摘要:

AbstractA phenomenological model has been developed to simulate the qualitative behavior of boiling water reactors (BWRs) in the nonlinear regime under deterministic and stochastic excitations. After the linear stability threshold is crossed, limit cycle oscillations appear due to interactions between two unstable equilibrium points and the phase-space trajectories. This limit cycle becomes unstable when the feedback gain exceeds a certain critical value. Subsequent limit cycle instabilities produce a cascade of period-doubling bifurcations that lead to aperiodic pulsed behavior.Under stochastic excitations, BWRs exhibit a single characteristic resonance, at∼0.5 Hz, in the linear regime. By contrast, this work shows that harmonics of this characteristic frequency appear in the nonlinear regime. Furthermore, this work also demonstrates that amplitudes of the limit cycle oscillations do not depend on the variance of the stochastic excitation and remain bounded at all times.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17663

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractA physical model of nonlinear boiling water reactor (BWR) dynamics has been developed and employed to calculate the amplitude of limit cycle oscillations and their effects on fuel integrity over a wide range of operating conditions in the Vermont Yankee reactor. These calculations have confirmed that, beyond the threshold for linear stability, the reactor’s state variables undergo limit cycle oscillations. This work shows that the amplitudes of these oscillations are very sensitive to changes in operating conditions and are not restricted to small magnitudes as observed in previous stability tests. Consequently, large-amplitude limit cycle oscillations become a possible scenario for BWR operation at low-flow conditions. The effects on fuel integrity of such large-amplitude oscillations have been studied in detail. In particular, it has been shown that limit cycles that oscillate with frequencies higher than 0.25 Hz and that reach the high-power safety scram level of 120% are not likely to compromise fuel integrity.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17664

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe development and demonstration of a new unfolding procedure involving pressure vessel surveillance dosimetry in pressurized water reactors are described. The complete methodology is contained in the LEPRICON code system, and provides techniques for calculating pressure vessel fluences and then adjusting them, with reduced uncertainties, on the basis of surveillance dosimetry measurements and a benchmark data base. An application of these techniques to an existing on-line commercial reactor is presented. Results indicate that the best estimate of the pressure vessel lifetime based on a limiting fluence above 1 MeV of 2×1019n/cm2is∼129±11 effective full-power years, whereas the unadjusted estimate has an uncertainty twice as large.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17665

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe thermal neutron capture cross section of232Th has been measured relative to that of197Au. Foils of gold, thorium metal, and thoria were irradiated together in the NRU reactor thermal column. The198Au activity was assayed in a 4πγionization chamber, which had been previously calibrated with samples of198Au standardized by the 4πβ-γcoincidence method. Protactinium-233 sources were also standardized by this method. Comparison of these sources with the irradiated thorium, by means of a Ge(Li) spectrometer, enabled the233Pa activity in the thorium-bearing foils to be determined.Taking the 2200 m/s capture cross section of197Au to be 98.8 b, that of232Th is found to be 7.33±0.06 b. The uncertainty is at the 95% confidence level and includes an estimate of the systematic uncertainties.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17666

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe prompt neutron emission spectrum from the spontaneous fission of252Cf has been measured for the 0.124- to 15.0-MeV energy range. In the measurement program, seven separate measurements were made of the spectrum between 7.0 and 15.0 MeV using a plastic scintillator as the neutron detector. For the 0.124- to 2.66-MeV energy range, a6Li glass scintillator was used as the neutron detector. The data are presented with respect to a Maxwellian distribution with T = 1.42 MeV. Some positive and negative deviations with respect to this distribution have been observed.

ISSN:0029-5639    

DOI:10.13182/NSE86-2

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe beta-delayed emission process of gamma rays was treated with a gross theory of beta decay and a cascade gamma transition model. The method proposed was applied to calculations of the delayed gamma-ray energy spectra for short-lived fission product nuclides that lack experimental information on their gamma-ray transition properties. The calculated results were used to complement the summation calculation of the aggregate gamma-ray spectrum from an irradiated sample of fissile material after a short cooling time. A satisfactory agreement was obtained between the calculated and the measured spectra, which supported the appropriateness of the coupled gross beta and cascade gamma model. The method was also applied to the calculation of the equilibrium energy spectrum of the delayed gamma rays in operating reactors. The resulting shape resembles the prompt fission-gamma-ray spectrum.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17668

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe direct statistical approach was used recently to obtain analytic expressions for the second moment and the average time per source particle in a general case of multisurface geometry splitting. A practical algorithm is given for the calculation of the second moment as a function of the splitting parameters on the surfaces. The algorithm is used to calculate an explicit expression for the efficiency in a problem involving streaming of neutrons in a straight section of a concentric coolant pipe of a fast reactor. The results are used to obtain the optimum splitting range on four surfaces.

ISSN:0029-5639    

DOI:10.13182/NSE86-A17669

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor