Results are related to experimental facilities 2, 3, 5 and 6 listed in Table I and are summarized in Table V, ref. [13]. Calculations related to PWR-1 of Table II are also discussed in Ref. [13]. These are not considered hereafter owing to a large ‘mass error’ that characterizes the achieved results as documented in the same Ref. [13]. Qualified nodalisations of the ITF, suitable for the Relap5/mod 2 code, were used. The qualification came from the simulation of the NC tests performed in the considered ITF, e. g. ref. [12], and from the demonstration that calculated results adequately reproduce the available experimental values.

The main results of the study can be summarized as follows, ref. [13]:

• A uniform increase of NC flowrate with core power is calculated, until core power achieves values around 40% of the nominal value. Further increases of core power do not cause proportional increases in core flow.

• Oscillatory flows are calculated for core power larger than 40% in Bethsy and Lobi.

• The primary mass inventory decrease occurs via the pressurizer relief valve that is assumed to open and to close in order to keep constant the system pressure.

• PWR cores, in the actual configuration can operate in NC conditions with power up to about 15% the nominal value.

• The largest facilities are designed to operate at low core power (ITF design finalized to the simulation of small break LOCA). This may explain the small value, in terms of % core power, at which dryout occurs.

• Neglecting the Lstf case, up to 70% core power can be removed by NC before experiencing dryout. This can be assumed as the thermalhydraulic limit for system (not any more PWR) operation in NC.