REactor TRansient ANalysis

RETRAN (REactor TRansient ANalysis) is a best-estimate transient thermal-hydraulic analysis computer program (sponsored by EPRI) designed to provide analysis capabilities for BWR and PWR transients, small-break LOCAs, balance-of-plant modeling, and anticipated transients without scram (ATWS). 

In recent years the nonsteady state mode has been used to an increasing extent because it permits accessing intermediate steps of the overall reaction. Very complete reviews of this topic are presented by Mills and Lerou [1993] and by Keil [2001]. Specific reactors have been developed for transient studies of catalytic reaction schemes and kinetics. One example is the TAP-reactor ( Transient Analysis of Products ) that is linked to a quadrupole mass spectrometer for on line analysis of the response to an inlet pulse of the reactants. The TAP reactor was introduced by Cleaves et al. in 1968 and commercialized in the early nineties. An example of appUcation to the oxidation of o.xylene into phthalic anhydride was published by Creten et al. [1997], to the oxidation of methanol into formaldehyde by Lafyatis et al. [1994], to the oxidation of propylene into acroleine by Creten et al. [1995] and to the catalytic cracking of methylcyclohexane by Fierro et al. [2001], Stopped flow experimentation is another efficient technique for the study of very fast reactions completed in the microsecond range, encountered in protein chemistry, e.g., in relaxation techniques an equilibrium state is perturbed and its recovery is followed on line. Sophisticated commercial equipment has been developed for these techniques. 

Spore, J.W., Giles, M.W., Singer, GE., Shumway, R.W., 1981. TRAC-BDl/MODl, an Advanced Best Estimate Computer Program for Boiling Water Reactor Transient Analysis Volume 1 Model Description. Idaho National Engineering I.aboratory Report, NUREG/ CR-2178, EGG-2109. 

Many elements of a mathematical model of the catalytic converter are available in the classical chemical reactor engineering literature. There are also many novel features in the automotive catalytic converter that need further analysis or even new formulations the transient analysis of catalytic beds, the shallow pellet bed, the monolith and the stacked and rolled screens, the negative order kinetics of CO oxidation over platinum,... 

Transient reactors, such as pulse (chromatographic) reactors, temporary analysis of products (TAP) reactors, multitrack reactors, and temperature-programmed reactors have been developed mainly to study gas-solid (catalyst) reactions. These are rather sophisticated techniques used to study mechanisms of catalytic processes at the molecular level in great detail. Since this is rarely done in the development of processes for the manufacture of fine chemicals and pharmaceuticals, these reactors are not discussed further. The interested reader is referred to works by Anderson and Pratt (1985) and Kapteijn and Moulijn (1997). 

The RTD for a flowing fluid is normally obtained by the so-called stimulus-response technique. This technique involves the injection of a tracer at the inlet stream or at some point within a reactor and the observation of the corresponding response at the exit stream or at some other downstream point within the reactor. A suitable flow model can then be selected by matching the experimental RTD curve with that obtained from the mathematical model. This approach implies that a transient analysis of reactor and flow model behavior is necessary. 

To examine the extent of this problem, an eigenvalue analysis was done for many different reactor transient and steady state time profiles. The range of stiffness ratios (absolute value of ratio of largest to smallest eigenvalue, real parts only) observed for the different reactor zones was as follows ... 

Utilize computational fluid dynamics (CFD) models to rmderstand and address heat and mass transfer issues and reactor performance for steady-state and transient analysis. 

Chemical relaxation techniques have been employed to study the rates of elementary reaction steps. The two most useful variables for the system control are the concentrations of the reactants and the reactor temperature. The dynamic responses from the system after the changes of these variables are related to the elementary steps of the catalytic processes. Chemical relaxation techniques can be divided into two general groups, which are single cycle transient analysis (SCTA) and multiple cycle transient analysis (MCTA). In SCTA, the reaction system relaxes to a new steady-state and analysis of this transition furnishes information about intermediate species. In MCTA, the system is periodically switched between two steady-states, e.g. by periodically changing the reactant concentration. 

Figure 5.2-1 shows the result of the transient analysis of reactor coolant pump start when a steam generator to reactor... 

The power-operated atmospherie rehef valves provide defence in depth by cooling down the steam generators and the reactor coolant system when the condenser is unavailable. The valves are sized such that the maximum flow at design pressure that would result in an acceptable (by tire analysis) reactor transient if one valve should inadvertently open and remain open (Section 10.3.2.2.3 of Reference 6.1). 

ANS 56.3 ANS 54.6 ANS 56.8 ANS 56.9 Overpressure protection of low-pressure system connected to the reactor coolant pressure boundary Pressure/temperature transient analysis for LWR containments Reactor containment leakage testing requirements Environmental envelopes to be considered in safety-related equipment... 

For steady state conditions, they calculated a 100°C buildup behind a small obstruction with a radius of 0.085 m. in a reactor 6 m in diameter. Their calculation showed that at the conditions they chose, the hot spot would materialize at about 0.2 m downstream from the obstruction. The transient analysis further showed that temperature could rise as much as 500°C in a short time, approximately 600 seconds. This dramatic rise in temperature is acconpanied by a depletion of the liquid phase and hydrogen. This hot spot temperature is several times higher than the adiabatic temperature rise given by the steady state value at the hot spot. 

A. 1605. This section should summarize the reactor parameters and the initial conditions used in transient analysis (paras A. 1618-A. 1623). These parameters and the permitted operating bands will form the basis of the operational limits and conditions in Chapter A. 17 (Operational Limits and Conditions). 

A. 1608. The permitted operating band on the reactor system parameters shall be specified, including the permitted fluctuations in a given parameter and the associated uncertainties. The most adverse conditions within the operating band shall be used as initial conditions for transient analysis. 

PHWR safety analysis requires a comprehensive set of physical models. Reactor physics analysis may require a transient three dimensional model for the large PHWR cores. The most demanding application is a large LOCA, because of the relatively fast kinetics and the spatial effects associated with flux tilts and shut-off rod (or liquid absorber) insertion. Three dimensional effects are also important in slow loss of reactivity control starting from distorted flux shapes. 

It is judged that RELAP5-3D could have been successfully validated for transient analysis of this JIMO reactor plant. 

Accident and Transient Analysis Mitigating Core Damage Additional Applied Reactor Physics TEST OUT of the following . Fundamentals Nuclear Science Material Science Radiation Protection Chemistry Print Reading Electrical Science Thermodynamics and Fluid Flow... 

Content of Safety Analysis Reports for Nuclear Power Plants." The content of the accident and transient analysis shall meet the general guidance of RG 1.70, as adapted for the SRS reactor design. 

The SSC-K is based on the methods and models of SSC-L [5], which was originally developed to analyze loop-type liquid metal reactor transients. Because of the inherent difference between the pool and loop designs, major modification to the SSC-L has been made for the analysis of the thermal hydraulic behaviour within a pool-type reactor. Now, the SSC-K code has the capability to analyze both, loop and pool type liquid metal cooled reactors. 

Y. Okano, S. Koshizuka, et al., Flow Induced Transient Analysis of a Supercritical Pressure, Light-Water-Cooled Fast Breeder Reactor, Proc. 3 rd JSME/ASME Joint International Conf. on Nuclear Engineering, Kyoto, Japan, April 23-27, 1995, 891-895 (1995)... 

Y. Okano, S. Koshizuka and Y. Oka, Flow and Pressure-Induced Transient Analysis of the Supercritical-Pressure, Light-Water-Cooled and Moderated Reactor, Proc. ICONE-4, New Orleans, LA, April, March 10-14, 1996, Vol. 1, 771-780 (1996)... 

The Light Water Reactor Fuel Analysis Code FEMAXI-6 developed by researchers at JAEA is used for the fuel rod analysis [35]. It is capable of obtaining a complete coupled solution of the thermal analysis and mechanical analysis, enabling an accurate prediction of pellet-clad gap size and pellet-clad mechanical interaction (PCMI) in high bumup fuel rods not only in normal operation but also in transient conditions. It is based on a deterministic method and the main features of its calculation models are as follows ... 

From the beginning of the conceptual study on supercritical water cooled reactors, several plant transient analysis codes have been developed, modified, and applied to them [1-9]. The general name of these codes is Supercritical Pressure Reactor Accident and Transient analysis code (SPRAT). SPRAT mainly calculates mass and energy conservations, fuel rod heat conduction, and point kinetics. The relation among these calculations is shown in Fig. 4.1. SPRAT can deal with flow, pressure, and reactivity induced transients and accidents at supercritical pressure. The flow chart is shown in Fig. 4.2. 

The results of the system transient analysis after the deaeration (see Sect. 5.7.3.2) are shown in Fig. 5.76. The reactor power is raised to 0.1% of the rated value and... 

The startup curves based on the results of the analysis are shown in Fig. 5.77. The condenser pressure and dissolved oxygen level in the reactor are plotted by referring to the startup curves of BWRs. In the system transient analysis, the MCST is also calculated in order to consider the fuel rod integrity during the startup. The MCSTs in the three hot channels are shown in Fig. 5.78. They do not exceed 650°C which is the criterion for the three-dimensional core design (see Chap. 7). 

The loss of turbine load is a t5 ical pressurization event The turbine bypass is not credited. The ADS is initiated at 5 s by the ATWS signal of the turbine cmitrol valve quickly closed and reactor power ATWS permissive for 5 s. The calculation results are shown in Fig. 6.49. The pressure increases due to the closure of the turbine control valves. As described in Sect. 6.7.1.3, the inherent characteristics of the Super LWR design make the reactivity insertion and the power increase very small. The peak power is only 104% of the initial value. When the SRVs open, the pressure begins to decrease. After initiating the ADS as the alternative action, the pressure, power, and cladding temperature decrease. The increase in the cladding temperature is about 50°C and the peak pressure is about 26.8 MPa. They are exactly the same as those obtained in the abnormal transient analysis with a reactor scram (see Sect. 6.7.1.3). 

The plant transient analysis code SPRAT-F, introduced in Sect. 7.9, is used to calculate the flow distribution and the MCST in the three hot channels with respect to the core power and feedwater flow rate. The nodahzation is shown again in Fig. 7.81 [32]. Since the core power and feedwater flow rate are raised very slowly at the power raising phase, the reactor can be practically treated as in a steady state... 

P. Hu and P. Wilson, Supercritical Water Reactor Steady State, Bumup and Transient Analysis with Extended PARCS/RELAP5, Proc. 4th Ira. Symp. on SCWR, Heidelberg, Germany, March 8-11, 2009, Paper No. 13 (2009)... 

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