[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]
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