An application of approximated decoupling control to a coupled-core nuclear reactor is described, which permits noninteractive regulation of the power level in the individual cores of a reactor that requires to be controlled with account taken of the interference between the cores. The control possesses the advantages of easy design and simple struc-ture of an approximated decoupling controller.
The controller is constituted of a precompensator and an output feedback compensator. The control function is ensured with the precompensator playing a key role in approxi-mately diagonalizing an open-loop transfer-function matrix in the frequency range of interest. The precompensator is devised by pseudo-diagonalization, the method being generalized by the authors for application to a wide frequency range.
Digital simulations and graphical studies based on the Gershgorin band analysis demon-strate the effectiveness of the approximated decoupling controller as well as the applicability of the generalized pseudo-diagonalization method. Sample results are compared with those obtained by the decoupling theory.

View full abstract

Some test calculations were carried out to demonstrate the usefulness of double-differen-tial cross sections for neutron transport calculations including anisotropic scattering. A transport code system NITRAN was applied for the purpose. In NITRAN, the anisotropy of elastic and inelastic scattering can be treated in a general form by double-differential total neutron-emission cross sections, which are generated from single-differential and/or original double-differential cross section data base.
The test calculations were performed for neutron flux spectra in aluminum and lead slabs, and also f, or tritium production rates in a natural lithium sphere. Since the treat-ment free from collision kinematics is possible by using the double-differential cross sections in the S_n calculations, the discretization of secondary neutron energy distribution becomes independent of the segmentation of angular distribution. A significant improvement due to this independence can be seen in calculating the anisotropy of general inelastic scatter-ing and the extreme anisotropy of elastic scattering by heavy nuclei. For precise aniso-tropic transport calculations, it is therefore concluded that the nuclear data of double-dif-ferential type are more suitable than those of single-differential type.

View full abstract

Previously pressurized (pre-pressurized) fuel rod tests recently performed in the Nuclear Safety Research Reactor (NSRR) investigate the effects of initial internal pressure on fuel rod behavior during reactivity initiated accident (RIA) conditions. A single PWR type fuel rod was contained within a waterfilled, ambient temperature and ambient pressure capsule. The fuel rod was then heated by the pulsing operation of the NSRR.
Results from the tests show that the effect of pre-pressurization was significant for the fuel rods with initial internal pressure of 0.8 MPa and above, and fuel rod failure occurred from rupture of the cladding with lower threshold energy deposition for failure as the initial internal pressure was increased, The cladding rupture was governed mainly by the cladding temperature rise, not by the rod internal pressure rise during the transient. The relationships between cladding burst pressure and cladding burst temperature and between cladding strain and cladding temperature at cladding rupture obtained in the present study under an RIA condition agree with the results obtained from various in- and ex-reactor ex-periments under a LOCA condition, although the obtained time-averaged strain rate of the Zircaloy cladding was much greater than that in a LOCA condition.

View full abstract

In order to study how the operating pressure has influence on the heavy water separa-tion characteristics for a pair of dual temperature multistage-type H₂/H₂O-exchange columns, the authors utilized the analytical expressions derived from the finite difference equation describing the material balance in the exchange column. The separation characteristics of the system were studied theoretically under the conditions where the temperature in a hot column t_h=200°C, the pressure in a hot column π ?? 50 atm and the pressure in a cold column π=550 atm.
As the results, the optimum modified specific column volume v^*_opt decreases with the increase of π and then keeps the nearly constant value, and is smaller at π=50 atm than at π =30 atm in the case where the temperature in a cold column t_c is constant. Other important parameters such as the optimum operating temperature in a cold column t_copt, the optimum numbers of stages in a hot column M_opt and in a cold column N_opt, the optimum hydrogen to feed water molar flow ratio r_opt and the optimum degradation ratio δ_opt were also calculated.

View full abstract

Containment spray tests for elemental iodine vapor removal were conducted under simulated BWR LOCA condition with large-scale JAERI Model Containment. The tests were carried out to determine the behavior of gas phase iodine removal by spray water containing carbonic acid, the mixing effect in the sump pool, and iodine deposition onto the containment wall.
In the tests, a half-life of the iodine concentration decrease in gas phase was obtained as 6-12 min and an iodine partition coefficient was also obtained as 80160 by the spray washout under pH range of 5.35.9. The effect on the mitigation of pH decrease of spray water caused by the iron corrosion process was discussed from the experiments. Results obtained from the tests were compared with those calculated by a code MIRA-PB.

View full abstract

Effect of TBP on the extraction of Pu (IV), Zr (IV), Nb(V), Nd (III) and Am (III) was studied with diisodecylphosphoric acid (DIDPA) as an extractant. Hydrolyzable elements contained in the high-level liquid waste of fuel reprocessing, i. e. Pu (IV), Zr (IV) and Nb (V), could be extracted with mixtures of DIDPA and TBP of different compositions. Addition of TBP to DIDPA causes an increase and a decrease of respectively distribution rate and ratio of Zr (IV). These elements extracted were completely stripped with the aid of oxalic acid. An effect of TBP on separation of transplutonides(III) from lanthanoids(III) in the DIDPA and DTPA extraction system was also studied.
Based on the results, a process flow sheet utilizing the extractant of DIDPA and TBP mixture was contrived for partitioning actinoids in the high-level liquid waste.

View full abstract