Achievability of radiological equivalence associated with closed nuclear fuel cycle with fast reactors: impact of uncertainty factors in scenarios of Russian nuclear power development through to 2100. Part 1. Fast and thermal reactors

The Russian Government approved the Energy Strategy of the Russian Federation (Government Decree No.1523-r of June 9, 2020). The Strategy envisages the use of both thermal (TR) and fast (FR) reactors. The Strategy points out that the problems of nuclear power are associated with po-tential high expenses for irradiated fuel and radioactive wastes management. The previously de-signed model of the Russian nuclear energy development suggested that fast reactors only would operate at NPPs after 2010. Radiological equivalence, expressed as the equivalence of lifetime radiation risks to the public from radioactive wastes and from primary uranium ore, was shown to be achieved after 100-year storage. The burnup of 241Am, 237Np и 242Сm in closed nu-clear fuel cycle with fast reactors is a key part in the achievability of radiation risks equivalence. Scenarios of the Russian nuclear energy development through to 2100 with account of uncertain-ty factors in the measurement of contribution of fast and thermal reactors to the electric energy production are considered in the paper. The following three scenarios were developed: uncer-tainty is replaced by FRs; uncertainty is replaced by TRs; 50 per cent of FRs and 50 per cent of TRs replace uncertainty. If the energy is produced by fast reactors only (scenario 1) radiological equivalence was found to be achieved in 412 years. In two other scenarios radiological equiva-lence will be achieved after more than 1000 years. Contribution of main dose-forming radionu-clides and relevant ratios of potential biological hazards is included in models regardless of whether uncertainty in nuclear energy development is taking or not taking into account. Results of the study of conditions for radiological equivalence achievement should be used for amending Strategic plan of Russian nuclear power development through to 2100 that meets requirements of radiation ecology and radiation protection of the public.

Model for calculating energy absorption in environmental objects from incorporated sources of monoenergetic electrons

Model is suggested to calculating energy absorption in organisms of various geometry from in-corporated sources of monoenergetic electrons. The effectiveness of the approach was demon-strated for spheres, ellipsoids, and cylinders by comparison of analytical values with large inter-national testing data. Model equations are free of any fitting parameters; computer approximating procedures are not employed. The method allows to make correct express-calculations of inter-nal absorbed doses in various biological objects from beta emitting radionuclides; the calcula-tions are performed without Monte Carlo codes. The model may be used in the internal radiation dosimetry for non-human biota, and in environmental radiation protection.

Radioecological assessment of forage agricultural land in the southwestern areas of the Bryansk region based on a set of statistical models

This paper presents a radioecological assessment of forage agricultural land in the southwestern districts of the Bryansk region based on data characterizing the variability of the radionuclides content in the soil. Concentration of 137Cs in forage was calculated taking into account the proba-bility distributions of 137Cs soil contamination density and the soil to plant transfer factor. The pro-cessing data of the radioecological survey has shown the soil contamination density with 137Cs of agricultural lands in the southwestern areas of the Bryansk region obeys a lognormal law. The authors have used statistical models and software modules for the radioecological assessment of forage lands. Risks of exceeding the 137Cs content standards in forage obtained on soils with different texture have been calculated. The limiting levels of contamination of pastures and hay-fields with 137Cs, ensuring compliance with the specified risks for forage, have been estimated. The lowest limiting soil contamination density is characteristic of organic soils, which can be con-sidered “critical” from the point of view of 137Cs intake into forage. The authors have predicted the time of remediation of forage lands in the southwestern districts of the Bryansk region in the ab-sence of protective measures based on a probabilistic approach. The time period during which the risk of forage contamination for sandy, sandy loam and clay loam soils will decrease to 10% varies for the areas under consideration in a wide range, not exceeding 64 years. It is concluded that it is advisable to substantiate the value of the acceptable risk of forage contamination, taking into account radiological and socio-economic aspects.

Late complication of the oral cavity and oropharynx after interstitial neutron therapy with sources of Cf-252

Radiotherapy is used to treat approximately 80% of patients with cancer of the head and neck. Despite enormous advances in radiotherapy planning and delivery, a significant number of pa-tients will experience radiation-associated toxicities. Many effective management options are available for acute radiotherapy-associated toxicities, but treatment options are much more lim-ited and of variable benefit among patients who develop late sequelae after radiotherapy. The present work is based on observations of 586 patients with oral and oropharynx cancer, for which interstitial neutron therapy was carried out in an independent version or in combination with re-mote radiation therapy. Radiation injuries occurred in 130 (22.2%) patients, in 92 (15.7%) they appeared in the form of radiation ulcers and in 38 (6.4%) – osteoradionecrosis of the lower jaw. The clinical picture and the course of radiation injuries after interstitial neutron therapy with sources of 252Cf did not differ significantly from radiation complications after photon irradiation.

Effect of administration route on the biodistribution of albumin microspheres labelled with Re-188

Nowadays the radiolabeled microspheres are established tools for radioembolization of primary and metastatic liver cancer. Human serum albumin microspheres (HSA) are unique carriers for selective and controlled radionuclide delivery to malignant tumors. Rhenium-188 (Re-188), which decays with beta particles (2.12 MeV (71.1%) and 1.965 MeV (25.6%) and gamma emission (155 keV (15.1%)) is one of the most available and promising generator-based radionuclide for cancer therapy. The purpose of this work was to study the biodistribution of microspheres based on hu-man serum albumin labeled with Re-188 (Re-188-HSA) in animals after different routes of admin-istration. The size of more than 95% of microspheres was 10-20 μm. The studies were carried out on outbred white mice and inbred C57BL/6 mice with transplanted Lewis adenocarcinoma after intravenous, intramuscular and intratumoral administration. After intravenous injection the high-est amount of Re-188-HSA in organs and tissues was observed: up to 311.3%/g in lungs, up to 74.30%/g in thyroid gland, up to 12.70%/g in liver, up to 0,81%/g in blood. After the intramuscular injection of 188Re-HSA, the concentration of 188Re-HSA in organs and tissues was significantly lower and did not exceed 1%/g, except for thyroid gland (1,10-17.80%/g). After intratumoral injec-tion the amount of Re-188-HSA in tumor varied from 16.7 to 26.8%/g, that was higher as compared with other organs and tissues. Thus, the routes of Re-188-HSA administration significantly affect its behavior in the body. The obtained results can be used to evaluate the Re-188-HSA potential for radionuclide tumor therapy after intravascular or intratumoral administration.

Evaluating application of fractal analysis of environmental radiation monitoring data for description of characteristics of radionuclides migration in the topsoil of the observation area of JSC "SSC RIAR"

The authors present their technique to describe characteristics of radionuclides migration in the topsoil. The developed method is based on the fractal analysis of spatial patterns. For the qualitative analysis Cs-137 and Sr-90 in the topsoil layer was measured. These radionuclides were selected for analysis due to their long half-life and the ability to be easily included in the food chain, that can cause internal or external exposure of the public to the radionuclides. Abnormal diffusion of the radionuclides detected with the use of the fractal analysis speaks on non-classical spatial distribution of the radionuclides. The technique allows improvement of radioenvironmental monitoring program.

Features of background radiation of different St. Petersburg districts

Radiation safety takes an essential part in the megalopolises' ecological system. Nowadays the influence of radiation factor on the biosphere is considered one of the determining factors and it causes the necessity to monitor the environmental and radiation safety of the population. The aim of the study is a comparative assessment of the ambient equivalent dose rate (ADER) of gamma radiation according to automated radiation monitoring system (АSКRО) data and its own measurements in the South-Western district of St. Petersburg. The article presents an analysis of the radiation background of St. Petersburg over the past five years based on the data of the АSКRО, as well as the results of own measurements of the ADER in the South-Western district of St. Petersburg using the dosimeter-radiometer "Ecologist profi". When analyzing the radiation levels of various districts of St. Petersburg, it was found that the regions with a relatively higher level of ADER included the Central and South-Western regions. The results of our own meas-urements are comparable with the data from АSКRО; there are no significant differences be-tween the data samples. The results of the study show that the АSКRО data can be used for a general description of the radiation situation in certain areas of St. Petersburg, but they can not serve as a substitute for operational radiation control (monitoring). It is necessary to constantly control and monitor the radiation situation in the region in order to obtain information for timely detection of changes in the radiation situation and to prevent possible negative consequences of radiation exposure for the population and the natural environment.

The use of radiation therapy in combination treatment of soft tissue sarcomas of the extremities with involvement of long tubular bones

Soft tissue sarcomas (STS) are rare malignant tumors of mesenchymal origin. They account for about 1% of all malignant neoplasms. Haematogenous spread is the most common route of me-tastasis for STS and bone metastases occur in 9.4% of cases. When creating treatment plan for STS, it is necessary to consider a multimodal approach. Combination treatment can include pre-operative or postoperative radiation therapy (RT), chemotherapy (CT), and local hyperthermia (LHT). Surgery for STS should be radical. This paper presents 9 STS clinical cases and treatment outcomes in patients with secondary bone disease. Four patients underwent chemotherapy and surgery. Two patients received chemoradiotherapy (CRT) and surgery. Three patients received thermo-chemo-radiotherapy (TCHRT) followed by surgery. Accelerated fractionation radiotherapy was given using a single tumor dose of 3 Gy, twice a day with interval of 4 hours between ses-sions, 3 times a week to a total tumor dose (TTD) of 30 Gy (isoeffective TTD – 42 Gy, TDF – 69 Gy). Local hyperthermia for soft tissue tumor treatment was performed over 6 sessions: 2 ses-sions were combined with CHT courses before and after RT, and 4 sessions were combined with RT. The follow up period for 6 patients varied from 12 to 1.5 months, for 3 patients it varied from 6 to 8 months, for 1 patient it lasted 3 months and for 1 patient – 2 years. According to the RECIST criteria, more than half of the patients had tumor stabilization and 22% of patients had a partial response. Grade III-IV the rapeutic pathomorphosis was observed in 70% of patients after pre-operative combination treatment. The use of CT, CRT or TCHRT in combination treatment of STS with secondary bone disease enabled us to achieve a pronounced therapeutic pathomorphosis of tumors and to perform organ preservation surgery with endoprosthetic replacement.

Effects of hypersensitivity and induced radioresistance in CHO-K1 cells following exposure to gamma-rays and accelerated carbon ions

The study presents results of investigations on chromosome aberrations (CA) yield in Chinese ham-ster ovary cells after exposure to gamma-rays and accelerated carbon ions (455 MeV/amu) at doses less than 1 Gy in the pristine Bragg curve plateau and behind the Bragg peak, where normal tissues are situated in the course of radiotherapy. Initial parts of dose curves for total CA and terminal deletions frequencies differed from linear-quadratic dependence and the region of induced radioresistance were observed at 0.1-0.6 Gy for gamma-rays. The similar curve shapes were detected for carbon ions, but plateau region was shorter (0.15-0.35 Gy). Despite the uniform shape of the dose curves for the CA yield, a definite dependence of the cytogenetic effect on the linear energy transfer (LET) is observed. The CA frequency increased with LET rising in the order: gamma-irradiation (0.2 keV/μm), carbon ions at the Bragg curve plateau (10-12 keV/μm) and at the «tail» of Bragg peak (25-27 keV/μm). Outside this range, the yield of chromosome aberrations also enhanced with increasing LET in the same order. The results obtained confirm that the hypersensitivity and induced radioresistance phenomena are characteristic for low level exposure to low-LET and middle-LET radiations when chromosome aberration test is used.

The significance of clinic-diagnostic factors in the course of estimation of side exposure of differentiated thyroid cancer patients after radioiodine therapy

The radioiodine therapy is the most well-known branch of radionuclide therapy. The therapy composed of thyroidectomy and iodine-131 radiopharmaceutical is the “gold standard” for treat-ment of differentiated thyroid cancer patients (DTC). Given metastases in lymph nodes such therapy is absolutely exclusive treatment mode. At the same time, despite the targeted effect of radioiodine on pathological foci a side internal exposure of healthy organs and tissues is noted in the course of radioiodine therapy. Therefore, a reliable assessment of the side exposure is nec-essary taking into account the individual characteristics of patients considering that the side dose varies significantly from patient to patient. For this reason, the identification of significance of personal clinic-diagnostic factors determined the side whole body exposure is the vital and im-portant task. In this aspect, the cytogenetic examination of DTC patients by means of the analysis of chromosomal aberrations in peripheral blood lymphocytes is the goal of essential importance. The certain types of chromosomal aberrations are specific radiation markers that unequivocally indicate radiation exposure. Using the frequency of radiation markers the side absorbed dose can be reliably estimated. In the present work, the statistical analysis of the significance of vari-ous clinic-diagnostic factors in relation to the induction of radiation markers in the blood lympho-cytes was performed. For that end the results of the cytogenetic examination of the group com-prised of 38 DTC patients have been used. The examined patients underwent a course of radio-iodine therapy in the department of radionuclide therapy of the A.F. Tsyb MRRC, Obninsk. The slide preparation and cytogenetic analysis were carried out in the laboratory of radiation cytoge-netic of the same Center. The performed analysis of the correlation matrix with respect to the dependence of the increased frequency of stable and unstable markers resulted from a one-time course of radioiodine therapy showed no meaningfulness at the level R>0.3 for all the studied factors. For the absolute value of the frequency of radiation markers, both before and after radioiodine therapy, the meaningful relationship was found at the level R>0.7 for unsta-ble and at the level R>0.8 for stable markers with a total administered activity of radioiodine dur-ing all the previous courses of radioiodine therapy.