No: 14-020 March 24, 2014
CONTACT: Scott Burnell, 301-415-8200
NRC Seeks Comment on Proposed Revision to Acceptance Criteria
For Emergency Cooling Systems at U.S. Reactors
The Nuclear Regulatory Commission is seeking comment on a proposed change to agency regulations regarding the acceptance criteria for emergency systems to cool the reactor core if an accident occurred at a U.S. nuclear power plant.
The proposed rule reflects recent research findings that identified new damage mechanisms for zirconium alloy-covered fuel rods during a loss-of-coolant accident. The proposed rule would also apply to all fuel types and cladding materials, as well as address a petition for rulemaking regarding crud, oxide deposits and hydrogen content in zirconium-alloy fuel cladding. The proposed rule would ensure an acceptable level of fuel rod performance following a loss-of-coolant accident, providing adequate protection of public health and safety. The proposed rule would also provide licensees the option to use risk-informed methods to address the effects of debris during long-term cooling following a loss-of-coolant accident.
The proposed rule is not part of the NRC’s response to the 2011 events at Fukushima, but an outcome of a Nuclear Energy Institute petition for rulemaking in 2000, direction given to the staff by -+_the Commission in 2003, and findings of a 10-year research program ending in 2008. Thus, the development of the proposed rule pre-dates the Japan events by several years.
For more information on the proposed rule, contact NRC staff members Tara Inverso by phone at 301-415-1024 or via e-mail tara.inverso@nrc.gov; or Paul M. Clifford by phone 301-415-4043, via e-mail paul.clifford@nrc.gov
.
Comments on the changes will be accepted until June 9, following publication of the proposed rule in the Federal Register . The Federal Register notice also opens a comment period for three related draft regulatory guides. The notice includes instructions and the relevant Docket IDs for submitting comments on both the rule and on the guides. Comments may be submitted on the Regulations.gov website; by e-mail to Rulemaking.Comments@nrc.gov ; hand delivered to: 11555 Rockville Pike, Rockville, Md., between 7:30 a.m. and 4:15 p.m. (EST) federal workdays; telephone: 301-415-1677; mailed to
Secretary
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
ATTN: Rulemakings and Adjudications Staff
http://adamswebsearch2.nrc.gov/webSearch2/doccontent.jsp?doc={56DE33D1-6742-42F2-8AFD-AF53BDA12DA6}
Regulatory Analysis for Proposed Rulemaking 10 CFR 50.46c:
“Emergency Core Cooling System Performance during Loss-of-Coolant Accidents”
March 24, 2014
From page 20
The proposed rule would require licensees to evaluate the thermal effects of crud and
oxide layers that accumulate on the fuel cladding during plant operation. Because licensees are
required to account for various thermal parameters under the current regulation, the NRC’s
position is that the proposed requirement to evaluate crud is a clarification of the current
requirement. As such, there would be no additional cost incurred as a result of the rule.
Blogger (Leyse) comment on the above paragraph. It certainly is not obvious that there would be no additional cost. If the rule includes: During or immediately
after plant operation, if actual crud
layers on reactor fuel are implicitly
determined or visually observed after
shutdown to be greater than the levels
predicted by or assumed in the ECCS
evaluation model, licensees would be
required to determine the effects of the
increased crud on the calculated results, that could be very expensive.
http://www.gpo.gov/fdsys/pkg/FR-2014-03-24/pdf/2014-05562.pdf
10 CFR Parts 50 and 52
[NRC–2008–0332, NRC–2012–0041, NRC–
2012–0042, NRC–2012–0043]
RIN 3150–AH42
Performance-Based Emergency Core
Cooling Systems Cladding Acceptance
Criteria
from page 16122
Technical Issues in PRM–50–84
Licensees use approved fuel
performance models to determine fuel
conditions at the start of a LOCA, and
the impact of crud and oxidation on fuel
temperatures and pressures may be
determined explicitly or implicitly by
the system of models used. With the
addition of an unambiguous regulatory
requirement to address the
accumulation of crud and oxide during
plant operation, the NRC believes that
fuel performance and LOCA evaluation
models must include the thermal effects
of both crud and oxidation whenever
their accumulation would affect the
calculated results. The NRC notes that
licensees are required to operate their
facilities within the boundary
conditions of the calculated ECCS
performance. During or immediately
after plant operation, if actual crud
layers on reactor fuel are implicitly
determined or visually observed after
shutdown to be greater than the levels
predicted by or assumed in the ECCS
evaluation model, licensees would be
required to determine the effects of the
increased crud on the calculated results.
In many cases, engineering judgment or
simple calculations could be used to
evaluate the effects of increased crud
levels; therefore, detailed LOCA
reanalysis may not be required. In other
cases, engineering judgment is used to
determine that new analyses would be
performed to determine the effect the
new crud conditions have on the final
calculated results. If unanticipated or
unanalyzed levels of crud are
discovered, then the licensee must
determine if correct consideration of
crud levels would result in a reportable
condition as provided in the relevant
reporting paragraphs. Should this
proposed rule be adopted in final form,
the NRC believes this regulatory
approach to address crud and oxide
accumulation during plant operation
would satisfactorily address the issues
raised by the petitioner’s first request.
The formation of cladding crud and
oxide layers is an expected condition at
nuclear power plants. Although the
thickness of these layers is usually
limited, the amount of accumulated
crud and oxidation varies from plant to
plant and from one fuel cycle to
another. Intended or inadvertent
changes to plant operational practices
may result in unanticipated levels of
crud deposition. The NRC agrees with
the petitioner (the petitioner’s second
request) that crud and/or oxide layers
may directly increase the stored energy
in reactor fuel by increasing the thermal
resistance of cladding-to-coolant heat
transfer, and may also indirectly
increase the stored energy through an
increase in the fuel rod internal
pressure. As such, to ensure that
licensee ECCS models properly account
for the thermal effects of crud and/or
oxide layers that have accumulated
during operations at power, the
proposed rule would add a requirement
to evaluate the thermal effects of crud
and oxide layers that may have
accumulated on the fuel cladding
during plant operation. If the NRC
adopts the proposed rule in final form,
then the second request of PRM–50–84
would be resolved.
The petitioner’s third request is for
the NRC to establish a maximum
allowable percentage of hydrogen
content in fuel rod cladding. The
purpose of this request is to prevent
embrittlement of fuel cladding during a
LOCA. Although the NRC has decided
not to propose the specific rule language
recommended by the petitioner, the
proposed new zirconium-specific
requirements, if adopted in final form,
would address the petitioner’s third
request by considering cladding
hydrogen content in the development of
analytical limits on integral time at
temperature.
The NRC believes that this proposed
rule addresses each of the three issues
raised in PRM–50–84. If the NRC adopts
the proposed rule in final form, PRM–
50–84 would be granted in part and
resolved.
http://www.inel.gov/relap5/rius/yellowstone/leyse.pdf
Unmet Challenges for SCDAP/RELAP5-3D
Analysis of Severe Accidents
for Light Water Nuclear Reactors
with Heavily Fouled Cores
“Emergency Core Cooling System Performance during Loss-of-Coolant Accidents”
March 24, 2014
From page 20
The proposed rule would require licensees to evaluate the thermal effects of crud and
oxide layers that accumulate on the fuel cladding during plant operation. Because licensees are
required to account for various thermal parameters under the current regulation, the NRC’s
position is that the proposed requirement to evaluate crud is a clarification of the current
requirement. As such, there would be no additional cost incurred as a result of the rule.
Blogger (Leyse) comment on the above paragraph. It certainly is not obvious that there would be no additional cost. If the rule includes: During or immediately
after plant operation, if actual crud
layers on reactor fuel are implicitly
determined or visually observed after
shutdown to be greater than the levels
predicted by or assumed in the ECCS
evaluation model, licensees would be
required to determine the effects of the
increased crud on the calculated results, that could be very expensive.
http://www.gpo.gov/fdsys/pkg/FR-2014-03-24/pdf/2014-05562.pdf
10 CFR Parts 50 and 52
[NRC–2008–0332, NRC–2012–0041, NRC–
2012–0042, NRC–2012–0043]
RIN 3150–AH42
Performance-Based Emergency Core
Cooling Systems Cladding Acceptance
Criteria
Following is from page
16140
(iv) To the extent practicable,
predictions of the ECCS evaluation
model, or portions thereof, must be
compared with applicable experimental
information.
from page 16122
Technical Issues in PRM–50–84
Licensees use approved fuel
performance models to determine fuel
conditions at the start of a LOCA, and
the impact of crud and oxidation on fuel
temperatures and pressures may be
determined explicitly or implicitly by
the system of models used. With the
addition of an unambiguous regulatory
requirement to address the
accumulation of crud and oxide during
plant operation, the NRC believes that
fuel performance and LOCA evaluation
models must include the thermal effects
of both crud and oxidation whenever
their accumulation would affect the
calculated results. The NRC notes that
licensees are required to operate their
facilities within the boundary
conditions of the calculated ECCS
performance. During or immediately
after plant operation, if actual crud
layers on reactor fuel are implicitly
determined or visually observed after
shutdown to be greater than the levels
predicted by or assumed in the ECCS
evaluation model, licensees would be
required to determine the effects of the
increased crud on the calculated results.
In many cases, engineering judgment or
simple calculations could be used to
evaluate the effects of increased crud
levels; therefore, detailed LOCA
reanalysis may not be required. In other
cases, engineering judgment is used to
determine that new analyses would be
performed to determine the effect the
new crud conditions have on the final
calculated results. If unanticipated or
unanalyzed levels of crud are
discovered, then the licensee must
determine if correct consideration of
crud levels would result in a reportable
condition as provided in the relevant
reporting paragraphs. Should this
proposed rule be adopted in final form,
the NRC believes this regulatory
approach to address crud and oxide
accumulation during plant operation
would satisfactorily address the issues
raised by the petitioner’s first request.
The formation of cladding crud and
oxide layers is an expected condition at
nuclear power plants. Although the
thickness of these layers is usually
limited, the amount of accumulated
crud and oxidation varies from plant to
plant and from one fuel cycle to
another. Intended or inadvertent
changes to plant operational practices
may result in unanticipated levels of
crud deposition. The NRC agrees with
the petitioner (the petitioner’s second
request) that crud and/or oxide layers
may directly increase the stored energy
in reactor fuel by increasing the thermal
resistance of cladding-to-coolant heat
transfer, and may also indirectly
increase the stored energy through an
increase in the fuel rod internal
pressure. As such, to ensure that
licensee ECCS models properly account
for the thermal effects of crud and/or
oxide layers that have accumulated
during operations at power, the
proposed rule would add a requirement
to evaluate the thermal effects of crud
and oxide layers that may have
accumulated on the fuel cladding
during plant operation. If the NRC
adopts the proposed rule in final form,
then the second request of PRM–50–84
would be resolved.
The petitioner’s third request is for
the NRC to establish a maximum
allowable percentage of hydrogen
content in fuel rod cladding. The
purpose of this request is to prevent
embrittlement of fuel cladding during a
LOCA. Although the NRC has decided
not to propose the specific rule language
recommended by the petitioner, the
proposed new zirconium-specific
requirements, if adopted in final form,
would address the petitioner’s third
request by considering cladding
hydrogen content in the development of
analytical limits on integral time at
temperature.
The NRC believes that this proposed
rule addresses each of the three issues
raised in PRM–50–84. If the NRC adopts
the proposed rule in final form, PRM–
50–84 would be granted in part and
resolved.
http://www.inel.gov/relap5/rius/yellowstone/leyse.pdf
Unmet Challenges for SCDAP/RELAP5-3D
Analysis of Severe Accidents
for Light Water Nuclear Reactors
with Heavily Fouled Cores
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