State Office For Nuclear Safety Research Articles

Development of a MELCOR Model for LVR-15 Severe Accidents Assessment

LVR-15 is a light-water-tank-type research reactor placed in a stainless-steel vessel under a shielding cover located in the Research Centre Rez (CVR) near Prague. It is operated at a steady-state power of up to 10 MWt under atmospheric pressure and is cooled by forced circulation. In 2011, the fuel was replaced, going from high-enriched uranium (HEU) to low-enriched uranium (LEU). After 2017, the State Office for Nuclear Safety (SUJB) asked CVR to evaluate the LVR-15 under Design Extended Conditions B (DEC-B). For this reason, a new model was developed in the MELCOR code, which allows for modelling the progression of a severe accident (SA) in light-water nuclear power plants and estimating the behaviour of the reactor under SA conditions. The model was built by collecting information about the LVR-15. Since the research reactor can have different core configurations according to the location of the core components, the core configuration with the most fuel (hottest campaign K221) was selected. Then, to create the radial nodalisation, the details of the core components were obtained and grouped in five radial rings and 27 axial levels. The simulation was run with the boundary conditions collected from campaign K221, and the results were compared with the reference values of the campaign with a negligible percentage of error. For the coolant inlet and outlet temperature, the reference values were 318.18 K and 323.5 K, respectively, while for the simulation, the steady state reached 319 K for the inlet temperature and 324 K for the outlet temperature. Additionally, the cladding temperature of the hottest assembly was compared with the reference value (353.72 K) and the steady-state simulation results (362 K). In future work, different transients leading to severe accidents will be simulated. When simulating the LVR-15 reactor with MELCOR, specific attention is required for the aluminium-cladded fuel assemblies, as the model requires some assumptions to cope with the phenomenological limitations.

Simulation of the Super Critical Water Loop Using ATHLET Code During an Abnormal Scenario

Abstract Supercritical water (SCW) has advantages like high thermal efficiency and can operate at high temperature and pressure. At the same time, however, these properties bring up related issues, such as material compatibility and corrosion resistance. In an effort to fully investigate the operating conditions, and solutions to these issues, test facilities are being built by many research organizations. One such organization, the Research Center Řež (CVR) located in the Czech Republic, has developed an experimental supercritical water loop (SCWL). The purpose of this loop is to provide experimental data from material testing in various conditions, including operating under the neutron field. This will be achieved by inserting a test channel into the existing experimental reactor light water reactor 15 (LVR-15), which will require a license from the state nuclear regulator (State Office for Nuclear Safety (SUJB)). Part of the licensing documentation is the safety analysis, which combines results from developed models using the thermohydraulic code ATHLET 3.1 A patch 1, as well as the experimental out of pile data. Among the postulated scenarios, an abnormal sequence (labeled A2—Loss of power in the loop) was analyzed in order to provide a preliminary benchmark. This scenario is similar to the postulated in-pile A2 and it was used for the benchmark activity. The aim of this paper is to present this activity including the adopted assumptions in the model. In particular, the paper presents, how these assumptions influenced the results indicating the discrepancies obtained in the first part of the transient.

THERMAL ANALYSIS OF DRY STORAGE AND TRANSPORTATION CASKS CASTOR USING COBRA-SFS

State Office for Nuclear Safety is a regulator body in the Czech Republic handling also licensing of storage and transportation casks (SCs) of the spent nuclear fuel (SNF). One of the main concerns for the dry storage of SNF is the safe removal of the residual heat resulting from the decay of fission products, actinides, and activated construction materials. There are many storage systems in use around the world with different storage configuration, fuel designs and boundary conditions that need to be evaluated. Two thermal models of SNF storage casks CASTOR 440/84 and CASTOR 440/84M were developed using the COBRA-SFS code, which is an internationally accepted and validated code used for licensing of dry storage casks and safety evaluation. The casks are in operation at the Nuclear Power Plant Dukovany for dry storage of the WWER-440 SNF. Both models were validated and used for evaluation of several problems in different configuration and particularly for licensing purposes at the SUJB.

Quantification of the Hazard Due to Releases of Radioactive Substances in Accidents and Fires in Workplaces with Radioactive Sources

Abstract In the Czech Republic, under normal conditions, the radioactive sources are used transported and stored in accordance with the relevant regulations and instructions of the State Office for Nuclear Safety (SONS), which is the regulatory authority of the state administration. Its main task is to ensure adequate safety and protection of persons in accordance with current international standards and guidelines. However, if there is an incidence, accident, or other emergency, these circumstances require taking some specific measures aimed at minimizing the impact of such situations on human health and the environment. During a fire in the workplace, the radioactive sources can get out of control or radioactive substances may begin to leak into the environment. In these cases, it is necessary to evaluate the radiation situation by means of measurement and monitoring both the external radiation and radioactive contamination of the air and the surrounding environment. For this purpose, a system of quantities and units has been developed for this purpose. If the system is not used correctly, this may cause serious confusion in some cases. Inappropriate use of quantities may also result in some misunderstanding regarding the evaluation of the severity of the radiation situation. The paper gives an overview of the relevant quantities and units in accordance with the latest recommendations of international organizations which are active in this area.

Radon program of the Czech Republic

The Radon Program of the Czech Republic 2010-2019--Action Plan is based on Governmental Decision No. 594/2009 (Radon Program of the Czech Republic 2010-2019--Action Plan, Government of the Czech Republic, Decision No. 594/2009, May 4 2009) and is coordinated by the State Office for Nuclear Safety. It covers both prevention in new house construction and intervention in existing houses with high indoor radon concentration. The Program is aimed at developing an effective public information system. It takes advantage of long-term experience and good scientific and technological background-staff, methods, standards and technologies.

Radon in private drinking water wells

At least 10% of inhabitants in the Czech Republic are supplied with water from private sources (private wells, boreholes). With the increasing cost of water, the number of people using their own sources of drinking water will be likely to increase. According to the Decree of the State Office for Nuclear Safety about the Radiation Protection 307/2002 as amended by Decree 499/2005, the guideline limit for the supplied drinking water ('drinking water for public supply') for radon concentration is 50 Bq·l(-1). This guideline does not apply to private sources of drinking water. Radon in water influences human health by ingestion and also by inhalation when radon is released from water during showering and cooking. This paper presents results of measurements of radon concentrations in water from private wells in more than 300 cases. The gross concentration of alpha-emitting radionuclides and the concentrations of radium and uranium were also determined.

Fullerene C60 and its Derivatives as Nanocomposites in Polymer Nanofibres

This work describes the application of oxo-derivatives of fullerene C60 and pristine fullerene as a nanocomposite in polymerous nanofibres. In this work we used oxo- fullerene derivative, of which preparation was presented by the authors of the State office for nuclear safety (Prague) on Nanocon 2009 and on Nanocon 2010 [1, 2]; there was presented its application in vivo as a radioprotective agens. With respect to wild spectrum of potential utilization of unique chemical, structural a electron properties of fullerene we investigate its another possible technical application as nanocomposite in polymer nanofibres. The nanocomposite polymer nanofibers were produced by needle-less electrospinning method. Polyvinyl alcohol, polyurethane a polyvinyl butharate were used as polymers. Thermal resistance of obtained nanofibres without and with nanocomposites was tested by simultaneous thermogravimetric analysis and differential thermal analysis (TGA/DTA). The retarding influence of fullerene and its derivative on the course of the thermal decomposition of nanofibres is discussed.

Radon data processing and outputs for the needs of the State Office for Nuclear Safety (according to the Czech Radon Programme)

Much of the population living in the Czech Republic is exposed to radiation from natural sources, especially to the radon effect. The aim of geological research defined by the State Office for Nuclear Safety (SONS) was to detect areas with estimated high radon concentration in soil gas. A uniform method of measurements and uniform methodology of radon risk category assessment of geological units and a centralized radon database was established. Radon risk classification was based on statistical evaluation of soil gas radon concentration and permeability in investigated geological units. Prognostic radon risk maps in various scales were the main outputs of this research. With the help of GIS tools spatial analyses were found a correlation between soil gas radon values in selected geological units and indoor measurements in dwellings. After verification of the efficiency of track etch detectors placed in dwellings with the help of prognostic maps 75% reliability of these maps was proven. This reliability of analyses induced the SONS to widely use radon risk maps to determine areas with predicted high radon risk category.

English

Requirements of the All-State Radiation Monitoring Network in the Czech Republic have been establishedby Regulation No. 319/2002 Sb, and its function and organisation are described in Regulation No. 27/2006Sb. The All-State Radiation Monitoring Network in the Czech Republic consists of two components–permanentmonitoring and emergency monitoring. The activity of the whole network is provided by the State Office forNuclear Safety. The selected central authorities of the state administration participate in operation and providingparticular components. There are two different modes of the operation of these components–normal andemergency. The modes of operation are controlled by the State Office for Nuclear Safety. The activity of wholenetwork is focused on continuous monitoring of the radiation situation in the Czech Republic and on earlydetection of radiation accidents in and around the country as well as beyond it. The acquired data shall serveas a basis for adopting urgent and subsequent radiological protection provisions. Defence Science Journal, 2008, 58(6), pp.728 -733 , DOI:http://dx.doi.org/10.14429/dsj.58.1700

Evaluation of occupational exposures to natural radiation in the Czech Republic

The Czech approach to limit the occupational exposures to natural radiation is based on the rules given by the Atomic Act and by the Decree of the State Office for Nuclear Safety (SONS) on radiation protection. Workplaces with potential risk of increased exposure to natural sources are specified explicitly. A new method to perform the above-mentioned measurements and to determine the effective doses of workers was proposed in 2005 and accepted by the SONS in 2007. The first experience illustrates its applicability.

History of the measurement of radon in central Bohemia

It is a little surprising, but radon has been measured by our Institute for >50 y. In the first phase this was carried out in underground mines (up to the present day) but more and more attention has been paid to domestic dwellings and NORM workplaces. The number of the measurements (grab sampling underground, SSNTDs application) was relatively high. To the routine work of the Institute is added research and calibration for radon measuring organisations. Since the formation of the Czech Republic, our previous institution was reformed by the State Office for Nuclear Safety and is one of the two organisations whose main task is, among others, radon measurement.

Report on the first patient group of the phase I BNCT trial at the LVR-15 reactor

The phase I study of the Protocol approved by State Institute for Drug Control and State Office for Nuclear Safety of the Czech Republic has been used to define the limiting toxicity of the BNCT procedure. The group of nine patients received BSH and underwent surgery, five patients with glioblastoma multiforme were treated using BSH and the epithermal neutron facility of LVR-15 reactor in NRI Rez.

The system of personal monitoring and the evaluation of occupational exposure in the Czech Republic.

New legislation concerning radiation protection, which was effective in the Czech Republic from 1997, followed from the recommendations of ICRP Publication 60 and the IAEA BSS, and included all new basic principles for the protection of radiation workers given in these documents. The requirements for the personal monitoring of category A workers and the recognition of the capacity of dosimetry services were identified as being very significant for radiation practice, and will be licensed by the State Office for Nuclear Safety (SONS). The license application will include the methodology of effective dose evaluation, the description of QA and QC of the service, the system of customer communication and dose recording and reporting. In accordance with legislation requirements, the licensee is obliged to report the personal and dosimetry data of category A radiation workers to SONS. For the purpose of data collection, SONS is developing the central registration system of occupational radiation exposure (CROE). Personal monitoring is managed for about 20,000 workers in 1500 workplaces. The paper describes in detail all current aspects of external monitoring of workers in the Czech Republic.

Transport Data Collection and Reporting in the Czech Republic

AbstractThe State Office for Nuclear Safety (SONS) as the responsible body for the safe transport of radioactive materials in the Czech Republic is required to maintain a national system for registration of: (i) the approvals of special form radioactive material, package designs and shipments; (ii) the records of exposure of persons coming into contact with ionising radiation sources at their work (including radiation exposures resulting from radioactive material transport); and (iii) the reports on radiological accidents (including reports on accidents in radioactive material transport). The system is described of registration of the above mentioned items in the Czech Republic following on from the obligations of the SONS stipulated in the Act No. 18/1997 on Peaceful Utilization of Nuclear Energy and Ionizing Radiation Act (‘Atomic Act’). The importance of the International Atomic Energy Agency databases PACKTRAM, SHITPTRAM, EXTRAM, EVTRAM and REDTRAM is discussed from SONS point of view.