Fission Fraction Research Articles

Performance of advanced self-shielding models in DRAGON Version4 on analysis of a high conversion light water reactor lattice

A high conversion light water reactor lattice has been analysed using the code DRAGON Version4. This analysis was performed to test the performance of the advanced self-shielding models incorporated in DRAGON Version4. The self-shielding models are broadly classified into two groups – “equivalence in dilution” and “subgroup approach”. Under the “equivalence in dilution” approach we have analysed the generalized Stamm’ler model with and without Nordheim model and Riemann integration. These models have been analysed also using the Livolant–Jeanpierre normalization. Under the “subgroup approach”, we have analysed Statistical self-shielding model based on physical probability tables and Ribon extended self-shielding model based on mathematical probability tables. This analysis will help in understanding the performance of advanced self-shielding models for a lattice that is tight and has a large fraction of fissions happening in the resonance region. The nuclear data for the analysis was generated in-house. NJOY99.90 was used for generating libraries in DRAGLIB format for analysis using DRAGON and A Compact ENDF libraries for analysis using MCNP5. The evaluated datafiles were chosen based on the recommendations of the IAEA Co-ordinated Research Project on the WIMS Library Update Project. The reference solution for the problem was obtained using Monte Carlo code MCNP5. It was found that the Ribon extended self-shielding model based on mathematical probability tables using correlation model performed better than all other models.

Use of Mini-Mag Orion and superconducting coils for near-term interstellar transportation

Interstellar transportation to nearby star systems over periods shorter than the human lifetime requires speeds in the range of 0.1–0.15 c and relatively high accelerations. These speeds are not attainable using rockets, even with advanced fusion engines because at these velocities, the energy density of the spacecraft approaches the energy density of the fuel. Anti-matter engines are theoretically possible but current physical limitations would have to be suspended to get the mass densities required. Interstellar ramjets have not proven practicable, so this leaves beamed momentum propulsion or a continuously fueled Mag-Orion system as the remaining candidates. However, deceleration is also a major issue, but part of the Mini-Mag Orion approach assists in solving this problem. This paper reviews the state of the art from a Phases I and II SBIT between Sandia National Laboratories and Andrews Space, applying our results to near-term interstellar travel. A 1000 T crewed spacecraft and propulsion system dry mass at .1 c contains ∼ 9 × 10 21 J . The author has generated technology requirements elsewhere for use of fission power reactors and conventional Brayton cycle machinery to propel a spacecraft using electric propulsion. Here we replace the electric power conversion, radiators, power generators and electric thrusters with a Mini-Mag Orion fission–fusion hybrid. Only a small fraction of fission fuel is actually carried with the spacecraft, the remainder of the propellant (macro-particles of fissionable material with a D-T core) is beamed to the spacecraft, and the total beam energy requirement for an interstellar probe mission is roughly 10 20 J , which would require the complete fissioning of 1000 ton of Uranium assuming 35% power plant efficiency. This is roughly equivalent to a recurring cost per flight of 3.0 billion dollars in reactor grade enriched uranium using today's prices. Therefore, interstellar flight is an expensive proposition, but not unaffordable, if the nonrecurring costs of building the power plant can be minimized.

Memory of entrance-channel deformation for fast-fission

Fission fragment anisotropies following fusion of 34S with 168Er have been measured for energies at which a substantial fraction of fission results from angular momenta where the fission barrier height is less than the temperature. Here, transition state model calculations were found to be larger than the measured anisotropies. This result contrasts with data for 19F+ 208Pb, where the transition state model underestimated the measured anisotropies. Both observations can be explained qualitatively assuming that high angular momentum events fission with some memory of the entrance-channel K-distribution, which is narrow for the spherical 208Pb target nucleus, and broad for the deformed 168Er.

Mass distribution in 19F induced fission of 232Th.

Formation cross sections of several fission products have been determined using the recoil catcher technique followed by {gamma}-ray spectrometry in {sup 19}F induced fission of {sup 232}Th at {ital E}{sub lab}=95 and 112 MeV. The data show significant admixture of fission from compound nuclei formed by complete fusion as well as targetlike nuclei formed by transfer reactions. Mass distributions for both the fissioning systems have been obtained using the systematics of charge distribution in low and medium energy fission. Mass distribution for complete fusion fission is broad Gaussian whereas it is asymmetric for transfer induced fission. At 95 MeV the transfer fission constitutes about 28{percent} of total fission cross section while at 112 MeV it is about 14{percent}, showing that the transfer fission fraction decreases with increasing projectile energy across the barrier. The evaporation residue cross sections of the targetlike nucleus formed in the {sup 232}Th ({sup 19}F, {sup 18}O) {sup 233}Pa reaction were also measured. The evaporation residue cross sections and the calculated decay probabilities of the targetlike nucleus {sup 233}Pa by PACE2 have been used to estimate the fraction of proton and {alpha} transfer fission in the total transfer fission cross section. {copyright} {ital 1996 The American Physicalmore » Society.}« less

Electromagnetic and nuclear fission of238U in the reaction of 100, 500, and 1000 A�MeV208Pb with238U

The folding- and azimuthal-angle and velocity distributions for the238U fission fragments have been measured in reactions with 100, 500, and 1000 A·MeV208Pb. These distributions were used to decompose the fission cross section into its electromagnetic and nuclear components. The fraction of electromagnetic fission was found to be 0.16±0.07, 0.48±0.08, and 0.60±0.04, respectively. The electromagnetic fission cross section as a function of the208Pb nucleus energy is compared with theoretical predictions. The measured fission cross section from nuclear reactions (≈1.5 b) is approximately constant between 100 and 1000 A·MeV.

大型高速炉炉心の静的核特性と｀２３８´Ｕ核分裂効果の評価

Neutronic behaviors, such as distributions of neutron flux, adjoint neutron flux in macroscopic aspects, and neutron spectra, adjoint neutron spectra, spacial distributions of fissile nuclei fission fraction and their burnup variations in microscopic aspects, and effects of 238U fission with high energy neutrons are compared and analysed for three type cores in 1, 000MWe class FBR plants, that is, homogeneous two region oxide and metal cores, and an axially heterogeneous oxide core, and then the following features are brought out.(1) For neutron spectra in large volume cores, influences of Pu enrichment difference in core regions are fairly moderated by neutron migration and 238U fission, and variations due to burnup effects are also reduced by 238U fission and its high conversion to 239Pu.(2) Adjoint neutron spectra have flattened distributions in common with three type cores and these are resulted in favorite effects on the stable behaviors of neutrons.Based on these microscopic neutron behaviors with small spacial and cycle variations in these cores, some considerations to future prospects of FBR core design are discussed.

Limits on equal energy back-to-back?-rays in252Cf decay

A search has been made for coincident, equal-energy, 180° correlatedγ-rays from252Cf fission decay. Theseγ-rays may arise if new neutral particles are produced in fission, and if they decay byγ-emission. The fraction of fissions which give rise to particles at rest with masses between 1.4 and 2.0 MeV, which then decay into twoγ-rays in a time ≲ 10−19s, is less than 8 × 10−7 at the 95% confidence level.

Measurement and calculation of the efficiency of fission detectors designed to monitor the time dependence of the neutron production of JET

Three pairs of fission counters (each pair one 235U and one 238U) are used at the Joint European Torus to determine the time dependence of the neutron production. In order to determine the absolute value of the neutron flux at the detector location it is necessary to know the neutron detection efficiency of the counter assemblies. This was measured using monoenergetic neutrons (at 2.5 and 14 MeV) and Cf and Am/Be sources. The fraction of fissions detected was determined by extrapolation of the pulse-height spectrum to zero pulse height. The calculation of efficiency was made with the Monte-Carlo neutron transport code MORSE. It was found that the detailed structure of the counter significantly affected the calculated efficiency and that the thermal cross-section values of the DLC37F nuclear data library had to be replaced with room-temperature values. The mean difference between calculation and experiment is (5.5±6.3)%.

Study of fission from Ag, Au, Pb, Bi, Th and U targets induced by 640 MeV α-particles

Makrofol was used as 4π track detector to determine the fission cross sections of Ag, Au, Pb, Bi, Th and U induced by 640 MeV α-particles. The cross sections for Bi, Pb, and Au were larger than those obtained with 100 MeV α-particles or with deuterons or protons of 2100 or 600 MeV, respectively. Kinematical studies show an important fraction of asymmetrical fission (∼88%) for Au, Pb, Bi, Th and U.

Characteristics of Coulomb fission

Within an extended semiquantal theory we perform large-sized coupled-channel calculations involving 260 collective levels for Coulomb fission of /sup 238/U. Differential Coulomb fission cross sections are studied as a function of bombarding energy and impact parameter for several projectiles. In the Xe + U case, total cross sections are also given. We find a strong dependence on projectile charge number, P/sup CF/(180/sup 0/) approx. (Z/sub p/)/sup 6/ in the region 50 < or = Z/sub p/ < or = 92 for a fixed ratio E/E/sub Coul/, which might be helpful to separate Coulomb fission experimentally from sequential fission following transfer reactions. Since the cross sections are sensitive to the moment of inertia THETA at the saddle point, Coulomb fission can serve as a tool to investigate the dependence of THETA on elongation. The fragment angular distribution exhibits deviations from 1/sintheta/sub f/ which are pronounced at low incident energies. Our theory indicates that the recently measured Xe + U fission cross sections contain a major fraction of Coulomb-induced fission at E < or = 0.85 E/sub Coul/.

Energy and Spin Dependence of Fission:H1andHe4Emission fromHg194Compound Nuclei

Reactions of $^{12}\mathrm{C}$ and $^{19}\mathrm{F}$ have been used to produce $^{194}\mathrm{Hg}$ compound nuclei at excitation energies of 98 and 142 MeV. This combination of entrance channels permits the separation of energy and spin effects on the exit channels. Fission probability clearly increases with angular momentum at fixed energy. However, there is no increase in the cumulative fission fraction from 98 to 142 MeV for essentially constant spin domain. In contrast the probability of $^{1}\mathrm{H}$ and $^{4}\mathrm{He}$ evaporation increases rapidly with energy and seems to shield the system from fission.

High-Energy-Proton Fission Cross Sections of U, Bi, Au, and Ag Measured with Mica Track Detectors

The interaction of 0.6-29-GeV protons with U, Bi, Au, and Ag was studied with mica track detectors. Binary fission events were identified as correlated pairs of tracks. A fragment registered an acceptable track if its mass was \ensuremath{\ge}30 and its kinetic energy &gt;6-8 MeV. The results show: The U fission cross section ${\ensuremath{\sigma}}_{f}(\mathrm{U})$ is 1400 mb up to 1.0 GeV and decreases monotonically to 670 mb at 29 GeV; ${\ensuremath{\sigma}}_{f}(\mathrm{Bi})$ increases from 125 mb at 150 MeV to a broad maximum of 215 mb at \ensuremath{\sim}600 MeV, and then decreases to 105 mb at 29 GeV; ${\ensuremath{\sigma}}_{f}(\mathrm{Au})$ varies little, 59-76 mb, in the energy region 0.6-29 GeV (the highest values appear at 2 and 3 GeV); no binary events were observed from Ag targets: upper limits are 0.3 mb at 0.6 GeV, 2 mb at 1.0 GeV, 5 mb at 2-13 GeV, and 6 mb at 29 GeV. Effects of secondary particles were shown to be negligible; the experimental uncertainty varies from \ifmmode\pm\else\textpm\fi{}10 to \ifmmode\pm\else\textpm\fi{}20%. Ternary fission events (140) were seen for U starting at 1.0 GeV, and for Bi and Au starting at 2.0 GeV. The yields are about 1-2 per 1000 binaries. Many single unpaired tracks were also observed, and their yield increases with beam energy. From U, most of these seem to be from a small fraction of asymmetric fissions where one of the partners is below recording threshold. From Bi and Au, most of the single tracks are high-energy spallation residues.

Fragment mass-angle correlation in U 238 + n fission

The U 238(n,f) process has been investigated between 1.2 and 1.7 MeV neutron energy. A photographic emulsion technique was used to identify individual fragments and their angular distribution for different range-ratio groups. The fraction of total fissions in each group was found to be independent of neutron energy. The angular distributions of all groups agree with previous measurements without mass discrimination except for the most nearly equal-fragment group. The data suggest that this group has a larger but less enegy-dependent anisotropy than other groups.