ML17326A101

LER 99-020-00: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: ML17326A099 ML17326A101
References
LER-99-020, NUDOCS 9908310153
Download: ML17326A101 (4)

Text

NRC FORM 366 U.S. NUCLEAR REGULA Y COMMISSION APPROV Y OMB No. 3150-0104 EXPIRES 06/30/2001 (6-1996)

Estimated burden per response to comply with this mandatory information LICENSEE EVENT REPORT (LER) 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 (See reverse for required number of Commission, Washington, DC 205550001, and to the Paperwork Reductron digits/characters for each block) 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, FACILITY NAME l1) DOCKET NUMBER (2) PAGE I3)

Cook Nuclear Plant Unit 1 05000-315 1 OF 4 Trrts I4)

Emergency Diesel Generators Declared Inoperable Due to Inadequate Protection of Air Intake, 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 SEQUENTIAL REVISION MONTH DAY YEAR FACILITY NAME DOCKET NUMBER NUMBER NUMBER Cook Nuclear Plant Unit 2 05000-316 1999 00 FACILITYNAME DOCKET NUMBER OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQU IREMENTS OF 10 CFR 5: (Check one or moro) (11)

MODE (9) 20.2201(b) 20.2203(a)(2) v 50. 3(a)(2)(I) 50. 3(a)(2)(viii)

POWER 20.2203(a)(1) 20.2203(a) (3)(i) X 50.73(a)(2)(ii) 50.73(a)(2)(x)

LEVEL (10) 20.2203(a)(2)(i) 20.2203(a)(3)(u) 0. 3(a)(2)(iil) 3.71 20.2203(a) (2) (ii) 20.2203(a) (4) 50.73(a)(2)(iv) OTHER 20.2203(a) 2) Bii) 0.36(c)(1) 50.73(a)(2)(v) pacify in Abstract below or in NRC Form 366A 20.2203(a)(2)(iv) 0.36(c)(2) 50.73(a)(2) (vii)

UCENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER tlndude Area Code)

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 CAUSE SYSTEM COMPONENT MANUFACTURER REPORTABLE TO EPIX TO EPIX SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED MONTH DAY YEAR YES NO (If yes, complete EXPECTED SUBMISSION DATE).

ABSTRACT (Limit to 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~""""tions to the health and safety of the public.

99083i0i53 990826

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (6-1999)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FAGIUTY NAME )1) DOCKET )2) LER NUMBER I6) PAGE )3)

NUMBER Cook Nuclear Plant Unit 1 05000-315 SEQUENTIAL NUMBER REVISION 2 OF 4 NUMBER 1999 020 00 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.

ANALYSIS OF 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 of the 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.

NRC FORM 366A (6-1999)

NRC FORM 366A Q.S. NUCLEAR REGULATORY COMMISSION (6-1998)

LICENSEE EVENT REPORT tLER)

TEXT CONTINUATION FACILITY NAME (1) DOCKET (2) LER NUMBER {6) PAGE I3)

NUMBER Cook Nuclear Plant Unit 1 05000-315 SEQUENTIAL NUMBER REVISION 3 OF. 4 NUMBER 1999 020 00 TEXT ilfmore spaceis required, use additional copies of hfRC Form 366AI (17)

ANALYSIS OF 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 if the 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% of the 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 will continue 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 of TS 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.

~ If either EDG in the affected unit becomes inoperable, then immediately suspend all core alterations.

In the event of severe weather, the following compensatory actions will be 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.

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

~ EDG combustion air intake

~ EDG exhaust outlet

~ EDG supply fan intake NRC FORM 366A (6.19981

NRC FORM 366A P.S. NUCLEAR REGULATORY COMMISSION I6-I 998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION DOCKET )2) LER NUMBER (6) PAGE (3)

NUMBER Cook Nuclear Plant Unit 1 05000-315 YEAR SEQUENTIAL NUMBER REVISION 4 OF 4 NUMBER 1999 020 00 CORRECTIVE ACTIONS cont'd If all of the 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.

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