ML18051A552
| ML18051A552 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 08/15/1983 |
| From: | CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | |
| Shared Package | |
| ML18051A543 | List: |
| References | |
| TASK-15-02, TASK-15-2, TASK-RR NUDOCS 8308230407 | |
| Download: ML18051A552 (15) | |
Text
ENCLOSURE 3 CONSUMERS POWER COMPANY PALISADES PLANT DOCKET 50-255 Palisades Plant Steam Generator/Auxiliary Feedwater Review August 15, 1983 14 Pages
--8308230407 830815
ENCLOSURE 3 PALISADES PLANT STEAM GENERATOR/AUXILIARY FEEDWATER REVIEW Three concerns exist with respect to adding Auxiliary Feedwater (AFW) to the steam generators given this proposed event (refer to Enclosure 2 for the event description). First, is the AFW system sufficiently reliable to assure water flow to the steam generators? Second, is it likely that the addition of this cold feedwater will cause failure of steam generator U-tubes due to thermal shock? Third, if the tube failures do not occur, will heat removal by AFW be significantly reduced by "steam binding" as the cold water contacts the hot steam generator? Each of these concerns is discussed in detail below.
- 1. The Auxiliary Feedwater System (AFWS) has undergone several modifications and will be further modified during the upcoming refueling outage scheduled for August to December 1983. Two figures are attached to illustrate these changes. Figure 1-1 shows the original system and Figure 1-2 shows the system as it will exist after the 1983 refueling outage. Changes between Figure 1-1 and Figure 1-2 are as follows:
a) The AFWS piping no longer joins the main feedwater piping outside the containment. AFW runs through its own 4-inch piping to each steam generator. It enters. the steam generator through a nozzle separated from the main feedwater nozzle by 30 inches. Inside the steam generator the AFWS has its own feed ring.
This change allows addition of AFW to a steam generator with a faulted main feedwater pipe.
b) A second motor-driven AFW pump (P8C) is being added. This pump will have separate discharge piping and flow control valves from the two existing pumps. This discharge piping will join that piping from the existing pumps just outside the containment penetration.
Suction is from a common source, but separate alternate supplies of Lake Michigan water are available. The original two pumps can be supplied via the fire system; the new pump via the service water system. The fire and service water systems are normally separate, but can be cross-connected.
The new pump, P8C, is powered by the 2.4 KV safeguards bus and diesel generator which are opposite to the bus and generator which serve the original motor-driven pump, P8A. Instrumentation power supplies for the two AFWS trains are separate DC supplies.
c) An automatic start for the AFW pumps has been added. Low level in either steam generator will start P8A. If P8A is not running AND supplying water to at least one steam generator in 15 seconds, P8C will auto start. (Similary, if P8C also fails to operate, the turbine NU090983A-NL01
driven pump, P8B will receive a start signal. This particular steam generator blowdown event, however, eliminates any steam supply.)
These changes significantly reduce the probability of total failure of the Auxiliary Feedwater System.
- 2) The FSAR Section 4.3.4 (Attachment 1 Pages 2 and 3) states that the steam generators are designed "such that no component will fail either by rupture or by developing deformations (elastic or plastic) that impair the function, performance, or integrity of the steam generator for further operation" when subjected to, among other transients, "eight cycles during which the primary side is at 2500 psia and 600°F while the secondary side is depressurized to atmospheric pressure" and "8 cycles of adding a maximum of 300 gpm of 70°F feedwater with the steam generator dry at 600°F."
While there are no analyses available for a two steam generator blowdown, the Steam Line Rupture Incident Analysis, Section 14.14 of the FSAR, shows PCS pressure and temperature, and steam generator pressure as functions of time (refer to Attachment 1 Pages 6, 7 and 8). With two steam generators blowing down, it can be assumed that the dryout would take somewhat longer while TAVE would drop approximately twice as much *
- Figure 14.14-4 (Attachment 1, Page 7) shows the failed steam generator "drying out" about 45 seconds into the accident. The first AFW pump should start five seconds after the steam generator level reaches the low level setpoint. If the first pump fails to start at that point, the second pump will start ten seconds later. Acceleration time for these pumps is less than five seconds. Assuming ten seconds for steam generator level to reach the low level alarm point, and assuming the first pump fails to start, the plant should still be adding AFW more than 20 seconds before the faulted steam generator goes dry. The other steam generator will empty more slowly due to blowing down through the entire main steam piping. It is, therefore not likely that AFW flow would be starting with a steam generator already dry.
FSAR Figures 14.14-3 and 5 (Attachment 1, Pages 6 and 8) show Tave to have cooled about 100 degrees to 475°F and PCS pressure reduced to 600 psia at the proposed time of AFW initiation. With two steam generators blowing down, the PCS would be significantly cooler and at a lower pressure. It should also be noted that AFW flow is initiated at 150 gpm; just half the design condition flow rate. Even if the operator delays the addition of AFW, due to the high initial cooldown rate, the referenced FSAR figures indicate PCS conditions stay far below the 600°F/2500 psia design condition even for a single steam generator blowdown. The thermal and hydraulic stresses on the steam generator tubes would thus be greatly reduced from the design condition of 600°F and 2500 psia *
- 3) The third concern, that of steam blanketing (or binding), is highly unlikely to be problem. This conclusion can be drawn when looking at a section view of a Palisades steam generator (see Figure 2).
NU090983A-NL01
If steam flow, caused by boiling a small portion of the AFW, is to carry the remainder of the AFW out of the break, it must take one of two paths from the tube sheet/tube bundle region to the break. The first path would be that of normal steam flow up through the tube bundle and through the steam separators, then either through the steam dryers and out a faulted main steam line or down around the outside of the separator deck and out a faulted main feedwater line. The second path would be back under the edge of the wrapper and up the outer annulus, then out through a faulted feed line or through the Chevron dryers and out a faulted main steam line.
The first flow path has separators and possibly dryers, capable of 6
reducing a steam flow of 5.86 x 10 lb/hr to less than 1/4% moisture.
Thus, there should be little carryover (carry out) with the AFW flow of 6
300 gpm (0.15 x 10 lb/hr). Significant AFW moisture carryout is unlikely even in the event that the separators and dryers structurally fail due to the velocity of the steam which is developed as an immediate result of the MSLB. The velocity of the steam that is developed by boiling of the incoming AFW is considered incapable of supporting agy significant AFW droplet size. Given the AFW flow rate of 0.15 x 10 2
lb/hr, a flow area of 288.5 ft near the entrance to the separator deck, a steam generator shell pressure of 20 psia and steam at saturated conditions, the resulting steam velocity is only about 2.9 ft/sec *
- 2 The second path has a free cross-sectional area of 80 ft mid-way up the conic section below the main feedwater ring. If all of the 300 gpm were to boil at a pressure as low as 20 psia, the velocity in this area would be about 10 ft/sec and would not support a very large droplet size. If the flow is out a failed steam line, the flow must still exit through the Chevron separators.
The ratio of free areas of path one to path two, at the middle elevation of the tube bundle, is greater than six to one. Most of the flow would therefore take path one where it will pass through the separators. Most of the feedwater added must then remain inside the generator where it must boil and remove heat.
NU090983A-NL01
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Enclosure 3 P.age l of 8 Attacbment 1 Palisades Plant Final Safety Analyses Report Extract
- 8 Pages STEAM GENERATOR The nuclear steam supply system utilizes two steam genera.tors, Figure 4-3, to transfer the heat generated in the reactor coolant system to the secondary system. The design para.meters for the steam genera.tors are given in Table 4-5 *
.*The steam generator is a vertical U-tube heat exchanger and is designed in accordance with ASME Boiler and Pressure Vessel Code,Section III, Class A. The steam generator operates with the primary coolant in the tube side and the secondary fluid in the shell side.
Primary coolant enters the steam generator through the inlet nozzle, flows through 3/4" OD U-tubes, and leaves through two outlet nozzles.
Vertical partition plates in the lower head separate the inlet and outlet plenums. The plenums a.re stainless steel clad, while the pri-mary side of the tube sheet is Ni-Cr-Fe clad. The vertical U-tubes are Ni-Cr-Fe alloy. The ex-plansion process is used for expanding the steam generator tubes in the tube sheet. The tube-to-tube sheet joint is welded on the primary side.
Feedwater enters the steam generator through the feed-water* nozzle where it is distributed via a feed-water distribution ring having bottom apertures which direct the flow through the downcomer. The downcomer is an annular passage formed by the inner surface of the steam generator shell and the cylindrical shell which encloses the vertical U-tubes.
Upon exit at the bottom of the downcomer, the secondary water is directed upward over the vertical U-tubes. Heat transfer from the primary side converts a portion of the l?econdary water into steam-Upon exiting from the verticai U-tube heat transfer surface, the r-v*
steam-water mixture enters the centrifugal type separators. These:::>
impart a centrifugal motion to the mixture and separate the water<-n particles from the steam. The water exits from the perforated co separator housing and combines with the feedwater. Final drying '0-£ the steam is accomplished by passage of the steam through the car~~
rugated plate dryers. The moisture content of the exiting steam is limited to a maximum of 0.2~ at design flow.
The power operated steam dump valves and steam bypass valve prevent opening of the safety valves following turbine and reactor trip from full power. The steam dump and bypass system is described in Section 9.
The steam generator shell is constructed of carbon steel. Manways and handholes are provided for easy access to the steam generator internals.
Overpressure protection for the shell side of the steam generators and the main steam line piping up to the inlet of the turbine stop valve is provided by twenty-four (24) safety valves. These valves 4-10
Page 2 of 8
~** are ASME Code spring loaded, open bonnet, safety valves and discharge to atmosphere. 'l'Welve safety valves are mounted on each of the main steam lines upstream of the steam line isolation valves but outside the containment. The valves are divided into three groups of four
- valves, each valve within a gr~up having the same nominal opening pressure, but with staggered group opening pressures consistent with ASME Code allowances. The valves can pass a steam flow equiv-alent to an NSSS power level of 2650 Mwt at the nominal 1000 psia set pressure. Parameters for the secondary safety valves are given in Table 4-4.
TABLE 4-4 SECONDARY SAFE!'Y VALVE PARAMB'I'ERS Design Pressure, Psia 1,000 0
Design Temperature, F 550 Fluid - Saturated Steam Capacity, Minimum per Valve, Lb/Hr 486,600 Total Capacity, Lb/Hr 11,678,400 Set Pressure Eight Valves, Four per Unit, Psia 1,025 Eight Valves, Four per Unit, Psia 1,005 Eight Valves, Four per Unit, Psia 985 Body Material ASTM 216, Gr WCB Trim Material Stainless Steel co The steam generators are mounted v~I1;ically on bearing plates tor-.;.,
allow horizontal motion parallel to the hot leg due to thermal CJ'1 expansion of the reactor coolant piping. Stops, are provided to iimit this motion in case of a coolant pipe rupture. The top of the unit is restrained from sudden lateral movement by energy absorbers mounted rigidly to the concrete shield.
In addition to the transients listed in S~ction 4.2.2 each steam generator is also designed for the following accident conditions such that no component will fail either by rupture or by developing deformations (elastic or plastic) that will impair the function, performance,- or integrity of the steam generator for further operation.
- 1. Eight cycles during which the primary side is at 2500 psia and 600° F while the secondary side is depressurized to atmospheric pressure.
4-11 Rev 4/10/69
Page 3 of 8
- 2. One cycle du~ing which the steam on the shell side is at 900 psia and 532 F while tube (primary) side is depressurized to atmospheric pressure.
2400 cycles of transient pressure differentials of 85 psi a.cross the primary head divider plate due to starting and stopping the primary coolant pumps.
- 4. 10 cy*cles of hydrostatic testing of the secondary side at 1250 psia.. '
- 5. 320 cycles of leak testing of the secondary side at 1000 psia.
- 6. 5,000 cycles of adding 425 gpm of 70° F feedwater with the plant in hot standby condition.
. 0 8 c;rcles of adding a maximum of 300 gpm of 70 F ~eedwater with the steam genera.tor secondary side dry and at 6oo F.
'nle unit is capable of withstanding these conditions for the pre-scribed numbers of cycles in addition to the prescribed operating conditions without exceeding the allowable cumulative usage factor as prescribed in ASME Code,Section III *
- 4-12
- Page 4 of 8 TABLE 4-5 STEAM GENERATOR PARAMETERS Number 2 Type Vertical U-Tube Number of Tubes 8,519 Tube Outside Diameter 0.750 Inch Quantity ~
Nozzles and Manways Primary Inlet Nozzle l 42 Inch ID Primary Outlet Nozzle 2 30 Inch ID Steam Nozzle l 34 Inch ID Feedwater Nozzle l 18 Inch Nominal Instrument Taps 9 1 Inch Nominal Primary Manways 2 16 Inch.ID Secondary Manways 2 16 Inch ID Secondary Ha.ndhole l 5-11/16 Inch ID Secondary Drain & Blowdown .*. l 2.Inch Nominal
- Surface Blowdown Spare Primary Side Design Design Pressure, Psia l
l l Inch Nominal 4 Inch Nominal Initial 2,500 Stretch 2,500 C)
~
co Design Temperature, °F 650 650 (_,,,
Design Thermal Power (NSSS), Mwt 2,212 2,650 co Cold Leg Temperature, °F 545 540.5 Hot Leg Temperature, °F 591 595 Coolant Flow Rate (Each), Lb/Hr 62.5 x 10 6 65.45 x 10?;-J Normal Operating Pressure, Psia 2,100 2,250 Secondary Side Design Design Pressure, Psia 1,000 1,000 Design Temperature, °F 550 550 Normal Operating Steam Pressure, Full Load, Psia 770 764
_ *Normal Operating Steam Temperature, Full Load, OF 514 514 Steam Moisture Content, Maximum, % 0.20 0.20 Blowdown Flow, Lb/Hr 2,000 2,000 Drying Capacity at 770 Psia, Maximum (Each),
Lb/Hr 5.86 x 10 6 5.86 x 10 6
Design Thermal Power (NSSS), Mwt 2,212 6 2,650 6 Steam Flow ( F.a.ch), Lb/Hr 4.701 x io 5.81 x 10 Feed-Water Temperature, °F 418 438 4-13 Rev 12/15/73
Page 5 of 8 TABLE 4-5 (Contd)
Dimensions Overall Height, Including Support Skirt 59 Feet - 2 Inches Upper Shell outside Diameter 20 Feet - 10 Inches lower Shell outside Diameter 13 Feet - 8 Inches Dry Weight 924,600 Lb Flooded Weight 1,496,000 Lb Operating Weight 1,109,000 Lb
- 4-14
Page 6 of 8
. STEAM LINE RUPTURE INCIDENT PRIMARY COOLANT TEMPERATURE VS TIME FULL LOAD INITIAL CONDITION 600 T
out 550 500 PRIMARY COOLANT TEMFERATURE,
°F. 450 400 Tavg = Average Core Coolant Temperature Tout = Core Outlet Temperature TSGl = Primary Coolant Temperature At Out-let Of Steam Generator With 350 Ruptured Stearn Line TSG 2 = Primary Coolant Temperature At Out-iet of Steam Generator Isolated From Rupture 0 120 160 200 TIME, SECONDS mcOMBUI~ iNOINHllNO, INC. FIG.
~ WiHDSOI.~ 14.14-3
Page 7 of 8 Boo
.STEAM LINE RUPTURE INCIDENT STEAM GENERATOR PRESSURE VS TIME 700 FULL LOAD INITIAL CONDITION 600 STEAM GENERATOR PRESSURE, PSIA 500 STEAM GENERATOR ISOLATED
. FROM RUPTURE 400 300 200 STEAM GENERATOR WITH RUPTURED LINE 100 0
0 40 80 120 160 200 TIME, SECONDS lfl1 COMDUSTION !NOINltRUHO, IMC. FIG.
~ . ~ COM<<naJT 14.14-4
Page 8 of 8 STEAM LINE RUPTURE INCIDENT PR!MARY COOLANT SYGTEM PRESSURE v:; 'l'lMr:
FULL LOAD INITIAL CONDITION 2500 2000 PRIMARY COOLANT PRESSURE, PSIA 1500 1000 C) 1'-.)
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500 co 20 100 120 140 160 180 200 TIME, SECONDS (rft COMIUSTION IHOINHllNO, INC. FIG.
~ WIHOSOI. COtMCTICUT 14.14-5