[Federal Register Volume 60, Number 162 (Tuesday, August 22, 1995)]
[Notices]
[Pages 43619-43622]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-20749]
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NUCLEAR REGULATORY COMMISSION
[Docket No. STN 50-530]
Arizona Public Service Company, et al. (Palo Verde Nuclear
Generating Station, Unit No. 3); Exemption
I
The Arizona Public Service Company, et al. (APS or the licensee) is
the holder of Facility Operating License No. NPF-41, which authorizes
operation of the Palo Verde Nuclear Generating Station (PVNGS), Unit
No. 3. The license provides, among other things, that PVNGS, Unit 3, is
subject to all rules, regulations, and orders of the U.S. Nuclear
Regulatory Commission (the Commission or NRC) now or hereafter in
effect. The PVNGS, Unit 3, facility is a pressurized water reactor
located at the licensee's site in Maricopa County, Arizona.
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.
III
By letter dated June 21, 1995, the licensee requested an exemption
from the requirements of 10 CFR Part 50, Appendix J, Paragraph
III.D.1.(a), on a one-time schedular extension which would permit
rescheduling the second containment integrated leak rate test (ILRT) in
the first 10-year service period from the fifth refueling outage (3R5)
currently scheduled for November 1995 to the sixth refueling outage
(3R6) planned for April 1997.
The current ILRT requirements for PVNGS, Unit 3, as set forth in
Appendix J, are that, after the pre-operational leak rate test, a set
of three Type A tests must be performed at approximately equal
intervals during each 10-year period. Also, the third test of each set
must be conducted when the plant is shut down for the 10-year plant
inservice inspection (ISI). The first periodic Type A test was
performed in May of 1991 during the second refueling outage in Unit 3
(3R2), 40 months from the date of Unit 3 commercial operation. The
second periodic test is currently scheduled to be performed in November
of 1995 during the fifth refueling outage (3R5), corresponding to an
interval of 54 months. The third Type A test is currently planned to be
performed during the seventh refueling outage (3R7) which would
coincide with the completion of the first 10-year ISI interval.
The proposed exemption would allow APS to delay the Unit 3 second
Type A test until the sixth refueling outage (3R6). The Type A test
would tentatively be scheduled for April of 1997, and would increase
the interval between the first and second Type A test from 54 months to
71 months. The third Type A test is not being altered by this exemption
request and will remain scheduled for the seventh refueling outage
(3R7). This exemption request proposes an increase to the interval
between the first and second Type A test but does not alter the
frequency of testing (three Type A tests performed in a ten year
period) during the first 10 year ISI interval.
IV
The previous testing history at PVNGS, Unit 3, provides substantial
justification for the proposed test interval extension. Type A testing
is performed to determine that the total leakage from primary
containment does not exceed the maximum allowable leakage rate
(La) as specified in the PVNGS, Unit 3, technical specifications
(TS). The primary containment maximum allowable leakage rate provides
an input assumption to the calculation required to ensure that the
maximum potential offsite dose during a design basis accident does not
result in a dose in excess of that specified in 10 CFR Part 100. The
allowable La for PVNGS, Unit 3, is 0.10 percent by weight of the
containment air per 24 hours at Pa, where Pa is defined as
the calculated peak internal containment pressure related to the design
basis accident, specified in the PVNGS TS as 49.5 psig. The acceptance
criteria for the Type A test is 75 percent of La or 0.075 percent
by weight of the containment air per 24 hours at Pa.
The licensee performed a plant-specific study concluding that the
extension of the Type A test has a negligible impact on overall risk.
This study relied heavily on the existing Type B and C testing program
which is not affected by this exemption, and will continue to
effectively detect containment leakage.
Additionally, the licensee stated that its exemption request meets
the requirements of 10 CFR 50.12, paragraphs (a)(2)(ii) (the underlying
purpose of the regulation is achieved).
The licensee categorized mechanisms that could cause degradation of
the containment into two types: (1) degradation due to work which is
performed as part of a modification or maintenance activity on a
component or system (activity based); or (2) degradation resulting from
a time based failure mechanism (i.e., deterioration of the containment
structure due to pressure, temperature, radiation, chemical or other
such effects). To address the potential degradation due to an activity
based mechanism, the licensee reviewed containment system related
modifications performed since the last Type A test. The licensee
concluded that the modifications performed did not impact containment
integrity, or the modifications have, or will be, tested adequately to
ensure that there is no degradation from an activity based mechanism.
In addition, the licensee maintains administrative controls which
ensure that an appropriate retest, including local leak rate testing,
if applicable, is specified for maintenance activities which affect
primary containment integrity.
Regarding time based failure mechanisms, the licensee concluded
that risk of a non-detectable increase in the primary containment
leakage is considered negligible due to the 10 CFR Part 50, Appendix J,
Type B and C testing program. The licensee stated that without actual
accident conditions, structural deterioration is a gradual phenomenon
which requires periods of time well in excess of the proposed 71-month
test interval which would result by performing the second periodic Type
A test during 3R6. Other than accident conditions, the only external
mechanism inducing stress of the containment structure is the test
itself. The licensee maintains that the longer test interval would,
therefore, lessen the frequency of stressing the containment.
Additionally, the licensee has performed the general inspections of
the accessible interior and exterior surfaces of the containment
structures and components prior to the previous Type A tests, as
required by 10 CFR Part 50, Appendix J, Section V.A. These inspections
are intended to uncover any evidence of structural deterioration which
may affect either the containment structural integrity or leak
tightness. At PVNGS, Unit 3, there has been no evidence of structural
deterioration that would impact structural integrity or leak tightness.
Although the containment inspections required by Appendix J are limited
in scope, they provide an important added level of confidence. The
licensee has committed to perform the general containment inspection as
originally scheduled, during the upcoming 3R5.
The preoperational and first periodic Type A tests performed in
Unit 3 both passed the acceptance criteria with
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adequate margin. The test results were 0.0521 and 0.062 percent by
weight of the containment air per 24 hours at Pa, respectively.
The Type A test results were confirmatory of the Type B and C tests,
and demonstrate that PVNGS Unit 3 is a low-leakage containment. A test
report for each of the Type A tests was submitted to the Commission for
staff review in accordance with the reporting requirements of 10 CFR
50, Appendix J, Section V.B.
The 10 CFR 50, Appendix J, Type B tests are intended to detect
local leaks and to measure leakage across pressure containing or
leakage limiting-boundaries other than valves, such as, containment
penetrations incorporating resilient seals, gaskets, doors, hatches,
etc. The 10 CFR 50, Appendix J, Type C tests are intended to measure
primary containment isolation valve leakage rates. The frequency and
scope of Type B and C testing are not being altered by this proposed
exemption request. The acceptance criteria for Type B and C testing is
0.6 La, or 0.06 percent by weight of the containment air per 24
hours at Pa. This acceptance criteria (0.6 La) is for the sum
of all valves and penetrations subject to Type B and C testing and
represents a considerable portion of the Type A test allowable leakage.
The test results of the combined Type B and C leakage rates for Unit 3
were shown in a table on the licensee's exemption request submittal.
The Unit 3 test results are substantially below the allowable
acceptance criteria for the combined Type B and C leakage rates. These
test results demonstrate a good historic performance of the containment
integrity system. The Type B and C testing program is not being altered
by this exemption request and will continue to effectively detect
containment leakage caused by activity based or time based failure
mechanisms.
A plant-specific analysis for PVNGS was performed to evaluate the
potential for extending the Type A test frequency. The PVNGS, Unit 3,
plant-specific analysis considered the extension of the interval to as
much as 240 months. The conclusion of the analysis was that the
extension of the Type A test interval has a negligible impact on
overall risk. The licensee's exemption request does not alter the
frequency for performance of Type A testing (i.e., it still maintains a
frequency of 3 tests per 10 years). However, the licensee maintains
that the data from this study support the requested exemption from the
requirement of 10 CFR Part 50, Appendix J, regarding ``approximately
equal intervals.'' The interval between the first and second Type A
tests would be 71 months with this exemption. The PVNGS, Unit 3, plant-
specific analysis supports the use of a 240-month interval with a
negligible impact on overall risk.
The licensee referenced 10 CFR 50.12(a)(2)(ii) as a basis for this
exemption. This section defines such a circumstance where ``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 10
CFR Part 50, Appendix J, Section III.D.1.(a), is to establish and
maintain a level of confidence that any primary containment leakage,
during a hypothetical design basis accident, will remain less than or
equal to the maximum allowable value, La, by performing periodic
Type A testing. Compliance with the ``approximately equal intervals''
clause of Appendix J is not necessary to achieve the underlying purpose
of the rule, as explained in the above technical justification.
V
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 adequate margin. The licensee has also 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). Additionally, the
licensee has committed to perform the general containment inspection
during the upcoming refueling outage (3R5), thereby providing an 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
three percent 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 PVNGS-3 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
1.0 La. 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 2 La; in one case the leakage
was found to be approximately 2 La; in one case the as-found
leakage was less than 3 La; one case approached 10 La; and in
one case the leakage was found to be approximately 21 La. 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 200 La,
as discussed in NUREG-1493).
Based on generic and plant-specific data, the NRC staff finds that
the licensee's proposed one-time exemption allowing APS to delay the
Unit 3 second Type A test until the sixth refueling outage (3R6), which
would increase the interval between the first and second Type A test
from 54 months to 71 months, is acceptable.
Pursuant to 10 CFR 51.32, the Commission has determined that
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granting this exemption will not have a significant impact on the human
environment (60 FR 42189).
This exemption is effective upon issuance and shall expire at the
completion of the 3R6 refueling outage.
Dated at Rockville, Maryland, this 16th day of August 1995.
For the Nuclear Regulatory Commission.
Jack W. Roe,
Director, Division of Reactor Projects III/IV, Office of Nuclear
Reactor Regulation.
[FR Doc. 95-20749 Filed 8-21-95; 8:45 am]
BILLING CODE 7590-01-P
