Title: STATUS OF IRSN LEVEL 2 PSA (PWR 900)
1 STATUS OF IRSN LEVEL 2 PSA(PWR 900)
- General objectives
- Content of the study
- Level 1 to Level 2 Interface
- Quantification of physical phenomena with
uncertainties in APET - A model for containment leakage through
containment penetrations - Radioactive releases model
- KANT a quantification software for level 2 PSA
2General objectives
- A level 2 PSA for French 900 MW PWR
- to contribute to reactor safety level
assessment, - to estimate the benefits of accident management
procedures, - to provide quantitative elements about
advantages of any reactor design or operation
modifications, - to acquire quantitative knowledge for emergency
management teams, - to help in definition of RD programs in the
severe accident field - learning from detailed studies are also extended
to other French Plants
3Steps
- 2000 - version (1.0) based on IRSN level 1 PSA
published in 1990 power states of reactor - 2003 version (1.1) - revision of 1.0 - power
states of reactor - 2004 version 2.0 - updated level 1 PSA
response surfaces method for uncertainties
assessment - hydrogen recombiners - 2005 version 2.1 shutdown states of reactor
-
4Content
- General methodology initially based on NUREG 1150
- Binning of level 1 PSA sequences in PDS
- Representation of important severe accident
events in an APET - Binning of level 2 PSA into Release Categories
- Assessment of radioactive releases for each
release category - Uncertainties assessment by Monte-Carlo method
5A detailed interface between level 1 to level 2
PSA
- 20 interfaces variables serve to define the Plant
Damage States and concern initiator event, system
and containment state, residual power, activation
of emergency plan.
PT RCS break size SF Component cooling or essential service water systems
PL RCS break localization AP Water makeup to RCS availability
RT SGTR number BA Safety injection water tank
VL V-LOCA SE Secondary system break
AS CHRS availability SO Pressurizer safety valve availability
BP Low pressure safety injection availability IE Containment isolation
HP High pressure safety injection availability CR Core criticity
GV SG availability PR Residual power
LC Electrical board availability (low voltage) PU Emergency plan
LH Electrical board availability (high voltage) RS Electrical network availability
6A detailed interface between level 1 to level 2
PSA
- A high level of description of system states
-
- Examples AS variables values
- 1 CHRS available and in service
- 2 CHRS available and not in service
- 3 CHRS not available, failure occurred at
demand - 4 CHRS not available, failure occurred in
function not contaminated - 5 CHRS not available, failure occurred in
function contaminated
7A detailed interface between level 1 to level 2
PSA
- 150 Plant Damage States have been defined for
power states. A representative thermal-hydraulics
transient is defined for each PDS
Number of PDS Number of thermal-hydraulics transients
LOCA (large break) 17 9
LOCA (medium break) 24 14
LOCA (small break) 8 8
LOCA (very small break) 10 10
SGTR 20 15
Secondary break 13 13
Loss of heat sink 13 10
Loss of steam generator water injection 17 17
Total loss of electrical power 12 6
8A detailed interface between level 1 to level 2
PSA
- Thermal-hydraulics transient are calculated with
the SCAR version of the simulator SIPA 2 (that
includes CATHARE 2). - Advantages of this approach
- to obtain a better evaluation of accident
kinetics and delays before releases, - to consolidate level 1 PSA assumptions,
- to define more precise conditions for severe acc.
Phenomena, - to provide a large panel of best-estimated
transients for use in other context (accident
management team, safety analysis)
9APET Quantification of physical phenomena with
uncertainties
- The different physical phenomena are organized in
physical models - each physical model represents a set of physical
phenomena that are tightly coupled - 2 separated models are linked by a limited
numbers of variables transmitted by the APET
10Physical models of APET
11Physical models of APETCodes
- Construction of physical model based on results
obtained by validated codes calculations.
Experts judgments are used for result
interpretation or when direct code calculations
are note possible
12Physical models of APETTwo methods are employed
- METHODE 1 RESPONSE SURFACES
- Downstream variables values F(upstream
variables values) - (Details provided in second workshop
presentation) - METHODE 2 GRID OF RESULTS
- For core degradation progression strong scenario
effects and discontinuities have to be taken into
account (valve opening, RCS cooling by SG, RCS
water injection ) - Construction of response surfaces would be a very
difficult task - Grid of result approach is used
13Physical models of APET Example of Core
degradation
- STEP 1 DEFINITION OF CALCULATIONS
- STEP 2 CONSTITUTION OF A RESULT GRID
Core degradation transient without actions
recommended by severe accident management guides
TH-system transient
PDS
Core degradation transient with actions
recommended by severe accident management guides
Transient N Identification variables values Identification variables values Identification variables values Identification variables values Identification variables values DCD downstream (results) variables values DCD downstream (results) variables values DCD downstream (results) variables values DCD downstream (results) variables values DCD downstream (results) variables values DCD downstream (results) variables values DCD downstream (results) variables values
14Physical models of APET Example of Core
Degradation
- STEP 3 RESULT GRID IN THE APET
- ONE SCENARIO DEPENDS ON SYSTEM AVAILIBILITY,
HUMAN ACTIONS, RESIDUAL POWER - A SELECTION TREE SELECTS THE MOST REPRESENTATIVE
TRANSIENT IN THE RESULTS GRID - THE DOWNSTREAM VALUES ARE EXTRACTED FROM THE
RESULTS GRID FOR THE REPRESENTATIVE TRANSIENT
15Leakage through containment penetrations b
mode
- A specific method has been developed to take into
account pre-existing leakage or isolation failure
during the accident - A specific software, BETAPROB has been developped
- A model is constructed
- System description (hydraulics components,
valves, pumps, sumps, rooms of auxiliary building
and ventilation/filtration level) - Failure probabilities (l, failure in operation,
g, failure on demand) - Severe (100 section) and non severe (1
section) are distinguished)
16Leakage through containment penetrationsAPET
Model
- For each system configuration, BETAPROB
calculates all the possible leakage paths and
proposes a classification of leakage paths as a
function of - Nature of release source (liquid from RCS or
gaseous from containment atmosphere) - Transfer mode to environment in function of
ventilation systems and filtration - Leakage section
- In the APET, for each systems configurations are
calculated - Probabilities of leak categories in term of
leakage section - Probabilities of leak categories in term of
filtration efficiency
17The radioactive releases calculation model
- A simplified model has been developed for level 2
PSA. - Each level 2 sequence is characterized by APF
variables that give information on accident
progression and containment failure. - The model can calculate radiaoactive releases as
a time function of time for each combination of
APF variables. - Uncertainties have been taken into account for
most influent parameters.
18The radioactive releases calculation
modelFission product emission
Noble Gases
Volatil molecular iodine
Progressive Aerosol Emission
Melt - corium
First corium flow
Vessel Break
1100 C
19Fission products behavior in containment
- Containment atmosphere composition
- Aerosol mass in suspension depends on emission,
energetic phenomena in RCS (steam explosion) or
in containment (Combustion), natural deposition,
spray system (CSHRS) efficiency and containment
leakage - Molecular iodine depends on emission, painting
adsorption, spray system (CSHRS) efficiency and
containment leakage - Organic iodine depends on adsorbed molecular
iodine to organic iodine and containment leakage - Noble gases depends on emission and
containment leakage - Radioactive releases depend on
- Containment leakage size (mass flow),
- Containment atmosphere composition,
- Aerosol filtration and iodine retention,
- Activity as a function of delay after SCRAM
-
20The radioactive releases calculation
modelGraphical interface
- A graphical interface allows interactive
calculation in function of APF variables values
21KANT A software for level 2 PSA quantification
- A specific software, able to take into account
the specifities of the IRSN methodologies has
been developed. - The software is linked with the releases model
- Operational for Windows operating system (C,
MFC, Access) - 3 main modules
- APET development (subtrees, specific language for
model) - APET quantification (Monte-Carlo method)
- Results vizualization
22KANTExample of results vizualization
23KANTPerspectives
- Future Improvements
- Extension of functionalities in terms of results
presentation - Identification and quantification of early
radioactive releases - Graphical presentation of the APET
- A convivial interface to give access to main
results
24Conclusions
- A detailed level 2PSA for French 900 MW is
performed by IRSN with some specifities - Systematic use of validated codes
- Original models (containment leakage, human
factor) - Detailed interface and large transient
calculation - A specific software, KANT, operational since
1998, with a development program - Future
- 2004 Analysis of French Utility approach for
level 2 PSA - 2004 Version 2.0 for power states of reactor
(recombiner, ) - 2005 Version 2.1 for shutdown states of
reactor - 2006 ? Improvement of methods (dynamic fiability
?, interface ?), - Other plant application (?)