Search

A novel method for measuring dead time in nuclear pulse processing circuitry has been developed using the autocorrelation measurement capability of the Nuclear Weapons Inspection System (NWIS). Initially developed for active neutron interrogation of nuclear weapons and other fissile assemblies, NWIS employs a custom gallium arsenide application specific integrated circuit and a new signature analysis software package to simultaneously acquire and display the autocorrelation and cross-correlation spectra of up to five detector/electronics systems. The system operates at clock frequencies up to 1 GHz, permitting the collection of timing pulses in bins as narrow as 1 ns. In normal operation NWIS uses well characterized detectors and constant fraction discriminators, but it may also be configured to accept pulses from any circuit and to use the autocorrelation spectrum to accurately determine dead-time. Unlike traditional dead-time assessment techniques that typically require multiple sources and an assumed dead-time model, NWIS provides single measurement assessment of circuit dead time and does not require an assumed dead-time model or a calibrated high count-rate source.

Electrostatic turbulence has been investigated in the edge region of the Advanced Toroidal Facility (ATF). A reversal in the poloidal phase velocity of the fluctuations has been observed (velocity shear) which determines a characteristic plasma radius. The location of this shear layer depends on the magnetic configuration, the limiter radius and the plasma conditions. Using the shear position as a reference point, the density fluctuation levels in ATF (currentless stellarator) are very similar to those previously reported in TEXT (ohmically heated tokamak), suggesting that the plasma current is not an important drive for the edge turbulence. The drives for the turbulence appear to be different inside and outside the shear location (ashear), with e/Te 1) and possibly larger e/Te in the plasma edge edge (r/ashear < 1). There is a spatial decorrelation in the fluctuations at the shear location; this suggests that the poloidal shear flow has an important influence on the edge turbulence. The poloidal correlation length depends on local plasma parameters (e.g. velocity and temperature). When neutral beam injection is added, the high frequency components of n increase.

The implementation plans and preparations for installation of the Fissile Mass Flow Monitor (FMFM) equipment at the ElectroChemical Plant (ECP), Zelenogorsk, Russia, are presented in this report. The FMFM, developed at Oak Ridge National Laboratory, is part of the Blend Down Monitoring System (BDMS), developed for the U.S. Department of Energy Highly Enriched Uranium (HEU) Transparency Implementation Program. The BDMS provides confidence to the United States that the Russian nuclear facilities supplying the lower-assay ({approx}4%) product low enriched uranium (P-LEU) to the United States from down-blended weapons-grade HEU are meeting the nonproliferation goals of the government-to-government HEU Purchase Agreement, signed between the Russian Federation and the United States in 1993. The first BDMS has been operational at Ural Electrochemical Integrated Plant, Novouralsk, since February 1999 and is successfully providing HEU transparency data to the United States. The second BDMS was installed at ECP in February 2003. The FMFM makes use of a set of thermalized californium-252 ({sup 252}Cf) spontaneous neutron sources for a modulated fission activation of the UF{sub 6} gas stream for measuring the {sup 235}U fissile mass flow rate. To do this, the FMFM measures the transport time of the fission fragments created from the fission activation processmore » under the modulated source to the downstream detectors by detecting the delayed gamma rays from the fission fragments. The FMFM provides unattended, nonintrusive measurements of the {sup 235}U mass flow in the HEU, LEU blend stock, and P-LEU process legs. The FMFM also provides the traceability of the HEU flow to the product process leg. This report documents the technical installation requirements and the expected operational characteristics of the ECP FMFM.« less

In this paper the implementation plans and preparations for installation of the Fissile Mass Flow Monitor (FMFM) equipment at the Siberian Chemical Enterprise (SChE), Seversk, Russia, will be presented. The FMFM, developed by Oak Ridge National Laboratory (ORNL), is part of the Blend Down Monitoring System (BDMS) for the U.S. Department of Energy (DOE) Highly Enriched Uranium (HEU) Transparency Implementation Program (TIP). The BDMS provides confidence to the United States that the Russian nuclear facilities supplying the lower assay (~4%) product low enriched uranium (P-LEU) to the United States from down-blended weapon-grade HEU are meeting the nonproliferation goals of the 1993 HEU Purchase Agreement signed between the Russian Federation and the United States. The first BDMS has been operational at Ural Electrochemical Integrated Plant (UEIP), Novouralsk, since February 1999. The second BDMS became operational at Electro Chemical Plant (ECP), Zelenogorsk, in March 2003. These systems are successfully providing HEU transparency data to the United States. The third BDMS was successfully installed on the HEU down-blending tee in the SChE Enrichment Plant in October 2004. The FMFM makes use of a set of thermalized californium-252 ( 252 Cf) spontaneous neutron sources for modulated fission activation of the uranium hexafluoride (UF6) gas stream for measuring the 235 U fissile mass flow rate. To do this, the FMFM measures the transport time of the fission fragments created from the fission activation process under the modulated source to the downstream detectors by detecting the delayed gamma rays from the fission fragments retained in the flow. The FMFM provides unattended nonintrusive measurements of the 235 U mass flow of the UF6 gas in the blending tee legs of HEU, the LEU blend stock, and the resulting P-LEU. The FMFM also confirms that HEUF6 gas identified in the HEU leg flows through the blending tee into the P-LEU leg. This paper will discuss details of the SChE FMFM equipment characteristics as well as the technical installation requirements.

In this paper, a detailed design description and the performance characteristics are presented for the gamma ray detector system developed for the fissile mass flow monitor (FMFM) to be used on 8-in.-diam process pipes. The FMFM continuously measures the 235 U fissile mass flow rate of a UF6 gas stream. It uses moderated and modulated 252 Cf neutron sources for fission activation of the UF6 gas. Four pairs of bismuth germinate (BGO) scintillation detectors are placed around the process pipe (on the top, bottom, front, and back) downstream of the neutron sources so that a high detection efficiency can be achieved for measuring the delayed gammas (> 0.3 MeV) emitted from the fission fragments in the stream for the flow measurements. The BGO crystal was selected because it is a novel scintillation material (a rugged, nonhygroscopic, neutroninsensitive, high-density, and high-Z material) with high absorption (stopping) power and because it has high peak photoefficiency for high-energy gammas. Each 4-in.-diam, 2-in.-thick BGO scintillation crystal is coupled to a 3-in.-diam photomultiplier tube (PMT). Both are shielded with lead to reduce the background signal. Each detector pair is housed in a metal enclosure that also contains an electronics board for signal shaping and counting. The front-end electronics boards independently amplify and shape the detector signals before they are summed. The combined signal is then fed into two single-channel analyzers (SCAs), which separate the pulses into low- and high-energy bands and subsequently determine the count rate in each band. A local area network node for providing secure data transmission to the FMFM computer and a local temperature sensor are also parts of each detector electronics board. The temperature response of the detector signal resulting from the intrinsic temperature coefficient of each BGOPMT assembly is used for real-time corrections of the system by monitoring the 186-keV spectrum line of 235 U obtained with the lower-energy SCA. The lower-energy SCA is also scanned during manual detector energy calibration to capture 186- or 96-keV spectral lines from the UF6, depending upon its enrichment. The higher-energy SCA output provides for the measurement of the 0.3- to 2-MeV delayed gamma ray signal from the fission fragments in the UF6 stream.

A computer controlled detector/electronics module has been designed and constructed for the Oak Ridge National Laboratory fissile mass flow (FMF) monitor. The FMF monitor employs a host computer, a modulated neutron source (Cf-252) and four of the gamma-ray detector/electronics modules described here to non-intrusively measure liquid or gas fissile-mass-flow rates in a pipe. The gamma-ray detector/electronics modules each consist of a bismuth germanate/photomultiplier-tube scintillation detector, an integrating preamplifier, a bipolar spectroscopy amplifier, two single channel analyzers, a temperature sensor and an on-board network communications node. The host computer automatically calibrates amplifier gain and single-channel analyzer thresholds via the network using a characteristic emission peak of the material flowing in the pipe and corrects for detector gain variations due to the temperature coefficients of the bismuth germanate. The single channel analyzer output pulses are counted by a microprocessor on board the network node and reported to the host computer. The key components of the detector/electronics module are described and initial data obtained with the FMF monitor are presented.

We describe a high‐gain (∼107) amplifier for use with large‐area silicon photodiodes for monitoring the intensity of plasma light from fusion experiments. To achieve the necessary gain without saturating the output signal, the amplifier design incorporates a bootstrap technique and capacitive coupling between amplifier stages. This design eliminates voltage offset at the amplifier output due to detector leakage, while retaining desirable low‐frequency response characteristics.

An experimental scheme to extend the investigation of plasma turbulence has been implemented. It involves driving waves into the plasma to modify the statistical properties of the fluctuations; the dynamical balance of the turbulence is perturbed via the injection of waves at selected spectral regions. New analysis techniques based on conditional sampling and high order correlation are developed for studying the wave launching and the wave‐wave coupling processes. Experimental results from TEXT‐U tokamak show that the launched waves interact with the intrinsic fluctuations both linearly and nonlinearly. The attainment of driven nonlinearity is necessary for this diagnostic scheme to work. It is also the key to an active modification and control of edge turbulence in tokamaks.

A simple and inexpensive 4-mm direct reading fast (rise time approx. 100 ..mu..s) microwave interferometer is described. The system is particularly useful for density measurements on the ELMO Bumpy Torus (EBT) during pulsed operation.

A computer model (RIPPLE) was developed to examine the magnetic field ripple effects on plasma transport and on scaling in circular and noncircular tokamaks. Calculations include the radial and poloidal variation in the magnitude of the field ripple. Two main magnetic field computer programs were used to calculate the magnetic field due to current flowing in a coil of finite rectangular cross section: BFULT for tori of circular coils, and BOVAL for tori of noncircular coils. This paper presents the relevant results and discusses the criteria for the choice of the number of toroidal field coils for a given tokamak configuration.

This report summarizes the results of a recent ELMO Bumpy Torus (EBT) reactor study that includes ring and core plasma properties with consistent treatment of coupled ring-core stability criteria and power balance requirements. The principal finding is that constraints imposed by these coupling and other physics and technology considerations permit a broad operating window for reactor design optimization. Within this operating window, physics and engineering systems analysis and cost sensitivity studies indicate that reactors with approx. 6 to 10%, P approx. 1200 to 1700 MW(e), wall loading approx. 1.0 to 2.5 MW/m/sup 2/, and recirculating power fraction (including ring-sustaining power and all other reactors auxiliaries) approx. 10 to 15% are possible. A number of concept improvements are also proposed that are found to offer the potential for further improvement of the reactor size and parameters. These include, but are not limited to, the use of: (1) supplementary coils or noncircular mirror coils to improve magnetic geometry and reduce size, (2) energetic ion rings to improve ring power requirements, (3) positive potential to enhance confinement and reduce size, and (4) profile control to improve stability and overall fusion power density.

For a typical size ELMO Bumpy Torus (EBT) reactor (approx. 1000 MWe), microwave frequencies required lie in the range of 60 to 110 GHz at power levels of 50 to 75 MW. As the frequency rises, the unloaded cavity (i.e., without plasma) quality factor Q decreases. Because of the short wavelengths of microwave heating power and the large cavity dimensions of a reactor, it is possible to apply quasi-optical principles in the efficient coupling of power to the plasma. The use of a confocal Fabry-Perot resonator with spherical mirrors is discussed; these serve to confine the microwave power to the region occupied by the plasma. The potential advantages of these resonators include high efficiency utilization of microwave power, minimal thermal burden on the cryopumping system, and significant benefit in preventing microwave leakage from the device. An estimation of the unloaded cavity quality factor Q and the design considerations of Fabry-Perot resonator are given.

A simple and inexpensive 4‐mm direct reading fast (rise time∼100 μs) microwave interferometer is described. The system is particularly useful for density measurements on the ELMO Bumpy Torus (EBT) during pulsed operation.