How will new knowledge be reflected to the management of geological disposal?
- Influence of an FEP not considered so far to some sub-scenarios Koichi ShinCentral Research Institute of Electric Power Industry
1646 Abiko, Abiko-shi. Chiba-ken. 270-1194 Japan
Key words; Stakeholder Involvement, Stepwise Decision, Decision Criteria, Safety Case, Pressure Solution

Abstract
After it became clear that geological disposal of high-level radioactive waste would not be realized without theunderstanding from the society when all siting approaches in western countries around 1980s tumbled,international communities and OECD/NEA made efforts to attain the understanding from the society andestablished important principles concerning social and ethical aspects. Some of the key words were
responsibility of present generation, safety case, stepwise decision, stakeholder involvement, preservation of
RKM (records, knowledge and memory), and so on. Safety case is stipulated to include the assessment of allfeatures, events and processes (FEPs) that could significantly influence the performance of the disposal system.
And as such, the safety case is a document to share the consensus on the safety of a disposal system among thepresent generation, to serve as the ground for stepwise decision, and to transmit the technical information about
the disposal system and our sincere endeavor on it to the future generation. In the stepwise approach, decisions
made in the previous steps may be changed based on new scientific knowledge and others.
Meanwhile, an FEP, pressure solution, which has not been dealt with in previous safety case documents, hasbeen pointed out that it can affect the geological disposal system through some sub-scenarios. One is a processof permeability evolution around a disposal tunnel due to mass transfer through pressure solution, diffusion andprecipitation. Another one is a process of sinking of a heavy container in the buffer due to pressure solution
creep. This report reviews the pressure solution phenomena and above mentioned sub-scenarios, points out thatthe phenomena and sub-scenarios need to be duly addressed in a safety case, and gives a thought to fulfilling the
responsibility of present generation.
1. Introduction
Countries that are using or have used nuclear
energy are making efforts to realize the final disposalof high-level radioactive wastes. Since it requires a
lot of time, it is a consensus among the international
community to adopt an approach of stepwise decision
making to cope with new knowledge and situationand to reverse the decisions in the former steps if
necessary. R&D’s are being undertaken to ensure
safe and rational disposal. When and if new
knowledge poses a concern which needs to beclarified, the disposal may be delayed, and the delay
can be unduly. What will be a rational strategy forthe realization of the disposal, which is the
responsibility of the present generation?
The section 2 of this report shows examples of new
knowledge which have not been considered in theprevious safety case documents. The FEP of concern
is pressure solution. There are papers pointing outthat pressure solution can affect some sub-scenarios
which can have significant effects on the safetyassessment. The sub-scenarios are evolution of
permeability of rock around disposal tunnel, canister
sinking in the bentonite buffer, and other.

In the 3rd section, the international endeavor so far
made and resultant principles established to gain theunderstanding from the society are reviewed.
The R&D is the pivot to ensure the safety of thedisposal, but there will not be a conclusive end to the
R&D for evaluating the safety for the far future. If
new knowledge obtained by a research createsanother research topic and the disposal is delayed, isit an adequate way to fulfill the responsibility of thepresent generation? This question is raised in the 4th
section.
2. Examples of New Scientific Knowledge
2.1 Pressure Solution
Although it is a phenomenon (FEP) which canaffect significantly the safety of disposable system,
pressure solution has never been considered in
relevant scenario analyses in previous safety cases.
Pressure solution is defined as enhanced
dissolution of solids into aqueous solution by stresses
in the solids, and it often broadly means the resultant
deformation process through dissolution anddiffusion. It was found in geological observations

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan

in as early as 1860s. Sorby pointed out in 1865 thatstylolite and impressed pebble were formed bypressure solution. Gibbs formulated the thermodynamic chemical potential of solid as a function oftemperature and stress on the surface concerning
the phase equilibrium in 1877. However, pressure
solution was considered as a relatively limited
geological phenomenon for a long time. Referring toJapanese geological dictionaries, the one publishedfrom Shin-kokin-shoin in 1973 has no entry forpressure solution and suggests the cause of stylolite
as partial melting. But another dictionary publishedfrom Heibonsha in 1996 includes pressure solution
and explains the cause of stylolite as pressure
solution as with the present understanding.
In recent years, pressure solution has come to berecognized as an omnipresent phenomenon observedin the crust deeper than about 90m [Tada & Siever,1989], and one of the most important mechanisms ofcrustal deformation [Gratier et al, 2013] (Fig 1). In
recent years, researches have been conducted not
only in the field of geology but also in engineering[Yasuhara et al, 2016] and others.

(Gratier & Guiget,1986)

Micro scale : diagenetic compaction

Large scale : geological folding(2014, Ake)

Fig.1 Omnipresent effects of pressure solution
Others include mica’s penetration into quartz, impressed
pebble, stylolite, salt flow under low T and P, etc.

2.2 Its effects on disposal system
In recent years it has been pointed out that pressure
solution affects geological disposal systems in some
way or other.
(1) Permeability of rock around disposal tunnel
Yasuhara et al (2016) (Fig 2) evaluated thefluctuation of permeability during 10,000 years
around a radwaste disposal facility through T-H-M-C
coupling simulations taking into account the pressure

solution. Parameters were taken from quartzite data.
The simulation suggested a favorable result for thesafety of geological disposal because the permeability
around a disposal tunnel decreased with time.
(Yasuhara et al, 2016)

Pressure Solution incorporated
T-H-M-C analysis
Half domain of rock around atunnel of 2.2m D.
Depth 450m
Porous quartzite

Evolution of normalized permeability

Fig.2 Permeability change due to pressure solution(2) Rock sinking in salt dome
Dislocation creep and pressure solution creep havebeen pointed out as the mechanisms of salt
deformation, and the pressure solution creep ispredominant at low temperature and pressure in wet
condition [Urai et al, 1986].
Burchardt et al (2012) have numerically simulated
the sinking of entrained anhydrite (2.9 g/cm3) in theGorleben salt diapir (2.2 g/cm3) and pointed out thatthe interaction between the sinking rocks and facility
in salt dome should be considered in a safetyassessment of waste disposal.
(3) Canister sinking
The sinking of canister in buffer can be detrimental
to safety because too small thickness of the buffer
deteriorates the buffer functions of water tightness
and nuclide adsorption. Therefore the sinking has
been quantitatively evaluated [SKB, 2011] [JNC,
2000], but only from the viewpoint of mechanicaldeformation of buffer. Shin(2017) has pointed outthat canister can sink also through chemical
deformation via pressure solution (Fig 3). A review
of previous works on pressure solution concluded
that the rate of sinking can be non-negligible
considering the assessment time of 1Ma (Table 1).
Buffer 2 g/cm3
Canister 6 g/cm3
At the bottom of a canister, larger stressenhances the dissolution of buffer.
The dissolved solute migrates by diffusion toless stressed region and precipitates.
Through this process of mass transfer, heavythings sink in geological time scale.

Fig.3 Canister sinking due to pressure solution

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan

Table 1 Rate of deformation by pressure solution
from various sources (Shin, 2017)

3. Principles for Acquiring Understanding fromthe SocietyCountries with nuclear power plants are making
efforts for geological disposal of high level
radioactive waste as the responsibility of the present
generation. Some countries in Europe and the US
started selecting the disposal site in 1970’s and1980’s but met with oppositions from thecommunities and the society. In this background,important principles and good practices have been
established by OECD/NEA and others to acquire theunderstanding from the society. They are in theperspective of ethics, safety case and decision making
including stepwise process, stakeholder involvement
and others. Some of them are listed in Appendix.
3.1 Ethics
NEA(1995) pointed out that our responsibilities tofuture generations are better discharged by a strategy
of final disposal, and that applying the same
standards of risk in the far future as it does to thepresent is required from the viewpoint ofintergenerational equity.
3.2 Safety Case
Safety case is the collection of arguments andevidences in support of the safety of a disposal
facility. The most important part of the safety caseis the safety assessment based on scenarios ofevolution of a disposal system.
IAEA(2012) stipulated that the process ofdevelopment and screening of scenarios should befully documented, and that all features, events andprocesses (FEP) that could significantly influence theperformance of the disposal system should be
addressed. NEA(2017) also mentioned scenario
development to the same effect as above.
NEA(1999) and NEA(2001) pointed out that
scenarios should be developed through clear
communication between implementer, regulator andother audiences.

3.3 Decision Making(1) Stepwise process
NEA(2017) pointed out that stepwise process
could secure flexibility in case of change in site
conditions, technical and political situations and newscientific knowledge and others.
NEA(2004) pointed out that stepwise approach
was necessary also to enable stakeholders not yetborn to involve in the decision process meaningfully.
(2) Stakeholder involvement
NEA(2003) pointed out the importance of fair andparticipatory decision making process, and ofnational commitment to its creation and involvement.
NEA(2014) pointed out that stakeholders otherthan regulator and implementer should be involved in
the national decision process, and that stepwise
approach involving various stakeholders is a
responsible way.
NEA(2015) stated that stakeholder involvement
should start early in time and upstream in process.
(3) Balance
NEA(2014) stated that decisional framework
should include the viewpoint not only of safety but
also of society, economics, technology, ethics, andothers.
(4) Records, knowledge and Memory (RK&M)
NEA(2011) pointed out the necessity ofpreservation of RK&M across generations in order tosupport the long and complex decision making
processes for radioactive waste management.
4. Radioactive Waste Management (RWM)
4.1 Involvement of General Public
The previous chapter dealt with the principles andgood practices established by OECD/NEA and IAEA,
both are the international organs for the promotion ofcivilian use of nuclear technology.
Meanwhile, US National Academy of Science(1999) and Science Council of Japan (2015) madecomments to the respective governments about RWM
as the representatives of the general publics, so to
speak.
NAS(1999) stated that the management had been
focused mostly on technology and societal aspects
had been insufficient. It suggested two principles
from the viewpoint of social science for gaining
public acceptance.
First, participation in thedecision process leading to a geological repository
should be open and transparent. For this, extensive
review of the repository program by independentscientific experts would be necessary. The second
principle is staged decision making, and if necessary,
the site selection process can be restarted.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, JapanNAS(2003) made a suggestion in response to arequest from the US DOE about staged decision
making. It pointed out that iterative review of thesafety case in view of new information is the central
to the staged decision making.
Science Council of Japan was requested by Atomic
Energy Commission of Japan to make suggestions on
how to explain and provide information to the public
about the radioactive waste disposal in Japan. In
reply to AEC of Japan, SCJ(2012) pointed out thatthe cause of the delay in site selection in Japan was
not the way how to explain but the lack of social
consensus in the nuclear energy policy in general.
Another cause was pointed out as the uncertainty ofsafety.
And SCJ(2015) made complementarysuggestions on RWM, one of which is the creation of
RWM Policy Commission to form policy based onconsensus among broad range of stakeholders.
4.2 Will We See Progress in RWM ?
As reviewed so far in chapter 3 and 4.1, in orderfor us to take responsibility of the present generation
as a whole, important principles and good practices
have been established. But will we be able to see
progress in RWM only with these?
(1) FEP not yet evaluated
Taking up pressure solution as an example of FEPs
not yet evaluated in previous safety cases, what willbe the right way to handle it? Pressure solution canaffect two sub-scenarios, evolution of permeability ofrock around disposal tunnel and canister sinking in
buffer. These sub-scenarios can have significant
influence on the safety of disposal system, and hence,these need to be evaluated in a safety case according
to the principle mentioned in section 3.2.
Conceptually, assessing the sub-scenario of canister
sinking via pressure solution may have two options.
Option A requires detailed study of pressure solution
and option B does not. In the case of option A,
dissolution rate will need to be clarified as a functionof pressure between contacting minerals, temperature,
pH, mineral species, and others. Diffusion rate ofdissolved mineral in buffer material and precipitation
process will also need to be studied.
Then
incorporating these mechanisms, a numerical modelneeds to be developed to evaluate quantitatively theprocess of canister sinking due to the pressure
solution. Taking into consideration the canister’s
position in the buffer in the future, safety will beassessed for the reference design of engineered
barrier and the site. Depending on the result, someadjustment to engineered barrier system (EBS) or
change of disposal concept may be required. In thecase of option B, the time needed for research onpressure solution is shortened by adopting a
conservative approach of sufficiently robust EBS or
disposal concept. Both options will require longtime and thus pose the problem of balance between
safety and time.
(2) Decision criteria for uncertain safety
Confirming the safety for the future generation isthe core of safety assessment.
But, as wellacknowledged, evaluation of the future entails
uncertainty. Decisions will be made at each stage ofstepwise process via renewed safety case. All
stakeholders including general public will be
participating in making safety case and in decision.
How can we, the present generation, evaluate theuncertain safety and come to agreeing? Presently
we do not have the decision criteria for uncertain
safety and hence it seems we cannot expect progress
in RWM.
(3) Balance between safety and economics,,
Securing safety is the foremost importance on the
one hand, economics and efficiency are also required
in implementing geological disposal on the other.
When various stakeholders are to reach an agreement,
they need an agreed methodology how to take thebalance. But it seems we do not have suchconsensus yet.
4.3 Conclusion
As discussed so far, it is not sure we can see
progress in RWM only with the principles and goodpractices which have been so far establishedhopefully to promote RWM.
The underlying
problems are how and at which level we can agree on
uncertain safety, and how to take a balance between
safety, economics, time and so on.
The most needed action now in order to resolve theRW problem is to develop decision criteria andmethodology how to take balance on which thepresent generation can agree, with the recognition of
our supreme responsibility for the RW disposal.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan

Appendix
Some of Principles and Good Practices for RWM

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, JapanReferences
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6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan