Solid State Track Recorders Research Articles

A Reliable Simple Automatic Micrometric Scanner for Counting the Fission Fragment Tracks

The design, construction and application of a counting system using simple automatic micrometric scanner (AMS) device for fission fragment tracks (FFT) are described in detail. The system is used to detect the etched fission fragment tracks in thin plastic solid state track recorders (SSTRs) (12 m thickness). The track-detection mechanism is based on scanning concentric circles of specimen rather than the usual XY scanning methods. The circumference of the circle can be traversed to within plusmn2 mum and the reproducibility of the rotation is within 0.001deg. The difference in the radii of the concentric circles is preset in the range of 1 to 99999 mum. The system is capable of obtaining reliable results for the track densities up to 2 times 104 tracks/cm2 and normal-incidence irradiations. The counting efficiency of the system is about 97% compared to visual methods employing a microscope equipped with CCD device, gas permeation technique and spark gas chambers for track densities up to the just-mentioned figure.

The light transmission method of automated track scanning

An empirical method of automated track scanning is described. This new method is based on the measurement of light transmission (LT) through solid state track recorders (SSTR). Fission fragment tracks in mica SSTR are used to demonstrate the utility of this method. Data analysis reveals that the LT method is equivalent to a point sampling method at the approximately 2% (1 σ) uncertainty level of the calibration data. The total (1 σ) uncertainty of the LT method decreases with increasing fission density from approximately 5% at a fission density of 4.0E + 06 fissions/cm 2 down to approximately 2.5% at a fission density of 1.2E + 07 fissions/cm 2. The current stage of development permits only a qualitative comparison of the LT and point sampling methods. Recommendations to refine the LT method are advanced with emphasis on processing procedures for mica SSTR.

98/03334 Analysis and elimination of trace organic compounds in smoke from burning coal: Wang, X.-H. et al. Gaodeng Xueriao Huaxue Xuebao, 1997, 18, (1), 24–28. (In Chinese)

Solid-state track recorder (SSTR) neutron dosimetry has been conducted in the Three-Mile Island Unit 2 (TMI - 2) reactor cavity (i.e., the annular gap between the pressure vessel and the biological shield) for nondestructive assessment of the fuel distribution. Two axial stringers were deployed in the annular gap with 17 SSTR dosimeters located on each stringer. SSTR experimental results reveal that neutron streaming, upward from the bottom of the reactor cavity region, dominates the observed neutron intensity. These absolute thermal neutron flux observations are consistent with the presence of a significant amount of fuel debris lying at the bottom of the reactor vessel. A conservative lower bound estimated from these SSTR data implies that at least 2 tonnes of fuel, which is roughly 4 fuel assemblies, is lying at the bottom of the vessel. The existence of significant neutron streaming also explains the high count rate observed with the source range monitors (SRMs) that are located in the TMI-2 reactor cavity.

Critical requirements for a posteriori track recorder neutron dosimetry at Hiroshima and Nagasaki

International programs have been carried out over the last four decades to quantify the exposure of atom bomb survivors from Hiroshima and Nagasaki. Unfortunately, the quest for accurate gamma-ray and neutron exposure doses of atom bomb survivors has proven illusive. In the most recent of these programs, designated as Dosimetry System 1986 (DS86), a serious and persistent discrepancy has arisen between neutron transport calculations and radiometric (RM) neutron dosimetry for the Hiroshima site, which has been called the DS86 neutron dosimetry enigma. A recently completed in-depth analysis demonstrates that a simple single factor panacea does not exist to explain the DS86 neutron dosimetry enigma. Careful treatment of a number of specific experimental and calculational effects is required before any progress can be achieved. Within this perspective, the applicability of solid state track recorder (SSTR) neutron dosimetry for the Hiroshima and Nagasaki sites is examined as an independent alternative to radiometric (RM) neutron dosimetry. The utility of the SSTR method for the Hiroshima and Nagasaki sites is analyzed in light of: (i) the current status of the DS86 neutron dosimetry enigma; and (ii) SSTR characteristics that are specifically germane to the Hiroshima and Nagasaki sites. On this basis, critical SSTR requirements are identified, recommended ways of meeting these critical requirements are advanced and the domain of applicability of SSTR neutron dosimetry at the Hiroshima site is estimated.

Advances in high fluence solid state track recorder neutron dosimetry

Neutron dosimeters based on measurements of neutron-induced fission rates with solid state track recorders (SSTRs) provide a versatile and accurate method for reactor dosimetry applications. The high fluence upper limit of the range of the SSTR neutron dosimetry method is determined by track counting limitations at very high track densities. The recent development of techniques for the preparation and calibration of ultra low-mass fissionable deposits has extended the high-fluence limit to about 5×10 18 neutrons/cm 2 . To date, more than 900 SSTR neutron dosimeters have been exposed in high neutron fluence applications at commercial nuclear power reactors. At the same time, parallel efforts have been carried out to further extend the range of the SSTR neutron dosimetry technique, to improve the precision of the present methods, and to verify the high accuracy of the method through controlled exposures in standard neutron fields. The present status of high fluence SSTR neutron dosimetry techniques as well as recent improvements in the method will be discussed.

Reaction rate measurements for nuclear reactor analyses and critically data

Neutron reaction rate measurements with solid state track recorders (SSTR) and radiometric (RM) neutron dosimeters have been conducted at the Pacific Northwest Laboratory (PNL) Critical Mass Laboratory (CML) as part of the U.S. Department of Energy (DOE) and the Power Reactor and Nuclear Fuel Development Corporation of Japan (PNC) Critically Data Development Program. These reaction rate measurements represent benchmark data that can rigorously test the adequacy of neutron transport calculations performed for nuclear reactor analyses as well as for critically safety assessments. In the 220 series of experiments, fast test reactor (FTR) plutonium fuel pins were assembled in a 0.761 cm square lattice array, which was immersed in an organic moderator. In-fuel and in-moderator dosimetry measurements were conducted near axial midplane. To obtain results at a single axial location, corrections were applied for the spatial variation (axial buckling) of the reaction rates. For the in-fuel measurements, dosimeters were placed between fuel pellets thereby creating gaps in the fuel pin column. Consequently, for these in-fuel measurements, the gap-perturbation effect was measured so that reaction rate data could be corrected to zero fuel gap, i.e. the reaction rates in the unperturbed fuel. Experimental uncertainties range from a low of 2–3 percent for U-238 and Th-232 fission rates to a high of 15–16 percent for U-238 capture rates. The uncertainty in the U-238 (n, Σ) moderator results is dominated by the uncertainty in the neutron self-shielding correction factor, which has been estimated to be approximately 15 percent. Uncertainties in U-235, Np-237 and Pu-239 fission rates range from approximately 4 to 7 percent. These latter uncertainties are larger than uncertainties normally achievable in SSTR neutron dosimetry and reflect the fact that the quality of the SSTR electrodeposits prepared for these isotopes was not completely satisfactory. Least-squares spectral analyses of these data were performed with the FERRET-SAND II computer code. These analyses confirm the general consistency of the experimental data and furnish absolute neutron fluxes with assigned uncertainties.

The effect of gamma irradiations on etching characteristics of some solid state track recorders

Abstract Solid state nuclear track recorders viz. CR-39 plastic, glass and phlogopite mica pre-exposed to 252Cf fission fragments are irradiated with gamma doses varying from 50 K rad to 50 M rad in order to study the effect of gamma irradiation on etching characteristics of these detectors. It is found that all these detectors are dose rate dependent. CR-39 is found to be more sensitive to gamma rays then any other solid state track recorder.

Pressure vessel surveillance at commercial light water reactors using solid state track recorder neutron dosimetry

Abstract The accumulation of neutron dose by the pressure vessel of a light water reactor results in radiation damage in the form of steel embrittlement. In order to ascertain the safe operating lifetime of the reactor pressure vessel, the neutron dose must be monitored. Solid state track recorder neutron dosimeters have been developed for pressure vessel surveillance dosimetry at commercial power reactors. To date a total of more than 200 neutron dosimeters from seven different power reactor dosimetry exposures have been analyzed, and more than 150 additional dosimeters are currently deployed. The techniques for carrying out these measurements and thier results will be discussed.

On the measurement of integral data in thermally driven LWHCR lattices

Abstract Integral reaction rate ratios and other k∞ -related measurements were carried out in Light Water High Converter Reactor (LWHCR) test lattices with different moderator states. The reaction rates were measured using fission chambers, foil activation or solid state track recorders. The main problems were associated with foil effects in the rodded, wet lattices. The estimated uncertainties on the various measured and evaluated integral data are discussed.

Solid state track recorder neutron dosimetry in a simulated basalt geological waste repository

Solid State Track Recorder (SSTR) techniques have been developed for neutron dosimetry applications related to geological storage of radioactive waste. The neutron irradiation environment of spent fuel stored in a simulated basalt geological waste repository was investigated using SSTR neutron dosimetry capsules which contained low mass deposits of fissionable isotopes in contact with mica SSTRs. After exposure for a period of years, the capsules were recovered and the mica SSTRs were retrieved and analyzed. The measured fission rates and derived neutron energy and fluence information are reported.

Neutron dosimetry in the three-mile island unit 2 reactor cavity with solid-state track recorders

Solid-state track recorder (SSTR) neutron dosimetry has been conducted in the Three-Mile Island Unit 2 (TMI - 2) reactor cavity (i.e., the annular gap between the pressure vessel and the biological shield) for nondestructive assessment of the fuel distribution. Two axial stringers were deployed in the annular gap with 17 SSTR dosimeters located on each stringer. SSTR experimental results reveal that neutron streaming, upward from the bottom of the reactor cavity region, dominates the observed neutron intensity. These absolute thermal neutron flux observations are consistent with the presence of a significant amount of fuel debris lying at the bottom of the reactor vessel. A conservative lower bound estimated from these SSTR data implies that at least 2 tonnes of fuel, which is roughly 4 fuel assemblies, is lying at the bottom of the vessel. The existence of significant neutron streaming also explains the high count rate observed with the source range monitors (SRMs) that are located in the TMI-2 reactor cavity.

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

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 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.

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

Solid State Track Recorder (SSTR) techniques have been used to measure 239 Pu, 235 U, and 237 Np fission rates for total neutron fluences approaching 5 × 10 17 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.

Neutron dosimetry in high intensity fields: A review

During the past decade, the range of sensitivity of solid state track recorder neutron dosimeters has been extended significantly. Neutron dosimeters based on measurements of neutron-induced fission rates are limited in high intensity neutron fields by the maximum track density that can be accurately counted. The development of ultra low-mass fissionable deposit fabrication techniques has made possible the extension of solid state track recorder neutron dosimetry to much higher intensity neutron fields. Recent advances in neutron dosimetry in high intensity fields are reviewed and summarized, and the limitations of solid state track recorder neutron dosimetry at high neutron fluences are discussed.

Neutron dosimetry with solid-state track recorders in the three-mile island unit-2 reactor cavity

Solid-state track recorder (SSTR) neutron dosimetry has been conducted in the Three-Mile Island Unit-2 (TMI-2) reactor cavity (i.e., the annular gap between the pressure vessel and the biological shield) for nondestructive assessment of the fuel distribution. Two axial stringers were deployed in the annular gap with 17 SSTR dosimeters located on each stringer. SSTR experimental results reveal that neutron streaming, upward from the bottom of the reactor cavity region, dominates the observed neutron intensity. These absolute thermal neutron flux observations are consistent with the presence of a significant amount of fuel debris lying at the bottom of the reactor vessel. A conservative lower bound estimated from these SSTR data implies that at least 2 tonnes of fuel, which is roughly 4 fuel assemblies, is lying at the bottom of the vessel. The existence of significant neutron streaming also explains the high count rate observed with the source range monitors (SRMs) that are located in the TMI-2 reactor cavity.

Imaging of fast neutron sources using solid state track recorder pinhole radiography

Pinhole imaging methods are being developed and tested for potential future use in imaging the intense neutron source of the Fusion Materials Irradiation Test (FMIT) Facility. Previously reported, extensive calibration measurements of the proton, neutron, and alpha particle response characteristics of CR-39 polymer solid state track recorders (SSTRs) are being used to interpret the results of imaging experiments using both charged particle and neutron pinhole collimators. High resolution, neutron pinhole images of a 252Cf source have been obtained in the form of neutron induced proton recoil tracks in CR-39 polymer SSTR. These imaging experiments are described as well as their potential future applications to FMIT.

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

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.

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

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/cm 2, demonstrating the extreme sensitivity of the SSTR method.

Some unique applications of solid state track recorder autoradiography in the nuclear industry

CR-39 solid state track recorder alpha autoradiography has been applied to the inspection of sectioned weld samples of parts containing plutonium. In addition to determining the amounts of plutonium present, information on the distribution and physical form of the plutonium has been obtained. In a separate application, autoradiographic methods developed previously for analysis of airborne actinide aerosols are extended to the analysis of fuel debris at TMI-2. Autoradiographic determination of the alpha decay rate and thermal neutron induced fission rate allows the 239Pu/ 235U ratio to be calculated on a particle-by-particle basis. This ratio is in turn dependent on local power density in the reactor core. Correlations of the 239Pu/ 235U ratio with particle size should provide useful data on mechanisms for core degradation and transport through the primary coolant system of the reactor.