Radiation situation dynamics at the Andreeva Bay site for temporary storage of spent nuclear fuel and radioactive waste over the period 2002–2016

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This article presents a method for assessing the radionuclide surface contamination density (SCD) on open sites and in premises of a radiation hazardous facility based on measurements of the ambient dose equivalent rate (ADER). The method is intended for use at the initial stage of the assessment of the radiation environment at facilities. The assessed SCD at a given location on the surface can differ from the directly measured SCD at that location, since sources located on the surface and distributed by the depth contribute to the ADER value. The method makes it possible to estimate SCD with reasonable accuracy without increasing the number of measurements, and thus avoid additional occupational exposure and the use of additional resources. SCD and ADER as spatial variables have different support of measurement data. For ADER, measured at a height of 1 m, the support of measurement data can be taken to be a circle in the centre of which a gamma-ray detector is located, with a radius of several tens of meters. In contrast, SCD has the support of measurement data, close to the overall dimensions of the beta detector (100 cm2). To solve the problem of SCD calculation on the basis of ADER measurements, the method of conversion coefficients (MCC) is usually applied, based on the use of conversion factors; however, this method provides an adequate estimate only under conditions of an SCD with low gradient over the surface. The method proposed in this article is applicable for an arbitrary distribution of SCD, and designed to deal with heterogeneous contamination patterns. The developed method is based on the numerical solution of the Fredholm equation of the first kind. The measurement data always contain an error, therefore, the task of the SCD calculation is an ill-posed problem, and the Tikhonov regularisation method (ridge regression) was used to solve it. The article presents the method developed and examples of use. Validation of the method was performed using 38 measurements of the radioactive contamination from 137Cs in soil. It is shown that the method proposed in the article demonstrates a significant superiority in comparison with the MCC method, because it allows more accurate localisation of areas contaminated with radionuclides and is applicable for an arbitrary distribution of SCD.

Section: Results For the Andreeva Bay Nwc Sevrao Technical Sitementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The development and application of a method for assessing radionuclide surface contamination density based on measurements of ambient dose equivalent rate

Chizhov

Sneve

et al. 2019

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“…Thus, it is easy to calculate that 37 empirical distributions of daily doses of the US-605 personnel are the implementation of the normal distribution, 15 are the implementation of the Weibull distribution and 27 are the implementation of the normal composition with a discrete two-digit distribution. Let us consider the second set of data on daily doses of the personnel of the Andreeva Bay NWC SevRAO Facility, which were obtained under the conditions of professional exposure of the personnel in 2016 [17]. The number of the personnel of this facility did not exceed a hundred people.…”

Section: Results For Occupational Dose Distributions Analysismentioning

confidence: 99%

Topographical classification of dose distributions: implications for control for worker exposure

Chizhov

Sneve

et al. 2020

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This paper deals with classification of dose distributions of nuclear workers based on antikurtosis (Q) and entropy coefficients (K) and their relationship presented in QK-diagrams. It is shown that determination of the most appropriate distribution to adopt, for a specific data set of a wide range of input data, requires building and analysing QK-diagrams for distributions of logarithms of individual doses. Actual dose distributions for emergency and occupational exposure situations were then considered, as well as doses for one day of work during clean-up and routine activities. It is shown that, in all cases, three types of distributions of logarithms of individual doses were present: normal, Weibull and Chapeau. The location of the representation point of a dose distribution reflects the degree of dose control of the group of workers whose individual doses are collectively displayed in the QK-diagram. The more the representation point of the analysed distribution of the logarithms of the individual dose of a given contingent of workers deviates from the point of the lognormal distribution, the more there was intervention in the process of individual dose accumulation. Thus, QK-diagrams could be used to develop a dose control function. It is shown that the hybrid lognormal distribution, which is widely used in the field of radiation safety, for the purpose of approximation of real dose distributions, is unable to satisfactorily describe many dose distributions arising in aftermath operations and occupational exposure.

“…Testing of radionuclide sorption between groundwater and soil showed that there would be migration of contamination via groundwater to the offshore marine environment. With the possibility of further contamination occurring because of radionuclide migration, dynamic surveillance has been necessary to monitor the radiation situation both during routine activities at the site, and during the process of spent nuclear fuel and radioactive waste removal (Chizhov et al 2018).…”

Section: Providing Proper Remediation Monitoring and Compliance Checkingmentioning

confidence: 99%

Practical radioecology support in the management and regulatory supervision of legacy sites

Sneve¹,

Smith²

2020

Legacy sites are a global issue. Experience has shown that every legacy site is different and case-specific management and remediation options have to be considered. Each site presents a unique mix of physical, chemical and radiological hazards and the significance of those hazards is likely to change over time. A life-cycle approach to remediation is therefore appropriate, with priority consideration allocated according to the major hazards, as technically determined by reference to policy on protection objectives and the corresponding regulatory requirements. Additionally, consideration will typically need to be given to wider issues as may be raised by stakeholders. The remediation approach also needs to take account of the waste management options on-site or involving off-site management and disposal. Radiological and wider environmental impact assessments are a crucial part of the holistic evaluation of hazards and risks (along with economic and societal impacts), which in turn underpin project planning, regulatory and wider decision making. This paper examines the role of radioecology in the assessment process, its contribution to reduction of scientific uncertainties in modelling ecosystem processes of release, transport and fate of radionuclides and evaluation of potential ensuing impacts on humans and the environment. Relevant examples are presented to illustrate the complexities of the processes in regulatory decision making, the various conditions that significantly affect the final solutions and how radioecology can be used in these situations. Whilst a case-specific approach will usually need to be taken to legacy sites, future remediation and clean-up work can be helpfully informed through sharing of experience from other sites. Continued international collaboration between all parties involved in legacy site management is therefore needed to inform on the development of practical regulatory guidance and to ensure that radioecological research is focussed on addressing the key issues that give rise to uncertainties that challenge regulatory and wider decision making.