Anti-hydrogen - Meta-stable helium elastic scattering at thermal energies

This article analyses the results for ground state anti-hydrogen scattering off meta-stable helium (He(2^1/3S)) targets at thermal energies using atomic orbital expansion technique. The variation of phase shifts indicates that the effective leptonic potential for each system has neither any barrier nor any hump. The zero energy cross sections for both the targets are much greater than the ground state target: and . The maxima of the p-wave cross sections occur in the vicinity of the minima of s-wave result.     

The influence of scattering interference on resonance absorption in 238U and 232Th

Comparison is made between the resonance integral calculated by the so-called IR-method and by a more exact method taking into account the scattering interference.Large differences-up to 25 % for strongly scattering resonanes—are found between the results of the two methods.Because of the peculiar behaviour of the lowest lying resonance of ²³⁸U the overall effect on the total resonance integral is rather low-2 to 3 %—for this nuclide, but owing to the same peculiarity greater differences-5 to 10 %—appear, when the Doppler effect is calculated by the two methods.Results for ²³²Th show greater differences-6 to 7%—on the resonance integral and a correspondingly lower error on the Doppler effect.     

The impact of thermal fatigue and other design limits on pulsed commercial tokamak reactor design

Methods of analysis for fusion first-wall design are developed. Several design limits have been evaluated and combined to present tradeoffs in the form of design windows. These considerations include limits related to thermal fatigue, primary membrane strength, displacement under loading, ratcheting, radiation damage, and plasma-wall interactions. Special emphasis is placed on the investigation of thermal fatigue using a two-dimensional treatment of a tubular first-wall configuration. The work is motivated by the proposal of the Ultra Long Pulse Commercial Reactor (ULTR), a machine capable of delivering plasma burn pulses of up to 24 hr in length. The present work looks in detail at the impact of pertinent characteristics of the first-wall design, such as pulse length, coolant pressure, first-wall thickness, and first-wall lifetime on the structural effects considered. Computer programs are developed and are used to consider several major structural effects on a cylindrical first-wall element for both 316 stainless steel and vanadium alloy. Results indicate that short pulse lengths (greater than a few minutes) can be tolerated in tokamak operation. For stainless steel this is true for heat depositions up to 1 MW/m², while vanadium can tolerate heat depositions as high as 2 MW/m². Long pulse operation can be used to increase modestly the allowable heat deposition or to increase useful wall thickness by 1–2 mm. It appears that irradiation swelling and embrittlement, not fatigue, ultimately limits the first-wall design.     

Burnup analysis for the pebble-bed fluoride-salt-cooled high-temperature reactor based on the energy-dependent elastic scattering cross-sectional model

To carry out accurate burnup calculations for a pebble-bed fluoride-salt-cooled high-temperature reactor,the energy-dependent cross-sectional model based on the Doppler broadening rejection correction method has been proposed to develop the energy-dependent elastic scattering cross-sectional model. In this study, the Monte Carlo continuous energy code PSG2/Serpent was used to examine the difference between the constant cross-sectional model and the energy-dependent cross-sectional model during burnup. For the cases analyzed in this study,numerical simulations show that the multiplication coefficient was improved by hundreds pcm and ~(239)Pu concentration was improved by approximately 1–2% during burnup when the energy-dependent elastic scattering crosssectional model is considered.     

The shielding effect of U238 resonances on the resonance absorption of U235

This paper discusses the question of the mutual effect of resonance neutron absorption by U²³⁸ and U²³⁵ inside a slug, where the resonance absorption is due mainly to volume absorption. As shown by the theoretical calculations and experiments given in the paper, the resonance absorption of neutrons by U²³⁵ in the epithermal region of energies for natural metallic and 10% uranium depends on the effect of the U²³⁸ resonance levels.Calculations may be made in a similar way for other elements.In conclusion the authors epress their gratitude to V. V. Orlov, G. Ya. Rumyantsev, and B. G. Dubovskii for their discussion of the present work. The authors also thank Pen-fan, A. P. Dolgolenko, A. P. Korneev, M.M. Kuzichkin, K. N. Mokhnatkin, and Yu. I. Starykh, who participated in the experiments and calculations.     

On the investigation of alpha-particle resonance elastic scattering from the 16O nucleus

Solid target measurements are conducted in order to investigate ¹⁶O(α, α₀)¹⁶O resonances in the energy region 2.0–3.6 MeV. Excitation functions are reported for scattering angles of 145° (θ_cm = 153°) and 165° (θ_cm = 168°), and resonances are observed at 2.522, 3.042, 3.082 and 3.372 MeV. The deduced widths of these resonances in the centre-of-mass frame are 19.00, 8.20, 3.36, and 15.10 keV respectively. It is reported that the widths of the first three resonances are in agreement with previous data, but the width of the 3.372 MeV resonance exceeds an early gas target result due to Cameron [5]. In addition, elastic scattering cross sections are compared with the gas target data and found to be consistent. It is concluded that the width of the 3^? resonance at 3.042 MeV is in agreement with the prediction due to multiparticle cluster calculations for ²⁰Ne.     

Influence of ~(235)U enrichment on the moderator temperature coefficient of reactivity in a graphite-moderated molten salt reactor

To optimize the temperature coefficient of reactivity(TCR) for a graphite-moderated and liquid-fueled molten salt reactor, the effects of fuel salt composition on the fuel salt temperature coefficient of reactivity(FSTC)were investigated in our earlier work. In this study, we aim to provide a more comprehensive analysis of the TCR by considering the effects of the graphite-moderator temperature coefficient of reactivity(MTC). The effects of ~(235)U enrichment and heavy metal(HM) proportion in the salt mixture on the MTC are investigated from the perspective of the six-factor formula based on a full-core model. For the MTC(labeled ‘‘a_(TM)'), the temperature coefficient of the fast fission factors(a_(TM)eeT) is positive, while those of the resonance escape probability(a_(TM)epT), the thermal reproduction factor(a_(TM)egT), the thermal utilization factor(a_(TM)ef T), and the total non-leakage probability(a_(TM)eKT) are negative. The results reveal that the magnitudes of a_(TM)eeT and a_(TM)epT for the MTC are similar. Thus, variations in the MTC with ~(235)U enrichment for different HM proportions are mainly dependent on a_(TM)egT, a_(TM)eKT, and a_(TM)ef T, but especially on the former two. To obtain a more negative MTC, a lower HM proportion and/or a lower ~(235)U enrichment is recommended. Together with our previous studies on the FSTC, a relatively soft neutron spectrum could strengthen the TCR with a sufficiently negative MTC.     

Characteristics of a reactor with power reactivity feedback

The point-reactor model with power reactivity feedback becomes a nonlinear system. Its dynamic characteristic shows great complexity. According to the mathematic definition of stability in differential equa-tion qualitative theory, the model of a reactor with power reactivity feedback is judged unstable. The equilib-rium point is a saddle-node point. A portion of the trajectory in the neighborhood of the equilibrium point is parabolic fan curve, and the other is hyperbolic fan curve. Based on phase locus near the equilibrium point, it is pointed out that the model is still stable within physical limits. The difference between stabilities in the mathematical sense and in the physical sense is indicated.     

Regions of reactor controllability during limited-speed reactivity insertions

Translated from Atomnaya Énergiya, Vol. 64, No. 3, pp. 170–173, March, 1988.     

Fuel-to-cladding gap evolution and its impact on thermal performance of high burnup fast reactor type uranium-plutonium oxide fuel pins

Drastic evolution of fuel-to-cladding gap is observed in high burnup JOYO Mk-II driver and MONJU type uranium-plutonium oxide fuel pins. The effect of the evolution is examined from viewpoints of fuel restructuring, gaseous FP release and retention and cesium migration behaviors. Its thermal impact on fuel pin performance is also studied by one-dimensional steady state thermal analysis. Threshold condition of the evolution depends on fuel pellet characteristics, burnup and probably temperature. The evolution directly relates to as-fabricated microstructures and to gaseous FP release and retention behavior. A comparison of fuel restructuring with predicted temperature profiles indicates that, even where large residual gaps are observed, non-gaseous filler always improves the heat transfer across the gaps.     

Theoretical study of aircraft impact on reactor containment structures

In containment design there is a requirement to protect the reactor system from the effects of external hazards and hence it is necessary to provide suitable wall thicknesses. Experimental work undertaken by the UKAEA is being carried out as a general study and this paper describes some theoretical studies for the particular case of an aircraft impact. The theoretical study utilizes a finite difference dynamic code based upon dynamic relaxation initially developed for static problems The code models concrete, reinforcement and prestressing throughout the short term non-linear range. Concrete is assumed to have a limited tensile stress capacity, coupled with a shear carrying capacity which is dependent upon the aggregate and crack size. In addition a yield condition can be specified to allow for triaxial stress states both initial and subsequent to failure. The paper briefly describes the theory and makes comparisons for different concrete thicknesses.