ML20009E205
| ML20009E205 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 07/20/1981 |
| From: | Groce R Maine Yankee |
| To: | Clark R Office of Nuclear Reactor Regulation |
| References | |
| TASK-2.B.1, TASK-TM FMY-81-107, NUDOCS 8107270228 | |
| Download: ML20009E205 (13) | |
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9 1671 WORCESTER ROAD s
g ggjj ENGINEERING OFFICE FRAMINGHAM. M ASSACHUSETTS 017o1 617-872-8100 O
2.C.2.1 FMY 81-107 July 20, 1981 CD d)
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United States Nuclear P.egulatory Commission s
Washington, D. C.
20555 8
y Atten tion : Office of Nuclear Reactor Regulation ob\\
Division of Licensing Sb Or erating Reactors Branch #3
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Mr. Robert A. Clark, Chief S/
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References:
(a) License No. DPR-36 (Docket No. 50-309) i (b) USNRC Letter to MYAPC dated October 31, 1980
Dear Sir:
As reques ted in your letter, Reference (b), Maine Yankee has compiled a description of the Reactor Coolant System Vents, Item II.B.l.
This description is provided in Attachment A to this letter, and has been braken down to address each applicable section of clarification Item II.B.1.
We trus t this information is satisfactory; however, should you have a.ty questions, please do not hestitate to contact us.
Very truly yours, MAINE YANKEE ATOMIC POWER COMPANY
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w Robert I. Groce Senior Engineer - Licensing RHG/kab At tachmen t 7pool S
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8107270228 810720 PDR ADOCK 05000309 P
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ATTACIIMENT A II.B.1 REACTOR COOLANT SYSTEM VENTS Fosition (1) Submit a description of the design, location, size, and po'wer supply for the vent system along with results of analyses for loss-of-coolant
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accidents initiated by a break in the vent pipe. The results of the
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analyses should demonstrate compliance with the acceptance criteria of 10 CFR 50.46.
Response
A flow diagram for the reactor coolant system vent system (RCSVS) is attached as Sketch A.
The system adds the capability to vent the reactor vessel head and the pressurizer steam space.
Both eats tie into existing connections on the vessels. The reactor vent ties into the sensing line to thc core differential pressure transmitter which taps into the existing manual vent o,n the reactor head, while the pressurizer vent ties into the sample line-from the safety valve connections to the pressurizer. Both vent lines are isolable from the vessels by existing manual valves.
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The pressurizer vent line has been orificed at tha connection to the existing line. The orifice is sized co that a break in the vent pipe will result in a leak rate that is less than the makeup capacity of l
l one charging pump. Therefore, a break in the vent pipe is not l
l considered a loss-of-coolant accident (LOCA) and no new analyses are i
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required to demonstrate compliance with the acceptance criteria of 10 CFR 50.46.
The line that the reactor vent ties into is smaller than the definition of a LOCA, and therefore no additional orifici.g is required.
Each vent line contains two (2) motor operated valves (MOVs) in series, a vent valve and a blo k valve. Two valves in series are utilized to allow terminating the venting process in the event of a failure of one valve to close. The two vent paths are cross-connected after the first MOV. The reason for this will be covered below in the description of power supplies. The discharges r4 both vent valves are tied into piping to the quench tank. This will allow for thc collection of any leakage by the vent valves or any small discharges in the quench tank. Any large releases will be released to the containment atmosphere via the rupture disk in the tank.
The reactor vent valve and pressurizer block valve are powered from the same emergency motor control center (MCC). The pressurizer vent valve and the reactor block valve are powered from the other emergency MCC.
In case of a failure of one of these emergency power supplies, the RCSVS can still function with the two MOVs powered from the remaining emergency power supply utilizing the cross-connect piping.
(2) Submit procedures and supporting analysis for operator use of the vents that also include the information available to the operator for
-initiating or terminating vent usagt. -..
Rerponse 1
Procedures for the operation of the vents will be prepared prior to making the system operational. At that time, the procedures will be available for NRC review.
I Clarification A.
General (1) The important safety function enhanced by this venting capability is core cooling. For events beyond the present design basis, this venting capability will substantially increase the plant's ability to deal with large quantities of noncondensible gas which could interfere with core cooling.
Response
No response required.
(2) Procedures addressing the use of the reactor coolant system vents should define the conditions under which the vents should be used, as well as the conditions under w',1ch the vents should not be c;;J.
The procedures should be diTected toward achieving a substantial increase in the plant being able to maintain core cooling without loss of containment integrity for events beyond the design basis. The use of vents for accidents within the normal design basis must not result in a violation of the requirements of 10 CFR 50.44 or 10 CFR 50.56. _
Response
See response above to Position (2).
(3) The size of the reactor coolent vents is not a critical issue. The desired venting capability can be achieved with vents in a fairly broad spectrum of sizes. The criteria for sizing a vent can be developed in several ways. One approach, which may be considered, it to specify a volume of noncondensible gas to be vented and in a specific venting 5
time. For containments particularly vulnerable to failure from large hydrogen releases over a short period of time, the necessity and desirability for contained venting outside the containment must be considered (e.g., into a decay gas collection and storage system).
Response
The main criteria used for sizing the RCSVS was to incure that in the event of an inadvertent actuation, the leak rate was within the capabilitieg of the normal makeup system. Therefore, an inadvertent
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actuation of the vent syrtem would not constitute a LOCA.
Once this was accomplished, the vent rate for noncondensible gases was determined. Based on the volume of noncondensible gases generated from a 100% Zr-H O reaction, this system would vent these gases in 2
from one to two hours.
Based on this criteria, the sizing of the system was judged to be adequate for both concerns; LOCA and noncondensible gas vent rate.
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(4) Where practical, tha reactor coolant systcs vents should ba kept smaller than the size corresponding to the definition of LOCA (10 CFR 50, Appendix A).
This will minimize the challenges to the emergency core cooling system (ECCS). since th= insdvertent opening of a vent smaller than the LOCA definition would nov require ECCS actuation, although it may result in leakage beyond Technical Specification limits. On PWRs, the use of new or existing lines, whose smallest orifice is larger than the LOCA definition, will require a valve in series with a vent valve that can be closed from the control room to terminate the LOCA that would result if an open vent valve could not be reclosed.
Response
The reactor and pressurizer vent lines are orificed such that in the event of an inadvertent opening of the vent, the resulting leak rate will be within the makeup capacity of one charging pump. An inadvertent opening of a vent will not constitute a LOCA as defined in 10 CFR 50, Appendix A, and will not result in ECCS actuation.
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Each vent path contains a block valve to prevent a prolonged venting process due to a stuck open vent valve.
(5) A positive indication of valve position should be provided in the
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control room.
Response
Positive indication of valve position will be provided in the control room.
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(6) Tha reactor coolant vent system chall ba operable from tha control
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room.
Response
The RCSVS will be operable from the control room.
(7) Since the reactor. coolant system vent will be part of the reactor coolant system pressure boundary, all requirements for the reactor pressure boundary must be met, and, in addition, sufficient redundancy should be incorporated into the design to minimize the probability of an inadvertent actuation of the system. Administrative procedures J
may be a viable option to meet the single-failure criterion. For vents larger than the LOCA definition, an analysis is required to demonstrate compliance with 10 CFR 50.46.
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Response
1 The RCSVS meets the requirements for the reactor pressure boundary.
As mentioned above, the vent lines are orificed so that the vents are smaller than the LOCA definition of 10 CFR 50, Appendix A.
The
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probability of an inadvertent actuation of the system has been minimized by the following design features:
1.
Each vent path contains two MOVs in series, therefore requiring the inadvertent operation of two valves to actuate the system.
2.
Operation of the RCSYS will be administrative 1y controlled by the control. room supervisor.
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The control switches for the four valves will be key-locked switches with the keys controlled by the control room supervisor.
(8) The probability of a vent path failing to close, once opened, should be minimized; this is a new requirement. Each vent must have its power supplied from an emergency bus. A single failure within the power and control aspects of the reactor coolant vent system should not prevent isolation of the entire vent system when required. On BWRs,
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block valves are not required in lines with safety valves that are used for venting.
Response
Each vent path contains two MOVs in series. Therefore, when it is desired to terminate venting from a vent path, only one of the two valves must function to terminate venting.
The two valves in each vent path are powered from different emergency power supplies, and do not utilize any common components. Also, separation of components has been maintained wherever possible.
Therefore, a single failure within the power and control aspects of the RCSVS will not prevent isolation of the system when required.
(9) Vent paths from the primary system to within containment should go to those areas that provide good mixing with containment air.
Response
For releases within containment, the area being released to will provide good mixing with the containment air.
(10) The r0 actor coolant vent system (i.e., vent valves, block valves, position indication devices, cable terminatio.ts, and piping) shall be seismically and environmentally qualified in accordance with IEEE 344-1975, as supplemented by Regulatory Guide 1.100, 1.92 and SEP 3.92, 3.43, and 3.10.
Environmental qualifications are in accordance with the May 23, 1980, Commission Order and Memorandum (CLI-80-21).
Response
The RCSVS piping is seismically supported. All equipment was purchased with both seiss!c and environmental qualifications as available.
Installation of vital electrical equipment was based on installation procedures established during plant constructiot.
(11) Provisions to test for operability of the reactor coolant vent system should be a part of the design. Testing should be performed in accordance with subsection IWV of Section XI of the ASME Code for Category B valves.
Response
The design will incorporate provisions for testing in accordance with subsection IWV of Section XI of the ASME Code for Category B valves.
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(12) It is important that the displays and controls added to the control room as a result of this requirement not increase the potential for operator error. A human-factor analysis should be performed taking into consideration: d
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(a) the use of this information by an operator during both normal and abnormal plant conditions, (b) integration into emergency procedures, (c) integration into operator training, and (d) other alarms during emergency and need for prioritization of
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alarms.
Response
This design adds control switches with position indicating lights on the main control board. The section of the control board chosen for the location of this equipment as chosen for two reasons:
1.
the indications needed for venting are in close proximity, 2.
the section of the control board presently requires only infrequent operator actions.
The other concerns mentioned will be considered during procedure preparation and operator training.
B.
BWR Design Considerations c
Not applicable.
C.
PWR Vent Design Considerations (1) Each PWR licensee should provide the capability to vent the reactor vessel head. The reactor vessel hecd vent should be capable of venting noncondensible gas from the reactor vessel hot legs (to the elevation.
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of the top of the outlet nozzle) and cold legs (through head jets and other leakage paths).
Response
The capability to vent the reactor vessel head is provided. This vent is capable of venting noncondensible gases from the reactor vessel
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hot legs and cold legs.
--c (2) Additional venting capability is required for those portions of each hot leg that cannot be vented through the reactor vessel head vent or pressurizer. It is impractical to vent each of the many thousands of tubes in a U-tube steam generator; however, the staff believes that a procedure can be develcped that assures sufficient liquid, or steam can enter the U-tube region so that decay heat can be effectively removed from the RCS.
Such operating procedures should incorporate this consideration.
Response
c The required procedure will be prepared prior to making the syste-operational. At that time, this procedure will be available for 4RC review.
c (3) Venting of the pressurizer is required to assure its availability for system pressure and volume control. These are important considerations, especially during natural circulation.
Response
The capability to vent the pressurizer is included in the RCSVS to,
meet this concern.
Additional Documentation Supporting information including logic diagrams, electrical schematics, piping and instrumentation diagrams, test procedures, and Technical Specifications.
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Response
The need for Technical Specification changes is being evaluated, however, at this time, no changes are anticipated.
Information, in support of this design change, will be available at the plant for NRC review.
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