ML20045D637

LER 93-005-01:on 930214,testing of SBGT Showed That Unthrottled Flow of Single Train Would Exceed TS Rated Flow Limit of 3,330 Cfm.Caused by Design Deficiency.Existing SBGT Heaters Upgraded & Rewired

ML20045D637
Person / Time
Site:	Brunswick
Issue date:	06/30/1993
From:	Thearling G CAROLINA POWER & LIGHT CO.
To:
Shared Package
ML20045D636	List: ML20045D635 ML20045D637
References
LER-93-005, LER-93-5, NUDOCS 9306290250
Download: ML20045D637 (4)

Text

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NRC FORM 366 U.S NUCLEAR REGULATORY COMMISSION APPROVED OMB NO. 3150-0104 (5/92) .

. EXPIRES: S/31/95 E STIM ATED BURDEN PER M SPONSE TO COMPLY WITH T HIS

, INFORMATICN COLLECTION REQUEST: 50.D HRS. FORWARD LICENSEE EVENT REPORT (LER) COuuENTS nGARDmo euRoEN EsimTE TO Tm m,ORuATiON AND RECORDS M ANAGEMENT BRANCH (MNBB 7714), U.S NUCLEAR REGULATORY COMM;S$0N WASHINGTON, DC 20555 0001. AND TO THE PAPERWORK REDUCTION PFOJECT (3150-0104), OFFICE OF M ANAGEMENT AND PUDGET, WASHINGTON DC 70503.

FACluTY NAME f1) DOCKET NUMBER {2) PAGE(3)

Brunswick Steam Electric Plant, Unit 1 05000325 1 TITLE Idi REACTOR BUILDING STANDBY GAS TREATMENT THROTTLE VALVES ARE PREVENTED FROM THROTTLING FLOW TO WITHIN TECHNICAL SPECIFICATION LIMITS BY INITIATION LOGIC AND VALVE SETTINGS.

EVENT DATE (5) LER NUMBER (6) REPORT DATE (7) OTHER FACILITIES INVOLVED (8)

SE QUE NTIAL REVISfDN F ACIUTY NAME DOCKET NUMBER MONT H DAY YEAR YEAR M ONT H DAY YEAR '

MM WEP. P 2  %%MM 02 14 93 93 - 005 - 01 06 30 93 'AC'uTY NAME oOcKET NuMeER 05000 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 1: (Check one or more of the following)(11) 4 MODE m) 20 402(b) 20.405lc) 50.73(aH2)iiv) 73.71(b)

POWER LEVE L (10) 0 20.405(aH1 Hii) So.36(cH2) So.73(aH2Hvii) OTHER 20 405(aH1Hiin X 50 73(aH2HD 50.73taH2)tviiiH A) (Specify in Abstract

' and Text) 20 405(aH1)iiv) 50 73(aH2Hi0 50.73(aH2Hviiil(B) 20.405(aH11tv) 50.73(aH2Hiid 50.73(aH2Hx)

LICENSEE CONTACT FOR THIS LER (12) 4 NAME TELEPHONE NUVBER Glen M. Thearling, Regulatory Compliance Specialist (919) 457-2038 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE S7 5 TEM C OMPONE NT M A NUF ACTURER CAUSE SYSTEM COMPONENT M A NUFACTURER T PD SUPPLEMENTAL REPORT EXPECTED (141 MONTH DAY YEAR EXPECTED YES y NO DATE (15)

M ves, empwe E Ar-ECTED SUBM:SSCN D ATE)

ABSTil ACT (Limit to 1400 spaces, i e approumately fifteen single space typewntten hnes) (16)

Both Units are in Cold Shutdown to support the Outages started on April 21, 1992.

On February 14, 1993, testing of Unit 1 Standby Gas Treatment (SBGT) showed that unthrottled flow of a single train would exceed the Technical Specification rated flow limit of 3300 cfm. The results of the as-found unthrottled flow for single SBGT train runs documented the 1A SBGT ficw at 4050 cfm and the 1B SBGT flow at 3950 cfm. This puts the as-found flow for the individual SBGT train approximately 22% over the Technical Specification flow limit. This design deficiency affects both Units and has existed since original construction. During events initiating a Primary Containment Group 6 isolation signal the Reactor Duilding Intake throttle valves (D-BFV-RB and H-BFV-RB) receive a sealed-in full open signal.

With the flow exceeding the rated limit, the heater sizing needed to reduce humidity to 70% would not be met. Also, above the rated flow the ' residence time' of the air moving through the carbon adsorber may be less than the 0.25 seconds needed to ensure adequate adsorber ' capture time.' As indicated above, this condition is a concern when a single SBGT train fails to start and both intake throttle valves on the common suction path remain un-throttled. This issue will be resolved prior to declaring the Standby Gas

. Treatment Operable.

This design deficiency is similar to the issue reported in LER 1-92-20.

i See Supplemental Information section.

9dD6290250'930624 PDR ADOCK 05000325 -

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NRC FORM 366A U. S. NUCLEAR REGULATORY COMMISSION APPROVED OMB NO. 3150-0104

.(5/92) EXPIRES: 5/31/95

, E STIM ATED BURDEN PER RESPONSE TO COMPLY WITH THIS INFORMATiON COLLECTION REQUEST: 50.0 HRS. FORWARD LICENSEE EVENT REPORT (LER) COMME,cs REoARDiNo eURoEN ESTiu ATE TO THE iNrORMATiON AND RECOFOS MANAGEMENT BRANCH IMNBB 7714), U.S. NUCLEAR TEXT CONTINUATION REGULATORY COMMISSION, WASHINGTON, DC20555 0001, AND TO THE PAPERWORK REDUCTION PROJECT (3160-0104). OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

SEOUENTIAL REVISION Brunswick Steam Electric Plant """"" """"*"

05000325 2 Unit 1 93 - 005 - 1 TEKT lit rno,e space is requard, use additionalNRC Form 366A's) (17)

TITLE REACTOR BUILDING STANDBY GAS TREATMENT DESIGN HAS RESULTED IN THROTTLE VALVE LOGIC ALLOWING FLOW BEYOND TECHNICAL SPECIFICATION LIMITS.

INITIAL CONDITIONS Both Units are in Cold Shutdown to support the Outages started on April 21, 1992.

EVENT NARRATIVE On February 14, 1993, testing of Unit 1 Standby Gas Treatment (SBGT) using Special Procedure 1-SP-93-014, Flow Throttling of SBGT Filter Trains, showed that unthrottled' flow of a single train would exceed the Technical Specification rated flow limit of 3300 cfm. The results of the as-found unthrottlec flow for single SBGT train runs documented the 1A SBGT flow at 4050 cfm and the 1B SBGT flow at 3950 cfm. This puts the as-found flow for the individual SBGT train approximately 22% over the Technical Specification flow limit. This design deficiency affects both Units and is a concern because, during events initiating a Primary Containment Group 6 solation signal, the Reactor Building Intake throttle valves (D-BFV-RB and H-BFV-RB) receive a sealed-in full open signal.

With the flow exceeding the rated limit, the heater sizing needed to reduce humidity to 70% wo tid not be met. Also, above the rated flow the ' residence time' of the air moving throug e.'.e carbon adsorber may be less than the 0.25 seconds needed to ensure adequate adsorte. ' capture time.' As indicated above this condition is a concern when a single SBGT train fails to start and both intake throttle valves on the common suction path-remain un-throttled.

CAUSE OF EVENT l

The cause of the design deficiency is unknown and has existed since original construction.

CORRECTIVE ACTIONS Design Engineering has prepared Engineering Evalaation Report (EER) 93-0216 to resolve this issue on both Units. It will throttle each SBGT train's inlet maintenance isolation valve (G-BFV-RB and C-BFV-RB) to maintain SBGT flows within the allowable range. This issue will be resolved prior to declaring the SBGT system Operable.

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NRC FORM 366A U. S. NUCLEAR REGULATORY COMMISSION APPROVED OMB NO. 3150-0104

.(5/92) EXPIRES: 5/31/95

. ESTIMATED SURDEN 'PER RE SPONSE To COMPLY WITH THIS INFORMAtiON COLLECTION RE QUEST: 50.0 HRS. FORWARD LICENSEE EVENT REPORT (LER)

' couMENTS REGARDING BURDEN ESTIMW TO THE INFORMATION TEXT CONTINUATION AND RECORDS M ANAGEMENT BRANCH (MNBB 7714), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC20556 0001, AND TO THE PAPf'RWORK REDUCTION PROJECT (3160-0104), CFFICE OF MANAGEMENT AND BUDGET, WASHINGTON. DC 20503, FACluTY NAME 0) DOCKET NUMBEH (2) LER NUMBER 16) PAGE (3)

SE QUF NTIAL REVISJON Brunswick Steam Electric Plant """*'" "" *

• Unit 1 05000325 3 93 - 005 - 1 TEKT lif more space is requiwd, use addivonalNRC form 366A's) (17)

SAFETY ASSESSMENT SBGT flow above the Technical Specification limit could result in an increased elevated release (monitored) made via the stack. The significance of this increase is still being evaluated, and the results will be included in a LER supplement.

PREVIOUS SIMILAR EVENTS A similar design issue was reported in LER 1-92-20.

EIIS COMPONENT IDENTIFICATION System / Component EIIS Code Standby Gas Treatment System BH Sucolemental Information The impact of excessive flow on adsorber efficiency was evaluated (EER 93-0327) for the effects of velocity and humidity. The evaluation determined the system could handle flows up to the maximum system design flow (4200 CFM @ 130 Deg. F)' and still perform its design basis function (i.e. filtration and adsorption) as necessary t_o maintain releases within acceptable 10CFR100 and General Design Criterion (GDC) 19 limits, Results of analysis and testing confirmed that the system as-installed provided the required adsorber ef ficiency at the higher flow rates. The as-installed design uses double 2" adsorber beds (4" effective depth) and therefore the increased flow rates do not result' in a residence time reduction below the recommended 0.25 seconds. Laboratory testing at a flow of 4100 CFM at ambient temperature also confirmed acceptable adsorber efficiency.

Measured adsorber efficiency was 99.977% versus a required efficiency of 99%.

Plant Modifications92-105 and 92-106 were recently installed to upgrade / rewire the existing SBGT heaters. Evaluation of available heater capacity versus required capacity determined that the heaters, as modified, will reduce the humidity to the 70% design standard at the increased flow rates. The analysis for available capacity assumed degraded voltage conditions and determined approximately 18.5 kw will be available. Analysis of the required heater capacity at maximum system design flow (4200 CFM 0130 Deg. F) and humidity (100% RH) determined that only 16.7 kw is required.

The previous heater wiring configuration'resulted in lower available power (14.6 kw) under degraded voltage conditions (Ref. LER 1-92-020). Under those conditions, the humidity may - 1 have only been reduced to approximately 73% at maximum system design flow. Oak Ridge National Laboratory (ORNL-NSIC-65) data show that impregnated charcoal adsorber ef ficiency is not af fected by humidity for elemental iodine and remains above 95% for organic (methyl) l iodide with a humidity of up to 85%. As Brunswick Nuclear Plant dose calculations assume '

95% adsorber efficiency, there would be no increase over analyzed releases. It is recognized that the 95% efficiency was established to provide additional conservatism in the analysis and is based on actual tested efficiency in excess of 99%. However, the marginal increase in relative humidity (70% to ~73%) *hich could have been present would i

NRC FORM

• 366A U. S. NUCLEAR REGULATORY COMMISSION APPROVED OMB NO. 3150-0104

. (5/92) EXPIRES: 5/31/95 e ESTIMATED BURDEN PE R RESPONSE TO COMPLY WITH T HIS INFORMATION COLLECTION REQUEST: 50,0 HMS. FORWARD LICENSEE EVENT REPORT (LER) COMMEN,S REGARoiNG suRDEN ESTiuiTE TO THE iNFORMAT,0N AND RECORDS MANAGEMENT BRANCH (MNBB 7714), U.S. NUCLEAR

• TEXT CONTINUATION REGULATORY COMMISSION, WASHINGTON, DC20555-0001, AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104h OFFICE OF MANAGf MENT AND 00DGET, WASHINGTON, DC 20503.

FActuTY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

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SEQUENTIAL REVISION Brunswick Steam Electric Plant """*'" """*'"

05000325 4 Unit 1 93 - 005 - 1 TEXT Uf snore space is required, use additionalNRC form 366A's](11) not challenge those additional margins and would not have resulted in releases in excess of 10CFR100 limits. In addition, the Safety Evaluation report for the Brunswick Plant assumes charcoal filtration efficiencies of 70% for organic iodines and 90% for elemental and particulate forms. Even with these conservative assumptions, offsite dose limits are still well below 10CFR100 guideline values.

Based on the determination that the system under the past and present configurations.

has/had the ability to perform its design basis function at maximum system design flow, there has not been, nor is there currently, any adverse safety significance associated with these flow conditions.

As the evaluation determined the design bases functions were met, at the maximum system design flow, the corrective action to throttle the SEGT trains inlet maintenance isolation valves was canceled.

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