Allegro project challenges
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ALLEGRO project challenges. Petr DAŘÍLEK , Radoslav ZAJAC [email protected] AER Working Group F Meeting „Spent Fuel Transmutations“ Konferenční centrum AV ČR – zámek Liblice, Czech Republic April 10 - 13 , 201 2. Content. ALLEGRO reactor recall ALLEGRO safety Selected challenges.

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Allegro project challenges

ALLEGROproject challenges

Petr DAŘÍLEK, Radoslav [email protected]

AER Working Group F Meeting

„Spent Fuel Transmutations“

Konferenční centrum AV ČR – zámek Liblice, Czech Republic

April 10-13, 2012

VUJE , Inc., Okružná 5, 918 64 Trnava, Slovakia


Content

Content

  • ALLEGRO reactorrecall

  • ALLEGRO safety

  • Selectedchallenges

VUJE , Inc., Okružná 5, SK 918 64 Trnava, Slovakia


Allegro project challenges

ALLEGRO reactor recall [1]

General frame: Gas-cooled Fast Reactor (GFR) development

Main motivations of GFR :

With an innovative fuel

- Fast N

- Robust and refractory

- High level of Fission Products confinement

- Increased resistance to severe accidents

The use of He as primary coolant:

- Neutronics transparency

- Without phase change (no cliff edge effects)

- Chemical inertness

- Optical transparency

- Opening the gate to high temperatures

Possible use of high temperatures

with

Sustainable resources management


Allegro project challenges

ALLEGRO reactor recall [1]

General frame: Gas-cooled Fast Reactor (GFR) development

GFR R&D : challenges

  • Self-sustainable cores

  • A robust safety approach

  • An attractive power density ~100 MW/m3

  • An innovative fuel (FPs confinement, fast neutrons, high HM content, high temperature)

  • Reactor design and safety systems / management of the decay heat removal

  • In common with the VHTR :

  • Technology of He circuits and components

  • High temperature materials

  • Power conversion

  • And together with the SFR:

  • Fuel recycling technologies

  • And possibly …:

  • Power conversion, Fuel materials and design?


Allegro project challenges

ALLEGRO reactor recall [2]

  • Objectives

  • Pilot scale demonstration of key GFR technologies demonstration (core behavior and control, refractory fuel qualification, gas reactor technologies) and dispose of a first validated Safety reference Framework

  • Fast flux irradiation and contribution to the development of future fuels (innovative or heavily loaded in Minor Actinides)

  • Potential test capacity of high temperature components or heat processes

A necessary step towards an electricity generating GFR prototype, for the demonstration of the chosen solutions and the whole reactor system merits confirmation


Allegro project challenges

ALLEGRO reactor recall [2]

MOX

Carbide

Control

Shutdown

Reflector

Shield

ALLEGRO main reference options

  • Reduced scale, power about 75 MWth, loop concept, GFR type primary Helium circuit,

  • Same as GFR core power density 100 MW/m3

  • No energy conversion, 2nd pressurized water circuit, atmospheric final heat sink

  • Step by step approach for the core, with 2 successive configurations:

    • Mox core, Tinlet/Toutlet He = 260/530 °C, with some GFR

      advanced refractory S/As (T max MOX # 1050 °C )

    • Full refractory core , Tinlet/Toutlet He = 400/850°C, representative of the GFR core

  • Reservation for a HT test circuit (about 10 MWth)


Allegro project challenges

ALLEGRO reactor recall [2]

Experiment

MOX

Control

Shutdown

Reflector

Shield

The 75 MWth MOX core

  • Studies for a 75 MW core (5 rows)

    • MOX ~25 %Pu

    • Frequency 1, 3at%, 660 EFPD

*1 year = 365 EFPD


Allegro project challenges

  • ALLEGRO reactorrecall

  • ALLEGRO safety

  • Selectedchallenges

VUJE , Inc., Okružná 5, SK 918 64 Trnava, Slovakia


Preliminary safety analysis background

ALLEGRO safety [2]

Preliminary safety analysis - background

  • Initial strategy relying on 3 DHR loops

  • + guard containment ( medium backup

  • Pressure)

  • - for pressurized situations, natural circulation is possible if the blowers fail

  • GFR CEA PSA(2007) studies led to add an additional level for pressurized situations

  •  use primary circuits at the 1st level and DHR loops as backup systems (2nd and 3rd level)

  • Same conclusions are anticipated for ALLEGRO

  • Primary circuits were doubled ( 2* 37 MWth)

  • Addition of pony motors to primary blowers

    (20% nom. speed for pressurized , 80-100% for depressurized cases) fed by diesels/batteries

     Possibility of main water secondary circuits nat. Circulation in case of water pump failure


Allegro dhr strategy

ALLEGRO safety [2]

ALLEGRO DHR Strategy

  • Global principle

  • 1st level : use of primary blowers with pony motors for pressurized and depressurized situations

  • 2nd level : DHR loops with forced circulation for pressurized and depressurized situations

  • 3rd level : DHR loops with natural circulation for pressurized situations only

  • Principle extended for unprotected transients

  • Pressurized: use of primary blowers at nom. speed, secondary and tertiary circuits forced circulation

  • Depressurized : (large breaks excluded)

  • use of primary blowers at nom. speed combined with nitrogen injection

  • (to be investigated)


Preliminary safety analysis allegro dhr strategy

ALLEGRO safety [2]

Preliminary safety analysis - ALLEGRO DHR Strategy

Graphic illustration of the (D)HR strategy proposed by CEA


Allegro provisional safety conclusions

ALLEGRO safety [2]

ALLEGRO – Provisional safety conclusions

  • Situation of the transient analysis for ALLEGRO MOX core

  • (Deliverable D1.4-1 of GOFASTR project)

  • Pressurized situations can be managed using the proposed

  • DHR strategy even with aggravating failures or combined failures

  • (complex sequences)

  • Depressurized situations can be controlled with 2 main loops operating

  • over the whole break size spectrum,

  • Small-break LOCAS could be controlled with one main loop active (single failure criterion) with broken loop closed,

  • Cooling strategy needs to be tested and refined for unprotected transients

  • The results of the Prevention phase are useful to define scenarios for

    MOX core severe accidents


Allegro project challenges

  • ALLEGRO reactorrecall

  • ALLEGRO safety

  • Selectedchallenges

VUJE , Inc., Okružná 5, SK 918 64 Trnava, Slovakia


Purpose of helium chemistry control

Selected challenges – He purification [3]

Specification for Primary Coolant Chemistry

Example :

control of the oxidizing potential in the coolant for HTR/VHTR

Water injection

and

Control of H2O/H2 ratio

Purpose of Helium chemistry control

Ensure safety during operation and in case of accident : limit the inventory of particles, fission products and activated species,

Increase service life : minimize the interactions between gas and structures (graphite, stainless steel,…).

Protect metallic materials against corrosion (oxide layer)

Limit the oxidation of carbon based material


Source of impurities in primary coolant

Selected challenges – He purification [3]

Maintenance operation

Fuel elements, reflector replacement, loading and unloading operations

Graphite degassing

O2, N2

H2, CO, CO2, N2, H2O

CH4, CO2, CO, H2, H20

Fission and activation products

Thermal insulator degassing

H20, CO2, N2, O2

N2, O2, H2, H2O

O2, N2

Metallic structure degassing

Welding, junctions

Particles :

Graphite, thermal insulator

Source of impurities in primary coolant

PRIMARY CIRCUIT


Htr10 purification unit

Selected challenges – He purification [3]

HTR10 purification unit

Primary circuit

30 Bar, 210 kg/h

Activated carbon bed

-160°C

Filtration

< 5 mm

Molecular sieve bed

Ambient T

CuO Oxidation bed

250°C

30 Bar, 10.5 kg/h

Filtration


Hpc objectives

Selected challenges – He purification [3]

HPC - objectives

Demonstration of the feasibility of an integrated process

for the purification of Helium

Purpose:

Demonstrate the efficiency of purification using industrial processes,

Demonstrate the feasibility of primary coolant composition control through purification and controlled injection of selected impurities,

Ensure the coolant chemistry quality control for a technological loop in reactor conditions (pressure and materials)


Hpc loop

Selected challenges – He purification [3]

Adsorption

Molecular sieve

Adsorption

Activated carbon

Oxidation

HPC loop


Hpc main characteristics

Selected challenges – He purification [3]

HPC – Main characteristics

  • For inlet impurities concentration of 40ppmV, regeneration frequency:

  • Oxidation column : 5 days

  • Molecular sieve column : 12 hours

  • Activated carbon column: 24 hours


Hpc 3d view

Selected challenges – He purification [3]

HPC – 3D view


Allegro primary system overview

Selected challenges – Coaxial tubes [2]

ALLEGRO Primary System Overview

DHR IHX

DHR loops

Main vessel

Main IHX

#2 x 40 MW)

HT IHX

(10 MW)

Main blower


Allegro project challenges

Selected challenges – Coaxial tubes [4]

ALLEGRO Safety Reference Design

Safety valve ( DP, p, K) in cold DHR branch

ON

Natural position

50 MW

Design

1PCS

OFF

Forced convection

from other blowers

Safety valve ( DP, p, K) in cold main branch

OFF

Natural position and

from other blowers

75 MW

Design

2PCS

ON

Forced convection

from main own blower

Coaxial branch design of loop circuits


He tightness

Selected challenges – Coaxial tubes [1]

External liner

Spring

Internal liner

Upper Flange

Lower flange.

"S" seal

He tightness

  • HETIQ :

    • Seals design & qualification in GCR conditions :

      • Economic aspect :Reduce the leaks to 10 % of the He inventory

      • Safety : reduce contamination due to leaks.

    • 2 seals type tested :

      • Helicoflex type

      • SPG type

Imposed deformation

Imposed load


He tightness1

Selected challenges – Coaxial tubes [1]

He tightness

  • HETIQ :

    • Outlook :

      • Improvement of Helicoflex seal :

        • Liner material modification (Monel, Tantale, …)

        • Bonding issue : used of coatings,

        • New seals flat seals with :

          • Thermiculite 866 (vermiculite exfoliated & laminated)

          • Sigraflex APX or APX2 (flexible graphite with low oxidation at high temperature

      • Seals behavior in dynamic loop.

Ultraseal

  • June2002 : Patent FD 355 « Smooth graphite seal with metallic liner for high temperature»


Water ingress

Selected challenges – Water in the core [5]

Water ingress

  • Water leaking to the primary and the core from the connected water-based system

    • Heat exchangers

    • Decay heat removal

  • Relatively slow leaking rate, operating conditions, nominal pressure and temperature kept, vaporized water

  • Ideal gas assumption for vapor + helium

  • ECCO+ERANOS RZ transport (BISTRO Sn ) calculation for different cores

ALLEGRO Safety Meeting, Budapest, 28-29 March 2012


Water flood

Selected challenges – Water in the core [5]

Water flood

  • Cooling the core in emergency situation by water. Is it possible to cool the shutdown core by water without boron?

  • Hot shutdown condition, below the saturation temperature of the water, inserted control rods

    • 260 ˚C, 70 bars, reference calculation without water

    • Water in liquid phase (0.787 g/cm3)

Water just under the fissile zone:

Reactivity decrease

ALLEGRO Safety Meeting, Budapest, 28-29 March 2012


Water in the core c onclusion s

Selected challenges – Water in the core [5]

Water in the core - conclusions

  • The water related accidents have no negative impact on the safety. The core will remain subcritical when water in vapor or in liquid phase enters the core.

  • In case of the water ingress – above the saturation temperature of the water - the reactivity increase remains very low, and if the vapor content is significant, than it will cause a reactivity decrease.

  • In case of flooding – below the saturation temperature - the reactivity increase is smaller than the absolute value of the shut down reactivity, consequently the reactor remains subcritical even in case of using not borated water.

  • Question of the presenter: Before an unintentional flooding, can the reactor be critical below the saturation temperature of the water? Are there technical solutions or/and operational rules to avoid this situation?

ALLEGRO Safety Meeting, Budapest, 28-29 March 2012


Allegro project challenges

Selected challenges – Refractory fuel evolution [6]

  • Evolutionofpininternals:

  • linermadeof Ta/Nb (W/Rhatpreviousdesign)

  • gapfilled by porous C or fibrousSiCf

VUJE , Inc., Okružná 5, 918 64 Trnava, Slovakia


Allegro project challenges

REFERENCES

VUJE , Inc., Okružná 5, 918 64 Trnava, Slovakia


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