Core Design and Nuclear Calculations
Core design calculations are a challenging reactor engineering discipline. Such calculations are reactor-specific and therefore they cannot be transferred from one power plant to another (especially if they have different reactor types). The fuel requirements also cannot be based on estimations because the core design has too many variables and too many restrictions. The nuclear calculations consist of following aspects:
- Mid-term analysis of reload strategy
- Proposal of a reference loading pattern
- Reload safety evaluation of proposed loading pattern
Mid-term analysis of reload strategy comprises especially calculations of the fuel requirements for several reloads in a row using simple nuclear codes that are based on point kinetics and linear reactivity model. This analysis aims to optimize number of fresh fuel assemblies, their enrichment and neutron leakage from the reactor core during several years (Mid-term analysis).
Proposal of a reference loading pattern or proposal of transition to a new fuel strategy is based on searching the loading patterns using 3D computational codes. Such outputs are crucial in respect of entire nuclear calculations. They provide detailed knowledge about behavior of the reactor core during the fuel cycle. The output consist of proposed fuel loading pattern which must meet energy (cycle length on full power) as well as all safety requirements such as power distribution, peaking factors, reactivity feedbacks. These calculations can be extended by a cycle optimization, meaning especially searching the low leakage loading patterns with enhanced neutron and fuel economy.
Each change in the project or operation of nuclear power plant requires safety assessment, let alone such a significant change as is the switching of the fuel cycle strategy. Type of the particular safety assessment always depends on nature of the change. Such calculations are then absolutely crucial for entire middle part of the fuel cycle. In general, it must be proven that the new fuel strategy meets all safety criteria that come from Safety Analysis Report (SAR). These criteria are divided into three areas:
- Neutron-physical criteria
- Thermal-hydraulic criteria
- Fuel rod criteria