John K. Hartwell

Comparison between digital and analog pulse shape discrimination techniques for neutron and gamma ray separation

Recent advancements in digital signal processing (DSP) using fast processors and a computer allows one to envision using it in pulse shape discrimination. In this study, we have investigated the feasibility of using a DSP to distinguish between neutrons and gamma rays by the shape of their pulses in a liquid scintillator detector (BC501). For neutron/gamma discrimination, the advantage of using a DSP over the analog method is that in an analog system, two separate charge-sensitive ADCs are required. One ADC is used to integrate the beginning of the pulse rise time while the second ADC is for integrating the tail part. In DSP techniques the incoming pulses coming directly from the detector are immediately digitized and can be decomposed into individual pulses waveforms. This eliminates the need for separate ADCs as one can easily get the integration of two parts of the pulse from the digital waveforms. This work describes the performance of these DSP techniques and compares the results with the analog method.

High-resolution Compton-suppressed CZT and LaCl/sub 3/ detectors for fission products identification

Room temperature semiconductor CdZnTe (CZT) detectors are currently limited to total detector volumes of 1-2 cm3, which is dictated by the poor charge transport characteristics. Because of this size limitation, one of the problems in accurately determining isotope identification is the enormous background from Compton scattering events. Eliminating this background will not only increase the sensitivity and accuracy of measurements, but will also help to resolve peaks buried under the background and peaks in close vicinity of others. We are currently developing a fission products detection system based on the Compton-suppressed CZT and LaCl3(Ce) detectors. In this application the detection system is required to operate in a high radiation field. Therefore, a small 10 mm times 10 mm times 5 mm CZT and Oslash13 mm times 15 mm LaCl3 detector are placed inside the center of a well-shielded Oslash76 mm by 76 mm long NaI detector. So far, we have been able to successfully reduce the Compton background by a factor of 3.7 to 4.0 for a 137Cs spectrum. In this work, we will discuss the performance of this detection system using both CZT and LaCl3 detectors. The results are compared with MCNP calculations.

Design and Expected Performance of the AGR-1 Fission Product Monitoring System (FPMS)

The effluent from each test capsule of the AGR-1 experiment will be monitored by a detector system consisting of a gamma-ray spectrometer and a gross radiation detector. This collection of radiation measurement systems will be known as the AGR-1 Fission Product Monitoring System (FPMS). Proper design and functioning of the FPMS is critical to the success of the AGR-1 fuel test experiment.This document describes the AGR-1 FPMS and presents calculations indicating that this design will meet the pertinent test requirements.

Installation and Final Testing of an On-Line, Multi-Spectrometer Fission Product Monitoring System (FPMS) to Support Advanced Gas Reactor (AGR) Fuel Testing and Qualification in the Advanced Test Reactor

The US Department of Energy (DOE) is initiating tests of reactor fuel for use in an Advanced Gas Reactor (AGR). The AGR will use helium coolant, a low-power-density graphite-moderated core, and coated-particle fuel. A series of eight (8) fuel irradiation tests are planned for the Idaho National Laboratorys (INLs) Advanced Test Reactor (ATR). One important measure of fuel performance in these tests is quantification of the fission gas releases over the nominal 2-year duration of each irradiation experiment. This test objective will be met using the AGR Fission Product Monitoring System (FPMS) which includes seven (7) online detection stations viewing each of the six test capsule effluent lines (plus one spare). Each station incorporates both a heavily-shielded high-purity germanium (HPGe) gamma-ray spectrometer for quantification of the isotopic releases, and a NaI(T1) scintillation detector to monitor the total count rate and identify the timing of the releases. The AGR-1 experiment will begin irradiation in December 2006. To support this experiment, the FPMS has been completely assembled, tested, and calibrated in a laboratory at the INL, and then reassembled in its final location in the ATR reactor basement. This paper presents the details of the equipment performance, the control and acquisition software, the installation in the ATR basement, and the test monitoring plan.

Fission Product Monitoring of TRISO Coated Fuel for the Advanced Gas Reactor-1 Experiment

The US Department of Energy has embarked on a series of tests of TRISO-coated particle reactor fuel intended for use in the Very High Temperature Reactor (VHTR) as part of the Advanced Gas Reactor (AGR) program. The AGR-1 TRISO fuel experiment, currently underway, is the first in a series of eight fuel tests planned for irradiation in the Advanced Test Reactor (ATR) located at the Idaho National Laboratory (INL). The AGR-1 experiment reached a peak compact averaged burn up of 9% FIMA with no known TRISO fuel particle failures in March 2008. The burnup goal for the majority of the fuel compacts is to have a compact averaged burnup greater than 18% FIMA and a minimum compact averaged burnup of 14% FIMA. At the INL the TRISO fuel in the AGR-1 experiment is closely monitored while it is being irradiated in the ATR. The effluent monitoring system used for the AGR-1 fuel is the Fission Product Monitoring System (FPMS). The FPMS is a valuable tool that provides near real-time data indicative of the AGR-1 test fuel performance and incorporates both high-purity germanium (HPGe) gamma-ray spectrometers and sodium iodide [NaI(Tl)] scintillation detector-based gross radiation monitors. To quantify the fuel performance, release-to-birth ratios (R/B’s) of radioactive fission gases are computed. The gamma-ray spectra acquired by the AGR-1 FPMS are analyzed and used to determine the released activities of specific fission gases, while a dedicated detector provides near-real time count rate information. Isotopic build up and depletion calculations provide the associated isotopic birth rates. This paper highlights the features of the FPMS, encompassing the equipment, methods and measures that enable the calculation of the release-to-birth ratios. Some preliminary results from the AGR-1 experiment are also presented.Copyright

Preliminary results of an on-Line, multi-spectrometer fission product monitoring system to support advanced gas reactor fuel testing and qualification in the advanced test reactor at the Idaho National Laboratory

The Advanced Gas Reactor-1 (AGR-1) experiment is the first experiment in a series of eight iow-enriched uranium oxycarbide tri-isotropic (TRISO) coated particle fuel (in compact form) experiments scheduled for irradiation in the Advanced Test Reactor (ATR) located at the Idaho National Laboratory (INL). The experiment began irradiation in the ATR with a cycle that reached full power on December 26, 2006 and will continue irradiation for about 2.5 years. Six separate test fuel capsules are being irradiated in an inert sweep gas atmosphere with on-line fission product monitoring of each capsules effluent to track fission gas emissions from the fuel during irradiation. The online fission product monitoring system incorporates 7 HPGe spectrometers and 7 Nal(Tl) gross radiation detectors to monitor and quantify the fission gas releases that are important indicators of fuel performance. Details of the design and operation of this detection system and the preliminary results of the fuel performance measurements are presented in this paper.

A comparison of the high count rate performance of several commercially available digital signal processors

Three commercial gamma-ray digital signal processors (DSPs), a Canberra InSpector 2000, an ORTEC DigiDART, and an X-ray Instrumentation Associates (XIA) Polaris system, coupled to a Canberra 2002C resistive-feedback preamplifier-equipped high-purity germanium (HPGe) detector, were performance tested to input rates of 440 kHz. This is a continuation study of work that was performed at the Idaho National Lab. In the first phase of this study the Canberra DSA2000 and the ORTEC DSPECPLUS were coupled to a transistor reset pre-amplifier (TRP) equipped HPGe gamma-ray detector and performance tested to input rates of 603 kHz. All spectrometers were evaluated on their throughput, stability and peak shape performance. The accuracy of their quantitative corrections for dead-time and pile-up were also tested. All of the tested units performed well at input rates that strain most analog spectroscopy systems