Computer codes validation

Methods for accident analysis have been considerably improved over the past two decades owing to better insights into physical phenomena through research, and enhancement of computer codes and computational capabihties. In parallel, the development of an experimental database and computer code validation studies have made it possible to switch from simplified codes to more sophisticated and mechanistic integral (system) codes. Finally, the ongoing improvements in computer capabilities have removed the main constraints to the use of computational tools. 

A complete duinmaty of experimental criticality data for (Pu, 0)0 fuel rods,in water is presented in TablesI and Fbel rod tlimenslons and isotopic compositions are presented in Tables in and IV. The information is sufficiently complete for use te computer-code validation. 

Computer codes validation considering the complexity involved in the analytical simulation of the entire phenomenon, agreement was reached on the necessity to quantify the approximations involved in the one-dimensional simulation codes with the help of experimental data from mock-up experiments of increasing complexity. This becomes even more important for larger cores. 

Computer System Validation US Code of Federal Regulations 21 CFR Part 11. 

The expression of chemical fate can be computerized using a code to perform the computations and predict the results when inputs simulating conditions of interest are provided. Two critical aspects of the use of computer codes for predicting geochemical fate are the verification and validation of the models on which the codes are based. 

The uncertainty in the predicted CHF of rod bundles depends on the combined performance of the subchannel code and the CHF correlation. Their sensitivities to various physical parameters or models, such as void fraction, turbulent mixing, etc., are complementary to each other. Therefore, in a comparison of the accuracy of the predictions from various rod bundle CHF correlations, they should be calculated by using their respective, accompanied computer codes.The word accompanied here means the particular code used in developing the particular CHF correlation of the rod bundle. To determine the individual uncertainties of the code or the correlation, both the subchannel code and the CHF correlation should be validated separately by experiments. For example, the subchannel code THINC II was validated in rod bundles (Weismanet al., 1968), while the W-3 CHF correlation was validated in round tubes (Tong, 1967a). 

In order to implement the control methodologies indicated, one needs proper measurements (sensors and diagnostics), controllers, and actuators. Extensive research and development are carried out to realize the most appropriate sensors and actuators for various applications. Diagnostics developed serve dual purpose to physically measure the various combustion parameters and interpret the results as quickly as possible, preferably in situ, so that the mechanisms involved can be understood and to validate the numerical computer codes so that... 

A number of proprietary computer codes for gas flow exist (see Annex 4). Many of these are intended for low velocity flow and do not handle choking. Before using such a code to evaluate relief system capacity, it should be checked that it is valid for high velocity choked flow (unless the use of equation (A6.5) indicates that flow will not be choked). 

However, using the newly developed nonorthogonal Valence Bond SCF (VBSCF) method these VB structures can be constructed directly from purely carbene localized orbitals, without the uncertainty introduced by the orthogonality tails15,16. The orthogonal LMO analysis described above (OVB) is more convenient computationally, but a limited number of real VB calculations need to be carried out on actual heteronuclear doublebond systems to compare with and to validate the LMO results. This analysis has been carried out here using ab initio VBSCF computer codes. 

Computer systems validation, as established in 21 CFR Part 211.68, Automatic, Mechanical, and Electronic Equipment, is one of the most important requirements in FDA-regulated operations and an element of the system life cycle (SLC). In addition to the testing of the computer technology, other verifications and inspection activities include code walkthroughs, dynamic analysis and trace analysis. These activities may require 40% of overall project efforts. 

Computer systems validation is an element of the SLC. In addition to the software and hardware testing, other verification activities include code walkthroughs, dynamic analysis, and trace analysis. 

Computer systems validation, as established in 21 Code of Federal Regulation (CFR) Part 11.10(a) and defined in the recent draft United States (US) Food... 

The development of the computer code RALOC at the German GRS for the simulation of the distribution of hydrogen, air, and steam in a LWR containment after severe accidents has started in 1974. RALOC is based on a lumped parameter approach with a differential equation system which describes the composition of the containment atmosphere, temperature, and the transport phenomena of convection and diffusion. Validation... 

Another important issue is the lack of documentation about the validation/verification of the developed computer codes with properly and internationally accepted QA-measures and well defined benchmark test problems so that the reliability of the software can be well established, especially for large-scale industrial applications. 

Validation essentially concerns establishing under which circumstances a given model is adequate, i.e. will the model predict the performance measures with sufficient certainty and confidence. A computer model validation may be split into verifying that the code solves the mathematical equations satisfactorily (code verification) and to explore to what extent the mathematical models embedded in the code actually represent reality. 

The effort should be concentrated on validation of available computer codes (RELAP 5, CATHARE, ATHLET, TRAC, MELCOR, RAINBOW) and applicability of their relevant correlations for thermohydraulic LPS conditions analysis. 

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