*TATSUYA KUNISHI, HITOSHI MUTA, KEN MURAMATSU AND YUKI KAMEKO
TOKYO CITY UNIVERSITY GRADUATE SCHOOL
1
Methodology of Treatment of Multiple Failure Initiating Events for Seismic PRA
(2)Success Criteria Analysis for Multiple Pipe Break Accidents of a PWR
Contents
2
• Background & Purpose • Position of this study • Analysis conditions • Results & Consideration • Conclusion & Future task
Background
3
• Multiple rupture events are not usually considered in PRAs of pressurized water reactors (PWRs) for internal events.
• Analyses assuming pipe break accidents in multiple location are not extensively performed.
• The possibility of Multiple Pipe Break Accidents occurrence by earthquake
is very small, but the release of radioactive material etc. may be considered .
• Understanding the thermal hydraulic behavior in the reactor vessel and success criteria for core cooling systems considering beyond DBA
Purpose
Position of this study
4
1. Location (Location dependency) Effects of differences in location of the break points Confirm the influence by a combination of various break points.
2. Number of break points (Number of break points dependency) Relationship between fracture area and number of break points Confirm the difference in behavior due to the number of break points, assuming the Fracture area of the primary system piping is constant.
3. Fracture area (Fracture Area dependency) Relationship between the fracture area and the number of break points when changing the fracture area Confirm how the behavior differs depending on the size of the fracture area of the primary system piping from the viewpoint of 2.
In this study, we analyzed the following viewpoint and organized the findings.
Analysis Conditions
5
• The target model plant is 3-loop PWR (Output Power 2660MWt)
• 3-loops were separately modeled • Detailed dimensions of the 3 loops PWR plant are not disclosed • Lack of detailed dimension data were filled with simplified models.
Model Plant
RELAP (Reactor Excursion Leak Analysis Program) series Thermal hydraulic analysis code RELAP5-3D It is a well known and widely used code for thermal-hydraulic analysis.
Analysis Code
Validity of the plant model was checked by comparison with published LOCA analyses for similar PWRs.
Noding diagram
6 Noding diagram used for analysis
Pipe rupture is simulated by valve
HPIS ACC LPIS
HPIS ACC LPIS
HPIS
ACC LPIS
: Volume
: Junction
: ECCS`s
Crossover(CR)
Hot leg(HL)
Cold Leg(CL)
Pressurizer surge pipe(Psu)
• Rupture of primary system piping • Loss of ECCS function Accident Scenarios
Analysis cases
7
Number of points Location Fracture area ECCS operation
1 CR CL HL Psu Large~Small* area HPIS 2 line LPIS 2 line ACC 3 line
(Combination of ECCS actuation)
2~ Combination of CR CL HL Psu
Changing the fracture area (Combination of Large
, Medium, Small*)
*:Large(rupture area of pipe inner diameter), Medium (rupture area of pipe inner diameter ½),Small is 2 inches rupture area
Location Diameter*[m] Fracture Area*[m2]
Large Medium Small Crossover pipe 0.79 0.490 0.1225 0.0081 Hot Leg pipe 0.74 0.430 0.1075 0.0081 Cold Leg pipe 0.70 0.385 0.0962 0.0081
Pressurizer surge pipe 0.28 0.062 0.0154 0.0081
Analysis Flow
8
②Select the Scenario and Pipe Combination
③Analysis the selected conditions Definition of Success Criteria and Analysis
Based on analysis result
Change scenario and reset piping combination
①Construction of Input Data and
Benchmark
④ Clear the event progress and summarized the technical knowledge on Success Criteria of core cooling
Applied to seismic PRA, contributing to safety improvement
Definition of conditions for success of core cooling in progress scenario of accident
Understanding the thermal-hydraulic behavior &
Grouping the analysis results that is Similar
Assumption of multiple piping rupture
9
1. Location (Location dependency) The fracture area are 100% rupture of the pressurizer surge pipe. Equal fracture is assumed for hot leg , crossover, cold leg .
2. Number of break points (Number of break points dependency) The fracture area are 100% rupture of the pressurizer surge pipe. In 2 break points, each points fracture area is 50% rupture of the pressurizer surge pipe.
3. Fracture area (Fracture area dependency) Fracture area twice as large as the pressurizer surge pipe in hot leg, crossover, cold leg.
Definition of core damage shall be when the surface temperature of cladding exceeds 1200 ͦC. (about 1500 K)
Evaluation
Analysis Cases
10
Number of points Location Fracture area ECCS operation
1 CR CL HL Psu Large~Small* area HPI 2 line LPI 2 line
ACC 3 line (Combination of ECCS
actuation) 2 Combination of CR CL HL Psu
Changing the fracture area (Combination of Large
, Medium, Small*)
Analysis Combination[Location]
11
Number of break points Piping Combination Case
1
Crossover pipe (CR) No ECCS operate HPI+LPI+ACCx3
HPIx2+LPIx2+ACCx3
Hot leg pipe (HL) No ECCS operate HPI+LPI+ACCx3
HPIx2+LPIx2+ACCx3
Cold leg pipe (CL) No ECCS operate HPI+LPI+ACCx3
HPIx2+LPIx2+ACCx3
Pressurizer Surge pipe (Psu) No ECCS operate HPI+LPI+ACCx3
HPIx2+LPIx2+ACCx3
Analysis Results (No ECCS operate)
12
0
500
1000
1500
2000
2500
0 100 200 300 400 500
Tem
pera
ture
of f
uel c
ladd
ing
[K]
Time [sec]
Surface temperature of fuel cladding
CL CR
HL Psu
Timings of temperature rise are different, however, temperature rise does not differ greatly each other CL break could represent because of it’s the severest behavior, if simplification needed
Analysis Results (HPI+LPI+ACCx3)
13
0
100
200
300
400
500
600
700
800
0 100 200 300 400 500
Tem
pera
ture
of f
uel c
ladd
ing
[K]
Time [sec]
Surface temperature of fuel cladding
CL CR
HL Psu
Cooling timing are different because of RV pressure behavior and cooling order is CL, CR , HL and Psu And the CL takes more time to cool down
Analysis Results (HPIx2+LPIx2+ACCx3)
14
0
100
200
300
400
500
600
700
0 100 200 300 400 500
Tem
pera
ture
of f
uel c
ladd
ing
[K
Time [sec]
Surface temperature of fuel cladding
CL CR
HL Psu
Behavior is same as the previous case HPI+LPI+ACCx3. Cool down little bit faster because of the capacity of injection
Conclusion for the Location
15
From the results, • Severer in the order of Cold leg > Crossover > Hot leg≧
Pressurizer surge pipe • Different behavior depending on the location and the severest one
is CL break
Location of break could affect plant behavior
Analysis Combination [break points]
16
Number of break points Piping Combination Case
1 Cold leg pipe (CL) No ECCS operate
HPIx2+LPIx2+ACCx3
2
CL+HL(Same loop) CL+HL (Different loop)
No ECCS operate HPIx2+LPIx2+ACCx3
CL+CL No ECCS operate
HPIx2+LPIx2+ACCx3
Analysis Results (No ECCS operate)
17
0
500
1000
1500
2000
2500
0 100 200 300 400 500Tem
pera
ture
of f
uel c
ladd
ing
[K]
Time [sec]
Surface temperature of fuel cladding
CL
CL+HL(Different loop)
0
500
1000
1500
2000
2500
0 100 200 300 400 500Tem
pera
ture
of f
uel c
ladd
ing
[K]
Time [sec]
Surface temperature of fuel cladding
CL
CL+HL(same loop)
0
500
1000
1500
2000
2500
0 100 200 300 400 500
Tem
pera
ture
of f
uel c
ladd
ing
[K]
Time [sec]
Surface temperature of fuel cladding
CL
CL+CL Same Behavior No dependency at breakpoints
There is Location
dependency influence
Location dependency exists in the case of different loops
Analysis Results (HPIx2+LPIx2+ACCx3)
18
0
100
200
300
400
500
600
700
0 100 200 300 400 500Tem
pera
ture
of f
uel c
ladd
ing
[K]
Time {sec]
Surface temperature of fuel cladding
CL
CL+HL(Different loop)
0
100
200
300
400
500
600
700
0 100 200 300 400 500Tem
pera
ture
of f
uel c
ladd
ing
[K]
Time [sec]
Surface temperature of fuel cladding
CL
CL+HL(same loop)
0100200300400500600700
0 100 200 300 400 500
Tem
pera
ture
of f
uel c
ladd
ing
[K]
Time [sec]
Surface temperature of fuel cladding
CL
CL+CL
It take more time to cool for the 2 points break case
If all ECCS inject into RV, the core will cool faster
Conclusion for the Break points
19
From the result, • 1 point break of CL and 2points break CL+CL are quite
similar behavior, so NO dependency could exist in number of break points
• However, 2 points break of the combination of different loops, location dependency could exist
There is no Dependency of Number of break points in the same position However,
Location dependency could exist in the different position
Analysis Combination[Fracture area]
20
Fracture area Piping Combination Case
100% Pressurizer surge pipe
Cold leg pipe (CL)
No ECCS operate
HPI+LPI+ACCx3
HPIx2+LPIx2+ACCx3
200% Pressurizer surge pipe
Cold leg pipe (CL)
No ECCS operate
HPI+LPI+ACCx3
HPIx2+LPIx2+ACCx3
Analysis Results (No ECCS operate)
21
0
500
1000
1500
2000
2500
0 50 100 150 200 250 300 350 400
Tem
pera
ture
of f
uel c
ladd
ing
[K]
Time [sec]
Surface temperature of fuel cladding
CL
CL200%
Timing of temperature rise are different However, In different of fracture area, temperature rise rate does not differ greatly
Analysis Results (HPI+LPI+ACCx3)
22
0
100
200
300
400
500
600
700
800
0 50 100 150 200 250 300 350 400
Tem
pera
ture
of f
uel c
ladd
ing
[K]
Time [sec]
Surface temperature of fuel cladding
CL
CL200%
The bigger fracture area size, the faster the clad temperature rise However, ECCS could operate earlier that core could be cooled down faster than smaller size of fracture area
Analysis Results (HPIx2+LPIx2+ACCx3)
23
0
100
200
300
400
500
600
700
800
0 50 100 150 200 250 300 350 400
Tem
pera
ture
of f
uel c
ladd
ing
[K]
Time [sec]
Surface temperature of fuel cladding
CL
CL200%
Same as ECCS injected case with single failure
The bigger fracture area size, the faster the clad temperature rise However, ECCS could operate earlier that core could be cooled down faster than smaller size of fracture area
Conclusion for the Fracture area
24
From the results • The size of fracture area is different, the temperature rising
point is different • However, the temperature rise does not differ greatly
regarding to the fracture area • Even in all ECCS operate or the case considering single
failure of ECCS, cooling speeds are not different greatly
Rupture fracture area could affect plant behavior
Summary
25
Considering to define Success Criteria, the followings need to be discussed • Location of break could affect plant behavior
Cold leg break is the severest case. • There could be no dependency of the number of break points in the same
position
• Fracture area dependency need to be noted in considering success criteria.
• In this presentation , primary piping ruptures are focused on, but consideration should also be given to the combinations with secondary piping such as steam generator tube.
• The technical knowledge on Success Criteria of core cooling should be summarized, and it should be applied to seismic PRA
Future task
Conclusion