ML19326C501
| ML19326C501 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 05/16/1978 |
| From: | David Williams ARKANSAS POWER & LIGHT CO. |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| 1-058-7, 1-58-7, NUDOCS 8004230620 | |
| Download: ML19326C501 (9) | |
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1 IlEGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS) 50-313 DISTRIBUTION FOR INCOMING MATERIAL DOCDATE: 05/16/78 ORG: WILLIAMS D H REC: REID R W DATE RCVD: 05/23/78 AR PWR & LIGHT NRC COPIES RECEIVED DOCTYPE: LETTER NOTARIZED: NO LTR 1 ENCL 40 FORWARDING RESPONSE TO NRC POSITION AND REQUEST FOR ADDL
SUBJECT:
CONCERNING THE OVERPRESSURE PROTECTION SYSTEM OF NRC LTR DTD 11/07/77 FACILITY.
REVIEWER INITIAL:
XJM PLANT NAME: ARKANSAS - UNIT 1 DISTRIBUTOR INITI AL: (
i ocooo************ DISTRIBUTION OF THIS MATERI AL IS AS FOLLOWS **********+:*****
GENERAL DISTRIBUTION FOR AFTER ISSUANCE OF OPERATING LICENSE.
(DISTRIBUTION CODE AOO1)
FOR ACTION:
BR CHIEF REID**W/7 ENCL NRC PDR**W/ ENCL
[ EG FILE **W/ ENCL )
OELD**LTR ONLY INTERNAL:
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' HECK **W/ ENCL HANAUER**W/ ENCL SHAO**W/ ENCL EISENHUT**W/ ENCL BUTLER **W/ ENCL BAER**W/ ENCL J COLLINS **W/ ENCL EEB**ll/ ENCL J.
MCGOUGH**W/ ENCL EXTERNAL:
LPDR'S RUSSELLVILLE, AR**W/ ENCL TIC **W/ ENCL NSIC**W/ ENCL ACRS CAT B**W/16 ENCL
,IHIS DOCUMENT CONTAINS PA P00R QUAUTY PAGES CONTROL NBR:'-;;_f2^p25' DISTRIBUTION:
LTR 40 ENCL 39 1,
SIZE: 1P+5P+2P THE END oco********************************
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Qhhhb ARKANSAS POWER & LIGHT COMPANY POST OFFICE BOX 551 LITTLE ROCK. ARKANSAS 72203 (501) 371-4000 May 16, 1978
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Director of Nuclear Reactor Regulation 3-]
Attn:
Mr. R. W. Reid, Chief E,'j y
Cperating Reactor Branch #4 e
U.
S. Nuclear Regulatory Commission li c.;
Washington, D.
C.
20555
Subject:
Arkansas Nuclear One-Unit 1 Docket No.
50-313 License No.
DPR-51 Reactor Vessel Overpressurization (File:
1510, 1511.1)
Gentlemen:
In response to your November 7, 1977 letter concerning the overpressure protection system of Arkansas Nuclear One-Unit 1 (ANO-1), please find attached our responses with regard to your positions and requests for additional information.
It should be noted that these responses are contingent upon your approval of our proposed technical specification submittal dated December 3, 1976, concerning boration of the reactor coolant system (RCS).
It is the position of Arkansas Power & Light Company that the postulated operating events identified in your letter could not occur concurrently and therefore should not be considered credible in determining the limiting mass addition overpressure transient at ANO-1.
Therefore, it is our conclusion that the present ANO-1 design for overpressure protection of the RCS coupled with the proposed addition of alarms identified in this submittal will adequately accommodate all postulated overpressure transients at ANO-1.
Very truly y urs, W
Dan..el
. Williams
/ Manager, Licensing DHW/DGM/ew Attachments o\\
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MEMDER MIDDLE SOUTH UTIUTIES SYSTEM J
-w RESPONSE TO NRC POSI" IONS
'I.
NRC Position The ANO-1 proposed system maintains a gas blanket or bubble in the presurizer at all times, in conjunction with a single (PORV).
low pressure setpoint power-operated relief valve This design has certain advantages over other concepts because failure of an operator to manually enable the low pressure setpoint of the relief valve does not totally The staff defeat protection against a pressure transient.
has concluded that your proposed s; 4 tem adequately accommodates all postulated overpressure transients with the exception of an inadvertent initiatfon of safety injection by the high pressure inj ection (HPI) pump.
Based on your analyses we have identified HPI as the limiting mass addition overpressure transier.t.
Operation of the HPI pump, which is capable of delivering flow against full system operating pressure, is required whenever a reactor coolant pump is in operation.
Since the discharge of the HPI pump is isolated from the reactor coolant system by a failure single injection valve, a single error or equipment could open the injection valve and initiate a pressure If failure of the single increase in the primary sys' m.
low setpoint power operated alief valve is then assumed as the single failure following initiation of the event, your analysis shows that operator action is required with-in five minutes to maintain primary system pressure below J
This is not in accordance with NRC Appendix G limits.
criteria for operator action which prohibits operator inter-vention for ten minutes.
AP&L Response The following discussion will provide additional information in support of our position that inadvertent actuation of an HPI (makeup) pump under the assumptions and conditions identified in your staff position is not a credible event at ANO-1.
The ANO-1 design has three (3) makeup pumps, P-36 A, P-36B and P-36C as shown on FSAR Figure 9-3 (Also shown as MU-PlA, B and C on Figure 6-2).
Two (2) of these pumps are normally aligned to provide High Pressure Injection (HPI) should it be required, with one of the pumps providing makeup to the RC System as well as seal water to the RC Pumps.
During a plant cooldown the Engineered Safeguard Actuation of the HPI System is bypassed at 1650 psig.
Bypass of the ES signal to the HPI during cooldown will ensure against If this function spurious ES actuation of the HPI System.
is not performed by the operator, he will receive an alarm.
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'TPrior to-going below 280 P, the circuit breakern for the four Hil motor operated valves are' " locked out" in the closed position.
This is accomplished by opening and tagging the selector switch in the Control Room and locking and tagging the breakers located at the Motor Control Center.
The operator will recieve an alarm in the Control Room if the RC temperature drops below 280 F and any of the breakers to the four HP injection valves has not been " locked out".
-Between 280 F and 150 F, the Decay Heat Removal System is placed in operation, the remaining.RC pumps are shut down, and the operating makeup pump is shut down.
This transition period from the time the RC temperature drops below 280 F and the operating makeup pump is shut down is approximately 1-1/2 hours.
Procedural steps requiring the removal of equipment from operation or the locking out of pump and valve breakers, etc. must be performed in accordance with plant procedures.
These procedures require that an operator must obtain from the Shift Supervisor a clearance order prior to removing equipment from service or locking out breakers of pumps and valves.
Once the clearance order has been executed by the operator, the equipment will be tagged in accordance with procedures.
For electrical purposes, tags are placed on all open switches or contiol handles when these switches are not to be closed.
For mechanical
. purposes, a tagged device shall not be operated or moved from its tagged position.
In the case of locking out breakers or pumps and valves, tags are placed on both the control room control / selector switches and at the breaker location.
Once this equipment has been placed under these administrative restrictions, the status of this equipment l
cannot be changed until the Shift Supervisor issues the appropriate order allowing the change of status.
During the heatup of the RCS, the reverse of the operating steps described above takes place.
It is during this transition period of approximately 1-1/2 hours during a plant cooldown or heatup that the postulated RC overpressure event due to inadvertent HPI injection must occur.
In determining the-credibility of this over-pressure event, one must consider the sequence of operating events that must be assumed to occur during the transition period.
1.
One makeup pump must be in operation below 2800F.
As described above, the time in which a makeup pump is in operation when the RC temperature is below 280 F, (Minimum RC temperature for which the vessel can be fully pressurized) is approximately 1-1/2 hours during unit heatup or cooldown.
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Also, the lant is in this heatup or cooldown mode (<280 F) only a few times per year.
The length of this operating period and the low number of transition periods per year, greatly reduce the likelihood of an overpressure event during this mode of operation.
2.
High Pressure Injection valve must open.
Two events could cause the HPI valve to open:
a)
Operator error, and b)
Mechanical failure of the valve.
In order for the valve to open as a result of operator error when the RC temperature is below 280 F, the following events must occur:
a)
The breakers to the injection valves must be left racked in during cooldown.
b)
If the breakers were locked out during cool-down and an operator attempted to rack in the breakers while the RC temperature is below 280 F, he would have to ignore the red tags placed on the locked out breakers and rack in 4
the breakers without an appropriate clearance order from the Shift Supervisor, c)
In either a) or.b), the operators (2 in the Control Room) would receive the annuciator alarm indicating the breakers are not locked out on the HPI valves.
To allow the HPI valve to be opened, both operators would have to ignore this alarm.
d)
The operator must then open the valve which is against standing operating procedures during this mode of operation.
It is our opinion that more than a single operator error by more than one operator is required to cause an HPI valvg to be opened with the RC tempera-ture is below 280 F.
We feel that this is not a credible assumption for initiating an overpressure event at ANO-1.
With regards to mechanical failure of the HPI valve, we do not believe there is a credible failure which would cause the valve to open short of gross failure of the entire valve.
These valves would be in their normally closed position and the power removed.
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tima only ift (1) charging pumps are out of service and all HPI injection valves are closed and power removed, or (2) the vessel head is removed.
Regarding HPI testing, the staff will require that your procedures state that the HPI valve-be allowed to be cycled only if all HPI pumps are'out of service, or vessel temperature is above the minimum value for which the vessel can be ful.ly pressurized, or the reactor vessel head is removed.
We will require that your technical specifications identify the system enabling temperature and the PORV setpoint.
In addition, you should propose specifications related to sys*.em testing.
These maintenance and testing restrictions should be examined to assure compatibi?.ity with present technical specification requirements regarding the operability and periodic testing of ECC and emergency boration systems.
Also, since the impact of the proposed technical specifications will be considered by the staff in determining the acceptability of the proposed overpressure mitigating system, you should provide a thorough evaluation of the effect of these maintenance and testing requirements on the susceptibility of the reactor coolant system to a pressure transient.
AP&L Position Appropriate technical specifications are presently being developed and reviewed for compatibility with existing ANO-1 technical specifications.
We will require until July 1, 1978, for submittal of these technical specifica-tions in order to permit a thorough review by the Plant Safety Committee and the Safety Review Committee.
Please be advised that our timely submittal will be contingent upon your approval of our December 3, 1976 technical specification submittal.
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This would preclude spurious actuation of the These values are seismic and nuclear valve.
Class I and we have been unable to identify any mechanism that would cause total failure of these valves under these conditions.
fail to 3
The electromatic relief valve (PORV) must actuate following the initiating overpressure event (HPI actuation).
II.
NRC Position To assure proper alignment of the overpressure protection system during plant cooldown, an enabling alarm must be the system enabling switch and provided which monitors the position of the isolation valve upstream of the PORV.
AP&L Response AP&L will install the alarms requested in the above NRC Specifically, a circuit will be provided to position.
actuate an alarm if either of two conditions are not When the reactor coolant temperature falls satisfied.
(280 F), a signal monitor below a predetermined setpoint will close a contact to set up part of the alarm circuitry.
With this condition established, the alarm will be actuated if the isolation valve CV-1000 to the electromatic relief valve PSV-1000 is closed or if the key-operated switch for the lower setpoint on the electromatic relief valve is In addition to the above-requested alarms, not enabled.
AP&L plans to add an alarm on the circuit breaker for the four HPI valves, CV-1219, 1220, 1227, and 1228.
A circuit will be provided to actuate an alarm if any of the four (4)
HPI valve circuit breakers is not de-energized (locked out) and the reactor coolant temperature has fallen below a predetermined setpoint.
The detailed design work associated with these modifications will be completed the next scheduled refueling shutdown.
Installation of thes additional alarms will be completed prior to startup following this scheduled refueling outage.
III.
NRC Position The staff as identified severa'l concerns related to mainte-nance and HPI testing for the currently proposes system.
If the relief valve requires maintenance, the upstream isolation valve would need to be closed, thereby removing Therefore the staff the single relief valve from service.
will require technical specifications which stipulate that when the reactor vessel temperature is below the minimum e for which the vessel can be fully pressurized the valu PORV mayEbe removed from service for a short period of
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RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION Assumptions made regrarding steam bubble collapse.
I.
AP&L Response No assumptions have ever been made regarding steam bubble collapse as a steam bubble or nitrogen blanket is continually See our letter of November 15, 1976, to you maintained.
for further discussions regarding a steam bubble.
Verification of the number of HPI pumps assumed in operation II.
on Figure A-1 of AP&L March 24, 1977 letter.
AP&L Response The number of pumps assumed is one (1) pump as this is the only number needed for makeup.
(Actuation of another If this pump will be the result of an operator error. incredible event were t can be accommodated with the makeup flow control valve.
Failure of the flow control valve can be accommodated by the electromatic relief valve.)
Result of AP&L investigation into lowering shutdown pressurizer III.
level to less than 180".
AP&L Response From oui previous discussion, the addition of the aforementioned alarms necessitates no further consideration of this aspect of pressurizer operation.
Also, the existing alarms for pressurizer high level (see our November 15, 1976 letter to you) adds another degree of protection and conser-vatism.
Description of HPI test referred to in a response to IV.
Question No. 6, AP&L March 24, 1977 letter.
AP&L Response The HPI test procedure ensures that only one (1) HPI pump is tested at a time and that no other HPI pump is operating (i.e., if an HPI pump other than the one during the test to be tested is running, the running pump is shut down with its breaker racked out and the test pump is started).
Makeup flow is then increased until the sum of the makeup The flow plus total seal injection flow equals 100 gpm.
letdown flow is then adjusted to maintain pressurizer After the appropriate readings are taken, makeup level.
and letdown flows are returned to normal.
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V.
Discussion of probability of operator error with regard to HPI test (response to Question No. 6, AP&L March 24, 1977 letter).
AP&L Response As stated above, during HPI test plant procedures require that the breakers to pumps not being tested are racked out and only one pump is tested at a time.
The probability of operator action is not considered likely as two (2) operators are required to be in the Control Room during the HPI test.
Also, the injection valves are disabled la the closed position when the RC temperature is below 280 F and would require multiple operator errors to allow inadvertent opening of one of the valves as outlined in our response to Position I.
VI.
Description of administrative controls to assure HPI trains (pumps and/or valves) are " racked out" when required and are " racked in" only when autlorized and then only for specific, controlled purposes, such as startup or HPI test.
AP&L Response As discussed in response to Position I, procedural steps requiring the removal of equipment from operation or the locking out of pump and valve breakers, etc., must be per-formed in accordance with plant procedures.
These pro-cedures require that an operator must obtain from the Shift Supervisor a clearance order prior to removing equipment from service or locking out breakers of pumps and valves.
Once the clearance order has been executed by the operator, the equipment will be tagged in accordance with procedures.
For electrical purposes, tags are placed on all open switches or control handles when these switches are not to be closed.
For mechanical purposes, a tagged device shall not be operated or moved from its tagged 1
position.
In the case of locking out breakers of pumps and valves, tags are placed on both the control room control /
selection switches and at the breaker location.
Once this equipment has been placed under these administrative restrictions, the status of this equipment cannot be changed until the Shift Supervisor issues the appropriate order allowing the change of status.
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