[Federal Register Volume 60, Number 49 (Tuesday, March 14, 1995)]
[Notices]
[Pages 13738-13739]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-6205]
-----------------------------------------------------------------------
NUCLEAR REGULATORY COMMISSION
[Docket No. 50-413]
Duke Power Company, et al. (Catawba Nuclear Station, Unit No. 1);
Exemption
I
The Duke Power Company, et al. (DPC or the licensee) is the holder
of Facility Operating License No. NPF-35, which authorizes operation of
the Catawba Nuclear Station, Unit No. 1 (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 a 10-year inservice
inspection of the primary containment.
III
By letters dated October 18, 1994, and February 7, 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 16 months (from the 1995 refueling outage,
which began on February 11, 1995, to the end-of-cycle 9 (EOC-9)
refueling outage, currently scheduled for June 1996) 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 1, is justified for the following reasons:
The previous testing history at Catawba Unit 1 provides substantial
justification for the proposed test interval extension. In each of the
two previous periodic ILRTs at Catawba Unit 1, the as-found leakage was
less than or equal to 22.5% of the allowable leakage, thereby
demonstrating that Catawba Unit 1 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 20 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-8 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 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 jailed; (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, proceduralize 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 22.5%
of the allowable leakage rate.
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, similar
conclusions 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 present in that the requirement to perform the third ILRT during
the ISI outage 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 1 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 22.5% 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
[[Page 13739]] 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 16 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 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 licenses 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 which 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 1 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 CFR 11125).
This exemption is effective upon issuance and shall expire at the
completion of the 1996 refueling outage.
Dated at Rockville, Maryland, this 7th day of March 1995.
For the Nuclear Regulatory Commission.
John A. Zwolinski,
Acting Director, Division of Reactor Projects -- I/II, Office of
Nuclear Reactor Regulation.
[FR Doc. 95-6205 Filed 3-13-95; 8:45 am]
BILLING CODE 7590-01-M