Effective delayed fraction

The neutron lifetime I and effective delay fraction pi for delay group may be computed directly from Equations (40) and (41) after solving for no and mo. Alternately, they may be evaluated without resorting to the calculation of the adjoint or to the integrations involved. Thus, a perturbation comparing the standard no reactor satisfying... 

Fig. 8. Combined effect of fractionated NS-398 and radiotherapy on the tumor growth delay of H460 (A) and HCT-116 (B) human tumor xenografts in nude mice. Day 0 is defined as the first day of treatment. Tumors were treated with vehicle (DMSO) or 36 mg/kg NS-398 on d 1 through 7. Radiation fractions (2 Gy) were given 2 h after drug administration starting d 2, for 5 consecutive days. Error bars represent the SE from 8-9 mice. (O), vehicle treatment alone ( ), NS-398 treatment alone ( ), radiation plus vehicle treatment ( ), radiation plus NS-398 treatment.

The goal of this programme was to reduce uncertaincies as to the effective delayed neutron fraction, peff, from 10 % ((2 o) to 5 % (2 a) in order to obtain better prediction of the reactivity scale. 

Table n gives a comparison of the measured and calculated temperature coefficients and eigenvalues between 74 and 464 F. The temperature defect between 74° and 464 F was estimated from integrated rod worths to be about 3%. Rod worths and temperature coefficients were b d on a calci ted effective delayed neutron fraction fi of 0.0074 (i.e., p/p = 1.16). In addition to having a small absolute bias (all calculated eigenvalues are within + 0.5 and - 0.9% of measured values), the model describes the temperature effects quite accurately. 

G. A.. Price,"Migration Areas and Effective Delayed Neutron Fractions by Critical Exq[>eriments, J. Nuclear Energy, fO. Ill (1959). 

Core Effective delayed neutron fraction, Plqrsical coresize (in.) Gd septum (w/o) Measured keff Variational treatment keff Normalized iterative treatment keff... 

The ratio of the effective delayed neutron fraction (3eff) to the effective prompt-neutron generation time (f ) was measured for several unpoisoned configurations, employing both pulsed neutron and nOise analysis methods. The two methods were in satisfactory agreement, giving a best value of 4.76 x 10 sec". The correspon ng value for the beryllium-reflected reactor has been measured as 1.38 X lO sec". The much greater f for the water-reflected assembly is attributable to reflector delayed neutrons. 

A si rles of experiments with unreflected and unmoderated cylinders of enriched-uranium metal (93.15% U-23S) has been performed at the ORNL Critical Experiments Facility to determine the dependence of the prompt-neutron lifcitime on the cylinder dimensions. Five cylinders ranging in diameter from 17.77 to 38.09 cm and in height-to-diameter ratio from about 0.2 to 0.7 were assembled and their prompt-neutron decay crnistants measured at delayed critical by the Rossi-a technique. Prompt-neu-tnm lifetimes were obtained from the measured decay constants and effective delayed-neutron fractions calculated by transport theory. The average uranium density for each assembly was greater tium 18.7 g/cm. . 

A computational study has been carried out on several plutonium-fueled and mixed-lueled critical assemblies of small to medium size to verify the plutonium cross sec-tlons of the twenty-six groiq> set recently produced at Argonne National Laboratory. Plutonium worths in some larger uranium-fueled reactors have been computed to ascertain the effect of softer spectra on the comparisons. Other reactor parameters included in the study were detector-response ratios and U-235,U-238 and B-10 central clanger coefficients, as well as effective delayed-neutron fraction and prompt-neutron lifetime. 

Central reactivity worths were calculated in spherical. geometry by void replacement. Effective delayed-neutron fractions were determined both by subtraction of delayed-group spectra from the fission-source distribution and by the standard diffusion-theory perturbation method. Prompt-neutron lifetimes were calculated by 1/v poison and by perturbation methods. 

The reactivity worth of each of the fuel-follower shims was determined from period measurements. The total rod worth was 274 mk, with Interior shims worth 60% more than exterior shims, The value of 0/1—effective neutron delayed fraction divided by prompt-neutron lifetime—was determined from reactor noise data to be 59.03 0.69 sec .. ... 

Calculations were performed for uiireflected spheres of molten UQ, (-1000 kg), the void content, accounted for in the equatlon-of-state [Eq. (1)], by setting the initial system density, p = po (l.-f), where f is the void volume fraction of the sphere. This geometry is conservative for the calculation of kinetic energy relative to fission energy. Static DTF-IV calculations were performed to determine the critical radii of spheres with varying void fractions. The reference density, po, was 8.7 m m , the initial temperature. To, 3123 K (assumed molten), and die initial power, 1 MW. The effective delayed-neutron frac-... 

T. MIHALCZO, The Effective Delayed Neutron Fraction from Firakm in an Unreflected Ur um Sphere from tirne Correlation Measurements with Californiuro-252, iVrici Set ng., 60.262 (1976). 

After the plant is brought to the nominal parameters, the reactor changes over to the power self-control mode when the compensation group absorber elements are all located in the upper part of the core they create an operating reactivity margin within the limits of one effective delayed neutron fraction (Peff), which does not threaten reactor safety under an erroneous or even malevolent personnel action. 

The delayed neutron fraction of U is lower than that of U and half of the delayed neutrons are generated outside the core therefore, the effective delayed neutron fraction in the FUJI-233Um is relatively small. However, safe control of the reactor is possible because of a large negative reactivity coefficient on fuel salt temperature and small overall reactivity margin ... 

In the design basis reactivity insertion accident (RIA) [XXX-25], the maximum reactivity insertion in the MSR corresponds to the drop of one graphite control rod into the core. Since the worth of a single graphite rod is only 0.06 %5K/K and less than one effective delayed neutron fraction, such initiating event does not result in any prompt criticality of the FUJI. 

When an amount of positive reactivity equal in magnitude to the average effective delayed neutron fraction is inserted into a critical reactor, the reactor is ... 

The delayed neutron fraction, p, is the fraction of delayed neutrons in the core at birth, that is, at high or fast energies. The effective delayed neutron fraction, is the... 

Define the effective delayed neutron fraction, Peff. 

Figure 3.3 Delayed Neutron Fraction and Effective Delayed...

The effective delayed neutron fraction, 0gff, is used in equation (3.10) because it is this relative number of delayed neutrons actually reaching thermal energies and causing fission that measures the impact on reactor control. Since the total fraction of core neutrons is one, the denominator of equation (3.10) is one. Also, since is small, the numerator... 

Measurements of subcriticality relative to the effective delayed neutron fraction can be made by calibrating a reference fine control rod by means of asymptotic period measurements following rod withdrawal, or by inverse kinetics analysis of the reactor power response following rod drop or rod withdrawal (fitting the response using the delayed neutron kinetics equations).There are imcertainties in total delayed neutron yields and in the time dependence of delayed neutron emission, the accuracy of this reactivity scale being estimated to be 5%. 

The effective delayed neutron fraction, p, is not only smaller for a plutonium-fueled fast reactor than for a uranium-fueled thermal system iP = 0.(X)21 for Pu, p = 0.0065 for but is also more difficult to predict accurately because of the relatively large number of isotopes (including fertile species such as and Pu " ) which may be making a significant contribution to the delayed neutron population. Taking into account the effect of the fast fission in which has a delayed neutron fraction of... 

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