[Federal Register Volume 69, Number 24 (Thursday, February 5, 2004)]
[Notices]
[Pages 5591-5594]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-2486]
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NUCLEAR REGULATORY COMMISSION
[Docket Nos. 50-275 and 50-323]
Pacific Gas and Electric Company, Diablo Canyon Power Plant, Unit
Nos. 1 and 2; Exemption
1.0 Background
The Pacific Gas and Electric Company (the licensee) is the holder
of Facility Operating License Nos. DPR-80 and DPR-82, which authorize
operation of the Diablo Canyon Power Plant (facility or DCPP), 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.
The facility consists of two pressurized water reactors located in
San Luis Obispo County, California.
2.0 Request/Action
Title 10 of the Code of Federal Regulations (10 CFR), part 50, Sec.
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 DCPP Technical Specifications (TS) 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. 10 CFR 50.68(b)(4) 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 submitted a license application to construct and
operate an Independent Spent Fuel Storage Installation (ISFSI) at DCPP.
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
[[Page 5592]]
nuclear fuel at DCPP 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:
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 TSs require 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 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 DCPP 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 DCPP. The staff reviewed the information
contained in Chapter 6 as well as information provided by the licensee
in its exemption request to determine if Criterion 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. 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 Diablo Canyon 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
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). Proposed TS
3.2.1, ``Dissolved Boron Concentration,'' requires 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 Diablo Canyon
ISFSI TSs, the staff finds that the licensee has satisfied Criterion 2.
Third, the staff reviewed the DCPP Final Safety Analysis Report
(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 DCPP 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 non-fuel 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.
Section 2.0, ``Approved Contents,'' of the proposed Diablo Canyon ISFSI
TS limits the cask contents to spent nuclear fuel, fuel debris, and
non-fuel hardware.
[[Page 5593]]
The Diablo Canyon ISFSI FSAR Tables 10.2-1 through 10.2-4 provide
limitations on the materials that can be stored in the various MPC
designs intended to be used at the Diablo Canyon ISFSI. The staff
determined that the loading limitations described in Tables 10.2-1
through 10.2-4 will ensure that non-fuel hardware loaded in the MPCs
will not result in a reactivity increase. Based on its review of the
loading restrictions for non-fuel 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.
At the staff's request, the licensee provided additional
information describing the boron dilution analysis it performed. First,
the licensee performed a criticality analysis to determine the DCPP
critical boron concentration, 1720 ppm, during MPC loading, unloading,
and handling operations. Therefore, the DCPP SPF boron concentration
would have to decrease from the ISFSI TS limit of 2600 ppm to the
critical boron concentration 1720 ppm before SPF criticality is
possible. This analysis assumed that a fully loaded MPC-32 canister
containing fresh fuel of the maximum permissible enrichment is
uniformly diluted to the critical boron concentration. The licensee
based the remainder of its boron dilution analysis and its preventive
and mitigative actions on preventing the MPC from reaching this
concentration.
The licensee referenced a detailed analysis of the boron dilution
event previously performed for DCPP and submitted to the NRC. In this
analysis, the licensee determined all of the potential dilution
pathways for adding makeup water to the DCPP SFP. The pathway with the
maximum flowrate is from the demineralized water system to the SFP via
valve 803, which can provide a maximum flowrate of 494 gallons per
minute (gpm). Based on this maximum flowrate, the licensee calculated a
time line for the boron dilution event, and determined that, starting
from the SFP low level alarm setpoint, it would take 39 minutes to
reach the SFP high level alarm. It would take an additional 10 minutes
before the SFP began to overflow. Finally, approximately five hours
after the SFP high level alarm setpoint was reached, the critical boron
concentration would be achieved.
To demonstrate that it has ample time and opportunity to identify
and terminate a boron dilution event, the licensee described the
alarms, procedures, and administrative controls it has in place. The
licensee described the alarms available to operators to identify a
boron dilution event. The SFP high level and low level alarms are
annunciated in the control room and the operator response is described
in a response procedure. Additionally, operators are trained to
terminate any boron dilution source within one-half hour of receiving
the high level alarm. In addition to the high level alarm, the
operators would receive indication of a boron dilution event from the
liquid waste systems alarms caused by the overflowing pool water ending
up in the fuel handling building floor drains. As part of its pool
monitoring program, operations personnel perform rounds in the SFP area
once every shift where they check the level of the pool and the
conditions around the pool. Also, while cask loading operations are in
progress, numerous plant personnel would be working next to the SFP
where they could easily identify any level changes. The licensee stated
that during any delays where the SFP is not continuously monitored,
exceeding those for normal shift changes and breaks, either trained
personnel will be assigned to monitor the SFP or the frequency of
operator rounds will be increased.
The licensee stated that it will implement additional temporary
administrative controls while the MPC is in the SFP to minimize the
possibility of a boron dilution event. The licensee stated that except
for the primary water station near the SFP, which is used for the
decontamination process and rinsing dry cask storage equipment as it is
removed from the SFP, at least one valve in each potential flow path of
unborated water to the SFP will be closed and tagged out. As an
additional precaution, the licensee will double isolate the flow path
with the highest potential flowrate of 494 gpm. The licensee will close
and tag out two valves in this flow path to minimize the potential that
it can cause a boron dilution event.
Finally, to ensure that operators are capable of identifying and
terminating a boron dilution event during MPC loading, unloading, and
handling operations, the licensee will incorporate the changes made to
the operating procedures relating to the SFP boron dilution flow paths
into the DCPP operator training program. The licensee stated that the
training will emphasize the importance of avoiding any inadvertent
additions of unborated water to the SFP, responses to be taken to
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.
Based on the staff's review of the licensee's exemption request,
the additional information it provided, and its boron dilution
analysis, the staff finds the licensee has provided sufficient
information to demonstrate that it satisfies Criterion 5.
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 DCPP
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 DCPP.
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 Pacific Gas and Electric
Company an exemption
[[Page 5594]]
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 DCPP. 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 2012).
This exemption is effective upon issuance.
Dated at Rockville, Maryland, this 30th day of January 2004.
For the Nuclear Regulatory Commission.
Ledyard B. Marsh,
Director, Division of Licensing Project Management, Office of Nuclear
Reactor Regulation.
[FR Doc. 04-2486 Filed 2-4-04; 8:45 am]
BILLING CODE 7590-01-P