Analysis of Representative DEC Events of the ETDR with RELAP5
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Transcript of Analysis of Representative DEC Events of the ETDR with RELAP5
Analysis of Representative DEC Events of the ETDR with RELAP5
LEADER Project: Task 5.5
G. Bandini - ENEA/Bologna
LEADER 5th WP5 MeetingJRC-IET, Petten, 26 February 2013
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Outline
Analysed DEC transients at EOC Transient results Conclusions
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Analyzed DEC transients at EOC
Main events and reactor scram thresholdTRANSIENT Initiating Event Reactor
scram Primary
pump trip MHX
FW trip MSIV
closure DHR startup
TR-4: UTOP Insertion of 250 pcm in 10 s No No No No No
TDEC-1: ULOF All primary pumps coastdown No 0 s No No No
TDEC-3: ULOHS All MHX feedwater trip No No 0 s 1 s DHR-1 at 2 s (3 IC loops)
T-DEC4: ULOHS+ULOF All primary pumps and MHXs feedwater trip No 0 s 0 s 1 s DHR-1 at 2 s
(3 IC loops)
T-DEC5: Partial blockage in the hottest FA
10% to 97.5% blockage at the hottest FA inlet No No No No No
TO-3: All prim. pumps stop + reduction of FW temperature
T-fw: 335330°C in 1s + all p. pumps stop
2 s, low pump speed 0 s 2 s 2 s DHR-1 at 3 s
(4 IC loops)
TO-6: All prim. pumps stop + increase of FW flow rate
FW-flow +20% in 25 s + all p. pumps stop
2 s, low pump speed 0 s 2 s 2 s DHR-1 at 3 s
(4 IC loops)
T-DEC6: SCS failure Depressurization of all secondary circuits
2 s, low sec. pressure No 2 s No No
UN
PRO
TECT
EDPR
OTE
CTED
TR-4: Reactivity insertion (UTOP) (1/2)
Core and MHX powers
ASSUMPTIONS: Insertion of 250 pcm in 10 s without reactor scram No feedwater control on secondary side Fuel-clad linked effect fuel expansion according to clad temperature (closed gap)
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Total reactivity and feedbacks
The reactivity insertion is mainly counterbalanced by Doppler effect initial core power rise up to 680 MW
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TR-4: Reactivity insertion (UTOP) (2/2)
Core temperatures
MAIN RESULTS: Maximum clad temperature remains below 650 °C Maximum fuel temperature of 2930 °C at t = 57 s (hottest FA, middle core plane,
fuel pellet centre) exceeds the MOX melting point (~2670 °C) only local fuel melting no extended core melting
Core temperatures
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T-DEC1: ULOF transient (1/2)
ASSUMPTIONS: All primary pumps coastdown without reactor scram No feedwater control on secondary side Fuel-clad not-linked effect fuel expansion according to fuel temperature (open gap)
Active core flowrate Core and MHX powers
Natural circulation in the primary circuit stabilizes at 23% of nominal value Core power reduces down to about 200 MW due to negative reactivity feedbacks
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T-DEC1: ULOF transient (2/2)
Core temperatures
Core temperatures
MAIN RESULTS: Initial clad peak temperature of 764 °C Max clad temperature stabilizes below
650 °C No clad failure is expected in the short
and long term No vessel wall temperature increase
Total reactivity and feedbacks
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T-DEC3: ULOHS transient (1/2)
ASSUMPTIONS: Loss of feedwater to all MHXs without reactor scram Startup of DHR-1 (3 out of 4 IC loops of in service) No heat losses for the external vessel wall surface
Core power progressively reduces down towards decay level Maximum clad and vessel temperatures rise up to 700 °C after about one hour
Core and MHX powers Core and vessel temperatures
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Total reactivity and feedbacksCore temperatures
T-DEC3: ULOHS (2/2)
MAIN RESULTS: No fuel rod clad rupture is expected in the medium term No vessel failure is expected in the medium term (to be verified) Enough grace time is left to the operator to take the opportune corrective actions
and bring the plant in safe conditions in the medium and long term
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T-DEC4: ULOHS+ULOF transient (1/2)
Active core flowrate Core and MHX powers
ASSUMPTIONS: Loss of feedwater to all MHXs and all primary pumps without reactor scram Startup of DHR-1 (3 out of 4 IC loops of in service) No heat losses from the external vessel wall surface
Natural circulation in primary circuit reduces down to very low value (around 1%) Core power progressively reduces down towards decay level
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T-DEC4: ULOHS+ULOF transient (2/2)
MAIN RESULTS: Max T-clad rises up to 800 °C after about 15 minutes and stabilizes around 825 °C
no fuel rod clad rupture is expected in the short and medium term (to be verified) No vessel failure is expected in the medium and long term Enough grace time is left to the operator to take the opportune corrective actions
and bring the plant in safe conditions in the medium and long term
Core temperatures Total reactivity and feedbacks
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TO-3: FW temp. reduction (1/2)
Active core flowrate (short term)
Active core flowrate (long term)
ASSUMPTIONS: Loss of one preheater (FW temperature
from 335 °C down to 300 °C in 1 s) + all primary pumps coastdown
Reactor scram at t = 2 s on low primary pump speed signal
Startup of DHR-1 (4 IC loops in service)
Core temperatures
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TO-3: FW temp. reduction (2/2)
Core decay and MHX powers Primary lead temperatures
MAIN RESULTS: Power removal by 4 IC loops of DHR-1 system is about 7 MW No risk of lead freezing after DHR-1 startup Lead freezing at MHX outlet is reached after about 2 hours (cold lead at the MHX
outlet flows to the core inlet without mixing with the hotter lead of the cold pool surrounding the MHXs)
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TO-6: FW flowrate + 20% (1/2)
Core temperatures
Active core flowrate (short term)
Active core flowrate (long term)
ASSUMPTIONS: FW flowrate increase of 20% + all primary
pumps coastdown Reactor scram at t = 2 s on low primary
pump speed signal Startup of DHR-1 (4 IC loops in service)
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TO-6: FW flowrate + 20% (2/2)
MAIN RESULTS: Power removal by 4 IC loops of DHR-1 system is about 7 MW No risk of lead freezing after DHR-1 startup Lead freezing at MHX outlet is reached after about 2 hours (cold lead at the MHX
outlet flows to the core inlet without mixing with the hotter lead of the cold pool surrounding the MHXs)
Core decay and MHX powers Primary lead temperatures
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T-DEC6: SCS failure (1/2)
Secondary pressure
Core and MHX powers
Primary lead temperatures
ASSUMPTIONS: Depressurization of all secondary circuits
at t = 0 s (no availability of the DHR) Reactor scram at t = 2 s on low
secondary pressure
Initial MHX power increase up to 850 MW no risk for lead freezing
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T-DEC6: SCS failure (2/2)
Core decay and MHX powers Core and vessel temperatures
MAIN RESULTS: No risk for lead freezing in the initial transient phase Slow primary temperature increase due to large thermal inertia of the primary
system (effective mixing in the cold pool surrounding the MHXs) large grace time for the operator to take opportune corrective actions
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TDEC-5: Partial FA blockage
ASSUMPTIONS: Total ΔP over the FA = 1.0 bar ΔP at FA inlet = 0.22 bar Partial flow area blockage
at FA inlet No heat exchange with
surrounding FAs
MAIN RESULTS: 75% FA flow area blockage 50% FA
flowrate reduction 85% blockage T-max clad = 700 °C No clad melting if area blockage < 95% Fuel melting if area blockage > 97.5% 50% inlet flow area blockage can be
detected by TCs at FA outlet
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Conclusions
The analysis of DEC transients with RELAP5 code has highlighted the very good intrinsic safety features of ALFRED design thanks to:
Good natural circulation characteristics, Large thermal inertia, and Prevalent negative reactivity feedbacks
In all analyzed transients there is no risk for significant core damage or risk for lead freezing large grace time is left to the operator to take the opportune corrective actions and bring the plant in safe conditions in the medium and long term
The RELAP5 results for unprotected transients (UTOP, ULOF, ULOHS and ULOHS+ULOF) are confirmed by the results of the analyses performed with the CATHARE code