Nuclear Regulatory Requirements Research Articles

Assessing the master curve reference temperature T0 estimated from the Charpy impact transition curve and consequences on the correlation between Charpy DBTT- and fracture toughness T0-shifts

Integrity assessment of reactor pressure vessels of light water reactors follows well established procedures relying on the surveillance program and defined by codes, standards and nuclear regulatory requirements. These procedures were developed in times where scientific knowledge was limited increasing therefore conservative safety margins to overcome the scientific shortcomings.Taking profit from the development of a number of test techniques and evaluation, it is possible nowadays to propose an alternative interpretation of the test results that provides a complementary information to the standard regulatory approach. In this work, the focus is on the Charpy impact test as it plays a critical role in surveillance programs monitoring reactor vessel degradation induced by neutron irradiation. The development of methodologies allowing experimental determination of fracture toughness from small size specimens triggered alternative approaches of extracting fracture toughness from the Charpy impact test. One of those approaches was recently successfully developed using the instrumented Charpy impact test from which the dynamic and static fracture toughness can be estimated with a reasonably good accuracy. This paper aims to provide an equally performant but simplified procedure allowing estimation of the master curve reference temperature, T0, from the Charpy impact transition curve applied to a large variety of reactor materials and irradiated conditions.

A New Low-Activity Nuclear Density Gauge for Soil Density Measurements

Abstract For decades, nuclear density gauges have been used to measure the density and moisture content of soil during compaction testing in road and embankment construction. Worldwide regulatory agencies consider nuclear density gauges as controlled devices because of their inclusion of radioisotope sources. Regulatory requirements, such as the need for licensing, special storage, special transportation procedures, gauge operator training, and personal dosimetry, have become burdens for gauge users. Recently, a new nuclear density gauge for measuring soil wet density was declared exempt from licensing and other nuclear regulatory requirements in the United States. The new gauge uses an extremely low-activity radioisotope source. It further incorporates a separate probe operating on electromagnetic principles for soil moisture measurement or any other moisture measurement method the user desires. This paper presents the design features and measurement properties of this low-activity nuclear density gauge and its associated moisture probe. The measurement properties were determined from laboratory and field studies that were conducted in North Carolina, United States. These studies showed that the sensitivity and precision of wet density measurements made by the low-activity nuclear density gauge were similar to those made by a conventional nuclear density gauge. The wet density measurements made by the low-activity gauge and conventional gauge showed a strong correlation and agreement. For the two field sites studied, a silty sand subbase and a cement-treated aggregate base course, the dry density agreement between the low-activity nuclear density gauge/moisture probe and the conventional nuclear density gauge was within 3 lb/ft3 (48 kg/m3).

Localization for Breast Surgery: The Next Generation.

- Preoperative localization of nonpalpable breast lesions using image-guided wire placement has been a standard of breast imaging, diagnosis, and treatment since its development in the 1970s. With this technique, coordinated, same-day wire placement by the radiologist and surgery are required, which can lead to significant inefficiencies in workflow. Other disadvantages of wire localization (WL) include limitations in surgical incision and dissection route and protruding wires that can be both bothersome for the patient and have risk of displacement. - To outline several recently developed techniques that could replace traditional WL and eliminate its disadvantages. The first developed was radioactive seed localization (RSL) using I-125, a technique adopted by many institutions during the last few years. The challenge to this method, however, is the strict nuclear regulatory requirements, which can be a significant burden and limitation. The disadvantages of WL and RSL have provided incentive for the development of other types of preoperative localization procedures. Two of these are recently US Food and Drug Administration-cleared, nonradioactive, non-wire location technologies emerging as alternatives to WL and RSL; SAVI SCOUT (Cianna Medical Inc, Aliso Viejo, California), which uses infrared light and a microimpulse radar reflector, and Magseed (Endomagnetics Inc, Austin, Texas), which uses a magnetic seed for localization. - We review the published literature on non-wire location technologies for breast tissue resection. - Non-wire location techniques are beneficial, allowing image-guided placement before the day of surgery and resulting in improved workflows. These techniques also eliminate bothersome protruding wires, risk of dislodging, and allow the incision site to be independent from the localization site.

Prediction of Radionuclide Inventory for the Low- and Intermediate-Level Radioactive Waste Disposal Facility by the Radioactive Waste Classification

To meet nuclear regulatory requirements, more than 95% individual radionuclides in the low- and intermediate-level radioactive waste inventory have to be identified. In this study, the radionuclide inventory has been estimated by taking the long-term radioactive waste generation, the development plan of disposal facility, and the new radioactive waste classification into account. The state of radioactive waste cumulated from 2014 was analyzed for various radioactive sources and future prospects for predicting the long-term radioactive waste generation. The predicted radionuclide inventory results are expected to contribute to secure the development of waste disposal facility and to deploy the safety case for its long-term safety assessment.

Advantages of variance reduction techniques in establishing confidence intervals for quantiles

Over the past two decades, U.S. nuclear power plant regulation has increasingly depended on best-estimate plus uncertainty safety analyses. As a result of the shift to best-estimate analyses, the distribution of the output metric must be compared against a regulatory goal, rather than a single, conservative value. This comparison has historically been conducted using a 95% one-sided confidence interval for the 0.95-quantile of the output distribution, which is usually found following the technique of simple random sampling using order statistics (SRS-OS). While SRS-OS has certain statistical advantages, there are drawbacks related to the available sampling schemes and the accuracy and precision of the resulting value. Recent work has shown that it is possible to establish asymptotically valid confidence intervals for a quantile of the output of a model simulated using variance reduction techniques (VRTs). These VRTs can provide more informative results than SRS-OS. This work compares SRS-OS and the VRTs of antithetic variates and Latin hypercube sampling through several experiments, designed to replicate conditions found in nuclear safety analyses. This work is designed as an initial investigation into the use of VRTs as a tool to satisfy nuclear regulatory requirements, with hope of expanded analyses of VRTs in the future.

Comparison of 99mTc activity measurements at LNMRI using SIRTI of the BIPM, a new instrument for comparing short-lived radionuclides

Technetium-99mTc is the most widely used radionuclide for obtaining diagnostic imaging in nuclear medicine and its demand is growing every year. In order to provide metrological traceability to producers and end users in Brazil to fulfil nuclear regulatory requirements for radiopharmaceuticals, National Laboratory of Ionizing Radiation Metrology/Institute of Radioprotection and Dosimetry attended, in 2013, an activity comparison measurement of 99mTc through BIPM Transfer Instrument SIRTI. The measurement results and the degree of equivalence between the key comparison reference value and LNMRI value are presented. The LNMRI result agreed with the measured value by SIRTI within one standard uncertainty.

Sensitivity in volcanic hazard assessment for the Yucca Mountain high-level nuclear waste repository site: The model and the data

Both advocates and critics disagree on the significance and interpretation of critical geological features which relate to the safety and suitability of Yucca Mountain as a site for the construction of a high-level radioactive waste repository. Recent volcanism in the vicinity of Yucca Mountain is recognized readily by geologists and others with a knowledge of nuclear regulatory requirements as an important factor in determining future public and environmental safety. We regard basaltic volcanism as direct and unequivocal evidence of deep-seated geologic instability. Direct disruption of a repository site by basaltic volcanism therefore is a possibility. In this paper, sensitivity analysis of volcanic hazard assessment for the Yucca Mountain site is performed, taking into account some significant geological factors raised by experts. Three types of models are considered in the sensitivity data analysis. The first model assumes that both past and future volcanic activities follow a Homogeneous Poisson Process (HPP). The second model uses a Weibull Process (WP) to estimate the instantaneous recurrence rate based on the historical data at NTS (the Nevada Test Site). The model then switches from a WP of past events to a predictive HPP. The third model assumes that the prior historical trend based on a WP would continue for future activities. Hazards (at least one disruptive event during the next 10,000 years) using both classical and Bayesian approaches are evaluated based on the data for the following two observation periods: Pliocene and younger, and Quaternary. Combinations of various counts of events at volcanic centers of controversy and inclusion (or exclusion) of the youngest date at Lathrop Wells Center (=0.01 Ma) generate 90 different data sets. Sensitivity analysis is performed for each data set and the minimum and the maximum hazards for each model are summarized. We conclude that the estimated overall probability of at least one disruption of a repository at the Yucca Mountain site by basaltic volcanism during the next 10,000 years is bounded between 2.02×105 and 6.57×10−3.

Integrated software system for seismic evaluation of nuclear power plant structures

This paper describes the capabilities and theoretical bases of the computer software CARES (Computer Analysis for Rapid Evaluation of Structures) developed by the Brookhaven National Laboratory (BNL) for the U.S. Nuclear Regulatory Commission. The development of CARES represents an effort to utilize established numerical methodologies commonly employed by industry for structural safety evaluations of nuclear power plant facilities and incorporate them into an integrated computer software package operated on personal computers (PC). CARES was developed with the objective to include all aspects of seismic performance evaluation of nuclear power structures, thereby it can be used to evaluate the validity and accuracy of analysis methodologies used for structural safety evaluations of nuclear power plants by various utilities. CARES is structured in a modular format, each module performing a specific type of analysis. This paper describes the features which have been implemented into the seismic module of CARES. The seismic module integrates the capabilities required to accomplish all steps of a complete seismic analysis into a single package with many user-friendly features such as interactiveness and quick turnaround. Linear structural theory and pseudo-linear convolution theory are utilized as the bases for the development with a special emphasis on the areas of nuclear regulatory requirements pertaining to structural safety of nuclear plants. The organization of the seismic module is arranged in eight options, each performing a specific step of the analysis with most of input/output interfacing processed by the general manager. Finally, CARES provides comprehensive post-processing capability to display results graphically or in tabular form so that direct comparisons can be easily made.