Grigory Ponomarenko

OKB “GIDROPRESS” Podolsk, Russian Federation

OKB GP

Innovations and Safety Ensuring in

WWERs on the Base of Collaboration

on the National and International

Levels

IAEA

INPRO DF9,

Vienna

21 November 2014

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Contents

1. Examples of enhanced innovative

analyses of safety parameters in

calculations and measurements 1.1 DECs modeling by up-to-date BE-codes developed in

collaboration in Russia and abroad

1.2 Innovative measurement of coolant mixing in

collaboration with “Bushehr” NPP

2. Achievement of reasonable balance

between efficiency and safety,

generally at WWER’s nuclear fuel’s

innovations

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The innovations are motivated by an increase in

competitiveness but create challenges for the safety.

Retention and even increase in safety level when power

uprating and other innovations is a complex problem. It

may be resolved on the basis of collaboration.

Here are presented some examples - enhanced

innovative safety analyses for the DECs modeling by up-

to-date BE-codes (SAPFIR, KORSAR/GP, MCU, MCNP),

developed by the different organizations (Kurchatov

institute, NITI (Sosnovy Bor, Russia), Los Alamos

National Lab.).

These are also example of the innovation

measurements of coolant mixing in the collaboration with

“Bushehr” NPP – (patent of RF №2503070 received by

OKB GP in December 2013 y.)

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As a result collaborations on international level (IAEA,

EUR and others) the innovations are also implemented

into the ideology of safety substantiation. This relates to

the amendment of knowledge and the removal of

excessive conservatism. It concerns to the statistical

approaches (BEPU) and also to the deterministic

conservative approach which is a first-priority till

nowadays.

The presence of the reasonable balance between the

effectiveness, reliability and safety in the innovations of

nuclear fuel of WWERs and PWRs is intensified also by

the processes of competition and inter-penetration of the

producers of fuel for the opposite market (Westinghouse

FAs for the WWERs and Russian producer of FAs for

PWRs).

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OKB GIDROPRESS is the

General Designer of WWER type of

Reactor installations.

OKB GIDROPRESS intensively

collaborates on innovations with many

organizations: NRC Kurchatov Institute,

TVEL, Rosenergoatom, VNIINM, NITI,

MSZ, NZHK, Rostechnadzor, OKBM,

MEPhI, NPPs, IAEA, NEA, AER and

other organizations in Russia and

abroad.

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So it relates to Topic 1: Driving forces of

collaboration on innovations, namely (from TOR

for this DF9):

-Examples of successful nuclear technology

development when the required levels of effort

and knowledge were available only through the

collaboration of different specialized parties;

-Motivation for collaboration: cost savings, enhanced

assurance for regulators, beneficial outcomes for

all parties);

-Examples of the actual impact of the collaboration

on the safety and economic of NES.

Precision Keff calculations by Monte-Carlo (MCU, MCNP) 7

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Fuel

Assemblies

Concrete

Reflector

Hermetic

Casks

Casks for

Cladding

Leak-

tightness

Inspection

Cooling pond

Keff < 0.95

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Multideck arrangement of transport containers for two fresh FAs

Concrete floor

Steel

Wood

Emergency Water inside

FA FA

Air

outside

Precision Keff calculations by

Monte-Carlo (MCU, MCNP)

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Deborated slug (i.e. some volume of water

without absorber CB=0) may be formed in of

circulation loops. First RCP start-up is the

most dangerous situation. Accelerated slug

enters into the core and may bring it into the

above-criticality with dangerous neutron

splash. Discharged energy may disrupt the

fuel rods.

However the reality is better due to the

coolant mixing. At the core enter there is a

coolant with CB more than zero.

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Deborated slug

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Russian NPPs WWER-

1000 were modernized

recently with increasing:

campaign (till 18 month),

power (till 104%), fuel

length (by 5+10=15cm)

and

Non-Overlapping

(NoCR) of CRs and fuel.

All these aspects worsen

the accident with

Heterogeneous Dilution

(deborated SLUG).

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O

ld F

uel A

ssem

bly

N

ew

F

ue

l A

ss

em

bly

In

se

rte

d C

on

tro

l R

od

s (

CR

s)

~16 cm for CRs at Bottom End Switch

~26 cm for CRs at Rigid Prop 10cm

5cm

Deborated slug

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Reactivity, βeff

Boron Concentration, g/kg

Sect 2

Sect 4

in Sect 2

average

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Sharp decrease

but CBmin in Slug

is not Zero !!

Δt~3 s

Deborated slug

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Local Power-

Linear Heat

Rate,W/cm

100-200

Nominals

Total Power,

%Nnom

2-5

Nominals

half-width Δt~20-30 ms

Deborated slug

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Reactivity DECs with Cooling (BEPU) OKB GP

Core Power (Nt) and Power by 4 core quadrants (Pow_sect_i, i=1,…,4) for 3 Phases of MSLB

Phase 1

ATWS

Phase 2

Re-criticality

Phase3

SLUG

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0

20

40

60

80

100

120

0 20 40 60 80 100 120 140 160

Time, s

Nt,

%N n

om

0

400

800

1200

1600

2000

0 20 40 60 80 100 120 140 160

Time, s

Ql h

ot,

W/c

m

-6

-5

-4

-3

-2

-1

0

1

0 20 40 60 80 100 120 140 160

Time, s

Re

act,

?e

f

0

1

2

3

4

5

6

7

8

9

0 20 40 60 80 100 120 140 160

Time, s

DN

BR

, re

l.un.

Reactivity DECs with Cooling (BEPU) 5 Nominals

No Crisis

Non-positive

reactivity

Up to Nominal

Up to 40%Nom

Reactivity, βeff

Integral power, % Local power W/cm

DNBR

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Coolant Mixing

Use of Emergency Boron System (TW) for

Coolant Mixing Studies at the Bushehr

NPP

By effect of TW system on Power Distribution it was

obtained good information about Coolant Mixing.

Besides it was revealed the good sensitivity of

systems of neutron and thermal monitoring.

This method is extremely cheap – in fact

Cost=Zero. But measurements on the

working Units gives a very useful and proper

knowledge.

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54 NTMC

(SPND+ТC) in

FAs of the

“Bushehr”

core.

SPND –

54 х 7 pcs.

(by height).

Coolant Mixing

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Four Circulation

Loops and six IKs

around the WWER-

1000 core

Coolant Mixing

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On the base of

neutron signals

SPND (KV)

Local mixing coefficients

when TW1 works

Loop1

Coolant Mixing

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On the base of

TC signals (DT)

Coolant Mixing

Local mixing coefficients

when TW1 works

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Tests by old and new methods have been

performed on the “Bushehr” NPP. New

method gives larger parameters than

Old one:

about 25-30o larger swirls;

1.5 times larger shares of flow rate

coming from each loop into the adjacent

(CCW) loop.

Coolant Mixing

Fuel efficiency in WWERs has been

increased during last 20 years particularly due

to:

- replacement of steel elements in active part of

FAs by Zr elements;

- transition from two-years fuel cycle to three,

and then four-year cycle, and

- reduction of lateral neutron leakage (L3P). It

promoted also the collateral increase the RPV

life time and increase of EP effectiveness.

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Fuel efficiency

However there is a competition in safety and

economical parameters between different variants.

Any implemented improvement has not only the

positive influence but also the negative one.

For example the very favorable implementation of L3P

loading scheme leads also to some disadvantages in

safety – worsening of Power Peaking Factor (Kq) and

Temperature Coefficient of Reactivity (TCR).

Another example is a competition between strategies

of frequent refueling (reactor campaign 6-12 months

with maximal Burn-up) and seldom ones (reactor

campaign 18-24 months with maximal Load Factor).

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Fuel efficiency

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35

40

45

50

55

60

65

250 300 350 400 450 500 550 600 650

Cycle length, EFPD.

Av

era

ge

bu

rnu

p o

f u

nlo

ad

ed

FA

s,

MW·day/kgU

4,0%

4,2%

4,4%

4,6%

4,8%5,0%

3642

4854

6066

7278

Fuel efficiency

Burnup vs Cycle Length for different enrichments and

quantities of fresh FAs for WWER-1200

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ОКБ ГП Fuel efficiency

Modern fuel cycles are able to satisfy the main

requirements of Russian and foreign customers.

In the short term characteristics of fuel cycles can

be improved by use of new uranium high-capacity FA

of the fourth generation.

In the long run the high enriched fuel with the erbium

oxide integrated in each fuel rod of FA is reasonable

to use. It will further improve the fuel usage efficiency

of an 18-24month fuel cycle.

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The following innovative measures implemented on

the basis of collaboration will help to improve

economy and to maintain the the necessary level of

safety:

evolution of safety methodology to BE-approach

and BE- codes,

the coupled simulation of 3D effects in the link

NF/TG/HD,

harmonization of DSA and PSA,

Risk-Informed Approach to decision making by the

optimum balance of safety and efficiency and

optimization of NTD. 25

Efficiency and Safety

Thanks for your attention