05000315/LER-1999-012, :on 990420,concluded That Auxiliary Bldg ESF Ventilation Sys Not Capable of Maintaining ESF Room Temps post-accident.Caused by Inadequate Control of Sys Design Inputs.Comprehensive Action Plan Being Developed

:on 990420,concluded That Auxiliary Bldg ESF Ventilation Sys Not Capable of Maintaining ESF Room Temps post-accident.Caused by Inadequate Control of Sys Design Inputs.Comprehensive Action Plan Being Developed

ML17325B600
Person / Time
Site:	Cook
Issue date:	05/20/1999
From:	Orourke B INDIANA MICHIGAN POWER CO.
To:
Shared Package
ML17325B598	List: 05000315/LER-1999-012, :on 990420,concluded That Auxiliary Bldg ESF Ventilation Sys Not Capable of Maintaining ESF Room Temps post-accident.Caused by Inadequate Control of Sys Design Inputs.Comprehensive Action Plan Being Developed
References
LER-99-012, LER-99-12, NUDOCS 9905260279
Download: ML17325B600 (4)

LER-1999-012, on 990420,concluded That Auxiliary Bldg ESF Ventilation Sys Not Capable of Maintaining ESF Room Temps post-accident.Caused by Inadequate Control of Sys Design Inputs.Comprehensive Action Plan Being Developed

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
3151999012R00 - NRC Website

text

NRC Form 366 U.S. NUCLEAR REGULATORYCOMMISSION (6-1998)

LICENSEE EVENT REPORT (LER)

(See reverse for required number of digits/characters for each block)

APPROVED BYOMB No. 3150.0104 EXPIRES 06/30/2001 ESTIMATED BURDEN PER

RESPONSE

TO COMPLY WITH THIS MANDATORY INFORMATIONCOLLECTION REOVESD 50.0 HRS. REPORTED LESSONS LEARNED ARE INCORPORATED BJTO THE UCEJISING PROCESS AND FED BACK TO INDUSTRY.

FORWARD COMMENTS REGARDUIG BURDEN ESTSJATE TO THE II&ORMATIONANO RECORDS MANAGEMENT BRANCH IT4 AS),

V.S.

NVCLEAR RFGUIATORY COMMISSION. WASHBJGTON. OC 205S54XI. ANO TO THE PAPERWORK REDUCTION PROJECT tst50410l), OFFICE OF MANAGEMENT AND BUCGEf, WASIeNGTceL DC 2050$

FACILITYNAMEI1)

Cook Nuclear Plant Unit 1 DOCKET NUMBERr2) 05000-315 PAGE I5) 1 of 3 TITLEI4)

Auxiliary Building ESF Ventilation System May Not be Capable of Maintaining ESF Room Temperatures Post-Accident MONTH 04 DAY YEAR 20 1999 EVENT DATE (5)

YEAR 1999 LER NUMBER (8)

SEQUENTIAL NUMBER 012 REVISION NUMBER 00 REPORT DATE (7)

MONTH DAY YEAR 05 20 1999 ILI D.C. Cook, Unit 2 A ILI NAM 05000-316 D

C NUMBER OTHER FACILITIESINVOLVED(8)

OPERATING MODE (9)

POWER LEVEL(10) 0%

20.2201 (b) 20.2203(a)(1) 20.2203(a)(2)(i) 20.2203(a)(2)(v) 20.2203(a)(3)(i) 20.2203(a)(3)(ii) 50.73(a)(2)(l) 50.73(a)(2)(ii) 50.73(a)(2)(iii) 50.73(a)(2)(viii) 50.73(a)(2)(x) 73.71 THIS REPORT IS SUBMITTEDPURSUANT TO THE REQUIREMENTS OF 10 CFR II: (Check one or more) (11) 20.2203(a)(2)(ii) 20.2203(a)(2)(iii) 20.2203(a)(2)(iv) 20.2203(a)(4) 50.36(c)(1) 50.36(c)(2)

LICENSEE CONTACT FOR THIS LER (12) 50.73(a)(2)(iv) 50.73(a)(2)(v) 50.73(a)(2)(vii)

OTHER Specii/y In Abstract bekrrr or nNRC Form 366A NAME Ms. Brenda W. O'ourke, Compliance Engineer TELEPHONE NUMBER (IIK5ude Area Code)

(616) 465-5901 x2604 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

.CAUSE SYSTEM COMPONENT MANUFACTURER REPORTABLE TO EPIX

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE TO EPIX SUPPLEMENTAL REPORT EXPECTED (14 X

YES (IfYes, complete EXPECTED SUBMISSION DATE)

NO EXPECTED SUBMISSION DATE 15 MONTH 10 DAY 31 1999 Abstract (Limitto 1400 spaces, I.e., approximately 15 singie-spaced typewritten lines) (16)

On April20, 1999, during performance of the Expanded System Readiness Review (ESRR) for the Auxiliary Building Ventilation Systems, it was concluded that there is insufficient assurance that the Engineered Safety Features Ventilation (AES) system is capable of performing its safety and accident mitigation function. This conclusion was based on a preliminary evaluation of numerous identified system deficiencies taken in the aggregate.

Specifically, significant errors in calculations for auxiliary building Engineered Safety Features cubicle temperatures expected during postulated accident scenarios, vulnerability of AES damper control air system modification to single failure; and lack of missile protection for the Component Cooling Water pump area supply fans.

Based on the combined effects of these deficiencies, the ability of the AES system to maintain auxiliary building temperatures to within safety-related equipment design temperatures under accident conditions cannot be assured.

The preliminary causes for identified conditions are: inadequate control of system design inputs; failure to adequately implement single failure design criteria during the modification process; and lack of a clear definition in design and licensing documents regarding design requirements for system protection against missile effects.

A comprehensive action plan is being developed to determine the auxiliary building design temperatures required to be maintained by the AES ventilation system.

In addition, a single failure analysis for the AES ventilation system willbe performed to identify failures that could prevent the system from performing its design and safety function. Based on the results of the completed evaluation, information regarding the safety significance, and corrective and preventive actions willbe provided in an update to this LER.

9905260279 990520 PDR ADOCK 050003'l5 S

PDRU.S. NUCLEAR REGULATORY COMMISSION (6-1998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITYNAME(1)

Cook Nuclear Plant Unit 1 DOCKET NUMBER(2) 05000-315 YEAR LER NUMBER (6)

SEQUENTIAL NUMBER REVISION NUMBER PAGE (3) 2of3 TEXT (Ifmore space is required, use additional copies ofNRC Form (366A) (17)

Conditions Prior to Event

Unit 1 was in Mode 5, Cold Shutdown Unit 2 was in Mode 5, Cold Shutdown 1999 012 00 Descri tion of Event On April20, 1999, during performance of the Expanded System Readiness Review (ESRR) for the Auxiliary Building Ventilation Systems, it was concluded that there is insufficient assurance that the Engineered Safety Features Ventilation (AES) system is capable of performing its safety and accident mitigation function. This conclusion was based on a preliminary evaluation of numerous identified system deficiencies taken in the aggregate.

Specifically, significant errors in calculations for auxiliary building Engineered Safety Features (ESF) cubicle temperatures expected during postulated accident scenarios, combined with small design margins that existed between calculated room temperatures and design requirements; vulnerability of AES damper control air system modification to single failure; and lack of missile protection for the Component Cooling Water (CCW) pump area supply fans which could result in a single catastrophic failure-generated missile impacting both trains of AES. Based on the combined affects of these deficiencies, the ability of the Unit 1 and 2 AES systems to maintain auxiliary building temperatures to within safety-related equipment design temperatures under all accident conditions cannot be assured.

In accordance with the requirements of 10CFR50.72(b)(2)(iii)(D), a 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> notification was made to the NRC on April20, 1999, at 1645 hours0.019 days <br />0.457 hours <br />0.00272 weeks <br />6.259225e-4 months <br />, for any event or condition that alone could have prevented the fulfillmentof the safety function of structures or systems that are needed to mitigate the consequences of an accident.

Cause of Event

The preliminary cause for the use of non-conservative and incorrect assumptions in auxiliary building heat load calculations is due to inadequate control of system design inputs. This issue was previously identified in AEP:NRC:1260GH, dated March 19, 1999, "Enforcement Actions98-150, 98-151,98-152 and 98-186, Reply to Notice ofViolation Dated October 13, 1998."

The preliminary cause for AES damper design single failure vulnerability is failure of the design change process to identify the potential adverse impact on the AES system created by the modification to the damper control air system in 1997.

The preliminary cause for CCW pump area supply fan susceptibility to missile effects is lack of a clear definition in design and licensing documents regarding AES design requirements for protection against missile effects.

Anal sis of Event This LER is submitted in accordance with 10CFR50.73(a)(2)(v)(D) for a condition that could prevent the fulfillmentof the safety functions of the AES system that are needed to mitigate the consequences of an accident:

The AES system safety and accident mitigation function is to provide sufficient cooling to the auxiliary building general areas and ESF equipment rooms required to operate during accident conditions. This includes the CCW, Containment Spray, Residual Heat Removal, Charging and Safety Injection equipment rooms. The AES system also maintains the auxiliary building at a negative pressure relative to the outside environment to ensure radioactive contamination released during an accident is contained within the auxiliary building, filtered and exhausted to the environment via a monitored, release path.

In addition, Technical Specification 3.7.6.1 requires that two independent AES ventilation system fan/filter exhaust trains be operable in Modes 1 through 4.

Calculations were developed to establish the auxiliary building heat loads, ESF cubicle room and general area temperatures during normal, shutdown and accident conditions.

During the ESRR review of these calculations, numerous discrepancies were identified. For example, calculation of auxiliary building area temperature during accident conditionsU.S. NUCLEARREGULATORY COMMISSION (6-1998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITYNAME(1)

Cook Nuclear Plant Unit 1 DOCKET NUMBER(2) 05000-315 YEAR LER NUMBER (6)

SEQUENTIAL NUMBER REVISION NUMBER PAGE (3) 3of3 1999 012 00 TEXT (ifmore space is required, use additional copies ofNRC Form (366A) (17) did not include the heat load for the CCW system piping. This equipment is considered a significant heat load in the auxiliary building and excluding it from the calculation could result in non-conservative auxiliary building area temperature values.

In addition, these values serve as input assumptions to other auxiliary building ventilation calculations.

As a result, actual auxiliary building area and ESF cubicle room temperatures could impact the qualification of the ESF equipment located in the areas served by the AES and CCW pump area ventilation systems.

The AES ventilation system consists of two fan/filter exhaust trains (one in standby) which draws air from the auxiliary building through the equipment cubicles from a common vent duct, and discharges the exhaust to the outside atmosphere via the vent stack.

Each train consists of a roughing filter, high efficiency particulate air (HEPA) filters, and a normally closed pneumatically operated face damper.

In addition, each train contains a bypass duct with a normally open pneumatically operated bypass damper which directs air flow around the charcoal adsorbers.

During normal operation, one fan/filter unit operates continuously, directing the exhaust air through the roughing and HEPA filters, bypassing the charcoal filters, and discharging to the unit vent. This operation aids in air distribution within the auxiliary building, isolates the atmosphere in the cubicies by inducing a draft through the entering portals and removes any heat generated within the enclosures.

In 1997, a modification to the damper control air system included the installation of solenoid valves in the air lines to the face and bypass dampers.

During the performance of surveillance test 12 OHP 4030 STP.25A/8, on two separate occasions, the face damper solenoid valve failed, resulting in the face damper failing to open while the bypass dampers remained closed.

For non-Sl initiated events, a failure of the face damper solenoid to open the'face damper or the bypass damper solenoid to open the bypass damper in response to a control signal could result in both the face and bypass dampers being in the closed position, blocking all air flow through the affected train.

In the event of a Phase B Isolation signal, the standby train is energized and the bypass dampers automatically close and the face dampers open to exhaust air directly through the charcoal filters, roughing and HEPA filters. Although the single failure of either the bypass or face damper solenoid valve would render one train of AES inoperable, it would not impact the capability of the standby fan/filter train from performing its safety and accident mitigation function.

The AES system design includes three vaneaxial supply fans located in the CCW equipment room which are located side by side, and connected to a common intake plenum and discharge duct. Because vaneaxial fans are susceptible to fan blade failures, the fan blades are a potential missile source which could impact the function of adjacent safety related components.

As a result, failure of the CCW pump area supply fans could impact the ability of the AES system to maintain ESF cubicle temperatures to within equipment design temperatures, impacting the qualification of the ESF equipment.

Because of the numerous system deficiencies identified during the ESRR, a comprehensive action plan is being developed to evaluate the identified conditions.

Until the aggregate effect of these conditions on AES system performance is evaluated, the overall safety impact cannot be determined.

Corrective Actions

A comprehensive action plan is being developed to determine the auxiliary building design temperatures required to be maintained by the auxiliary building ventilation systems:

In addition, a single failure analysis for the AES ventilation system willbe performed to identify failures which could prevent the system from performing its design and safety function. Based on the results of the completed evaluation, additional information regarding safety significance, including corrective and preventive actions willbe provided in an update to this LER.

Previous Similar Events

LER 315/97-023-00