Christopher C. Preston

Proton and alpha particle response characteristics of CR-39 polymer for reactor and dosimetry applications

Proton and alpha particle response characteristics of CR-39 polymer for reactor and dosimetry applications have been investigated. The investigation included measurement of track etch rate as a function of proton and alpha particle energy. A calibration curve of track diameter versus proton energy is presented. The promising capabilities for reactor proton spectrometry and passive fast-neutron personnel dosimetry techniques are discussed.

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.

Applications of solid state track recorder neutron dosimetry for fuel debris location in the three mile island unit 2 makeup and purification demineralizers

Abstract As a result of the Three Mile Island Unit 2 (TMI-2) accident on March 28, 1979, fuel debris was dispersed into the primary coolant and auxilliary systems of the reactor. The presence of fuel may be traced by using the neutron activity which is associated with the burn-in of higher actinides (about 300 neutrons/sec/kgU). Solid state track recorder (SSTR) neutron dosimetry is the most sensitive technique for measuring low neutron fluxes. Hence, neutron dosimetry is being performed at TMI-2 to locate fuel debris and subsequently aid the reactor recovery effort. Herein, the results of a scoping measurement on the fuel content of TMI-2 Makeup Demineralizer A are reported along with relevant calibration measurements. The total amount of fuel estimated in Demineralizer A, 1.7 kg, corresponds to a total neutron source of about 500 neutrons/sec. At the detector positions, data were obtained with neutron fluxes as low as 10-3 n/sec/cm2, demonstrating the extreme sensitivity of the SSTR method.

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.

Light water reactor pressure vessel surveillance dosimetry using solid state track recorders

Abstract The accumulation of neutron dose by the pressure vessel of an operating nuclear power plant results in damage in the form of steel embrittlement. For example, the ductile to brittle transition temperature increases with increasing damage. To ascertain the safe operating lifetime of the reactor pressure vessel, dosimetric measurements must be made to evaluate the neutron dose to the pressure vessel which is then used to estimate cumulative radiation damage. Advanced dosimetry techniques, including solid state track recorder (SSTR) techniques, are being evaluated for surveillance of operating reactors. Low neutron fluence calibration and standardization measurements using SSTRs in pressure vessel mockup benchmark neutron fields in the U.S.A., Belgium, and England are described. In addition, high fluence SSTR dosimetry capsules have been irradiated with metallurgical specimens in a pressure vessel mockup facility. The design and deployment of advanced SSTR dosimetry capsules in operating power reactors are also described.

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...

Annealing of alpha particle tracks in cellulose nitrate

Abstract An annealing study of α-tracks in cellulose nitrate has been conducted. Annealing temperatures between 20 and 60°C were used for time durations up 1024 h. Annealing of both normally incident and isotropic α-tracks were observed. A calibration curve was obtained relating isotropic α-track density loss to time-temperature annealing history in cellulose nitrate. Results of the study imply that annealing effects must be quantitatively addressed in health physics applications of α-sensitive solid state nuclear track detectors (SSNTD). The higher than statistical uncertainty that exists in environmental radon monitoring can, in large measure, be explained by lack of accurate corrections for annealing. Annealing data obtained in this study show that the range of applicability of passive temperature monitoring with cellulose nitrate extends down to approximately 30°C. Extension of the lower bound of SSNTD passive temperature monitoring should be possible through application of SSNTDs that possess higher sensitivity than cellulose nitrate.

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.

SOLID-STATE TRACK RECORDER NEUTRON DOSIMETRY IN LIGHT WATER REACTOR PRESSURE VESSEL SURVEILLANCE MOCKUPS

Sol id-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’s (NRC) Light Water Reactor Pressure Vessel Surveillance Dosimetry Improvement Program (LWR-PV-SDIP).

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.