Radiative Boundary Condition
 

Can someone please tell me how to put radiative boundary condition in an 1-D unsteady radiative heat conduction problem with one side to the slab with insulation and other side of the slab suddenly exposed to HOT environment, Tsur>Ts, while solving it for numerically.
Ts=T(x,0);
x E [0,1];

gde for the problem is:-

ro*Cp*dT/dt=d(KdT/dx)/dx;

I'm using Forward Time Central Space scheme of discretization of the governing differential equation.