05 Nuclear fuels (scientific, technical)

96104965 Development of a modular nodal method for solv- Ing three dlmenslonal spherical harmonic equations Inane. F. Ann. Nucl. Enernv, May 1996, 23, (7), 597-611. A nodal method based uponthe least squares minimization technique has been developed for solving the neutron transport equation using spherical harmonics approximation in 3-dimensional Cartesian coordinates. The sec- ond order form of the spherical harmonic differential equations based upon the even parity form of the transport equation are utilized. The governing equations are casted into a set of elliptic type differential equations for which the coefficients can be generated for any spherical harmonics approximation order automatically. The coefficients of the mixed type boundary conditions are obtained through recurrence relationships for any order as well.

96104966 Evaluatlon of the Franc0 finite element fuel rod analysis code Feltus, M. A. and Lee, K. Ann. Nucl. Energy, May 1996, 23, (7), 5.53-565. Knowledge of the temperature distribution in a nuclear fuel rod is required to predict the thermal-and mechanical response of the strongly tempera- ture-dependent fuel elements. In this research, the FRANC0 (Finite Ele- ment Fuel Rod ANalysis Code) computer code was developed for use on an IBM-PC to oredict thermal and mechanical fuel oerformance character- istics for reactor operating conditions. A cross-sectional area of a fuel rod is discretized using constant strain triangular elements. To simplify the time-depent fuel performance analysis, this code uses quasi-steady state conditions or slow power changes for time-independent problems; thus, time-dependent cases can be represented by quasi-static ‘snap shots’.

96104987 External cooling of a pressurized water reactor vessel during a severe accident Kolev, N. I. Kernrechnik, May 1996, 61, (2) 67-76. The effects of external cooling of a pressurized water reactor vessel are investigated by means of model calculations, The buoyancy driven convec- tion, the dynamics of the metallic layer, wall ablation, and the spatial and temooral heat flux distribution uhenomena in the lower head of the vessel afte; relocation of the molten core are analysed. It is demonstrated that the dynamics of the formation of the metallic layer has a decisive influence upon the thermal attack on the vessel wall.

96104966 Incidence

The Fermi beam solution generalized to oblique

Su, B. and Pomraning, G. C. Ann. Nucl. E/tergy, May 1996, 23, (8), 695-709. The authors consider the time-independent, monoenergetic searchlight problem for a purely scattering, homogeneous slab of finite thickness. This problem corresponds to a pencil beam of radiation impinging upon one surface of a source-free slap at an arbitrarv obliaue angle of incidence. The scatterine orocess is assumed sufficientlv oeaked in tithe forward direction so that tge’Fokker-Planck differential scattering operator can be used. Fur- ther, the slab is assumed sufficiently thin so that radiation backscattering is negligibly small. Under these assumptions, a full three-dimension solution is obtained for the angular flux of radiation. This solution is a generaliza- tion of the classic Fermi solution, obtained in the special case of perpendic- ular beam incidence.

96104969 First and higher order, heuristically based genera- lized perturbation theory (HGPT) with optional control reset variable Gandini, A. Ann. Nucl. Energy, May 1996, 23, (8), 681-693. The heuristically based generalized perturbation theory (HGPT), to first and higher order, applied to the neutron field of a reactor system, is dis- cused in relation to the criticality reset procedure.

96104990 lgnalina Nuclear Engineering Inf., Aug. 1996, 41, (50.5), 35-36.

Reoorts that with around 80% of its electricitv coming from the two RBMK-1500s at the Ignalina station: the continuing operation of these reactors is a major national issue for Ltthuania, which regained its indepen- dence from the Soviet Union in 1991. The West have called for immediate closure of all the RBMKs, but clearly the Lithuanians cannot just walk away from their one nuclear power sation.

96104991 Information contraction and extraction by MAR modeling. II. Domlnant noise sources In BWRs Morishima, N. Ann. Nucl. Energy, Jun. 1996, 23, (9), 757-764. The multivariate autoregressive (MAR) modelling of a vector noise pro- cess is discussed in terms of the estimation of dominant noise sources in BWRs. The discussion is based on a physical approach: a transfer function model on BWR core dynamics is utilized in developing a noise model; a set of input-output relations between three system variables and twelve different noise sources is obtained. By the least-square fitting of a theoreti- cal PSD on neutron noise to an experimental one, four kinds of dominant noise sources are selected.

96104992 Investigation of power oscillation mechanisms based on noise analysis at Forsmark-1 BWR Oguma, R. Ann. Nucl. Energy, Apr. 1996, 23, (6), 469-485. Noise analysis has been performed for stability test data collected during reactor start-up in January 1989 at the boiling water reactor (BWR) For- smark unit 1. ‘A uniaue instrumentation to measure local coolant flow in this reactor allowed hvestigation of dynamic interactions between neutron flux and coolant flow noise signals at different radial positions in the core. The causal relationship for these signals was evaluated based on a method called signal transmission paths analysis with the aim of identifying the principal mechanism of power oscillations in this reactor. The results of the study indicated that large amplitude power oscillations were induced by two instability mechanisms concurrent in the core.

96104993 Keeping vigilant for RPV cracks. Improved NDT tools look for SCC In bottom head penetrations Trumpff, B. er al., Nuclear Engineering fnt., Aug. 1996, 41, (505), 24-27. Reports that although no stress corrosion cracks have been found in RPV bottom head penetrations to date, PWR operators are remaining vigilant in case they occur. Framatome has a set of advanced NDT tools to detect and characterise this type of cracking, which has been used to inspect nine EDF plants.

96104994 Low temperature overpressurization protectlon system setpoint analysis using retran for Salem Dodson, R. J. and Feltus, M. A. Attn. .vucl. Energy, Apr. 1996, 23, (6), 487-498. The Low Temperature Overpressurization Protection System (LTOPS) is designed to protect the Reactor Pressure Vessel (RPV) from brittle failure during startup and cooldown manoeuvres in Westinghouse Pressurized Water Reactors. For the Public Service Electric and Gas Company Salem power plants, the Power-Operated Relief Values (PORVs) mitigate pres- sure increases above a setpoint where an operational startup transient may put the RPV in the embrittlement fracture zone. The 10 CFR 50 Appendex- G limit, given by the Salem Technical Specifications, conservatively bounds the maximum pressure allowed during those transients where the RPV can suffer brittle fracture (usually below 3SO”F).

96104995 MAX-imising Oskarshamn 1 Wahlberg, L. G. Nuclear Engineering Int., Aug. 1996, 41, (505), 22-23. Sweden’s oldest operating reactor, Oskarshamn 1, was reconnected to the grid in January 1996 following a three and a half years renovation pro- gramme, but this is not the end of the story. The plant still has to complete further modernisation works, which includes replacing the reactor internals, to be done during the next three annual outages under the title Project MAX.

96104996 NAC seeks free market for spent fuel shipping (USA) Nuclear Engineering Inr., Aug. 1996, 41, (505), 2-3.

Reports that an idea proposed by the US Department of Energy to encourage the development of a spent fuel transport infrastructure capable of meeting the rapid escalation in demand for shipping services expected over the next few years has the industry leader NAC International worried. The company feels that the agency is on the verge of creating a costly governmental boondoggle.

96104997 Neutron production in fissile targets under ion beam irradiation Barashenkov, V. S. er al., Kern~echlik_ May 1996, 61, (2), 103-105. The electro-nuclear method of energy conversion, allowing to utilize ura- nium-238 and thorium-232 to transmute a signficant fraction of long-lived radioactive waste and providing at the same time sufficient safety, is being considered as a oersoective wav to develoo the svstem of enerev conver- sion in nuclear installations. Taking into a’ccount’the importance of these factors for the design of such a system the authors repeated Monte Carlo calculations using an improved model and more accurate parameters.

96104996 Neutron scattering from elemental uranium and thorium Smith, A. B. and Chiba, S. Am Nucl. Energy, Apr. 1996, 23, (6), 459-467. Differential neutron-scattering cross sections of elemental uranium and thorium are measured from approximately 4.5 to 10.0 MeV in steps of approximately 0.5 MeV. Forty or more differential values are obtained at each incident energy, distributed between approximately 17 and 160”. Scat- tered-neutron resolutions are defined to encompass contributions from the first four members of the ground-stage rotational band. The experimental results are interpreted in the context of coupled-channels rotational models, and comparisons made with the respective ENDFIB-VI evaluated fi$s. These comparisons suggest some modifications of the ENDFIB-VI U and ?h evaluations.

Fuel and Energy Abstracts September 1996 351