Final Status Survey Research Articles

Uranium Mine Proposed Experimental Design for Natural Background Gross Gamma Exposure Rates, Post Remediation Final Status Survey Sampling Density, and Radiological Water Quality Modeling for a Worst-case Catastrophic Failure, Coles Hill, Virginia.

Completely randomized experimental design statistical modeling techniques were employed to analyze exposure rate measurements for evaluating hypothetical natural background post uranium mill operations at Coles Hill, Virginia uranium milling processes. The proposed Coles Hill Uranium Mine is situated upstream of the Banister River. This River is nearly homogenous throughout the reach length used in analysis and feeds into the mouth of Kerr Reservoir, Lake Gaston, which serves as the main drinking water source for cities in the Hampton Roads area including Norfolk, Virginia Beach, and Chesapeake. A critical scan value (=DCGLscan) was developed to flag anomalies of surface contamination during simulated post remediation final status surveys. The natural background was critical for meeting the Multi-Agency Radiation Survey and Site Investigation Manual guidance for post remediation final status surveys. The overarching null hypothesis suggested that the selected mean natural background is equal to the survey unit's mean natural background. Using SAS Procedures Shapiro-Wilk Test, ANOVA, and CR, it was decided the exposure rate data was normal, had no extreme outliers, and no collinearity between the number of samples (=treatment) and the areas (=block). Using the q-hyper (hypergeometric) distribution, the soil sampling density was decided for a final status survey unit. The most likely worst-case catastrophic failure analysis, 500-year event, such as the1969 Hurricane Camille of 69 centimeters of rain in Nelson County, Virginia was included in the model. The model showed impact was minimal at most to the Banister River's drinking water and likely less than the Virginia's Drinking Water Standards for gross alpha, 226Ra and 228Ra, and total uranium.

Novel approach to predicting the release probability when applying the MARSSIM statistical test to a survey unit with a specific residual radioactivity distribution based on Monte Carlo simulation

For investigating whether the MARSSIM nonparametric test has sufficient statistical power when a site has a specific contamination distribution before conducting a final status survey (FSS), a novel approach was proposed to predict the release probability of the site. Five distributions were assumed: lognormal distribution, normal distribution, maximum extreme value distribution, minimum extreme value distribution, and uniform distribution. Hypothetical radioactivity populations were generated for each distribution, and Sign tests were performed to predict the release probabilities after extracting samples using Monte Carlo simulations. The designed Type I error (0.01, 0.05, and 0.1) was always satisfied for all distributions, while the designed Type II error (0.01, 0.05, and 0.1) was not always met for the uniform, maximum extreme value, and lognormal distributions. Through detailed analyses for lognormal and normal distributions which are often found for contaminants in actual environmental or soil samples, it was found that a greater statistical power was obtained from survey units with normal distribution than with lognormal distribution. This study is expected to contribute to achieving the designed decision error when the contamination distribution of a survey unit is identified, by predicting whether the survey unit passes the statistical test before undertaking the FSS according to MARSSIM.

Theoretical basis for reduction of number of survey units of MARSSIM final status survey at decommissioning facilities

To investigate the effects of combining two survey units quantitatively in the final status survey of MARSSIM for a decommissioning facility, an expression for the sample size of combined survey unit was developed, which consists exclusively of related parameters of the two survey units. The simulation results using the expression showed that all combining cases considered always result in a decrease in the overall sample size and that it is beneficial to combine two survey units whose radiological characteristics are similar or not significantly different from each other to obtain more decrease in the overall sample size. The results also show that it is necessary to check the practicability of a specific combining case since not all the combined survey units have reasonable sample sizes to obtain. The results also implied that dividing a single survey unit into two separate survey units would result in an increase in the overall sample size.

Monte Carlo simulation for verification of nonparametric tests used in final status surveys of MARSSIM at decommissioning of nuclear facilities

In order to verify the statistical performance of the nonparametric tests used in the MARSSIM approach, all plausible contamination distribution types that can be encountered in a survey area should be investigated. As the first of such investigations, this study aims to perform the verification for normal distribution of the contamination in a survey area by simulating the collection of random samples from it through the Monte Carlo simulation. The results of the simulations conducted for a total of 81 simulation cases showed that Sign test and WRS test both exhibited an excellent statistical performance: 100% for the former and 98.8% for the latter. Therefore, in final status surveys of the MARSSIM approach, a high statistical performance can be expected in applying the nonparametric hypothesis tests to survey areas whose net contamination can be assumed to be normally distributed.

Proposal for the list of potential radionuclides of interest during NPP site characterization or final status surveys

In the research or project planning for the decommissioning of a nuclear power plant, one of several preparations will be the establishment of a list of potential radionuclides to be considered at the time of characterization or final status surveys. Reliable data for selection of potential radionuclides during the transition period to prepare for decommissioning will depend heavily on historical data at the site or, where possible, sampling analysis. However, during the transition period, direct sampling can be challenging, depending on the circumstances of the site or national regulation. A methodology of selecting potential radionuclides for nuclear facility sites which largely consists of three major processes: production of initial list of radionuclides, selection of the insignificant radionuclide that will be eliminated, and consideration of site characterization or sampling. For developing a preliminary list of potential radionuclides for Kori Unit 1 decommissioning, the list of initial radionuclides was made referring to the technical documents applied at decommissioned NPPs in the U.S and additional reference materials applied until the operation of NPPs in Korea. For the screening of insignificant radionuclides, we applied criterion of less than 0.1% of the amount of radioactivity inventory and confirmed the dose fraction using the RESRAD code. The final suit of radionuclides was established, which should be supplemented by reflecting site characterization and sampling process in the future. Thus, the methodology and results for the selection of potential radionuclides suggested in this paper can give an insight as a future reference to deriving DCGLs in relation to site remediation of decommissioning nuclear plants.

Probe area effect on performance of phoswich detectors for simultaneous alpha and beta detection

According to the Multi-Agency Radiation Survey and Site Investigation Manual, a site characterization and a final status survey are required to determine whether a potentially contaminated site satisfies the release criteria. Before conducting sampling at a site, direct measurements with a portable instrument to identify hotspot areas can provide an outline of the sampling plan to facilitate accurate analysis. As the instrument, a phosphor sandwich (phoswich) detector has the advantage of being able to detect alpha and beta rays simultaneously. In this study, large-area phoswich detectors with various probe sizes were fabricated, optimized, and calibrated to investigate variations in the minimum detectable concentration (MDC). To determine the optimal thickness of the light guide, commercially available optical design software LightTools was used to simulate light transport. Each phoswich detector was coupled to an optimal light guide to achieve the highest instrument efficiency. The proposed instrument was calibrated using 241Am, 90Sr/Y, 99Tc, and 14C radioactive sources, and experimental data were employed in the MDC calculation. Although it is well known that a large probe size improves the overall performance, the results indicated that probe sizes greater than 20 × 20 cm do not enhance instrument performance.

Theoretical comparative study of t tests and nonparametric tests for final status surveys of MARSSIM at decommissioning sites

Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) recommends the use of nonparametric tests (Sign test and WRS test) for designing final status surveys because of their robust statistical performance with data which do not show normal distribution. However, for a survey unit whose measurement data can be assumed to come from normal distribution, parametric tests such as t tests can generally provide a higher statistical power than nonparametric tests. To provide a theoretical basis for using t tests, sample sizes of final status surveys designed with t tests have been compared with those designed with nonparametric tests for practically conceivable hypothetical survey units. The results show that, to achieve the same level of statistical power, t tests require smaller sample sizes than their nonparametric equivalents with the maximum sample size reductions being about −70% for Sign test and −60% for WRS test.

An approach for determining reasonable sample sizes of MARSSIM final status surveys in decommissioning of nuclear facilities

In many countries which adopted a radiological criterion for decommissioning or site release, a Multi-Agencies Radiation Survey and Site Investigation Manual methodology has been extensively used as a guide for designing decommissioning surveys, especially a final status survey, in order to demonstrate a decommissioned site’s compliance with the radiological criteria. The methodology recommends the use of nonparametric hypothesis testing in a final status survey as a statistical tool in making a decision on whether or not the mean contamination level in a survey unit meets a concentration limit which is derived from the radiological criterion. When designing a final status survey, it is of a great importance to ensure that the hypothesis test of the survey has a sufficient power to release a survey unit in question when it is clean by determining the sample size necessary for achieving the power. For this purpose, the MARSSIM methodology recommends using sample sizes which are 20% greater than statistically necessary for the test. However, this study shows that, the MARSSIM-recommended sample size generally provides a conservatism much larger than necessary. Therefore, it is recommended to determine a reasonable sample size of the final status survey for a survey unit not by just following the recommendation of the MARSSIM but by performing a detailed investigation of the power of the test. This kind of effort is valuable as it could result in saving lots of costs when the determined reasonable sample size is smaller than recommended by the MARSSIM methodology.

Derivation of preliminary derived concentration guideline levels for surface soil at Kori Unit 1 by RESRAD probabilistic analysis

Abstract Preliminary surface soil Derived Concentration Guideline Levels (DCGLs) were derived conforming to the Multi-Agency Radiation Site Survey and Investigation Manual (MARSSIM) procedure for the site release and reuse of Kori Unit 1 in Korea. Based on the decommissioning experiences of the U.S. nuclear power plants, a suite of residual radionuclides was determined, and uncertainties contributed to the resultant dose by the input parameters were quantified via the sensitivity analysis of parameters. The peak of the mean dose was obtained via the probabilistic analysis of the RESRAD (RESidual RADioactivity)-ONSITE code. Consequently, DCGLw of Kori Unit 1 in accordance with two scenarios, industrial worker and residential farmer scenario, were derived and the results were compared respectively with other NPPs. It could be used as a basic guideline for establishing regulatory standards for reuse planning, designing the site characterization surveys and implementing final status survey (FSS).

A Radionuclides Suite Selection for Site Characterization and Final Status Survey in the U.S. NPPs

노후 원전 해체의 경우 부지 특성 및 최종 상태 조사 보고서에 해당 부지내 잔존가능성이 있는 방사성 핵종 정보에 대한 내용을 포함하여야 한다. 미국 NRC의 경우 이에 해당하는 해체기술관련문서(DTBD)를 부지 특성 조사시에 부지이력조사(HSA) 와 같이 사업자 측이 제출하도록 규제하고 있다. 또한 해체기술관련문서는 방사선학적 부지 조사와 해체완료계획서에 포함되어야 하는 내용으로써 부지 규제 해제와 재이용에 관해서 중요한 자료를 제공한다. 이 논문은 부지 별 잠재적 핵종에 대해미국 원전의 해체 사례중 부지 특성 및 최종 상태조사 과정에서 결정하는 방법론을 분석하고 2017년 고리 1호기의 영구 운전정지 후 이루어질 해체 과정에 필수적인 규제 지침과 기술적 근거 수립에 도움이 되고자 한다.

Application of In Situ Measurement for Site Remediation and Final Status Survey of Decommissioning KRR Site

Background: In situ gamma spectrometry has been used to measure environmental radiation, assumptions are usually made about the depth distribution of the radionuclides of interest in the soil. The main limitation of in situ gamma spectrometry lies in determining the depth distribution of radionuclides. The objective of this study is to develop a method for subsurface characterization by in situ measurement. Materials and Methods: The peak to valley method based on the ratio of counting rate between the photoelectric peak and Compton region was applied to identify the depth distribution. The peak to valley method could be applied to establish the relation between the spectrally derived coefficients (Q) with relaxation mass per unit area (β) for various depth distribution in soil. The in situ measurement results were verified by MCNP simulation and calculated correlation equation. In order to compare the depth distributions and contamination levels in decommissioning KRR site, in situ measurement and sampling results were compared. Results and Discussion: The in situ measurement results and MCNP simulation results show a good correlation for laboratory measurement. The simulation relationship between Q and source burial for the source layers have exponential relationship for a variety depth distributions. We applied the peak to valley method to contaminated decommissioning KRR site to determine a depth distribution and initial activity without sampling. The observed results has a good correlation, relative error between in situ measurement with sampling result is around 7% for depth distribution and 4% for initial activity. Conclusion: In this study, the vertical activity distribution and initial activity of 137Cs could be identifying directly through in situ measurement. Therefore, the peak to valley method demonstrated good potential for assessment of the residual radioactivity for site remediation in decommissioning and contaminated site.

Practical application of the MARSSIM process to the site release of a Uranium Conversion Plant following decommissioning

The final stage in the decommissioning process consists of releasing a site and a building from regulatory control. In this study, we describe the practical application of MARSSIM process in performing a site remediation and conducting a final status survey and discuss the lessons learned. The release criterion for the site and the building were set up using site-specific parameters that were calculated using RESRAD and RESRAD-Build codes. The planning stage of the final status survey consisted of classifying the site, identifying the survey units and selecting the background reference area using the DQO process. The planning, implementation and assessment of the final status survey for the site and the building of the Uranium Conversion Plant were carried out to demonstrate that residual radioactivity levels meet the release criterion. The null hypothesis must reject in order to demonstrate the objective, null hypothesis is that residual radioactivity in the survey unit exceed the release criterion. The survey results containing the hot spots in the building, a nonparametric statistical test (Wilcoxon Rank Sum) was chosen for assessment due to the presence of the uranium contamination in background soil. The final status survey results showed that the release criteria were satisfied.

해체사업의 최종현황조사를 위한 MARSSIM 적용

해체의 최종단계는 대상 부지 및 건물을 규제로부터 제외하는 것이다. MARSSIM은 부지를 개방하기 위한 최종현황조사를 수행함에 있어 요구되는 자료의 수집 등의 다양한 요건을 만족키기 위한 총괄적인 지침을 제공한다. 연구로 해체 후 부지 및 건물의 최종현황조사를 위해 MARSSIM에서 제시하고 있는 방법을 적용하였다. 연구로 부지의 특성을 반영한 개방기준을 도출하기 위해 RESRAD 및 RESRAD-Build 전산코드를 이용하여 부지 및 건물에 대해서 계산하였다. 부지 및 건물의 조사설계(Survey Design)를 위해서 잠재적 오염도 및 측정 결과를 활용하여 조사구역을 구분하였고, 개략조사 및 특성조사를 통해 수집된 다양한 결과에 기초하여 통계학적 검사를 통해 조사구역 별로 요구되는 시료의 수를 산정하게 된다. 측정된 결과에 기초하여 연구로 최종 개방기준에 만족하는 것으로 평가되었다. The release of a site and building from regulatory control is the final stage of the decommissioning process. The MARSSIM (Multi-Agency Radiation Survey and Site Investigation Manual) provides overall framework for conducting data collection for a final status survey to demonstrate compliance with site closure requirements. The KAERI carried out establishing a final status survey by using the guidance provided in the MARSSIM for of a site and building of the Korea Research Reactor. The release criteria for a site and building were set up based on these results of the site specific release levels which were calculated by using RESRAD and RESRAD-Build codes. The survey design for a site and building was classified by using the survey dataset and potential contamination. The number of samples in each survey unit was calculated by through a statistical test using the collected data from a scoping and characterization survey. The results of the final status survey were satisfied the release criteria based on an evaluation of the measured data.

Comparison of Standard Radiological Risk Models and Using RESRAD to Derive Generic Risk‐Based Area Factors for Final Status Surveys

The RESidual RADioactivity (RESRAD) computer code has been used for years to calculate carcinogenic risk and radiological dose from exposure to radionuclides. The basic ingestion, inhalation, and direct gamma intake equations used by RESRAD, Risk Assessment Guidance for Superfund (RAGS), and the Soil Screening Guidance for Radionuclides (SSG) are similar and can produce similar results, but there are some notable differences. Of particular interest is the fact that RESRAD incorporates sophisticated environmental transport models. Associated environmental parameters allow risk assessors to consider, among other variables, the size (i.e., surface area) of the contaminated zone, a variable not typically addressed quantitatively under the RAGS/SSG paradigm. Considering the similarities between basic RESRAD, RAGS, and SSG intake equations and given the broad acceptance of RESRAD, it stands to reason that RESRAD-derived area factors may be used to supplement RAGS/SSG human health risk calculations. This would allow risk assessors to retrofit existing results or otherwise modify standard RAGS/SSG equations for use in site closeout planning under the Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM), given a key component of the MARSSIM method is the consideration of small areas of elevated activity or "hot spots" through the use of area factors.

Triad case study: Rattlesnake Creek

AbstractThe U.S. Army Corps of Engineers (US ACE) is responsible for conducting the cleanup of radiological contaminated properties as part of the Formerly Utilized Sites Remedial Action Program. One property is the Rattlesnake Creek (RSC) portion of the Ashland sites. The RSC stream sediments are contaminated with thorium‐230, radium‐226, and uranium. The US ACE is closing RSC using protocols contained within the Multi‐Agency Radiation Survey and Site Investigation Manual (MARSSIM). At RSC, the US ACE developed site‐specific derived concentration guideline level (DCGL) cleanup requirements consistent with the MARSSIM guidance. Because of uncertainty about the distribution of contamination within the creek, the US ACE used the Triad approach to collect data and design remedial actions. Systematic planning helped target the areas of concern, develop a conceptual site model, and identify data gaps to be addressed before remediation plans were finalized. Preremediation sampling and analysis plans were designed to be explicitly consistent with final status survey requirements, allowing data sets to support both excavation planning needs and closure requirements in areas where contamination was not encountered above DCGL standards. Judicious use of real‐ time technologies such as X‐ray fluorescence and gamma walkover surveys minimized expensive off‐ site alpha spectrometry analyses, and at the same time provided the ability to respond to unexpected field conditions. © 2004 Wiley Periodicals, Inc.

Application of MARSSIM at the Big Rock Point Restoration Project.

Big Rock Point was Michigan's first commercial power reactor and operated for 35 years. It was permanently shut down in August of 1997, and the site is currently being returned to its natural state. Guidance contained in the Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) is being applied in preparation for the final status survey. Unlike other commercial power reactors currently undergoing decommissioning, all Big Rock Point structures will be removed prior to the final status survey. A historical site assessment along with characterization surveys formed the basis to designate 1.6 square kilometers (395.9 acres) of the site as non-impacted and the remaining 0.7 square kilometers (184.5 acres) as impacted as defined by MARSSIM. Also, a source term abstraction has been performed using historical waste stream data to identify radionuclides potentially present in site soils, hard-to-detect (HTD) radionuclides and surrogate radionuclides for the HTD radionuclides.

MARSSIM vs. DOE Order 5400.5: the Final Status Survey plan at the Rocky Flats Environmental Technology Site.

A challenge unique to the decommissioning of Department of Energy (DOE) facilities involves the compromise between the existing and newly recommended standards for the unrestricted release of property and materials. The Rocky Flats Environmental Technology Site (RFETS) is currently decommissioning numerous plutonium contaminated facilities. The default DOE standard for unrestricted release, Order 5400.5, defines surface activity guidelines as averaged over a 1-square-meter area with a maximum value defined for any given 100-square-centimeter area. While the Order was initially developed to release property and materials from an operating site, it is restrictive in its use when performing Final Status Survey and, to date, no new complex wide standard has been developed. However, the RFETS stakeholders selected the MARSSIM, which provides a progressive method to demonstrate compliance with the defined "dose-based" limits for a specific site, as the governing document in developing a final survey method. The end result is a hybrid final status survey plan that incorporates the requirements of both documents. This plan represents several years of development and negotiation between the contractor, the DOE, the Colorado Department of Public Health and Environment, the Rocky Flats stakeholders, and other interested parties.

Scan MDCs for multiple radionuclides in Class 1 areas.

The MultiAgency Radiation Survey and Site Investigation Manual (MARSSIM), published in December 1997, has been used for designing final status surveys at a number of D&D sites to date. One of the more challenging aspects of the MARSSIM survey design is the strategy employed when multiple radionuclides are present, particularly in Class 1 survey units. The MARSSIM recommends that potential hot spots in a Class 1 survey unit--that could exceed the derived concentration guideline levels for small elevated areas of radioactivity (i.e., DCGL(EMC))--have a reasonably good probability of being detected. Soil sampling on a specified grid size, in conjunction with gamma radiation surface scanning, is used to obtain an adequate assurance level that these hot spots are not missed during the final status survey. Therefore, it is sometimes necessary to supplement the sample size required by the statistical test to provide additional assurance that potential hot spots of concern are detected.

Technical considerations for using in situ gamma spectroscopy in conducting final status surveys.

Facilities undergoing decommissioning are required to conduct radiological surveys to initially characterize contaminants, guide remediation activities, and demonstrate that cleanup criteria have been met, based on screening or site-specific derived concentration guideline levels. This paper presents a number of technical considerations, not all inclusive, associated with the use of in situ gamma spectroscopy that should be addressed when such a method is proposed for conducting final status surveys. The technical issues identified here do not yet reflect the policy of the NRC on this subject.

A guided tour of COMPASS.

The COMPASS software was designed to facilitate the use of MARSSIM and guide the user into making informed decisions in designing final status radiological surveys. COMPASS also simplifies the application of the statistical tests by performing the statistical calculations and providing prospective power curves that help in determining what level of confidence the user is willing to accept for a particular number of measurements or samples for a survey unit. After performing the final status survey, COMPASS assesses the data for comparison to the release criteria. The purpose of this article is to provide the COMPASS user with an overview of the features of the software and to demonstrate how COMPASS implements the MARSSIM guidance.