Evaluation of the /sup 252/Cf-source-driven neutron noise analysis method for measuring the subcriticality of LWR fuel storage casks

The /sup 252/Cf-source-driven neutron noise analysis method was evaluated to determine if it could be used to measure the subcriticality of storage casks of burnt LWR fuel submerged in fuel storage pools, fully loaded and as they are being loaded. The motivation for this evaluation was that measurements of k/sub eff/ would provide the parameter most directly related to the criticality safety of storage cask configurations of LWR fuel and could allow proper credit for fuel burnup without reliance on calculations. This in turn could lead to more cost-effective cask designs. Evaluation of the method for this application was based on (1) experiments already completed at a critical experiments facility using arrays of PWR fuel pins typical of the size of storage cask configurations, (2) the existence of neutron detectors that can function in shipping cask environments, and (3) the ability to construct ionization chambers containing /sup 252/Cf of adequate intensity for these measurements. These three considerations are discussed

A portable measurement system for subcriticality measurements by the CF-source-driven neutron noise analysis method

A portable system has been assembled that is capable of measuring the subcriticality of fissile materials using the /sup 252/CF-source-driven neutron noise analysis method. The measurement system consists of a parallel-plate ionization chamber containing /sup 252/CF, two /sup 3/He proportional counters with their associated electronics, and a small computer containing anti-aliasing filters and A/D convertors. The system Fourier analyzes the digitized data and forms the appropriate auto and cross-power spectral densities. These spectra are used to form a ratio of spectral densities, G/sub 12/G/sub 13//G/sub 11/G/sub 23/, where 1 refers to the ionization chamber, and 2 and 3 refer to the /sup 3/He counters, from which subcriticality can be determined. The chamber and detectors are located appropriately near the fissile material. The system is capable of sampling signals at rates of up to 80 kHz and processing these data at rates of 2 kHz to form the appropriate spectra. The presently configured system is a two-channel system, hence the measurement of G/sub 12/, G/sub 13/, and G/sub 23/ must be done sequentially before the ratio of spectral densities is obtained. Future improvements of the system will allow simultaneous measurement of all spectra and will further reduce size, thereby enhancing portability. This measurement system can provide reliable, cost effective, and convenient determination of the subcriticality of a wide variety of fissile materials and moderators

Dry spent fuel cask monitoring by {sup 252}Cf-source-driven frequency analysis measurements

If developed, a nondestructive method would be useful for verifying canister contents without requiring the canister to be opened. This paper addresses the application of the {sup 252}Cf-source-driven frequency analysis measurements for verification of the fissile material content of sealed spent fuel canisters. The cross-power spectral density (CPSD) between the {sup 252}Cf source in an ionization chamber and external neutron detectors depends only on the induced fission rate in the fissile system and is independent of inherent sources. Thus the source-to-detector CPSD is ideal for determination of fissile material content of the spent fuel. This paper evaluates the application of this method to a 125 ton spent fuel canister that contained 21 pressurized-water reactor fuel elements. The results demonstrate that the fissile materials content of a sealed spent fuel canister could be obtained using the {sup 252}Cf frequency analysis method if calibration standards were available. The results also indicate that a measurement could be performed in less than a day for burnups up to 36 GWd/MTU and in less time for lower burnups

Characterization of an enriched uranyl fluoride deposit in a valve and pipe intersection using time-of-flight transmission measurements with {sup 252}Cf

A method was developed and successfully applied to characterize large uranyl fluoride (UO{sub 2}F{sub 2}) deposits at the former Oak Ridge Gaseous Diffusion Plant. These deposits were formed by a wet air in-leakage into the UF{sub 6} process gas lines over a period of years. The resulting UO{sub 2}F{sub 2} is hygroscopic, readily absorbing moisture from the air to form hydrates as UO{sub 2}F{sub 2}-nH{sub 2}O. The ratio of hydrogen to uranium can vary from 0--16, and has significant nuclear criticality safety impacts for large deposits. In order to properly formulate the required course of action, a non-intrusive characterization of the distribution of the fissile material within the pipe, its total mass, and amount of hydration was necessary. The Nuclear Weapons Identification System (NWIS) previously developed at the Oak Ridge Y-12 Plant for identification of uranium weapons components in storage containers was used to successfully characterize these deposits

Benchmarking criticality safety calculations with subcritical experiments

Calculation of the neutron multiplication factor at delayed criticality may be necessary for benchmarking calculations but it may not be sufficient. The use of subcritical experiments to benchmark criticality safety calculations could result in substantial savings in fuel material costs for experiments. In some cases subcritical configurations could be used to benchmark calculations where sufficient fuel to achieve delayed criticality is not available. By performing a variety of measurements with subcritical configurations, much detailed information can be obtained which can be compared directly with calculations. This paper discusses several measurements that can be performed with subcritical assemblies and presents examples that include comparisons between calculation and experiment where possible. Where not, examples from critical experiments have been used but the measurement methods could also be used for subcritical experiments

ISX objectives and physics

The ISX-B program has achieved average beta values of 1.8% in a relatively clean plasma with neutral beam injection power greater than 10 times ohmic power input. Total beta has increased smoothly with beam power so far and exceeded theoretical limits with no indication that ballooning or any other instability is significantly increasing the energy loss rate

Brief summary of unreflected and unmoderated cylindrical critical experiments with oralloy at Oak Ridge

This report lists and briefly describes {approximately}50 critical and {approximately}20 subcritical experiments with unreflected and unmoderated uranium (93.2 wt% {sup 235}U) metal that could easily be incorporated into the International Handbook of Evaluated Criticality Safety Benchmark Experiments. Photographs of several assemblies are included

Prompt alpha and reactivity measurements on fast metal assemblies

This paper summarizes and reviews the methods of reactivity determination and measurement of the prompt neutron decay, briefly describes the equipment requirements for such measurements for unmoderated and unreflected metal assemblies and presents experimental results to illustrate the methods. The primary reactivity determination methods used have been (1) stable reactor period measurements, which are usually used near delayed criticality to calibrate the reactivity prior to burst initiation, (2) prompt reactor period measurements which are useful to determine the reactivity early in the excursion, (3) inverse kinetics rod drop measurements which obtain the reactivity as a function of time after a rod or reactor component is removed from the assembly, and (4) prompt neutron decay constant measurements from which the reactivity can be obtained if corrections are made for changes in the neutron lifetime. Inverse kinetics and decay constant measurements are usually used below delayed criticality although decay constant measurements have been performed above delayed critical. (auth

Radiation Detection for Active Interrogation of HEU

This report briefly describes the neutrons and gamma rays emitted by active interrogation of HEU, briefly discusses measurement methods, briefly discusses sources and detectors relevant to detection of shielded HEU in Sealand containers, and lists the measurement possibilities for the various sources. All but one of the measurement methods detect radiation emitted by induced fission in the HEU; the exception utilizes nuclear resonance fluorescence. The brief descriptions are supplemented by references. This report presents some active interrogation possibilities but the status of understanding is not advanced enough to select particular methods. Additional research is needed to evaluate these possibilities

A small graphite-reflected UO{sub 2} assembly

An unmoderated, graphite-reflected, critical assembly of UO{sub 2}, enriched to 93.15 wt % in {sup 235}U, is described. The UO{sub 2} pellets (density, 9.71 g/cm{sup 3}) were contained in 253 1.27-cm-diam stainless steel tubes, which, in turn, are close packed in an aluminum container 22.87 cm in diameter and 31.11 cm long. This mockup of a small, potassium-cooled space power reactor, which was under study at Oak Ridge National Laboratory in 1963, provided data for validation of reactor physics methods. Two combinations of top and side reflectors were found to make the assembly critical. In one configuration, the thickness of the top and the side reflectors was 12.70 and 19.25 cm respectively; in the other, these dimensions were 5.08 and 24.34 cm. Fission distribution measurements axially through the assembly with the thicker radial reflector and radially through the reflector showed a peak in the reflector 3.5 greater than at the center of the core. The {sup 235}U cadmium ratio measured in the side reflector at the core midplane for the assembly with the 19.25-cm-thick side reflector varied from 1.77 near the core boundary to 2.43 beyond 10 cm into the side reflector