[Federal Register Volume 63, Number 214 (Thursday, November 5, 1998)]
[Notices]
[Pages 59811-59813]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-29644]


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NUCLEAR REGULATORY COMMISSION

[Docket No. 50-302]


Florida Power Corporation et al. (Crystal River Unit 3); 
Exemption

I

    The Florida Power Corporation et al. (FPC or the licensee) is the 
holder of Facility Operating License No. DPR-72, which authorizes the 
operation of Crystal River Unit 3. The license states that the licensee 
is subject to all rules, regulations, and orders of the Nuclear 
Regulatory Commission (NRC or the Commission) now or hereafter in 
effect.
    The facility consists of a pressurized-water reactor at the 
licensee's site located in Citrus County, Florida.

II

    The Code of Federal Regulations at 10 CFR Part 50, Appendix K, 
Section I.D.1, ``Single Failure Criterion,'' requires that accident 
evaluations use the combination of emergency core cooling system (ECCS) 
subsystems assumed to be operative ``after the most damaging single-
failure of ECCS equipment has taken place.'' The proposed action would 
exempt the licensee from the single-failure requirement for very-low-
probability scenarios under certain circumstances. The exemption is 
limited to the systems required for preventing boron precipitation 
during the long-term cooling phase of a loss-of-coolant accident 
(LOCA). 10 CFR 50.46(b)(5) requires that the ECCS be capable of 
providing long-term core cooling. Post-accident boron precipitation is 
a potential, but unlikely, challenge to maintaining long-term core 
cooling.
    By letter dated October 31, 1997, as supplemented by letters dated 
December 13, 1997, February 27, 1998, and April 24, 1998, FPC requested 
an amendment to its operating license for Crystal River Unit 3. The FPC 
amendment request addressed prevention of boron precipitation following 
a LOCA that involved the following:
    (1) Reactor vessel vent valves (RVVVs) that are effective when 
needed for all LOCA conditions except for (a) some LOCAs between the 
reactor coolant pumps and the reactor vessel (RV) at an elevation below 
the cold-leg mid-pipe at the junction with the RV and (b) decay heat 
generation rate comparable to approximately a month following extended 
operation at full power for some LOCAs.
    (2) If the RVVVs are not effective, then, according to the 
licensee's

[[Page 59812]]

calculations, Motor Control Center (MCC) 3AB is needed to provide power 
to open valves within 8 hours for the worst-case LOCA to (a) initiate 
water injection via auxiliary pressurizer spray (APS) or (b) initiate 
the dump-to-sump (DTS) method of moving water from a hot leg to the 
reactor building sump.
    Should MCC 3AB fail before the APS or DTS initiates, both of these 
systems will fail to initiate in these licensing scenarios. In a June 
4, 1998, submittal, FPC requested an exemption from the single-failure 
requirement with respect to this failure. FPC justified its request by 
stating that the proposed exemption meets the underlying purpose of the 
rule in that there are conservatisms in the calculations that cause 
underprediction of available repair time, so that, using realistic 
assumptions, sufficient time would be available to perform repairs to 
restore MCC 3AB if needed. As a result, the licensee stated that there 
was reasonable assurance of the availability of an active boron 
precipitation method (APS or DTS) if one were needed. FPC states that 
timely recognition of boron precipitation is assured by compliance with 
plant procedures and further states that prompt operator actions will 
be taken to restore an active method in the event of MCC 3AB failure.
    One element of the licensee's justification was to credit flow 
through the hot-leg nozzle gaps. According to FPC's calculations, APS 
is not fully effective until 21 hours after LOCA initiation, but it may 
be needed within 8 hours if a single failure other than the failure of 
MCC 3AB makes DTS unavailable. FPC addressed this problem by crediting 
flow through hot-leg nozzle gaps to provide a boron dilution means for 
the first 21 hours. However, the NRC does not accept credit for hot-leg 
nozzle gap flow because FPC has not established that the nozzle gaps 
will remain functional after a LOCA. Therefore, during this time 
period, a failure to meet the Appendix K Item I.D.1 single-failure 
criterion remains. However, the NRC has determined that the licensee 
has given adequate justification in its submittal to extend the 
exemption to this scenario.

III

    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 (1) when 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. Special circumstances are 
present whenever, according to 10 CFR 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. . . .''
    The underlying purpose of the single-failure criterion requirement 
is to assure long-term cooling performance of the ECCS in the event of 
the most damaging single-failure of ECCS equipment. As a licensing 
review tool, the single-failure criterion helps assure reliable systems 
as an element of defense in depth. As a design and analysis tool, it 
promotes reliability through enforced redundancy. Since only those 
systems or components that are judged to have a credible chance of 
failure are assumed to fail, the criterion is applied to such responses 
as valve movement on demand, emergency diesel generator start, short 
circuit in an electrical bus, and fluid leakage caused by gross failure 
of a pump or valve seal during long-term cooling. Reactor vessels or 
certain types of structural elements within systems, when combined with 
other unlikely events, are not assumed to fail because the 
probabilities of the resulting scenarios have been deemed sufficiently 
small that they need not be considered. Certain passive failures 24 
hours or more after initiation of a LOCA, such as pipe breaks, are not 
addressed as single failures because the compounded probabilities were 
judged sufficiently small that they could be discounted without 
affecting overall systems reliability.
    The single-failure criterion was developed without the benefit of 
numerical failure assessments. Regulatory requirements and guidance 
consequently were based upon categories of equipment and examples that 
must be covered or that are exempt, and do not allow a probabilistic 
consideration during routine implementation. Hence, a single failure, 
whether or not there is a substantial impact upon overall system 
reliability, would not meet the regulatory requirements. A non-
beneficial result is inconsistent with the objective of the single-
failure criterion, which was not intended to force changes if 
essentially no benefit would accrue. This is the case with the 
potential MCC 3AB failure.
    FPC estimated that the combined probability of the LOCA of concern 
and failure of MCC 3AB is 10-10/reactor-year. (The 
probability of the LOCA of concern is 10-7/reactor-year and 
the failure probability of MCC 3AB given the LOCA of concern is 
10-3/reactor-year.) If MCC 3AB were to fail, FPC would 
initiate its Emergency Plan Implementing Procedure to re-power MCC 3AB 
from an alternate electric power source. FPC stated that sufficient 
time will be available and that radiological conditions should permit 
such activities.
    In addition, there are other conservatisms in the licensee's 
analyses. These include:
     Presence of buffer compounds may increase solubility limit 
margins. FPC concluded that solutes in the sump water will increase 
boron solubility, but did not credit the effect in its calculations. 
This is a conservatism when considering MCC 3AB repair and APS 
unavailability time.
     Decay heat was calculated using Appendix K methods. FPC's 
calculations, in accordance with its licensing basis, use a decay heat 
generation rate that is roughly 25 percent too high. A realistic decay 
heat would increase the time available before boron precipitation 
became a concern. This is a significant conservatism when considering 
MCC 3AB repair and APS unavailability time.
     Boron solubility. FPC used a boron solubility decreased by 
4 weight percent from the published values, consistent with previously 
accepted evaluation models. This is a conservatism when considering MCC 
3AB repair and APS unavailability time.
     Boron precipitation. The approved evaluation models are 
based upon preventing precipitation. Should precipitation occur, 
significant boron would have to precipitate to prevent core cooling. 
This unquantified conservatism is significant when considering MCC 3AB 
repair and APS unavailability time.
    Despite the licensee's determination that there is no safety-
significant vulnerability associated with the two particular instances 
of failing to meet the single-failure criterion, FPC has developed and 
implemented procedures to address the conditions should they occur. It 
has shown that there is essentially no benefit to be achieved by 
investing in additional equipment to eliminate the single-failure 
aspects since the combined probability of the LOCA of concern with the 
failure is very low. With regard to the availability of APS during the 
first 21 hours following a LOCA should DTS be unavailable, realistic 
calculations without the conservative assumptions discussed above 
predict that APS would be available.
    These calculations, along with the low estimate of core damage 
probability resulting from this scenario, result in a

[[Page 59813]]

conclusion that essentially no benefit would be achieved by requiring 
modifications to meet the single-failure criteria for the specific 
scenario during this time period.

IV

    For these foregoing reasons, the NRC staff has concluded that it is 
not necessary to meet the single-failure requirement of Appendix K, 
Section I.D.1, with respect to (1) failure of Motor Control Center 3AB 
and the resulting inability to initiate an active means of controlling 
core boron concentration and (2) the active methods not meeting the 
single-failure criterion for the period when approved licensing methods 
predict that APS is not effective following certain LOCAs to adequately 
ensure that boron precipitation does not interfere with long-term 
cooling. The NRC staff has determined that there are special 
circumstances present, as specified in 10 CFR 50.12.(a)(2)(ii), in that 
application of 10 CFR Part 50, Appendix K, Section I.D.1, is not 
necessary in order to achieve the underlying purpose of this 
regulation, which is to provide adequate assurance that boron 
precipitation will not interfere with the capability of the ECCS to 
provide long-term core cooling.
    Accordingly, the Commission has determined that, pursuant to 10 CFR 
50.12(a), this exemption is authorized by law, will not endanger life 
or property or the common defense and security, and is otherwise in the 
public interest. Therefore, the Commission hereby grants the following 
exemption:

    The Florida Power Corporation, et al., is exempt from the 
single-failure criterion requirement of 10 CFR Part 50, Appendix K, 
Section I.D.1, with respect to (1) failure of Motor Control Center 
3AB and the resulting inability to initiate an active means of 
controlling core boron concentration and (2) failure of the active 
means to meet the single-failure criterion for the period when 
approved licensing methods predict that APS is not effective 
following reactor coolant pump discharge breaks provided that: 
procedural guidance shall be maintained that describes the actions 
necessary to restore an active method of boron precipitation 
mitigation in the event of a failure of Motor Control Center 3AB.

    Pursuant to 10 CFR 51.32, the Commission has determined that the 
granting of this exemption will have no significant impact on the 
quality of the human environment (63 FR 54162).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 29th day of October, 1998.

    For the Nuclear Regulatory Commission.

Frank J. Miraglia,
Acting Director, Office of Nuclear Reactor Regulation.

[FR Doc. 98-29644 Filed 11-4-98; 8:45 am]
BILLING CODE 7590-01-P