Research &
Development
Excerpts from EPRI’s The Nuclear
Connection Summer 2016 newsletter.
These were reprinted with the permission
from EPRI. Contact Renita Crawford at
(704) 595-2888 or
with any comments or questions.
ISFSI Aging
Management Guidelines
Nuclear power plant operators
with independent spent fuel storage
installations (ISFSIs) due for Nuclear
Regulatory
Commission
(NRC)
relicensing within the next five years
urgently need suitable strategies to
address canister aging degradation. For
this reason, EPRI has been working to
develop aging management guidelines
that address the potential for chloride-
induced stress corrosion cracking
(CISCC) in welded stainless steel
canisters in dry cask storage systems.
Now in its fourth year, this initiative has
three key focus areas:
• Understanding the potential for
degradation to predict how, where,
and when CISCC has the greatest
risk of occurring,
• Developing guidance and technology
for inspections and management, and
• Understanding
and
developing
response measures for CISCC failure.
EPRI will publish aging management
and inspection guidance in early 2017.
This report will serve as a follow-up to
the Literature Review of Environmental
Conditions
and
Chloride-Induced
Degradation Relevant to Stainless
Steel Canisters in Dry Cask Storage
Systems published in March 2014 and
the Susceptibility Assessment Criteria
for Chloride-Induced Stress Corrosion
Cracking (CISCC) of Welded Stainless
Steel Canisters for Dry Cask Storage
Systems published in September 2015.
In addition, EPRI will work
through 2019 to transition its research
and technical guidance to the American
Society of Mechanical Engineers for a
code case.
Risk Factors
EPRI’s
susceptibility
criteria
report has been particularly valuable
to members, said Shannon Chu, senior
technical leader for EPRI’s Used Fuel
and High Level Waste program. “I expect
that members will benefit from EPRI
providing a technical basis to focus the
concern for CISCC on particular sites
that have more susceptibility factors,
mainly being close to a source of salt like
the ocean and being in an environment
that has high humidity,” Chu explained.
EPRI concluded that CISCC of
stainless steel reactor components can
occur when the following three elements
are present:
• Tensile stress
• Susceptible material
• Corrosive environment, such as
surface contamination by atmospheric
chlorides and sufficient humidity
There is currently very little
experience and no tools have yet been
fully demonstrated for inspection in dry
storage configurations. The challenges
for inspecting canisters include limited
access to the surface via cask vents,
and a high-temperature, high-radiation
environment. EPRI is working to develop
remotely operated vehicles and low-
profile sensors in order to meet these
challenges.
Consequences of Degradation
To date, much of EPRI’s research
has been focused on understanding
susceptibility to CISCC and developing
aging management guidelines, but
the institute has begun looking at the
actual consequences of such a failure.
EPRI expects to publish a literature
survey in early 2017 that will evaluate
available references for determining the
consequences of a through-wall crack
occurrence in a used fuel dry storage
canister, including general and work-
related exposure to radiation.
“The expectation and understanding
among most people in the industry and
even with the NRC is that there is very
minimal dose impact and that the presence
of through-wall CISCC wouldn’t result
in exceeding the normal operating dose
limits,” Chu explained. “We don’t have an
analysis yet that confirms this, especially
at a generic level that applies to any site.
So, we’re working to develop that.”
Analysis and guidelines for this
phase are expected in 2018.
While Chu admits, this will be a
unique challenge, her goal is to ensure
that EPRI members—many of whom
face relicensing of their ISFSIs in 2020—
are prepared for a new approach to aging
management that answers plant operator
and NRC concerns.
“I’m hoping for a path forward
for continued storage and continued
operation indefinitely, but at least for
another 40 years,” Chu said.
Long Term Operations
EPRI is working with our members
and various government and international
agencies to support the technical basis
for nuclear plant license renewals. In
the Unites States, most plants already
have been approved for the first period
of license renewal (out to 60 years of
operation), and are interested in second
license renewal, out to 80 years.
The EPRI Long Term Operations
(LTO) program was established in
2010 and leverages decades of previous
research to focus on the technical basis
for operation to 80 years. So far, no
generic technical “show stoppers” have
been identified, said Rich Tilley, senior
technical leader for EPRI’s LTO program.
As of October 2015, 250 nuclear
power plants worldwide had been
in operation for more than 30 years,
and 68 more than 40 years. This
successful operating experience is
providing valuable data on plants and
their maintenance processes to support
safe, extended operations. Importantly,
without license renewal beyond 60 years,
the United States will lose 30,000 MW
of power between 2029 and 2035. This
represents a major loss of non-carbon
dioxide producing generation.
Renewal Process
The lead time for the renewal process
is driven by both the utilities’ need to
perform due diligence and the Nuclear
Regulatory Commission’s review process
to ensure continued safe operations in
compliance with the plant licensing basis.
The original license period for nuclear
plants was 40 years, and more than 70%
of the plants in the United States have
received the first license renewal for an
additional 20 years of operation.
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NuclearPlantJournal.com Nuclear Plant Journal, September-October 2016
