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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
2
OKB GP
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
3
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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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ОКБ ГП
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
OKB GP
Fuel
Assemblies
Concrete
Reflector
Hermetic
Casks
Casks for
Cladding
Leak-
tightness
Inspection
Cooling pond
Keff < 0.95
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OKB GP
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)
9
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
10
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.
OKB GP
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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.
OKB GP
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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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ОКБ ГП
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
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