Integrated system for population dose calculation and decision making on protection measures in case of an accident with air emissions in a nuclear power plant.

The accidents in Chernobyl and Fukushima remind us that nuclear power plants should continuously invest resources in improving safety and in risk management. This paper presents the methodology for developing a measuring and modelling system with a high degree of automation, which enables predicting the effects of the spreading of radionuclides from the nuclear power plant to the atmosphere. The end result is the calculated population doses in the event of an accidental release, which is an essential piece of information needed by first responders to take proper action. The key challenge addressed by this methodology is how to build a system so that its operation is maximally automated, ongoing and in real time. Moreover, in a way that "fresh", normalized results for the hypothetically most probable types of emissions are always available to operators. The principle that normalized, fresh results are always automatically available to operators is the only real assurance that they will almost surely be available in the event of an accident and panic. This way, we can avoid performing complex model calculations at the operator's request when the accident is already taking place. The methodology divides the building of the system into key modules, which are substantiated and described. The theoretical section is followed by a description of implementation on the example of the Measuring and Modelling System at the Krsko Nuclear Power Plant (in Slovenia). The system has been tested in regular nuclear emergency exercises and rated excellent by IAEA inspections; it has been operating automatically, continuously and in real time for many years. The availability of automatic results is counted for the last two years. Measurements and diagnostic modelling results were available for more than 96% and forecasts were available in more than 91% of all half-hour intervals.

Measurement of tritium in the Sava and Danube Rivers.

Two nuclear power plants (NPP), the KrskoNPP (Slovenia) on the Sava River and the Paks NPP (Hungary) on the Danube River, are located in the immediate vicinity of Croatia and Serbia. Some of the radioactivity monitoring around the NPPs involves measuring tritium activity in the waters of rivers and wells. The authors present the tritium measurement results taken over several years from the Sava and Danube Rivers, and groundwater. The measurements were carried out in two laboratories including an impact assessment of the tritium released into the rivers and groundwater. The routine methods for determining tritium (with/without electrolytic enrichment) were tested in two laboratories using two different instruments, a Tri-Carb 3180 and Quantulus 1220. Detection limits for routine measurements were calculated in compliance with ISO 11929 and Currie relations, and subsequently the results were compared with those determined experimentally. This has shown that tritium can be reliably determined within a reasonable period of time when its activity is close to the calculated detection limit. The Krsko NPP discharged 62 TBq of tritium into the River Sava over a period of 6 years (23% of permitted activity, 45 TBq per year). The natural level of tritium in the Sava River and groundwater is 0.3-1 Bq/l and increases when discharges exceed 1 TBq per month. Usually, the average monthly activity in the Sava River and groundwater is maintained at a natural level. The maximum measured activity was 16 Bq/l in the Sava River and 9.5 Bq/l in groundwater directly linked to the river. In the majority of water samples from the Danube River, measured tritium activity ranged between 1 and 2 Bq/l. The increased tritium levels in the Danube River are more evident than in the Sava River because tritium activity above 1.5 Bq/l appears more frequently on the Danube River. All measured values were far below the allowed tritium limit in drinking water. Dose assessment has shown that tritium released from NPPs contributes negligibly to annual doses in comparison to natural sources.