ML18100B210

Deficiency Rept Re PORV Plug & Stem Material Defects. Initially Reported 940714.PORV Internals Were Replaced W/Plug Stellited

ML18100B210
Person / Time
Site:	Salem
Issue date:	07/14/1994
From:	Thompson F Public Service Enterprise Group
To:
References
NUDOCS 9407210139
Download: ML18100B210 (6)

Text

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IPOWER REACTOR II EVENT NUMBER: 2 7 53 2 II FACILITY: SALEM REGION: 1 NOTIFICATION DATE: 07/14/94 UNIT: [l] [ ] [ ] STATE: NJ NOTIFICATION TIME: 15:56 [ET]

RX TYPE: [1] W-4-LP I [2] W-4-LP EVENT DATE: 07/14/94 EVENT TIME: OO:OO[EDT]

NRC NOTIFIED BY: F. x. THOMSON LAST UPDATE DATE: 07/14/94 HQ OPS OFFICER: THOMAS ANDREWS NOTIFICATIONS EMERGENCY CLASS: NOT APPLICABLE 10 CFR SECTION:

cccc 21. 21 UNSPECIFIED PARAGRAPH UNIT SCRAM CODE I Rx CRITIINIT PWRI INIT RX MODE CURR PWRI CURR RX MODE 1 N y 100 POWER OPERATION 100 POWER OPERATION EVENT TEXT

- - - PORV PLUG AND STEM MATERIAL DEFECTS AT SALEM UNIT 1 - - -

THE FOLLOWING IS A

SUMMARY

OF THE RESULTS OF PSE&G'S EVALUATION IN ACCORDANCE WITH 10CFR21 CONCERNING A DEFICIENCY DUE TO THE CRACKING IDENTIFIED IN THE VALVE STEM AND PLUG CONNECTION PINNING COLLAR AREA ON UNIT 1 PORVS lPRl & 1PR2. THE CAUSE OF THIS CRACKING HAS BEEN ATTRIBUTED TO EITHER INTERGRANULAR STRESS CORROSION CRACKING (IGSCC) OR HYDROGEN ASSISTED CRACKING. THE CRACKING IN THE PINNING COLLAR AREA COULD CONTINUE TO PROPAGATE EVENTUALLY RESULTING IN THE PLUG SEPARATING FROM THE STEM RENDERING THE PORVS INOPERABLE. THE UNIT 2 PORVS CURRENTLY ARE PROVIDED WITH INTERNALS MANUFACTURED FROM 17-4 PH MATERIAL, AND THEREFORE UNIT 2 IS NOT WITHIN THE SCOPE OF THIS 10CFR21 EVALUATION.

THE REACTOR TRIP AND INADVERTENT SI INITIATION THAT OCCURRED ON APRIL 7, 1994 AT SALEM UNIT 1 RESULTED IN THE TWO (2) PRESSURIZER POWER OPERATED RELIEF VALVES (PORV) TO CYCLE MULTIPLE TIMES DURING THE EVENT. SUBSEQUENT INSPECTION OF THE VALVE INTERNALS (PLUG, STEM, AND CAGE) REVEALED CRACKS IN THE PINNING COLLARS OF EACH OF THE TWO PLUGS, AND SIGNIFICANT UNEXPECTED WEAR AND GALLING ON THE 1PR2 STEM AND PLUG. FOLLOWING IDENTIFICATION OF THE CRACKING, THE 10CFR21 EVALUATION PROCESS WAS INITIATED ON MAY 9, 1994.

INSPECTION OF SPARE VALVE INTERNALS LOCATED IN THE WAREHOUSE ALSO REVEALED CRACKS IN THE PINNING COLLAR. THE THREE SETS OF VALVE INTERNALS WERE EXAMINED BY WESTINGHOUSE TO DETERMINE THE CAUSE OF THE CRACKING. THE SUBSEQUENT INVESTIGATION AND EXAMINATIONS REVEALED THAT THE CRACKS ORIGINATED AND GREW PRIMARILY AS A RESULT OF EITHER INTERGRANULAR STRESS CORROSION CRACKING OR HYDROGEN ASSISTED CRACKING. IT IS NOTED THAT A FOURTH SET OF INTERNALS THAT HAD BEEN INSTALLED IN THE PLANT FOR 1 WEEK ALSO REVEALED CRACKING.

(Continued on next page)

(

9407210139 940714 PDR ADOCK 05000272 1I S PDR

FACILITY: SALEM PAGE # 2 OF EVENT NUMBER: 27532 THE CAUSE OF THE STRESS CORROSION CRACKING WAS ATTRIBUTED TO THE FOLLOWING FACTORS. THE PLUG WAS MANUFACTURED FROM TYPE 420 STAINLESS STEEL AND SUBJECTED TO A 975 [DEGREE] F TEMPERING HEAT TREATMENT. THIS CAUSED THE MATERIAL TO BECOME SENSITIZED REDUCING ITS CORROSION RESISTANCE, AND CAUSED THE MATERIAL TO BECOME LESS DUCTILE REDUCING ITS FRACTURE TOUGHNESS. A TAPERED FIT BETWEEN THE STEM AND THE PLUG CAUSED HOOP STRESSES TO BE EXERTED ON THE PLUG AT THE PINNING COLLAR. THE COMBINATION OF THE MATERIAL CONDITION AND THE HOOP STRESSES WERE SUCH THAT STRESS CORROSION CRACKING OCCURRED IN A RELATIVELY SHORT PERIOD OF TIME, ESPECIALLY FOR THE SPARE VALVE INTERNALS WHICH HAD NOT SEEN ACTUAL SERVICE BUT ONLY LEAK TESTING AND ENVIRONMENTAL HUMIDITY WHILE IN STORAGE. THE INVESTIGATION WAS UNABLE TO DETERMINE IF THE CRACKING WOULD HAVE ARRESTED ITSELF AFTER SOME PERIOD OF OPERATION OR CONTINUED TO PROPAGATE.

THE PORVS AT SALEM ARE 2" AIR OPERATED-SPRING RETURN VALVES SUPPLIED BY THE COPES VULCAN, INC. THE VALVES HAVE A WORKING PRESSURE RATING OF 2485 PSIG AT 680 [DEGREES] F PER ANSI B16.5 FOR 1500 LB. RATING. THE NORMAL OPERATING PRESSURE FOR THE PORVS IS 2235 PSIG AT 650 [DEGREES] F. THE PORVS ARE SET TO OPEN AT A PRESSURE OF 2335 PSIG AND CLOSE AT 2315 PSIG ..

THE VALVE INTERNALS ARE COMPRISED OF THE PLUG, STEM AND CAGE. THE CAGE IS A HOLLOW CYLINDER SURROUNDING THE. PLUG, AND IS PROVIDED WITH A NUMBER OF FLOW PORTS WHICH EVENLY DISTRIBUTE FLOW THROUGH THE VALVE. THE PLUG/STEM ASSEMBLY MOVES WITHIN THE CAGE CYLINDER IN RESPONSE TO OPEN OR CLOSE CONTROL SIGNALS TO THE ACTUATOR EITHER OPENING OR THE CAGE FLOW PORTS. THE PLUG IS JOINED AND SECURED TO THE STEM THROUGH A CONICAL THREADED CONJUNCTION. AT THE TOP OF THE PLUG IS AN INTEGRAL PINNING COLLAR.

FOLLOWING ASSEMBLY OF THE PLUG/ STEM A PINNING HOLE IS DRILLED THROUGH THE PLUG COLLAR AND STEM AND A ROLL PIN IS INSERTED. IN MOST CASES, THE PINNING HOLE IS DRILLED PRIOR TO HEAT TREATMENT. IT IS AT THE PINNING COLLAR LOCATION WHERE STRESS 'CORROSION CRACKING OCCURRED. SINCE BOTH OF THE PORV PLUGS INSTALLED AT UNIT 1 (AS WELL AS THE THIRD AND FOURTH PLUG ASSEMBLIES UTILIZED AS SPARES) WERE CONSTRUCTED USING THE SS 420 MATERIAL, A COMMON MODE TYPE FAILURE DUE TO THE PLUG CRACKS IDENTIFIED MAY HAVE AFFECTED BOTH PORVS. IT IS BELIEVED THAT SHOULD THE CRACKS HAVE CONTINUED TO PROPAGATE THROUGH THE PLUG, BOTH PORVS COULD HAVE BEEN RENDERED INOPERABLE IN EITHER THE OPEN OR CLOSED POSITION.

DURING DESIGN BASIS TRANSIENTS, THE PORVS ARE UTILIZED TO PREVENT CHALLENGES TO THE PRESSURIZER SAFETY VALVES AND PROVIDE RCS OVERPRESSURE PROTECTION. THE PORV(S) ARE ASSUMED TO BE AVAILABLE OR MADE AVAILABLE IN THE EVENT OF (A) THE INADVERTENT SAFETY INJECTION (SI) AT POWER TRANSIENT AND (B) THE LOW TEMPERATURE OVERPRESSURE PROTECTION (LTOP) TRANSIENT DURING SHUTDOWN. WITH THE EXCEPTION OF THESE TWO TRANSIENTS, THE PRESSURIZER SAFETY VALVES WOULD BE AVAILABLE TO PROVIDE RCS OVERPRESSURE PROTECTION SHOULD THE PORVS FAIL. SHOULD THE PORVS OPEN AND FAIL TO CLOSE, THE FAILED PORVS WOULD BE MANUALLY ISOLATED BY THE PORV BLOCK VALVES TO PREVENT A LOSS OF REACTOR COOLANT.

THE INADVERTENT SI AT POWER TRANSIENT [(A) ABOVE] CREDITS THE AVAILABILITY OF THE PORVS SHOULD THE PRESSURIZER BECOME WATER SOLID TO PROVIDE RCS OVERPRESSURE PROTECTION. SINCE THE PRESSURIZER SAFETY VALVES ARE NOT DESIGNED TO RELIEVE WATER UNDER SATURATED CONDITIONS, AND COULD POTENTIALLY FAIL IN THE OPEN POSITION IF THE PORVS ARE UNAVAILABLE DURING THIS (Continued on next page)

• I FACILITY: SALEM PAGE # 3 OF EVENT NUMBER: 27532 TRANSIENT, THE TRANSIENT COULD DEGRADE FROM A CONDITION 2 EVENT TO A CONDITION 3 EVENT. HOWEVER, EVEN IN THE EVENT OF A PRESSURIZER SAFETY FAILING IN THE OPEN POSITION, THE CONSEQUENCES OF THIS ACCIDENT WOULD STILL BE BOUNDED BY THE SMALL BREAK LOCAL ANALYSIS RESULTS. SHOULD THE PORVS FAIL IN THE OPEN POSITION, PORV BLOCK VALVES CAN BE CLOSED TO ISOLATE THE RCS AND PREVENT COOLANT LOSS.

DURING (B) ABOVE, THE PORVS LIFT SETTING IS ADJUSTED TO A SETPOINT EQUAL TO OR LESS THAN 375 PSIG WHEN THE RCS COLD LEG TEMPERATURES ARE LESS THAN 312

[DEGREES] F DURING MODE 4 AND MODE 5 TO PROVIDE LOW TEMPERATURE OVERPRESSURE PROTECTION. THE SETPOINT FOR THE PORVS HAS BEEN DEVELOPED SUCH THAT IN THE EVENT OF A MASS INPUT TRANSIENT (I.E., THE START OF A SI PUMP) OR A HEAT INPUT TRANSIENT (I.E., THE START OF AN IDLE RCP) WITH THE RCS WATER SOLID, THE PRESSURE-TEMPERATURE (P-T) LIMITS CALCULATED IN ACCORDANCE WITH 10CFR50, APPENDIX G AND CONTAINED IN TECHNICAL SPECIFICATION 3.4.9.1 WOULD NOT BE EXCEEDED. A MINIMUM OF ON PORV SHOULD BE AVAILABLE TO MITIGATE THESE TYPES OF OVERPRESSURE TRANSIENTS AND MAINTAIN RCS PRESSURE WITHIN P-T LIMITS. THEREFORE, THE FAILURE OF THE PORVS TO OPEN DUE TO THE STRESS .CORROSION CRACKING IDENTIFIED COULD RESULT IN EXCEEDING THE P-T LIMITS. IT IS BASED ON THIS FUNCTION OF THE PORVS THAT PSE&G HAS CONCLUDED THAT THIS DEFICIENCY COULD RESULT IN A SUBSTANTIAL SAFETY HAZARD, AND IS THEREFORE REPORTABLE IN ACCORDANCE WITH 10CFR21.

PRIOR TO RESTART FOLLOWING THE APRIL 7 EVENT, THE UNIT 1 PORV INTERNALS (PLUG AND STEM) WERE REPLACED WITH INTERNALS MANUFACTURED FROM SS 316 MATERIAL WITH THE PLUG STELLITED. THE REPLACEMENT CAGES WERE MANUFACTURED FROM 17-4 PH STAINLESS STEEL.

• 4-94 : 15=14 ; 301 8165151;# 2/ 4

• ~ENT

..B);:

~ i 1

INITIAL 10CFR21 Nq IFICATION PORV PLUG AND STEM MATERIAL P.UBLIC SERVICE ELECTR.C AND GAS CO.

SALEM GENERATING STATi ON UNIT 1 I

I The following is a summary of the re'ults of PSE&G 1 S evaluation in accordance with 10CFR21 concernin' a deficiency due to the cracking identified in the valve ste'. and plug connection pinning collar area on Unit 1 PORVs lPRl & i* *R2. The cause of this cracking has been attributed to eith*r Intergranular Stress Corrosion Cracking (IGSCC) or hydrog.n assisted cracking. The cracking in the pinning collar area ::ould continue to propagate eventually resulting in the plug sep'rating from the stem rendering the PORVs inoperable. The~ \unit 2 PORVs currently are provided with internals manufactured: :from 17-4 PH material, and therefore Unit 2 is not within the s: 'ope of this 10CFR21 evaluation.  ::

i The reactor trip and inadvertent SI ~

nitiation that occurred on April 7, 199,4 at Salem Unit 1 result: :a in the two (2) pressurizer Power Operated Relief Valves (PORV) : :*o cycle multiple times during the event. Subsequent inspec.. ion of the valve internals (plug, stem and cage) revealed crack: in the pinning collars of each of the two plugs, and significa. ,t unexpected wear and galling on the 1PR2 seem and plug. '.allowing identification of the cracking, the 10CFR.21 evaluation\ \process was initiated on May 9, 1994. Inspection of spare valve nternals located in the 1

warehouse also revealed cracks in th: : pinning collar. The three sets of valve internals were examine . by Westinghouse to determine the cause of t.he cracking.!; The subsequent investigation and examinations revea *ed that the cracks originated and grew primarily as a r *sult of either intergranular stress corrosion cracking or hydroge '. assisted cracking. It is noted that a fourth set of internals! '.that had been installed in the plant for 1 week also revealed c *acking.

I!

I' The cause of the stress corrosion er :eking was attributed to the following factors. The plug was man :factured from type 420 stai11less t;teel and subjected to a 9 ;s°F tempering heat treatment. This caused the material I *to become sensitized reducing its corrosion resistance, a~'.~ caused the material to become less ductile reducing its fra;ture toughness. A tapered fit between the stem and the plug ca :sed hoop stresses to be exerted on the plug at the pinning c~'.llar. The combination of the material condition and the hoop 'tresses were such that stress corrosion cracking occurred i,; a relatively short period of time, especially for the spare va.ve internals which had not seen actual se:r.-vice but only leak te, !ting and environmental humidity while in storage. The inve tigation was unable to determine if the cracking would havei~rrest.ed itself after some period of operation or continued to ~opagate.

Page 1 of ~

"SENT B~: 15: 15 PSE&G LI C &10 301 8165151;# 3/ 4 The PORVs at Salem are 2* air operat1d-spring return valves supplied by Copes Vulcan, Inc .. Tlle!valves have a working pressure rating of 2485 psig at 680° '. per ANSI B16.5 for 1500 lb.

rating. The normal operating pressu'.e for the PORVs is 2235 psig at 650°F. The PORVs are set to open* :at a pressure of 2335 psig and close at 23lS psig. The valve '.nternals are comprised of the plug, stem and cage. The cage i

• a hollow cylinder surrounding the plug, and is provide with a number of flow ports which evenly distribute flow throughithe valve. The plug/stem assembly moves within the cage cylin.er in response to open or close control signals to the actuate: either opening or closing the cage flow ports. The plug is jo$ned and secured to the stem through a conical threaded connectio~. At the top of the plug is an integral pinning collar. Followi g assembly of the plug/stem, a pinning hole is drilled through th ' plug collar and stem and a roll pin is inserted. In most cases !' the pinning hole is drilled prior to heat treatment. It is at t :e pinning collar location where stress corrosion cracking occu red. Since both of the PORV plugs installed at Unit 1 (as well a

• the third and fourth plug assemblies utilized as spares) were .onstructed using the SS 420 material, a common mode type failurel\due to the plug cracks identified may have affected both PO~Vs. It is believed that should the cracks have continued to ~ropagate through the plugl both PORVs could have been rendered ~'.noperable in either the open or closed position. i During design basis transients, the .ORVs are utilized to prevent challenges to the pressurizer safety !valves and provide RCS overpressure protection. The PORV (s}I are assumed to be available or made available in the event of (a)lj the Inadvertent Safe~y Injection (SI) at Power transient and; (b} the Low Temperature Overpressure Protection (LTOP) traris~ent during shutdown. With the exception of these two transient :, the pressurizer safety valves would be available to provide ~CS overpressure protection should the PORVs fail. Should the P ~Vs open and fail to close, the failed PORVs would be manually i '.olated by the PORV Block Valves to prevent a loss of reactor '.oolant.

I The Inadvertent SI at Power t:ransien 1 [(a) above] credits the availability of the PORVs should the pressurizer become water solid to provide RCS overpressure pr :tection. Since the pressurizer safety valves are not de !igned to relieve water under saturated conditions, and could pate !tially fail in the open position if the PORVs are unavailabl : during this transient, the transient could degrade from a Condi lion 2 event to a Condi ti on 3 event. However, even in the event o ! a pressurizer safety failing in the open position, the co.~equences of this accident would still be bounded by the Small ~eak LOCA analysis results.

Should the PORVs fail in the open po !ition, PORV Block Valves can be closed to isolate the RCS and pre ~nt coolant loss.

Page 2 of ~

~SENT,, B'f.: *4-94 ; 15=16 301 8165151;# 4/ 4 v

During (b) above, the PORVs lift set~ing is adjusted to a setpoint equal to or less than 375 p~ig when the RCS cold leg ternp7ratures are less than 312°F during Mode.4 and Mode 5 t~

provide Low Temperature Overpressure~*Protection. The setpoint

• for the PORVs has been developed sue : that in the event of a mass input transient (i.e., the inadverte ,"t start of a SI pump} or a heat input transient (i.e., the star~ of an idle RCP) with the RCS water solid, the Pressure-Temperature {P-T) limits calculated in accordance with 10CFRSD, Appendix ;*G and contained in Technical Specification 3.4.9.1 would not be ~ceeded. A minimum of one PORV should be available to mitigate!these types of overpressure transients and maintain RCS pressure ;.within P-T limits.

Therefore, the failure of the PORVs ~o open due to the stress corrosion cracking identified could result in exceeding the P-T limits. It is based on this function of the PORVs that PSE&G has concluded that this deficiency could :.result in a substantial safety hazard, and is therefore repo:ri."table in accordance with 10CFR2l.

Prior to restart following the April'7 event, the Unit l PORV internals {plug and stem) were replaeed with internals manufactured from SS 316 material with the plug stellited. The replacement cages were manufactured from 17-4 PH stainless steel.

Should you have any questions regarding this notification, please contact Mr. David Smith at (609) 339.1'1202.

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