29 FIG. 15. Calculated concentrations (Bq/m3) for surface water at the end of the simulation period. 3.3. EXERCISE 2: HOMOGENIZATION OF WATER CIRCULATION 3.3.1. Introduction Exercise 2 was carried out using the same water circulation for all models. Water circulation computed by the hydrodynamic model JCOPE2 was used and, as in the case of Exercise 1, the magnitude of the input/source term is 1.0 × 106 Bq/s of a long lived radionuclide so that radioactive decay can be ignored. The release is modelled to start on 26 March 2011 and the time frame of calculations extends until 30 May 2011. The exercise was carried out for two cases: a tracer (perfectly conservative radionuclide) and 137Cs (including interactions with bed sediments). Thus, the first case is exactly the same as Exercise 1, but using the same water circulation for all models. Other model settings are left as