Consultants’ Meeting: Education Training Seminar on Fast Reactors Science and Technology ITESM Campus Santa Fe, Mexico City – 29 June -03 July 2015 m… [628388]

1
ALFRED
Alessandro Alemberti

Consultants’ Meeting: Education
Training Seminar on Fast Reactors
Science and Technology
ITESM Campus Santa Fe, Mexico City –
29 June -03 July 2015 m

2 SUMMARY
• Main Goals of ALFRED
• ALFRED Design from LEADER project
• Core
• Safety Systems
• General lay -out
•Summary of recent developments
•Primary arrangement
•New Decay heat removal
•Safety vessel
•DHR -1 with non -condensable

ALFRED

3 ALFRED – MAIN DESIGN GUIDELINES
ALFRED will be connected to the electrical grid (Reactor Power ~ 125 MWe )
ALFRED design should be as much as possible based on available technology
to speed up the construction time
ALFRED shall use structural materials compatible with the corrosive Lead
used as coolant (Selected material AISI 316LN, T 91, 15-15/Ti)
ALFRED design shall limit coolant flow velocity compatible with the erosive
Lead used as coolant
ALFRED design solutions shall allow components to be removed from the
Reactor Vessel to facilitate inspection, maintenance, replacement
ALFRED design solutions (especially for Safety and Decay Heat Removal
function) should be characterized by very robust and reliable choices to
smooth the licensing process
ALFRED Decay Heat Removal Systems shall be based on passive technology
to reach the expected high Safety level (low primary system pressure drops
to enhance natural circulation ) ALFRED

4
MAIN
COOLANT
PUMP
REACTOR
VESSEL SAFETY VESSEL FUEL ASSEMBLIES
STEAM
GENERATOR
ALFRED – Reactor Configuration
ALFRED Main Characteristics
Electrical capacity: 125MWe
Thermal capacity: 300MWth
Primary Coolant Lead
Primary Circulation
Normal Operation
Accident Conditions
Forced ( 8mechanical pumps)
Natural
Primary System Pressure: < 0.1MPa
Primary System Temperature: 400÷480 °C
Primary System Flowrate 26000 kg/s
Secondary Coolant: Water/Superheated -Steam
Secondary System Pressure: 18 MPa
Superheated Steam
Temperature: 450 °C
Secondary Coolant Flowrate 193 kg/s
Fuel Material: MOX
Fuel Cycle/Residence time: 12 Months / 5 Years
Residual heat removal
systems: 2 DHR systems, 4 loops each –
Passive
Design Life: 40 Years

5 ALFRED – Core Configuration
Power (MWth ) 300
Fuel Assemblies
Inner core
Outer core 171
57
114
Fuel type MOX
Pu enrichment
Inn/Out (at %) 21.7 /27.8
Control/shutdown
Rods 12
Safety Rods 4
Dummy elements 110
Fuel Batches 5
Fuel cycle length 365 EFPD
Peak/ avg BU ( MWd /t) 103/73.3

6 ALFRED – Fuel Pin & Assembly
1390
Overall length 8000

7 ALFRED – Reactor Control and Shutdown System
•Two redundant, independent and diverse shutdown systems
are designed for ALFRED (derived from MYRRHA design)
•The Control Rod (CR) system used for both normal control of
the reactor and for SCRAM in case of emergency
–CR are extracted downward and rise up by buoyancy in case of
emergency shutdown (SCRAM)
–During reactor operation at power CR are most of the time partly
inserted allowing reactor power tuning (each rod is inserted for a
maximum worth less than 1$ of reactivity)
•The Safety Rod (SR) system is the redundant and diversified
complement to CR used only for emergency shutdown SCRAM
–SR are fully extracted during operation at power
–SR are extracted upward and inserted downward by the actuation
of a pneumatic system (insertion by depressurization – fail safe)
–A Tungsten ballast is used to maintain SR inserted
•Reactive worth of each shutdown system is able to shutdown
the reactor even if the most reactive rod of the system is
postulated stuck
CR SR

8 ALFRED – Upper and Lower Core Support Plates
Lower core support plate
Box structure with two horizontal perforated plates
connected by vertical plates .
Plates holes are the housing of FAs foots .
The plates distance assures the verticality of Fas.
Hole for
Instruments Box structure as lower grid but more stiff.
It has the function to push down the FAs during
the reactor operation
A series of preloaded disk springs presses each FA
on its lower housing Upper core support plate

9
ALFRED – Inner Vessel
Inner Vessel assembly
Upper grid
Lower grid Pin Inner Vessel has the
main functions of
core support and
hot/cold plena
separation.
Fixed to the cover by
bolts and radially
restrained at bottom
(replaceable).
Core Support plate is
mechanically
connected to the IV
with pins for easy
removal/replacement

10 ALFRED – Steam Generator
Bayonet vertical tube with
external safety tube and
internal insulating layer

The internal insulating layer
(delimited by the Slave tube )
has been introduced to
ensure the production of
superheated dry steam

The gap between the
outermost and the outer
bayonet tube is filled with
pressurized helium to permit
continuous monitoring of
the tube bundle integrity . high
conductivities particles are
added to the gap to enhance
the heat exchange capability

In case of tube leak this
arrangement guarantees that
primary lead does not interact
with the secondary water

Water
Hot Lead
Cold Lead Steam Bayonet Tube Concept

11 ALFRED – Steam Generator Geometry &Performances
Steam Generator Performance
Removed Power [MW] 37.5
Inlet Lead Temperature [ C] 480
Outlet Lead Temperature [ C] 400
Feed -water Temperature [ C] 335
Steam Temperature [ C] 450
SG steam/water side global ∆p [bar] 3.3
Steam Generator Geometry
Number of coaxial tubes 4
Slave tube O.D 9.52 mm
Slave tube thickness 1.07 mm
Inner tube O.D 19.05 mm
Inner tube thickness 1.88 mm
Outer tube O.D 25.4 mm
Outer tube thickness 1.88 mm
Outermost tube O.D 31.73 mm
Outermost tube
thickness 2.11 mm
Length of exchange 6 m
Number of tubes 510

12 ALFRED – Primary Pump – LEADER Option
Parameters Value
Flow rate, kg/s 3250
Head, bar 1.5
Outside impeller diameter, mm 590
Hub diameter, mm 390
Impeller speed, rpm 315
Number of vanes 5
Vane profile NACA 23012
Suction pipe velocity, m/s 1.1
Vanes tip velocity, m/s 9.8
Meridian (at impeller entrance
and exit) velocity, m/s 2.0 Axial Mechanical Pump Type

13 ALFRED – Primary Pump – New Option

Screw Pump Type
•Promising design
•Low relative speed
•Good performance

14 ALFRED – Reactor Vessel
Cylindrical Vessel with a torispherical bottom head
Anchored to the reactor cavity from the top
Cone frustum, welded to the bottom head, provides radial support
of the Inner Vessel
Inner Vessel radial
support Support flange Cover
flange
Main Dimensions

Height, m 10.13
Inner diameter, m 8
Wall thickness, mm 50
Design temperature, C 400
Vessel material AISI 316L

15 ALFRED – Decay Heat Removal Systems
•DHR Systems
–One non safety -grade system, the secondary system, used for
normal decay heat removal
–Two independent, high reliable passive and redundant safety –
related Decay Heat Removal systems (DHR N 1 and DHR N 2):
•in case of unavailability of the secondary system, the DHR system N 1
is called to operate and
•in the unlike event of unavailability of the first two systems, the DHR
system N 2 is called to operate
•DHR N 1:
–Isolation Condenser system connected to 4 out of 8 SGs
•DHR N 2:
–Isolation Condenser system connected to the other four SGs
•Considering that, each SG is continuously monitored , ALFRED is a
demonstrator and a redundancy of 266% is maintained, the Diversity
concept could be relaxed
•DHR Systems features:
Independence: two different systems with nothing in common
Redundancy: three out of four loops (of each system) sufficient
to fulfil the DHR safety function even if a single failure occurs
Passivity: using gravity to operate the system (no need of AC
power)

16 ALFRED – Isolation Condenser Heat Exchanger
•Upper and lower spherical header
diameter 560 mm
•Tube diameter 38.1 mm
•Number of tubes 16
•Average tube length 2 m
•Material Inconel 600

17 ALFRED – DHR System Performances
300320340360380400420440460480500
0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000°C
sCore inlet temp
Core outlet temp
300350400450500550
0 5,000 10,000 15,000 20,000 25,000°C
sCore inlet temp
Core outlet temp
3 Loops in operation (Minimum performances)
Lead Peak Temperature  500C
Time to freeze > 8 hours 4 Loops in operation (Maximum performances)
Lead temperature < nominal
Time to freeze  4 hours Freezing temperature Freezing temperature

18 ALFRED – Secondary System
•Power conversion system based on superheated
cycle
•with dual turbine configuration, three extractions in
the HP and in the LP with an axial outlet
•Net cycle efficiency greater than 41% Plant net output, MWe 125
Cycle Net Efficiency, % 41
Mass Flow, kg/s 193
Pressure, MPa 18
Steam Temperature, C 450

19 09/07/2015 ALFRED – Reactor Building: Vertical Section

20 09/07/2015 ALFRED – RECENT DEVELOPMENTS
From the end of the LEADER project we performed a
complete review of the main primary arrangement and
components following also recommendations received
from TSOs and suggestions of the partners of a
consortium (FALCON) dedicated to ALFRED development
and construction.

The main modifications are illustrated in the following
slides concerning the following aspects:

•Primary arrangement
•Safety vessel
•New Decay heat removal (DHR -2)
•DHR -1 with non -condensable

21 09/07/2015 ALFRED – NEW PRIMARY ARRANGEMENT
The main modification are:

•4 primary pumps
•4 Steam Generators
•Elimination of direct
connection between SG and
Core (the SG outlet do not
feed directly the lower
plenum below the core)
•Introduction of DHR -2 HX

22 09/07/2015 ALFRED – SAFETY VESSEL MODIFICATION
No more Safety Liner  Safety Vessel

•Enlargement of the Reactor cavity (+ 800 mm);
•Concrete refractory layer (~ 770 mm) between the Safety Vessel
and the concrete structure;
•additional air gap placed between the Safety Vessel and the
refractory concrete (~ 30 mm) (thermal expansion);
•Reduction of the Vessel’s gap dimension ( -150 mm);
•Implementation of a Reactor Cavity Cooling System;
•Change of the Reactor Support;

Main Requirements:
Refractory
Insulating
Uncompressible (as needed)
Formable by casting
4 intakes
4 chimneys new vessel support
to chimney
from intake hot collector
hot collector
refractory filler
safety vessel
Lightweight
concrete reactor vessel

24 09/07/2015 ALFRED – SAFETY VESSEL MODIFICATION
CFD analysis
confirm that
structural concrete
temperatures are
acceptable

heat losses from
vessel (normal
operation are close
to 200 KW)

25 ALFRED DHR CONFIGURATION IN LEADER
•Main problem to be
solved is the short
time to freezing when
ICs are called to
operate

•Ansaldo registered a
patent….
Steam
Generators DHR -1 anti-freezing system

26 Piacenza 17 – 04 –
2014 “Anti -freezing” system for DHR in
HLM -cooled reactors :
•Noncondensable gas tank
connected to IC lower header;
•When power removed by ICS >
primary coolant power
 ICS depressurises
 noncondensable gas expands
 NC-Gas reach IC tubes
 heat exchange is reduced
•pICS stabilised;
•Tprimary stabilised > Tfreezing

Pb pool Steam Generator Condenser Noncondensable gas tank ANSALDO “ANTI -FREEZING” SYSTEM

27 ALFRED – New DHR 1 – grace time to freezing
300 350 400 450 500 550 600
0 1 2 3 4 5 6 7 8 9 10Temperature [ °C]
time [days](d) Pb temperature at SG outlet
SG outlet T
Pb freezing point
300 350 400 450 500
0 50 100 150 200 250Temperature [ °C]
time [min](c) Pb temperature at SG outlet
SG outlet T
Pb freezing point
Innovative DHR System Old DHR System ALFRED: Lead temperature during Station Black Out

OLD DHR 1- about 4 hours to freezing

NEW DHR 1 with NC – 4-5 Days (judged sufficient for
operator action)

28
ALFRED