ML20030B930
| ML20030B930 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 08/21/1981 |
| From: | Randazza J Maine Yankee |
| To: | Clark R Office of Nuclear Reactor Regulation |
| References | |
| FMY-81-121, NUDOCS 8108250209 | |
| Download: ML20030B930 (10) | |
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T United States toclear Regulatory Commission S '1 gc p W -
Washington, D.C.
20555 gG Attention: Office of tbclear Reactor Regulation Division of Licensing 4
Operating Branch #3 N
Mr. Robert A. Clark, Chief
Reference:
(a) License tb. DFR-36 (Docket tb. 50-309)
(b) UStRC Letter to MYAPC, dated April 30, 1981.
(c) MYAPC Letter WMY79-138 to USNRC, dated November 20, 1979 (d) MYAPC Letter FMY81-67 to USNRC, dated April 28, 1981
Subject:
Maine Yankee Auxiliary Feedwater System Design
Dear Sir:
Reference (b) forwarded Amendment No. 55 to Reference (a) and requested additional 3nformation to assist in completion of the enclosed Safety Evaluation Report.
Please find herein Maine Yankee's responses to the requested information numbered to coincide with the numbering in Reference (b).
We trust this information is satisfactory. Should you have any further questions, please feel free to contact us.
Very truly yours, MAINE YAtKEE ATOMIC POWER COMPAt4Y hD bO John B. Randazza OO 09 P
PDR Vice President, Operations
,ER/plb 9
U Enclosure 6\\\\
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1 1.
Short Term Recommendation - 2 STAFF POSITION t
The licensee did not submit sufficient information for the staff to conclude that all failures will result in opening the pneumatic-operated l
AFW flow control valves. We conclude that the licensee should establish suitable emergency procedures for operation of the pneumatic-operated valves in the event that valves were to fail closed due to an unanticipated failure mode of the common AC bus.
RESPONSE
Maine Yankee Emergency procedures include direction for manual control of l
feedwater regulating valves if necessary.
Improvements to the emergency procedures to include action to compensate for multiple failures, and operator errors of orr.ission and commission are ongoing in response to NtREG-0737 Item I.C.1.
Maintenance of necessary Steam Generator feedwater flow will be included in these improved procedures.
2.
Additional Short-Term Recommendation - 1 The licensee has not met our recommendation for redundant level indicators and low level alarms on the primary water source to alert the operator 20 minutes prior to loss of water to the suction side of the AFW pumps.
RESPONSE
In our letter, Reference (c), Maine Yankee indicated that the control board has a level indicator, a low level alarm (approximately 100,000 gal.) and a low-low level alarm (approximately 10,000 gal.). Based upon the information available to the operator from these alarms, we believe a redundant alarm is unnecessary.
In addition, by procedure, the auxiliary J
operator records the level of the Primary Water Storage Tank (PWST) twice i
per shift. Upon receipt of the low-low level alarm the operator has sufficient time to valve in the Demineralized Water Storage Tank (DWST).
Before any action will be considered by Maine Yankee, we request a written technical justification of the bases for the staff's belief that redundant level indicators and low level alarms are necessary, given the information provided above.
5.
Long Term Recommendation GL-2 STAFF FOSITION The licensee has not provided adequate assurt.nce that the single, locked open valve in the line to the primary water source cannot fail closed.
More positive steps to eliminate this concern are required.
RESPONSE
Testing in accordance with Maine Yankee Technical Specification #4.6.B verifies the adequacy of flow through the single locked open valve in the line to the primary water source on a monthly basis. Maine Yankee considers that this test provides adequate assurance that this water source will be available when called upon.
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6.
Long Term Recommendation - 48 The licensee has not submitted sufficient information to conclude that the licensee's instrumentation meets the requirements of NUREG-0578, 2.1.7b.
RESPONSE
1 The long-term recommendation - Ab requires the isolation of the auxiliary l
feedwater flow path to the affected steam generator in the event of a steam or feedwater line break.
The auxiliary feedwater system design changes presently being implemented at Maine Yankee to automatically detect, isolate the break, and direct flow to the intact steam generators before they boil dry are described in our Reference (d). We plan no further action on this item until after the NRC response to our letter.
)
7.
Recommendation (Enclosure 2)
The licensee has not provided a response to Enclosure 2 of our October 18, 1979 letter concerning a request for informatian regarding the design basis for AFW system flow requirements -
RESPONSE
l See Attachment A to this letter.
i 8.
tew Requirements STAFF POSITION Luring the review we became aware of the fact that the licensee had not I
been required to respond to two generic recommendations regarding the turbine driven AFh pumps:
GS-5 which requires the licensee' design to provide required system flow without AC dependency and GL-3 which requires the licensee's design to provide required system flow automatically without AC dependency and to sustain that flow for two hours.
RESPONSE
Generic recommendation GS-5 requires the licensee's design to provide required system flow without AC dependency. The Maine Yankee AFW design incorporates two,100%, automatic starting, motor driven pumps. Each of l
these pumps receives its power from a separate, independent, diesel generator backed, safeguards power supply. Either of these two pump / power supply combinations is capable of providing required system flow without external AC dependency. Maine Yankee considers this degree of redundancy, which is acceptable for ECCS equipment, to be acceptable for the AFW System.
However, in addition to the above, the Maine Yankee AFW System also includes a turbine driven AFW Pump that provides required flow without AC power dependency.
Cooling water for Turbine bearings and lube oil is provided by a tap off the pump discharge and is therefore independent of all AC power sources.
The air operated governor for this pump has an independent air receiver which provides four hours of reserve control air.
The solonoid operated valves in the steam supply to the AFW pump T
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f turbine are powered from the vital AC bus which is backed up by the station battery through inverters or directly from the station battery.
Generic recommerdation GL-3 requires:
"At least one AFW system pump and its associated flow path and l
essential instrumentation should automatically initiate AFW system flow and be capable of being operated independently of any AC power source for at least two hours. Conversion of DC j
power to AC power is acceptable."
)
As discussed above the turbine driven AFW pump and its associated flow path is capable of being operated independently of any AC power source for l
at least two hours. To provide this capability automatically under all j
potential power failures would require that the containment isolation j
valves in the steam supply line fail open on a loss of power. Maine Yankee considers the immediate need for containment isolation, when required, to be a more significant safety consideration than the perceived need to automatically start the turbine driven auxiliary feed pump.
The.
I isolation valve installed isolates both the turbine which discharges directly to the environment and the atmospheric decay heat release valve.
I As discussed in Attachment A, for a station blackout, at least 30 minutes are available for the operator to start the steam driven AFW Pump.
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Attachment A to NRC Letter to MYAPCO, October 18, 1979 Basis For Auxiliary Feedwater System Flow Requirements As a result of recent staff reviews of operating plant auxiliary feedwater systems (AFWS), the staff concludes that the design bases and criteria provided by licensees for establishing AFWS requirements for flow to the steam generator (s) to assure adequate removal of reactor decay heat are not well defined or documented.
We require that you provAde the following AFWS flow design basis information as applicable to the design basis transients and accident conditions for your plant.
1.
a.
Identify the plant transient and accident conditions considered in establishing AFWS flow requirements, including the following events:
- 1) Loss of Main Feed (LMFW)
- 2) LMFW w/ loss of offsite AC power
- 3) LMFW w/ loss of offsite and onsite AC power
- 4) Plant cooldown
- 5) Turbine trip with and without bypass
- 6) Main steam isolation valve closure
- 7) Main feed line break
- 8) Main steam line break
- 9) Small break LOCA
- 10) Other transient or accident conditions not listed above.
b.
Describe the plant protection acceptance criteria and corresponding technical bases used for each initiating event identified above.
1he acceptance criteria should address plant limits such as:
-Maximum RCS pressure (PORV o. safety valve actuation)
-Fuel temperature or damage limits (DM3, PCT, maximum fuel central temperature.
-RCS cooling rate limit to avoid excessife coolant shrinkage
-Minimum steam generator level to assure sufficient steam generator heat transfer surface to remove decay heat and/or cooldown the primary system.
2.
Describe the analyses and assumptions and corresponding technical justification used with plant conditions considered in 1.a. above including:
a.
Maximum reactor power (including instrument error allowance) at the time of the initiating transient or accident.
b.
Time delay from initiating event to reactor trip.
c.
Plant parameter (s) which initiates AFWS flow and time delay between initiating event and introduction of AFWS flow into steam generator (s),
d.
Minimum steam generator water level when initiating event occurs, e.
Initial steam generator water inventory and depletion rate before and after AFWS flow commences - identify reactor decay heat rate used, f.
Maximum pressure at which steam is released from steam generator (s) and against which the AFW pump must develop sufficient head.
m
4 g.
Minimum number of steam generators that must receive AFW flow, e.g.,1 of 2, 2 of 47 h.
RC flow condition-continued operation of RC pumps or natural circulation.
1.
Maximum AFW inlet te" ature.
J. Following a postulat.
steam or feed line break, time delay assumed to isolate break and direct ^FW flow to intact steam generator (s). AFW pump flow capacity allowance to accomodate the time delay and maintain minimum steam cer' 'stor water level. Also identify credit taken for primary systet tac removal due to blowdown.
k.
Volume and maximum temperature of water in main feed lines between steam generator (s) and AFWS connection to main feed line.
i 1.
Operating condition of steam generator normal blowdown following
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initiating event.
m.
Primary and secondary system water and metal sensible heat used for cooldown and AFW flow sizing.
n.
Time at hot standby and time to cooldown RCS to RHR (or SCS) system cut in temperature to size AFW water source inventory.
3.
Verify that the AFW pumps in your plant will supply the necessary flow to the steam generator (s) as determined by items 1 and 2 above considering a single failure.
Identify the margin in sizing the pump flow to allow for pump recirculation flow, seal leakage and pump wear.
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Attachment A Auxiliary Feedwater Flow Design Bases The primary event considered in the sizing of the Auxiliary Feedwater System (AFWS) flow requirements is the Loss of Main Feedwater (LMFW) transient. The reference safety analysis of this event is contained in references 1, 2 and 3.
Without auxiliary feedwater addition the minimum time to steam generators dryout is 13 minutes.
This assumes an initial power level of 1.02 times the rated thermal power of 2630 MWth and decay heat equal to 1.2 times the ANS standard values for end of cycle core conditions. Coincident loss of offsite AC power extends this dryout time to approximately 30 minutes.
As currently configured, the AFWS would receive an automatic start signal from a low steam generator level signal approximately 30 seconds after initiation of the LMFW. The two electrically driven AFWS pumps start automatically following a fie minute delay time. Modifications to the AFWS are underway which will remo,e the 5 minute time delay from the circuit for LMFW events, in which case the AFW pumps will start immediately upon receipt of the low SG level signal (see reference 5).
The maximum Steam Generator (SG) pressure against which the AFW pumps must develop sufficient head occurs for the coincident loss of offsite AC power and is equal to the setpoint. cf the lowest bank of SG safety valves (1000 psia or 2333 ft of water @ 12(PF). Against this pressure each AFW pump can deliver at least 590 gpm. A single pump, can deliver sufficient flow to remove the combinatien of non-nuclear heat a Q tion (13.9 MWth) from the reactor coolant pumps and core decay heat seven miautes after the initiation of the LMFW.
The volume of main feedwater piping downstream of the AFWS piping " tee" junction is approximately 15 ft3 per Steam Generator. Assuming a single AP.
pump feeding all three Steam Generator's this volume would be displaced !.
less than 40 seconds after AFW flow initiation. Maximum expected main feedwater temperature during operation at 2630 MWth is approximately 4450F.
l Steam Generator normal blowdown was assumed to remain in its pre-event conditon during the LMFW (see reference 3) however, no credit as taken for primary system heat removal due to this blowdown flow.
Technical Specification 3.8, Reactor Core Eneroy Remr"'
_: quires a minimum inventory of over 100,000 gallons of prima. gr, water to be available for a steam generator to be considered opt,Rhlt..se decay heat removal.
This inventory is sufficient for an event iniH ted from full power i
to remove reactor coolant pump and decay heat for at least 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> for decay heat alone.
This event is considered bounding with respect to AFWS flow requirements for the Maine Yankee design basis events listed in Table 1 (station blackout and main feedline break are not included in the MY design basis). Analysis assumptions and plant protection acceptance criteria for these events are listed in the referenced safety analysis contained in references 1, 2 and 3. i
Per reference 4, partial level (approximately 1/3 of tube bundle height) in a single steam generator provides sufficient heat transfer area to support decay heat removal via natural circulation.
For a station blackout, at least 30 minutes are available for the operator to start the steam driven AFW pump before the level in the Steam Generator's drop too low to support natural circulation within the RCS.
Against the maximum expected SG pressure (1000 psia) the steam driven AFW pump can deliver 630 gpm. Steam generation due to decay heat removal alone is sufficient to continuously run the steam driven AFW pump for a minimum of 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />, after j
which intermittent operation of the pump should be possible.
Following a postulated feedline break, operator action as credited with isolating AFW from the break and directing it to intact Steam Generators 10 minutes after event initiation.
Auxiliary feedwater flow from a single AFW pump is sufficient to restore Steam Generator water levels above that required to remove decay heat and or cooldown the primary system.
Following a postulated steamline brea<, auxiliary feedwater flow will start after the 5 minute timer delay. All flow will be to the faulted Steam Generator until operator action at 10 minute switches flow to the intact Steam Generators.
Installation of an AFW isolation system is underway (see i
reference 5) which will automatically isolate AFW flow from a faulted Steam Generator.
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Table 1
- 1) Loss of Main Feedwater (LMFW)
- 2) LMFW w/ loss of offsite AC Power
- 3) Turbine Trip with and without bypass
- 4) Main Steam Isolation valve closure
- 5) Main Steam Line Break
- 6) Small break LOCA i
References 1.
YAEC-ll32, Justification for 2630 MWt Operation of the Maine Yankee Atomic Power Station, P. A. Bergeron et.al., July 1977.
2.
YAEC-ll48, Justification for Operation of the Maine Yankee Atomic Power Station with a Positive Moderator Temperature Coefficient, P. J. Guimond and P. A. Bergeron, April 1978.
3.
YAEC-1259, Cycle 6 Core Performance Analysis, A. S. DiGiovine et.al.,
April 1981.
CEN-128, Volume 1, Response of Combustion Engineering Nuclear Steam Supply 4.
System to Transients and Accidents, Appendix A, Emergency Procedure Guidelines, April 1980.
5.
MYAPC letter to U5NRC, FMY 81-67, Feedwater and Auxiliary Feedwater Modifications, April 28, 1981.
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