RUSSIAN RESEARCH CENTERKURCHATOV INSTITUTE

Development of annealing for VVER-1000 reactor vessels

Experimental assessment ofpossibility for performance of restoration anealing

Ya.I. ShtrombakhYa.I. Shtrombakh

The lifetime of VVER reactor vessels mainly depends on irradiation embrittlement of weld joint materials

Generation 1 Generation 2

VVER - 440/230 VVER - 440/213 VVER - 1000

To 0,22%To 0,22%

To 0,048%To 0,048%To 0,027%To 0,027% < 0,012%

< 0,3% 1,2 - 1,9% 1,2 - 1,9%

To 0,22%To 0,22%

< 0,3%

2

< 0,08%

Elements impacting irradiation embrittlement

Performance of restoration annealing at VVER-440 reactor vessels

3

VVER-440VVER-440

Annealing efficiency

Annealing efficiency

Annealing temperatureAnnealing temperature

Rating of VVER-440 units by chemical composition of the weld joints

By TecSpec for weld joints of Rovno NPP-1 0.037%Р

Rovno NPP 1 0.21%Р

4

Cutting of templates for assessment of the real conditions in VVER-440/320 reactor vessels

If Tk 55 0°C: Tk

1010 = 53.5 + 0.94Tk 55 + 2.6210-4 (Tk

55)2 , °C

If Tk 55 0°C: Tk

1010 = 53.5 + 1.00Tk 55 + 1.3710-4 (Tk

55)2 , °C

5×5

10×10

5

VVER-1000 RO MKR raises significantly with increase of Ni concentration

6

Range of Ni concentration

change in the weld joints

Activities necessary for LTE

1.70 - 1.88Monitoring of radiation loads for ensuring of the designed life and ANNEALING for

LTE

1.57 - 1.64Monitoring of radiation loads for ensuring of the designed life additional attestation

for LTE

1.10 - 1.21The designed life is ensuredAdditional attestation for LTE

7

Mechanisms of irradiation embrittlement caused by nano-structure evolution

Radiation-induced precipitates

Brittle intergranular

destruction

Irradiation strengthening Development of intergranular segregations of impurities

IRADIATION EMBRITTLEMENT

Radiation defects

8

Brittle intergranular destruction

0 100 200 300 400 500 600 700 800 900 1000

CuNi

Fe

CrOCr

CMo

P

Ин

тен

сив

но

сть

, у.е

.Кинетическая энергия, эВ

The spectrum of OZ electrons from the intergranular surface of the reactor vessel

destruction (F=6,51023 м-2). The presence of phosphor intergranular segregations is visible

The spectrum of OZ electrons from the intergranular surface of the reactor vessel

destruction (F=6,51023 м-2). The presence of phosphor intergranular segregations is visible

9

Kinetic energy, eVKinetic energy, eV

Intensity, s.u.Intensity, s.u.

Changes of density of the radiation induced segregations in the weld joint of VVER-1000

Ф = 11,6×1023н/м2

N=700-800×1021м-3

Ф = 6,5×1023н/м2

N=300-500×1021м-3

Ф = 3,1×1023н/м2

N=70-90×1021м-3

10

Changes of density in the dislocation loops of VVER-1000 weld joint

Ф = 11,6×1023н/м2

N=400-600×1021м-3

Ф = 6,5×1023н/м2

N=10-20×1021м-3

Ф = 3,1×1023н/м2

N=5-6×1021м-3

11

Radiation induced segregations in the weld joints of

VVER-1000 made of the atoms of Ni, Mn, Si

M.K. Miller, A. Chernobaeva, Y.I. Shtrombakh, M.K. Miller, A. Chernobaeva, Y.I. Shtrombakh, K.K. F. Russell, R.K. Nanstad, D.Y. Erak, O.O. Zabusov., Evolution of F. Russell, R.K. Nanstad, D.Y. Erak, O.O. Zabusov., Evolution of the nanostructure of VVER-1000 RPV materials under neutron the nanostructure of VVER-1000 RPV materials under neutron irradiation and post irradiation annealing., JNM, irradiation and post irradiation annealing., JNM, 20092009

The higher the

segregations density,

The bigger displacement of ТК

12

Dependence of maximum temperature for temper brittleness from nickel concentration in the steel

(duration 100 hrs)

13

Temperature-time diagram of isothermal embrittlement of Cr-Ni-Mo steels

Temperature-time diagram of isothermal embrittlement of Cr-Ni-Mo steels

Displacement of embrittlement temperatureDisplacement of embrittlement temperature

Tem

peratu

reT

emp

erature

Experimental effectiveness justification for the annealing of VVER-1000 reactor vessel weld joints

Material Balakovo NPP, unit 1 Kalinin NPP, unit 1

Composition of elemets, % Ni=1,88Mn=1,1

Ni=1,76Mn=0,98

Fluency during primary receiving of the templates (flux 2-4 ×1014 м-2с-1),

×1022 м-2

32 37

Displacement of the embrittlement temperature after the primary irradiation of the templates, º С

93 90

Annealing mode 565 º С/ 100 hrs, cooling less than 20 º С/hr. to 100 º С; further on with disconnected heaters

Displacement of the embrittlement temperature after the restoration

annealing, º С

4 8

Fluency during the secondary irradiation, ×1022 м-2

50 27 27

Flux during the secondary irradiation, ×1016 м-2с-1

17,0 2,1 2,1

Displacement of the embrittlement temperature after the secondary

accelerated irradiation, º С

44 17 36

14

Change of density in radiation-induced segregations under irradiation in the weld joint VVER-1000

SECONDARY SPEEDED-SECONDARY SPEEDED-UP IRRADIATIONUP IRRADIATIONФ=5,0×1023 н/м2

PRIMARY IRRADIATION

Ф=3,2×1023 н/м2

RESTORATION ANNEALING

15

The velocity of the secondary embrittlement of the VVER-1000 reactor steels after the restoration annealing is significantly slower than during the primary irradiation

16

InitialInitial

Loops

Precipitates

Loops

Precipitates

Primary irradiationPrimary irradiation Secondary irradiationSecondary irradiation

Restoration annealingRestoration annealing

State, fluencyState, fluency

Dose dependences of the density in the radiation-induced structure Dose dependences of the density in the radiation-induced structure elementselements

PrecipitatesPrecipitates Radiation defectsRadiation defects

17

FluencyFluency FluencyFluency

The share of brittle intergranular destruction in the Charpy tests of the main material thermal sets (Ni < 1.2 %) and weld

joints with increased concentrations of Ni (>1.6 %)

18

Weld joint,

Kalinin 2

Weld joint,

Kalinin 2

Main material,

Kalinin 2

Main material,

Kalinin 2

Main material,

Rovno 3

Main material,

Rovno 3

Weld joint,

Rovno 2

Weld joint,

Rovno 2

Duration of thermal treatment, eff. hrs.Duration of thermal treatment, eff. hrs.InitialInitial

Th

e share of in

tergranu

lar destru

ction, %

Th

e share of in

tergranu

lar destru

ction, %

19The share of brittle intergranular destruction, displacements of brittleness temperature and viscosity limits in various

states for the weld joint of Balakovo NPP-1

The share of brittle intergranular destruction

Displacement of brittle temperature

Displacement of viscosity limit

The share of brittle intergranular destruction

Displacement of brittle temperature

Displacement of viscosity limit

InitialInitial

IrradiationIrradiation AnnealingAnnealing AnnealingAnnealing AnnealingAnnealing

The share of brittle intergranular destruction, %

The share of brittle intergranular destruction, %

Annealing 565 C/100 hrs + secondary accelerated

irradiation

Annealing 565 C/100 hrs + secondary accelerated

irradiation

Displacement of brittleness temperature in different states of Balakovo NPP-1 reactor vessel steels

20

Weld jointWeld jointWeld jointWeld joint

Main materialMain material

InitialInitial IrradiationIrradiation IrradiationIrradiation IrradiationIrradiation IrradiationIrradiation IrradiationIrradiation IrradiationIrradiation

+ annealing+ annealing + annealing+ annealing + annealing+ annealing + annealing+ annealing + annealing+ annealing

+ irradiation+ irradiation + irradiation+ irradiation

Comparison of primary and secondary irradiation embrittlement in the materials of Balakovo NPP unit

1 reactor vessel

Main metalMain metal Weld jointWeld joint

21

1. Consideration of temperature ageing effect1. Consideration of temperature ageing effect 1. Consideration of flux effect

2. Consideration of temperature ageing effect

1. Consideration of flux effect

2. Consideration of temperature ageing effect

22Comparison of the primary and secondary radiation embrittlement in the weld joint at Balakovo NPP, unit 1

0 20 40 60 80 1000

20

40

60

80

100

120

После отжига 565°С/100ч

Повторное РО

- модель го

ризонтального сдвига

Сварной шов ВВЭР-1000

TF ,

°C

Флюенс, 1022 нейтрон/м2 (E>0.5МэВ)

Перви

чное РО

После отжига 565°С/30ч

VVER-1000 weld jointVVER-1000 weld joint

FluencyFluency Neutron, m2Neutron, m2

Primary irradiation

embrittlement

Primary irradiation

embrittlement

Secondary irradiation

embrittlement

Secondary irradiation

embrittlement

After annealing 565

0C/30 hrs

After annealing 565

0C/30 hrs

After annealing 565

0C/100 hrs

After annealing 565

0C/100 hrs

Computed diagram of temperature distribution along the VVER-1000 reactor vessel in the process of the restoration annealing

(stationary task)

2323

24

The irradiation embrittlement of the vessel steels caused by radiation strengthening due to radiation induced changes of its nano-structure, as well as formation of intergranular and boundary-granular phosphor segregations.

It is demonstrated that the velocity of radiation embrittlement in weld joints of VVER-1000 reactors is higher the one of main VVER-1000 materials.

The maximum of temperature intervals for phenomenon of temper brittleness is raising along with increase of nickel concentration in the steel, which required to increase the restoration annealing temperature for weld joints of VVER-1000 with increased nickel concentration.

The parameters of time and temperature for restoration annealing of VVER-1000 weld joints with increased nickel concentration are identified.

The restoration of features and structure of steels in VVER-1000 reactor vessels after restoration annealing is demonstrated.

It is identified that the velocity of the embrittlement after the annealing under the speeded-up irradiation is lower than during the primary irradiation.

It is shown the presence of «flux effect» during the speeded-up irradiation after the restoration annealing.

The flowchart of temperature distributions along the VVER reactor vessel within the scope of the stationary task is computed for the restoration annealing process.

ConclusionsConclusions