Basic formulas to describe the propagation of a periodically modulated driving source are derived on the distributed model of at-power reactors.
Disturbances in the neutron field are regarded as being promptly spread over the whole core in the frequency domain of usual interest for noise and frequency response analyses. On the basis of this approximation, a coupled set of kinetic equations for neutrons, fuel and coolant temperature is derived and solved for the case where a driving source of unit strength is imparted. The relations between the solutions obtained and the formulas for analyzing experiments are established. Comparisons are made qualitatively between the results and those of the lumped model. The existence of a sink and a resonance frequency is examined. The power spectral density of neutron fluctuations in a water reactor under forced circulated cooling shows a sharply varying configuration when the inlet coolant temperature fluctuations are the major noise sources. When the reactor is under natural convective cooling or under liquid metal cooling, no such characteristic features appear.

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The effect of boron compound additives on hydrazine formation in the radiolysis of an aqueous solution of ammonia has been studied. Suitable boron compounds such as NH₄BF₄ and C₂H₅NH₂BF₃ were used as source of ¹⁰B(n, α)⁷Li reaction. Ammonium hydroxide containing an additive was irradiated with thermal neutrons in the reactor KUR, When NH₄BF₄ was added to 15M ammonium hydroxide, the yield of hydrazine depended on the boron concentration but did not depend on the irradiation time. On the other hand, hydrazine formed in the presence of C₂H₅NH₂BF₃ had a maximum value at about 5×10²¹eV/ml absorption dose. The characteristics of the added boron compounds are discussed with comparisons made between radiolysis incited by in-pile and ⁶⁰Co γ irradiation. The effects of the additives are explained in terms of the hot atom effect of ¹⁰B(n, α)⁷Li reaction and the protecting effect of the resulting Lewis type acid, which inhibits the decomposition of hydrazine by scavenging the •H and •NH₂ radicals.

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A new difference equation for the numerical solution of the one-dimensional diffusion equation was obtained by using a semi-analytic method, in which the only approximation employed is that the source distribution within a mesh-region is represented by a linear function.
A test program, EXX-1, was prepared and run for BWR calculations, and comparisons were made with the conventional method. The results show that by using the new difference equation, a very coarse mesh model (1 mesh point per material region) can be applied without seriously impairing the computational accuracy.
It is also shown that the conventional difference equation becomes identical to the new expression if group-constants are multiplied by correction factors and the treatment of the source term appropriately modified.
New difference equations for spherical and cylindrical geometries are also given, in an appendix.

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Approximate solutions to the one-velocity time dependent neutron transport equation are derived by means of the eigenfunction expansion method of Case for a slab geometry. A finite set of discrete time eigenvalues is determined by a simple formula. This formula, which is derived for the case of large slab thickness, is found to be valid also for fairly thin slabs. Each time eigenvalue generates a pair of spatial modes. The expansion coefficients to these modes are examined by numerical evaluation for various slab thicknesses. Higher spatial modes are found to play an important role in the transient time evolution of neutrons.

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In airborne radioiodine monitoring, it is essential to establish an effective sampling technique that gives results independent of the form taken by the radioiodine and that works effectively under high humidity. Experiments were made to improve the performance of an iodine sampler embodying (a) cellulose asbestos filter paper (Toyo Roshi, Type HE-40) and activated charcoal filter paper (Toyo Roshi, Type CP-20) and (b) HE-40 filter paper and activated charcoal cartridge (Toyo Roshi, Type CHC-50). Based on the results, a new sampler was devised in which the air is heated to 70°∼90°C before reaching the filters. The dependence of the collecting efficiency on the chemical form taken by the airborne iodine and also on the duration of sampling period was studied.
Severe conditions of environment, such as high humidity, were simulated in the experimental apparatus. The airborne radioiodine used was a mixture of inorganic and organic iodides, identified by radio-gaschromatography. It was found that the collecting efficiency of the sampler with activated charcoal cartridge and the activated charcoal filter paper, respectively, exceeded 99.5% and 85%, regardless of the form of airborne iodine even at 100% relative humidity throughout the whole range of sampling duration up to 16hr. Under conditions of high humidity, the collecting efficiencies were found superior to that of charcoal filter paper and charcoal cartridge impregnated with TEDA or SnI₂ used without air heating.

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In the determination of ²³⁹Pu deposited in the lungs of exposed subjects by external "in vivo" counting, some corrections must be made for the calibration factor obtained from a phantom, to take account of differences in body size between the phantom and the exposed subjects. Three such correction factors were considered in this work, and determined experimentally: (1) the geometrical efficiency of the exposed subject was estimated using lung-shaped plane sources of actual size; (2) the shielding effect of the sternum and ribs viewed by the NaI(Tl)-detector of large area was measured from chest X-ray plates of the fifteen subjects; and (3) the effective chest wall thickness was evaluated by means of an empirical formula. Estimations of ²³⁹Pu in the lungs are expected to contain errors up to about 24.8%, due to the uncertainities in these correction factors.

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To measure the gas pressure in fuel pins during irradiation, a null-balance type pressure sensor embodying bellows and a self-regulating apparatus was devised. An innovation applied to the device was the method of sealing with alumina plug the end of the mineral-insulated cable constituting the lead wire for conveying the signals from the pressure sensor. After verifying by out-of-pile test that the gas pressure could be measured up to 70kg/cm²G, with error within ±2.4%, an irradiation capsule was prepared in which a fuel pin containing UO₂-pellets and the pressure sensor were accommodated, and it was irradiated during three cycles of JMTR operation. The pressure sensor and the controller worked-satisfactorily, the gas pressure being recorded through the three cycles of reactor operation. The applicability of this technique to practical measurements of gas pressure in fuel pins was thus established.

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