Title: Progress in reliability methodology for passive systems
1- Progress in reliability methodology for passive
systems
C. Bassi, N Devictor, M. Marquès CEA France
A.K. Nayak, D. Saha BARC India
2Advances
- Applications of RMPS on Gen IV Reactors at CEA
- APSRA Methodology and application at BARC
- Passive system reliability analyses at MIT
- Reliability Analysis of CAREM like PRHRS
(presented by Mr Gimenez)
3Applications on Gen IV Reactors at CEA
- Gas-cooled Fast Reactor (GFR) application to
the Decay Heat Removal system (DHR) - Very High Temperature Reactor (VHTR)
application to decay heat removal by radiation
and conductivity
4Decay Heat Removal system (DHR) of GFR
- The DHR system consists on
- a metallic guard containment enclosing the
primary system, not pressurized in normal
operation and maintaining a backup pressure of
1.0 MPa, in case of primary circuit
depressurisation - three dedicated DHR loops in helium (3100
redundancy) with secondary loops with pressurised
water connected to an external water pool
(ultimate heat sink). - Each DHR loops can remove the decay heat
- few minutes after the reactor SCRAM by natural
circulation in case of blackout transient (in
this case the primary pressure is nearly
constant, close to the nominal pressure 7 MPa) - few minutes after the SCRAM by forced circulation
in case of large break LOCA (in this case the
pressure is equal to the chosen back-up pressure
1Â MPa) DHR forced circulation is obtained by
one blower driven by an electrical motor which
can be supplied by batteries during one day, - one day after the SCRAM by natural circulation
and with a pressure of 1.0 MPa.
5RMPS application to the DHR system of GFR
- Objective Quantify the reliability of the DHR
in pressurised situation - Scenario
- Initiating event short duration Loss of Offsite
Power (10-2/reactor.year) - complete loss of Forced Circulation
(emergency diesel generators fail to start or
circulator failure) - Failure criteria
- Tfuel_max gt 1600C or Tupper_max gt 1250C between
0 and 24 hours - Critical parameter identification
- by deductive approach
6RMPS application to the DHR system of GFR
DHR nodalization in the CATHARE 2 code
Probabilistic distribution of the critical
parameters
- 100 simulations
- Latin Hypercube Sampling of these 9 random
variables - Evaluation by CATHARE code of core max
temperature
7RMPS application to the DHR system of GFR
100 CATHARE evaluations, no failure case
Sensitivity analysis
- FRPLAQ (multiplicative factor for laminar NC
pressure drop in the core region) - REPLAQ (Reynolds number for turbulent to laminar
transition in the core region) - T2DHR (ternary pool and secondary circuit
temperature level at DHR initiation)
Linear correlation between Tmax and 6 parameters
(R2 0,97)
TMAX 1016.5 (T2DHR0.30211) - (FUITE449.71)
(FRPLAQ63.027) - (ECPLAQ18.222)
-Â (REPLAQ2.415710-3) (ECDHX15.5575)
Failure probability lt 5.10-6
106 simulations
8RMPS application to the DHR system of GFR
Sensitivity study upon the DHR isolating valve
opening fraction
(1) Valve modelling in CATHARE Cv ? DP f(Pu)
(3) Criteria f(DP loop)
(2) Prametric study for ? Pu i.e. DP in NC loop
Propagation of uncertainty in CATHARE
calculations and reliability evanuation of the
DHR
Critical parameters and sampling identical to the
reference case
100 CATHARE evaluations
106 simulations
2272 cases gt 1600C (max. 1609C !)
Failure probability ? 2,3.10-3
9The European RAPHAEL Project RMPS exercise
to the Decay Heat Removal of an HTR
SP Safety - WP4 Safety approach and licensing
issues Nicolas DEVICTOR (CEA)
10RAPHAEL - SP Safety - WP4Exercise - Decay Heat
Removal
- Aim of the study
- to illustrate the application of method RMPS
(Reliability Method for Passive System) - to illustrate the different types of results and
their possible use in help of design and safety
analysis - Support for the exercise
- Simplified modelling of the GT-MHR
- See CRP 3 (on Heat Transport and Afterheat
Removal for Gas Cooled Reactors under accident
conditions) and report IAEA RECDOC-1163 - Content of the exercise
- Transient Loss of Fuel Coolant with
depressurization - Taking into account some uncertainty sources (see
slide 3), computation of the probability than
Tmax exceed 1600C and assessment of the most
influential uncertainty sources. - Note Tmax maximal value of the averaged
temperatures in the compacts
11RAPHAEL - SP Safety - WP4Exercise - Decay Heat
Removal
Simplified model
- Modelling developed under Cast3M environment
(ARCTURUS) - Components core, reflectors, core barrel,
baffle, reactor vessel, RCCS, concrete - Physical phenomena
- conduction,
- cavity radiation,
- exchange RCCS
- Boundary conditions
- Fixed heat exchange at the external concrete wall
- Fixed RCCS water temperature
- Model provided by CEA/DM2S/SFME
12RAPHAEL - SP Safety - WP4Exercise - Decay Heat
Removal
Uncertainty sources taken into account (without
correlation)
Result for nominal values Maximal temperature
1340.5C at 93 hours
13RAPHAEL - SP Safety - WP4Exercise - Decay Heat
Removal
- Conditional exceedance probability 0,0214
- Conditional to the scenario
- Conditional to the uncertainty model
- Reliability index (?) 2,0258Â
- Co-ordinates of the most probable failure point
- FORM method used
- 97 calls
- 1 call ?10mn
Comment the result should be confirmed by
Importance Sampling
14RAPHAEL - SP Safety - WP4Exercise - Decay Heat
Removal
15RAPHAEL - SP Safety - WP4Exercise - Decay Heat
Removal
- Sensitivity and elasticities on the ?
- Information for steering RD
- Average value of the conductivities
- in the reflector and the core
- Variability of conductivity
- in the reflector
- Bounds of the thermal inertia
- in the graphite
16APSRA methodology and application
- Assesment of Passive System ReliAbility (ASPRA)
developed by BARC (India) - A.K Nayak, M.R. Gartia, A. Antony, G. Vinod and
R.K.Sinha - Reliability analysis of a boiling two-phase
natural circulation system using the ASPRA
methodology. - Proceedings of ICAPP 2007, Nice, France
17APSRA methodology and application
APSRA methodology
18APSRA methodology and application
- Application to the MHT system of the AHWR
- Evaluation of the reliability of the boiling
two-phase system
The Main Heat Transport (MHT) system consists of
a common reactor inlet header from which 452
inlet feeders branch out to an equal number of
fuel channels in the core. The two-phase mixture
leaving the core is separated into steam and
water in the steam drum, by gravity. The feed
water issues in the form of jets through J tubes
allowing proper mixing of feed water with the
saturated water
19APSRA methodology and application
- Identification of natural circulation failure
(steps II and III) - For normal operational states, natural
circulation failure in AHWR occurs if - Clad surface temperature rises above 400C (673K)
or/and - CHF occurs with or without flow induced
instability - Key parameters causing the failure (step IV)
- Fission heat generation rate
- Level in steam drum
- Pressure in the system
- Feed water temperature/subcooling
- Calculation with best estimate code RELAP5/mod
3.2
20APSRA methodology and application
Parametric studies to determine the failure
points and generation of the failure surface
(step V)
21APSRA methodology and application
- Identify the causes for the deviation of key
parameters (step VI) - The deviation of key parameters caused by
- Failure of active components valves, pumps,
control systems - Failure of passive components passive valve
Fault tree /event tree analyses
22APSRA methodology and application
- Evaluation of failure probability for the system
(step VII)
the probability of failure for each point of the
failure surface can be calculated by considering
the probability of deviations of all those
parameters which are responsible for causing the
failure
23Passive system reliability analyses at MIT
The impact of uncertainties on the performance of
passive systems. L.P. Pagani, G.E. Apostolakis
P. Hejzlar Nuclear Technology Vol. 149 Feb. 2005
1
- Reliability analysis of the DHR system (2x50
loops) of a 600 MW GFR cooled by helium - Scenario LOCA transient
- Uncertain parameters power, pressure, cooler
wall temperature, Nusselts number and friction
factor, in forced, mixed and free convection. - Failure criteria Tcore gt 1600C in the hot
channel or Tcoregt 850C in the average channel - Simulation of the steady-state behavior
simplified T-H code - Reliability evaluation 10000 Monte Carlo
simulations
24Passive system reliability analyses at MIT
- Comparison passive (DHR in natural circulation)
VS active (DHR in forced circulation with
blowers) - Functional failure (due to uncertainties)
- ? Functional failure important for passive
system, negligible for active system - Functional failure hardware (components)
failures
? Active system failure dominated by the common
cause failure of the blowers. ? Active system
more reliable then passive for 2 and 3 loop
design ? Increase of redundancy more effective
for functional reliability
25Passive system reliability analyses at MIT
Incorporating reliability analysis into the
design of passive cooling systems with an
application to a gas-cooled reactor F.J. Mackay,
G.E. Apostolakis P. Hejzlar Nuclear Engineering
Design (Article in press)
- Reliability analysis of the DHR system (2x50
loops) of a 600 MW GFR cooled by helium - Scenario LOCA
- Failure criteria Tcladgt1600C or TDHR pipe
wallsgt850C - Simulation transient analysis with RELAP5-3D
- (the 2 DHR loop are modeled)
- Uncertain parameters core roughness, DHR
12check valve leakage, Containment structure
and core heat transfer coefs, shaft inertia - Reliability evaluation 128 LHS Monte Carlo
simulations - Failure probability estimation 0.305
26Passive system reliability analyses at MIT
- An important finding was the discovery that the
smaller pressure loss through the DHR heat
exchanger than through the core would make the
flow to bypass the core through one DHR loop, if
two loops operated in parallel. - This finding is a warning against modelling only
one lumped DHR loop and assuming that n of them
will remove n times the decay power. - Failure probability too high.
- Risk-based design changes insulation of DHR
pipes inner surface, minimise heat transfer of
the structure (increase back up pressure), use of
more reliable valve. - Proposal of use of a combination of active and
passive systems. - This study is an example of the kind of insights
that can be obtained by including a reliability
assessment of design process.