ML20249B604
| ML20249B604 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 06/05/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20249B603 | List: |
| References | |
| NUDOCS 9806230365 | |
| Download: ML20249B604 (10) | |
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1 NUCLEAR REEULATORY COMMISSION WASNmeTON, D.C. 20036 0001 o
SAFETY EVALUATION BY THE OFFICE OF NUCI FAR REACTOR REGULATION RELATED TO AMENDMENT NO.126 TO FACILITY OPERATING LICENSE NO. DPR-80 ANQLLMENDMENT NO.124 TO FACILITY OPERATING LICENSE NO. DPR-82 PACIFIC GAS AND Fi ECTRIC COMPANY DIABLO CANYON NUCI FAR POWER PLANT. UNITS 1 AND 2 DOCKET NOS. 50-275 AND 50 M'4 1.0 INTRODUcIlQN By application dated February 14,1997, as supplemented by letters dated October 9,1997, March 31,1998, and April 15,1998, Pacific Gas and Electric Company (or the licensee) requested changes to the Technical Specifications (Appendix A to Facility Operating License Nos. DPR-80 and DPR-82) for the Diablo Canyon Nuclear Power Plant, Units 1 and 2. The proposed changes revise the combined Technical Specifications (TS) for the Diablo Canyon Power Plant (DCPP) Unit Nos.1 and 2 to:
(a) extend the surveillance test intervals (STis) of TS surveillance for 8 slave relays,20 electrical systems and 5 miscellaneous systems from at least once every 18 months to at least once per refueling interval of nominally 24 months, not to exceed 30 months, and (b) revise one electrical TS Bases to provide an exception to the 18-month battery service life testing.
The October 9,1997, March 31,1998, and April 15,1998, supplemental letters provided
' additional clarifying information and did not change the initial no significant hazards consideration determination published in the Federal Register on March 26,1997 (62 FR 14466).
2.0 BACKGROUND
The NRC staff has reviewed a number of requests by licensees to extend current 18-month surveillance intervals to accommodate a 24-month fuel cycle. The staff concluded that extending the current surveillance intervals at nuclear power plants to accommodate a 24-month refueling cycle have a small effect on safety. It was determined that the safety impact 9906230365 980605 PDR ADOCK 05000275 P
, l was small because all safety systems at nuclear power plants use redundant electrical and mechanical components and licensees perform other surveillance during plant operation that confirm that these systems and components can perform their safety function.
Therefore, the NRC staff subsequently issued GL 91-04, " Changes in Technical Specification Surveillance Intervals to Accommodate a 24-Month Fuel Cycle," which provides guidance on the preparation of a license amendment request for changes to surveillance intervals to accommodate a 24-month fuel cycle. The GL requires licensees to (1) evaluate the effect on safety of an increase in 18-month surveillance intervals to accuir,,vcdate a 24-month fuel cycle; (2) confirm that the effect on safety is small; (3) confirm that historical plant maintenance and surveillance data support all conclusions; and (4) confirm that assumptions in the plant licensing basis would not be invalidated by performing surveillance at a bounding surveillance interval limit to accommodate a 24-month fuel cycle.
Consistent with the guidance in GL 91-04, the licensee also proposed to remove the retrition "during shutdown" from several of the technical specifications. This GL guidance is not consistent with the current NRC Office of Nuclear Reactor Regulation, Electrical Engineering Branch's technical position for several electrical power system TSs. This technical position is reflected in NUREG-1431, " Standard Technical Specification - Westinghouse Plants," April 1995.
3.0 EVALUATION The licensee recently conducted a feasibility study for increasing the length of the fuel cycle from the current 18 months to 24 months for both units of DCPP, in accordance with GL 91-04.
The results of this study indicated that a 24-month fuel cycle is not only feasible but also is beneficial because of fewer refuelings, improved outage scheduling and reduced personnel dose. Therefore, the licensee has decided to implement the extended 24-month fuel cycles at both units of the DCPP, extending the current refueling interval from 18 months to 24 months.
Current DCPP TS require that surveillance tests for some functional units be performed at least once per refueling interval. Therefore, STis for these functional units have been identified by a notation "R" in an appropriate column of the current TS tables. With the extended fuel cycle, STis for these functional units will be 24 months. Therefore, for the 24-month (new refueling interval) STI, a new notation "R24" will be used. The licensee has decided to retain the current 18-month STI for some functional units. In their submittal, the licensee indicated that they would retain the existing notation "R" to indicate the 18-month STI. This will allow clear differentiation between 24-month and 18-month STis.
In their submittal, the licensee stated that the request for the proposed modifications in STis is based on guidance provided by the staff in Generic Letter (GL) 91-04, " Changes in Technical Specification Surveillance Intervals to Accomm Mate a 24-month Fuel Cycle" dated April 2, 1991. GL 91-04 provides guidance on how licensees should evaluate the effects of an extension to a 24-month surveillance interval on the safety of the plant. The licensee performed a detailed engineering analysis of the affected systems and instrument-loops to establish the basis for a maximum 30 month (24 months + 25% additional surveillance frequency allowance)
.. I calibration frequency and to verify that the surveillance interval extensions have an insignificant l
effect on plant safety by verifying that the extended frequency of surveillance would not invalidate any assumptions in the plant's licensing basis.
The licensee is proposing the following changes to the DCCP TS for Units 1 and 2 based on the guidance provided in NRC GL 91-04.
3.1 ESFAS Instrumentation - Slave Relay Tests Proposed change: TS 4.3.2.1, Table 4.3-2, Engineered Safety Features Actuation System (ESFAS) instrumentatbn Surveillance Requirements, for Functional Units 1.b,2.b,3.a.2),
3.b.2),3.c.1),4.b,5.s and 6.b.
This change revises slave relay test surveillance requirements from "R," at least once per 18 months, to "R24," at least once per REFUELING INTERVAL (nominal 24 months, maximum 30 months including allowable tolerance).
Justification for the Change: Engineered safety features (ESF) components are actuated by slave relays in the solid state protection system (SSPS). The slave relays are actuated by master relays, which are actuated by the logic circuits of the SSPS. Each slave relay may actuate multiple ESF components. In their submittal, the licensee stated that Westinghouse performed an evaluation to determine the reliability of PB MDR Model 4103-1 and 4121-1 slave J
relays. This evaluation was documented in Westinghouse topical reports, WCAP-13878,
" Reliability Assessment of Potter & Brumfield MDR Series Relays", June 1994, and WCAP-13900, " Extension of Slave Relay Surveillance Test intervals," April 1994, which were reviewed and accepted by the NRC. The Westinghouse evaluation concluded that the PB slave relays used in the SSPS are highly reliable and that testing at a frequency coincident with the 24-month refueling interval does not significantly decrease margins of safety assumed in the plant safety analysis. The licensee stated that, PB MDR Model 4102 and 4103 relays are used at DCPP which are similar in design to those analyzed in the Westinghouse evaluation, and therefort the analysis adequately covert the DCPP PB relays. In addition, the licensee noted that the staff previously reviewed the reliability of the DCPP slave relays when it approved a TS amendment to extend slave relay surveillance from quarterly to refueling outage intervals.
in their submittal, the licensee stated that assurance of equipment operability is also provided by routine and frequent tests performed in accordance with other TS requirements. TS 4.3.2 requires testing the ESFAS logic for each protection train once every 62 days on a staggered frequency. Part of this test verifies continuity of relay coils without operation of the relay. TS 4.8.1.1.2.a requires testing the ability of the emergency diesel generator to start and load at least once a month. This test utilizes a substantial portion of the circuitry and equipment used to transfer power during loss of offsite power events or conditions requiring safety injection initiation. ESFAS pumps, fans, and valves are tested pursuant to the DCPP in-service Testing Program. Most ESFAS equipment is also tested to satisfy various TS requirements at monthly or quarterly intervals. The licensee further stated that the DCPP's successful operating, surveillance, and maintenance history for the subject slave relays supports the conclusion that
4 the effect on safety of extending the surveillance intervals for slave relay testing will be negligible.
Considering the results of the approved Westinghouse slave relay reliability evaluation,
- additional testing of slave relays covered by other TS tests, and the results of the licensee evaluation of historical data for DCPP operation, surveillance, and maintenance, the staff finds the proposed change acceptable.
3.2 Pressurizer Heater Capacity Prooosed Chanpe: TS 4.4.3.2, Pressurizer Surveillance Requirement. This change revises verification of pressurizer heaters electric capacity from at least once per g2 days to at least once each REFUELING INTERVAL.
Jushficationfor the Change: The current technical specification (CTS) requires verification of pressurizer heater group power greater than 150 kW for two groups of heaters at least once per 92 days. This verification is performed by reading heater output indicators in the main control room while the heater is tumed on. NUREG-1366 states that because most of the heaters are in constant use, operators should be aware of problems that may arise with the heaters.
NUREG-1366 recommended that the capacity of heaters should be tested once each refueling interval for those plants without dedicated safety-related heaters. Diablo Canyon has four.
l groups of heaters, none of which are safety-related. The heater groups are normally powered from the nonvital 480 V busses. Two groups have emergency backup power supplied from vital 480 V busses. These two groups are the TS required pressurizer heaters. These groups with emergency power normally provides 300 to 500 kW. The normal supply circuit breakers are cycled manually during normal operation and failures would be noticed by the operators. The licensee stated that a review of surveillance, maintenance and operational history indicated that the effect on safety by extending the surveillance interval is small and that there were no unsatisfactory time-related dependence for operability of heater elements or normal 480 V supply breakers for the past 10 years and that the effect on safety is small. The normal and j
emergency breakers were replaced between 1986 and 1990 with a more reliable model and there are sufficient heater elements in each group to allow elements to be removed from service if they fail. The staff finds the proposed change acceptable.
3.3 Reactor Coolant System - PORVs Prooosed Changes: TS 4.4.4.1a, Relief Valves Surveillance Requirement. This change revises testing of power operated relief valve (PORV) during MODES 3 and 4 with the block valve closed from at least once per 18 months to at least once per REFUELING INTERVAL.
.TS 4.4.4.3a, Relief Valves Surveillance Requirement. This change revises the operability requirement for the safety-related nitrogen supply for the PORVs by isolating and venting the normal air supply from at least once per 18 months to at least once per REFUELING INTERVAL
.. TS 4.4.4.36, Relief Valves Surveillance Requirement. This change revises the operability _
requirement for the safety-related nitrogen supply for the PORVs by verifying that any leakage of the Class 1 backup nitrogen system is within its limits from at least once per 18 months to at least once per REFUELING INTERVAL TS 4.4.4.3c, Relief Valves Surveillance Requirement. This change revis. 5 the operability requirement for the safety-related nitrogen supply for the PORVs by ope,ating the PORV through orts complete cycle of full travel using the safety-related nitrogen supply from at least once per 18 months to at least once per REFUELING INTERVAL.
Justification for the Changes: The PORVs provide pv64vn for the reactor coolant system l
(RCS) during power operation and during shutdown conditions when low temperature overpressure protection is required. Each PORV has an upstream block valve to provide a I
positive shutoff capability should a relief valve become inoperable. The non-Class 1 valve is used only as a backup to the two redundant Class 1 PORVs and block valves for accident mitigation. The two safety-related valves have individual Class 1 backup nitrogen supplies capable of operating the valves given the loss of the nomial air supply. The CTS has the PORV full stroke test performed in MODES 3 and 4 on a refueling frequency (18 months). The test is performed during refueling because if performed at power could cause plant transients.
In addition to the refueling frequency the parts of the PORVs and their associated actuation circuitry is tested on a more frequent basis by other TSs. The block valve has a full stroke test performed every 2 days, the position indicators are tested monthiy, the pressurizer pressure g
channels associated with the PORV automatic actuation circuitry receive channel checks every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and a quarterly operation test, and the RCS water inventory balance is performed every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to check for PORV leaking. The licensee stated that a review of surveillance, maintenance and operational history indicated that the effect on safety by extending the surveillance interval is small and that there is no time-dependent failures associated with PORV testing. There had been some failures of the valve actuator diaphragms due to high ambient temperatures at the top of the pressurizer enclosure. The licensee modified the actuator cover and diaphragm materials and have placed the diaphragms in a replacement program and no failures have occurred since. The air pressure regulators contain elastomeric parts which may deteriorate in high ambient temperature areas. These parts are in a planned replacement program and no failures have occurred. The staff finds the proposed change acceptable.
3.4 A_C. Sources - Bus Transfers Prooosed Changes: TS 4.8.1.1.1b, Electrical Power Sources - A.C. Sources Surveillance Requirements. This change revises the requirement to perform bus transfers from at least once per 18 months during shutdown to at least once por REFUELING INTERVAL during shutdown.
TS 4.8.1.1.1.b.1), Electrical Power Sources - A.C. Sources Surveillance Requirements. This change revises the requirement to verify the operability of transfening 4 kV vital bus power supply from the normal circuit to the altamate circuit (manually and automatic), and to the
' delayed access circuit (manually).
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. TS 4.8.1.1.1.b.2), Electrical Power Sources - A.C. Sources Surveillance Requirements. This change revises the requirement to verify that on a safety injection (SI) test signal, without loss of offsite power, the preferred, immediate access offsite power source energizes the emergency busses with permanently connected loads and energizes the autc> connected emergency (accident) loads through sequencing timers.
Justification for the Changes: The Diablo Canyon 4 kV vital power supply provides power for the operation and control of Class 1E loads during all plant operating modes. The safety-related loads are supplied from three vital 4 kV busses on each unit. Each bus can be powered l
from any of three main sources: (1) the auxiliary transformer supplied by either the main generator or the 500 kV system (normal), (2) the 230 kV switchyard startup transformer (altemate), or (3) the dedicated emergency diesel generator (EDG) for that bus. Several i
initiating events will cause the 4 kV busses to attempt to autotransfer to startup power, which j
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results in the tripping of the normal auxiliary power supply breaker. When the normal source is lost, each bus will automatically attempt to slow transfer to the startup power supply, The busses may be manually transferred to the sitemate startup source from the control room when required by plant conditions. Power may be manually transferred to the delayed access circuit when the unit is shutdown. This power is from the 500 kV power system backfed via the main unit transformer to the auxiliary transformer. The main generator disconnect switch is opened to prevent energizing the main generator. Testing vital bus transfer capability during power operation could cause plant transients, therefore it is tested during refueling outages. The 4 kV bus operability is ensured by other TS surveillance requirements which overiaps a portion of the components tested in the bus transfer test. The licensee stated that a review of the surveillance, maintenance and operating history indicated that the effect on safety by extending the surveillance interval is small and that there are no time-dependent failures involved with the 4 kV bus' transfers. The staff finds the proposed change acceptable.
3.5 Diesel Generator Operability Proposed Changes: TS 4.8.1.1.2b, Electrical Power Systems - A.C. Sources, EDGs. This change revises the requirement for EDG operability from at least once per 18 months during shutdown to at least once per REFUELING INTERVAL during shutdown.
TS 4.8.1.1.2.b.1), Electrical Power Systems - A.C. Sources, EDGs. This change revises the requirement to perform an inspection in accordance with manufacturer's recommendations.
TS 4.8.1.1.2.b.2), Electrical Power Systems - A.C. Sources, EDGs. This change revises the i
requirement to verify that the engineering safety feature (ESF) and autotransfer load sequence timers are OPERABLE.
.TS 4.8.1.1.2.b.3), Electrical Power Systems - A.C. Sources, EDGs. This change revises the requirement to verify that the generator has the capability to load reject a load of greater than or equal to 508 kW with voltage and frequency restrictions.
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-7 TS 4.8.1.1.2.b.4), Electrical Power Systems - A.C. Sources, EDGs. This change revises the requirement to verify that the generator has the capability to load reject a load of greater than or equal 2484 kW without tripping or exceeding 4580V during and following the load rejection.
TS 4.8.1.1.2.b.5), Electrical Power Systems - A.C. Sources, EDGs. This change revises the requirement to simulate a loss of offsite power by itse,1f and verifying deenergizing and load -
shedding of the emergency busses, and verifying auto-start and loading of the EDG.
TS 4.8.1.1.2.b.6), Electrical Power Systems - A.C. Sources, EDGs. This change revises the requirement to verify that on a safety injection (SI) test signal without loss of offsite power, that the EDG auto starts and loads.
TS 4.8.1.1.2.b.7), Electrical Power Systems - A.C. Sources, EDGs. This change revises the requirement to simulate a loss of offsite power in conjunction with a Si test signal and verifying doenergizing and load shedding of the emergency busses, verifying autatart and loading of j
the EDG, and verifying certain automatic EDG trips are bypassed in the required alignment.
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TS 4.8.1.1.2.b.8), Electrical Power Systems - A.C. Sources, EDGs. This alange revises the j
requirement to perform a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> load run.
TS 4.8.1.1.2.b.9), Electrical Power Systems - A.C. Sources, EDGs. This change revises the I
requirement to verify the maximum rating of autoconnected loads for each EDG.
TS 4.8.1.1.2.b.10), Electrical Power Systems - A.C. Sources, EDGs. This change revises the requirement to verify the EDG's capability to synchronize its isolated bus with the offsite power source, transfer its load to the offside power source, and be restored to standby status.
TS 4.8.1.1.2.b.11), Electrical Power Systems - A.C. Sources, EDGs. This. change revises the '
requirement to verify the EDGs ability to respond to a simulated Si signal while operating in the test mode.
TS 4.8.1.1.2.b.12), Electrical Power Systems - A.C. Sources, EDGs. This change revises the requirement to verify proper operation of the EDG shutdown relay lockout feature.
TS 4.8.1.1.2.e, Electrical Power Systems - A.C. Sources, EDGs. This change revises the requirement to verify the timing of the EDG start and stabilization of voltage and frequency.
3 Justification for the Changes: The EDGs provide independent onsite power for operation and L
control of Class 1E loads when offsite power is unavailable. The EDGs are one of three sources of power to the three vital 4 kV busses on each unit. Each bus has an independent transfer scheme with three circuit breakers dedicated to the three power sources. Testing of the EDGs during power operation could cause plant transients. Therefore, the above surveillance will be performed during refueling outages while in shutdown conditions. The tests performed on a refueling outage basis are only part of the surveillance requirements
. required to assure operability of the EDGs and their associated components. A review by the licensee of the operating history of the EDGs resulted in ten EDG failure reports where there
8-was a valid demand and a failure of the EDG to respond to that demand since 1990. A review of these failure reports indicated that the problems were resolved satisfactorily and did not recur, and that maintenance was completed on line as necessary. The licensee reviewed the surveillance, and maintenance history for the EDGs and determined that there were no effects on safety and no time-dependent failures which would be affected by extending the frequency of the surveillance. The staff finds the proposed change acceptable.
3.6 Batterv Capacity Proposed Changes: TS 4.8.3.1c, Electrical Power Systems - D.C. Sources, Batteries. This change revises the requirement for visual inspection, connection verification, resistance readings, and battery charger capacity testing from at least once per 18 months to at least once per REFUELING INTERVAL during shutdown.
TS 4.8.3.1d, Electrical Power Systems - D.C. Sources, Batteries. This change revises the requirement for verifying the ability of the battery to supply the actual and/or simulated emergency loads for the design duty cycle when subjected to a battery service test from at least once per 18 months during shutdown to at least once per REFUELK3 INTERVAL during shutdown.
TS 4.8.3.1f, Electrical Power Systems - D.C. Sources, Batteries. This change revises the requirement to perform the discharge tests of any battery that shows signs of degradation or has reached 85 percent of the service life expected for the application from at least once per 18 months during shutdown to at least once per REFUELING INTERVAL during shutdown.
TS Bases 3/4.8.1, 3/4.8.2, 3/4.8.3, Electrical Power Systems - A.C. Sources, D.C. Sources, and Onsite Power Distribution. This change revises the Bases to add the exception to the 18-month L
battery service test recommendation provided by Regulatory Guide (RG) 1.129.
Justification for the Changes: The vital D.C. power sources and associated distribution systems help ensure that sufficient instrumentation and control capability is available for monitoring and maintaining the plant status when A.C. power is lost. Each DCPP unit has three 60 cell,125V vital batteries and five full capacity battery chargers. The three 125V vital busses has a dedicated battery and charger, supplied from its associated 480V vital bus, with the capability of being supplied by an attemate charger supplied from another.480V vital bus. The battery chargers supply the total load requirements of the D.C. system as well as maintaining a constant floating charge on the batteries. The recommendations of RG 1.129 states,'The battery service test should be performed during refueling operations or at some other outage, with intervals between tests not to exceed 18 months." DCPP is also committed to the 1980 version of IEEE-450, which does not make any recommendation for service test frequency, but does state that performance test should be performed at five year intervals until the battery is at 85 percent of its service life or shows signs of degradation. IEEE 450-1980, also states that quarterly visual inspections should be augmented with yearly detailed visual inspections. Many battery tests may be performed during power operations, however testing the battery capacity requires discharging the battery. Therefore, performance and capacity surveillance are performed with the plant shutdown. The batteries and chargers are tested on a refueling
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interval, and other operational tests are performed to ensure operability. The licensee stated that a review of the surveillance, operational and maintenance history for the batteries and battery chargers determined that there were no effects on safety and no time dependent failures which would be affected by extending the frequency of the surveillance. The staff finds the proposed changes acceptable.
During the review of this proposed change, the staff identified some issues that were outside the scope of the current license amendment request. During a conference call on January 30, 1998, the staff posed questions to the licensee regarding the following battery surveillance tests.
The first concem was related to the determination of battery degradation consistent with the more recent IEEE Std. 450-1995. The IEEE Std. bases the degradation determination on the most recent battery test, rather than the average of all previous battery test. The staff has concluded the most appropriate way to determine battery degradation is when the battery capacity drops more than 10 percent of rated capacity from the previous performance test.
This position is reflected in the improved " Standard Technical Specification for Westinghouse Plants."
Presently, the licensee, in battery surveillance 4.8.3.1f, determines battery degradation when the battery capacity drops more than 10 percent of rated capacity from its average on previous performance tests, or is below 90 percent of the manufacturer's rating. The staff identified the use of the average previous performance test as a concem. However, the licensee stated that they have recently submitted their improved " Standard Technical Specifications" to the NRC staff for review and this particular battery surveillance has been changed to be consistent with the IEEE 450-1995.
The second issue is related to the licensee conducting a performance discharge test in lieu of a service test. TS 4.8.3.1 e indicates that the licensee may perform a performance discharge test in lieu of the battery service test required by TS 4.8.3.1d. The staff has concluded that the performance test should be capable of enveloping the load profile of the service test if it is to be performed in lieu of the service test. This position is reflected in the improved " Standard Technical Specification for Westinghouse Plants."
1 The licensee has stated that their performance test does envelope the battery service test. The licensee has confirmed that the performance test envelopes the battery service test oer plant j
procedure STP M-12A," Vital Station Battery Modifed Performance Test."
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4.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Califomia State official was notified of the proposed issuance of the amendments. The State official had no comments.
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5.0 ENVIRONMENTAL CONSIDERATION
These amendments change surveillance requirements. The NRC staff has determined that the -
amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (62 FR 14466). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that (1) there is reasonabin assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributors: S. Athavale S. Bloom T. Dunning M. Pratt Date:
June 5, 1998 l
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