological equivalence (100 y of storage) over the timescale of 109 y, the principle of migration radiological equivalence is satisfied. It would take 106 y after radioactive waste disposal to reach the migration radiological equivalence if only thermal reactors were operated. As regards consumption of well drinking water, the radiation risk does not exceed 10-5 y-1 for a two-component nuclear power system, while being 10-3 y-1 (socially unacceptable level) for a power system using only thermal reactors. Radionuclides 241Am, 239Pu, and 240Pu in drinking water make the main contribution to the doses and radiation risks of people for 104 y after the disposal of radioactive waste.

Formation of potential radiation risk groups to render timely targeted medical care: lessons of Chernobyl.

The paper discusses technology for establishing potential cancer risk groups, based on methods of molecular and radiation epidemiology. Assay of gene mutations at the T-cell receptor (TCR) locus as the method of molecular epidemiology was used for measuring the frequency of TCR-mutations in 320 nuclear workers of the Institute of Physics and Power Engineering (IPPE). The method of radiation epidemiology was applied to the estimation of attributable risk fraction (ARF) for solid cancers in these groups. The main estimates of radiation risk after the Chernobyl accident are in close agreement with the International Commission on Radiological Protection (ICRP) Publication, 103 models published in 2007. In nuclear workers of the IPPE with ARF ≥ 10%, the increased level of TCR-mutations occurs more often (risk ratio=9.7; 95% CI: 2.9; 32.1).

[The identification of potential radiation risk groups in case of chronical occupational exposure: individual cancer risks among the industrial firm "Maiak" personnel].

The draft new recommendations of the ICRP emphasize the need for transition from the collective dose to the dose matrix concept with optimization of the radiation protection system. In fact, this means assessment of the attributive (radiation-induced) risk at individual level with allowance for the dynamics of dose accumulation during the whole length of professional experience. The work provides assessments for high potential risk group from the "Mayak" personnel based on the dose matrix and using the UNSCEAR technique for assessing the attributive risk. It was found that about 2% of "Mayak" personnel subject to individual dosimetric monitoring in 2005 can be attributed to this group.

Leukaemia and thyroid cancer in emergency workers of the Chernobyl accident: estimation of radiation risks (1986-1995).

This work focuses on the direct epidemiological assessment of the risks of radiation-induced leukaemia and thyroid cancer in emergency workers (EW) after the Chernobyl accident. The Russian National Medical Dosimetric Registry (RNMDR) contains data for 168,000 EW as of January 1, 1996. The analysis relates to 48 leukaemias and 47 thyroid cancers, diagnosed and verified. Radiation risks are estimated by comparing the EW data with national data for a male population of the same age distribution. For leukaemia, an excess relative risk per Gy (ERR/Gy) of 4.30 (95% CI: 0.83, 7.75) is obtained, while the excess absolute risk per 10(4) person-years (PY) Gy (EAR/10(4)PY Gy) is found to be 1.31 (95% CI: 0.23, 2.39); for thyroid cancer an ERR/Gy of 5.31 (95% CI: 0.04, 10.58) is obtained, and an EAR/10(4)PY Gy of 1.15 (95% CI: 0.08, 2.22).

[Evaluation of calcium content in the human spine by in vivo neutron activation]. / Opredelenie soderzhaniia kaltsiia v pozvonochnike cheloveka in vivo metodom aktivatsii neitronov.

A technique of in vivo neutron activation analysis (NAA) of calcium levels in lumbar, thoracic and cervical segments of the spinal column separately and as a whole has been developed. Special device provides selective irradiation by neutrons of a vertebral segment under study while a highly-sensitive spectrometric unit registers radionuclides induced in bone tissue during radiation exposure. For radiation exposure 5 or 10 238Pu-Be neutron sources with 5.10(7) neutrons s-1 output of each source are used. The spectrometric unit consists of 4 scintillation detectors with NaI (Tl) crystals of 150 mm in diameter and 100 mm- thickness arranged in a line tightly one after another. The time of exposure depends on the number and mutual arrangement of the neutron sources and is selected given the dose equivalent at depth of positioning of the spinal cord does not exceed 1 cZv (REM), the quality factor for fast neutrons equals 10. The recording duration is 20 min, the intervals between radiation exposure and recording do not exceed 3 min. The magnitude of the total error of an individual measurement estimated by reproducibility of the data obtained in 2 series of in vivo NAA of the spinal calcium levels in 6 volunteers with the use of 5 neutron sources amounts to an average of 4.8%. When used 10 sources, this error can be reduced to 2.0-3.2%.