Probabilistic safety assessment
Also known as a probabilistic risk assessment, the PSA uses probabilities to analyze the overall risk to a nuclear power plant under abnormal conditions. PSA has been accepted all over the world as an important tool to assess the safety of a facility and to aid in ranking safety issues by order of importance. The main benefit of PSA is to provide insights into design, performance, and environmental impacts, including the identification of dominant risk contributors and the comparison of options for reducing risk.
At GCR AD we conduct both Level 1 and Level 2 PSA.
A Level 1 PSA analyzes the sequences that could lead to severe reactor core damage, also known as reactor meltdown. At this level, the emphasis is on plant responses to various types of accidents, whether they are initiated by external events (such as earthquakes or floods), internal events (such as system malfunctions) or human error.
A Level 2 PSA builds on the results of a Level 1 PSA. It examines the containment response to the accident and assesses the likelihood and magnitude of potential radioactive releases to the environment.
Over the past years, many nuclear power plant organizations have performed probabilistic safety assessments to identify and understand key plant vulnerabilities. As a result of the availability of these PSA studies, there is a desire to use them to enhance plant safety and to operate the plants in the most efficient manner. PSA is an effective tool for this purpose as it assists plant management to target resources where the largest benefit for plant safety can be obtained.
Living PSAs are the basis for the risk informed approach to decision making;
Development and use of safety/risk monitors as tools for configuration management is spreading fast;
The different uses of PSA to support NPP testing and maintenance planning and optimization are amongst the most widespread PSA applications
Plant specific PSAs are being used to support the safety upgrading programmes of plants built to earlier standards;
Not all countries have a regulatory framework for the use of the probabilistic approach in decision making. Some countries are still far from ‘risk-informed’ regulation, and this means that there is still considerable work ahead, both for regulators and utilities, to clarify approaches, to establish a framework and to reach a common understanding in relation to the use of PSA in decision making.
GCR AD has experts in the field of thermohydraulic safety analysis for nuclear power plants with pressurized water reactors (VVER and PWR). The long-term experience of our specialists includes not only the development of models and conducting analysis for various areas of application in this field, but also conducting independent expertise.
From the point of view of the activities related to the use of thermohydraulic programs (system thermohydraulic codes), GCR AD covers the following activities:
- Development of plant thermohydraulic models (Input Data Decks) for VVER and PWR reactor installations. State-of-the-art means for visualization and modeling (visual and functional representation of a main and an animated model) are applied.
- Verification, validation, and optimization of the developed plant models.
- Preparation of extended documentation for the developed models.
- Development of training courses for the developed plant models and computational means applied.
- Proactive documentation and reporting of discrepancies for the applied computational means (participation in improving the functionality and stability of software).
- Optimization of the process for application of the thermal-hydraulic system codes and the post-processing of the results.
The main areas in conducting thermohydraulic safety analysis, which GCR AD covers are as follows:
- Supporting deterministic analyses for the purposes of PSA level 1 (design and beyond design accident sequences).
- Supporting deterministic analyses for the purposes of PSA level 1 (severe accidents).
- Substantiating analysis for the purposes of SAR.
- Substantiating analysis for confirmation of new design solutions while expanding the scope of the unit’s systems and strategies for emergency management.
Analyses for verification of emergency procedures.
Structural strength calculations
GCR AD has at its disposal experts in design and investigation of power facilities. With its specialists working in the area of design, equipment analyses and assessment, GCR AD covers all the tasks referring to project full-scale engineering. Our specialists continuously work on mastering new technologies and means to facilitate the implementation of set tasks.
An important aspect of the activity is analysis of the state of facilities operating beyond operation standards. GCR AD has performed analyses for the operation of facilities beyond design life, emergency operation of facilities, operation of facilities in case of accidents.
We have the necessary knowledge and experience in designing pipelines and heating systems in energy projects and we offer:
- 3D design of pipelines, machines, auxiliary equipment and pressure vessels
- Preparation of numerical models based on the finite element method
- Conducting strength analyzes of the equipment, in linear and nonlinear models of the material with criteria: static strength, seismic resistance, thermal strength, cyclic strength.
Strength analysis of structures, systems and components
GCR AD offers a variety of services in the field of construction design and subsequent construction activities.
The competences of the team include the design of buildings and facilities from reinforced concrete and steel, and when necessary other, non-standard materials.
In addition to designing new structures, the GCR AD team competences include strengthening and reconstruction of existing sites in poor condition due to their intensive operation.
GCR AD has many years of experience in the design of various types of foundations, including pilot foundations and supporting structures under technological and electrical equipment, especially in the development of completely new and the reconstruction and strengthening of existing turbine foundations.
Regardless of the type and complexity of building structures, their design (strengthening) goes through the following stages:
- Inspection and survey of the structure (if any);
- Collection of archive materials, organization of inspections;
- Generation of three-dimensional computational models;
- Construction and sizing of the details and the main elements of the construction
- Preparation of project documentation in a volume sufficient for the implementation of the site;
- Designer supervision and technical assistance during the execution of construction and installation works, which is a real challenge when it comes to old and damaged structures.
For the design of building structures according to their type and complexity, the team of GCR AD uses the software products SAP 2000 and PSCAD.
Depending on the client’s requirements, it is designed on the basis of the normative requirements of the EUROCODE system or according to the old national norms.
Nuclear reactors operate by a chain nuclear reaction with reactivity maintained around unity. In that process fuel assemblies radiate heat and complex fields of radiation. Fuel assemblies, depending on reactor design, may remain in the reactor for several years. After that the assemblies are put into a reactor pool to be cooled down until reaching appropriate temperature and radiation parameters in order to be moved to a wet storage facility outside the reactor building. Fuel assemblies usually remain in wet storage condition for several years. It is then possible to move the assemblies either to reprocessing or to dry storage facilities. This is a complicated issue which is still a subject of intensive studies in countries with well-developed nuclear industry such as France, United Kingdom, the United States and others. In accordance with the Bulgarian National Strategy (approved by the Parliament) on spent fuel and radioactive waste management, Bulgaria has chosen the option to store the spent nuclear fuel under dry conditions in specifically designed containers for another fifty years. It will then be determined how to proceed anticipating possible technological advances. It has to be emphasized that spent nuclear fuel is not waste since it still contains a lot of energy and may be utilized in the next generation nuclear reactors.
Our competencies in the field of NPP nuclear fuel management lie in:
- nuclear fuel technical design review and approval
- nuclear spent fuel facilities assessments
- spent fuel management
- nuclear fuel handling and transportation safety assessments
- nuclear fuel performance analyses
- core management – economic aspects
- RPV lifetime assessment
- nuclear fuel verification and validation reports review
Assessment of consequences related to radiation
Given rising environmental concerns, waste management gains more and more attention. This is especially true for radioactive waste management. The nuclear industry is only fifty years old and cannot be considered mature in this field of the industry. Keen debate is on-going throughout the world and leading technology nations such as the USA, U.K., Germany, France etc. dedicate significant efforts to the field.
A leading engineering company in Bulgaria, GCR AD has developed a team of highly qualified engineers and physicists to offer state-of-the-art services. Ranging from nuclear fuel performance analysis to spent nuclear fuel storage facility assessments, our engineers are experienced in every aspect of radioactive waste management.
Technical and economic analysis of measures to increase safety
Nuclear safety is a paramount consideration in any nuclear project. Analyses like probabilistic safety assessment (commonly required in three levels) play an important role to nuclear safety evaluation. Fire, seismic and flooding analyses are involved in the total assessment of safety. In the process of safety assessment, each nuclear facility must show the ability to handle the unlikely and low-probability events which may have harsh consequences on the environment. Such events are referred to as severe accidents.
GCR AD is a Bulgarian company with capability to perform full-scope severe accident management analyses and to develop the resulting guidelines which constitute the final step in the process of licensing a nuclear power plant.
Severe accident management guidelines are developed on the base of the, so-called, level two probabilistic safety assessment. Based on identification of specific features, a set of risk-significant sequences is analyzed and relevant severe accident phenomena are assessed.
GCR AD offers consulting services in the area of Configuration Management of industrial facilities.
Purpose and Scope
Configuration Management is an integrated management process aimed to ensure that:
- Design requirements for plant systems, structures, components, software and hardware are defined and documented
- Changes to design requirements are identified, documented, controlled, evaluated, and approved or rejected
- Approved design changes and their status of implementation are recorded and reported throughout the life of the plant, which results in the accurate implementation of design output information into the physical configuration of the plant (i.e. the as-built status matches the design documents)
- Plant configuration documents specifications of operations, maintenance, testing, installation, procurement, inspection, and training requirements are updated and maintained consistent with the plant design
Our company offers the following services:
- Training personnel
- Streamlining and structuring of a configuration management process
- Development of Configuration Management program guidelines, procedures and instructions
- Assistance in configuration management program implementation
- Assessment of effectiveness.
Training of NPP personnel
Systematic Approach to Training (SAT)
An approach to training which provides logical progression from the identification of the competences required to perform a job to its development and implementation, and achieving these competences, and the subsequent evaluation of the performed training. Experience has shown that SAT is the best method available for producing fully auditable training programs for nuclear power plant personnel.
After the enactment of the new revision of the act on safe use of nuclear energy in Bulgaria, application of the systematic approach to training became a must for Bulgarian nuclear operators. Therefore, measures were taken by the operating organization of the nuclear power plant at Kozloduy to meet the legal and regulatory requirements.
After intensive studying, necessary organization of activities was recommended. In addition, required training materials were developed. Kozloduy Nuclear Power Plant was granted a license for specialized training in September 2006 and the system advised and designed by our experts operates successfully thereafter.
Accounting for the influx of circumstances (equipment modifications, operational experience etc.) as well as the requirement for continuous improvement of the system, we work constantly with Kozloduy Nuclear Power Plant in order to keep training materials and system features up-to-date and in line with internationally recognized best practices.