ML17216A456

Submits Addl Info Re 850726 & 1018 Commitments to Respond to TMI Item II.D.1 on Relief & Safety Valve Test Requirements

ML17216A456
Person / Time
Site:	Saint Lucie
Issue date:	03/18/1986
From:	Woody C FLORIDA POWER & LIGHT CO.
To:	Thadani A Office of Nuclear Reactor Regulation
References
TASK-2.D.1, TASK-TM L-86-114, NUDOCS 8603240265
Download: ML17216A456 (46)

Text

REGULATORY, JFORI JATION DISTRIBUTION ~cN (RIDS)

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FACIL: 50-335 St. Lucie Planti Unit ii Florida Power 5 Light Co. 05000335 50-389 St. Lucie Planti Unit 2i Florida Power 5 Light Co. 05000389 AUTH. MANE AUTHOR AFFILIATION MOODY> C. O. Florida Poeer Kc Light Co.

RECIP. NANE REC IP IENT AFFIL I*TIQN THADANIiA. C. PWR Prospect Directorate 8

SUBJECT:

Submits addi info re S50726 8c 1018 commitments to respond to TNI Item II. D. 1 on relief- 5 safety valve test requirements.

DISTRlBUTION CODE: A046D COPIES RECEIUED: LTR I CL 4 IZE:

TITLE: OR Submittal: TMI Action Plan Rgmt NUREG-0737 8c NUREG-Ohb0 NOTES:

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NANE LTTR ENCL ID CODE/NANE LTTR ENCL PMR-8 ADTS 1 1 PMR-8 EB 1 1 PMR-8 PEICSB 2 2 PMR-8 FOB 1 PMR-8 PDS PD 01 5 5 SELLS> D 1 1 PMR-8 PEICSB 1 1 PMR-8 RSB 1 1 INTERNAL: *DN/LFMB 1 0 ELD/HDS2 0 I E/DEPER DIR 33 1 1 IE/DEPER/EPB 3 3 NRR BMR ADTS 1 1 NRR PAULSON> M. 1 NRR PMR-A *DTS 1 1 NRR P MR-8 ADTS 1 1 1 1 NRR/DSRO ENR IT 1 04 1 RGN2 1 1 EXTERNAL: 24X 1 LPDR 03 1 1 NRC PDR 02 1 1 NSIC 05 1 1 Q6 TOTAL NUMBER OF COPIES REQUIRED: LTTR 31 ENCL

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L-86-I I 4 Office of Nuclear Reactor Regulation Attention: Mr. Ashok C. Thadani, Director PWR Project Directorate 88 Division of PWR Licensing - B U. S. Nuclear Regulatory Commission Washington, D. C. 20555

Dear Mr. Thadani:

Re: St. Lucie Units I and 2 Docket Nos. 50-335 and 50-389 Relief and Safet Valve Test Re uirements By letter dated June 2l, l985 (NRC TAC No. 446I7), the NRC staff requested additional information on the St. Lucie Unit I docket regarding TMI Action Item II.D.I. A similar request was made on the St. Lucie Unit 2 docket by NRC letter dated July I I, l 985 (NRC TAC No. 5I605).

By letters L-85-29I (July 26, l985) and L-85-397 (October I8, l985), Florida Power 8 Light Company committed to respond to both information requests by March l5, l986. In compliance with our commitment, the requested information is attached.

Very truly yours, C. O. Woody Group Vic sident Nuclear E rgy CO W/MAS/gp Attachment cc: Dr. J. Nelson Grace, USNRC, Region II Harold Reis, Esquire, Newman & Holtzinger 8603p4 0>~S 860318 PDR O~<

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TMI ACTION ITEM H.D.1 ST. LUCIE 1 uestions related to the selection of transients and valve inlet conditions:

Question 1.

The Combustion Engineering Report on operability of PORV's in CE Plants indicated that the limiting inlet fluid conditions during low temperature pressurization transients are a water discharge event. The CE Inlet Fluid Conditions Report stated that the pressurizer water solid condition and resulting PORV liquid discharge case was chosen for the cold overpressurization event since it gave the most severe pressurization transients. The report further states that a steam bubble can also exist in the pressurizer during low temperature operation whereby the PORV could lift on steam. No low pressure steam tests were performed by EPRI on the Dresser PORV. Provide verification that the St. Lucie 1 PORVs will operate satisfactorily on low pressure steam. Also, since the submittal does not identify the PORV set points for either normal operation or low temperature overpressure protection, please provide this information.

Res onse to uestion l.

The EPRI tests demonstrated that Dresser PORVs operate satisfactorily, i.e., open and close on demand, under a wide range of inlet fluid conditions.

These conditions included steam at high pressures (2000-2500 psia), water at pressures of 2000-2500 psia, and water at low pressure (630-700 psia).

Additionally, a series of saturated steam tests with various PORV set pressures were conducted by the manufacturer (Reference 1). In these tests, the PORV opened and closed without failure and with no apparent leakage. PORV opening pressures of 00 psig to 1960 psig were recorded in these tests. Consequently, Dresser conservatively concluded that the minimum operating pressure for these PORVs is 75 psig.

The PORV's tested in both programs were representative of those at St.

Lucie Unit 1. Since the inlet fluid conditions in their tests either enveloped or approximated St. Lucie Unit 1 plant-specific inlet fluid conditions presented in Reference 2, it is concluded that the PORVs in St.

Lucie Unit 1 are expected to operate satisfactorily under all anticipated inlet fluid conditions including low pressure steam.

Both PORVs in St. Lucie Unit 1 have the same setpoints, namely: a high pressure setpoint of 2900 psia for hot standby and power operation, and a low pressure setpoint of 065 psia for low,temperature overpressure protection.

uestions related to valve o erabilit:

Question 2.

NUREG-0737, Item II.D.l requires that the plant-specific PORV Control Circuitry be qualified for design-basis transients and accidents. Provide information which demonstrates that this requirement has been fulfilled.

Res onse to uestion 2.

Desi n Basis for Power 0 crated Relief Valves (PORV)

1. RCS Over ressure Protection {HPRO)

The reactor coolant system is protected against overpressure by control and protective circuits such as the high pressure reactor trip and by ASME code safety valves and Power Operated Relief Valves (PORVs) connected to the top head of the pressurizer. The PORV's are designed to relieve sufficient steam during abnormal transients to prevent actuation of the code safety valves. The combined capacity of the PORV's is large enough to relieve the maximum surge volume associated with the continuous Control Element Assembly (CEA) withdrawal starting from low power. The total relief capacity is also large enough to prevent opening of the pressurizer code safety valves during a loss of load from full power. These two design requirements assume normal operation of the pressurizer spray system and a reactor trip on high pressurizer pressure.

The PORV's are solenoid-actuated, pilot operated, balanced valves, operated automatically or by remote manual control. The PORV is opened by energizing a solenoid which opens the pilot valve causing a differential pressure across the main disc which forces the valve open. The valve is shut by de-energizing the solenoid and allowing steam pressure and spring force to shut the pilot valve. This creates a differential pressure across the main disc which forces the valve shut.

Each PORV has a hand control switch on RTGB l03. They are three position switches, each having LOW RANGE - NORMAL RANGE-OVERRIDE positions. By selecting the OVERRIDE position, all other input signals to the PORV are blocked and the valve remains shut, or will shut if in the process of opening or already opened. This manual control feature is provided to shut the associated PORV during an undesired opening {or upon failure to shut after proper actuation).

The two remaining positions select the, operating mode of the PORV.'s relative to RCS operating conditions. NORMAL RANGE is selected any time RCS tempe'rature and pressure is above 279oF (TC) and 035 psia, respectively. In this mode each PORV will open when the following conditions are satisfied:

a) PORV handswitch is in NORMAL RANGE b) AND a High Pressure Relief Open (HPRO) signal from the Reactor Protective System (RPS) is present (RCS. pressure

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greater than 2000 psia).

Res onse to uestion 2. (continued)

The open signal originates from four redundant pressure transmitters, PT-1102 A, B, C, dc D, which provide input signals to the RPS comparator circuits. When any two of the four senses 2000 psia increasing pressure, the HPRO signal is generated to open the PORV's. Additionally, this same signal is used to generate the reactor high pressure trip.

The LOW RANGE position activates a special low temperature overpressure mitigation system that protects the RCS from pressurization beyond the limit defined by the Minimum Pressurization Temperature (MPT) curves of the Technical Specifications, while the RCS is at low temperatures.

2. The Over ressure Miti ation S stem (OMS)

The Overpressure Mitigation System (OMS) protects the RCS from being pressurized beyond the limit defined by the Minimum Pressurization Temperature (MPT) curves of the Technical Specifications, while the RCS is at low temperatures.

The Overpressure Mitigation System (OMS) achieves its purpose by pressure comparison in two independent redundant OMS trains, one for each PORV. The OMS generates an open PORV signal from pressure comparator PC-1103 and/or PC-1100 when pressure reaches 065 psia increasing. The actuation point of 065 psia is designed to prevent the pressure transient in a solid RCS (pressurizer steam volume full of water) from exceeding the pressure-temperature relationship defined by the 10 EFPY heatup curve in the event of either of the below transients.

a) A RCP start when steam generator temperature exceeds reactor vessel temperature by 50oF or less (maximum 4T, 50oF).

b) Inadvertent safety injection by two high pressure safety injection pumps and three, charging pumps.

Note that the LTOP analysis is presently being re-evaluated for use beyond the present curves. Assumptions, setpoints and hardware changes may be implemented to increase the present operating window.

The.LOW RANGE position is selected any time RCS temperature and pressure is below 275oF or 015 psia, respectively. In this mode, each PORV will,open when the following conditions are satisfied:

. a) Associated PORV handswitch is in LOW RANGE.

b) AND an open signal from the associated OMS pressure comparator is present (pressure greater than 065 psia).

OMS open signals originate in two redundant trains with pressure comparators PC-1103 and PC-1100 supplying open signals to V1002 and V1000, respectively.

Res onse to uestion 2. (continued)

3. PORV Position'Indication In The Control Room Red (open) and green (closed) lamps on RTGB 103 in the control room provide PORV position indication derived from limit switches operated by the valve solenoid.

In addition to the valve position indicating lights, an acoustic monitor system is provided. The acoustic monitor system provides positive control room indication of safety valve and PORV position. The parameter actually monitored is flow. The safety valves have no other positive position detectors such as switches operated by the valve stem. While the PORV's have position indication, it is not positive because their indication is actuated by energizing the operating PORV solenoid. The valve may not operate if a mechanical failure occurs, 'even though the solenoid is energized. Therefore, one piezoelectric accelerometer is clamped to the outside of each code safety valve and PORV tailpipe. Flow through the tailpipe, which constitutes positive indication that the 'valve is open, causes acoustical accelerations (flow noise and pipe vibrations). The accelerometer produces a piezoelectric charge proportional to acceleration (g's); this charge is then converted to voltage by a remote charge converter mounted inside the containment. This voltage is then applied to the valve flow monitor module, located in the control room. The valve flow monitor module processes the voltage signal and indicates the relative value of flow on a bar graph display of Light Emitting Diodes (LED's) calibrated in increments of full flow, which is 1.0. The discrete flow value LED's are: 0.01, 0.00, 0.09, 0.16, 0.25, 0.36, 0.09, 0.81, and 1.0. The monitor module contains a signal processing channel and display for each monitored valve.

The flow indicators and recorder FR-1200 are located on the Post-Accident Panel (PAP) in the control room. A common alarm is actuated by any one of the five flow indicators if indicated flow exceeds approximately 00 gpm. The alarm is labeled SAFETY RELIEF VALVE OPEN, located on RTGB 103 annunciator in the control room.

In addition, a temperature detector (RTD), installed in the combined PORV relief line, indicates that one or both PORV's have lifted or are leaking. The detector supplies an input to a temperature indicator-controller in the control room. This actuates an alarm "Pressurizer Relief Line High Temperature" to warn of PORV actuation or le'akage.

I

0. 10CFR50 A endix "R" Considerations A fire in the control room and/or cable spreading room may cause control room evacuation and the plant must be placed in a safe shutdown condition by utilizing alternate shutdown equipment. To pievent spurious PORV opening during a fire, selector switches

Res onse to uestion 2. (continued) outside the control room are provided for each PORV. The selector switches are located in the electrical cable penetration rooms. These switches when placed in the "Isolate" position will disconnect spurious signals generated by the fire and de-energize PORV solenoids causing PORV's to close.

5. Electrical Power Su lies The PORV's are operated from Class 1E 125V DC redundant buses for maintaining operability of these valves following off-site power loss.

The PORV's are designed to fail closed on valve solenoid deenergization.

Motor operated blocking valves are operated from Class 1E 080V, 3PH redundant MCC's; These MCC's are powered from the Emergency Diesel Generators following off-site power loss.

6. Environmental Criteria The environmental conditions under which equipment must function, are provided in the St. Lucie Unit 1 FSAR Section 3.11. The following safety related electrical equipment located in the Reactor Containment Building (RCB) is qualified for use under the specified environment:

PT-1102 A, B, C, D PT-1103 PT-1100 PORV Acoustic Flow Monitoring System Electrical cables Electrical penetrations This equipment can be found listed in the St. Lucie Unit 1 Environmental Qualification (EQ) list for IOCFR50.09. Complete record of this documentation can be found at the St. Lucie Records Vault at the plant site. 4 All other electrical components for indication and control, are located in mild environment areas in the Reactor Auxiliary Building.

These components have been installed taking into consideration their specification and the available environmental data to assure the adequacy of the installation for the specified environmental service.

7. Seismic Criteria Class 1E electrical equipment such as switches, electronic devices, cables and power supplies, including their supports, are seismically qualified to IEEE-323. The seismic qualification criteria of Class I instrumentation and electrical equipment is described in St. Lucie Unit 1 Updated Final Safety Analysis Report (UFSAR) Section 3.10.

Question 3.

The information referenced by the submittal states that bending moments imposed by the discharge piping did not impair valve operability. Thermal expansion of the pressurizer causing displacement of the piping nozzles and thermal expansion of the piping from the nozzles to the valves can contribute to the bending moment induced in the valve body. The submittal does not make clear what loads were considered in calculating the bending moments applied to the plant safety valves and PORVs.

Provide additional discussion comparing the measured moment on the tested valves to the calculated induced moments from all effects including those described above on the plant specific valves. Verify that the bending moments would have no adverse effect on the operability of the plant valves.

Res onse to uestion 3.

For the sake of determining the effects of piping loads on the operability of pressurizer safety and power operated relief valves, only the bending moments imposed on the valve discharge flange were evaluated. To evaluate the impact of these calculated loads on valve operability, the emergency condition was utilized. The emergency'ondition includes the conservative load combination of pressure, dead weight, DBE and valve discharge loads.

1. Safet Valves (Crosb HB-BP-36 3K6)

The bending moments recorded during the EPRI Safety Valve Test Program represent an as-tested valve loading where both valve operability and structural integrity were demonstrated. With the measured bending moment acting on the safety valve, the valve opened, discharged, and closed in a satisfactory manner. These tests demonstrated that all valve body or component distortion due to this bending moment was small and did not cause binding or interference.

The measured bending moments which act on the safety valve can be directly compared to analytically calculated moments since both challenge valve operability and structural integrity. Note that the tested load acceptance criterion is not an upper limit load based on failure criteria. This acceptance limit represents the highest measured load with acceptable valve operability during the test program. During the entire test program, the measured bending moments never caused a valve to malfunction. This test record indicates that valve operability is not sensitive to bending moments and that actual bending moment limits are higher than the measured values.

The. results of the-EPRI Safety Valve Test Program demonstrate that the bending moments on the safety valve flanges due to thermal expansion of the pressurizer and piping and by the discharge loads will not impair valve operability provided that the anticipated loads are less than these measured in the tests.

Res onse to uestion 3. (continued)

For St. Lucie Unit 1, the maximum calculated bending moment acting on the safety valve discharge flange is 60,068 in-lbs. The maximum as-tested bending moment for this type of valve was 133,000 in-lbs (see Reference 33. This tested value is two times greater than the maximum calculated value. It is therefore concluded that the plant-specific bending moments will have no adverse effect on the operability of the St. Lucie Unit 1 safety valves.

2. PORV's (Dresser 31533VX-30)

The maximum calculated bending moment imposed on the St. Lucie Unit 1 PORV is 25,808 in-lbs. The EPRI test program (Reference 3) provided only one test point for a similar PORV in which a measured bending moment of 25,500 in-lbs was observed. Although valve operability was not impaired by this induced moment, a formal conclusion between calculated and test values could not be made due to insufficient test data. However, because the maximum calculated moment is nearly identical to the tested moment, it can be inferred that the plant-specfic bending moment will have no adverse effect on the operability of the St. Lucie Unit 1 PORV's.

Question o.

Based on information obtained, on other plants, the manufacturer of the Dresser PORV recommends that a heavier spring be installed in both main valve and the pilot valve in order to prevent leakage at lower pressures.

Provide verification that this modification has been made or other information which demonstrates the valve will not excessively leak causing valve seat damage during low pressure fluid inlet conditions.

Res onse to uestion 0.

According to Dresser (Reference 0); the heavier springs are necessary for valve operability below 100 psig, when the dead weight of the activating lever may cause the pilot valve to open or to remain open. Accordingly, the main valve,may also partially open.

Heavier springs have not been provided to the St. Lucie Unit 1 PORVs."

However, even with the existing springs, if inlet pressure increases rapidly to above 100 psig, the valve (pilot and main) should properly load and seal off without leakage. From cold start, there may be some cyclic type leakage until the valve comes thermally stable.

To improve. seat tightness at pressures of,100 .to 1000 psig, Dresser recommended that the original valve type 1 design be modified into type 2 (sometimes called Dash 2) design. Both EPRI and Dresser tests were performed with Dresser PORVs of the type 2 design. The original St. Lucie Unit 1 type 1 PORV's were modified to the type 2 design prior to the EPRI test program.

uestions on thermoh draulic anal sis:

Question 5.

The submittal states that a thermal-hydraulic analysis was performed using RELAP5 and the results input into the postprocessor code CAPLOTFIII for the development of the appropriate forcing functions and time histories.

Some details of the analyses were not provided. To allow for an evaluation of the methods used provide a sketch of the model and identify the valve opening times used in the analysis. The code CAPLOTFIII is a special purpose code without wide use. Provide a discussion on how this code has been verified to provide confidence that it computes correct forcing functions. Also, since the ASME Code requires derating of the safety valve to 90% of expected flow capacity, the actual flow would be expected to exceed the rated flow. Flows measured during the EPRI tests confirmed this expectation. These higher flows would produce higher piping loads; therefore, explain the method used to establish the flow rates of the safety valves and the PORVs used in the analyses.

Res onse to uestion 5.

The models used in the thermal hydraulic transient analyses are shown in Figures 1 and 2. Also attached is a copy of the model utilized by EDS in their piping analysis (Figure 3). The valve opening times used in the analyses are 6 msec for the SRV and 110 msec for the PORV. As described in the Reference 5 report, they are the shortest opening times measured in the EPRI safety and relief valve test program (Reference 3).

The post processor CALPLOTFIII was programmed to convert the transient flow conditions (calculated by RELAP5/MOD 1) into transient forces on the piping system. The derivation of the governing equations are shown in Appendix l. The validity of the program coding was verified by comparing hand calculation results against the values computed by the program. The program was further assessed with the GE 0-inch pipe blowdown test results. Favorable comparisons were observed in comparing the computed results against the test data.

Due to the discrepancy in the RELAP5/MOD1 choke flow model, as was demonstrated in EPRI RELAP5/MODl application (Reference 6), adjusted valve flow areas have to be used to generate the required flow rates. The actual calculated flow rates for the SRV actuation case are shown in Table

l. \

uestions on structural anal sis:

Question 6.

The submittal states that the results of the thermal-hydraulic analysis were compared with the analysis which had resulted in the present design and the conclusion was reached that the piping and supports are adequate for the calculated hydraulic loads. Since the loading is a time dependent loading at numerous locations, dynamic considerations are necessary in making the comparison. Details of the comparison were not provided. To allow an evaluation of the comparison explain how the comparison was made. If computer programs were used in the comparison identify the programs and explain how they have been verified for this application.

Identify the load combinations considered and the allowable stress criteria for each combination. If the combinations and acceptance criteria differ from those recommended in the "EPRI Safety and Relief Valve Test Program Guide for Application of Valve Test Program Results" provide the rationale for the selection.

Res onse to uestion 6.

The comparison of the hydrodynamic loads was based on the approximate peak values of the segment forcing functions. In estimating the reaction loads on the restraints, it was observed that the characteristic time duration of each oscillation in the load was shorter than the with which the pressurizer relief piping system would respond. It fundamental'eriod was concluded, therefore, that the expected dynamic amplification factor in the response of the piping system should be close to unity. Therefore, the expected hydrodynamic loadings were calculated with a dynamic load factor of 1.0. The comparison of the hydrodynamic loads calculated in the report with those used in 'the or iginal stress analysis and pipe support/restraint design was based solely on basic engineering principles and good engineering judgement. No computer programs were used in this process. The load combination used in the EDS stress analysis are consistent with SRP 3.9.3 Revision 1 requirements, which are as or more conservative than those recommended by EPRI; namely OBE combined with the maximum values of PORV and SRV loads have been evaluated using Level B limits, and DBE combined with the maximum values of PORV and SRV loads have been evaluated using Level C limits. The loading used in the design of the restraints was the combination of the worst thermal, dead weight, seismic and PORV/SRV discharge loads. The restraint design considered this combination and normal allowable stress values.

TMI ACTION ITEM ILD.I ST. LUCIE 2 uestions related to the selection of transients and valve inlet conditions:

Question i.

The Combustion Engineering Report on operability of PORVs in CE Plants indicated that the limiting inlet fluid conditions during low temperature pressurization transients is a water discharge event. The CE Inlet Fluid Conditions Report stated that the pressurizer water solid condition and .

resulting PORV liquid discharge case was chosen for the cold overpressurization event since it gave the most severe pressurization transients. The report further states that a steam bubble can also exist in the pressurizer during low temperature operation whereby the PORV could lift on steam. No low pressure steam tests were performed by EPRI on the Dresser PORV. Provide verification that the St. Lucie 2 PORVs will operate satisfactorily on low pressure steam. Also, since the submittal does not identify the PORV set points for either normal operation or low temperature overpressure protection, please provide this information.

Res onse to uestion 1.

St. Lucie Unit 2 does not utilize Dresser PORV's, but rather Garret PORV's. According to the Garret Technical Manual the St. Lucie-2 PORVs will operate satisfactorily with an inlet steam pressure as low as 100 psig with zero back pressure.

During hot standby and power operations, the PORVs will open at a high pressure setpoint of 2000 psia. For low temperature over pressure protection during heatup and cooldown and during extended periods of cold shutdown, low pressure setpoints are incorporated in the PORV circuitry.

These low pressure setpoints are staggered as follows: 060 psia in PORV V-1070 and 090 psia in PORV V-1075.

uestions related to valve o erabilit:

Question 2.

NUREG 0737, Item II.D.l requires that the plant-specific PORV Control Circuitry be qualified for design-basis transients and accidents. Provide information which demonstrates that this requirement has been fulfilled.

Res onse to uestion 2.

Desi n Basis for Power 0 crated Relief Valves (PORV)

l. RCS Over ressure Protection (HPRO)

The PORV's are 'designed to relieve sufficient steam during abnormal transients to prevent actuation of the code safety valves. The combined capacity of the PORV's is large enough to relieve the maximum surge volume associated with a continuous Control Element Assembly (CEA) withdrawal starting from low power. The total relief capacity is also large enough to prevent opening of the pressurizer code safety valves during a loss of load from full power.

These two design requirements assume normal operation of the pressurizer spray system and a reactor trip on high pressurizer pressure. Because one PORV is sufficient to meet the design requirements for Unit 2, one PORV is isolated during normal plant operation.

The PORV's are solenoid-actuated, pilot operated, balanced valves, operated automatically or by remote manual control. The PORV is opened by energizing a solenoid which opens the pilot valve causing a differential pressure across the. main disc which forces the valve open. The valve is shut by de-energizing the solenoid and allowing steam pressure and spring force to shut the pilot valve. This creates a differential pressure across the main disc which forces the valve shut.

Each PORV has two associated hand control switches on RTGB 203.

There is an individual three-position, OFF-OVERRIDE-TEST switch and a two-position, LTOP-NORMAL mode selector switch for each PORV. The two-position mode selector switch, HS-1070 (HS-1075),

selects the operating mode of the PORV's relative to RCS operating conditions. The NORMAL position is selected any time RCS temperature is above 320oF. In this mode each PORV opens when all of,the following conditions are satisfied:

a) Mode selector switch in NORMAL.

e b) PORV override/test switch in OFF.

c) AND a High Pressure Relief Open (HPRO) signal from RPS present (RCS pressure greater than 2000 psia).

-1 1-

Res onse to uestion 2. (continued)

The HPRO signal orginates from four redundant pressure transmitters, PT-1102 A, B, C R D, which provide input signals to the RPS comparator circuits. When any two of the four sense 2000 psia increasing pressure, the HPRO signal is generated to open the PORV's. Additionally, this same signal is, used to generate reactor high pressure trip.

The LTOP position activates a special low temperature overpressure mitigation system that protects the RCS from pressurization beyond the limit defined by the MPT curves of the Technical Specifications while the RCS is at low temperatures.

2. Low Tem erature Over ressure Protection S stem (LTOPS)

The Low Temperature Overpressure Protection System (LTOPS),

achieves its purpose by pressure comparison in two redundant LTOP channels, A and B, one for each PORV. The LTOPS generates open signals from pressure comparators PC-1103, PC-1100, PC-1105, and PC-1106 to actuate the PORV's at staggered setpoints. The actuation points of 060 and 090 psia are designed to prevent the pressure transient in a solid RCS (pressurizer steam volume full of water) from exceeding the curves that define allowable pressure-temperature relationships, in the event of either of the below transients:

a) An RCP starts when steam generator temperature exceeds reactor vessel .temperature by 100oF or less (maximum > T, 100oF).

b) Inadvertent safety injection by two high pressure safety injection pumps and three charging pumps.

Note that the LTOP analysis is presently being re-evaluated for use beyond the present curves. Assumption,'setpoints and hardware changes may be implemented to increase the present operating window.

Since each PORV has sufficient capacity to mitigate either of the transients discussed above, staggered setpoints can be used to avoid opening of the second PORV (V1075 at 090 psia) during minor pressure excursions that are immediately arrested by actuation of the first PORV (V1070 at 060 psia). Thus, the LTOPS provides totally redundant protection while minimizing the possibility of unnecessary RCS depressurization.

The LTOP position is selected any. time RCS temperature is below 280oF (TC). In this mode, PORV V1070 (V1075) opens when all of the following conditions are satisfied:

a) PORV mode selector switch is in LTOP.

b) PORV override/test switch is in OFF.

Res onse to uestion 2. (continued) c) TC is not above 320oF.

d) AND a Low Pressure Relief Open (LPRO) signal is present.

The LPRO signal originates from two redundant channels with four pressure comparators; PC-1103 and PC-1105 supply the input signal to open PORV V1070, PC-1100 and PC-1106 supply the output signal to open PORV V1075.

A temperature interlock prevents PORV actuation above 320oF,(TC) if the mode selector switch is inadvertently positioned to the LTOP position. The normal 2000 psia setpoint remains in effect when this interlock is in effect. This feature provides PORV overpressure protection even if the mode selector switches were to be left in the LTOP position.

The LTOPS provides two instructive alarms and two warning alarms for the operator. They are SELECT LTOP, SELECT NORMAL, and LTOP TRANSIENT CHANNEL A (B) alarms, located on RTGB 203,

-annunciators H-02, H-06, H-03 and H-07, respectively. The two instructive alarms direct the operator to make selections on the PORV mode selector switches. These alarms are common to both LTOP channels. Also, both LTOP channels'provide transient alarms which warn the operator when actual pressure is 060 psia as sensed by channel A; the channel B transient alarm is actuated at 090 psia.

The three-position override/test selector switch provides the capability to override actuating signals and to test actuating circuits without operating valves. This switch is normally in the OFF position. The OVERRIDE position shuts the PORV if it is open and overrides any signal to open the valve. This manual control feature is provided to shut the PORV during an undesired opening (or upon failure to shut after proper actuation). The TEST position simulates an open signal to the PORV, to test the circuit, without physically opening the valve. The switch is spring returned to OVERRIDE from TEST when released (OFF and OVERRIDE are maintain contacts).

The operator is alerted by a PORV TEST CONDITION indicating light on RTGB 203, whenever the override/test switch is in the OVERRIDE or TEST position.

3. PORV Position Indication in the Control Room Red (open) and green (closed) lamps on RTGB 203 in the control room provide positive PORV position indication derived from limit switches opera'ted by'the valve operator.

In addition to the valve position indicating lights, an'coustic monitor system is provided. The acoustic monitor system provides positive control room indication of safety valve and PORV position. The parameter actually monitored is flow. The safety valves have no other positive position detectors such as switches operated by the valve stem. While the PORV's have position indication, it is not positive because their indication is actuated by energizing the operating PORV solenoid. The valve may not operate if a mechanical Res onse to uestion 2. (continued) failure occurs, even though the solenoid is energized. Therefore, one piezoelectric accelerometer is clamped to the outside of each code safety valve and PORV tailpipe. Flow through the tailpipe, which constitutes positive indication that the valve is open, causes acoustical accelerations (flow noise and pipe vibrations). The accelerometer produces a piezoelectric charge proportional to acceleration (g's); this charge is then converted to voltage by a remote charge converter mounted inside the containment. This voltage is then applied to the TEC valve flow monitor module, located in the control room. TEC is just the manufacturer's acronym.

The valve flow monitor module processes the voltage signal and indicates the relative value of flow on a bar graph display of light emitting diodes (LED's) calibrated in increments of full flow, which is 1.0. The discrete flow value LED's are: 0.01, 0.00, 0.09, 0.16, 0.25, 0.36, OA9, 0.81, and 1.0. The monitor module contains a signal processing channel and display for each monitored valve.

The flow indicators and recorder FR-1200 are located on the Post-Accident Panel (PAP) in the control room. A common alarm is actuated by any one of the five flow indicators if indicated flow exceeds approximately 00 gpm. The alarm is labeled SAFETY RELIEF VALVE OPEN, located on RTGB 203 annunciator in the control room.

In addition, St. Lucie Unit 2 has a temperature element located in each PORV discharge pipe. They supply independent 'temperature indicators on RTGB 203. Each temperature indicator actuates a common alarm labeled PRESSURIZER RELIEF LINE HIGH TEMPERATURE.

0. 10CFR50 A endix "R" Considerations A fire in the control room and or cable spread room may cause control room evacuation and the plant must be placed in a safe shutdown condition by utilizing alternate shutdown equipment. To prevent spurious PORV opening during a fire, key operated selector switches are provided for each of PORV. The selector switches are located in the physically seperated electrical containment cable penetration rooms. These switches when placed in the "ISOLATE" position will disconnect spurious signals generated by the fire and deenergize PORV solenoids causing PORV's to close.

50 Electrical Power Su lies The PORV's 'are operated from Class IE 125V DC redundant buses for maintaining'operability of these valves following offsite power loss.

The PORV's are designed to fail closed on valve, solenoid deenergization.

Response to Question 2. (continued)

Motor operated blocking valves are operated from Class lE 080V, 3PH, 60HZ redundant MCC's. These MCC's are powered from the Emergency Diesel Generators following off-site power loss. The motor operated valves fail "as is" upon power failure.

6. Environmental Criteria The environmental conditions under which equipment must function, are provided in the St. Lucie Unit 2 FSAR Section 3.11. The following safety related electrical equipment located in the Reactor Containment Building (RCB) is qualified for use under the specified environment:

o PT-1102 A, B, C, D o PT-1103 o PT-1100 o PT-1105 o PT-1106 o -

PORV Acoustic Flow Monitoring System o Electrical Cables o Electrical Penetrations This equipment can be found listed in the St. Lucie Unit 2 Environmental Qualification (E.Q.) list for IOCFR50.09. A complete record of this documentation can be found at the St. Lucie Records Vault at the plant site.

All other electrical components for indication and control, are located in mild environment areas in the Reactor Auxiliary Building.

These components have been installed taking into consideration their specification and the available'nvironmental data to assure, the adequacy of the installation for the specified environmental service.

7. Seismic Criteria The seismic design of equipment presently installed is maintained.

The PORV's were designed and manufactured in accordance with ASME Boiler and Pressure Vessel Code Section III and are Class I valves. Class 1E electrical equipment such as switches, electronic devices, cables, power supplies, including their supports, are seismically qualified to IEEE-300-75. The seismic qualification criteria for Class 1E, Seismic Category I electrical and

. inst'rumentation is described in St. Lucie Plant Unit No. 2 Updated

~ ~

Final Safety Analysis Report (UFSAR) Section 3.10,and.Appendix'.10A.

Question 3.

The CE owners group summar'y report on the operability of Pressurizer Safety Valves in CE Designed Plants (CEN-227) identified three qualified ring settings for the two St. Lucie plant safety valves. These are -55, -10;.

-05, -10; and -95, -10 which resulted in projected blowdown from 8.9 to 15.79o. The submittal does not state what ring settings are actually used on the plant valves. The licensee should identify what ring settings are used,and justify any departure from the recommended settings.

Res onse to uestion 3.

At the completion of the EPRI Safety Valve Test Program, Combustion Engineering, recommended ring settings of (-55, -10) for the pressurizer safety valves. This ring setting adjustment was performed by a Crosby representative during construction of St. Lucie Unit 2. Additionally, plant maintenance procedures ensure that the ring settings are properly adjusted to this value any time maintenance is performed on the pressurizer safety valves.

~uestion 0.

The information referenced by the submittal states that bending moments imposed by the discharge piping did not impair valve operability.'hermal expansion of the pressurizer causing displacement of the piping nozzles and thermal expansion of the piping from the nozzles to the valves can contribute to the bending moment induced in the valve body. The submittal does not make clear what loads were considered in calculating the bending moments applied to the plant safety valves and PORVs.

Provide additional discussion comparing the measured moment on the tested valves to the calculated induced moments from all effects including those described above on the plant specific valves. Verify that the bending moments would have no adverse effect on the operability of the plant valves.

Res onse to uestion 0.

The general discussion included in the St. Lucie Unit 1 response to Question 3 is applicable to St. Lucie Unit 2 and is omitted from this reponse to avoid repe ti tion.

1. Safet Valves (Crosb HB-BP-36 3K6)

A maximum calculated bending moment acting on the St. Lucie 2 safety valve discharge flange is 72, 718 in-lbs. Since this moment is significantly lower than the maximum as-tested bending moment of 133,000 in-lbs (Reference 3) and the as-stated moment did not impair valve operability, it is concluded that plant-specific bending moments will have no adverse effect on the operability of the St. Lucie Unit 2 safety valves.

2. PORV's (Carrett 3750010)

The maximum calculated bending moment acting on the St. Lucie Unit 2 PORV discharge flange is 83,635 in-lbs. The EPRI Test Program (Reference 3) provided only one. test point for a similar.

PORV: in Test 98-GA-2S, a 'bending.-moment of 33,200 in-lbs was induced on the valve discharge flange. Although the valve operability was not impaired by the induced moment, a formal'conclusion based on a comparison between the as-tested and calculated values could not be made because of insufficient test data and also the fact that the as-tested bending moment is less than the plant-specific calculated bending moment.

Res onse to uestion 4. (continued)

The subject valve design report (Reference 5), however, provides a maximum allowable design value of the bending moment.

Comparison of this value, which is equal to 193,200 in-lbs, with the plant-specific calculated bending moment of 83,635 in-lbs demonstrates that the St. Lucie 2 PORV discharge flanges will be subjected to an anticipated bending moment of less than one-half of the maximum allowable design value.

It is concluded, therefore, that the anticipated bending moments will have no adverse effect on the operability of the St. Lucie 2 PORVs.

Question 5.

The Marshall steam tests proved that the original method for compensating for thermal growth in the'arrett PORV was inadequate. A number of design changes were made to the test 'valve. Provide information addressing this concern. Verify that the recommended changes of the manufacturer have been incorporated into the PORV valves used at St.

Lucie 2.

Res onse to uestion 5.

The internal design of the Garrett PORV, part 3220718-1, tested in the EPRI Test Program at Marshall Steam Station included a single-piece cage and seat assembly held down by means of a flexitallic spring gasket.

Although the valve operated normally throughout 77 cycles with dry saturated steam at 2000 psig, a seat leakage of 0.006 gpm after two cycles and 0.01 gpm during the remainder of the test was detected. Upon valve disassembly and inspection, the seat gasket was found to have been completely washed out, which was considered to have been the cause of the leakage.,

According to Reference 7, post-test analysis showed that the problem was caused by differential thermal growth during the first opening cycle. A flexitallic gasket between the cage and bonnet had the dual function of holding the cage down against the seat gasket and compressing sufficiently to compensate for differential thermal growth. The gasket proved unable to withstand the applied load and took a permanent set, thus allowing the cage to become unloaded and lift up off the seat gasket. The seat jacket was, therefore, exposed to the scouring action of the steam and all of the asbestos was washed out during the first cycle of operation.

1 At the time of the Marshall test, Garrett intended to 'utilize the single-piece cage and seat asse'mbly design in production PORVs including those supplied to'St. Lucie Unit 2. However, upon reviewing the test results, Garrett concluded that an improved design was possible'and changed both the test and production valve designs to incorporate these design improvements. Test valve 3220718-I was modified to the 3220718-2 configuration which incorporated all the design features of the improved St. Lucie 2 valve design.

Note that the Garrett test FORV, Part 3220718-2, was subsequently tested at V/yle Laboratories.

Res onse to uestion 5. (continued)

The following design changes were made to the test PORV Part 3220718-2, and the St. Lucie 2 PORVs Part 3750010:

a) Designing a separate, bolted down seat, b) allowing the valve cage to float, independent of the seat, for thermal compensation, c) replacing the seat and body/bonnet flexitallics with a sheet metal/graphoil-type Selco seal, and d) changing the cage-to-bonnet seal from a flexitallic to a carbon piston ring bore seal.

Compensation for thermal growth caused by different heating rates between the valve cage and body is provided by a gap which is maintained between the bottom of the cage and the top of the seat. When the valve is closed, the cage is held up against the bonnet by a light spring. When the valve opens, pressure forces the cage up into the bonnet with a high load, thus maintaining the gap between the base of the cage and the seat. Even under worst-case thermal growth conditions the thermal compensator gap is never reduced to zero. Thus, thermal growth has no ef feet on operability of the valve.

Some additional design changes have been incorporated into the St.'Lucie 2 PORVs since the Marshall steam tests. They are as follows:

a) Installation of Garrett designed and manufactured, direct-acting, integral, IEEE Qualified three-way solenoids.

b) Installation of flexitallic gaskets at the body-to-bonnet joints and the body-to-solenoid joints. This redesign corrected slight external steam leakage problems encountered during the first fuel cycle at St.

Lucie 2.

c) Installation of magnets stabilized at 300oC for the main valve position indicating switches. This prevents loss of magnet strength at operating temperatures and thus loss of position indication. This problem was encountered during the first fuel cycle at St. Lucie 2 and resulted from magnets being stabilized at too low a temperature (200oC).

Installation of longer magnet rods to allow additional range of adjustment of. the main valve position indicating switches. During

=

initial switch adjustments at'St. Lucie 2, it was found that'the closed position indication switches had to be set close to the end of the adjustment range.

uestions related to the block valves:

~uestion 6.

The March 22, 1983 submittal states that the PORV block valves at St.

Lucie Unit 2 are Westinghouse 0306GM88FNH (88 Series) motor operated gate valves. This information does not agree with the information transmitted by R. C. Youngdahl on behalf of member utilities which indicates that the block valves at St. Lucie 2 are 2 I/2 inch model 75-L-012 Target Rock Gate Valves.

The Youngdahl transmittal test results indicate that some problems have been identified relating to the torque requirements to operate the Westinghouse valve. The tests indicated that the model 3GM88 valve with the vendor-recommended actuator and - torque switch setting was insufficient to reliably close the valve.

Please confirm what PORV block valves and actuators are actually used at St. Lucie 2. If the valves are Westinghouse series 88, then provide information to identify how the special torque requirements of this valve have been accommodated. If the block valves used at St. Lucie 2 are Target Rock, then information should be provided to meet the requirements of NUREG Item II.D.I regarding the block valves. The Target Rock Valve was not included in EPRI Marshall block valve tests.

Res onse to uestion 6.

The St. Lucie Unit 2 PORV block valves are Westinghouse Model 0300GM88FNH (Series 88) gate valves with Limitorque Model SB-00-15 operators. Prior to the actual Westinghouse block valve testing (during calibration and checkout activities), the valve failed to close against flow and differential test conditions. Subsequent investigation and testing performed by Westinghouse and detailed in Reference 8 indicated that the stem thrust required to clo'se the valve under design conditions was underpredicted. To assure full closure of the valve, Westinghouse recommended a gear ratio change and a rewire of the 'motor operator to achieve limit switch closure control in lieu of the standard torque switch control. Both of these modifications were implemented on the St. Lucie Unit 2 PORV block valves by Limitorque prior to installation.

Westinghouse has further certified that these block valves will fully open and close under design differential pressure and full flow conditions.

uestions on thermoh draulic anal sis:

Question 7.

. The submittal states that a thermal-hydr'aulic analysis was performed using RELAP5 and the results input into. the postprocessor code CAPLOTFIII for the development of the appropriate forcing functions and time histories.

Some details of the analyses were not provided. To allow for an evaluation of the methods used provide a sketch of the model and identify the valve opening times used in the analysis. The code CAPLOTFIII is a special purpose code without wide use. Provide a discussion on how this code has been verified to provide confidence that it computes correct forcing functions. Also, since the ASME Code requires derating of the safety valve to 90% of expected flow capacity, the actual flow would be expected to exceed the rated flow. Flows measured during the EPRI tests confirmed this expectation. These higher flows would produce higher piping loads; therefore, explain the method used to establish the flow rates of the safety valves and the PORVs used in the analyses.

Res onse to uestion 7.

A The models used in the thermal hydraulic transient analyses are shown in Figures 0 and 5. The stress analysis models have also been attached to this response as Figures 6 thru 8. Also, attached as Figure 9 is the pressurizer model included in the piping stress analysis. The valve opening times used in the analyses are 6 msec for the SRV and 130 msec for the PORV. As described in the report, they are the shortest opening times measured in the EPRI PWR safety and relief valve test program (Reference 3).

The postprocessor CALPLOTFIII was programmed to convert the transient flow conditions (calculated by RELAP5/MODl) into transient forces on the piping system. The derivation of the governing questions are shown in Appendix 1. The validity of the program coding was verified by comparing hand calculation results against the values computed by the program. The program was further assessed with the CE 0-inch pipe blowdown test results. Favorable comparisons were observed in comparing the computed results against the test data.

Due to the discrepancy of the RELAP5/MOD1 choke flow model, as was demonstrated in the EPRI RELAP5/MOD1 application (Reference 6),

adjusted valve flow areas have to be used to generate the required flow rates. The actual calculated flow rates for the SRV actuation case are shown in Table 2.

uestions on structural anal sis:

uestion 8.

The submittal states that the results of the thermal-hydraulic analysis were compared with the analysis which had resulted in the present design and the conclusion was reached that the piping and supports are adequate for the calculated hydraulic loads. Since the loading is a time dependent loading at numerous locations, dynamic considerations are necessary in making the comparison. Details of the comparison were not provided. To allow an evaluation of the comparison explain how the comparison was made. If computer programs were used in the comparison identify the programs and explain how they have been verified for this application.

Identify the load combinations considered and the allowable stress criteria for each combination. If the combinations and acceptance.criteria differ from those recommended in the, "EPRI Safety and Relief Valve.. Test

'Program Cuide for Application of Valve Test Program Results" provide the rationale for the selection.

Res onse to uestion S.

A dynamic analysis has been performed for the St. Lucie Unit 2 pressurizer PORV and safety valve discharge piping. Therefore, no comparison of hydraulic forces was necessary since the piping and supports have been qualified using calculated loads. The program used for the dynamic analysis is PIPESTRESS2010 which is a benchmarked program discussed in the St. Lucie Unit 2 FSAR. The specific technique used was generalized response analysis where the time history of the applied load is used to calculate a model bound solution. The pipe stress load combinations are consistent with SRP 3.9.3 Revision 1 requirements, which are as or more conservative than the EPRI recommendations; namely, OBE combined with the maximum values of PORV and SRV loads have been evaluated using Level B limits and DBE combined with the maximum values of PORV and SRV loads have been evaluated using Level D limits. The loading used in the design of the restraints was the combination of the worst thermal, dead weight, seismic and PORV/SRV discharge loads. The restraint design considered this combination and normal allowable stress values.

REFERENCES

1. Dresser Report SV-203A, dated June 30, 1983.

2. Summary Report on the Operability of Power Operated Relief Valves in CE Designed Plants, CEN-213, dated June, 1982.

3. EPRI Safety and Relief Valve Test Program, EPRI Report NP-2628-SR, December, 1982. "

0. Heavier Rate Springs for 31533VX-30 Electromatic, Dresser Technical Review No. 32-85-65-RSH, October 29, 1985.

5. Garrett Engineering Report 10-3135B, End Load Analysis for the Solenoid Operated Relief Valves for CE Power Systems, May, 1983.

6. Application of RELAP5/MODl for Calculation of Safety and Relief Valve Discharge Piping Hydrodynamic Loads, EPRI Report NP-2079, December, 1982.

7. EPRI Safety and Relief Valves Test Program, Valve Selection/Justification Report, EPRI Report NP-2292, dated December, 1982.

8. EPRI Summary Report: Westinghouse Gate Valve Closure Testing Program, prepared by Westinghouse Electro-Mechanical Division, March 31, 1982.

WP/DISC j/PSL0005/TMI Action NUREG/0286/L

TABLE l St Lucie Unit 1 Steady State Backpressure Calculations SRV Downstream SRV Flowrate Calculated Flowrate* Pressurizer Pressure (psia) (ibm/sec) Rated Flowrate Pressure (psia)

Valve/Pressure a) 3 SRV's V-1200/351 71. 1 1.202 2528.7 (at end of RELAP5 run. Y-1201/362 71.1 1.202 time =0.6 sec) V-1202/337 71.1 1. 202 b) 2 PORV's V-1200/125 0.0 2434.7 (at end of RELAP5 run Y-1201/124 0.0 time ~ 0.6 sec) V-1202/123 0.0 SRV Rated Flowrate is 2i3000 ibm/hr (Crosby 3K6)

TABLE 2.

ST, LUCIE UNIT 2 STEAOY STATE BACKPRESSURE AND FIOW RATE CALCULATIONS DOWNSTREAM FLOWRATE CALCULATED F MWRATE CASE VALVE NUMBER PRESSURE sia 1bm sec a) PORV actuation V-1200 205 0.0 (at end of RELAP5 V-1201 201 0.0 run

, V-1202 200 0.0 time ~ 0.6 sec) V-1474 116.0 1.06 318 V-1475 321 115.0 1. 05 b) SRV actuation .

V-1200 308 72.2 1.22 (at end of RELAP5 V-1201 306 72.2 1.22 06,) 298 72.2 1.22 V-1474 186 0.0

.V-1475 184 0.0

• SRV Rated Flovrate is 213000 1bm/hr PORV Rated Flovrate is 395000 1bm/hr

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APPENDIX I DESCRIPTION OF CALPLOTFIII

B-I . Mathematical Model The CALPLOTFIXIcomputer code has been written to convert the transient flow conditions calculated in a piping system by the RELAP5H)D 1 Computer code into transient forces on the piping system, Specifically~ CALPLOTFIIIcalculates and plots the forces on straight lengths of pipe between changes in pipe direction (bends) ~ or between a change in direction and a pipe break, The derivation of the equations used in the code are given below.

B-I-l Strai ht Len ths of Pi es Between Directional Chan es The force on a straight length of pipe between direction changes (Figure B.l) is calculated using the momentum equation:

F + Bpdv ~ V (pV ~ dA) + V (pdv) (Bl) cv cs cv If the gravity term is assumed negligible, the following equation results:

F ~ ~V (pV ~ dA) + Bt/ V (pdv) (B2) cv Since the force on the straight pipe length only exists in one dimension, the above equation can be written in a scalar form:

F s

~ V (pV ~ dA)+- at Vpdv (B3) cs cv Since the RELAP5 MOD 1 i', Computer code calculates the pressures and the flowrates.at different physical positions in the piping system, it. is necessary to subdivide a piping length into two control

'volume types for application of the momentum equation The first division

~

creates the pressure control volumes; The divisions for the pressure

'ontrol, volumes are thepositions'in'he pipe length where the pressures are calculated by the computer code, and serve as the boundaries across which the control volume surface forces are calculated. The second control volume divisions are due to flow conditions The boundaries of the flow control volumes are located at the pipe length locations where flows are calculated by the computer code. The forces in the pipe length which are due to the rate of efflux of momentum across a control volume and the change of momentum in a control volume are calculated using the flow boundaries as flow control volume divisions

The resultant force on the fluid across the boundary of the pressure .

control volumes 1 ~ 2 ~ and 3, shown in Figure B.l, are:

F Sl

~ -(P A -P a ) AA + R (B4)

(B A) (B5)

FS3 2 A A "B ') "B B

'3 B

F 2

(B6)

The net surface force on the straight pipe length is obtained by summing equations B4, B5, and B6:

(B7)

Sl S2 S3 1 2 3 F ~ R (Bg)

S Therefore, the force on the straight pipe length due to surface forces is equal to the net normal and shear stresses on the pipe wall length+

The right side of equation B3 can now be evaluated for each of the flow Sl,g control volumes A and B:

2 P2 2 BMA F hA + ae, (B9) 2 p> Vg A< 8+

S2

+ ~t hB (Blo) 8 Since the RELAP5 computer code calculates non thermal equlibrium conditions for two phase flow conditions and allows the two phases to possess different velocities, the parameters of equations(B9), (B10) are defined as:

MA 1A 1A ~ A A A (B11) lB1B B '+~B BB) "B (B12) 2 2 P2 2 l2 12 2 g2 g2 2 (BX3)

Summing equations B9 and B10, and using equation BS, the net fluid force on the pipe length can be obtained:

K > -F S

~ <<R ~

-aae, Bt hA - Be hB (B14)

If the straight length of pipe considered is bounded by a directional change and an open end, a break, the forces obtained using equation Bll must be modified to account for the force developed at the pipe exit plane. Consequently, using the momentum equation, the force on the straight pipe length shown on Figure B.2, for unchoked break flow, can be written as:

2

-p2 V2 A2 BMA K hA (B15)

Unc 8 Be If choked break flow is determined to exist by the fluid transient computer code, then equation B15 must be modified to account for the pressure unbalance that occurs at the pipe exit plane. A rederivation of the equation for the straight pipe length for this case results in the following relation:

K ch

- -(P 2 -P)a A

<<p g

2 A

-BA Be h hA (B163 or Kh ch

~ K unc

- (P 2 -P)a A (Blg where:

'22

~ 'A 2h +

Y 2g

'2 h P2 2g 2

2 Qp f - 4P acc

- hP el (Blg )

=P A +PAh V2 V2 P

2 22 2g 2g (B19) pAVA 2 - p v2 (1-a)+p v (B20)

A gA gA A

Nomenclature flow area B body force of a control volume surface force resultant on a control volume gravitational constant force of fluid on piping control volume flowrate pressure P pressure outside pipe control volumes R normal and shear stresses in a control volume time volume of a control volume velocity of fluid in a control volume Greek Letters P density in'ontrol volume a void fraction Subscripts acc icceleration friction

,'h choked flov cs control surface control volte el eIevation unc unchoked 1 liquid gas

'VOL. 2 I

+ FORCE I

I I

I B I

I I

I I

I l

I I

I LEGEND:

PRESSURE BOUNDARY

--FLON BOUNDARY

Pique B.2 VOL. 1 VOL. 2 I

+ FORCE I

LEGEND:

PRESSURE BOUNDARY

-- - FLOW BOUNDARY