05000315/LER-1999-020, :on 990727,EDGs Were Declared Inoperable.Caused by Inadequate Protection of Air Intake,Exhaust & Room Ventilation Structures from Tornado Missile Hazards. Implemented Compensatory Measures in Form of ACs

:on 990727,EDGs Were Declared Inoperable.Caused by Inadequate Protection of Air Intake,Exhaust & Room Ventilation Structures from Tornado Missile Hazards. Implemented Compensatory Measures in Form of ACs

ML17326A101
Person / Time
Site:	Cook
Issue date:	08/26/1999
From:	Depuydt M INDIANA MICHIGAN POWER CO.
To:
Shared Package
ML17326A100	List: 05000315/LER-1999-020, :on 990727,EDGs Were Declared Inoperable.Caused by Inadequate Protection of Air Intake,Exhaust & Room Ventilation Structures from Tornado Missile Hazards. Implemented Compensatory Measures in Form of ACs
References
LER-99-020, NUDOCS 9908310153
Download: ML17326A101 (4)

LER-1999-020, on 990727,EDGs Were Declared Inoperable.Caused by Inadequate Protection of Air Intake,Exhaust & Room Ventilation Structures from Tornado Missile Hazards. Implemented Compensatory Measures in Form of ACs

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(ii) 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 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
3151999020R00 - NRC Website

text

NRC FORM 366 U.S. NUCLEAR REGULA Y COMMISSION (6-1996)

LICENSEE EVENT REPORT (LER)

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

APPROV Y OMB No. 3150-0104 EXPIRES 06/30/2001 Estimated burden per response to comply with this mandatory information collection request: 50 hrs.

Reported lessons learned are incorporated into the Icensing process and fed back to industry, Forward comments regarding burden estimate to the Records Management Branch (TR F33), U.S. Nuclear Regulatory Commission, Washington, DC 205550001, and to the Paperwork Reductron Project (31504104). Offce of Management and Budget. Washington. DC 20503.

If an information coltection does not disphy a currently valid OMB control number. the NRC may not conduct or sponsor, and a person is not required to respond to, the Information collection, FACILITYNAME l1)

Cook Nuclear Plant Unit 1 DOCKET NUMBER (2) 05000-315 PAGE I3) 1 OF 4

Trrts I4)

Emergency Diesel Generators Declared Inoperable Due to Inadequate Protection of AirIntake, Exhaust and Room Ventilation Structures from Tornado Missile Hazards EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED(6)

MONTH DAY YEAR 1999 SEQUENTIAL NUMBER REVISION NUMBER 00 MONTH DAY YEAR FACILITYNAME Cook Nuclear Plant Unit 2 FACILITYNAME DOCKET NUMBER 05000-316 DOCKET NUMBER OPERATING MODE (9)

POWER LEVEL (10)

THIS REPORT IS SUBMITTED PURSUANT TO THE REQU 20.2203(a)(2) v 20.2203(a) (3)(i) 20.2201(b) 20.2203(a)(1) 20.2203(a)(2)(i) 20.2203(a)(3)(u)

IREMENTS OF 10 CFR 5: (Check 50.

3(a)(2)(I)

X 50.73(a)(2)(ii)

0. 3(a)(2)(iil) one or moro) (11) 50.

3(a)(2)(viii) 50.73(a)(2)(x) 3.71 NAME 20.2203(a) (2) (ii) 20.2203(a) 2) Bii) 20.2203(a)(2)(iv) 20.2203(a) (4) 0.36(c)(1) 0.36(c)(2)

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

(12)

TELEPHONE NUMBER tlndude Area Code)

OTHER pacify in Abstract below or in NRC Form 366A Mary Beth Depuydt, Regulatory Compliance (616) 465-5901 X1589 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DES CRIBED IN THIS REPORT (13]

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE TO EPIX

CAUSE

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

YES (If yes, complete EXPECTED SUBMISSION DATE).

NO EXPECTED MONTH DAY YEAR ABSTRACT (Limitto 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

(16)

On July 27, 1999, D. C. Cook Unit 1 was in Mode 5 (Cold Shutdown) and Unit 2 was defueled.

During the Expanded System Readiness Review (ESRR) for the Emergency Diesel Generators (EDGs), it was identified that the combustion air intake and exhaust piping, and the room ventilation supply duct for the EDGs do not meet the design criteria specified in the Updated Final Safety Analysis Report (UFSAR). These structures are not protected from tornado-generated missiles.

Based upon the determination that the EDGs may not have performed their safety function during a tornado event, they were declared inoperable at 1845 hours0.0214 days <br />0.513 hours <br />0.00305 weeks <br />7.020225e-4 months <br /> EDT. A four hour non-emergency ENS Report was made to the NRC at 2110 hours0.0244 days <br />0.586 hours <br />0.00349 weeks <br />8.02855e-4 months <br /> EDT pursuant to the requirements of 10CFR50.72(B)(2)(i).

Subsequent evaluation determined that there was minimal safety significance associated with the identified condition, therefore, the notification under 10CFR50.72(B)(2)(i) is hereby retracted. This event is still reportable,

however, in accordance with the requirements of 10CFR50.73(a)(2)(ii)(B),

as an event or condition that resulted in the nuclear power plant being outside of its design basis.

The apparent cause for this event was the failure to adequately address tornado missile hazards in the original plant design.

Compensatory measures in the form of administrative, controls and restrictions on plant operations have been implemented until the non-confolmance with UFSAR design criteria is resolved. A long term solution for this condition will be completed by Mode 4 for each unit.

The operability evaluation performed to evaluate this condition concluded that the EDGs were operable, but degraded, and that the identified condition had rniniiyln<<nfo<< l~""""tionsto the health and safety of the public.

99083i0i53 990826U.S. NUCLEAR REGULATORY COMMISSION (6-1999)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FAGIUTY NAME )1)

DOCKET )2)

NUMBER LER NUMBER I6)

PAGE )3)

Cook Nuclear Plant Unit 1 05000-315 SEQUENTIAL NUMBER 1999 020 REVISION NUMBER 00 2

OF 4

TEXT /lfmore spaceis required, use additional copies of NRC Form 366A/ I17)

CONDITIONS PRIOR TO EVENT

Unit 1 was in Mode 5, Cold Shutdown Unit 2 was defueled

DESCRIPTION OF EVENT

On July 27, 1999, during the Expanded System Readiness Review (ESRR) of the Emergency Diesel Generator (EDG) system, it was identified that the EDG (EIIS: DG) combustion air intake and exhaust piping, and the room ventilation supply duct (EIIS: NB/DUCT) for the EDGs do not meet the design criteria specified in the Updated Final Safety Analysis Report (UFSAR).

These structures are not protected from tornado-generated missiles.

Based upon the determination that the EDGs may not have performed their safety function during a tornado event, they were declared inoperable at 1845 hours0.0214 days <br />0.513 hours <br />0.00305 weeks <br />7.020225e-4 months <br /> EDT and Technical Specification Action Statement 3.8.1.2, Electrical Power Systems, A. C. Sources

- Shutdown, was entered.

CAUSE OF EVENT

The apparent cause for this event was the failure to adequately address tornado missile hazards in the original plant design. Combustion air intake and exhaust piping, and the room ventilation supply duct for the EDGs do not meet the design criteria specified in the UFSAR. This design oversight was not identified in 1991 when postulated tornado effects on the EDGs were re-evaluated due to a concern at another plant.

It was concluded, at the time, without adequately verifying the assumptions made in the evaluations, that tornado-generated missile effects need not be considered.

ANALYSISOF EVENT As a result of the Expanded System Readiness Reviews (ESRR), it was identified that EDG exhaust and air intake piping and EDG room ventilation supply duct are not protected from tornado-generated missiles.

As a

result of this nonconformance, the required operable EDG on Unit 1 (in Mode 5 at that time) could have been rendered inoperable in the unlikely event of a tornado event capable of generating design basis missiles.

Based on this possibility, D.C. Cook conservatively declared the EDGs for both units inoperable on July 27, 1999. A four hour non-emergency ENS Report was made to the NRC at 2110 hours0.0244 days <br />0.586 hours <br />0.00349 weeks <br />8.02855e-4 months <br /> EDT pursuant to the requirements of 10CFR50.72(B)(2)(i).

Subsequent evaluation of this condition concluded that the identified condition had minimal safety significance.

Therefore, the notification made under 10CFR50.72(B)(2)(i) is hereby retracted.

This event is still reportable,

however, as a Licensee Event Report (LER) pursuant to the requirements of 10CFR50.73(a)(2)(ii)(B), as an event or condition that resulted in the nuclear power plant being outside of its design basis.

The design criterion specified in the UFSAR, Section 1.4.1, states that "structures, systems and components of reactor facilities which are essential to the prevention, or to the mitigation of the consequences, of nuclear accidents which could cause undue risk to the health and safety ofthe public shall be designed, fabricated, and erected to performance standards that enable such structures, systems and components to withstand, without undue risk to the health and safety of the public, the forces that might reasonably be imposed by the occurrence of an extraordinary natural phenomenon such as earthquake, tornado, flooding condition, high wind or heavy ice."

In the event of a loss of offsite power, the EDG system provides an onsite A. C. standby power source to the essential loads necessary to safely shutdown the reactor under normal operating or accident conditions.

The combustion air intake and exhaust air subsystem supports the EDG system by providing combustion intake supply air and combustion exhaust discharge to support EDG engine operation.Q.S. NUCLEAR REGULATORY COMMISSION (6-1998)

LICENSEE EVENT REPORT tLER)

TEXT CONTINUATION FACILITYNAME (1)

Cook Nuclear Plant Unit 1 DOCKET (2)

NUMBER 05000-315 LER NUMBER {6)

SEQUENTIAL NUMBER REVISION NUMBER PAGE I3) 3 OF.

4 1999 020 00 TEXTilfmore spaceis required, use additional copies ofhfRC Form 366AI (17)

ANALYSISOF EVENT cont'd The exhaust subsystem also provides motive power to the EDG turbocharger, which increases the air intake manifold pressure and increases the horsepower rating of the engine.

In addition, the EDG room ventilation subsystem supports the EDG system by providing the EDG room adequate supply and exhaust ventilation to maintain acceptable equipment operating temperatures.

A vulnerability evaluation of CNP to tornado-generated missiles was performed.

The purpose of this evaluation was to determine ifthe probability of a tornado missile strike was acceptably low for vulnerable equipment required in Modes 5 and 6.

Using a parameter comparison to results from a probabilistic approach acceptable in the Standard Review Plan and applied at 12 other nuclear plant sites, it was concluded that the tornado missile strike frequency will be less than 3.0 E-06 per year, and possibly as low as 1.0 E-06 per year.

As part of this evaluation, a field walkdown of both the unit's diesel external structure areas verified that each unit's EDG supply ventilation structures are separated by 40 feet and that approximately 80% ofthe area surrounding the EDG structures is shielded by other structures such as transformers, tanks, Containment, and the Auxiliary Building, which severely limits the available pathway of a tornado-generated missile. Due to the low tornado missile strike frequency determined from the vulnerability evaluation and the separation between EDG supply ventilation structures, it was concluded that this condition was of minimal safety significance to the health and safety of the public.

In accordance with the provisions of NRC Generic Letter (GL) 91-18, Revision 1, "Information to Licensees Regarding NRC

~

Inspection Manual Section on Resolution of Degraded and Nonconforming Conditions," an Operability Determination was performed and concluded that the EDGs are "operable, but degraded".

This conclusion supports continued operation if reasonable assurance of safety has been demonstrated.

This reasonable assurance is provided through the implementation of compensatory

measures, which will be required in the event of adverse weather conditions. Therefore, under the provisions of the Operability Determination, the EDGs are considered operable, with the compensatory measures helping to ensure that the health and safety of the public willcontinue to be maintained.

CORRECTIVE ACTIONS

Compensatory measures in the form of Operations Standing Order OSO.138, "Diesel Generator Operability in the Event of Adverse Weather," have been implemented until the non-conformance with UFSAR design criterion is resolved.

The following compensatory actions will be taken prior to beginning and during core alterations:

~

Both EDGs in the affected unit shall be operable. This exceeds the requirements ofTS 3.8.1.2, which requires only one EDG and one circuit between the offsite transmission network and the onsite Class 1 E distribution system to be operable.

~

Ifeither EDG in the affected unit becomes inoperable, then immediately suspend all core alterations.

In the event of severe weather, the following compensatory actions willbe taken:

~

Declare all EDGs inoperable and comply with the Action Statement of TS 3.8.1.2. The Action Statement requires that with less than the required minimum A. C. electrical power sources operable, suspend all operations involving core alterations or positive reactivity changes until the minimum required power sources are restored to operable status.

Aftersevere weather has passed, verify that the following EDG structures are intact:

~

EDG combustion air intake

~

EDG exhaust outlet

~

EDG supply fan intakeP.S. NUCLEAR REGULATORY COMMISSION I6-I998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION Cook Nuclear Plant Unit 1 DOCKET )2)

NUMBER 05000-315 YEAR LER NUMBER (6)

SEQUENTIAL NUMBER REVISION NUMBER PAGE (3) 4 OF 4

1999 020 00 CORRECTIVE ACTIONS cont'd Ifall ofthe above structures are still intact for a given EDG, then the EDG may be declared operable.

For the purposes of Standing Order OSO.138, severe weather is defined as any of the following conditions:

~

The plant is experiencing sustained winds in excess of 60 MPH.

~

A tornado warning for the area around the plant and Berrien County has been declared.

~

A tornado watch has been issued for the area of southern Berrien County.

~

A tornado has been sighted by on-site personnel.

An evaluation which addresses wind and tornado analysis as well as missile protection of vulnerable safe shutdown targets is being performed under the Calculation Reconstitution Program.

A long term solution for this condition will be completed by Mode 4 for each unit.

As part of the Restart effort, System and Programmatic assessments in the Expanded System Readiness Reviews and Licensing Basis Reviews are reestablishing and documenting the plant's Design and Licensing Basis.

These reviews are intended to identify and correct, via the Corrective Action Program, significant plant design and licensing discrepancies such as the condition identified in this report.

SIMILAREVENTS 315/99-011-00 315/99-010-00 315/99-018-00 315/99-013-00 315/99-012-00 315/91-005-00