[Federal Register Volume 60, Number 164 (Thursday, August 24, 1995)]
[Notices]
[Pages 44089-44090]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-21032]
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NUCLEAR REGULATORY COMMISSION
[Docket No. 50-414]
Duke Power Company, et al. (Catawba Nuclear Station, Unit No. 2);
Exemption
I
The Duke Power Company, et al. (DPC or the licensee) is the holder
of Facility Operating License No. NPF-52, which authorizes operation of
the Catawba Nuclear Station, Unit No. 2 (the facility), at a steady-
state reactor power level not in excess of 3411 megawatts thermal. The
facility is a pressurized water reactor located at the licensee's site
in York County, South Carolina. The license provides, among other
things, that the Catawba Nuclear Station is subject to all rules,
regulations, and Orders of the U.S. Nuclear Regulatory Commission (the
Commission or NRC) now or hereafter in effect.
II
Section III.D.1.(a) of Appendix J to 10 CFR Part 50 requires the
performance of three Type A containment integrated leakage rate tests
(ILRTs) at approximately equal intervals during each 10-year service
period of the primary containment. The third test of each set shall be
conducted when the plant is shut down for the 10-year inservice
inspection of the primary containment.
III
By letters dated May 18, 1995, and May 31, 1995, the licensee
requested temporary relief from the requirement to perform a set of
three Type A tests at approximately equal intervals during each 10-year
service period of the primary containment. The requested exemption
would permit a one-time interval extension of the third Type A test by
approximately 30 months (from the 1995 refueling outage, which begins
in October 1995, to the end-of-cycle 8 (EOC-8) refueling outage,
currently scheduled for March 1997) and would permit the third Type A
test of the second 10-year inservice inspection period to not
correspond with the end of the current inservice inspection interval.
The licensee's request concluded that the proposed change, a one-
time extension of the interval between the second and third ILRTs at
Catawba Unit 2, is justified for the following reasons.
The previous testing history at Catawba Unit 2 provides substantial
justification for the proposed test interval extension. In each of the
two previous periodic ILRTs at Catawba Unit 2, the as-found leakage was
less than or equal to 48.7% of the allowable leakage, thereby
demonstrating that Catawba Unit 2 is a low-leakage containment. There
are no mechanisms which would adversely affect the structural integrity
of the containment, or that would be a factor in extending the test
interval by 30 months. However, as a preventative maintenance measure,
a containment civil inspection, currently required by Appendix J prior
to a Type A test, will be performed during EOC-7 in October 1995 to
verify that no structural degradation exists. Any additional risk
created by the longer interval between ILRTs is considered to be
negligible, primarily because Type B and C testing will continue
unchanged.
Additionally, the licensee stated that its exemption request meets
the requirements of 10 CFR 50.12, paragraphs (a)(1) and (a)(2)(ii), for
the following reasons:
In order to justify the granting of an exemption to the
requirements of 10 CFR Part 50, paragraph 50.12(a)(1) requires that
the licensee show that the proposed exemption will not pose an undue
risk to the public. That this proposed change will not pose an undue
risk is demonstrated by the analysis presented in draft NUREG-1493,
which concludes that an increase in the test interval to once every
20 years would ``lead to an imperceptible increase in risk.'' The
analyses in draft NUREG-1493 are considered to be specifically
applicable to Catawba because: (1) The requested exemption would
result in a one-time increase in the test interval to about 5 years,
not 20; (2) the population density around Catawba is less than that
used in the study (329 people per square mile, vs. 340 used in the
study); (3) no ILRT at Catawba has failed; 4) the core inventory
used in the study was represented by a 3412 Mwt PWR [pressurized
water reactor]. Catawba is a 3411 Mwt PWR. Other factors which lead
to the conclusion that the proposed change will not pose an undue
risk include the fact that local leak rate testing, which identifies
97% of leakage in excess of prescribed limits, will remain in place
at its current test frequency; the detailed, proceduralized
containment civil inspection which is normally performed in
conjunction with an ILRT will be performed in place of the scheduled
ILRT, to identify potential structural deteriorations; and the
historical leak-tightness of the containment structure, as evidenced
by two successive ILRTs in which the as-found leakage did not exceed
48.7% of the allowable leakage rate. A table which shows the leak
test history of Catawba Unit 2 follows this Attachment.
[[Page 44090]]
A comparison was made between the risk analysis presented in
draft NUREG-1493 and a probabilistic risk assessment performed for
Catawba Nuclear Station. While the quantitative results of the NUREG
are not directly applicable to plants not used in the study,
conclusions similar to those presented in the NUREG can be made
concerning Catawba. NUREG-1493 indicates that reactor accident risks
are dominated by accident sequences that result in failure or bypass
of the containment. This conclusion is also valid for Catawba.
Considering only the Catawba accident sequences that do not result
in containment failure, containment leakage contributes
approximately 0.08 to 0.09 percent to off-site risk (whole-body
person-rem, thyroid nodules, and latent fatalities). NUREG-1493
indicated that containment leakage contributed from 0.02 to 0.10
percent to latent cancer risk. The comparison between the analysis
of NUREG-1493 and the Catawba PRA concludes that increases in
containment leakage at Catawba are expected to produce increases in
accident risk similar to the results in NUREG-1493.
Special circumstances, as defined in 10 CFR 50.12(a)(2)(ii), are
considered to exist if ``application of the regulation * * * is not
necessary to achieve the underlying purpose of the rule.'' The
purposes of the rule, as stated in Section I of Appendix J, are to
ensure that: a) leakage through the primary reactor containment and
systems and components penetrating containment shall not exceed
allowable values, and b) periodic surveillance of reactor
containment penetrations and isolation valves is performed so that
proper maintenance and repairs are made. One of the significant
factors in assuring that the proposed exemption will not pose an
undue risk to the public, as noted above, is the local leak rate
testing (LLRT) which is performed. That the LLRT program at Catawba
provides an effective mechanism for maintaining containment
integrity is perhaps best demonstrated by the fact that the most
recent ILRT at Catawba Unit 2 was performed at the front end of the
refueling outage; before any repairs or adjustments were made to
valves or penetrations. Nevertheless, the as-found leakage did not
exceed 48.7% of the allowable leakage rate. The fact that no leakage
paths were identified by an ILRT, and that the ILRT met the
acceptance criteria with significant margin confirms the results of
the Type B and C testing.
The frequency and scope of the Type B and C LLRT program are not
being changed by this exemption request. The LLRT program will
continue to effectively detect containment leakage resulting from
the degradation of active containment isolation components, as well
as containment penetrations. Administrative limits have been
established for each Type B or C component at a fraction of the
allowable leak rate, such that any leakage detected in excess of the
administrative limit will indicate a potential valve or penetration
degradation. In instances in which a component's leakage exceeds its
administrative limit, proceduralized controls in the test program
require that a work order be written to repair the component.
IV
Section III.D.1.(a) of Appendix J to 10 CFR Part 50 states that a
set of three Type A leakage rate tests shall be performed at
approximately equal intervals during each 10-year service period.
The licensee proposes an exemption to this section which would
provide a one-time interval extension for the Type A test by
approximately 30 months. The Commission has determined that, pursuant
to 10 CFR 50.12(a)(1), this 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. The Commission further
determined, for the reasons discussed below, that special
circumstances, as provided in 10 CFR 50.12(a)(2)(ii), are present
justifying the exemption; namely, that application of the regulation in
the particular circumstances is not necessary to achieve the underlying
purpose of the rule. The underlying purpose of the requirement to
perform Type A containment leak rate tests at approximately equal
intervals during the 10-year service period, is to ensure that any
potential leakage pathways through the containment boundary are
identified within a time span that prevents significant degradation
from continuing or becoming unknown. The NRC staff has reviewed the
basis and supporting information provided by the licensee in the
exemption request. The NRC staff has noted that the licensee has a good
record of ensuring a leak-tight containment. All Type A tests have
passed with significant margin and the licensee has noted that the
results of the Type A testing have been confirmatory of the Type B and
C tests which will continue to be performed. The licensee has stated
that it will continue to perform the general containment civil
inspection although it is only required by Appendix J (Section V.A.) to
be performed in conjunction with Type A tests. The NRC staff considers
that these inspections, though limited in scope, provide an important
added level of confidence in the continued integrity of the containment
boundary.
The NRC staff has also made use of a draft staff report, NUREG-
1493, which provides the technical justification for the present
Appendix J rulemaking effort which also includes a 10-year test
interval for Type A tests. The integrated leakage rate test, or Type A
test, measures overall containment leakage. However, operating
experience with all types of containments used in this country
demonstrates that essentially all containment leakage can be detected
by local leakage rate tests (Type B and C). According to results given
in NUREG-1493, out of 180 ILRT reports covering 110 individual reactors
and approximately 770 years of operating history, only 5 ILRT failures
were found that local leakage rate testing could not detect. This is 3%
of all failures. This study agrees with previous NRC staff studies
which show that Type B and C testing can detect a very large percentage
of containment leaks. The Catawba Unit 2 experience has also been
consistent with this.
The Nuclear Management and Resources Council (NUMARC), now the
Nuclear Energy Institute (NEI), collected and provided the NRC staff
with summaries of data to assist in the Appendix J rulemaking effort.
NUMARC collected results of 144 ILRTs from 33 units; 23 ILRTs exceeded
1.0La. Of these, only nine were not due to Type B or C leakage
penalties. The NEI data also added another perspective. The NEI data
show that in about one-third of the cases exceeding allowable leakage,
the as-found leakage was less than 2La; in one case the leakage
was found to be approximately 2La; in one case the as-found
leakage was less than 3La; one case approached 10La; and in
one case the leakage was found to be approximately 21La. For about
half of the failed ILRTs, the as-found leakage was not quantified.
These data show that, for those ILRTs for which the leakage was
quantified, the leakage values are small in comparison to the leakage
value at which the risk to the public starts to increase over the value
of risk corresponding to La (approximately 200La, as
discussed in NUREG-1493).
Based on generic and plant-specific data, the NRC staff finds the
licensee's proposed one-time exemption to permit a schedular extension
of one cycle for the performance of the Appendix Type A test to be
acceptable.
Pursuant to 10 CFR 51.32, the Commission has determined that
granting this exemption will not have a significant impact on the human
environment (60 FR 32567).
This exemption is effective upon issuance and shall expire at the
completion of the 1997 refueling outage.
Dated at Rockville, Maryland, this 17th day of August 1995
For the Nuclear Regulatory Commission.
Steven A. Varga,
Director, Division of Reactor Projects--I/II, Office of Nuclear Reactor
Regulation.
[FR Doc. 95-21032 Filed 8-23-95; 8:45 am]
BILLING CODE 7590-01-P
