ALLEGRO project challenges

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

ALLEGROALLEGROproject challengesproject challenges

Petr DAŘÍLEK, Radoslav [email protected]

AER Working Group F Meeting„Spent Fuel Transmutations“

Konferenční centrum AV ČR – zámek Liblice, Czech RepublicApril 10-13, 2012

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

Content

ALLEGRO reactor recallALLEGRO reactor recall

ALLEGRO safety

Selected challenges

ALLEGRO reactor recall [1]

The use of He as primary coolant: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

With an innovative fuelWith an innovative fuel

- Fast N- Robust and refractory

- High level of Fission Products confinement

- Increased resistance to severe accidents

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

Possible use of high temperaturesPossible use of high temperatureswithwith

Sustainable resources managementSustainable resources management

Main motivations of GFR :Main motivations of GFR :

In common with the VHTR :

Technology of He circuits and components

High temperature materials

Power conversion

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

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

And together with the SFR:

Fuel recycling technologies

And possibly …:

Power conversion, Fuel materials and design?

GFR R&D : GFR R&D : challengeschallenges


Objectives1.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

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

3.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


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)

MOX

ControlShutdown

Carbide

Reflector

Shield

ALLEGRO main reference options


For one GFR Sub-Assembly (U,Pu)C , per year*

GFR2400

F Core

ALLEGROMox 75 MW Frequency 1

GFR S/A Pu enrichment 17.3% 30.5%

X 1.8

Fast Φ max

n/cm²/s, E > 0.1 MeV

12.4 1014 8.4 1014

-32%

Burn-up max 2. at% 1.8 at%

-10%

Dose max

dpa SiC

22 15

-32%

R = Dose/Burn-up.

dpa SiC/at%

11.0 8.3

-25%

*1 year = 365 EFPD

Experiment

Control

Shutdown

MOX

Reflector

Shield

The 75 MWth MOX core

Studies for a 75 MW core (5 rows)MOX ~25 %PuFrequency 1, 3at%, 660 EFPD



ALLEGRO reactor recall

ALLEGRO safetyALLEGRO safety

Selected challenges

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 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)

ALLEGRO safety [2]

Preliminary safety analysis - ALLEGRO DHR Strategy

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

ALLEGRO safety [2]

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 – Provisional safety conclusions

ALLEGRO safety [2]


ALLEGRO reactor recall

ALLEGRO safety

Selected challengesSelected challenges

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,…).

Specification for Primary Coolant Chemistry

Limit the oxidation of carbon based material

Protect metallic materials against corrosion (oxide layer)

Water injectionand

Control of H2O/H2 ratio

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

Selected challenges – He purification [3]

Source of impurities in primary coolant

PRIMARY PRIMARY CIRCUITCIRCUIT

Thermal insulator

degassing

Graphite degassing

Metallic structure degassing

H2 , CO, CO

2 , N2 , H

2 O

H20, CO2, N2, O2

N 2, O 2

, H 2, H 2

O

Welding, junctions

Fuel elements, reflector replacement, loading and unloading operations

Maintenance operation

O2 , N

2

CH 4, C

O 2, C

O, H2, H

20O

2,

N2

Particles :

Graphite, thermal insulator

Fission and activation products


HTR10 purification unit

Amount before and after purification unit (ppmV)

H2O

CO

N2

H2

CH4

CO2

O2

1 <0.1

9 <0.1

10 <0.1

9 <0.2

10 <0.2

11 <0.1

1 <0.1

Filtration< 5 m

CuO Oxidation bed250°C

Activated carbon bed-160°C

Molecular sieve bedAmbient T

Filtration

30 Bar, 210 kg/h

30 Bar, 10.5 kg/h


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 loopOxidation Adsorption

Molecular sieveAdsorption

Activated carbon


HPC – Main characteristics

Flow rate

(g/s)

Pressure

(bars abs.)

Temperature

(°C)

Volume

(L)

Oxidation

(CuO)

5 - 20 25 - 80 300

Regeneration: 350°C

10

Molecular sieve 5 – 20 25 – 80 25


50 (x 2)

Activated carbon 5 – 20 25 – 80 -180


20

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


ALLEGRO Primary System Overview

DHR loops

Main blower

Main IHX#2 x 40 MW)

DHR IHX

HT IHX(10 MW)

Main vessel

Selected challenges – Coaxial tubes [2]

ALLEGRO Safety Reference Design

Coaxial branch design of loop circuits

50 MWDesign1PCS

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

75 MWDesign2PCS

ONNatural position

OFFForced convectionfrom other blowers

OFFNatural position andfrom other blowers

ONForced convectionfrom main own blower

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


He tightnessHETIQ : 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 typeHelicoflex type

• SPG typeSPG type

Spring

External liner

Internal liner

"S" seal

Lower flange.

Upper Flange

Imposed deformationImposed deformation

Imposed loadImposed load


He tightnessHETIQ : HETIQ : – Outlook :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.

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

Ultraseal


ALLEGRO Safety Meeting, Budapest, 28-29 March 201225

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

Hevaporwatertot PPbarsP 70

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

Selected challenges – Water in the core [5]

ALLEGRO Safety Meeting, Budapest, 28-29 March 2012 26

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)

Core type Δρ

0efpd MOX+6GFR -626.7

0efpd MOX+6STEEL -625.5

660efpd MOX+6GFR -671.6

660efpd MOX+6STEEL -668.2

Water just under the fissile zone:Reactivity decrease


ALLEGRO Safety Meeting, Budapest, 28-29 March 201227

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?



Selected challenges – Refractory fuel evolution [6]

Evolution of pin internals:•liner made of Ta/Nb (W/Rh at previous design)•gap filled by porous C or fibrous SiCf


REFERENCES

[1] L. Cachon: Helium technology & components design, Presentation at Allegro technical meeting, 28.-29. February 2012, Cadarache

[2] Ch. Poette: Recall of ALLEGRO main design&safety options from past CEA studies, Presentation at Allegro technical meeting, 28.-29. February 2012, Cadarache

[3] K. Liger: Helium chemistry control and monitoring for Gas Cooled Reactors, Presentation at Allegro technical meeting, 28.-29. February 2012, Cadarache

[4] ALLEGRO Design, CEA presentation at Allegro technical meeting, 28.-29. February 2012, Cadarache

[5] Z. Elter, V. Brun-Magaud, D. Blanchet: Analysis of reactivity effects in the ALLEGRO reactor, Presentation at ALLEGRO Safety Meeting, 28.-29.3.2012,Budapest

[6] M. Zabiego: Task 2.2: Modelling results and updated pin design, GoFastR 3rd Progress Meeting, 27-28 March 2012, Budapest

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ALLEGRO project challenges