REMADA: An Emergency Decision-Making Software for Radiation Dose Estimation of Mitigation Tasks in a Reactor Building During Severe Nuclear Accidents

Abstract

In the event of a postulated severe accident, fission products may leak into the reactor building through the containment wall, exerting a radiological impact on the emergency response team as they are tasked with performing mitigative missions. It is thus important to estimate the potential radiological consequences of the mission before taking action so that an optimized plan can be devised to avoid putting the team in harm’s way unintentionally. Some of the most well-known accident simulation codes were attempted to do the estimation, but were found to be too time consuming to get the results, making them not suitable for emergency use. The problem evidently arises from the fact that there are too many (about 200) compartments in a typical reactor building.

In this study, the software REMADA is developed to simulate fission product dispersion in a reactor building (with about 200 compartments) within a reasonable timeframe, and to estimate the radiation doses to those who are carrying out mitigative missions in the reactor building. The results show that the software is not only fast, but also informative, to provide support for well-informed emergency decision making.

Keywords:

• Severe accident
• reactor building
• fission product dispersion
• dose rate
• emergency decision making

Nomenclature

Nodes

A =	=	aerosol settling area, which is the sum of all horizontal areas at node (m2)
m =	=	mass of air in node (kg)
P =	=	pressure (Pa)
T =	=	temperature (K)
V =	=	volume converted to a cuboid (m3)
$\mathit{\rho }$ =	=	air density (kg/m3)

Links

$A_O$ =	=	opening area between nodes (m2)
F =	=	mass flow rate between nodes (kg/s)
u =	=	airflow velocity (m/s)

Boundaries

$\mathit{H}$ =	=	height of the building (m)
$m_a$ =	=	total mass of air in the containment, constant by assumption (kg)
$P_0$ =	=	pressure in environment (Pa)
$Q_b$ =	=	air volumetric exchange rate induced by temperature difference (m3/s)
$Q_w$ =	=	air volumetric exchange rate induced by wind (m3/s)
$T_0$ =	=	temperature of air in environment (K)
$\mathit{v}$ =	=	wind speed in environment ($\mathrm{m}/\mathrm{s}$)
$\mathit{\phi }$ =	=	containment leak rate, which is fraction of containment volume per second ($/\mathrm{s}$)
${\rho }_0$ =	=	air density in environment ($\mathrm{kg}/{\mathrm{m}}^3$)

FPs

$\mathit{M}$ =	=	mass of FPs (kg)
$u_s$ =	=	settling velocity of the FPs (m/s)

Dose

$\mathit{BR}$ =	=	breathing rate of people (m3/s)
${\mathrm{DCF}}_{\mathit{eff}}^{\mathit{cls}}$ =	=	cloud shine DCF (Sv·m3/Bq/s)
${\mathrm{DCF}}_{\mathit{eff}}^{\mathit{grs}}$ =	=	ground shine DCF for nuclide $\mathit{i}$ (Sv·m2/Bq/s)
$\mathit{DC}{F}_{\mathit{eff}}^{\mathit{inh}}$ =	=	inhalation DCF (Sv/Bq)
$\mathit{S}{F}^{\mathit{cls}}$ =	=	cloud shine shielding factor
$\mathit{S}{F}^{\mathit{grs}}$ =	=	ground shine shielding factor
$\mathit{S}{F}^{\mathit{inh}}$ =	=	inhalation shielding factor

Parameters

$C_d$ =	=	air discharge factor, which equals 0.65 in this study
$\mathit{g}$ =	=	gravity constant, which equals 9.8 m/s2
$R_a$ =	=	individual gas constant for air, which equals 287.05 J/kg·K

Disclosure Statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The project was supported by the National Natural Science Funds of China (no. 72104207) and the Fundamental Research Funds for the Central Universities (no. 20720220118).