James H. Roberts

Annealing phenomena in solid state track recorders

Abstract Accepted descriptions of the annealing process in Solid State Track Recorders (SSTR) are reviewed with emphasis on current misconceptions. In particular, it is shown that the Arrhenius equation should not be used to describe the decrease in observable track density induced by annealing. Results of annealing experiments in different SSTR media are examined. On this basis, a general reaction rate theory of the annealing process in SSTR is advanced. This formalism is used to introduce the new concept of the energy per etchable detect for SSTR. An important qualitative outgrowth of this work is the establishment of a general sensitivity-annealing correlation for SSTR. Observed annealing induced correlations between track size and track density for fission fragments are readily understood in terms of this general theory. Qualitative explanations of current enigmas in SSTR cosmic ray work are also advanced.

The status of automated nuclear scanning systems

Abstract Present day minicomputers and microprocessors enable a range of automation, from partial to total, of tasks once thought beyond approach. The status of three computer controlled systems for quantitative track measurements is reviewed. Two systems, the Hanford optical track scanner (HOTS) and an automated scanning electron microscope (ASEM) are used for scanning solid state track recorders (SSTR). The third system, the emulsion scanning processor (ESP), is an interactive system used to measure the length of proton tracks in nuclear research emulsions (NRE). Current limitations of these systems for quantitative track scanning are presented. Experimental uncertainties attained with these computer controlled systems are described using results obtained from reactor neutron dosimetry.

Application of solid state track recorder neutron dosimetry for three mile island unit 2 reactor recovery

Abstract Application of neutron dosimetry for assessment of fuel distribution throughout the Three Mile Island-2 (TMI-2) reactor core region and the primary coolant system is advanced. Neutron dosimetry in the reactor cavity, i.e. the cavity between the pressure vessel and the biological shield, could provide data for the assessment of the core fuel distribution. A more immediate task entails locating and quantifying the amount of fuel debris in the ex-core primary coolant system in the range of 1 to 1000 kg. Solid state track recorder (SSTR) neutron dosimetry is considered for such exploratory scoping experiments at TMI-2. The sensitivity of mica- 2 3 5 U (asymptotically thick) SSTR has been ascertained for such environments. For plausible geometric assumptions and environmental conditions, it has been demonstrated that the SSTR method has adequate sensitivity to properly respond and detect fuel quantities of the order of 1 kg in the ex-core primary coolant system.

Interactive system for scanning tracks in nuclear research emulsions

A computer‐based interactive system has been developed and successfully used for scanning proton‐recoil tracks in nuclear research emulsions. To our knowledge, this system is the first truly interactive system developed and used for emulsion scanning. Interfaces have been developed between the three fundamental interacting entities, namely man, microscope, and computer. Computer codes can be developed for different applications, thereby providing wide flexibility and versatility. Use of this system for neutron metrology is described. Differential neutron spectrometry as well as integral neutron dosimetry have been carried out in both 4π and unidirectional neutron fields. Results are presented which quantify the accuracy attained with this system for each of these different neutron measurement emulsion techniques. This system provides a substantial advance in the state‐of‐the‐art of emulsion scanning in terms of both accuracy and cost effectiveness. The ability to store, in computer memory, all relevant em...

Light water reactor pressure vessel surveillance using reactor cavity solid state track recorder neutron dosimetry

Abstract Solid State Track Recorder (SSTR) Neutron Dosimeters have been developed for use in power reactors to provide information on the cumulative neutron dose received by the reactor pressure vessel during operation. The accumulation of neutron dose by the pressure vessel results in radiation damage in the form of steel embrittlement. In order to ascertain the safe operating lifetime of the reactor pressure vessel, the results of dosimeter measurements are evaluated and used to estimate the extent of radiation damage. Among the requirements for SSTR neutron dosimetry are high accuracy and ability to provide useful data at high neutron fluences. To this end, ultra low-mass fissionable deposit preparation techniques have been developed, and the absolute accuracies of the measurements have been maintained at the 3–5% level. The status of the deployment of SSTR dosimetry capsules in the reactor cavity region of operating power reactors will be summarized.

Characterization of Fuel Distribution in the Three Mile Island Unit 2 (TMI-2) Reactor System by Neutron and Gamma-Ray Dosimetry

Neutron and gamma-ray dosimetry are being used for nondestructive assessment of the fuel distribution throughout the Three Mile Island Unit 2 (TMI-2) reactor core region and primary cooling system. The fuel content of TMI-2 makeup and purification Demineralizer A has been quantified with Si(Li) continuous gamma-ray spectrometry and solid-state track recorder (SSTR) neutron dosimetry. Results obtained from these gamma- ray and neutron dosimetry experiments were 1.3 ± 0.6 kg and 1.7 ± 0.6 kg, respectively, for the fuel content of TMI-2 Demineralizer A.

Automatic scanning of solid state track recorders: Calibration

Abstract A computer controlled microscope has been upgraded for the automatic scanning of solid- state track recorders. The system has been calibrated by using Muscovite mica exposed in direct contact with thin deposits of 2 4 2 Pu on stainless steel backing. These deposits were uniform in density and of accurately known mass. Calibrations were carried out for exposure ranging from 3.6 × 10 4 to 6.8 × 10 5 fissions cm -2 . Repeated scans generally give a reproducibility ∼2%. The scanning time for an area of 1.3 cm 2 varies from 30 min for low track densities up to a few hours for high track densities. Further upgrading of the system to increase speed and accuracy is planned.

Automated scanning of solid state track recorders: Computer controlled microscope

Abstract A computer controlled microscope for rapid processing of solid state nuclear track recorders is described. Specimen stage movements and autofocusing are controlled by stepping motors. A videcon camera and high speed digitizer produce the digital image for computer analysis. Processing times for a 1.3 cm2 track recorder range from 45 to 150 min depending on track density. Track counting accuracy of 2 – 3 percent is readily achievable with the automated system.

Solid state track recorder fission rate measurements at high neutron fluence and high temperature

Abstract Solid State Track Recorder (SSTR) techniques have been used to measure 239Pu, 235U, and 237Np fission rates for total neutron fluences approaching 5 × 1017 n cm-2 at temperatures in the range 680–830°F. Natural quartz crystal SSTRs were used to withstand the high temperature environment, and ultra low-mass fissionable deposits of the three isotopes were required to yield scannable track densities at the high neutron fluences. The results of these high temperature, high neutron fluence measurements are reported.

Solid state track recorder fission rate measurements in low power light water reactor pressure vessel mockups

Abstract Solid State Track Recorder (SSTR) measurements of neutron-induced fission rates have been made in several pressure vessel mockup facilities as part of the U.S. Nuclear Regulatory Commission sponsored Light Water Reactor Pressure Vessel Surveillance Dosimetry Improvement Program. These measurements have been made at U.S., Belgian, and British facilities which have been designed to replicate various aspects of light water reactor core, water gap, thermal shield, pressure vessel and reactor cavity geometries. The results of SSTR fission rate measurements, comparisons of these measurements with other techniques, and comparisons to theoretical calculations are presented.