[en] The ^99m Tc is the more used radioisotope in nuclear medicine, used in 80% of procedures of nuclear medicine in the world. This is due to their characteristics practically ideal for the diagnostic. The ^99mTc is obtained by decay of the ⁹⁹Mo, which can produce it by irradiating enriched targets in ⁹⁸Mo, or as fission product, irradiating uranium targets or by means of homogeneous solution reactors. The pattern of the used reactor in the neutron analysis possesses a liquid fuel composed of uranyl nitrate dissolved in water with the attach of nitric acid. This solution is contained in a cylindrical recipient of stainless steel reflected with light water. The reactor is refrigerated by means of an helicoidal heat exchanger immersed in the fuel solution. The heat of the fuel is removed by natural convection while the circulation of the water inside the exchanger is forced. The control system of the reactor consists on 6 independent cadmium bars, with followers of water. An auxiliary control system can be the level of the fuel solution inside container tank, but it was not included in the pattern in study. One studies the variations of the reactivity of the system due to different phenomena. An important factor during the normal operation of the reactor is the variation of temperature taking to a volumetric expansion of the fuel and ghastly effects in the same one. Another causing phenomenon of changes in the reactivity is the variation of the concentration of uranium in the combustible solution. An important phenomenon in this type of reactors is the hole fraction in the nucleus I liquidate due to the radiolysis and the possible boil of the water of the combustible solution. Some of the possible cases of abnormal operation were studied as the lost one of coolant in the secondary circuit of the heat exchanger, the introduction and evaporation of water in the nucleus. The reactivity variations were studied using the codes of I calculate MCNP, WIMS and TORT. All the calculations show a safe neutronic behavior of this class of reactors with big negative reactivity coefficients. The burnt of the fuel and their effects in the reactivity is small considering the good production and efficiency. (Author)

[en] CRISPV (Criticality and Spectrum code) is a multigroup neutron spectrum code for homogeneous reactor cores and is actually a somewhat modified version of the original CRISP programme. It is a combination of DATAPREP-II and BIGG-II programmes. It is assumed that the reactor cell is a cylindrical fuel rod in the light or heavy water moderator. DATEPREP-II CODE forms the multigroup data for homogeneous reactor and prepares the input parameters for the BIGG-II code. It has its own nuclear data library on a separate tape in binary mode. BIGG-II code is a multigroup neutron spectrum and criticality code for a homogenized medium. It has as well its own separate data library. In the CRISPV programme the overlay structure enables automatic handling of data calculated in the DATAPREP-II programme and needed in the BIGG-II core. Both programmes are written in FORTRAN for CDC 3600. Using the programme is very efficient and simple

[en] Aqueous Homogeneous Reactor is a nuclear reactor with fuel solution and homogeneously mixed with a moderator and being developed as a means to produce medical isotopes. To perform its function of producing radioisotope, AHR will require radioisotope separation facility. In general, radioisotope separation facilities connected with AHR, will consist of several parts, such as extraction section, waste and gas management section, iodine separation section, purification section, delivery section and also the connecting sections. Results of the assessment shows that several safety related things needs to be considered for the radioisotopes separation facility of AHR. Exposure to high radiation from the fuel solution that will enter radioisotopes separation facilities will need a shielded room to hold or reduce exposure to workers. The use of materials particularly on the piping must be resistant to corrosion or against radiation. The potential leak or absorption gas saturation of iodine and other fission products also needs to be considered. It should also be noted related waste generated from this facility such as fuel solution, absorption materials, fission product gases, pipes or other process materials. (author)

No abstract available

[en] In this paper a general polynomial expression is obtained for the Bickley and Exponential integral functions (Kin and En, n 1-7), where only coefficients are different. These coefficients can be obtained, depending on the accuracy we require. One problem of a homogeneous reactor has been considered here where it is shown that a polynomial of limited accuracy also can give converged results, depending upon the problem. (author)

No abstract available

[en] One of the phenomena at Aqueous Homogeneous Reactor (AHR) of uranium solution fuel is radiolysis process that breaks the water molecules into oxygen and hydrogen gases by both neutron and gamma radiations. The reduction of water molecules in the solution causes the concentration of uranium solution increases and eventually leads to core reactivity change. As AHR is equipped with recombiner to recombine the oxygen and hydrogen gases into water, the fuel concentration will become lower. This will also induce core reactivity change. The periodic changes in reactivity due to fluctuation in uranium concentration will lead to power fluctuation. The paper aims at determining reactivity change due to the change in uranium concentration, and other reactivity change such as doppler effect. The analyses were performed using two Monte Carlo method codes, MCNP and MVP. For the reactor being analyzed, with power of 20 kW and 1 kW/l of power density, has the doppler reactivity coefficient -1,01 × 10-2 %dk/k. This system also has strong negative feedback reactivity from void generation. (author)

[en] Technetium-99m, which is generated from the decay of molybdenum-99, is the most commonly used medical radioisotope in the world. To produce molybdenum-99, nuclear reactor types namely aqueous homogeneous reactor (AHR) are being developed by many researcher. Although many AHRs-related research have been done, references that discuss the aspects of the material are rarely available. At the same time, material is one of important aspects to consider in designing AHR. In this case, one thing that needs to be investigated in relation to the structural integrity of AHR vessels is the stress caused by the pressure and temperature of the reactor operation. The design of vessels needs to consider many aspects such as normal operating conditions and also a possibility of accident or abnormal conditions. This research was performed through a computer simulation by using finite element method (FEM) available in ANSYS. The simulation results shows that pressure and temperature in the vessel affect the stress of the vessel material. Higher pressure and temperature in the vessel also makes the stress of the vessel material higher. However the equivalent (von-Mises) stresses obtained from all of the simulation are still below the yield strength of the AHR vessel material so that the integrity of the vessel is maintained. (author)

No abstract available

[en] In Mexico there is one operational research reactor, a 1 MW TRIGA reactor, and one operational subcritical facility. Another reactor, a SUR-100 homogeneous reactor, was decommissioned after shutdown in 1984, and another subcritical facility is in the condition of 'shut down'. A brief description of these reactors is given