ML19321A056

Analysis of 800226 Pressurizer Transient Relief Valve Discharge

ML19321A056
Person / Time
Site:	Crystal River
Issue date:	06/30/1980
From:	Arauz G, Bunker P GILBERT/COMMONWEALTH, INC. (FORMERLY GILBERT ASSOCIAT
To:
Shared Package
ML19321A054	List: ML19321A053 ML19321A056
References
NUDOCS 8007220385
Download: ML19321A056 (12)

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ANALYSIS OF FEBRUARY 26, 1980 PRESSUR1ZER TRANSIENT RELIEF VALVE DISCHARGE I

t CRYSTAL RIVER UNIT 3 NUCLEAR PLANT FLORIDA POWER CORPORATION June 1980 l

Gonzalo A. Arauz Piping Engineering Department 4

Gilbert Associates, Inc.

Paul L. Bunker Nuclear Analysis Department Gilbert Associates, Inc.

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INDEX Section Title Page 1.0 OBJECTIVES 1

2.0 PERTINENT ANALYSIS ASSUMPTIONS 1

3.0 APPLICABLE CODE 2

4.0 REFERENCES

2 5.0 COMPUTER PROGRAMS 3

6.0 THEORY AND ANALYTICAL TECHNIQUE 3

7.0 DATA USED AND SOURCES 4

8.0

SUMMARY

OF RESULTS 4

ATTACHMENTS Appendix Table CR Load Comparison of Transient Analyses for RCV-8(F)

l Figure 1 - Thrust vs. Time - RCV-8(F)

Figure 2 - Thrust vs. Time - RCV-10(F)

Figure 3 - Piping Isometric - RCV-8(F) Discharge Line Figure 4 - Piping Isometric - RCV-10(F) Discharge Line a

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g 1.0 OBJECTIVES To calculate the loadings induced on the pressurizer relief nozzles and relief valve, pipe stresses and pipe support loads during relief valve operation that occurred during the transient on February 26, 1980.

Also, to find out if these loadings were in excess of the original design loads.

This report is a response to the recommendation specified in Section IV, paragraph H-2 of the " Transient Assessment Report" No. 07-80-02, Rev. 00, dated March 2, 1980, prepared by the Babcock and Wilcox Company.

2.0 PERTINENT ANALYSIS ASSUMPTIONS 2.1 Based on the information given in reference 4.1, the pressure, temperature, and flow conditions experienced by the power operated relief valve RCV-10(F) were not outside its design parameters. Relief valve RCV-8(F) was the only valve that discharged water during the transient conditions. The remaining relief valve RCV-9(F) is assumed to have never opened.

If RCV-9(F) did open, we would expect its results to be the same as those of RCV-S(F) because of the similarity of their discharge lines.

2.2 The assumptions and data used to determine the thermal-hydraulic conditions in the piping system are given below:

a.

Pressurizer Conditions Incident - Pressurizer solid - Ref. 4.1.

It was assumed that no steam existed in the pressurizer or pressurizer nozzle. The temperature of the pressurizer water was assumed to be at the RCS hot leg temperature of 560 F (s100 subcooled). The highly subcooled water results in higher flow rates through the valve yielding conservatively high pipe forces.

The pressurizer pressure for the incident transient,is 2410 psia.

b.

Valve Data & Assumptions The valve flow area was conservatively calculated using design rated flow with 10% accumulation and assuming a 5% error, yielding a maximum calculated flow of 1.17 x design rated flow.

The flow area was calculated at design pressure by'using the Moody critical flow data.

The valve opening time ranges from.04 to.06 seconds Ref. 4.14 for design conditions. An opening item of.04 seconds was assumed for the analysis. A linear valve opening was assumed for both design and water discharge cases.

2.3 All of-the hydraulic snubbers were assumed to be functional at the time of the incident.

3.0 APPLICABLE CODE ANSI B31.1 Power Piping, 1967

4.0 REFERENCES

4.1 Preliminary transient assessment report for reactor trip at Crystal River 3 nuclear station on February 26, 1980; report number 07-80-02, revision 00, prepared by Nuclear Power Generation Division, The Babcock and Wilcox Company, Lynchburg, Virginia, dated March 2, 1980.

4.2 GAI time history analysis CR-32, dated December 1974 for normal transient conditions of the pressurizer relief line from RCV-8(F) to R.C. drain tank, reactor building.

4.3 GAI time history analysis CR-33, dated December 1974 for normal transient conditions of the pressurizer relief line from RCV-9(F) to R.C. drain tank, reactor building.

4.4 GAI time history analysis CR-34, dated December 1974 for normal transient conditions of the pressurizer relief line from RCV-10(F) to R.C. drain tank, reactor building.

. 4.5 GAI time history analysis CR-32, dated June 19, 1980, for abnormal transient condition (water discharge) of the pressurizer relief line from RCV-8(F) to R.C. drain tank, reactor building.

4.6 GAI transient analysis "CR-32 Design," job #J31, dated April 10, 1980 (Design case for RCV-8(F)).

4.7 GAI transient analysis "CR-32, COMPFL," job #J136, dated June 17, 1980

'(Incident case for RCV-8(F)).

4.8 GAI transient analysis "CR-34, Design," job #J390 dated April 11, 1980 (Design case for RCV-10(F)).

4.9 Unbalanced force analysis "A1131 RCV-8(F) Force 5 Data," dated April 11, 1980 (Design case for RCV-8(F)).

4.10 Unbalanced force analysis "A1131 CR32-COM100 Data," dated June 17, 1980 (Incident case for RCV-8(F)).

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1 4".11 Unbalanced for analysis "A1131 RCV10 Force 1 Data," dated April 11, 1980 (Design case for RCV-10(F)).

4.12 Safety valve drawing CP-1877 by Dresser Industrial Valve and Instrument Division (GAI file 4203-77-263).

4.13 Electromatic relief valve drawing CP-1548 by Dresser Industrial Valve and Instrument Division (GAI file 4203-77-262).

3 4.14 Telecon - Roland Hoffman, Consolidated Valves Dresser Industries, Ron Snow, GAI, March 19, 1980 - Subject - Opening Times of Valves RCV-8(F), RCV-9(F), and RCV-10(F).

4.15 Strong, B.R.' and Baschiere, R.J., " Steam llammer Design Loads for

. Safety / Relief Valve Discharge Piping," paper presented at 1978 ASME/CSME Pressure Vessel and Piping Conference Session 36, Montreal, Canada.

5.0 COMPUTER PROGRAMS 4

5.1 PIPDYN II, a computer program for the complete analysis and evaluation of piping systems and three dimensional frame structures, the Franklin Institute, applied mechanics laboratory.

1' 5.2 RELAP/ MOD 5 THERMAL HYDRAULIC computer program for the time history of i

pressute and flow inside the relief lines.

(ANCR-NUREG-1335, Sept. 1976) 5.3 THRUST PROGRAM, a post processor of RELAP4/ MOD 5 program in paragraph 5.2, to_ calculate the unbalanced piping acceleration loads along each section of pipe.

6.0 THE0nf AND ANALYTICAL TECHNIQUE 6.1 Determination of Unbalanced Forces The Relap4/ Mod 5 Ref. Section 5.2 computer code was used to model the pressurizer, relief valve, discharge piping, and reactor coolant drain tank. The models for the 4 in. Line (PORV) and 6 in. line (RCV-8) were 4

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37 and 34 nodes respectively. The discharge lines were modeled with the nodes symmetric about the bends. Junctions between nodes were modeled using the compressible form of the momentum equation with momentum flux.

Flow choking was allowed only at the valve and spargers in the reactor coolant drain tank. The critical flow models used are Henry-Fauske for stabcooled conditions and Moody for the two phase and saturated conditions. A critical flow multiplier of 1,was used.

The results of the Relap model were used in the TERUST code which calculates unbalanced forces on each segment of pipe using the force equivalent area method as desribed in Reference 4.15.

Computer results in references 4.6, 4.7, 4.8, 4.9, 4.10 and 4.11.

6.2 Using the results from reference 4.10, a time history analysis was performed to calculate the incident transient loading induced on the pressurizer relief nozzle and also the loading on the restraints for relief line from RCV-8(F) to the drain tank. The computer program in' paragraph 5.1 was used for this analysis.

(Computer results in reference 4.5.)

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4 6.3 The incident transient loads were calculated for the first 4 sections of pipe downstream of the pressurizer, since these sections are the major contributors to the loads on the pressurizer nozzle (see Fig. 3).

The loads on the remaining sections will have an insignificant effect on the pressurizer, because the restraints protecting the pipe would absorb these loads. The resultant loads and stresses for these sections of pipe would be similar to the ones calculated for the first 4 sections closer to the pressurizer. Therefore, analysis of the entire discharge pipe is not necessary to prove the pressurizer's structural integrity during the incident transient.

6.4 The final step was to compare the results from paragraph 6.3, reference 4.5, to the original design trans e loads from reference 4.2.

(See table CR-32 for comparison.)

7.0 DATA USED AND SOURCES 7.1 Design Pressure Reference 4.12 states that the relieving pressure to be used for relief valves RCV-8(F) and RCV-9(F) is 2500 psig, and from reference 4.13 the relieving pressure for power operated valve RCV-10(F) is 2300 psig.

7.2 Incident Pressure From reference 4.1, the relieving pressure during the incident conditions for relief valve RCV-8(F) is assumed to be 2410 psia.

7.3 Ma::imum Steam Flow Rate From reference 4.12, the design flow rate for both relief valves RCV-8(F) and RCV-9(F) is 317,973 lbs per hour.

From reference 4.13, the design flow rate for the power operated relief valve RCV-10(F) is 100,000 lbs per hour.

7.4 Maximum Water Flow Rate (Incident)

From reference 4.1, the waterflow rate during the incident for relief valve RCV-8(F) is calculated to be 370 lbs per second (1,333,000 lbs per hot'r). This is based on the Henry-Fauske Critical Flow model.

8.0

SUMMARY

OF RESULTS 8.1 Normal Transient The original transient loadings for the design conditions of RCV-8(F) and RCV-10(F) were verified with the analytical methcds described in sections 5.2 and 5.3.

The results from this verification (reference 4.9 and 4.11) are shown in Figure No. I and No. 2.

We would like to point out that the " Thrust vs. Time" curves shown in figures 1 and 2 represent the maximum thrust load on leg #1 (see figures 3 and 4 for o

5 location). The magnitude of the impact of the valve discharge forces on the pressurizer and piping system is dependent on both the time of the force buildup and the magnitude of the forces. Therefore, even though the updated design transient rises faster than the original design transient, the overall impact on the pressurizer and piping system is less than before since the magnitude of the updated design transient is much lower.

8.2 Inci/.ent' Transient (Water Discharge)

A comparison of the original design transient and the incident transient loadings for RCV-8(F) is shown in table CR-32.

This table is a partial comparison for the first 4 sections of pipe downstream of the pressurizer.

The loads for the remaining sections would be similar to the ones shown on this table as explained in paragraph 6.3.

The calculated incident transient loadings at the nozzle connection to the pressurizer are larger than the original design. The maximum calculated pipe stress for this location is 1788 psi. This stress is relatively low when compared to the allowable stress for sustained loads given by the applicable code ANSI B31.1.

The calculated maximum piping stress anywhere in the piping system is still below the code allowable stress level.

The incident loads on the pipe supports are higher than the original design loads. The hydraulic snubbers all have adequate capacity to accommodate these higher loads. The pipe and structural attachments are currently being checked to determine if they meet all code allowable limits. A visual inspection of all the supports has revealed no failures or damage.

8.3 Conclusion Based on the results obtained by this analytical investigation, we believe that even though the incident forces and moments are higher than the original design loads, it can still be concluded that no damage occurred to the pressurizer, reactor coolant drain tank, and the safety valve dis-harge piping and pipe supports, and this system can still be considerei safe to support the continued operation of Crystal River Unit 3.

This conclusion has been verified by the various system inspections performed to date at the Crystal River Unit 3 plant site.

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