Decay heat curve

An analytical expression given by El-Wakil (1978), which correlates with the decay heat curves of ANL report (ANL, 1963), estimates heat loads about one-half the heat loads calculated above. This heat load expression is... 

The decay heat curve, Qdh (f)/ is proportional to the reactor size and is also dependent on the power history, which is the enthalpy of vaporization of water. It is further discussed... 

Core decay heat generation is based on the decay heat curve for a ihree-region core having bum-ups consistent with a 24-month or 18-month refuelling schedule and based on the ANSI/ANS-5.1-1994 decay heat curve. 

The total heat load and rejection rate of heat from spent fuel should be evaluated on the basis of the maximum number of spent fuel elements that can be stored on-site at any one time. Either the decay heat curves for the particular fuel, with appropriate individual post-shutdown times applied to the various fuel elements, or a conservative average post-shutdown time for all fuel elements should be used. 

For the experiments in type C catalysts, the pellets were overfilled with cyclohexane and initially cooled to 230 K. They were then reheated in steps of 1 K and allowed to equilibrate for 10 min before each measurement. The signal was determined from 32 accumulations with an echo sequence of 20 ms echo time to ensure that the signal from the plastically crystalline phase of cyclohexane had decayed fully. The typical heating curves of cyclohexane in the fresh and coked catalyst are displayed in Figure 3.3.3(a) As the temperature is increased, larger and... 

The heat supplied to the primary system is principally the core decay heat, set equal to the one given by the ANS curve minus 5 per cent, according to a suggestion by Tong (1982) intended to originate better approximation evaluations (best estimates) as opposed to very conservative evaluations. This curve can be multiplied by a factor higher than one, foreseen by the program (KQD factor) in order to obtain conservative results, even if less similar to reality. (See Table A2-2.)... 

Based on several experimental data American Nuclear Society (ANS) has assembled decay heat standard ANS-5.1-1979 that contained a single curve to represent all uranium-fueled reactors (Schrock, 1979). The latest version of the standard is ANS-5.1-1994 (Current Standard, Revision of ANSl/ANS-5.1-1979 R1985). The standard was developed to fulfill a need for evaluations of fission reactor performance dependent upon knowledge of decay heat power in the fuel elements. The ANS-5.1 standard provides bases for determining the shutdown decay heat power and its uncertainty following shutdown of LWRs. 

The input data to APRIL.MOD3 included the plant geometry and pre-accident operating conditions as well as some parameters concerning the acdd t sequmce. The latter included, in particular, flie decay heat power curve used before in BWRSAR calculations (see Fig. 1) and the prescribed timing of selected events, as shown in Table 1. 

Three trains of the AFS are provided for the backup of these RCPs. It should be noted that the motor-driven RCPs are not credited in the safety analyses just as they are not credited in BWRs. The capacity of a single train is 4% of the rated flow this is determined on the basis of removing the decay heat up to 6% of the rated power by two trains considering a single failure. The AFS also plays the role of reactor core isolation cooling (RCIC) because the main steam is extracted upstream from the main steam isolation valves (MSIVs). The start time of the AFS is determined by reference to the turbine-driven RCIC of ABWRs. The start-up curve to be used in safety analysis is shown in Fig. 6.5 [2]. The influence of its start time on the reactor safety is investigated in Sect. 6.7. 

Owing to this large concentration of OH relative to O and H in the early part of the reaction zone, OH attack on the fuel is the primary reason for the fuel decay. Since the OH rate constant for abstraction from the fuel is of the same order as those for H and O, its abstraction reaction must dominate. The latter part of the reaction zone forms the region where the intermediate fuel molecules are consumed and where the CO is converted to C02. As discussed in Chapter 3, the CO conversion results in the major heat release in the system and is the reason the rate of heat release curve peaks near the maximum temperature. This curve falls off quickly because of the rapid disappearance of CO and the remaining fuel intermediates. The temperature follows a smoother, exponential-like rise because of the diffusion of heat back to the cooler gases. 

Figures 4.6—4.8 are the results for the stoichiometric propane-air flame. Figure 4.6 reports the variance of the major species, temperature, and heat release Figure 4.7 reports the major stable propane fragment distribution due to the proceeding reactions and Figure 4.8 shows the radical and formaldehyde distributions—all as a function of a spatial distance through the flame wave. As stated, the total wave thickness is chosen from the point at which one of the reactant mole fractions begins to decay to the point at which the heat release rate begins to taper off sharply. Since the point of initial reactant decay corresponds closely to the initial perceptive rise in temperature, the initial thermoneutral period is quite short. The heat release rate curve would ordinarily drop to zero sharply except that the recombination of the radicals in the burned gas zone contribute some energy. The choice of the position that separates the preheat zone and the reaction zone has been made to account for the slight exothermicity of the fuel attack reactions by radicals which have diffused into...

After these early stages, the observations show an increase in the bolometric luminosity. The energy source that continually heats up the expanding star is certainly the decaying 56Co as evident from the light curve tail after 120 d. 

This suggests that the heat source had actually been mixed into outer layers and its effect began to dominate the light curve from t 26 d. From the observational side, Phillips (1988) noted that the changes and kinks of the color started from t = 25 d, which may indicate the appearance of heat flux due to radioactive decays. 

Relative intensities of ESR spectra observed at 77 K after heat treatments at various temperatures higher than 77 K are plotted against the temperatures of the heat treatments. The curve obtained by this procedure reflects well the decay behavior of the radical, because the ESR intensity is proportional to the concentration of radicals, decaying at higher temperatures. This is the reason why this curve is called a Decay Curve . Such a curve contains information on the characteristic decay behavior of the radical trapped in the polymer matrix. Actually the decay curves of the radiation induced radicals of PE (7P, 80) and PP (81) demonstrate that the radicals decay with increasing temperatures. Such decay with temperature is the normal behavior for the... 

Decay curves of PP radicals are shown in Fig. 12. The solid curve in Fig. 12 is a decay curve of the If mechano-radical produced by the sawing and tl dotted line is that of the PP radical produced by 7-iiradiation. The radicals i oduced by 7-irradiation decay step-wise with increasing temperature of the heat treatments, and no increase of the ESR intensity is observed as a result of the heat treatments. This is common and normal behavior in the dec y of polymer radicals (79-81). Contrastly the decay curve of the mechano-radical increases to a maximum at 173 K and decreases more rapidly than that by 7-irradiation in the higher temperature region. It was also found that the ESR spectra changed in shape during this anomalous increase of the intensity, as shown in Fig. 13. The ESR spectrum observed before the heat treatment was... 

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