ML20008F953
| ML20008F953 | |
| Person / Time | |
|---|---|
| Site: | Allens Creek File:Houston Lighting and Power Company icon.png |
| Issue date: | 05/11/1981 |
| From: | Chopra O Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20008F949 | List: |
| References | |
| NUDOCS 8105120390 | |
| Download: ML20008F953 (15) | |
Text
t 05/11/81 9
U:4ITED STATES OF AMERICA flVCLEAR REGULATORY COMMISSIO:1 BEFORE THE AT0flIC SAFETY AliD LICEliSIf4G BOARD In the itatter of
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HOUST0:1 LIG!iTI!iG A!!D POWER COMPA:4Y )
Docket tio. 50-466 (Allens Creek fluclear Generating Station, Unit 1)
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liRC STAFF TESTIMO:1Y OF OH P. CH0PRA Of4 DOHERTY C0iiTEf4TI0 tis 10 Ar4D 30 Q.
Please state your name and position with the f1RC.
A.
My name is Om P. Chopra.
I an employed by the U.S. fluclear Regulatory Comission as a Senior Reactor Systems Engineer (electrical) in the Division of Systems Integration. A copy of my professional qualifications is attached.
Q.
What is the purpose of your testimony?
A.
The purpose of this testinony is to respond to Doherty Contentions 10 and 30. Tnese ';ontentions will be responded to separately bel ow.
Doherty Contention 10 Intervenor contends that his health and safety interests are not sufficiently protected because applicant's diesel generator systen to the High Pressure Core Spray (HPCS) and to the rest of the nuclear plant is unreliable in start up and operation. Specifically, Applicant's systen is identical (largely) to one that according to fiUREG-0660 (Feb.1979) produced 122 start-up failures and which included 54 of these failures among BWR licensees from 1969 to 1979, and according to liuclear Safety 19(1), p. 81, had 74 " Reportable 82 es a coggo L
Occurrences" in 1976 and 76 (Nuclear Safety, 20(1),
- p. 84) in 1977. Further that diesel generators are subject to other than inherent failure through worker error (Oyster Creek, Deceaber 1975), poor adainistrative practice, i.e., fuel oil stored with lubricating oil and used as a lubricant (Brunswick, Unit 2, October 1975) and outside storage of diesel generators prior to plant sta:'-up, resulting in water logging (Ft. St. Vrai.b June 1975).
tiUREG-0660 has concluded that interpretation by the utilities of the NRC regulatory guides on diesel generators has varied widely and been a problem source.
Intervenor contends that the data above show the need for either (a) a third generator be -
installed for both the HPCS and a third for the balance of the plant systeas, (b) a higher standard than 93 starts per 100 be used in requiring additional information to the NRC, (General Electric Technical Specification 4.8.1.1.4 for BWR's) and that (c) Surveillance Requirement 4.8.1.1, should required an every three-day surveillance, and all other surveillance tines halved in view of the serious consequences of power failure to a nuclear plant.
Q. Has the Staff made any recorraendations to improve diesel generator reliability?
A.
Yes. NUREG-CR-0560, " Enhancement of Onsite Energencuy Diesel Generator Reliability," made specific reco..nendations for increasing the reliability of nuclear power plant emergency diesel generators. These recommendations are based on comprehensive study cf diesel generator operating experience at nuclear power plants and on consultations with cajor diesel generator manufacturers. These recomendations address ths following areas:
1.
Hoisture in the Air Start System 2.
Dust cnd dirt in D/G room 3.
Turbochdrger gear orive problem
e,
4.
Personnel training 5.
Autonatic prelube 6.
Testing, test loading and preventative maintenance 7.
Iaprove identification of root cause of failures 8.
D/G ventilation and combustion air systems 9.
Fuel storage and handling
- 10. High temper ture insulation for generator
- 11. Engine cooling water temperature control
- 12. Concrete dust control
- 13. Vibration of instruments and controls Q.
Will plants in review, including Allens Creek, be required to implement the recommendations set forth in NUREG-CR-0660?
A.
All plants in the licensing process are being required to revied their designs for conformance to these recomendations, and to make design and procedural changes in this regard as deemed necessary by the Staff to enhance the overall reliability of the diesel generator units.
The Applicant for Allens Creek will be required to implement the recoumendations in its design as may be dee.ned necessary by the Staff.
Any design or procedural changes will be reviewed at the operating license stage of review.
Q.
Will the Staff require a qualification progra,a to demonstrate l
the reliability of the diesel generators?
A.
In addition to the above, the Staff requires that new or larger 7
diesel generator designs than those already proven in nuclear plant service undergo a prototype qualification program to demonstrate the capability of the design. This prograra requires 300 tests with no more l
l I
i than three' failures allowed. This yields an' unavailability of no greater than 10-2 per demand. During plant operation, application of Regulatory Guide 1.108, " Periodic Testing of Diesel Generator Units Used as Onsite Electric Pawer Systems at fluclear Power Plants," would provide for periodic testing of the diesel gneerators on a progressive schedule which is directed toward a goal of unavailability no greater.than 10-2 per demand. This is accomplished by looking back at the last 100 tests and tallying the number of failstes experienced. Should the' failures per last one hundred tests sta.t to increase, this is a clear and inmediate indication that the current unavailability of the on-site systen is increasing. The guide then requires increased surveillance based upon the number of experienced failures until the current unavailability is deconstrated to be no larger than 10-2 per denand. -The Applicant has a cocnitment in the PSAR to cooply with the recommendations of Regulatory Guide 1.108 with certain exceptions found acceptable by the Staff (SER Supp. lio. 2 page 8-9).
Q.
What does the Staff conclude with respect to the reliability of the diesel generators at Allens Creek during the construction pernit review process?
A.
In vied of the abote, we believe that the implementation of the i
recommendations of IlUREG-0660 will improve the reliability of the Allens Creek diesel generators. We further believe that implementing the preoperational and periodic testing provisions set forth in Regulatory Guide 1.108 will provide a basis for taking those corrective actions needed to naintain high inservice reliability of the installed diesel generators. The Staff will review the Applicant's implementation of the
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HUREG-CR-0660 recoamendations at the operating license stage and will require any necessary design and procedural changes daring that review.
l Therefore, I conclude there is not need for additional diesel generators, ur changes in Technical Specifications at this time.
Doherty Contention 30 Intervenor contends his health, safety and econinic interests are imperiled because Applicant refuses to interconnect with any utility which interconnects with an ~ out of state utility. This refusal nakes ACHGS safety systens more vulnerable to lack of power in the event there is loss of off-site power daring severe climatic conditions or other disturbances, and the proposed unit must turn on on-site diesel generators which are not highly reliable, and unpreferred to the use of off-site power. Further, in July,1974, the Venaont Yankee BWR experienced a turbine trip due to ligntning during severe climatic conditions and in September, 1977, the Donald C. Cook-Unit 1, had the same event.
Applicant's gric may become too highly centered around ACNGS because it will produce a high proportion of the power and will be a base load operating plant particularly during non-peak hours and non-peak seasons. Applicant should be required to show that interconnection is not necessary to provide grid stability and adequate power to the ACNGS safety systems without use of the unpreferred power source, with the condition that if this cannot i
be shown, Applicant will be required to interconnect with out-of-state interconnected utilities before a construction license is granted. Or, alternatively Applicant should be required to either:
a.
shut down ACNGS when there are severe clinatic conditions; or i
b.
provide a third generator and generatur i
start-up when severe clinatic conditions occur.
Q.
Wnat does the NRC require with respect to the availability of electric power to perfora all necessary safety functions?
A.
Inere is no HRC safety criterion that requires the Applicant to interconnect with out-of-state interconnected utilities.
General Design i
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Criterion (GDC) 17 of 10 C.F.R. Part 50, Appendix A sets forth the fundanental requirenents for the off-site power systens and on-site power systens..Either systen is required to be able to perfora all necessary safety functions independent of the other system. The regulations do not specify either the on-site or off-site power systen as the " preferred" source of power for nitigating postulated events. Traditionally, as reflected in Regulatory Guides and industry standards, the off-site power 4
system has been assigned this role.
The overall assurance that electric power will be provided to the safety systens of a nuclear power generating station is based upon the availabilities of the on-site and off-site systens taken togetner. Any weakness found in either systea can to a large degree be compensated for by strengths (either inherent or imposed) in the other systen until such weaknesses can be corrected. This is in accordance with tne Cox.ission's defense-in-depth concept.
In this connection, the on-site power systen is fully qualified as a seisnic Category ! systen.
Q.
What does GDC 17 require with respect to the off-site power i
systea?
i A.
GDC 17 requires that the off-site power systen be able to sustain the loss of the largest operating unit or the nost critical component of the electrical grid. Tne off-site power systen is not designed to meet tne stringent requirenents imposed by NRC on nuclear reactor systens (including the on-site power systens). Tne off-site power systen-is not seismically qualified against standards similar to those resulting fron application of GDC 2; similarly, the entire grid is
i
. generally not designed to withstand all natural phenomena to the same extent as that required for the nuclear plant itself.
Q.
How does the Staff review the off-site power system to assure stability of the grid?
A.
The Staff in their review of the off-site power syf ten assures that the loss of the most critical operating unit on the grid or the loss of the operating nuclear unit or the loss of the most critical transmission line, will not affect the grid's ability to provide off-site power to the emergency systems of the plant. The assurance for the above capability of the off-site power system is gained by requiring the Applicant to provide to us the results of various grid stability studies performed to assess system stability in the event of such contingencies.
The results of such studies were provided for our review of Allens Creek and our evaluation of the results of these stability studies is included in our Allens Creek SER dated November 1974.
Q.
Does the Staff also review the impact of the degradation of the off-site power systea on the operability of the on-site A. C. power systea?
A.
The Staff also assures that any degradation of the off-site power systeu does not affect the operability of the on-site A.C. power system and the connected safety loads.
In this regard, the Staff has l
developed a posit' an PSB #1 (see enclosure 1) on " Adequacy of Station Electric Distribution System Voltages." We are currently requiring all i
i j
licensees and applicants for operating licenses and construction permits L
to revies the on-site energency power systems of their facility to assess the susceptibility of their associated redundant safety-related l
~_
. 4 electrical equipment to:
(a) sustain degraded voltage conditions at the uff-site power sources; (b) interaction between the off-site and on-site energency power systems.
In addition, the design is reviewed to assure that each plant's station electrical distribution system will provide an adeuqate supply of power to essential loads during the contingency which presents the largest load demand on the auxiliary systen.
Q. What is the Staff's conclusion with respect to this contention?
A.
The Staff concludes that the present off-site power systen design for Allens Creek will provide adequate power to all the safety systems and there is no need for installing an additional diesel generator or shutdown ACNGS in severe climatic conditions. Our conclusion is based on our rt view of the Applicant's grid stability analysis coupled with the taplementation of the above-nentioned Staff positions which will provide sufficient level of assurance of safety requisite at the construction permit stage.
Further, overall assurance will be provided when details of any contingencies assumed in their analysis will be reviewed during the operating license review of the Alle.is Creek plant.
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ENCLOSURE 1 BRANCH TECHNICAL POSITION PSB 1 ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES A.
BACKGROUND Events at the Millstone station have shown that adverse effects on the Class lE loads can be caused by sustained low grid voltage conditions when the Class lE buses are connected to offsite power.
These low voltage conditions will not be detected by the loss of voltage relays (loss of off-site power) whose low voltage pickup setting is generally in the range of
.7 per unit voltage or less.
The above events also demonstrated that improper voltage protection logic can itself cause adverse effects on the Class IE systems and equipment such as spurious load shedding of Class lE loads from the standby diesel generators and spurious separation of Class 1E systems from offsite power due to normal motor starting transients.
A more recent event at Arkansas Nucle'ar One (ANO) station and the subsequent analysis performed disclosed the possibility of degraded voltage conditions existing on the Class lE buses even with normal grio voltages, due tc deficiencies in equipment between the grid and the Class lE buses or by the starting transients experienced during certain accident events not originally considered in the sizing of these circuits.
I
B.
BRANCH TECHNICAL POSIT 10]i 1.
In addition to the undervoltage scheme provided to detect loss of offsite power at the Class lE buses, a second level of undervoltage protection with time delay should also be provided to protect the Class lE equipment; this second level of undervoltage protection shall satisfy the following criteria:
a) The selection of undervoltage and time delay setpoints shall be determined from an analysis of the voltage requirements of the Class lE loads at all onsite system distribution levels; b) Two separate time delays shall be selected for the second level of undervoltage protection based on the following conditions:
- 1) The first time delay should be of a duration that establishes the existence of a sustained dr; graded voltage condition (i.e.,-
something longer than a motor starting transient). Following this delay, an alarm in the control room should alert the operator to the degraded condition. The subsequent occurrence i
of a safety injection actuation signal (SIAS) should innediately separate the Class lE distribution system from the offsite power system.
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- 2) The second time delay should be of a limited duration such that l
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the pemanently connected Class 1E loads will not be damaged.
Following this delay, if the operator has failed to restore adequate voltages, the Class 1E distribution system should be
3-automatically separated from the offsite power system.
Bases and justification must be provided in support of the actual delay chosen.
c) The voltage sensors shall be designed to satisfy the following applicable requirements de' rived from IEEE Std. 279-1971, "Criterie for Protection Systems for Nuclear Power Generating Stations":
- 1) Class lE equipment shall be utilized and shall be physically located at and electrically connected to the Class lE switchgear.
- 2) An independent scheme shall be provided for each division of the Class lE power system.
- 3) The undervoltage protection shall include coincidence logic on a per bus basis to preclude spurious trips of the offsite power j
source;
- 4) The voltage sensors shall automatically initiate the disconnection of offsite power sources whenever the voltaae set point and time delay limits. (cited in item 1.b.2 tbove) have been exceeded;
- 5) Capability for test and calibration du.-ing power operation shall be l
provided.
- 6) Annunciation must be provided in the control room for any bypasses incorporated in the design.
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4 d) The Technical Specifications shall include limiting conditior.s for operations, surveillance requirements, trip setpoints with zinimum and maximum limits, and allowable values for the second-level voltige protection sensors and associated time delay devices.
2.
The Class 1E bus load shedding scheme should automatically prevent shedding caring sequencing of the emergency loads to the bus. The load shedding feature should, however, be reinstated upon completion of the load sequencing action. The technical specifications must include a test requirement to demonstrate the operability of the automatic bypass and reinstatement features at least once per 18 months during shutdown.
In the event an adequate basis can be provided for retaining the load shed feature during the above transient conditions, the setpoint vulue in the Technical Specifications for the first level of undervoltage protection (loss of offsite power) must specify a value having maximum and minimum limits.
The basis for the setpoints and limits selected must be document?d.
3.
The voltage levels at the safety-related buses should be optimized for the maximum and minimum load conditions that are expected throughout the anticipa:ed range of voltage variations of the offsite power sources by appropriate adjustment of the voltage tap settings of the intervening trans formers. The tap settings selected should be based on an analysis
of the voltage at the terminals of the Class IE loads. The analyses performed to determine minimum operating voltages should typically consider maximum unit steady state and transient loads for events such as ; unit trip, loss of coolant accident, startup or shutdown; with the offsite power supply (grid) at minimum anticipated voltage and only the offsite source being considered available. Maximum voltages should be analyzed with the offsite power supply (grid) at maximum expected voltage concurrent with minimum unit loads (e.g. cold shutdown, refueling). A separate set of the above analyses should be performed for each available connection to the offsite power supply.
4.
The analytical techniques and assumptions used in the voltage analyses cited in item 3 above must be verified by actual measurement. The verification and test should be performed prior to initial full power reactor operation on all sources of offsite power by:
a) loading the station distribution buses, including all Class lE buses down to the 120/208 y level, to at least 30%;
b) recording the existing grid and Class lE bus voltages and bus loading down to the 120/208 volt level at steady state conditions and during the starting of both a large Class lE and non-Class lE motor (not concurrently);
Note: To minimize the number of instrumented locations, (recorders) during the motor starting transient tests, the bus voltages and loading need only be recorded on that string of buses which previously showed the lowest analyzed voltages ?.um item 3 abore.
c) using the analytical techniques and assumptions of the previous voltage analyses cited in item 3 above, and the measured existing grid voltage and bus loading conditions recorded during conduct of the test, calculate a new set of voltages for all the Class 1E buses down to the 120/'")8 volt level d) compare the analytically derived voltage values against the test results.
With good correlation between the analytical results and the test results, the test verification requirement will be met. That is, the validity of the mathematical model used in performance of the analyses of item 3 will have been established; therefore, the validity of the results of the analyses is also established.
In general the test results should not be more than 3% lower than the analytical results; however, the difference between the two when subtracted from the voltage levels determined in the original analyses should never be less than the Class lE equipment rated voltages.
l C.
REFERENCES l
1.
General Design Criterion 17 2.
IEEE Std. 279, " Criteria for Protection Systems for Nuclear Power Stations" 3.
Millstone Unit No. 2. Safety Evaluation Supporting Amendment No.16 to license No. DPR-65 4
NRC Summary of Meeting for Arkansas Nuclear One Inciden'. of September 16, 1978, dated February 9,1979.
B.CLC3dRE 2 EDUCATION AND PROFESSIONAL QUALIFICATIONS OF OM P. #40PRA
. Education DIPLO!!A -
Electrical Engineering,1963; Thaper Institute of Engineering and Technology, Patiala, India B.S. Electrical Engineering, 1967; Howard University, Washington, D.C.
Major:
Electrical Power Professional Qualifications I am a Reactor Systems Engineer (Electrical) assigned to the Power Systems Branch, Division of Systems Safety, Office of Nuclear Reactor Regulation.
In 4
this position, which I have held since February 1977, I am responsible for performing technical reviews, analyses and evaluations on electric power systems (onsite and offsite) that supply power to plant safety systems.
Prior to this assignment, from November 1974 to February 1977, I was assigned to the Electrical, Instrumentation and Control Systems Branch where I performed technical reviews of instrumentation, control and electrical systems of nuclear power stations.
From 1968-74 I was employed as a electrical engineer with Bechtel Power Corporation in Gaithersburg, Maryland where my responsibilities included design and engineering of nuclear power plants including auxiliary systems design, voltage drop and short circuit calculations, selection and setting of protective relays etc.
Design of electrical protection schemes, wiring details, circuit scheduling of generating stations, transmission and distribution lines, substations and their distribution systems.
Member Institute of Electronics and Electrical Engineers
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