who believe in progress
risk of being born too early"
sense of the term, nuclear fuel forms the core of nuclear power plants.
Although there are many equipment items important for their safety function
or for their participation in NPP availability, the fuel, in essence renewable,
is one of the key elements which have to be acted upon if utilities are
to be helped to fulfil their mission of generating power in total safety
and supplying the kWh to their customers at the best price.
fuel is also the core business of the Framatome-ANP Fuel Business Group:
pooling and rationalizing the available skills - technical, cultural and
human - supplied by each of the partners forms a challenge (Ref
which it is up to each and every one to meet in a cooperative spirit.
Where Are We Coming
the end of the seventies, when most of the installed generating capacity
came on stream in Europe and the USA, the management of LWR cores has
radically changed due to a number of advances in the nuclear fuel field.
These fuel enhancements have been made possible by huge R&D programmes
and by perfecting the analytical methods implemented to support the new
fuel designs before obtaining their qualification through in-reactor experience
utility which intends to generate power during a given period - typically
between 12 and 24 months - the most economical answer is to find
a trade off between loading the smallest possible number of assemblies
enriched in U235 to the highest possible value, and the lowest dispersion
of the resulting burnups when the assemblies are discharged. Of course,
other significant parameters such as outage duration and back end costs
have also to be considered.
specific to a 900 MWe PWR but valid in principle for
any other unit, illustrates the entire range which has been covered by
the utilities: with the same origin (52 assemblies enriched at 3% U235
for 12-month cycles), the fuel managements practised in 2000 in most of
the European PWRs were still situated, owing to the French NPPs, in the
3.7%-4.2% band (Figure
with cycle lengths between 12 and 18 months; outside EDF, European units
already operate at the limit of their respective authorized enrichments
(4.5%-4.7%) and in the USA, 40% of PWRs operate in 20-24 month cycles,
using assemblies enriched between 4.6% and 4.95%.
over the 1980-2000 period in the average burnups reached by the discharged
fuels is supplied per world region for the PWR (Figure
and the BWR (Figure
Three to five years hence, assemblies with average burnups of 50-52GWd/t
will be discharged in large numbers, with peaks at more than 55GWd/t.
It is important to observe that, given the qualification timeframe, the
design of these assemblies had to be undertaken as early as the first
half of the 1990s: this means that at the very least, fifteen or so years
elapse between the first engineering office sketches and the supply of
energy by cores fully loaded with the new fuel assembly.
primarily shows that the existence of enrichment limits is a major constraint
to continuing the fuel cycle cost improvement from the in-reactor fuel
management standpoint. At the present rate of reload enrichment increase,
the level of 5% U235 will be the general rule around 2010-2015 in all
reactors which already have - or will have - authorization. Five years
later, discharging will take place of the first reloads made up of assemblies
designed and dimensioned for this purpose, at 60-63GWd/t average and 70-73
GWd/t maximum assembly burnups.
Brief Outline of
Fuel Assembly Upgrades
take as a reference the UO2 fuel assembly (PWR or BWR) as it
was, coming from the USA at the start of European nuclear development,
we note that a first wave of three major upgrades, improved with time,
rapidly enriched the original concept, not only for UO2 but
also for MOX or REPU fuels.
removability: this new feature soon became necessary when the first
assembly damage occurred during handling; today, beyond the technological
solutions found, the optimum solution remains to conduct the restoration
of assembly during outages, requiring fast action and zero waste. This
expectation has found a response in the top nozzle quick disconnect
system of the HTP and ALLIANCE fuel assemblies.
use of Zircaloy, a less neutron-absorbing material than the original
stainless steel or Inconel, now in general use for the fuel rods, guide
thimbles and mixing grids. Various versions of this material, both in
texture, chemical composition (through tin content adjustment) and in
form (duplex, coating of a corrosion-resistant outer liner, for Siemens-designed
hot reactors) have had to be developed to recover margins continuously
eaten into by operating conditions.
fitting of an anti-debris device at the bottom of the assembly
to protect the rods from attack by any loose parts. We now have several
devices at Framatome-ANP: Fuelguard, IDF and Trapper, similar in principle
and effectiveness (Figure
wave of fuel upgrades came into being when the time came to enhance fuel
assembly core management through "low leakage" loading patterns,
with the aim of improving the overall neutron balance. This category covers
use of burnable poisons to provide fine control of the power generated
by the fresh fuel rod bundle. Although many variants have been perfected
- discrete poisons (clusters outside the assembly) or lumped poisons
(co-milled with Uranium or deposited on the outside of the pellets)
- Framatome-ANP has always stayed faithful to the UO2-Gd2O3
mixed oxide, which is readily adjustable by content.
improvement of the mixing capacity of the grids, in order to get the
most out of the relaxation of the FΔH and FQ-LOCA
factors arising from the updated safety analyses. Owing to its threefold
task of providing coolant mixing, restraining the fuel rod bundle and
contributing to mechanical strength, the grid is the area with greatest
innovation potential for the designer. The HTP grid, commissioned
in 1988, is a significant example of this: its main feature is strip
doublets which produce curved internal flow channels and which also
serve as spring elements to firmly hold the rods in radial alignment.
Similarly, one can point to the Mark-BW grid, which is characterized
in particular by its well-known unlocking-locking key used during rod
loading, but above all by its outstanding critical heat flux performance
which has been reproduced with the ALLIANCE grid.
search for advanced materials intended to ultimately replace Zircaloy,
whose in-service results indicate that it is reaching its technological
limits. On a pre-emptive basis, Framatome decided to undertake from
the mid-eighties a series of huge programmes for the research, selection
and qualification of new alloys using our entire Company resources while
calling upon those of the CEA and university laboratories: the M5
solid-wall alloy, boasting extremely high irradiation performance
is now, and will be for many years, the reference commercial alloy for
the claddings and structures of Framatome-ANP PWR products almost everywhere
in the world; for the Siemens-designed plants, considered hottest, we
have alloy DX-D4, which is the most accomplished version of the
Duplex alloys (Ref
the fringe of the development work just referred to, the occurrence
– fortunately rare – of in-service incidents is a strong incentive to
improve fuel products. For example, what utility, having experienced
the RCCA incomplete insertion incident, has not appreciated all the
advantages of the Monobloc™ guide thimble equipping our
AFA 3G and ALLIANCE fuel assemblies?
the BWR fuel field, the motivations behind assembly upgrading are the
same as for the PWR: establishing wider margins to design limits for
enhancing operating reliability and exploiting an appropriate amount
of them in order to optimise cost-effectiveness. However, the near-absence
of any constraint other than that dictated by the support of the fuel
channel outer envelope allows the near-continuous flow of new features.
The history of the successive versions of our BWR assemblies illustrates
transition from the 8x8 fuel assembly used in the late 1970s to the
9x9 fuel assembly (at the beginning of the 1980s) with a central water
rod brings a 20% reduction in average linear heat generation rate,
and increases the margin to the critical power ratio.
replacement of the innermost rods with additional water rods, then
with an internal water channel of square cross section (1992) as the
first ATRIUM design, produces a very flat thermal neutron flux distribution,
and thus, by permitting a more homogeneous distribution of U235 enrichments
in the fuel rods, leads to better fuel utilization.
introduction of the Ultraflow spacers with swirl vanes has increased
margin to critical power and that of the Fuelguard anti-debris device
has contributed to prevent debris-related damage; the implementation
of part-length fuel rods for improving shut down reactivity margin
and reducing the 2-phase pressure drop, as well as of natural uranium
blankets, axial gadolinium loading and enrichment zoning, have improved
the mid-1980s, when PCI was the root cause of the majority of BWR
fuel failures, cladding with pure Zirconium inner liner was introduced.
The development and testing of improved cladding materials continued,
resulting in the introduction of Zy-2 cladding with an iron-enhanced
these intrinsic product improvements, fuel utilization can also be made
more efficient by optimizing the NSSS-fuel combination. To do this,
Framatome-ANP's Engineering Group has devised US-3D, a three-dimensional
system for continuous monitoring of reactor core power distribution,
consisting of fixed neutron instrumentation based on rhodium self-powered
neutron detectors installed in the core and giving permanent access
to local fuel duty conditions. The available operating margins to authorized
limits are thus on permanent display to the operator.
up this outline of fuel technological upgrades (Ref
3), let us reiterate how much the anticipation of market needs is
paramount: it is difficult to know how to undertake and manage heavy,
high-cost R&D programmes so that they come to fruition at just the
right time. If they come to fruition too late, there will be an inevitable
loss of market share; if too early, there will be the risk of poor sales.
To protect itself from risks like these, Framatome-ANP's policy has always
been to foster partnerships with the utilities.
High Burnup Experience at a Glance (Figure
6b, Figure 6c)
benefits from experience built up for nearly forty years, with the fuel
families developed by Framatome and Siemens: 95,000 PWR and 45,000 BWR
fuel assemblies have been supplied throughout Europe, the Americas, Asia
PWR fuel, more than 830 of our assemblies have reached burnups between
50 GWd/tU and 65 GWd/tU. This experience in high burnups has been
gained through many different core management strategies, from 12 to
24 month cycle length, and from 1/6 to 1/2 core reload size ratio.
BWR fuel, thanks to the implementation of 9x9 then 10x10 designs, the
average burnups have been increased from 25 GWd/tU at the middle of
the 1980s to more than 40GWd/tU at the end of 2000, with four Atrium-10A
LTAs discharged at 71 GWd/tU representing by far the highest value in
LWRs world-wide. There are altogether 43 BWR fuel assemblies with a
burnup higher than 50 GWd/tU, and 13 complete reloads have reached an
averaged batch burnup higher than 40 GWd/tU.
the first MOX fuel loading in 1966 in Germany, more than 2700 MOX fuel
assemblies (mainly of AFA 2G, Focus and Atrium types) have been irradiated
in 36 European LWRs. Today, most of the MOX batches are discharged at
burnups of around 45GWd/tHM reached after four annual cycles of irradiation,
with some individual elements irradiated up to 54-55GWd/tHM. Our experience
includes MOX rods with plutonium fissile concentration amounts up to
4.8 w/o (about 7.1 w/o Pu). This extensive MOX European experience shows
that no technical problem resulting from the MOX fuel has ever been
encountered, and the reliability of our MOX fuels is as good as for
our UO2 fuels (Ref 4).
claddings were developed especially for the very demanding Siemens PWR
to further leverage the proven mechanical characteristics of Zircaloy-4
and significantly improve corrosion behaviour. Industrialised since
1989, Duplex cladding tubes have been irradiated, successfully reaching
maximum assembly burnup of 62 GWd/tU. In addition, LTAs with 5% U enriched
fuel rods are going to be inserted in 2001 in the Gösgen NPP for
irradiation during at least 5 annual cycles (Ref
recently, the M5 alloy, a ternary Zr-1.0Nb-O, has been industrialised
to fully equip our products. This results from the extensive irradiation
programs implemented in 28 commercial PWRs world-wide, that have successfully
shown its impressive benefits at extended burnup relative to corrosion
(20 μm at 70 GWd/MTU), hydriding, creep and growth behaviour (≤0.7%).
A rod burnup value of 78 GWd/MTU is planned to be reached in early 2002
after the completion of a seventh irradiation cycle in progress in a
BWR, the Zy-2 LTP cladding material, produced using a special Low-Temperature-Process,
has been found to exhibit an optimum resistance to both nodular and
uniform corrosion. As a countermeasure against PCI, Fe-enhanced inner
liner was developed to prevent secondary damage. As of today, irradiation
experience has been cumulated on more than 500,000 Zy-2 LTP fuel rods
including up to 62 GWd/MTU with positive results.
What Track Record?…
For What Prospects?
speaking, as contributors to nuclear power generation, we all have reason
to feel proud of our collective track record.
things considered, nuclear power generation remains economically competitive.
The plants have reached maturity, for many the costs are written off,
and their operation is fully controlled. In the USA, where plant closures
were feared, there are clear signs that this will not happen: rather
there are examples of buyout of individual plants by consortia, the
extension of operating licences to 60 years, projects for power uprating
and for the resumption of work at the construction sites most advanced
at the time of interruption. In Asia, despite a slowdown due to the
last economic crisis, new units are being commissioned and new jobsites
energy is environment-friendly: it meets the growth needs intrinsic
to any human society and ensures breathable air for future generations.
The findings of the "Dilemma" report of European Union DG
XVII (Ref 6), which assesses
the consequences of the Kyoto protocol, are clear-cut: typically, for
only a scenario based on strong nuclear maintained at around 70% of
power generation needs will enable it to meet its commitments up to
2025. Turning to waste, we observe that, for example, if today's assemblies
had kept their original irradiation capacity of 33 GWd/t, EDF would
need almost an extra 500 tonnes or 1000 assemblies per annum to generate
its usual production level of 400TWh. Further, the reprocessability
of all our products, which enables the residual energy material (plutonium)
to be recovered for recycling, along with their capacity for interim
storage, justify the application of the label "Green Fuel" to nuclear
this means that Framatome-ANP's track record on the fuel front speaks
for itself, we have a hand stuffed with aces:
high-performance fuel products: AFA 3G, HTP, Mark-BW, Atrium fuel assemblies,
M5 and Duplex materials, which allow us to meet the range of market
needs, even including some local specific requirements (Focus assembly
for Siemens reactors, Mark-B assembly for B&W reactors), and are
able to accommodate MOX or REPU,
fabrication facilities which cover the whole spectrum of assembly manufacturing
comprehensive array of services and associated equipment, served by
is that with 40% of the market share, we are the foremost vendor of LWR
fuel world-wide (Figure
The objective we have set ourselves, at the very least, is to hold
on to this advantageous position.
areas of skills and industrial resources, Framatome-ANP now possess extensive
facilities in Belgium, France, Germany and USA, which we intend to adapt
to our needs but also to streamline, with the aim of achieving better
as Framatome-ANP was created in January 2001, we embarked upon a large-scale
restructuring operation, FIT2WIN, aimed at characterizing and gauging
best practices and individual skills at identifying redundancies. By combining
the recommendations made by the mixed analysis groups with the strategic
interests of the market and our shareholders, we should be in a position
by end 2001 to settle upon the organizational structure which best meets
the global objective of cutting our operating costs.
fuel-specific areas of design, R&D and fabrication, we have a substantial
progress margin, particularly in the PWR field, to streamline our organization
and working practices: sales force, engineering, etc. There is the strong
expectation that in the short term the use of alloy M5 can be extended
to the assemblies of the German market, and that the HTP grid can reinforce
any other assembly skeleton. We have at Framatome-ANP, in the ALLIANCE
assembly, developed and built by Franco-American teams, a PWR
assembly capable of reaching burnups of at least 70 GWd/t, thus meeting
the needs of the most economic fuel managements that can be contemplated
with 5%-enriched uranium. Its in-core qualification has been ongoing in
European NPPs since 1999 and in American NPPs since 2000. It is destined
to be the reference fuel for the future EPRs. With the products of the
ATRIUM family, we also have a BWR fuel assembly capable of getting
the best out of the 5% enrichment. Its advanced variant Atrium-12 is the
reference product of the SWR-1000 reactor.
has been made several times of the 5% enrichment limit which is the source
of the 70-75 GWd/t burnups. On the assembly designer's time scale, this
limit is close to being reached and the right fuels for this situation
are already at hand. The question which will then arise is whether to
maintain the R&D effort in the future, bearing in mind that this effort
is central to the accomplishing of fuel performance gains whose impact
is felt well beyond fabrication costs. It is in our power to achieve more,
but if we are to aim for more without raising the number of "those
who believe in progress run the risk of being born too early", we
shall soon need to receive from utilities tangible signs about the future
and signs which go beyond benevolent neutrality.