[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]


-----------------------------------------------------------------------

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