Use of ROKO Database for Analysis of Radiological Data

Transcription

1 ABSTRACT Use of ROKO Database for Analysis of Radiological Data Michel Cindro, Barbara Vokal Nemec, Titina Banjac Slovenian Nuclear Safety Administration Železna cesta 16, SI-1000 Ljubljana, Slovenia In an effort to closely monitor the levels of radioactivity in Slovenia, the Slovenian Nuclear Safety Administration (SNSA) is gathering data from many different sources. In the last few years a substantial effort was made to organize and archive those data [1]. The aim was to ensure easy access and efficient analysis of all off-line gathered data collected in the scope of government mandated program for environmental monitoring or operational monitoring of nuclear facilities. All off-line measurements used to be reported in printed media, regularly since the first measurements were performed in 1961 [2,3]. SNSA has undertaken the project of transfer of all those data into the electronic media and making it available for easy access. The resulting database was named ROKO, the Slovenian acronym for Radioactivity in the environment. The database had to be manually completed with old data, what turned out to be a very difficult operation because of the large amount of data and their diversity. The scope of possible uses of the ROKO database is very wide. Most commonly, it is used for long term trend analysis of long lived nuclides resulting from nuclear tests and the Chernobyl accident in the environment, as well as any inccident that occurred close enough that it impacted the Slovenian territory (Paks NPP, Cadiz Algeciras). In this paper we will describe some aspects of data analysis and validation, followed by examples showing possible uses of the database. We pointed out strengths of the user interface and data presentation package, as well as shortcomings that were identified through the use. 1 INTRODUCTION The database ensures easy administration through its relational design, which proved essential in the process of data consolidation. The user interface, available to the public at website is an integral part of the database, designed for data exploitation. It has many features needed for thorough analysis of data. It is user friendly, with fast data retrieval. Apart from basic data trends, users can also export data in various numerical and graphical formats for further exploitation. At the moment, the database comprises validated measurements. Further measurements, mostly from the Krško NPP, are being validated. For all future measurement campaigns, the SNSA prescribed an electronic data submission in specific format, which will make possible easy transfer of data to ROKO

2 MATERIALS AND METHODS After the completion of the initial transfer from printed media, many inconsistencies were found, mostly due to the fact that many different persons were entering data. The inconsistencies were mostly in locations descriptions and sample types. One of the best examples was the air sampling at Golovec, Ljubljana. Some data were entered as Ljubljana, some as Ljubljana (Golovec), some as Golovec, while the sample types were air, aerosols or air particles. As a result, we didn t have a single set of data for these measurements, but instead up to 9 different sets, complementing each other, yet useless for users since they could not follow a single trend. Once data were broken in such a manner, it is very hard and time consuming to compile them back together, so the emphasis must be on consistent use of all measurement attributes, location and sample type being the most important ones. In order to achieve data consistency, many automatic tools were designed. The one that proved most useful was a tool that makes spreadsheets of measurements for chosen location/sample type pairs, as shown in Figure 1. Location: Ljubljana ( E, N) Sample type: Air aerosol Izotope: Cs-137 Unit: Bq/m3 Year Januar Februar Marec April Maj Junij Julij Avgust September Oktober November December Average ,8E-06 5,0E-06 3,6E-06 4,3E-06 2,0E-06 2,5E-06 1,9E-06 2,4E-06 2,7E-06 2,2E-06 2,3E-06 4,4E-06 3,3E ,7E-06 5,6E-06 4,2E-06 3,7E-06 2,0E-06 4,8E-06 6,9E-06 3,4E-06 7,3E-06 2,8E-06 7,7E-06 8,8E-06 5,2E ,0E-06 3,3E-06 1,1E-06 2,5E-06 1,8E-06 7,6E-06 5,4E-06 3,4E-06 3,1E-06 3,3E-06 4,2E-06 5,7E-06 3,9E ,9E-05 3,5E-06 1,6E-06 3,7E-06 1,3E-05 1,2E-05 1,9E-05 1,9E-05 5,0E-06 1,8E-05 2,0E-05 1,2E-05 Location: Ljubljana ( E, N) Sample type: Air Izotope: Cs-137 Unit: Bq/m3 Year Januar Februar Marec April Maj Junij Julij Avgust September Oktober November December Average ,3E-05 1,1E-05 8,3E-06 7,0E-06 6,0E-06 4,7E-06 5,3E-06 4,5E-06 7,8E-06 9,4E-06 9,4E-06 8,8E-06 7,9E ,2E-05 1,3E-05 1,3E-05 1,7E-05 1,4E-05 1,7E-05 9,0E-06 1,4E-05 1,4E-05 2,5E-05 5,0E-06 1,4E ,0E-06 5,0E-06 4,0E-06 3,0E-06 3,0E-06 3,0E-05 3,0E-06 3,4E-06 4,5E-06 6,0E-06 4,0E-06 5,0E-06 6,6E ,0E-06 6,7E-06 3,1E-06 1,6E-06 2,1E-06 9,9E-05 3,7E-06 3,4E-06 1,6E-06 2,0E-06 2,0E-06 8,3E-06 1,2E ,0E-06 4,2E-06 3,8E-06 2,8E-06 2,4E-06 3,5E-06 1,1E-06 3,2E-06 3,1E-06 5,0E-06 2,7E-06 2,1E-06 3,2E ,4E-05 4,8E-06 2,4E-06 3,6E-06 3,4E-06 4,7E-06 1,4E-06 1,9E-06 9,9E-06 1,7E-06 2,4E-06 1,4E-06 7,6E ,3E-06 3,5E-06 1,7E-06 3,6E-06 5,1E-06 5,1E-06 1,2E-06 1,6E-06 6,5E-06 4,1E-06 2,9E-06 2,8E-06 3,5E ,5E-06 5,4E-06 2,9E-06 8,3E-06 3,4E-06 3,2E-06 9,4E-06 2,8E-06 7,5E-06 4,6E-06 4,3E-06 4,9E-06 Figure 1: Measurements of air in Ljubljana, broken in two sample sets: air and air aerosol. It is obvious at the first glance that all data belong to a same data set, split between 2 sample types. The data missing in the upper one (Air aerosol) are present in the lower (Air). The results were consolidated and the resulting data set is shown in Figure 2. During the consolidation process we made many improvements to the database and user interface based

3 905.3 on day to day use. The empty cells represent missing data, measured values are shown in bold, while measurements under LLD are shown in normal typeface. Location: Ljubljana (Golovec) ( E, N) Sample type: Air Izotope: Cs-137 Unit: Bq/m3 Year Januar Februar Marec April Maj Junij Julij Avgust September Oktober November December Average ,0E-05 8,5E-06 1,3E-05 5,0E-06 6,0E-06 3,3E-06 3,0E-06 6,0E-06 4,4E-06 9,4E-06 4,5E-06 1,3E-05 7,2E ,3E-05 1,1E-05 8,3E-06 7,0E-06 6,0E-06 4,7E-06 5,3E-06 4,5E-06 7,8E-06 9,4E-06 9,4E-06 8,8E-06 7,9E ,2E-05 1,3E-05 1,3E-05 1,7E-05 1,4E-05 1,7E-05 9,0E-06 1,4E-05 1,4E-05 2,5E-05 5,0E-06 1,4E ,0E-06 5,0E-06 4,0E-06 3,0E-06 3,0E-06 3,0E-05 3,0E-06 3,4E-06 4,5E-06 6,0E-06 4,0E-06 5,0E-06 6,6E ,8E-06 5,0E-06 3,6E-06 4,3E-06 2,0E-06 2,5E-06 1,9E-06 2,4E-06 2,7E-06 2,2E-06 2,3E-06 4,4E-06 3,3E ,7E-06 5,6E-06 4,2E-06 3,7E-06 2,0E-06 4,8E-06 6,9E-06 3,4E-06 7,3E-06 2,8E-06 7,7E-06 8,8E-06 5,2E ,0E-06 6,7E-06 3,1E-06 1,6E-06 2,1E-06 9,9E-05 3,7E-06 3,4E-06 1,6E-06 2,0E-06 2,0E-06 8,3E-06 1,2E ,0E-06 4,2E-06 3,8E-06 2,8E-06 2,4E-06 3,5E-06 1,1E-06 3,2E-06 3,1E-06 5,0E-06 2,7E-06 2,1E-06 3,2E ,4E-06 4,8E-06 2,4E-06 3,6E-06 3,4E-06 4,7E-06 1,4E-06 1,9E-06 9,9E-06 1,7E-06 2,4E-06 1,4E-06 3,6E ,3E-06 3,5E-06 1,7E-06 3,6E-06 3,5E-06 5,1E-06 1,2E-06 1,6E-06 6,5E-06 4,1E-06 2,9E-06 2,8E-06 3,3E ,5E-06 5,4E-06 2,9E-06 8,3E-06 3,4E-06 3,2E-06 9,4E-06 2,8E-06 7,5E-06 4,6E-06 4,3E-06 4,9E ,0E-06 3,3E-06 1,1E-06 2,5E-06 1,8E-06 7,6E-06 5,4E-06 3,4E-06 3,1E-06 3,3E-06 4,2E-06 5,7E-06 3,9E ,9E-05 3,5E-06 1,6E-06 3,7E-06 1,3E-05 1,2E-05 1,9E-05 1,9E-05 1,5E-06 1,8E-05 2,0E-05 3,5E-06 1,1E ,5E-06 3,3E-06 2,4E-06 2,6E-06 2,4E-06 2,3E-06 3,3E-06 2,2E-06 3,9E-06 3,2E-06 1,7E-06 1,8E-06 2,6E-06 Figure 2: consolidated data trend for Cs-137 in air at Ljubljana (Golovec) Since the database contains roughly 1000 locations and 400 sample types, it is nearly impossible to identify such cases, so the emphasis must be on data control before input is done into the database. 3 RESULTS Since the database is only a tool for analysis, we have decided to show the possibilities and limitations of data use. 3.1 Concentration of Cs-137 in air in Ljubljana With the use of ROKO database, it is very easy to identify the influence of major incidents and discharges of radioactive materials to the atmosphere in last three decades. Even older data are available, but due to different measuring methods (total beta radiation particle measurement with Geiger Muller counter was measured from 1961 till 1980 and gamma ray spectroscopy has been used since then) it is not possible to directly compare these data. In the early 1980s, influence of nuclear weapons testing in China can be seen, while the Chernobyl accident in 1986 is obviously by far the biggest source of caesium. We can also see the consequences of the Cs-137 source smelting in the Acerinox plant near Cadiz, Spain in During the Paks NPP incident in 2003 I-131 was released, which, due to its short half life, could not be measured. In the scope of the regular environmental monitoring program, air samples are measured on monthly bases, so the iodine would decay below levels of detection before it could be measured. The user interface enables presentations of several locations simultaneously, useful since the measurement location was transferred from Golovec to Ljubljana suburbs of Podgorica in 2006 and to Polje in 2007.

4 905.4 Figure 3: Concentration of Cs-137 in air (μbq/m 3 ) in Ljubljana, yearly averages 3.2 Tritium in Sava river as a consequence of Krško NPP liquid discharges. Figure 4: Tritium (H-3) in liquid discharges from the Krško NPP

5 905.5 In the year 2008 we have expanded the ROKO database by including data on radioactive discharges. The Krško NPP is reporting activities of the radionuclides discharged to the atmosphere and to Sava river each month. At the same time, river Sava is sampled upriver of the plant, downriver in Brežice and further down in Jesenice na Dolenjskem at the border with Croatia. While trying to derive a trend we are limited by the ROKO interface. The discharges are measured in units of Bq. As a consequence, we can draw separate trends for total tritium activity in liquid discharges (Figure 4) and for tritium concentration (Bq/m 3 ) in Sava river (Figure 5). Figure 5: Tritium concentration in Sava river around the Krško NPP To combine these trends, we have to export the data into MS EXCEL (ROKO interface feature) and combine it, as it is shown in Figure 6. H-3 from NEK-2007 H-3 in Sava [Jesenice na Dolenjskem]-2007 Unit:GBq Date of measurements Unit: Bq/m 3 Figure 6: Tritium in liquid discharges from Krško NPP and concentration in river Sava combined

6 905.6 This is an aspect of the interface that could be improved, currently limited only by the software used for drawing. If possible, we plan to implement it in the future. 3.3 Air, precipitation, feeding stuff, milk The purpose of many monitoring programs is to follow the potential contamination along the pathways from the source to the public. One example is following the atmosphere contamination through concentrations in air, subsequent precipitation, inclusion into feeding stuff and food, in this case into milk. It is hard to find quality data to follow this pathway in environmental and operational monitoring programs, so this may be an indicator that the programs themselves could be adjusted. The measurements of milk were performed monthly since 1980 (Figure 7). Concentration of Cs-137 in cow milk is the consequence of feeding cattle with fresh grass and feeding stuff. Due to Chernobyl accident the peak value of Cs-137 is in the years 1986 and Figure 7: Concentration of Cs-137 in cow milk in Ljubljana By combining data for Cs-137 in atmosphere (Figure 3) and Cs-137 in cow milk (Figure 7) at same location we can observe a very good agreement (Figure 8). One should note the delayed effect of the contamination as a consequence of feedstuff storage. The only discrepancy is due to method of collecting milk samples after year 1999 when the milk distributors started to collect milk also from some other parts of Slovenia.

7 905.7 Unit:Bq/kg 1,00E+02 1,00E+01 1,00E+00 1,00E-01 Milk [cow]-ljubljana Air-Ljubljana 1,00E+00 1,00E-01 1,00E-02 1,00E-03 1,00E-04 1,00E-05 Unit:Bq/m 3 1,00E Date of measurements 1,00E-06 Figure 8: Comparison between Cs-137 concentration in cow milk and Cs-137 in atmosphere 4 CONCLUSIONS The results show that ROKO base is a sophisticated base enabling different ways of analysis and at the same time it is user-friendly. Assessing large data collections is possible by comparing data on contamination sources such as air pollution and consequences such as milk or other feed stuff. There is also room for improvement, with the possibility of representing two connected sample types measured in different units on the same chart. For the purpose of environmental radioactivity and radioactivity discharges monitoring the ROKO base is very useful for all kind of analyses which may also be interesting for the public. On the regulatory side, the SNSA is now better equipped to analyze annually collected data, look for anomalies, for inconsistent analysis and reports as well as to evaluate the quality of laboratory analyses. In this manner, any measurable impact on the environment as a consequence of nuclear facility operation can be identified. The results of these analyses can be used as feedback to further refine monitoring programs either for nuclear facilities or for environmental measurements. REFERENCES [1] STRITAR, Andrej, MITIĆ, Dragan. ROKO-database of the environmental radioactivity measurements in Slovenia. V: MAVKO, Borut (ur.), KLJENAK, Ivo (ur.). International Conference Nuclear Energy for New Europe 2005, September 5-8, 2005, Bled, Slovenia. Proceedings. Ljubljana: Nuclear Society of Slovenia, 2005, p [2] Radioactivity in the living environment, Republic of Slovenia, Annual reports for the years , Institute for Occupational Safety, Ljubljana, [3] Off-site monitoring of Krško NPP operation- Annual reports for the years , Jožef Stefan Institute, Ljubljana,