05000285/LER-1992-016, Revises Commitment to AEC Safety Guide 1 (Reg Guide 1.1), Contained in Section 6.2 of Updated Sar.Commitment Covers Method of Calculating Available Net Positive Suction Head for Containment Spray Sys Per LER 92-016

Revises Commitment to AEC Safety Guide 1 (Reg Guide 1.1), Contained in Section 6.2 of Updated Sar.Commitment Covers Method of Calculating Available Net Positive Suction Head for Containment Spray Sys Per LER 92-016

ML20118B259
Person / Time
Site:	Fort Calhoun
Issue date:	09/18/1992
From:	Gates W OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RTR-REGGD-01.001, RTR-REGGD-1.001 LIC-92-291R, NUDOCS 9210020018
Download: ML20118B259 (18)

LER-2092-016, Revises Commitment to AEC Safety Guide 1 (Reg Guide 1.1), Contained in Section 6.2 of Updated Sar.Commitment Covers Method of Calculating Available Net Positive Suction Head for Containment Spray Sys Per LER 92-016

Event date:
Report date:
2852092016R00 - NRC Website

text

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Omaha Public Power District -

444 South 16th Street Mall Omaha. Nebraska 68102-2247 402/636 2000 September 18, 1992 llc-92-291R U. S. Nuclear Regulatory Commission AT1N: Document Control Desk Mail Station Pl-137 Washington, DC 20555

Reference:

1. Docket 50-285

2. Letter from OPPD (W. G. Gates) to NRC (Document Control Desk) dated May 18, 1992 (LIC-92-135L)

Gentlemen:

SUBJECT:

Change in Commitment to AEC Safety Guida 1 (Regulatory Guide 1.1)

Omaha Public Power District (OPPD) is revising a commitment tr iEC Safety Guide 1 contained Analysis in Section Report 6.2This (USAR). of the fort Calhoun changes the method Stationof(FCs)he calculating available t NetUpdated Safety Positive Suction Head (NPSH) for the Containment Spray system during the recirculation mode of operation. OPPD committed to this action in Licensee Event Report LER 92-016 (Reference 2), which reported the potential for inadequate NPSH fo(r th)e FCS Containment Spray system during the recirculation mode of operation.

This issue was discussed between Mr. R. W. Short of my staff and the NRC prior to fort Calhoun returning to power operation following the 1992 refueling outage.

The attachment contains the approved revision and marked-up page changes to USAR Section 6.2. This revision will be included in the next USAR update as required by '.0 CfR 50.71(c). Details supporting this revision are noted below.

IDUlliflMI.10!N 0f CHMiGI AEC Safety Guide 1, Regulatory Position C, states that " Emergency core cooling and containment heat removal systems should be designed so that adequate net positive suction head (NPSH) is provided to system pumps assuming maximum expected temperatures of pumped fluids and no increase in containment pressure from that present prior to postulated loss of coolant accidents." OPPD has been committed to this Safety Guide position in USAR Section 6.2.

OPPD has completed a 10 CfR 50.59 evaluation supporting revision of Section 6.2 of the USAR to reflect taking credit for a portion of the suction head provided by containment sump water subcooling during the recirculation mode of operation.

This subcooling is due to temperatures less than the saturation temperature as calculated in the FCS containment transient analysis. The new NPSH calculation conservatively credits only 25 percent of the minimum available sump water subcooling. Since use of the new NPSli analysis is contrary to the above noted position in AEC Safety Guide 1, OPPD is revising the commitment to this position, 9210020010 920918 DR ADOCK ODOO 5

.5 sm ~--

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recynentghgpirtunity i-Gs

U. S. Nisclear Regulatory Commission LIC-92-291R Page 2 REASON FOR CHANGl During OPPD's Design Basis Reconstitution of the Containment Spray (*,5) system, it was discovered that an as-built hydraulic analysis of the CS system was not available. As art of the resolution of the Design Basis Document open item, a hydraulic inal sis of the CS system was performed. The analysis revealed that using the NPSH alculation criteria of AEC Safety Guide 1 (R99ulatory Guide 1.1, the CS pumps would deliver higher flow rates than previously analyzed and as)a result would not have adequate suction head during the recirculation phase of operation for all postulated accidents. in LER 92-016, OPPD reported this condition and committed to revise USAR Section 6.2.1 to reflect a change in the method of calculating the available NPSH.

BASIS FOR CONCLUSION-2 ABB Combustion Engineering evaluated the NPSH reqcired (NPSH,) against NPSH available (NPSH under various operating modes to determine the scenario with the highest NPSU) and the -lowest NPSH,. , Using the previous values contained in USAR Section 6.2 for sump water elevation, frict'> , losses and the revised calculated flow, a deficit of approximately 4 feet existed octween the NPSH, and i NPSH,.

Based on the FCS containment transient analysis, the amount of subcooling available at the time of recirculation actuation would be 90 feet of head. As ,

containment pressure continued to decrease the - amount of subcooling would decrease; however, the water in the sump would continue to cool since the heat load due to containment temperature and decay heat load would be decreasing. The minimum amount of subcooling calculated to be available would be 35.95 feet of head.

As stated in Safety Guide 1, the basis for not depending on the increase in pressure within containment is to ensure that too low an internal pressure,  ;

resulting from impaired containment integrity, or oaeration of tht containment heat removal system at too high a rate would not sign' ficantly affect the ability of the system to accomplish its safety function.

The previous USAR Section 6.2, which did not credit subcooling, is based on a aump flow of 2000 gpm. The analysis performed to address the Desion Basis

)ocument open item has calculated the maximum NPSH, with the minimum NFSH, at a flow rate of 3100 gpm. Since the maximum flows were calculated, the potential of operating the CS system at too high a rate as discussed'in Safety Guide 1 is -

not a- concern. The analysis conservatively credits only 25 percent of the minimum NPSH available from subcooling, thereby maintaining a 75 percent margin.

Therefore, adequate ,nargin existr to ensure that no deliberate continuation of a high containment pressure would be required-to maintain adequate pump NPSH.

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4 U. S. Auclear Regulatory Consission LIC-92-291R Page 3 CONCLUSION 1he plant-specific analysis noted above credits 25 percent of the minimum NPSH available from sump subcooling. OPPD has concluded through a 10 CFR 50.59

, evaluation that, using this analysis, the required NPSH for the Containment Spray l system would be maintained during the recirculation mode of operation and an  :

unreviewed safety question is not involved. However, use of this analysis is l contrary to a previous connitment to AEC Safety Guide I contained in USAR Section 6.2. OPPD has therefore rescinded this commitment.

If you should have any questions, please contact me, ,

Sincerely,

//A>M MG W. G. Gates Division Manager Nuclear Operations WGG/brh Attachment c: LeBoouf, 1amb, Leiby & MacRae J. L. Milhoan, NRC Regional Administrator, Region IV R. P. Hullikin, NRC Senior Resident inspector S. D. Bloom, NRC Acting Project Manager I

~

U. S. Nuclear Regulatory Commission LIC-92-291R Attachment l

l 8

MARKED-UP USAR REVISION

e l 'I % dti, ear Regulatory Commission W 291R S tachment NRSH-requirement +-for--the4CCS-oumps-were-4n-eompl4ance-with the des 49n er44er44-se t-4er t h-in-Sa fety-Gu4 d e-# 1-and-Des 441n-Gr44 erl+-35-and-38-as shown-and-ex plained-4 n-the-ealcula t4ons-g iven-belowr Adequate NPSH is available in the redundant ECCS injection and containment spray systems asE shown"and E explained 11n . the : calculations 1 given belows NPSH calcula t4en s-da-no t-t a ke-<redit-for-su bcoo14 n(f-4 n--4 he-con teinment du r4g-t4>e-rec 4rc ulat4on-mode-of-opera t4 onM he-MP SH-<aleula t4ons-are as-fe Hows +

1. Safety injection During the safety injection operating mode, the HPSI, LPSI, and the containment spray pumps receive suction from the safety injection refueling water tank. The available NPSH for the HPSI, LPSI and containment spray pumps during safety injection was evaluated as follows:

NPSH (available) = f P+Pa _P n) 2.31 + Z h, sp. gravity P- pressure on liquid in SIRW tank or sump Pa - atmospheric pressure (psia)

Pvp - vapor pressure of liquid at specific temperature T (psia)

Z- vertical distance from liquid surface to centerline of pump suction (ft) h- water icvel above baseline elevation of SIRWT (ft) h, - max. friction losses in suction lines (ft)

A. LPSI Pumps Required NPSH of LPSI pumps (2400 gpm/ pump) - 20 ft.

Centerlinc suction nozzle elevation - 973.25 ft.

Minimum water level elevation in SIRWT - 989 ft. l P (psig) = 0.0 Pa (psia) - 14.7 Pvp 9100*F (psia) - .95 Z (ft) - 15.75 h, maximum (ft) = 6.3 Minimum HPSH (available) - (0+14.7 95) (2.31)+(15.75-6.3)- 41.21 ft.

1.0-6.2-2 R1 08/92

, U. S. Nuclear Regulatory Commission LIC-92 291R Attachment Since the maximum available NPSH of 41.51 ft. is above the required NPSH of '

11.0 f t. , adequate NPSH is alwa safety injection operating mode.ys available to the HPSI pumps during the and containment Summarizing spray pumps, the it is above NPSH concluded that evaluations adequate NPSH for thewill HPSI, always LPSI, be available for the emergency core cooling systems and the containment spray pumps.

II. Recirculation A. Containment Spray Pumps Required NPSH of containment spray pumps - 46,8 26. 0 f t .

(2000 3100 gpm/ pump)

True center'ine suction elevation - 973.25 ft. j Minimum water level elevation inside containment - 996.8 ft.

Subcooling P (ps4a ft) - Pvp* 8.99*

1. vpdps4a) -pt Z (ft) - 23.55 h, maximum (ft) -

2 c74 3 '_8.7..

Minimum NPSH (avallable) - 42MS-2,-76)- --20J9-f4, *

(23.554.8~.99:3!87) V 28.67lft.:

Since the suction pressure NPSH is above the required NPSH of the CS pumps, adequate NPSH will always be available during recirculation.

B. LPSI Pumps Note' that the LPSI pumps are not required for recirculation, and they will be secured upon receipt of the recirculation actuation signal.

C. HPSI Pumps NPSH required for HPSI pumps (400 gpm/ pump) - 11 ft.

Centerline-suction nozzle elevation - 973.25 ft.

Minimum water level' elevation inside containment - 996.8 f t .

Subcooling. P (prde ft) - Avp* 8?99*

Rvp-fpsla} 4 h, maximum (ft) = 2.21 Minimum NPSH (avai1able) - 2M&-2,4M4v34-f-tv r (23.55+8.99f2.21)T30)33:fth 6.2-4 R1 08/92

m _ __ . _ _ _ _ _ . _ _ _ _ _ _ _ . _ _ _ _ _ . _ _

U. S. Nuclear Regulatory Commission LIC-92-291R Attachmant ,

d Since the suction pressure NPSH is above the required NPSH of the HPSI pumps, adequate NPSH will always be available during recirculation.

A comparison between the minimum available NPSH and the required NPSH of the containment spray pumps and HPSI aumps leads to the conclusion that adequate NPSH will be always available to the above mentioned j pumps during the recirculation mode of operation. >

• - 4<Hmedit Credit is taken for subcooling. The.subcooling head 71s above the' vapor pressure'of the water; therefore vapor pressure;is appropriately considered.-

Figures 6.2-1 and 6.2-2 show pump elevations and piping runs.

A portion of the recirculation piping shown in figure 6.2-1 is buried directly in concrete. Under post accident conditions compressive thermal stresses will occur in the pipe. These thermal stresses will not cause failure of the piping since the stainless steel is a ductile-material and the stresses are compressive. Reinforcing bars will absorb the tensile stress in the surrounding concrete.

If degradation of the buried piping is suspected, it can be inspected from the inside.

6.2.2 System Description The safety injection system and the containment spray system piping and instrument diagram is shown in PalD E-23866-210-130, SHTS 1 and 2.

The safety injection system for this plant consists of both passive and active components. The four pressurized safety injection tanks are of the passive type and require no outside power or safety injection actuation signal to operate. The safety injection tanks inject large quantities of borated water into the reactor coolant system immediately following a large pipe break. The water rapidly covers and cools the core, thereby limiting clad melting and metal water reaction. The separate and independent tanks are each connected to one of the four safety injection nozzles; one nozzle is located on each of the four reactor coolant system cold 1 cgs. The driving head for water injection is provided by a nitrogen cover gas at a pressure of 240 psig minimum (255 psig normal). As the reactor coolant system pressure falls below tank pressure, check valves open in the line connecting each tank to the system. Thus, these tanks will initiate their discharge when the reactor coolant pressure drops below approxim?'ely 240 psig minimum (255 psig normal).

The active components which require safeguard actuation signals include the high and low pressure safety injection pumps as well as the containment spray pumps.

Safety injection is initiated by either a low-pressure signal from the pressurizer or a high containment pressure signal. A description of the derivation of the safeguard actuation signals is presented in  :

Section 7.3.2.

Figure 6.2-4 presents a plot of time to actuate the safeguards via the containment high pressure and the pressurizer low pressure signals as a function of break size. Figure 6.2-4 also presents a pint of time to uncover the core 6.2-5 R2 08/92

. U. S. Nuclear Regulatory Commission LIC 92-291R Attachment 9

The containment water temperature transients following a LOCA were

analyzed with respect to possible adverse effects on the available net positive suction head (NpSH) for the safety injection and containment spray pumps when the system shifted to the recirculation mode. The analyses were calculated based on the same conservative conditions and assumptions utilized in the containment pressure transient analyses as described in Section 14.16 of the USAR. The heat transfer coefficients' initial conditions, and heat sinks are as listed in Section 14.16.

The containment water temperature transients were calculated assuming that when the coolant flashes, it comes into equilibrium with the containment at the containment atmosphere temperature. The portion of reactor coolant which does not flash drops to the floor as saturated liquid. The initial water mass on the containment floor is reactor coolant from the blowdown (1-0 Sec.) and the contents of one stored energy flask that does not reach the core. No spray or pumped safety injection is assumed until 30 seconds after the accident. Water is added to the sump by spillage from the core, condensation of steam from the containment atmosphere, and by the sprays. The water from all sources is assumed to be at containment atmosphere temperature. With three spray pumps and one spray header available, the containment water temperature from a double ended rupture of a 32 inch diameter reactor coolant pipe is considered for two safety injection modes.

A. Minimum safety injection, per Section 14.16 of the USAR, consists of three of the four stored energy tanks, one charging pump, one low prersure safety injection pump and one high pressure safety injection pump.

B. Full safety injection, per Section 14.16 of the USAR, consists of three of the four stored energy tanks, two charging pumps, two low pressure safety injection pumps and two high pressure safety injection pumps.

tank Assuming thatadverse is at its most the safety injectionminimum condition, and refueling wa'er level of (SIRW)llons f83,000 ga (314,000 gallons design), the following are the system parameters at the start of recirculation:

Minimum full Safety In.iection

_ Sa.fetY IDieClion Recirculation Start Time 3740 Sec. 2815 Sec.

Containment Water 172 *F. 174 *F.

Atmosphere 150 *F. 148 *F.

ard to not positive suction head, the-emergency-core-cool 4ng With reg and-con {a4nment-spr-ay-systems-have-been-designed-assuming-no-increas 4 n-con ta 4 nmen t-p res s u re-from-t he4 ni t4 al-a t mos phere-p re s su re-pre sent p r4 o r-t o-t he-po s tul a ted40 ss-o f-coola n t-act-iden t s . The-44pSM-value.

44 sted-4 n-the-U SAR-a re-ba sed-on4h i s-a ssump t4 on-and-do-not-include 4he N pSH-t ha t-is-a va i-la bl e-d ue-to-thenon t-ai nmen t-wa t e r-bei ng4 ess-t ha n 24EF-4n-temperature. Thereforer-6.2-18 R2 08/92

. U. S. Nuclear Regulatory Commission LIC-92-291R Attachment tho' recirculation phase calculation ~ takes credit for1 suction head provided by containment sump water subcooling due to temperaturas lOs than saturation as calculated in~ the containment transient: analysis.

This-is an exception from t!,a design criteria set forth in Safety Guide

1. 1; however the _NPSH calculation conservatively credits 'only,25ff of the'availabiesumpwatersubcoolingwith-theconclusionthatadequate NPSH is avallable.' 4hese-<ond414 ens-cemply-with-the-requirement 4-of Safety--Guide-44c. 1. Fur-ther-aAssuming that only one shutdown cooling heat exchanger is available at recirculation, the spray tem)erature for minimum safety injection would be 144*F and for full safe"y injection 145'f. Figures 6.2-5 and 6.2-6 show plots of the containment water temperature vs time.

6.2.6 Availability and Re' 4bility 6.2.6.1 Normtl Operation During normal plant operation, there are no components of the system in operation. All components are on standby for possible amergency

• operation.

6.2.6.2 Plant Shutdown System operation for shutdown cooling is discussed in Section 9.3.

6.2.6.3 Emergency Operation Safety Iniection The five safety injection pumps (three high-pressure and two low-pressure) are started via the sequer.cers by PPLS and/or CPHS. PPLS and/or CPHS also ener ize the safety injection actuator relays (SIAS),

opening the safety in ection valves and closing the check valve leakage coolcr valves. If al normal power sources are lost and one emergency diesel-generator fails to start, one low-pressure and at least one high-pressure pump are automatically started (see Sectinn 8.4). The rest of the system is always aligned for safety injection during power operation. The safety injection tanks will discharge into the reactor coolant system when the pressure drops below approximately 255 psig.

Spill through the break is limited to c maximum of 25 percent by use of the flowmeter in each injection line and the remote-manual throttling capability of each safety injection valve.

Recirculat ion When the water in the SIRW tank reaches a predetermined low level, the STLS is initiated by coincident low level signals from two of four level switches in the SIRW tank. An STLS in coincidence with either a CPHS or PPLS will initiate the recirculation actuation signal (RAS).

The RAS opens the containment recirculation valves, closes the SIRW tank valves, stops the low- pressure pumps, closes the valves in the pump minimum recirculation lines and cuts in full component cooling water flow to the shutdown heat exchangers. The valves are arranged to ensure at least a 1-minute overlapping stroke to allow mixing and ensure adequate NPSH during the transfer, if cool water is available 6.2-19 R2 08/92

. U. S. Nuclear Regulatory Commission LIC-92-291R Attachment 4

from the spray pumps and shutdown cooling heat exchangers, a portion of the water discharged from the shutdown cooling heat exchangers may be manually diverted to the high pressure pump suction. This is a preferred mode of operation, but is not necessary to meet core cool ng requirements. Tha low-pressure pumps may be manually restarted by operation of override switches to obtain increased cooling flow when the reactor coolant system pressure is reduced. One or more spray pumps can also be used to augment flow to the core after the pressure is reduced.

I 6.2-19 R2 08/92

.- - . -. _ - . . . _ - . . _ . - -. - ~__ - - .

. U.'S Nuclear Regulatory Commission -

LIC-92-291R Attachment TABLE 6.3-1 C011TAINMENT SPRAY SYSTEM COMPONENT PERFORMANCE Containment Soray Pumps. Item No's. SI-3A. 3B & 3G Number of Units 3 Motor Nameplate Voltage 460 Horsepower, hp 300 injection Recirculation Capacity (each), gpm 1700 2000 3100 Head, ft 450 437 "322 NPSH Available, ft 20 48 ~ 28.67-NPSH Required ft 14.5 MA 26 ~. 0 "

NPSHMargin,it 5.5 Iv3 ~2.67 .

Shutdown Heat Exchanaers. Item No's. AC-4A & 48 Number of Units 2 Capacity (each) 87.5x10' Btu /hr based on 4,000 gpm of component cooling water at ll4*F inlet temp *erature and 1,420 gpm of spray water at 283 F inlet temperature TABLE 6.3-2

SUMMARY

OF PIPING. VALVE AND SPRAY N07ZLE CHARACTERISTICS Code USAS B31.7 1968, Class 11 Material Valves & Piping 304 Stainless Steel

_Desion Temperature, 'F 300 Desi n Pressures, psig  ;

Pi ng, Suction 60 Pi ng, Discharge 500 Va ves, Suction 150 Valves, Discharge, 2 in. 300 Valves, Dischar e,1-1/2 in. 600 Wall thickness, p pi g 2 in. and smaller suction)- Sch. 40S 2-1/2 in. through 2 in. Sch. 10S 14 in, through 20 in., nominal, in.0.250 6.3-2 R3 08/92

U. S. Nucleai Regulatory Commission LIC-92-291R Attachment USAR REVISION

U. S. Nuclear Regulatory Commission LIC-92-291R Attachnlent Adequate NPSH is available in the redundant ECCS injection and containment spray systems as shown and explained in the calculations given below.

I. Safety In.iec tion During the safety injection operating mode, the HPSI, LPSI, and the containment spray pumps receive suction from the safety injection refueling water tank. The available NPSH for the HPSI, LPSI and containment spray pumps during safety injection was evaluated as follows:

NPSH (available) - (P+Pa-Pvo) 2.31 + Z-h, sp. gravity P- pressure on liquid in SIRW tank or sump Pa - atmospheric pressure (psia) ,

Pvp - vapor pressure of liquid at specific temperature T (psia)

Z- vertical distance from liquid surface to centerline of pump suction (ft) h- water level above baseline elevation of SIRWT (ft) h, = max. friction losses in suction lines (ft)

A. LPSi Pumps y Required NPSH of LPSI pumps (2400 gpm/ pump) - 20 ft.

Centerline suction nozzle elevation - 973.25 ft. -

Minimum water level elevation in SIRWT - 989 ft.

(psig) - 0.0 Pa (psia) - 14.7 Pvp @ 100*f (psia) - .95 Z (ft) - 15.75 h, maximum (f t) - 6.3 Minimum NPSH (available) = 10+14.7 .95) (2.31)+(15.75-6.3)- 41.21 f t.

1.0 6.2-2 R1 08/92

, U. S. Nuclear Regulatory Commission LIC-92-291R Attachment Since the maximum available NPSH of 41.51 ft. is above the required NPSH of i 11.0 ft., adequate NPSH is alwa safety injection operating mode ys available to the HPSI pumps during the Summarizing the above NPSH evaluations for the HPSI, LPSI, and containment spray pumps, it is concluded that adequate NPSH will always be available for the emergency core cooling systems and the containment spray pumps.

II. Recirculation A. Containment Spray Pumps Required NPSH of containment spray pumps 26.0 ft.

(3100 gpm/ pump)

True centerline suction elevation - 973.25 ft.

Minimum water level elevation inside containment - 996.8 ft.

Subcooling P (ft) - 8.99*

Z (ft) - 23.55 h, maximum (ft) - 3.87 .l Minimum NPSH (available) - (23.55+8.99-3.87) - 28.67 ft. l Since the suction pressure NPSH is above the required NPSH of the CS pumps, adequate NPSH will always be available during recirculation.

B. LPSI Pumps Note that the LPSI pumps are not required for recirculation, and they will -be secured upon receipt of the recirculation actuation signal.

C. HPSI Pumps NPSH required for HPSI pumps (400 gpm/ pump) - 11 ft.

Centerline suction nozzle elevation - 973.25 ft.

Minimum water level elevation inside containment - 996.8 ft.

Subcooling P (ft) - 8.99*

h, maximum (ft) - 2.21 Minimum NPSH (available) = (23.55+8.99-2.21) - 30.33 ft. l.

6.2-4 R1 08/92-

_a

O. S. Nuclear Regulatory Commission LIC-92 291R Attachment Since the suction pressure NPSH is above the required NPSH of the HPSI pumps, a; quate NPSH will always be available during recirculation.

A comparison between the minimum available NPSH and the required NPSH of the containment spray pumps and HPSI pumps leads to the conclusion that adequate NPSH will be always available to the above mentioned pumps during the recirculation mode of operation.

• - Credit is taken for subcooling. The subcooling head is above the vapor pressure of the water; therefore vapor pressure is appropriately considered.

Figures 6.2-1 and 6.2-2 show pump elevations and piping runs.

A portion of the recircriation piping shown in Figure 6.2-1 is buried directly in concrete. Under post accident conditinns compressive thermal stresses will occur in the pipe. These thermal stresses will not t.ause f ailure of the piping since the stainless steel is a ductile material and the stresses are compressive. Reinforcing bars will absorb the tensile stress in the surrounding concrete.

If degradation of the buried piping is suspected, it can be inspected from the inside.

6.2.2 Sntem Descrijil2n The safety injection system and the containment spray system piping and instrument diagram is shown in P&l0 E-23866-210-130, SHTS I and 2.

The safety injection system for this plant consists of both passive and active components. The four pressurized safety injection tanks are of the passive type and require no outside power or safety injection actuation signal to operate. The safety injection tanks inject large quantities of borated water into the reactor coolant system immediately following a large pipe break. The water rapidly covers and cools the core, thereby limiting clad melting and metal water reaction. The separate and independent tanks are each connected to one of the four safety injection nozzles; one nozzle is located on each of the four reactor coolant system cold legs. The driving heaa for water injection is provided by a nitrogen cover gas at a pressure of 240 p,ig minimum (255 psig normal). As the reactor coolant system pressure falls below tank pressure, check valves open in the line connecting each tank to the system. Thus, these tanks will initiate their discharge when the reactor coolant pressure drops below approximately 240 psig minimum (255 psig normal).

The active components which require safeguard actuation signals include the high and low pressure safety injection pumps as well as the containment spray pumps.

Safety injection is initiated by either a low-pressure signal from the pressurizer or a high containment pressure signal. A description of the derivation of the safeguard actuation signcis is presented in Section 7.3.2.

Figure 6.2-4 presents a plot of time to actuate the safeguards via the containment high pressure and the pressurizer low pressure signals as a function of break size. Figure 6.2-4 also presents a plot of time to uncover the core 6.2-5 R2 08/92 1

U. S. Nuclear Regulatory Commission LIC 92-291R Attachment The containment water temperature transients following a LOCA were analyzed with respect to possible adverse effects on the available net -

positive suction head (NPSH) for the safety injection and containment spray pumps when the system shifted to the recirculation mode. The analyses were calculated based on the same conservative conditions and assumptions utilized in the containment pressure transient analyses as described in Section 14.16 of the USAR. The heat transfer coefficients' initial conditions, and heat sinks are as listed in Section 14.16.

The containment water temperature transients were calculated assuming that when the coolant flashes, it comes into equilibrium with the containment at the containment atmosphere temperature. The portion of reactor coolant which does not flash drops to the floor as saturated liquid. The initial water mass on the containment floor is reactor coolant from the blowdown (T-0 Sec.) and the contents of one stored energy flask that does not reach the core. No spray or pumped safety injection is assumed until 30 seconds after the accident. Water is added to the sump by spillage from the core, conuensation of steam from the containment atmosnhere, and by the sprays. The water from all sources is assumed to be at containment atmosphere temperature. With three spray pumps and one spray header available, the containment water temperature from a dovble ended rupture of a 32 inch diameter reactor coolant pipe is considered for two safety injection modes.

A. Minimum : afety injection, per Section 14.16 of the USAR, consists of three of the four stored energy tanks, one charging pump, one low pressure safety injection pump and one high pressure -safety injection pump.

B. Full Jaf ety injection, per Section 14.16 of the USAR, consists of three of the four stored energy tanks, two charging pumps, two low pressure safety injection pumps and two high pressure safety injection pumps.

tank Assuming is at its most thatadverse the safety injection condition, and refueling minimum level ofwater (SIRW)llcns 283,000 ga (314,000 gallons design), the following are the system parameters at the start of recirculation:

Minimum Full Safety 1.giection Eafety iniection Recirculation Start Time 3740 Sec. 2815 Sec.

• Containment Water 172 *F. 174 *F.

Atmosphere 150

• F. 148 *F.

With regard to net positive suction head, the recirculation phase -

i calculation takes credit for suction head provided by containme> sump i water subcooling due to temperatures less than saturation as calt . lated in the containment transient analysis. This is an exception from the design criteria set forth in Safety Guide #1; however, the NPSH calculation conservatively credits only 25% of the available sump water subcooling with the conclusion that adequate NPSH is available.

l 6.2-18 R2 08/92

U. S. Nuclear Regulatory Commission LIC-92-291R Attachrgent Assuming that only one shutdown cooling heat exchanger is available at l recirculation the s ray temperature for minimum safety injection would-be 144*F and for ful safety injection 145'F. Figures 6.2-5 and 6.2-6 show plots of the containment water temperature vs. time.

6 2.6 Availability and Reliability 6.2.6.1 Normal Operation ,

During normal plant operation, there are no components of the system in operation. All components are on standby for possible emergency operation.  ;

6.2.6.2 Plant Shutdown  ;

i System operation for shutdown cooling is discussert in Section 9.3.

l 6.2.6.3 Emergency Operation Safety Iniection The five safety injection pumps (three high-pressure and two low- are started via the sequencers by PPLS and/or CPHS. PPLS and/orpressure)lso CPHS a energize the safety injection actuator relays (SIAS , i opening the safety infection valves and closing the check valve leakag)e-  !

cooler valves. If all normal power sources are lost and one emargency  !

diesel-generator fails to start, one low-pressure and at least one i high-pressure pump are automatically started see Section 8.4). The rest of the system is always aligned for safet injection during power  ;

operation. The safety injection tanks will di charge into the reactor '

coolant system when the pressure drops below approximately 255 psig.

Spill through the break is limited to a maximum of 25 percent by use of '

the flowmeter in each injection line and the remote-manual throttling capability of each safety injection valve.

Recirculation When the water in the SIRW tank reachcs a predetermined low level, the STLS is initiated by coincident low level signals from two of four level switches in the SIRW tank. An STLS in coincidence with either a CPHS or PPLS will initiate the recirculation actuation signal (RAS).

The RAS opens the containment recirculation valves, closes the SIRv.?

tank valves, stops the low-pressure pumps, closes the valves in the pump minimum recirculation lines and cuts in- full component cooling water flow to the shutdown heat exchangers lhe valves are arranged to ensure at least a 1-minute overlapping stroke to allow mixing and ensure adequate NPSH during the transfer. If cool water is available from the spray pumps and shutdown cooling heat exchw,ars, a partion of the water discharged from the shutdown cooling heat exchangers nay be manually diverted to the high-pressure pump suction. This is a preferred mode of operation, but is not necessary to nmet core cooling requirements. The low pressure pumps may be manually restarted by operation of override switches to obtain increased cooling flow when the reactor coolant system pressure is reduced. One or more spray pumpe can also be used to augment flow to the core after the pressure is reduced.

6.2-19 R2 08/92

.- - _.,m, _

U. 5. Nuclear Regulatory Commis; ion LIC-92-291R Attachmer t TABLE 61 3 1 CONTAINMENT SPRAY SYSTEM C2[PONENT PERf0RMANg, Containraent SoraY Pumps . Item No'_sd.;;.A. 3B & _3C Number of Units 3 Motor Nameplate Voltage 460 Horsepower, hp 300 Mode iniection Becitqu].uiga Capacity (each), gpm 1700 3100 Head, ft 450 322 NPSH Available. f t 20 28.67 NPSH Required, ft 14.5 26.0 i b NPSH Margin, ft 5.5 2.67 i

Shutdown _}D3LExctan_gers item No's. &C-4A & 4B Number of Units 2 Capacity (each) 87.5x10' Btu /hr based on 4,000 gpm of component cooling water at ll4*F inlet temperature and 1,420 gpm of spray water at 283'F inlet temperature TABLE 6.3-2

SUMMARY

Of PLPING. VA(VE AND SPRAY N072LE CHARACTERISTICS ,

Code USAS B31.7 1968, Class 11 Muterial Valves & Piping 304 Stainless Steel I Design Temperature, 'F 300 .

o Design Pressures, psig Piping, Suction 60

, Piping, Discharge 500 <

Valvas, Suction 150 Valves, Disctarge, 2 in. 300 Valves, Discharge, 1-1/2 in.

600 Wall thic.kness, pipirig 2 in, and smaller (sucticn) Sch, 40S 2-1/2 in. througn 12 in. Sch. 10S 14 in. tnrough 20 in., nominal, in,0.250 9

6.3-2 R3 08/92 i

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