REPORTREPORT

Enhancing nuclear safety

Assessment of dry storage
possibilities for MOX or ERU
spent fuels
IRSN Report No. 2019-00903

Report prepared in response to arequest from the French National
Public Debate Commission

French Issue
April 2019

This report is the English translation of the IRSN report n°2019-00265 entitled “Analyse des possibilitésd’entreposage à sec de combustibles nucléaires usés de type MOX ou URE ” issued in April 2019.

REPORT SUMMARY
As part of preparations for the public debate on the 2019-2021 French National Plan for the Management ofRadioactive Materials and Waste (2019-2021 PNGMDR), the President of the National Public Debate Commission asked
the French Institute for Radiological Protection and Nuclear Safety (IRSN), by letter dated February 15, 2019, to
conduct an assessment of the dry storage of spent nuclear fuels containing mixed uranium and plutonium oxide (MOX)or enriched reprocessed uranium oxide (ERU).
The assessment carried out is presented in this report.

The characteristics of the MOX fuel used by EDF have changed over time. In particular, their plutonium content was
successively 5.30%, 7.08% and 8.65% (current level). Given the periods during which MOX fuels with theaforementioned plutonium contents have been used, dry storage solutions based on current concepts could now be
considered for all spent MOX fuels with a plutonium content of 5.30% and for most of those with a plutonium content
of 7.08%, i.e. around 2,500 fuel assemblies. For the first spent MOX fuels with a plutonium content of 8.65%, usedsince 2007, this type of storage may not be suitable until around 2040. To reduce the duration of wet storage toaround ten years, dry storage concepts should first be developed for spent fuels with a residual heat of around 3 kW
per fuel assembly.
Approximately 1,150 ERU fuel assemblies were loaded into reactors by EDF between 1994 and 2013. All of the spent
ERU fuels currently stored have a residual heat of less than 2 kW and are therefore compatible with current dry
storage concepts.
Considering only the safety requirement related to the temperature of the fuel cladding, it is possible to change theload configurations of existing concepts so that spent fuels with a residual heat greater than 2 kW can be stored.
Similarly, transport configurations and even cask should be able to be adapted in order to transport fuels with aresidual heat exceeding the reference value of 6 kW per fuel assembly. However, in addition to the constraint related
to fuel cladding temperature, casks must meet a set of safety and radiation protection requirements, as well as
industrial constraints (feasibility, capacity, cost, etc.). A comprehensive analysis integrating all these factors would
therefore be required.
Furthermore, the operations to be performed at the end of the spent fuel storage phase, whether wet or dry, must be
taken into account from the design stage of the storage facilities. Specific safety requirements will also have to be
adopted for these operations, for example concerning the mechanical characteristics of spent fuel after storage.
Demonstrating compliance with these requirements, particularly for spent MOX fuel, may require specificdevelopments and the monitoring program for stored fuels must take these requirements into account. The definitionand study of all these requirements would impact the time required to construct the first potential spent MOX fuel dry
storage facility in France.
In conclusion, the assessment carried out by IRSN did not reveal any factors that would rule out storing in dry
conditions some of the MOX and ERU fuels currently stored underwater. Nevertheless, the various possible options
should be examined, incorporating the related safety and radiation protection requirements as well as all industrial
constraints.

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Contents

TABLE OF ILLUSTRATIONS ...................................................................... 3
1

PRESENTATION OF THE REQUEST ..................................................... 52

BACKGROUND.............................................................................. 5

3

COMPATIBILITY OF MOX OR ERU SPENT FUEL WITH DRY STORAGE ............. 7

3.1

Spent MOX Fuel ............................................................................................... 7

3.2

Spent ERU fuels ............................................................................................... 9

4

POSSIBLE CHANGES TO DRY STORAGE CONCEPTS ................................ 10

4.1

Reminder about current dry storage concepts ....................................................... 10

4.2

Analysis of possible changes to current dry storage concepts.................................... 11

5

POSSIBLE CHANGES TO TRANSPORT CONCEPTS................................... 13

6

CONCLUSION ............................................................................. 14
LETTER OF REQUEST ......................................................... 16

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Table of Illustrations
Figure 1: Storage solutions based on the residual heat of the spent fuel ............................................... 6
Figure 2: Residual heat decay curves for the different types of MOX fuels used by EDF ............................. 8
Figure 3: Residual heat decay of the various MOX fuels according to the date of their unloading fromthe reactor.............................................................................................................. 9
Figure 4: Residual heat decay of the various ERU fuels according to the date of their unloading fromthe reactor............................................................................................................. 10
Figure 5: Admissible residual heat of fuel assemblies according to the number of empty compartmentsin the packaging ...................................................................................................... 12
Figure 6: For three non-uniform load configurations, the relationship between the residual heat of thehottest and the coldest fuel assemblies in order to ensure a maximum fuel temperature ofless than 400°C ....................................................................................................... 12

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REFERENCES[1] Letter of request from the National Public Debate Commission dated February 15, 2019.

[2] IRSN Report No. 2019-00181 “Storage of nuclear spent fuel: concepts and safety issues” - June 2018.

[3] Report by the French High Committee for Transparency and Information on Nuclear Safety, “Présentation
du « Cycle du combustible » français en 2018” (Presentation of the French ‘Fuel Cycle’ in 2018) - updateof September 21, 2018.

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1

PRESENTATION OF THE REQUEST

As part of preparations for the public debate on the 2019-2021 French National Plan for the Management ofRadioactive Materials and Waste (2019-2021 PNGMDR), the President of the National Public Debate Commission asked
the French Institute for Radiological Protection and Nuclear Safety (IRSN), by letter dated February 15, 2019, [1]appended in Appendix 1 of this report, to conduct two assessments to supplement the information contained in thecontracting authority1 file. These assessments focus, firstly, on the dry storage of spent nuclear fuels made frommixed uranium and plutonium oxide (MOX) or enriched reprocessed uranium oxide (ERU) and, secondly, on the current
state of international research on alternatives to the deep geological disposal of high-level, long-lived waste.
This report concerns the assessment of dry storage; the second part of the request will be the subject of a dedicatedreport.
Since the management of spent fuel from French nuclear power reactors, including its storage, is one of the topics
covered in the 2019-2021 PNGMDR, the Special Public Debate Commission (CPDP) mandated for the debate on the
PNGMDR, in preparing for the debate, considered the IRSN [2] report on concepts and safety issues related to thestorage of spent nuclear fuel published in June 2018 in response to a request from the Parliamentary Committee ofInquiry into the Safety and Security of Nuclear Facilities in France. In the report, IRSN details the possible spent fuelstorage options based on a residual heat decay curve for two typical fuels, representative of:● current EDF reactor loads (MOX fuel and fuel made from enriched natural uranium oxide: ENU),● the characteristics of transport and wet or dry storage concepts currently implemented in France and aroundthe world.
In particular, for transport and dry storage concepts in their current state, IRSN indicates that the residual heat ofspent fuels must be below 6 kW for transport and below 2 kW for dry storage.
The CPDP found that these are determining values in defining the minimum cooling time of spent fuels before
transport or the implementation of a dry storage solution. It also wanted IRSN to provide further information, firstly
on the suitability of dry storage for the MOX and ERU fuels currently stored underwater and, secondly, on potentialchanges to current transport and dry storage concepts in order to raise the reference residual heat values citedearlier.
These points are the subject of this IRSN report.

2

BACKGROUND

In the report “Storage of spent nuclear fuel: concepts and safety issues” [2], IRSN reviewed the wet and dry storage
concepts existing worldwide and in France, as well as the safety issues associated with the different solutions forstoring spent fuel underwater or in dry conditions, either on the site where it is produced or at a central facility. To
conclude its analysis, IRSN found that decisions about the type of storage to be used for spent fuel must be assessed in
the light of the following considerations.

1

The Directorate-General for Energy and the Climate (DGEC), within the Ministry for the Ecological and Inclusive Transition, and theFrench Nuclear Safety Authority (ASN) are the contracting authorities.
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Wet storage and dry storage of spent fuel do not serve exactly the same needs. Storage in pools is absolutely
necessary for fuel leaving the reactor core and that has hardly cooled. Dry storage is suitable for fuel that has cooled
substantially.
The type of spent fuel, whether made from enriched natural uranium oxide (ENU), mixed uranium and plutoniumoxide (MOX) or enriched reprocessed uranium oxide (ERU), influences the storage devices possible, at least for acertain period of time after unloading. In particular, MOX fuels have a significantly higher residual heat than ENU and
ERU fuels, regardless of the cooling period considered.
IRSN also illustrated the suitability of storage solutions in relation to the residual heat of spent fuel in a figure (seefigure 1 in report [2]) for two typical fuels representative of those currently used by EDF in 900 MW reactors in the
CPY series, namely:● a fuel made of enriched natural uranium oxide (ENU), initially enriched to 3.7% uranium-235 and irradiated at
50 GWd/t 2;● a fuel made of mixed uranium and plutonium oxide (MOX), with an average total plutonium content of 8.65%
and irradiated at 50 GWd/t.

Figure 1: Storage solutions based on the residual heat of the spent fuelThis curve is based in particular on two reference values:● the maximum residual heat of spent fuel that can be transported on public roads, equal to 6 kW under thetransport licenses currently valid in France;● the highest average residual heat of fuel assemblies, around 2 kW, in current dry storage concepts.

2

Gigawatt-days per metric ton: fuel burnup unit giving the level of irradiation of fuel assemblies, expressed as energy produced by
the assembly in the reactor per ton of initial uranium.
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From a safety point of view, regardless of the type of storage, the decisive parameter is the residual heat of the spent
fuel to be stored. Wet storage (i.e. in a pool), which generally contains hotter fuel, requires more substantial safetymeasures than dry storage, for which more passive measures can be implemented. In dry storage, however, cladding(the first containment barrier) is subject to greater thermal stress and is more difficult to inspect.

3

COMPATIBILITY OF MOX OR ERU SPENT FUEL WITH DRY STORAGE

For the record, ERU and MOX fuels are not currently reprocessed and are stored, after cooling in EDF reactor pools, inthe pools on the Orano Cycle site in La Hague. This is because EDF’s current strategy is to store them underwater andto reprocess them in due course (after 2050), in order to use the plutonium in future generations of reactors, such as
fast neutron reactors (FNR) [3]. The storage time of these fuels, their future and therefore their final destination
depend on decisions about the development of these new generations of reactors.

3.1

Spent MOX FuelAs previously indicated, the residual heat decay curve of spent MOX fuel presented in the June 2018 IRSN reportcorresponds to the MOX fuel currently used in EDF reactors (CPY series), taking into account bounding characteristics(maximum burnup, for example).
However, it is important to remember that the characteristics of the MOX fuel used by EDF in its reactors havechanged over time, with regard to their plutonium content and burnup. Thus, since 1987, the date that MOX fuels
were first used, there have been four periods (see Table 1) between which the characteristics of MOX fuel and thenumber of reactors concerned changed.
Table 1: Changes in the characteristics of MOX fuels and the reactors that use them since 1987

Loading period

1987 - 1994

1994 - 2000

2000 - 2007

Since 2007 *Average plutonium content of
MOX fuel

5.30%

7.08%

8.65%

Average burnup

36 GWd/t

39 GWd/t

46 GWd/t

20

22

around 1,500

more than 2,500

Number of reactors concerned
Number of MOX fuel assemblies
involved ***620around 1,200

It should be noted that, in the future, EDF plans to use MOX fuel with an average plutonium content of
9.08%.

** The number of fuel assemblies was estimated from Figure 14 - Record of MOX fuel loaded in reactors in
the fleet in the report by the High Committee for Transparency and Information on Nuclear Safety citedin reference [3].

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As shown in figure 2 below, drawn up by considering an average burnup rate for the fuels, the residual heat decay
differs according to the type of MOX fuel. The time required for these fuels to cool to the reference value of 2 kW
therefore varies significantly. For example, MOX fuel with a 5.30% plutonium content is compatible with dry storage
after around 5 years of cooling; on the other hand, MOX fuels with a 7.08% plutonium content and with an
8.65% content require 10 years and 30 years of cooling, respectively.

Figure 2: Residual heat decay curves for the different types of MOX fuels used by EDF

Thus, taking into account the dates from which the different types of fuel 3 were used and the reference value of
2 kW, it appears that, from the point of view of residual heat removal, spent MOX fuels with a 5.30% plutonium
content and most of those with a 7.08% plutonium content are compatible with certain dry storage concepts (seefigure 3). This represents around 2,500 spent fuel assemblies.
However, the first spent MOX fuels with an 8.65% plutonium content may only be compatible with dry storage inaround 2040.

In this respect, figure 2 shows that a dry storage solution designed with a maximum residual heat per assembly ofaround 3 kW would allow spent MOX fuels with an 8.65% plutonium content to be stored after 5 to 10 years of cooling.
In the rest of this report, IRSN uses this 3 kW value as a reference value to analyze the changes in dry storage
concepts that would significantly reduce the cooling time required before dry storage could be implemented forthe spent MOX fuels currently in use.

3

Fuels are generally unloaded from reactors after three years of irradiation for MOX fuels with plutonium contents of 5.30% and7.08% and after four years for MOX fuels with plutonium contents of 8.65%.
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Figure 3: Residual heat decay of the various MOX fuels according to the date of their unloading from the reactor

3.2

Spent ERU fuels

Between 1994 and 2013, ERU fuels were loaded into the 900 MW reactors at the Cruas site. EDF plans to resume theuse of this type of fuel in 2023 [3].
As with MOX fuels, the characteristics of ERU fuels used by EDF have changed over time, with regard to uranium-235
enrichment and burnup. This means that since ERU fuel was first used in 1994, there have been three periods (seeTable 2) between which the characteristics of this fuel and number of reactors using it changed.
Table 2: Changes in the characteristics of ERU fuel used since 1999

Loading period

1994 - 1999

235U enrichment

3.70%

4.10%

Average burnup

46 GWd/t

46 GWd/t

Numberconcernedofreactors

Numberof
ERU
assemblies involved *fuel1999 – 20092

About 250

2009 – 20132

4

About 900

* The number of fuels was estimated from the figure Annual quantity of ERU fuel loadedat Cruas between 1994 and 2013 in Appendix 6 of the report by the High Committee forTransparency and Information on Nuclear Security cited in reference [3].
The residual heat characteristics of spent ERU fuels are similar to those of ENU fuels. As illustrated in figure 4
below4, all of EDF’s spent ERU fuels are currently compatible with current dry storage concepts. This represents
around 1,150 spent fuel assemblies.

4

ERU fuels are generally unloaded from reactors after three years of irradiation.
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Figure 4: Residual heat decay of the various ERU fuels according to the date of their unloading from the reactor

4

POSSIBLE CHANGES TO DRY STORAGE CONCEPTS

4.1

Reminder about current dry storage concepts

In countries that do not reprocess spent fuel, the fuels unloaded from reactors (mainly ENU fuels) are generally placedin dry storage after a period of cooling in a pool of several years. These storage facilities are specifically designed toguarantee a maximum spent fuel cladding temperature of around 400°C. For the storage devices currently in use, thisleads to the maximum residual heat of the fuels stored being defined, depending on the concept, between around
1 kW and 2 kW. These values mean that the dry storage of ENU spent fuels is possible in any case before 10 years ofcooling.
As detailed in the IRSN report cited in reference [2], three main dry storage concepts for spent fuel have beendeveloped around the world:● vault storage5;● silo storage;● cask storage.
Dry storage, whether at the reactor site or at a centralized site, requires the spent fuel to first be conditioned,
depending on the case, by placing it:● in a basket placed in a cask with a screwed closure system;● in a container, first fitted, where necessary, with a basket, onto which the lid is then welded to make itleaktight; the whole system is then placed in a storage module (pit, horizontal or vertical concrete structure).

5

In French, ‘entreposage en casemates ou puits’.
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4.2

Analysis of possible changes to current dry storage concepts

At the request of the CPDP, IRSN studied the possible changes to current transport and dry storage concepts thatwould make it possible to change the above-mentioned reference values for the residual heat of spent fuel assemblies(2 kW for dry storage and 6 kW for transport).
For this analysis, IRSN conducted sensitivity studies for a dry storage concept in a metal cask for which it had
sufficient data (geometry, materials, etc.) to quickly prepare a computational model. The selected cask consists of a
thick steel shell covered with a resin to limit the dose rate around it. Its outer layer is not fitted with a specificsystem (cooling fins), intended to increase the surface area for exchange with the outside air and therefore the heatdissipation of the cask. The basket placed inside the cask contains 24 compartments to hold spent fuel assemblies.
The maximum residual heat of spent fuel stored in this cask, assuming a complete and uniform load (reference case),is just less than 1.5 kW.
At first glance, IRSN considers that the conclusions of its study could be extended to all concepts. However, theincreases in the residual heat of spent fuel concluded from this study should be considered as orders of magnitude,
since these may vary depending on the storage concept.
IRSN mainly studied different load configurations of the cask selected for storage. In particular, the following wereanalyzed:● incomplete loads: one or more compartments were left empty and the used compartments contained spent
fuels with the same residual heat;● non-uniform loads: the cask was loaded with two types of spent fuel with different residual heat levels.
The parameters of the alternative configurations (number and residual heat of spent fuel assemblies) studied were
defined such that the maximum temperature of the spent fuel cladding in the reference case was respected (below
400°C).
In the configurations with incomplete loads, there were significant gains in the maximum admissible residual heat of
the spent fuel assemblies stored.
Figure 5 shows, for a given number of empty compartments in the cask, the different incomplete load configurations
that present the greatest possible gain in the maximum residual heat per fuel assembly compared to the referencecase cited.
However, they lead to a significant decrease in storage density. This would entail an increase in the number of casks
required, the surface area of the storage units and, potentially, the buildings housing them. These changes would leadto a significant increase in the cost of storage.

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Figure 5: Admissible residual heat of fuel assemblies according to the number of empty compartments in the packaging

Non-uniform load configurations also present significant gains with regard to the maximum admissible residual heat of
the spent fuel assemblies stored compared to the reference case. figure 6 shows, for three non-uniform load cases,
the gain6 in residual heat of the hottest fuel assemblies compared to the decrease 6 in residual heat of the coldest fuelassemblies (see the example in Figure 6 below). Moreover, they do not lead to a reduction in storage density.
However, they require spent fuel assemblies with a lower residual heat to ensure that the cask is fully loaded. The
French strategy of reprocessing spent ENU fuel limits the possibility of using this alternative.

Figure 6: For three non-uniform load configurations, the relationship between the residual heat of the hottest and the coldest fuelassemblies in order to ensure a maximum fuel temperature of less than 400°C

6Gain and decrease compared to the residual heat of fuel assemblies in the reference case.
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In conclusion, the results obtained show that, by considering only the criterion of the maximum cladding
temperature for the spent fuels stored, it would be possible to store, in the cask considered for the study, alimited number of spent fuel assemblies with a residual heat of two to three times that of the maximum in thereference case (complete and uniform cask load). This significantly reduces the underwater cooling timerequired before implementing dry storage. In this respect, the reference value of 3 kW, introduced inparagraph 3.1 of the report, appears achievable.
Nonetheless, the industrial implementation of the configurations studied should be the subject of analyses (onsafety and technical and economic aspects), particularly in the French context. This is because they lead to asignificant decrease in storage density or require the availability of a large number of spent fuel assemblies with‘low’ residual heat.
Furthermore, some cask design choices promote heat exchange between spent fuels and the external environment(cooling fins, for example). These measures would increase the admissible residual heat of the spent fuel assemblies
stored. By way of example, installing cooling fins around the packaging modeled by IRSN would increase the maximum
admissible residual heat of fuels by several tens of percent. However, this could make the cask manufacturing
process, and even storage facility construction, more complex in order to promote heat exchange.
Finally, in addition to the requirement regarding the maximum spent fuel cladding temperature, casks must meetradiation protection requirements, particularly when they are used for both transport and storage operations. In thisrespect, the results presented above do not take into account either radiation protection requirements (in particular
those related to transport on public roads) or the maximum admissible temperature of the resin commonly used forthis type of cask.
Taking these constraints into account could reduce the estimated gains. For example, in the case studied by IRSN, thegreatest gains in residual heat were obtained by placing the hottest fuel assemblies in the outer compartments of thebaskets. However, this configuration is the least favorable in regard to dose rate value for storage devices,
particularly given the neutron fluence rates7, which increase with the initial plutonium content in the fuel.

5

POSSIBLE CHANGES TO TRANSPORT CONCEPTS

As the storage concept studied above is similar to that of the transport casks, the results obtained can be transposedto spent fuel transport configurations (increase in the maximum admissible residual heat of spent fuels for incomplete
or non-uniform load configurations). However, in this case, radiation protection requirements could become more
restrictive than residual heat removal requirements.
Transport configurations and even conditioning must therefore be able to be adapted in order to transport fuelswith a residual heat higher than the reference value of 6 kW per fuel assembly. However, depending on theconfiguration chosen, this could lead to an increase in the number of related shipments (particularly forincomplete loads).
As with storage, the industrial implementation of such changes should be the subject of analyses (on safety andtechnical and economic aspects).

7

The fluence rate corresponds to the neutron flux density.
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6

CONCLUSION

The fuel used in French nuclear power plant reactors contains enriched natural uranium oxide (ENU) or mixed uranium
and plutonium oxide (MOX). In the past, fuel made from enriched reprocessed uranium oxide (ERU) was used. Unlike
ENU fuels, ERU and MOX fuels are not currently reprocessed. They are stored for cooling in EDF reactor pools and thenin those at the Orano Cycle plant in La Hague.
The characteristics of the MOX and ERU fuel used by EDF have changed over time. In particular, the plutonium content
of MOX fuels was successively 5.30%, 7.08% and 8.65% (content of fuel currently loaded in EDF reactors).
The residual heat of spent MOX fuels depends on this content and their burnup rate. Thus, the cooling time required
for the residual heat of these fuels to be reduced to less than 2 kW per fuel assembly, the reference value adopted by
IRSN to consider the possible implementation of current dry storage concepts, is around 5 years, 10 years and 30 years
respectively, considering the average burnup rate per assembly.
Consequently, given the periods during which MOX fuels with the above-mentioned plutonium contents have been
used, dry storage solutions based on current concepts could now be considered for all spent MOX fuels with aplutonium content of 5.30% and for most of those with a plutonium content of 7.08%, i.e. around 2,500 fuelassemblies.
For the first spent MOX fuels with a plutonium content of 8.65%, used since 2007, this type of storage may not besuitable until around 2040. In any case, for this type of spent MOX fuel, wet storage solutions are required over a
period of nearly 30 years after the end of their irradiation, taking into account the reference value of 2 kW
associated with current dry storage concepts. To reduce this time to around ten years, dry storage concepts
should first be developed for spent fuels with a residual heat of around 3 kW per fuel assembly.
Approximately 1,150 ERU fuel assemblies were loaded into reactors by EDF between 1994 and 2013. All of the spent
ERU fuels currently stored have a residual heat of less than 2 kW and are therefore compatible with current dry
storage concepts.
The 2 kW reference value chosen by IRSN for the implementation of dry storage is based on a bibliographic analysis of
the average residual heat of spent fuels chosen for dry storage concepts currently in use around the world. These
values, which vary between approximately 1 kW and 2 kW, correspond to compromises between safety requirements(maximum temperature of the spent fuel cladding, radiation protection, etc.), storage capacity (number of fuelassemblies per storage device), the characteristics of the spent fuels to be stored (residual heat and therefore
required cooling time) and costs.
Considering only the safety requirement related to the temperature of the fuel cladding, it is possible to change
the load configurations of existing concepts so that spent fuels with a residual heat greater than 2 kW can be
stored.
Therefore, by reducing, for example, the number of spent fuel assemblies per storage device or by storing fuels withvarying residual heats (significantly higher and lower than the average value) in the same device, spent fuels withresidual heats two to three times higher than the average value associated with the devices currently in use could be
stored. This would significantly reduce the underwater cooling time required before implementing dry storage.
Moreover, changes in the design of storage devices (to increase heat dissipation, etc.) could be developed.

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However, the reduction in the number of spent fuel assemblies per storage device proportionally reduces the storage
density (a half-loaded cask requires twice as much conditioning and storage space for the same number of fuelassemblies as a full cask). Similarly, while non-uniform loads do not lead to a decrease in storage density, theyrequire the availability of spent fuel assemblies with ‘low’ residual heat. The French strategy of reprocessing spent
ENU fuel limits the possibility of using this alternative.
A similar analysis can be carried out for transport casks. Therefore, with the suggestions provided above, it should bepossible to adapt transport configurations and even conditioning in order to transport fuels with a residual heat higher
than the reference value of 6 kW per fuel assembly. However, depending on the configuration chosen, this could leadto an increase in the number of related shipments (particularly for incomplete loads).
More generally, in addition to the constraint related to fuel cladding temperature, casks must meet a set ofsafety and radiation protection requirements, as well as industrial constraints (feasibility, capacity, cost, etc.). A
comprehensive analysis integrating all these factors would therefore be required to consolidate the gains
mentioned above while taking into account both storage and, where applicable, transport operations.
Furthermore, the operations to be performed at the end of the spent fuel storage phase, whether wet or dry, must be
taken into account from the design stage of the storage facilities. For instance, it must be possible to unload the fuels
for either reprocessing or reconditioning with a view to disposal. In an industrial dry storage project, the facilities
required for these operations should be identified from the outset. Specific safety requirements will also have to be
adopted for these operations, for example concerning the mechanical characteristics of spent fuel after storage.
Demonstrating compliance with these requirements, particularly for spent MOX fuel, may require specificdevelopments and the monitoring program for stored fuels must take these requirements into account. The definitionand study of all these requirements would impact the time required to construct the first potential spent MOX fuel dry
storage facility in France.

In conclusion, the assessment carried out by IRSN did not reveal any factors that would rule out
storing in dry conditions some of the MOX and ERU fuels currently stored underwater. Nevertheless,the various possible options should be examined, incorporating the related safety and radiation
protection requirements as well as all industrial constraints.

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LETTER OF REQUESTIRSN Report No. 2019-00903

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LIST OF ABBREVIATIONS USED IN THE REPORT

ASN

French Nuclear Safety Authority

CNDP

Commission nationale du débat public (French National Public Debate Commission)

CPDP

Commission particulière du débat public (Special Public Debate Commission)

DGEC

Directorate-General for Energy and Climate

EDF

Electricité de France (the French national electric utility)

ENU

Enriched natural uranium

ERU

Enriched reprocessed uranium

FNR

Fast neutron reactor

HCTISN

French High Committee for Transparency and Information on Nuclear Safety

IRSN

French Institute for Radiological Protection and Nuclear Safety

MOX

Mixed uranium and plutonium oxide

MW

Megawatt electric.

NPP

Nuclear power plant

PNGMDR

National Plan for the Management of Radioactive Materials and Waste

PWR

Pressurized water reactor

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