Page 106 - AERB

(a) (b)

Fig. 7.2: Raffinate Temperature Transients for (a) Case-1 and (b) Case-2

7.1.3 Inadvertent Opening of PDHRS Valves in 700
MWe PHWRs
For removal of core decay heat following a severe
accident scenario, nuclear reactors are equipped with
passive heat removal systems that depend on the
natural circulation principle. Studies were conducted to
evaluate the effect of inadvertent opening of the Passive
Decay Heat Removal System (PDHRS) valve during
normal operation. The study revealed that reactor trip
occurs on the low SG pressure signal and the changes in
various parameters attain stabilized conditions within 30
minutes and all the thermal hydraulics parameters were
within the prescribed operating limits.

7.1.4 Studies on Passive Containment Cooling
System (PCCS) Fig. 7.3: Typical Flow Transient in the Scaled-down PCCS
Loop
A conceptual model of PCCS for 700 MWe PHWR
containment consisting of parallel heat removal loops 7.1.5 CFD Simulations of HR 49 Test of THAI Facility
was developed earlier. A scoping study was initiated
for setting up small scale PCCS experimental facility. Computational Fluid Dynamics (CFD) simulations
A generalized model to simulate two-phase natural were carried out as part of OECD/NEA Project with
circulation in parallel channels was developed to study an objective to study the onset of recombination of
the performance of the proposed facility. This model Hydrogen in presence of counter current flow and
can simulate various conditions of heat sink (infinite, saturated steam environment at elevated pressure
open to atmosphere and external cooling etc.). To using FLUENT. The analysis methodology and models
arrive at the design features of the PCCS facility, several were validated against experimental data of HR 49
parametric studies were conducted. Variation of flow test of THAI-3 facility. Analyses have been carried
rate is depicted in Fig. 7.3. out for various counter-current velocities ranging from

78 AERB Annual Report 2019