[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