[Federal Register Volume 69, Number 113 (Monday, June 14, 2004)]
[Notices]
[Pages 33075-33079]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-13253]
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NUCLEAR REGULATORY COMMISSION
[Docket Nos. 50-327 and 50-328]
Tennessee Valley Authority, Sequoyah Nuclear Plant, Unit Nos. 1
and 2; Exemption
1.0 Background
The Tennessee Valley Authority (the licensee) is the holder of
Facility Operating License Nos. DPR-77 and DPR-79, which authorize
operation of the Sequoyah Nuclear Plant (facility or SQN), Unit Nos. 1
and 2, respectively. The licenses provide, among other things, that the
facility is subject to all rules, regulations, and orders of the
Nuclear Regulatory Commission (NRC, the Commission) now or hereafter in
effect.
[[Page 33076]]
The facility consists of two pressurized water reactors located in
Hamilton County, Tennessee.
2.0 Request/Action
Title 10 of the Code of Federal Regulations (10 CFR), part 50,
section 50.68(b)(1) sets forth the following requirement that must be
met, in lieu of a monitoring system capable of detecting criticality
events.
Plant procedures shall prohibit the handling and storage at any
one time of more fuel assemblies than have been determined to be
safely subcritical under the most adverse moderation conditions
feasible by unborated water.
The licensee is unable to satisfy the above requirement for
handling of the 10 CFR part 72 licensed contents of the Holtec HI-STORM
100 Cask System. Section 50.12(a) allows licensees to apply for an
exemption from the requirements of 10 CFR part 50 if the regulation is
not necessary to achieve the underlying purpose of the rule and other
conditions are met. The licensee stated in the application that
compliance with 10 CFR 50.68(b)(1) is not necessary for handling the 10
CFR part 72 licensed contents of the cask system to achieve the
underlying purpose of the rule.
3.0 Discussion
Pursuant to 10 CFR 50.12, the Commission may, upon application by
any interested person or upon its own initiative, grant exemptions from
the requirements of 10 CFR part 50 when (1) the exemptions are
authorized by law, will not present an undue risk to public health or
safety, and are consistent with the common defense and security, and
(2) when special circumstances are present. Therefore, in determining
the acceptability of the licensee's exemption request, the staff has
performed the following regulatory, technical, and legal evaluations to
satisfy the requirements of 10 CFR 50.12 for granting the exemption.
3.1 Regulatory Evaluation
The SQN Technical Specifications (TSs) currently permit the
licensee to store spent fuel assemblies in high-density storage racks
in each spent fuel pool (SFP). In accordance with the provisions of 10
CFR 50.68(b)(4), the licensee takes credit for soluble boron for
criticality control and ensures that the effective multiplication
factor (keff) of the SFP does not exceed 0.95, if flooded
with borated water. As stated in 10 CFR 50.68(b)(4), it also requires
that, if credit is taken for soluble boron, the keff must
remain below 1.0 (subcritical), if flooded with unborated water.
However, the licensee is unable to satisfy the requirement to maintain
the keff below 1.0 (subcritical) with unborated water, which
is also the requirement of 10 CFR 50.68(b)(1). Therefore, the
licensee's request for exemption from 10 CFR 50.68(b)(1) proposes to
permit the licensee to perform spent fuel loading, unloading, and
handling operations related to dry cask storage, without being
subcritical under the most adverse moderation conditions feasible by
unborated water.
Title 10 of the Code of Federal Regulations, part 50, Appendix A,
``General Design Criteria (GDC) for Nuclear Power Plants,'' provides a
list of the minimum design requirements for nuclear power plants.
According to GDC 62, ``Prevention of criticality in fuel storage and
handling,'' the licensee must limit the potential for criticality in
the fuel handling and storage system by physical systems or processes.
Section 50.68 of 10 CFR part 50, ``Criticality accident
requirements,'' provides the NRC requirements for maintaining
subcritical conditions in SFPs. Section 50.68 provides criticality
control requirements which, if satisfied, ensure that an inadvertent
criticality in the SFP is an extremely unlikely event. These
requirements ensure that the licensee has appropriately conservative
criticality margins during handling and storage of spent fuel. Section
50.68(b)(1) states, ``Plant procedures shall prohibit the handling and
storage at any one time of more fuel assemblies than have been
determined to be safely subcritical under the most adverse moderation
conditions feasible by unborated water.'' Specifically, 10 CFR
50.68(b)(1) ensures that the licensee will maintain the pool in a
subcritical condition during handling and storage operations without
crediting the soluble boron in the SFP water.
The licensee has received a license to construct and operate an
Independent Spent Fuel Storage Installation (ISFSI) at SQN. The ISFSI
would permit the licensee to store spent fuel assemblies in large
concrete dry storage casks. In order to transfer the spent fuel
assemblies from the SFP to the dry storage casks, the licensee must
first transfer the assemblies to a Multi-Purpose Canister (MPC) in the
cask pit area of the SFP. The licensee performed criticality analyses
of the MPC fully loaded with fuel having the highest permissible
reactivity, and determined that a soluble boron credit was necessary to
ensure that the MPC would remain subcritical in the SFP. Since the
licensee is unable to satisfy the requirement of 10 CFR 50.68(b)(1) to
ensure subcritical conditions during handling and storage of spent fuel
assemblies in the pool with unborated water, the licensee identified
the need for an exemption from the 10 CFR 50.68(b)(1) requirement to
support MPC loading, unloading, and handling operations, without being
subcritical under the most adverse moderation conditions feasible by
unborated water.
The staff evaluated the possibility of an inadvertent criticality
of the spent nuclear fuel at SQN during MPC loading, unloading, and
handling. The staff has established a set of acceptance criteria that,
if met, satisfy the underlying intent of 10 CFR 50.68(b)(1). In lieu of
complying with 10 CFR 50.68(b)(1), the staff determined that an
inadvertent criticality accident is unlikely to occur if the licensee
meets the following five criteria:
1. The cask criticality analyses are based on the following
conservative assumptions:
a. All fuel assemblies in the cask are unirradiated and at the
highest permissible enrichment,
b. Only 75 percent of the Boron-10 in the Boral panel inserts is
credited,
c. No credit is taken for fuel-related burnable absorbers, and
d. The cask is assumed to be flooded with moderator at the
temperature and density corresponding to optimum moderation.
2. The licensee's ISFSI TS requires the soluble boron concentration
to be equal to or greater than the level assumed in the criticality
analysis and surveillance requirements necessitate the periodic
verification of the concentration both prior to and during loading and
unloading operations.
3. Radiation monitors, as required by GDC 63, ``Monitoring Fuel and
Waste Storage,'' are provided in fuel storage and handling areas to
detect excessive radiation levels and to initiate appropriate safety
actions.
4. The quantity of other forms of special nuclear material, such as
sources, detectors, etc., to be stored in the cask will not increase
the effective multiplication factor above the limit calculated in the
criticality analysis.
5. Sufficient time exists for plant personnel to identify and
terminate a boron dilution event prior to achieving a critical boron
concentration in the MPC. To demonstrate that it can safely identify
and terminate a boron dilution event, the licensee must provide the
following:
a. A plant-specific criticality analysis to identify the critical
boron concentration in the cask based on the highest reactivity loading
pattern.
b. A plant-specific boron dilution analysis to identify all
potential dilution pathways, their flowrates, and the time
[[Page 33077]]
necessary to reach a critical boron concentration.
c. A description of all alarms and indications available to
promptly alert operators of a boron dilution event.
d. A description of plant controls that will be implemented to
minimize the potential for a boron dilution event.
e. A summary of operator training and procedures that will be used
to ensure that operators can quickly identify and terminate a boron
dilution event.
3.2 Technical Evaluation
In determining the acceptability of the licensee's exemption
request, the staff reviewed three aspects of the licensee's analyses:
(1) Criticality analyses submitted to support the ISFSI license
application, (2) boron dilution analysis, and (3) legal basis for
approving the exemption. For each of the aspects, the staff evaluated
whether the licensee's analyses and methodologies provide reasonable
assurance that adequate safety margins are developed and can be
maintained in the SQN SFP during loading of spent fuel into canisters
for dry cask storage.
3.2.1 Criticality Analyses
For evaluation of the acceptability of the licensee's exemption
request, the staff reviewed the criticality analyses provided by the
licensee in support of its ISFSI license application. Chapter 6,
``Criticality Evaluation,'' of the HI-STORM Final Safety Analysis
Report (HI-STORM FSAR) contains detailed information regarding the
methodology, assumptions, and controls used in the criticality analysis
for the MPCs to be used at SQN. The staff reviewed the information
contained in Chapter 6 as well as information provided by the licensee
in its exemption request to determine if Criteria 1 through 4 of
Section 3.1 were satisfied.
First, the staff reviewed the methodology and assumptions used by
the licensee in its criticality analysis to determine if Criterion 1
was satisfied. The licensee provided a detailed list of the assumptions
used in the criticality analysis in Chapter 6 of the HI-STORM FSAR as
well as in its exemption request. The licensee stated that it took no
credit in the criticality analyses for burnup or fuel-related burnable
absorbers. The licensee also stated that all assemblies were analyzed
at the highest permissible enrichment. Additionally, the licensee
stated that all criticality analyses for a flooded MPC were performed
at temperatures and densities of water corresponding to optimum
moderation conditions. Finally, the licensee stated that it only
credited 75 percent of the Boron-10 content for the fixed neutron
absorber, Boral, in the MPC. Based on its review of the criticality
analyses contained in Chapter 6 of the HI-STORM FSAR, the staff finds
that the licensee has satisfied Criterion 1.
Second, the staff reviewed the proposed SQN ISFSI TS. The
licensee's criticality analyses credit soluble boron for reactivity
control during MPC loading, unloading, and handling operations. Since
the boron concentration is a key safety component necessary for
ensuring subcritical conditions in the pool, the licensee must have a
conservative TS capable of ensuring that sufficient soluble boron is
present to perform its safety function. The most limiting loading
configuration of an MPC requires 2600 parts-per-million (ppm) of
soluble boron to ensure the keff is maintained below 0.95,
the regulatory limit relied upon by the staff for demonstrating
compliance with the requirements of 10 CFR 72.124(a). SQN's ISFSI TSs
require the soluble boron concentration in the MPC cavity be greater
than or equal to the concentrations assumed in the criticality analyses
under a variety of MPC loading configurations. In all cases, the boron
concentration required by the proposed ISFSI TS ensures that the
keff will be below 0.95 for the analyzed loading
configuration. Additionally, the licensee's proposed ISFSI TS contains
surveillance requirements which ensure it will verify that the boron
concentration is above the required level both prior to and during MPC
loading, unloading, and handling operations. Based on its review of the
proposed SQN ISFSI TS, the staff finds that the licensee has satisfied
Criterion 2.
Third, the staff reviewed the SQN FSAR Update and the information
provided by the licensee in its exemption request to ensure that it
complies with GDC 63. GDC 63 requires that licensees have radiation
monitors in fuel storage and associated handling areas to detect
conditions that may result in a loss of residual heat removal
capability and excessive radiation levels and initiate appropriate
safety actions. As a condition of receiving and maintaining an
operating license, the licensee must comply with GDC 63. The staff
reviewed the SQN FSAR Update and exemption request to determine whether
it had provided sufficient information to demonstrate continued
compliance with GDC 63. Based on its review of both documents, the
staff finds that the licensee complies with GDC 63 and has satisfied
Criterion 3.
Finally, as part of the criticality analysis review, the staff
evaluated the storage of nonfuel related material in an MPC. The staff
evaluated the potential to increase the reactivity of an MPC by loading
it with materials other than spent nuclear fuel and fuel debris. SQN's
spent fuel and nonfuel hardware are bounded by the spent fuel and non-
fuel hardware analyzed and represented in Holtec Hi-Storm 100
Certificate of Compliance (COC) No. 1014, Appendix B, ``Approved
Content and Design Features.'' The COC provides limitations on the
materials that can be stored in the MPC design intended to be used at
the SQN ISFSI. The staff determined that the loading limitations
described in the COC will ensure that nonfuel hardware loaded in the
MPCs will not result in a reactivity increase. Based on its review of
the loading restrictions for nonfuel hardware, the staff finds that the
licensee has satisfied Criterion 4.
3.2.2 Boron Dilution Analysis
Since the licensee's ISFSI application relies on soluble boron to
maintain subcritical conditions within the MPCs during loading,
unloading and handling operations, the staff reviewed the licensee's
boron dilution analysis to determine whether appropriate controls,
alarms, and procedures were available to identify and terminate a boron
dilution accident prior to reaching a critical boron concentration.
By letter dated October 25, 1996, the staff issued a safety
evaluation of licensing topical report WCAP-14416, ``Westinghouse Spent
Fuel Rack Criticality Analysis Methodology.'' This safety evaluation
specified that the following issues be evaluated for applications
involving soluble boron credit: The events that could cause boron
dilution, the time available to detect and mitigate each dilution
event, the potential for incomplete boron mixing, and the adequacy of
the boron concentration surveillance interval.
The TS requirements for the HI-STORM 100 Cask System include a
minimum boron concentration of 1900 ppm boron when spent fuel
assemblies with enrichments less than or equal to 4.1 weight-percent
(wt-percent) U-235 are loaded into an MPC-32 canister. When fuel
assemblies are enriched to greater than 4.1 wt-percent U-235 and less
than or equal to 5.0 wt-percent U-235 and loaded into an MPC-32, the
minimum boron concentration is 2600 ppm. These TS requirements ensure
that keff is maintained less than 0.95. TS surveillance
requirements require the boron concentration in the MPC water to be
verified by two independent measurements within 4 hours prior to
commencing any loading or unloading
[[Page 33078]]
of fuel; verified when one or more fuel assemblies are installed if
water is to be added or recirculated through the MPC; and verified
every 48 hours thereafter while the MPC is in the SFP when one or more
fuel assemblies are installed.
The licensee contracted with Holtec International to perform a
criticality analysis to determine the soluble boron concentration that
results in a keff equal to 1.0 for both 4.1 wt-percent and
5.0 wt-percent U-235 fuel enrichments using the same methodology as
approved in the HI-STORM 100 Cask System Final Safety Analysis. The
analysis determined the critical boron concentration level for 4.1 wt-
percent U-235 enriched fuel was 1180 ppm and for 5.0 wt-percent U-235
enrichment was 1780 ppm. Therefore, the boron concentration within the
canister would have to decrease from the TS limit to the respective
critical boron concentration before criticality is possible. The
licensee based its boron dilution analyses and its preventive and
mitigative actions on dilution sources with the potential to reduce the
boron concentration from the TS minimum values for the two fuel
enrichment bands to the respective concentration for criticality.
The licensee reviewed plant drawings to identify potential dilution
sources and performed a plant walk-down to verify the drawing review.
This review identified that, with the exception of the raw cooling
water (RCW) system piping, large diameter piping with the potential to
dilute the spent fuel pool boron concentration was seismically
qualified to assure the piping would adequately maintain its position
and pressure boundary integrity during the design basis safe-shutdown
earthquake. Subsequently, the licensee evaluated the RCW piping and
components on the refueling floor and concluded the RCW system would
also adequately maintain its position and pressure boundary integrity
during the design basis safe-shutdown earthquake. Therefore, an
instantaneous complete severance of these piping systems is not
credible. However, the licensee reviewed its calculation for moderate
energy line breaks and performed calculations for these piping systems
in the refueling pool area to determine dilution potentials from
postulated critical cracks in the piping. Numerous smaller piping
systems may experience critical cracks; however, the most limiting
critical crack flow rate is the calculated value of 314 gallons per
minute (gpm) for the RCW system.
The licensee identified the following additional credible bounding
dilution sources and their flow rates: 250 gpm from the demineralized
water system through an open isolation valve to the SFP cooling system;
5 gpm from the demineralized water system to make up for undetected,
small leaks from the SFP or its cooling system; and 150 gpm from the
fire protection system through a fire hose station to the spent fuel
pool. The staff found the scope and results of the dilution source
evaluation acceptable.
To demonstrate that it has ample time and opportunity to identify
and terminate a boron dilution event, the licensee calculated the time
necessary for dilution from the TS boron concentration to the critical
boron concentration for each fuel enrichment range and described the
alarms, procedures, and administrative controls it has in place. The
RCW critical crack flow rate of 314 gpm, which is the limiting high
flow-rate dilution event, would require more than 8 hours to dilute the
SFP to the critical boron concentration. The licensee modified the SFP
high level setpoint and procedural limits for initial SFP water level
prior to cask loading operations to assure the SFP high level alarm
would be effective in detecting dilution during cask loading
operations. The RCW critical crack would cause the SFP water level to
reach the high level alarm setpoint within several minutes of water
beginning to spill into the pool, allowing operators ample time to stop
the dilution after the alarm. The indications and response to a high-
rate dilution event from the demineralized water system through the
spent fuel cooling system would be similar, but the licensee committed
to the additional action of tagging closed the demineralized and
primary water supplies to the spent fuel cooling system during cask
loading and unloading operations.
Dilution to the critical boron concentration resulting from
addition of water to compensate for an undetected slow loss of SFP
coolant is also not credible. The licensee calculated that the dilution
from the TS required boron concentration would require hundreds of
hours at leakage rates that could credibly go unnoticed. The 48-hour TS
surveillance interval for boron concentration measurement provides
strong assurance that such a dilution would be detected and corrected
well before the critical boron concentration could be reached.
The configuration of the cask pit could allow localized boron
dilution and stratification because the pit is open to the SFP only
through a narrow transfer path above the level of stored fuel. Addition
of cold water directly to the cask pit (e.g., through a fire hose) that
is denser than the warm, borated pool water could fill the bottom of
the cask pit with water having a low boron concentration. However, the
licensee stated that the spent fuel cooling system with a normal flow
rate of 2300 gpm discharges flow through one 4-inch line into the cask
pit and one 10-inch line into the SFP. The cooled return flow to the
cask pit provides assurance that localized boron dilution and
stratification would not occur within the cask pit during canister
loading operations.
In addition to the conservative criticality and boron dilution
analyses it performed, the licensee will enhance its procedures and
operator training to ensure that the casks can be safely loaded,
unloaded, and handled in the SQN spent fuel pool. The licensee
committed to enhance its operation procedures to explicitly describe
reaction to alarms and indications which are indicative of a boron
dilution event prior to initial dry cask loading operations.
Additionally, SQN committed to provide training on the new procedures
to ensure that operators can effectively identify and terminate boron
dilution sources in a minimum amount of time prior to reaching a
critical boron limit. The licensee stated in its supplement that the
training will emphasize the importance of avoiding any inadvertent
additions of unborated water to the SFP, responses to be taken for
notification or alarms that may be indicative of a potential boron
dilution event during cask loading and fuel movement in the SFP, and
identification of the potential for a boron dilution event during
decontamination rinsing activities and abnormal SFP make-up with the
fire protection system. Finally, in order to ensure rapid
identification of an ongoing boron dilution event, the licensee
committed either to increase the frequency of its normal rounds or
station a trained monitor who is assigned to watch for a dilution event
in SFP area.
Based on the staff's review of the licensee's exemption request
dated February 20, 2004, the supplemental information provided by
letter dated April 27, 2004, and its boron dilution analysis, the staff
finds the licensee has provided sufficient information to demonstrate
that an undetected and uncorrected dilution from the TS required boron
concentration to the calculated critical boron concentration is not
credible. Based on its review of the boron dilution analysis and
enhancements to the operating procedures and operator training program,
the staff finds that the licensee has satisfied Criterion 5.
[[Page 33079]]
Therefore, in conjunction with the conservative assumptions used to
establish the TS required boron concentration and critical boron
concentration, the boron dilution evaluation demonstrates that the
underlying intent of 10 CFR 50.68(b)(1) is satisfied.
3.3 Legal Basis for the Exemption
Pursuant to 10 CFR 50.12, ``Specific Exemption,'' the staff
reviewed the licensee's exemption request to determine if the legal
basis for granting an exemption had been satisfied, and concluded that
the licensee has satisfied the requirements of 10 CFR 50.12. With
regards to the six special circumstances listed in 10 CFR 50.12(a)(2),
the staff finds that the licensee's exemption request satisfies
50.12(a)(2)(ii), ``Application of the regulation in the particular
circumstances would not serve the underlying purpose of the rule or is
not necessary to achieve the underlying purpose of the rule.''
Specifically, the staff concludes that since the licensee has satisfied
the five criteria in Section 3.1 of this exemption, the application of
the rule is not necessary to achieve its underlying purpose in this
case.
3.4 Staff Conclusion
Based upon the review of the licensee's exemption request to credit
soluble boron during MPC loading, unloading, and handling in the SQN
SFP, the staff concludes that pursuant to 10 CFR 50.12(a)(2) the
licensee's exemption request is acceptable. However, the staff limits
its approval to the loading, unloading, and handling of the components
of the HI-STORM 100 dual-purpose dry cask storage system at SQN.
4.0 Conclusion
Accordingly, the Commission has determined that, pursuant to 10 CFR
50.12(a), the exemption is authorized by law, will not present an undue
risk to the public health and safety, and is consistent with the common
defense and security. Also, special circumstances are present.
Therefore, the Commission hereby grants Tennessee Valley Authority an
exemption from the requirements of 10 CFR 50.68(b)(1) for the loading,
unloading, and handling of the components of the HI-STORM 100 dual-
purpose dry cask storage system at SQN. Any changes to the cask system
design features affecting criticality or its supporting criticality
analyses will invalidate this exemption.
Pursuant to 10 CFR 51.32, the Commission has determined that the
granting of this exemption will not have a significant effect on the
quality of the human environment (69 FR 31849).
This exemption is effective upon issuance.
Dated in Rockville, Maryland, this 7th day of June, 2004.
For the Nuclear Regulatory Commission.
Ledyard B. Marsh,
Director, Division of Licensing Project Management, Office of Nuclear
Reactor Regulation.
[FR Doc. 04-13253 Filed 6-10-04; 8:45 am]
BILLING CODE 7590-01-P