Nuclear Materials Storage Facility Research Articles

Evaluation of microbiologically influenced corrosion and biofouling in a nuclear storage basin

Biofouling and microbiologically influenced corrosion are major concerns to the long-term integrity of nuclear waste storage basins. The results of long-term microbial monitoring of nuclear storage at the Savannah River Site L-Basin nuclear material storage facility were examined to determine corrosion potential and biofouling. The densities of specific microbial species that can impact microbial corrosion and biofouling, including sulfate-reducing bacteria (SRB) and acid-producing (e.g., iron-oxidizing) bacteria (APB), were quantified by colony forming units (CFU). Several trends in microbial activity were observed during this time period. Overall microbial densities decreased slightly between 2000 and 2012. Metabolic diversity of microorganisms as measured by BIOLOG™ also decreased dramatically during this time. Aerobic microbial densities decreased from 2001 to 2010. Aerobes were most prevalent at 3.23 average CFU/mL and APB densities were lower at 0.80 average CFU/mL. From 2017 to present, iron-reducing bacteria were most prevalent at 3.41 average CFU/mL and APB were least prevalent at 0.44 average CFU/mL. All bacterial densities decreased except that of low-nutrient bacteria, which averaged 2.90 CFU/mL, and SRB averaged 0.19 CFU/mL. No distinct correlations between microbial concentrations, temperature, and either water chemistry parameters (pH and conductivity) or radiological conditions (19–30 disintegrations per minute (DPM) beta-gamma/mL; the equivalent to 0.32–0.50 Bq per mL) were determined. The occurrence of microbial biofilm formation on storage cannisters created biofouling issues in recent years. Although cleaning the biofouled surfaces provided temporary relief, the biofouling returned. Based on these results and physical observations of coupons, there has been minimal evidence of corrosion to date.

Importance of location dependencies such as cable and pipe runs when identifying the vital areas

Abstract Vital area analysis study and its application for nuclear facilities have been performed since the late 1970s. The Korea Atomic Energy Research Institute (KAERI) has performed a development of VAI methodology since the early 2000s, and the Vital area Identification Package Expert (VIPEX) was developed to identify vital areas using the conventional Probabilistic Safety Assessment (PSA) models, including internal and external PSA models. This study is to demonstrate the applicability of KAERI's VAI methodology to a hypothetical facility containing processes that could have unacceptable onsite and offsite consequences if interrupted due to a security threat, and to identify the importance of location dependencies, such as cable and pipe runs, when identifying the vital areas. The hypothetical facility is assumed to be a nuclear material processing and storage facility in order to identify the vital areas. The target sets and Top Event Prevention Sets (TEPS) are calculated by two conditions: the first condition is to analyze the target sets and TEPS with information of the cable and pipe runs, and the second is to analyze them without it. It is necessary to consider cable and pipe runs in order to determine accurate and realistic TEPS. If the information about cable and pipe runs of a nuclear power plant is not considered when determining TEPS, it is absolutely impossible to acquire complete TEPS, and the results are distorted. When determining TEPS, it is more efficient, and requires lower costs than other methods using location fault trees to use the plant-specific internal and external PSA models including the information of cable and pipe runs.