This paper presents a comprehensive analysis performed by a new cluster analysis code ' MESSIAH ' on reactor physics constants measured in the critical facility for a pressure-tube-type, heavy-water-moderated reactor. The MESSIAH code system utilizes the method of the collision probability to solve the neutron transport equation. The effective space dependent cross sections are calculated in the thermal and resonance energy range before the eigenvalue calculation for the whole energy range. With use of these cross sections, the multi-group, space dependent transport equation is solved, and the flux distribution, spectrum and k_eff are obtained to the input bucking. In the above three steps the method of the collision probability is used consistently and extensively. The treat-ment of leakage neutrons from lattices in MESSIAH is also confirmed by an independent method using a Monte Carlo calculation. The calculated reactor physics constants, espe-cially the micro-parameters and the activation traverse of Dy, agreed fairly well with the experiment. The diffusion calculation with use of the group constants calculated by MESSIAH predicts the reactivity of 0% void core excellently (<0.12%). However, for a 100% void core, the calculated reactivity was slightly lower than the experiment (0.74%), which was attributed to over prediction of the diffusion constants.

View full abstract

A study of a cylindrical core test facility (CCTF) test was performed for modeling the system behavior during the reflood phase of a PWR-LOCA and the following conclu-sions were obtained:
(1) With the exception of some points, the observed phenomena are similar to a model derived from an evaluation model for a PWR safety evaluation.
(2) The different points are the water accumulation in the upper plenum, the ECC bypass in the downcomer, the reduction of the effective downcomer head and the pressure drop at the broken cold leg nozzle and in the inter-connected pipes.

View full abstract

Flow characteristics in relation to heat transfer characteristics in parallel channel with turbulence promoters were studied experimentally. Flow visualization experiments were made in paralle channel with one or two turbulence promoters for Reynolds number region of 100 ?? Re_ω ?? 3, 600. The vortex patterns behind one promoter were that a steady vortex was formed for low Reynolds number and vortex was shed for high Reynolds number. For higher Reynolds number, it was observed that shedding vortex caused other vortices or disappeared itself randomly. The results indicate that the shedding vortices will aug-ment heat transfer, whereas the steady vortex will give rise to deterioration in heat trans-fer. This inference agrees with the experimental results of Hishida et al. The results of two promoters experiment showed that the maximum performance of promoter would be attained at p/d7. This agrees with the results formerly studied by other investigators.

View full abstract

The experimental study was conducted to examine the applicability of boiling potassium two-phase flow to the blanket cooling of fusion power reactors. A high flux heater pin of 44 mm heating length and 6.5 mm 0. D. with eight thermocouples of 0.5 mm 0. D. was inserted from the bottom of a vertical channel which was made of a 4 m long, 14.9 mm I. D. and 17.5 mm O. D. stainless steel tube and placed in a D. C. magnet of 50 cm long poles. The experimental conditions were the heat flux : 067 W/cm², the magnetic field strength : 01.8 T, the Ar cover gas pressure : 1.0 bar, the potassium level above heater : 1.8 m, and the temperature of upper unheated section : 400°C.
In the absence of magnetic field, boiling occurred intermittently, repeating the cycles between superheating with moderate temperature fluctuation and desuperheating with con-densing shock pulses. When a weak magnetic field was applied, the temperature fluctua-tion was enhanced by natural convection, the incipient boiling superheat was reduced, and the boiling pattern became continuous. With increasing the magnetic field strength, the fluctuation was suppressed and the incipient boiling superheat increased but tended to level off around 1.5 T. Violent incipient boiling caused by a large superheat inherent in liquid metals was mitigated by magnetohydrodynamic interaction under a transverse magnetic field of 1.0 T or larger, and subsequently followed by continuous saturation boiling with small fluctuation. No burn-out of the heater pin occurred in spite of symptom of dryout within the experimental range : g =67 W/cm² and B=1.5 T.

View full abstract

The effect of neutron irradiation on the iodine stress corrosion cracking (SCC) of Zircaloy-2 tubing of 8×8 type design was studied by means of ring tension test, using specimens unirradiated and irradiated to 3.2×10¹⁹ and 3.0×10²⁰ n/cm² (E>1 MeV). The SCC threshold stresses were determined from constant load tests and the SCC initiation stresses were defined from constant cross-head rate tests. Both stresses increased with increasing neutron fluence, reaching a maximum at a neutron fluence between 1019 and 10²⁰ n/cm² and then decreased. The tendency is qualitatively in good agreement with the hypothetical conclusion derived by Lunde & Videm, for SCC failure stresses from internal gas pressurization tests on various Zircaloy cladding tubes irradiated at different reactor conditions. The cause of the increase in the SCC susceptibility at neutron fluences above 10²⁰ n/cm² would be ascribed to radiation anneal hardening phenomenon and resultant inhomogeneous incipient deformation characterized by dislocation channels.

View full abstract

The general properties of discrete eigenvalues of the one-speed neutron transport equa-tion with quadratically anisotropic scattering are studied analytically. We investigate the asymptotic behaviors of boundary curves of the complex discrete eigenvalues carefully and plot the distribution of the discrete eigenvalues in parameter space. Our predictions agree with numerical calculation

View full abstract

The concentration profiles of ²²²Rn in the soil air are measured at several selected sites in different parts of Japan, together with the 226Ra concentrations in soil, ²²²Rn escape-to-production ratios of soil and the characteristic physical properties of the soil. The re-sulting data are used to derive the vertical soil concentration profile of ²²²Rn, which is found to differ distinctly from site to site. Measurements are also made of the concentra-tions in soil of ²³²Th and ⁴⁰K.
Based on these data, the exposure rates due to the nuclides in the soil are calculated for a level 1 m above ground at each site. The lowering of exposure rate due to the dif-fusion loss of ²²²Rn is estimated to be 213% of the total exposure rate due to naturally occurring radionuclides in the soil.

View full abstract