[Federal Register Volume 60, Number 67 (Friday, April 7, 1995)]
[Notices]
[Pages 17829-17831]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-8585]
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NUCLEAR REGULATORY COMMISSION
[Docket No. STN 50-528]
Arizona Public Service Company, et al.; (Palo Verde Nuclear
Generating Station, Unit No. 1), 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, Unit No. 1
(PVNGS-1). The license provides, among other things, that PVNGS-1 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-1 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 December 28, 1994, 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 20 months
(from the 1995 refueling outage, which begins in May 1995, to the sixth
refueling outage (1R6), currently scheduled for September 1996) and
would permit the third Type A test of the 10-year inservice inspection
period not to correspond with the end of the inservice inspection
interval.
The licensee's request concluded that the proposed changes for
PVNGS-1, a one-time extension of the interval between the second and
third ILRTs and a decoupling of the third test from the outage
corresponding to the end of the 10-year inservice inspection period, is
justified for the following reasons:
The previous testing history at PVNGS-1 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-1 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 100. The allowable
La for PVNGS-1 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-1 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.
In each of the two previous periodic ILRTs at PVNGS-1 (the results
were 0.066 percent and 0.067 percent by weight of the containment air
per 24 hours at Pa, respectively), the results obtained were below
the test acceptance criteria of 75 percent of La or 0.075 percent
by weight of the containment air per 24 hours at Pa, thereby,
demonstrating that PVNGS-1 is a low-leakage containment.
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), and (a)(2)(iii) (compliance
would result in undue hardship or other costs that are significantly in
excess of those contemplated when the regulation was adopted), for the
following reasons:
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 81-month
test interval which would result by performing the third periodic Type
A test during the sixth refueling outage in Unit 1. 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-1, there has been no evidence of structural
deterioration that would impact structural integrity or leak tightness.
In a phone conversation with the licensee on March 23, 1995, the staff
noted that these inspections, though limited in scope, provide an
important added level of confidence. The licensee committed to perform
the general containment civil inspection during the upcoming refueling
outage (1R5).
The 10 CFR Part 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 [[Page 17830]] resilient seals, gaskets,
doors, hatches, etc. The 10 CFR Part 50, Appendix J, Type C tests are
intended to measure reactor system primary containment isolation valve
leakage rates. The frequency and scope of Type B and C testing is not
being altered by this proposed exemption request. The acceptance
criterion for Type B and C testing is 0.6 La. This acceptance
criterion 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 results of the as-left combined Type B and
C leakage measured since the last Unit 1 Type A test are 0.054 La,
0.06 La, and 0.13 La (for the February 1991, May 1992, and
November 1993 outages, respectively). The licensee maintains that these
test results are substantially below the acceptance criterion of 0.60
La and demonstrate a good historic performance of containment
integrity.
The proposed schedular exemption would allow the third Type A
leakage rate test in Unit 1 to be performed during the Fall 1996 (IR6)
refueling outage, which meets the 10 CFR Part 50, Appendix J,
requirement of performing three tests in a 10-year time period. The
performance of a fourth Type A test during the Unit 1 seventh refueling
outage, in order to coincide with the outage at the completion of the
extended 10-year ISI interval, is not deemed to be appropriate, as it
would result in additional radiation exposure to personnel, increased
length of the refueling outage and significant additional cost.
Omitting the test will result in dose savings by eliminating
contamination and by reducing radiation exposure from the venting and
draining of piping penetrations necessary to establish the appropriate
test conditions. There would also be dose savings from eliminating the
need to install and remove the temporary instrumentation necessary to
perform the Type A test. Performing a fourth Type A test would also
increase the duration of the affected outage by approximately 3 days
and result in additional costs associated with this increase.
A PVNGS-1 plant-specific analysis was performed to evaluate the
potential for extending the Type A test frequency. The PVNGS-1 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 second and third Type A tests
would be 81 months with this exemption. The PVNGS-1 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.
The licensee also referenced 10 CFR 50.12(a)(2)(iii) in its
submittal, which states the NRC may grant exemptions from requirements
of 10 CFR Part 50 when ``compliance would result in undue hardship or
other costs that are significantly in excess of those contemplated when
the regulation was adopted, or that are significantly in excess of
those incurred by others similarly situated * * *.'' The current PVNGS-
1 Type A test schedule would require that four Type A tests be
performed in an extended ISI interval. This current schedule would
result in unnecessary additional radiation exposure in order to perform
the test and unnecessary costs associated with the performance of the
test and the costs associated with the increase in the length of the
refueling outage. Regarding the impact of this exemption on overall
risk, it is the staff's experience that risk is insensitive to the Type
A test frequency at values of leakage close to La. Therefore,
while the staff agrees with the licensee's conclusion that the risk
increase resulting from granting this exemption is small, the time
interval has no particular significance. Additionally, the staff has
previously discussed with the licensee that its scheduling of
containment ILRTs early in the ISI interval is largely responsible for
the necessity of performing an additional test, and would not
constitute a hardship that was not anticipated at the time the rule was
written. Therefore, the staff has reviewed this exemption request
against the criteria of 10 CFR 50.12(a)(2)(ii).
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 20 months. Additionally, for schedular reasons, the final
Type A test of the 10-year inservice inspection period is proposed to
be decoupled from the requirement to perform it during the same outage
(the final Type A test would be performed the outage prior (1R6) to the
end of the inservice inspection period).
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 civil
inspection during the upcoming refueling outage (1R5), thereby
providing an added level of confidence in the continued integrity of
the containment boundary. [[Page 17831]]
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-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
1.0 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 then 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 the La (approximately 200 La,
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, and the
decoupling of the third test to be performed coincident with the
completion of the inservice inspection period, 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 16180).
This exemption is effective upon issuance and shall expire at the
completion of the 1R7 refueling outage.
For the Nuclear Regulatory Commission.
Dated at Rockville, Maryland, this 31st day of March 1995.
Elinor G. Adensam,
Acting Director, Division of Reactor Projects--III/IV, Office of
Nuclear Reactor Regulation.
[FR Doc. 95-8585 Filed 4-6-95; 8:45 am]
BILLING CODE 7590-01-M
