Emission rate estimation through data assimilation of gamma dose measurements in a Lagrangian atmospheric dispersion model

Abstract

This paper presents an efficient algorithm for estimating the unknown emission rate of radionuclides in the atmosphere following a nuclear accident. The algorithm is based on assimilation of gamma dose rate measured data in a Lagrangian atmospheric dispersion model. Such models are used in the framework of nuclear emergency response systems (ERSs). It is shown that the algorithm is applicable in both deterministic and stochastic modes of operation of the dispersion model. The method is evaluated by computational simulations of a 3-d field experiment on atmospheric dispersion of ⁴¹Ar emitted routinely from a research reactor. Available measurements of fluence rate (photons flux) in air are assimilated in the Lagrangian dispersion model DIPCOT and the ⁴¹Ar emission rate is estimated. The statistical analysis shows that the model-calculated emission rates agree well with the real ones. In addition the model-predicted fluence rates at the locations of the sensors, which were not used in the data assimilation procedure are in better agreement with the measurements. The first evaluation results of the method presented in this study show that the method performs satisfactorily and therefore it is applicable in nuclear ERSs provided that more comprehensive validation studies will be performed.

Predicting and Controlling Nuclear Accident Hazards: Issues and Challenges

“…In addition, data assimilation methods that optimize the match between an observed and predicted field are known to be an effective means to reduce hazard prediction error (Zheng et al, 2007;Astrup et al, 2004;Tang et al, 2011). Recently, novel assimilation techniques, such as ensemble Kalman filter (Zheng et al, 2009;Tang et al, 2011) and ensemble simulations of meteorology (Hu et al, 2014;Sheng et al, 2014), have been applied to enhance the hazard estimation using synthetic dose rate data (Tsiouri et al, 2012) and air concentration and deposition measurements (Winiarek et al, 2014). However, more in-depth theoretical studies and comparison tests on the hazard prediction mechanism based on observational and experimental simulations are required (Bieringer et al, 2013;Draxler, et al, 2015).…”

Radiation source rate estimation through data assimilation of gamma dose rate measurements for operational nuclear emergency response systems

“…An innovative and efficient methodology based on variational DA is used for estimating the unknown emission rate (Tsiouri et al, 2011(Tsiouri et al, , 2012. The main objective of the DA method is the minimisation of the following cost function with respect to the control vector ψ which consists of the source rates corresponding to times of releases of puffs:…”

“…For substantial improvement in numerical efficiency and accuracy and to enable using the DA method also in the framework of the stochastic Lagrangian atmospheric dispersion models, the control vector reduction technique explained in detail in Tsiouri et al (2012) is used. This technique is based on the assumption that during small enough time interval Δt, the source rate can be considered as constant with sufficient accuracy.…”

“…The algorithm is based on assimilation of gamma dose rate measured data in the Lagrangian atmospheric dispersion model DIPCOT (Andronopoulos et al, 2009) used in the framework of the nuclear emergency response system (ERS) RODOS (Raskob, 2007) and uses variational principles. The method is described in Tsiouri et al (2011Tsiouri et al ( , 2012. In the latter work (Tsiouri et al, 2012) the method was successfully evaluated against the fluence rate measurements in field experiment of Ar-41 atmospheric dispersion in Mol, Belgium (Drews et al, 2002).…”

“…The method is described in Tsiouri et al (2011Tsiouri et al ( , 2012. In the latter work (Tsiouri et al, 2012) the method was successfully evaluated against the fluence rate measurements in field experiment of Ar-41 atmospheric dispersion in Mol, Belgium (Drews et al, 2002). In the present work, the method is evaluated against a more complicated case using gamma dose rate measurements from Ar-41 routine releases at the Australian Nuclear Science and Technology Organisation's (ANSTO) previous research reactor, HIFAR, located in Sydney, Australia.…”