ML20058E062

Safety Evaluation Supporting Amend 91 to License DPR-75

ML20058E062
Person / Time
Site:	Salem
Issue date:	05/30/1990
From:	Office of Nuclear Reactor Regulation
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ML20058E061	List: ML20058E057 ML20058E062
References
NUDOCS 9011070009
Download: ML20058E062 (7)

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UNITED STATES "4

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. WASHINGTON, o. C 20666 NUCLEAR REGULATORY COMMISSION i"

1 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION m

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SUPPORTING AMENDMENT N0.91'TO FACILITY OPERATING LICENSE N0. DRP-75 I

PUBLIC SERVICE ELECTRIC & GAS COMPANY

. PHILADElfHI A ELECTRIC COMPANY 1

DELMARVA POWER AND LIGHT CCMPANY i

ATLANTIC CITY ELECTRIC COMPANY SALEM GENERATING STATION. UNIT NO. 2 DOCKET NO. 50-311 1.0. INTR 000CTION' By. letter dated April 4 1990 (Ref. 1), and supplemented by letters dated l

April 12,'1990 (Ref. 2), April 20, 1990 (Ref. 3), and May 7, 1990 (Ref. 4),

Public. Service Electric & Gas Company requested an amendment to Facility.

I Operating License No. DPR-75 for the Salem Generating. Station, Unit No -2.

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' 'The proposed amendment would increase the allowable main steam isolation j

-valve (MSIV) closure time from 5 seconds to 8 seconds until restart from

the_'7. 1990 letter provided information concerning the schedule for sixth refueling outage, currently scheduled for the.fa11 1991. The May developing the corrective actions required to resolve the MSIV closure issues and did not increase the. scope of the original amendment request and did not' affect the staff's original;no significant. hazards determi-nation.

The amendment for, Salem Unit I was processed as an emergenc technicalspecificationchangeinaccordancewith10CFR50.91(a)(5)y 2.0 EVALUATION

2.1 Background

The response time of main steam line isolation upon high steam flow in two steam lines coincident with low steam line= pressure, high-high containment pressure, and high steam flow in two steam lines coincident with low-low average reactor coolant temperature are specified in Technical Specifica-e tionLTS) Table 3.3-5.forSalemUnits1and2. The surveillance requirements for main steam isolation valves are specified in TS 3/4.7.1.5. The current TS ref1'ect the requirement of MSIV closure time of 5 seconds upon receipt of signal to close MSIVs following a postulated accident.

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, 4 In October 1989, Salem Unit 2 MSIVs were stroke tested during a shutdown Lfor maintenance.

Three out of four of the valves failed to close within Lthe allowable time of five seconds. A special test of Unit 2 MSIVs I

performed en March 31, 1990, concluded the potential for a slow closure problem at.both Unit 1 and 2 existed. The root cause was not conclusively i

identificd.

i By letter dated April 4 1990(Ref.1)andsupplementedbylettersdated April-12,1990(Ref.2),, April 20,1990(Ref.3),andMay7,1990(Ref.4),.

the Public Service Electric and Gas Company, the licensee for the Salem Units 1 and 2, submitted information regarding the proposed TS Table 3.3-5 and 3/4.7.1.5 which reflected a change in the MSIV closure time of B seconds, and the justification for the proposed changes.

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2.2 Accident Reevaluation i

'In support of its proposed TS charges, the licea ee has performed a reevaluation of the limiting accident scenarios which rely upon MSIV closure in the safety analyses. The Salem Units 1 and 2 safety analyses l

which model the steam line isolation include the following svents: main

-steam line break (MSLB), feedline break, steam generator tube rupture (SGTR), and lossofcoolantaccident(LOCA).

j 2.2.1. Main Steam Line Break (MSLB) Core Response Limiting Case

.To support the. proposed increase in MS!Y closure time, thermal hydraulic analyses were reanalyzed for-the Salem licensing basis steam line break a

cases.. A main steam line isolation time of 12 seconds was assumed in this reanalysis. The results of the licensee's analyses show that the return

'to poweri and' core condition transients for the case of.a double ended steam line break upstream of the steam flow restrictor at hot zero power with offsite power available are much more severe than that calculated for the remaining cases and would result in the lowest calculated departure fromnucleateboiling(DNBR). Therefore, the limitine MSLB case for the

. current Salem licensing basis MSLB analysis will reaIn limiting for the

' increased MSIV closure time. The results of the-licensee's analysis for the limiting MSLB case associated with 12 secena steam line isolation time yielded a minimum DNBR of.2.48, which is greater than the 1.45 DNBR limit, and is acceptable.

-2.2.2 Main Feed 11ne Break (MFLB)

Following a main feedline break (MFLB), the reactor coolant system (RCS) will initially Ghdergo a cooldown due to the expulsion of secondary water through the broken feedline. The RCS temperature transient will quickly turn around following the isolation of the main steam lines. An increase in the MSIV closure tin will result in additional heat removal from RCS.

Hence, the-RCS will stabilize at a slightly lower temperature than in the l

licensing basis MFLB analysis. Thus, the results of a MFLB analysis with 1

increased MSIV closure time are less severe than the results of the licensing basis MFLB analysis.

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-2.2.3 Steam Generator Tube Rupture (SGTR)

In the licensing basis SGTR analysis, the primary to secondary break flow was' assumed to be terminated at 30 minutes after accident initiation.

The operator actions to close the MSIV associated with the ruptured steam generator and_to terminate the break flow were not explicitly modelled in

.the analysis.

Therefore, there will be no impact of an increase in the MSIV closure time to the thermal hydraulic analysis of the SGTR accident.

2.2.4 Loss of Coolant Accident (LOCA)

In the licensing basis Loss of Coolant Accident (LOCA), the main steam isolation was assumed to occur immediately after the low pressure reactor trip setpoint is reached. As a result of this assumption, the stored i

energy in the secondary coolant is conservatively greater than what would exist if the analyses modelled main steam isolation when the MSIVs closed with time. delay.. For the Small Break Loss of Coolant Accident (SBLOCA)..

.the high energy stored in the secondary coolant will reduce the amount of' thermal energy to be transferred out from the RCS which maximizes the steam produced in the RCS and minimizes the transient water level in the core. This will result in a more conservative calculation with respect to the core uncovery fo11cwing a SBLOCA.

In the large Break Loss of Coolant Accident (LBLOCA), the high energy stored in the secondary coolant as a 4

resultof.theassumptionofinstantaneousclosureoftheMSIVs,will increase the amount of thermal energy to be transferred into the RCS which increases the potential for steam binding to occur in the steam generator tubes during tie blowdown phase of.the transient. This will prolong the i

time of blowdown and result'in higher peak cladding temperature for this event than would occur if the delayed closure of the MSIVs was modelled.

The above assessment supports the conclusion that an increased MSIV closure time will not cause negative effects to the LOCA analysis.

As discussed above, the licensee's reevaluation of the limiting accident scenarios =which rely upon MSIV-closure supports a total main steam.

isolation response time of 12 seconds.

In ceder to preserve the safety margin,.the licensee proposes an allowable steam line isolation response time.'of:10 seconds for the signals modelled in the safety analyses.

Eight seconds of this response time is being allocated to MSIV stroke time for closing and two seconds of this response time is for the signal stocessing.

The proposed TS Table 3.3-5 and TS 3/4.7.1.5 reflect t'+ above c1anges.

The change of steam

line isolation response time from 10.75 seconds to

'13.75 seconds upon high steam flow in two steam lines coincident with

. low-low average reactor coolant temperature on TS Table 3.3-5 is acceptable since it was considered as:a backup signal and was not modelled in the Salem licensing basis safety analyses.

2.3 Containment' considerations The licensee has reanalyzed the limiting case accident scenarios associated with a postulated main steau line break (MSLB) inside containment and evaluated the-impact of the MSIV closure time change on containment pressure response and environmental qualification of equipment important to plant safety. The following is the staff's evaluation of the licensee's safety analyses related to these concerns.

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2.3.1 containment Integrity Analysis The licensee has reanalyzed the consequences of a MSLB with the increased MSIV closure time and calculated the r, ass and energy releases inside containment to ensure thet the peak containment pressure does not exceed the' design limit. The pressure and temperature profiles generated by the analyses were used to evaluate environmental qualification of equipment inside-containment. The following assumptions and input changes were made in calculating contairment response following a MSLB:

-(1)= Auxiliary-feedwater runcut flow to a ruptured steam generator was assumed at 2010 ppm.

(?) ESF feedwater control valve closure time was changed from 8 to 10 seconds.

(3)' Safety injection delay time of 22 seconds was used in the mass and~

energy-release analysis.

(4) Minimum safety injection (one train) from the high head safety injection pump was-assun.ed, j

j (O 4 of 5 containment fan coolers and bcth trains of containment i

s? ray were assumed operable. A 20 second fan cooler actuation 4

delay and a 44 second cortainment spray delay were assumed i

consistent witn the availabil.ity of offsite power.

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Constant' Moderator Density Coefficient (MDC) of 0.43 delta k/g/cc

'was used in the analysis (variable moderator. feedback i

i methodoloay was previously used).-

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' Ths licensee calculated containment pressure and temperature responses for

..the MSLB based en.MSIV closure at 8 seconds.'The most limiting cases for

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the cortcinment pressure criterion are the split breaks at.an initial-

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power level of 30% assuming failure of the auxiliary feedwater runout protection equipment or failure of a containment safeguards train. For the failure of the auxiliary feedwater runout protection equipment case, the 14 peak contktement pressure as-a result of the MSLB was calculated to be 46.9. psia with a 12 second engineered safety features'.(ESF) steam line isolation response time. For the failure of a containment safeguard case, the peak containment pressure was calculated to be 46.6 psia with a steam line: isolation response time of 12 seconds. These calculated peak containment pressures are higher than previous analyzed results but remain within the containment design pressure of 47 psia.

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The licensee also analyzed the next most limiting cases for the split

' breaks at an initial power level of 70% assuming failure of the auxiliary feedwater runout protection or a containment safeguards train. The peak contairrent pressures were calculated to be 45.7' psia for the runout of 1

auxiliary feedwater case and a6.8 psia for the failure of containment

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safeguard case. Since the results of these cases at 70% pcwer provide calculated values less than the maximum calculated value at 30% power, the 30%~ power cases are considered to be the most limiting.

An increase in the allowable HSIY closure time will affect the containment

-i pressure and temperature responses under MSLB accident conditions through changes in the mass and energy release rates because more blowdown through y

the ruptured main steam pipe from other steam generators gces into the o

containment. The staff has reviewed the licensee's scoping analysis _and finds. that the assumptions for. the analysis are conservathe and acceptable.

Since the-calculated containment. seak pressures are within the design limit, the staff concludes that tie licensee's containr.ent integrity

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a-analysis 1s-' acceptable.

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' 2.3.2 Equipment' Qualification 1

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'With regard to the effect of the change in the MSIV closure time on the environmental qualification of equipment important to safety, the licensee-provided revised pressure and temperature profiles that. reflected increases 4'

in both pressure and ten erature inside containment. However, the licensee

, stated t1at the, lowest qualified pressure for the affected safety related m

equipment inside containment is 60 psig, which is above the new peak containment pressure of 46.9 psig. The licensee also stated that although' the temperature ~ profile has increased from 264 degrees Fahrenheit (F) to 275 degrees F a review of'all affected equipment indicates that the originalcua1Ificationtestconditionssupplementedinalimitednumber'of 1

cases with thermal lag analysis bounds the revised temperature profile. In addition, the licensee has stated that the proposed increase in MSIV closure time has no impact on environmental qualification of equipment outside containment.

The staff has reviewed the_ applicable information provided by the licensee and finds that the licensee has acceptably addressed environmental

. qualification concerns.

2.4 Valve Characteristic Considerations In response to the staff's request via a telecon on April 5, 1990, the licensee submitted Reference 2 to provide additional information relating to main steam line break and its rationale for selecting eight seconds as bm the proposed allowable MSIV stroke time.

It also provided the basis for l

the licensee's identification of water accumulation as the sole cosmon f

l cause of MSIV slow closure time experienced at the Salem generating ctation. The Mechanical Engineering Branch (EMEB) was requested to review the information pertaining to valve performance. A telephone conversation i

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i4 with the licensee was held on April 16, 1990 to discuss the results of EMEB's review of References 1 and 2.

The staff indicated th6t test data at Salem and other utilities with similar MSIV's appeared to support the licensee's conclusion that the delay in closing can be attributed to the water accumulation. The test results also s y gested that slow :losures are less than eight seconds. However, it should be noted that this conclusion is based on a limited data base that is currently available.

The staff: indicated.that the licensee needs to pursue a permanent solution including analytical evaluations of the parameters affecting MSIV closure time as well as appropriate corrective action.-

In response-to the staff's request, the licensee submitted letters dated April 20 and May 7, 1990 (References 3 and 4). The licensee stated that an engineering evaluation hn been initiated. Completion of a preliminary Design' Change Package (DC9) acceptable to the MSIV vendor ~and cognizant licensee technical and enjineering personnel is. planned for July 30, 1900.

Finalization and approval of.the DCP is targeted for the first week of September 1990. The corrective actions will be implemented prior to restart from the Unit 2 sixth refueling outage. The licensee'also requested that the' proposed TS change to increase MSIV closure time be granted for the interim period before completion of the necessary corrective action.

t Based on the experience of Salem and other facilities, MSIV's suspected of j

being affected by water accumulation had closure times less than eight seconds. Therefore, the staff has determined that.the licensee's proposed action plan is acceptable.

2.5 Conclusion Based on the staff evaluation in Section 2.1.thru 2.4 above, the staff concludes.that the licensee proposed Technical Specifications Table 3.3-5 and 3/4.7.1.5 are sup Unit 2' and therefore, ported by the applicable safety analyses for Salem -

are. acceptable until corrective actions are completed during the sixth' refueling outage of Unit 2..

2.6Refere'nces

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Letter from S. E. Miltenberger, Public Service Electric and Gas Company to =USNRC, " Increase to Allowable MSIV Closure Time Request for Emergency License Amendment," dated April 4,1990.

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Letter from S. LaBruna, Public Service Electric and Gas Company to j

USNRC, " Supplemental Information Increase to Allowable MSIV Closure Time Request for Emergency License Amendment," dated April 12, 1990.

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Letter from S. LaBruna, Public Service Electric and Gas Company to USHRC, " Supplemental Information Increase to Allowable MSIY Closure Time Request For License Amendment", dated April 20, 1990.

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' Letter from T. Crinnins, Jr., Public Service Electric and Gas C)mpany to USNRC, " Supplemental Information Proposed Increase to Allowable MSIV Closure Time", dated May 7, 1990.

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.rt 3.0 ENVIRCNMENTAL CONSIDERATION This' amendment involves a change to a'reouirement with respect to the installation or use of a facility component located within the restricted arca as defined in 10 CFR Part 20 and changes to the surveillance requirements. The staff bas determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any. effluents that may be released offsite and that there is no

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significant increase in individual or cumulative occupational radiation exposure. The Comission has previously issued a proposed finding that j

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.l this amendment involves no significant hazards consideration end there has been ne public comment on such finding. Accordingly, this amendment meets the'elig)ibility criteria for categorical exclusion set forth in 10-CFR 51.22(c)(9.; Pursuant to 10 CFR 51.22(b), no. environmental impact statement or environmental assessment need be prepared in connection.with 4

the issua'nce of this amendment.

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4.0 CONCLUSION

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The Commission made a proposed determination that the amendment involves c

'no significant hazards consideration which was published in the Federal 1

Register (55 FR 17683) on April 26, 1990 and consulted with the State of New Jersey. No public comments were received and the State of New Jersey did not 'have any consnents..

M The. staff has concluded,' based on the considerations discussed ebove, that:- (1) there' is reasonable assurance that the health. and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in cog.iance with the Comission's regulations and the issuance of this amendment will not be inimical to the common defense and security.or to the health and safety of the public.

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Dated:: May 30, 1990 iPrincipal Contributors:

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C. Liang, SRXB "J.:Guo, SPLB.-

.H. Walker, SPLB R.lLi, EMEB 4

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