[en] An analytical/experiment method was developed to monitor the subcritical reactivity and unfold the k/sub infinity/ distribution of a degraded reactor core. The method uses several fixed neutron detectors and a Cf-252 neutron source placed sequentially in multiple positions in the core. Therefore, it is called the asymmetric multiple position neutron source (AMPNS) method. The AMPNS method employs the nucleonic codes to analyze in two dimensions the neutron multiplication of a Cf-252 neutron source. The method uses the tilt independent asymmetric count rate ratios of two neutron detectors positioned at opposite sides of the core to determine the core k/sub eff/. An optimization program, GPM, has been utilized to unfold the K/sub infinity/ distribution of the degraded core, in which the desired performance measure minimizes the error between the calculated and the measured count rates of the degraded reactor core. The analytical/experimental approach was validated by performing experiments using the Penn State Breazeale TRIGA Reactor (PSBR). The experiments involved supercritical, critical and subcritical cores. A comparison of the experimental data with the analytical results showed good agreement, indicating the analytical model of the core used is valid

[en] The main purpose of a criticality alarm system (CAS) is to protect personnel by detecting a criticality event (neutron radiation) and actuating an alarm system to initiate emergency response. Inadvertent criticality alarms from noncritical events, such as spurious voltage spikes or intense gamma radiation fields, can produce work cessation and time-consuming and costly event assessments and may result in harm to personnel during an evacuation. It therefore becomes a major concern to ensure that inadvertent or false criticality alarms do not occur or at least are minimized. Minimization of inadvertent criticality alarms due to intense gamma radiation emitted from spent-nuclear-fuel (SNF) elements as opposed to neutron radiation from an actual criticality event is the primary focus of this calculational and experimental study. The Irradiated Fuel Storage Facility (IFSF) located at the Idaho National Engineering and Environmental Laboratory is a government-owned, contractor-operated facility whose mission is to provide safe handling and dry storage for various types of SNFs. Although other fuel types (lower burnup) are stored in the IFSF, it is the high-burnup elements with the associated intense gamma radiation fields that have the potential to inadvertently set off the criticality alarms in the fuel-handling area adjacent to the storage vault. Typically, in the fuel-handling cave or hot cell of the IFSF, the cask lid is removed, and individual fuel elements are extracted from the cask and placed in special storage canisters. It is during the time period when fuel elements are extracted from their casks or when fully loaded canisters are moved in the hot cell that the CAS detectors are exposed to the intense gamma radiation fields from the spent fuel. The neutron detectors positioned in one of the manipulator ports are designed such that fast neutrons from a criticality event are thermalized by a polyethylene moderator, strike the scintillator detector material, and generate a light pulse. The cluster is composed of three scintillator tubes bound tightly together in a lead sheath. The lead plug and sheath provide gamma radiation shielding, but unfortunately, the sheath design does not fully shield the tube axial length circumferentially. The top of the sheath is basically open and can allow SNF scatter gamma rays that penetrate the concrete wall to encounter and strike the scintillator material without attenuation. Despite the fact that the detector cluster is at the 13 ft 1 in. elevation above the IFSF floor 0 ft 0 in. elevation, the potential for this detector cluster to inadvertently alarm is real. The CAS detector has been designed with a 10,000:1 gamma rejection ratio and zero response above background in gamma radiation fields le10 rads/h. The authors solution to prevent inadvertent criticality alarms involves setting up an exclusion zone around the detectors. Individual elements or loaded canisters would be prohibited from entering the exclusion zone. Centered about the CAS and extending from the north wall into the hot cell and from the hot-cell ceiling to an elevation below the detector elevation, the exclusion zone boundaries and dimensions were determined analytically

[en] Flux wire measurements recorded during operation of the Advanced Test Reactor (ATR) were used to validate a three-dimensional (3D) PDQ model developed for the ATR physics analysis in the updated Final Safety Analysis Report (FSAR). The 3D PDQ benchmark analysis utilized the flux synthesis method as well as the explicit method in solving for the spatial flux distribution in the core. Measured data used for comparison were X-Y specific powers in flux wire monitors positioned at the core midplane of the forty fuel elements. Also used were measured data of axial specific power distributions in selected regions of the core for comparison to PDQ generated results. Additionally, ATR lobe ad fuel element powers derived from previously established weighting schemes were available for comparison with PDQ results. Good agreement was achieved in the X-Y-Z specific power comparison of the flux wire data in the fuel elements. However, the PDQ predictions were higher than the measured data in the flux traps because the PDQ model did not have the stainless steel (SS) tubes around the flux wire monitors. The SS tubes were used to position the flux wires. These tubes did not affect the axial profile which was well characterized by the PDQ model. Comparison of the results provided valuable data for the assessment of the 3D analytical model and techniques to be employed in the updated ATR FSAR physics analysis. The study also indicated that the PDQ 3D synthesis solution method is a surprisingly accurate and economical technique for determining global and/or local 3D flux/power distributions in the core. 4 refs., 8 figs., 1 tab

[en] Results of PARET/ANL and RELAP5/MOD2 computations on one of the Spert-IV tests are compared to select the code that best predicts the peak power and fuel plate temperature resulting from reactivity-induced transients for use in the University of Missouri Research Reactor (MURR) upgrade safety-related analysis. The D-12/25 core of the Spert-IV tests was selected for comparison because the test was performed under forced coolant circulation in a low-pressure and low-temperature environment, and this test used plate-type fuel as does MURR. The square-shaped D-12/25 core consisted of a 5 x 5 array of 20 fuel assemblies, 4 control rod assemblies, and 1 transient rod assembly. Control of the reactor was accomplished by the use of four boron/aluminum control rods, and the power excursion was initiated by a step reactivity addition established by ejecting the poison section of the transient rod from the core

[en] Recent program requirements of the US Department of Energy/NNSA have led to a need for a criticality accident alarm system to be installed at a newly activated facility. The Criticality Safety Group of the Lawrence Livermore National Laboratory (LLNL) was able to recover and store for possible future use approximately 200 neutron criticality detectors and 20 master alarm panels from the former Rocky Flats Plant in Golden, Colorado when the plant was closed. The Criticality Safety Group participated in a facility analysis and evaluation, the engineering design and review process, as well as the refurbishment, testing, and recalibration of the Rocky Flats criticality alarm system equipment to be used in the new facility. In order to demonstrate the functionality and survivability of the neutron detectors to the effects of an actual criticality accident, neutron detector testing was performed at the French CEA Valduc SILENE reactor from October 7 to October 19, 2010. The neutron detectors were exposed to three criticality events or pulses generated by the SILENE reactor. The first excursion was performed with a bare or unshielded reactor, and the second excursion was made with a lead shielded/reflected reactor, and the third excursion with a polyethylene reflected core. These tests of the Rocky Flats neutron detectors were performed as a part of the 2010 Criticality Accident Alarm System Benchmark Measurements at the SILENE Reactor. The principal investigators for this series of experiments were Thomas M. Miller and John C. Wagner of the Oak Ridge National Laboratory, with Nicolas Authier and Nathalie Baclet of CEA Valduc. Several other organizations were also represented, including the Y-12 National Security Complex, Lawrence Livermore National Laboratory, Los Alamos National Laboratory, CEA Saclay, and Babcock International Group.

[en] A method has been developed to monitor the subcritical reactivity and unfold the k/sub infinity/ distribution of a degraded reactor core. The method uses several fixed neutron detectors and a Cf-252 neutron source placed sequentially in multiple positions in the core. It is called the Asymmetric Multiple Position Neutron Source (AMPNS) method. The AMPNS method employs the nucleonic codes to analyze in two dimensions the neutron multiplication of a Cf-252 neutron source. Experiments were performed on the Penn State Breazeale TRIGA Reactor (PSBR). The first set of experiments calibrates the k/sub infinity/'s of the fuel elements moved during the second set of experiments. The second set of experiments provides a means for both developing and validating the AMPNS method. Several test runs of optimization calculations have been made on the PSBR core assuming one of the subcritical configurations is a damaged core. Test runs of the AMPNS method reveals that when the core cell size and source position are correctly chosen, the solution converges to the correct k/sub eff/ and k/sub infinity/ distribution without any oscillations or instabilities. Application of the AMPNS method to the degraded TMI-2 core has been studied to provide some initial insight into this problem

[en] The most important objective of the Comet Nucleus Sample Returm Mission is to return samples which could reflect formation conditions and evolutionary processes in the early solar nebula. It is expected that the returned samples will consist of fine-grained silicate materials mixed with ices composed of simple molecules such as H₂O, NH₃, CH₄ as well as organics and/or more complex compounds. Because of the exposure to ionizing radiation from cosmic-ray, gamma-ray, and solar wind protons at low temperature, free radicals are expected to be formed and trapped in the solid ice matrices. The kind of trapped radical species together with their concentration and thermal stability can be used as a dosimeter as well as a geothermometer to determine thermal and radiation histories as well as outgassing and other possible alternation effects since the nucleus material was formed. Since free radicals that are known to contain unpaired electrons are all paramagnetic in nature, they can be readily detected and characterized in their native form by the Electron Spin Resonance (ESR) method. In fact, ESR has been shown to be a non-destructive, highly sensitive tool for the detection and characterization of paramagnetic, ferromagnetic, and radiation damage centers in terrestrial and extraterrestrial geological samples. The potential use of ESR as an effective method in the study of returned comet nucleus samples, in particular, in the analysis of fine-grained solid state icy samples is discussed

[en] The inductively coupled plasma (ICP) device is one of the high-density plasma sources being used for the present integrated circuit etching process on an ultra-large scale. Here, we develop a Fokker-Planck code for the ICP source, and evaluate an electron energy diffusion coefficient based on the solution of the wave equations for an ICP reactor. The electron energy distribution function (EEDF) dependence on various external parameters, such as wave frequency, gas pressure and magnetic field, is investigated using the Fokker-Planck code. The effects of changing external parameters on ICP heating characteristics are also discussed. It is shown that the heating of low-energy electrons is enhanced with increasing system collisionality, which is defined as the ratio of collision frequency to effective wave frequency

[en] Partition function of diatomic molecular gases can be obtained directly from statistical mechanics form. And then, it is get to be Helmholtz free energy, internal energy, entropy and specific heat capacity is given by partition function of quantum statistic form that made up energy of rotation, vibration and electronics excitation. (Author)

[en] The effects of uranium, amine and sulfuric acid concentrate, and temperature on the extraction of uranium(VI) from acidic sulphate solutions by Amberlite Lsub(A-1) in benzene was studied. The extraction of sulfuric acid by Amberlite Lsub(A-1) in benzene was also examined. It was found that 92 to 98 percent extraction was obtained for a uranyl sulphate solution of 5g/1 concentrate containing of 0.2M to 0.3M sulfuric acid, a Amberlite Lsub(A-1) of 5 to 10 percent (weight) in benzene, at a temperature of less than 20⁰C. The mechanism of uranium extraction was discussed on the basis of the resluts obtained. (author)