This document discusses the design of a passive safety system for CANDU6 nuclear power plants to provide safety for 72 hours during a station blackout accident. The proposed system is based on the ALFRED LFR reactor project and uses isolation condensers to provide long-term passive heat removal without active systems. Modeling with RELAP5 is being used to validate the design of the isolation condenser system and natural circulation capabilities. Engineering design by CITON is also being done in parallel to develop specifications and layouts. The goal is to provide full passive safety for 72 hours compared to the current 23 hour capability at Cernavoda plant through cooperation between modeling and engineering design of the new isolation condenser system.

1. A PASSIVE SAFETY
SYSTEM FOR CANDU6
Luminita Nitulescu Iulian Pavel NITA,
Institute for Nuclear Research, Pitesti, Romania Centre of Technology and Engineery for Nuclear
Projects, Magurele, Romania
luminita.nitulescu@nuclear.ro nitai@router.citon.ro
Modelling RELAP - ICN
General arrangement - lateral view of the DHR system
General arrangement - top view of the DHR system
Section through the water tower.
Isolating condenser
concept design
System process diagram
Engineering - CITON
Main scheme of CANDU 6 NPP used in
RELAP5/MOD3.2 computer code
The scheme adopted in the
modelling of the secondary
side of the steam generator
The scheme adopted in modelling the
isolation condenser coupled to Steam
Generator 1 and 2
-1.00E+06
0.00E+00
1.00E+06
2.00E+06
3.00E+06
4.00E+06
5.00E+06
6.00E+06
7.00E+06
8.00E+06
0 2000 4000 6000 8000 10000 12000
pressure
[Pa]
time[s]
p 655050000-IC1 p 615050000-IC1 p 630010000-IC1
p 645050000-IC2 p 617050000-IC2 p 620010000-IC2
p 139010000
RATEN ICN and RATEN CITON Cooperation
CANDU 6 Heat Transport System
0.00E+00
2.00E+06
4.00E+06
6.00E+06
8.00E+06
1.00E+07
1.20E+07
1.40E+07
0 5 10 15 20 25 30 35 40 45 50
pressure
[pa]
time [s]
p 102010000-RIH-T1
p 103010000-ROH-T1
p 104010000-RIH-T2
p 101010000-ROH-T2
Evolution of the pressure in
PHTS during of LFW event
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 10 20 30 40 50 60 70 80 90 100
void
fraction
time [s]
voidg 102010000-RIH-T1
voidg 103010000-ROH-T1
voidg 104010000-RIH-T2
voidg 101010000-ROH-T2
Evolution of the void fraction in
0
50
100
150
200
250
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
mass
flow
[kg/s]
time [s]
mflowj 141000000-ASDV-GA1
mflowj 241000000-ASDV-GA2
mflowj 165000000-CSDV
Evolution of steam discharge
through the ASDVs and CSDV
during LFW event
Design a passive safety system
(level D) For 72 hours of Station
Black out Accident – CANDU6
Cooperation between
engineering design and
simulation /
modeling of the plant
Evolution of pressure in the
steam generators and in the
passive isolation condense
during SBO event
CONCLUSIONS
The current situation of Cernavoda CANDU6 has 23 hours of time in order for operation in complete
passive safety condition (SBO accident) in order to preserve integrity of combustible bundle.
In this paper we presented steps forward in order to implement a complete new passive safety system for
CANDU6 NPP, a system derived from ALFRED LFR demonstrator reactor project, a system capable to
increase window time opportunity for main operator in order to find a proper heat sink from existing 23
hours to at least 72 hours time. The work is very complex and its needed a interaction between
engineering design from CITON and modelling in RELAP5 at ICN of the system. The modelling of the
system is required in order to validate elevation of IC pool and diameters of connection pipes in order to
have enough natural circulation in secondary circuit.
Moreover, RELAP5 model is compulsory to verify IC heat exchanger heat flux and feasibility of
synchronously of two natural circulation in PHTS and in secondary circuit.
ICN - RELAP5 modelling of heat transfer with non-condensable gases and natural circulation
of water/gases combination is to be validated with experimental data in PIACE Project at ENEA
Laboratory.
CITON – engineering design for general layout, technical solution, civil engineering and in
general technical specification
We are confident that in very short time the system will have a complete technical specification
with isometric drawings, layout plans, data sheets, PID, ATH with RELAP5 model
and a very good integration in existing safety principle and proceedings of the
CANDU6 Cernavoda NPP.
S4-P4
Passive Isolation Condenser
Grant Agreement N. 847715