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[en] In order to maintain competence or to train new employees, it is necessary to prepare and organize some training sessions suitable to the concerned audience. As a TSO (Technical and Scientific Support Organization), IRSN (Institute for Radiation Protection and Nuclear Safety) is particularly implicated in this issue, specifically in the field of human radiation protection, protection of the environment and nuclear safety. IRSN created recently an 'In-house University' containing different 'Schools': 'Assessment', 'Emergency Planning/Response'.... The main objective is to support IRSN employees following a specific route. Concerning the 'Assessment' school, this route is first composed of a training on general topics (e.g. 'how to perform an assessment?'), then of other training on specific topics ('nuclear criticality safety', 'fire risks', 'containment'...). Implemented teaching methods are innovative and less academic than it used to be. These methods have been taught by training professionals specialized in andragogy (methods and principles used in adult education). In this context, the 'nuclear criticality safety' (NCS) training has been completely renewed by the SNC department (Neutronics and Criticality Safety Department)of IRSN. Scheduled over a period of one week, each day an expert teacher stays with the participants and interacts with the other speakers planned in the agenda, which allows dynamic discussions. Moreover, various exercises in groups (using paper boards, post-its, videos...) give the opportunity to test the newly acquired knowledge. The session begins with general notions concerning NCS (physical properties, consequences of a nuclear criticality accident...). Then, each control mode (mass, geometry...) is discussed considering lots of examples from actual facilities. Finally, a review of past nuclear criticality accidents is done, and the impact of other risks (fire, flood,...) on NCS is evaluated. A future project is to propose an international training in English intended in particular for other TSOs via the ENSTTI organization (European Nuclear Safety Training and Tutoring Institute). (authors)
[en] This annex provides an example of a protection strategy for a nuclear or radiological emergency. The example protection strategy has been developed using the outline given in Appendix II and is intended to help States identify the relevant information to be given in a strategy, as foreseen in this document, notwithstanding the fact that the level of information and details to be given in the national protection strategy will be driven by the national emergency preparedness and response framework.
[en] Hands on training for Fissile Material Handlers (FMH) from TA55 at Los Alamos National Laboratory (LANL) is being performed at Sandia National Laboratories and at the National Criticality Experiments Research Center (NCERC) at the Nevada Test Site. The courses are designed to give operators experience in taking special nuclear material critical in a controlled environment, and experience on how different parameters effect nuclear criticality for different types of systems. The Sandia course involves the use of an experimental reactor containing low enriched uranium fuel pins. Approach to critical experiments range from adding mass, adding water to an over massed system, separating two halves of the core, or removing fuel rods to achieve criticality. The last two experiments are designed to show the counterintuitive nature of nuclear criticality safety, which demonstrates precisely why we back away from any system that is a suspected process deviation. The experiments at NCERC are performed in conjunction with the critical experiments group at Los Alamos involving neutronically fast, reflected systems as well as an experiment involving polyethylene plates that mimics a solution system. This curriculum also encompasses specific training for Criticality Safety Officers (CSO) as well as nuclear material supervisors, known as Operations Responsible Supervisors (ORS) at LANL. As CSOs and ORSs interact more frequently than other individuals with the Nuclear Criticality Safety Division (NCSD), the training focuses on day to day interfacing with NCSD. These interfaces include how to request/schedule work with the division, how the Criticality Safety Evaluation (CSE) process develops, and the basics of a Credible Events Analysis (CEA) which determines normal and credible abnormal conditions within each operation. In addition, the class emphasizes the importance of an on-going and positive relationship between the NCSD and operations personnel. Fissile material handling training is also offered in a graded scale at LANL, in order to give the necessary information to the correct people, depending on what that individual's work entails. For example, operators who are regularly handling nuclear material inside of a glovebox enclosure will receive very detailed criticality safety training, which includes examples of previous criticality accidents and the lessons learned from those events. However, an operator working with waste drums will receive less detailed instruction, as those activities are lower risk due to the nature of the process. This ensures that operators will be given pertinent information related to their specific process, thus aiding in the retention of the important objectives. (authors)
[en] The medical management of victims of a radiological accident is often driven by the information on the dose distribution or dose at organs at risk that is the main pertinent information expected. Since the Chernobyl accident with the feedback experience on the medical management of highly exposed liquidators, there is nowadays a medical management to treat patients if possible before clinical signs appear and therefore to develop a treatment strategy based in particular on dosimetry information. For criticality accidents, dosimetry is more complex, because of the possible high doses, high dose rates and complex gamma/neutron fields . A high dose from a criticality accident requires dose estimation with a short delay to be effective. It is important to segregate the different contributions of the radiation field, due to the difference in biological detriment. As the neutron dose is mainly deposited in the first few cm of the body that implies to take into account the morphology specificity, difference in organ doses could be up to 30%. This article presents the various techniques used (physical retrospective dosimetry, cytogenetic, activation of blood and hairs and nails, Monte Carlo simulation, etc.) to estimate doses in case of criticality accident. Then, the needs for this specific field of dosimetry will be presented, including firstly the necessity for an international collaboration and cooperation, in order to maintain and to share the few facilities still available, and secondly to have scientific cooperation for future developments and improvements. (authors)
[en] The Nuclear Criticality Safety (NCS) Division at Los Alamos National Laboratory (LANL) has established partnerships with Texas AM University (TAMU) and the University of California, Berkeley (UCB) in order to develop a Nuclear Criticality Safety University Pipeline Program. The goal of this program is to teach students the basics of NCS, preparing them to enter the field upon graduation. The courses consist of lectures that provide the students with the fundamentals of criticality safety, rules and regulations governing criticality safety practices, and the application of skills for writing an evaluation. Offered as a prerequisite, or in conjunction with the class, is a Monte Carlo N-Particle (MCNP) that teaches students the technical skill-set applicable to becoming a successful criticality safety engineer. The program thus far has been a success. More than 40 students were enrolled in the program during the fall 2018. The university pipeline results in several benefits: -1) reduced training time and costs, -2) interested students will naturally self-sort and pursue the discipline at the university level, and -3) a pipeline of criticality safety candidates is readily available within the DOE Complex so that unexpected organizational or mission changes can be reacted to with increased agility.
[en] As criticality safety is a niche profession, the training of new members has usually followed an apprenticeship pattern. Experienced engineers mentor incoming engineers through a variety of on-the-job training activities until the trainee demonstrates competence. Each experienced engineer must balance work and mentoring priorities, with an emphasis on mentoring because new staff represents the future of the organization. Important characteristics of the mentor is an attitude of being willing and interested in mentoring, technical credibility based on qualification, experience or expertise, and enough soft skills to be an effective communicator and teacher. One of our more successful ventures involved leveraging people who have previous experience as criticality safety engineers or have a special skill set in one of the core technical competencies. A detailed and well-documented training program will optimize the efforts of the mentor; however, it does not change the fact that the critical element of the training program is the need for face-to-face interaction between mentors and trainees on a regular basis. One of the best ways to support this interaction is by co-location of mentors and mentees in the same workspace, including routine on-the-job mentoring visits within the operating facility.
[en] The underground nuclear power plant (NPP) makes full use of land resources, reduces costs, makes better use of its passive safety, and avoids radioactivity release into the atmosphere in serious nuclear accidents. In this paper, for obtaining comprehensive and integrated analyses on this new NPP design, we introduce four kinds of underground NPP designs, analyze the feasibility of each design from various aspects, and use the multiple criteria decision analysis method to choose the best option. (authors)
[en] The French Nuclear Authority for civil facilities (ASN) resolution number 2014-DC-0462, published in 2014, presents the objectives to be achieved to prevent a criticality accident in nuclear facilities (except reactor cores once loaded). Despite the provisions implemented to prevent such an accident, in line with the principle of defense in depth, the ASN resolution requires that licensees implement an emergency management to 'limit the consequences of a criticality accident, in particular by implementing dedicated emergency management resources, when a conceivable combination of anomalies could lead to a criticality accident, and if they could provide significant benefits for the protection of people or the environment'. The same approach is applied by French Nuclear Safety Authority for Defense-related facilities and activities (ASND). This paper presents the main points assessed by IRSN (French institute for radiological protection and nuclear safety) to answer authorities' requests regarding the licensees' propositions to limit the criticality accident radiological consequences. This assessment covers the following issues: -) detection of a criticality accident (need for CAAS, probes implementation, maintenance and failure, detection without CAAS, etc.), -) emergency response (evacuation, assembly station, etc.), -) strategy to stop the criticality accident. Each subject is addressed in the form of questions to ensure that the main issues are assessed. The main issues will be illustrated by examples drawn from previous IRSN assessments. Finally, the paper will present the latest works done by IRSN to support French nuclear authorities in case of a criticality accident. (authors)
[en] For decades, the training of French criticality experts has implied performing critical experiments on dedicated devices, which have all been shut down during the last few years. A work for substituting these reactors as a learning tool has then been undertaken. The idea of supplementing the ISIS hands-on with a more criticality-accident-oriented sequence led to the development of a numerical simulator aimed at reproducing the physics of criticality accidents for a range of configurations, while being easy to use. This simulator was written in C++ for the engine and python for the user interface (UI), and was intended to be run on common hardware available in a computer lab, and the simulation running within a reasonable time-span. The developed tool calculates the evolution of a super-critical solution of uranyl nitrate placed in a tank, by solving point kinetics equation and taking into account every meaningful physical phenomenon (radiolysis, thermodynamics, heat exchange, dilatation...) in a simplified way. Reactivity feedbacks are implicitly implemented; they are estimated from neutronic pre-calculations done with APOLLO2 neutron transport code for a given set of physical properties (void fraction, concentration, temperature). Users can configure experiments, tune physics and display physical observable variation with time through a graphical user interface.
[en] In order to detect the occurrence of a criticality accident, Criticality Accident Alarm Systems (CAAS) use the emission, at the beginning of the criticality accident, of an important flux of neutrons and gamma rays. CAAS are not a mean of prevention, but may limit the consequences of an ongoing criticality accident: even with a CAAS installed, personnel may die or be seriously irradiated. Once a criticality accident has just started, CAAS are intended to trigger an alarm for the evacuation of personnel in order to limit their doses. In order to determine the best location of the CAAS probes in a facility, a 'minimum' criticality accident to be detected should be defined. This 'minimum' criticality accident is also named 'minimum accident of concern' (MAC) in the standards related to CAAS. Some of them are currently under revision. The current MAC defined in these standards corresponds to a slow kinetic criticality accident for unshielded solution systems but its origin, its expression and its justification are not well documented and discussions about the MAC are in progress. This paper brings some technical points about these discussions. In particular, this paper will remind the link between the detection and the radiological consequences of criticality accidents. Then the various expressions used to define the MAC over the years will be discussed and compared. In addition, the lessons learned from past criticality accidents, the use of past experiments (like CRAC divergences) and the possible use of computer tools will be discussed to better define the MAC. Finally, the specificities of the devices detecting criticality accidents below the MAC are discussed for the definition of a MAC value. (author)