Coupled Source Term Estimation Using Both Forward and Backward Method for Nuclear Power Plant Accident

2016 ◽  
Author(s):  
Sida Sun ◽  
Sheng Fang ◽  
Yun Liu ◽  
Hong Li
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Environmental Monitoring ◽  
Nuclear Power ◽  
Source Term ◽  
Nuclear Accident ◽  
Monitoring Data ◽  
Source Term Estimation ◽  
Status Data ◽  
Environmental Monitoring Data

The source term information of radioactive release in a nuclear accident is important for nuclear accident classification, radiological consequences evaluation and emergency response. Two major categories of source term estimation techniques are forward method based on the status data of the nuclear reactor and backward method based on environmental monitoring data. Although the forward method is more widely used, it may introduce large uncertainties into the source term estimate due to its subjective parameters and low quality of reactor status data in a severe accident. To reduce these uncertainties, a coupled source term estimation method that combines both forward and backward models, is proposed in this study. The forward part provides a source term forecast model based on Response Technical Manual RTM-96. Under the framework of sequential data assimilation, the backward part iteratively reduces the uncertainties in the source term estimate using environmental monitoring data. Numerical experiments with different uncertainties are performed using the reactor and monitoring point information of real Chinese nuclear power plant and its atmospheric tracer experiments.

scholarly journals An inverse modeling method to assess the source term of the Fukushima nuclear power plant accident using gamma dose rate observations

2013 ◽  
Vol 13 (6) ◽  
pp. 15567-15614 ◽  
Author(s):  
O. Saunier ◽  
A. Mathieu ◽  
D. Didier ◽  
M. Tombette ◽  
D. Quélo ◽  
...  
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Dose Rate ◽  
Inverse Modeling ◽  
Nuclear Power ◽  
Source Term ◽  
Noble Gases ◽  
Atmospheric Dispersion ◽  
Nuclear Accident ◽  
Dose Rates

Abstract. The Chernobyl nuclear accident and more recently the Fukushima accident highlighted that the largest source of error on consequences assessment is the source term including the time evolution of the release rate and its distribution between radioisotopes. Inverse modeling methods, which combine environmental measurements and atmospheric dispersion models, have proven efficient in assessing source term due to an accidental situation (Gudiksen, 1989; Krysta and Bocquet, 2007; Stohl et al., 2012a; Winiarek et al., 2012). Most existing approaches are designed to use air sampling measurements (Winiarek et al., 2012) and some of them also use deposition measurements (Stohl et al., 2012a; Winiarek et al., 2013) but none of them uses dose rate measurements. However, it is the most widespread measurement system, and in the event of a nuclear accident, these data constitute the main source of measurements of the plume and radioactive fallout during releases. This paper proposes a method to use dose rate measurements as part of an inverse modeling approach to assess source terms. The method is proven efficient and reliable when applied to the accident at the Fukushima Daiichi nuclear power plant (FD-NPP). The emissions for the eight main isotopes 133Xe, 134Cs, 136Cs, 137Cs, 137mBa, 131I, 132I and 132Te have been assessed. Accordingly, 103 PBq of 131I, 35.5 PBq of 132I, 15.5 PBq of 137Cs and 12 100 PBq of noble gases were released. The events at FD-NPP (such as venting, explosions, etc.) known to have caused atmospheric releases are well identified in the retrieved source term. The estimated source term is validated by comparing simulations of atmospheric dispersion and deposition with environmental observations. The result is that the model-measurement agreement for all of the monitoring locations is correct for 80% of simulated dose rates that are within a factor of 2 of the observed values. Changes in dose rates over time have been overall properly reconstructed, especially in the most contaminated areas to the northwest and south of the FD-NPP. A comparison with observed atmospheric activity concentration and surface deposition shows that the emissions of caesiums and 131I are realistic but that 132I and 132Te are probably underestimated and noble gases are likely overestimated. Finally, an important outcome of this study is that the method proved to be perfectly suited to emergency management and could contribute to improve emergency response in the event of a nuclear accident.

scholarly journals An inverse modeling method to assess the source term of the Fukushima Nuclear Power Plant accident using gamma dose rate observations

2013 ◽  
Vol 13 (22) ◽  
pp. 11403-11421 ◽  
Author(s):  
O. Saunier ◽  
A. Mathieu ◽  
D. Didier ◽  
M. Tombette ◽  
D. Quélo ◽  
...  
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Dose Rate ◽  
Inverse Modeling ◽  
Nuclear Power ◽  
Source Term ◽  
Atmospheric Dispersion ◽  
Nuclear Accident ◽  
Fukushima Accident ◽  
Dose Rates

Abstract. The Chernobyl nuclear accident, and more recently the Fukushima accident, highlighted that the largest source of error on consequences assessment is the source term, including the time evolution of the release rate and its distribution between radioisotopes. Inverse modeling methods, which combine environmental measurements and atmospheric dispersion models, have proven efficient in assessing source term due to an accidental situation (Gudiksen, 1989; Krysta and Bocquet, 2007; Stohl et al., 2012a; Winiarek et al., 2012). Most existing approaches are designed to use air sampling measurements (Winiarek et al., 2012) and some of them also use deposition measurements (Stohl et al., 2012a; Winiarek et al., 2014). Some studies have been performed to use dose rate measurements (Duranova et al., 1999; Astrup et al., 2004; Drews et al., 2004; Tsiouri et al., 2012) but none of the developed methods were carried out to assess the complex source term of a real accident situation like the Fukushima accident. However, dose rate measurements are generated by the most widespread measurement system, and in the event of a nuclear accident, these data constitute the main source of measurements of the plume and radioactive fallout during releases. This paper proposes a method to use dose rate measurements as part of an inverse modeling approach to assess source terms. The method is proven efficient and reliable when applied to the accident at the Fukushima Daiichi Nuclear Power Plant (FD-NPP). The emissions for the eight main isotopes 133Xe, 134Cs, 136Cs, 137Cs, 137mBa, 131I, 132I and 132Te have been assessed. Accordingly, 105.9 PBq of 131I, 35.8 PBq of 132I, 15.5 PBq of 137Cs and 12 134 PBq of noble gases were released. The events at FD-NPP (such as venting, explosions, etc.) known to have caused atmospheric releases are well identified in the retrieved source term. The estimated source term is validated by comparing simulations of atmospheric dispersion and deposition with environmental observations. In total, it was found that for 80% of the measurements, simulated and observed dose rates agreed within a factor of 2. Changes in dose rates over time have been overall properly reconstructed, especially in the most contaminated areas to the northwest and south of the FD-NPP. A comparison with observed atmospheric activity concentration and surface deposition shows that the emissions of caesiums and 131I are realistic but that 132I and 132Te are probably underestimated and noble gases are likely overestimated. Finally, an important outcome of this study is that the method proved to be perfectly suited to emergency management and could contribute to improve emergency response in the event of a nuclear accident.

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