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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

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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

AL

FR

ED

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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, T91, 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)

AL

FR

ED

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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

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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

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ALFRED – Fuel Pin & Assembly

1390

Overall length 8000

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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

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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

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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

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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

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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

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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

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ALFRED - Primary Pump – New Option

Screw Pump Type

• Promising design

• Low relative speed

• Good performance

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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

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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 N1 and DHR N2): • in case of unavailability of the secondary system, the DHR system N1

is called to operate and • in the unlike event of unavailability of the first two systems, the DHR

system N2 is called to operate

• DHR N1: – Isolation Condenser system connected to 4 out of 8 SGs

• DHR N2: – 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)

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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

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ALFRED - DHR System Performances

300

320

340

360

380

400

420

440

460

480

500

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

°C

s

Core inlet temp

Core outlet temp

300

350

400

450

500

550

0 5,000 10,000 15,000 20,000 25,000°C

s

Core inlet temp

Core outlet temp

3 Loops in operation (Minimum performances)

Lead Peak Temperature 500C

Time to freeze > 8 hours

4 Loops in operation (Maximum performances)

Lead temperature < nominal

Time to freeze 4 hours

Freezing temperature Freezing temperature

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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

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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

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ALFRED – SAFETY VESSEL MODIFICATION

CFD analysis

confirm that

structural concrete

temperatures are

acceptable

heat losses from

vessel (normal

operation are close

to 200 KW)

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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

DH

R-1

an

ti-f

ree

zin

g s

ys

tem

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

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ALFRED – New DHR1 – grace time to freezing

300

350

400

450

500

550

600

0 1 2 3 4 5 6 7 8 9 10

Te

mp

era

ture

[°C

]

time [days]

(d) Pb temperature at SG outlet

SG outlet TPb freezing point

300

350

400

450

500

0 50 100 150 200 250

Te

mp

era

ture

[°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 DHR1- about 4 hours to freezing

NEW DHR1 with NC – 4-5 Days (judged sufficient for

operator action)

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ALFRED