ML17265A823

LER 98-037-01:on 990422,determined That Ice Condenser Bypass Leakage Exceeds Design Basis Limit.Caused by Pressure Seal Required by Revised W Design Not Incorporated Into Aep Design.Numerous Matl Condition Walkdowns & Assessments Made

ML17265A823
Person / Time
Site:	Cook
Issue date:	05/24/1999
From:	Berry L INDIANA MICHIGAN POWER CO.
To:
Shared Package
ML17265A821	List: ML17265A820 ML17265A823
References
LER-98-037, LER-98-37, NUDOCS 9906030254
Download: ML17265A823 (6)

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NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION 16.19981 L(CENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITYNAME I1) DOCKET I2) LER NUMBER Iel PAGE I3)

Cook Nuclear Plant Unit 1 O5000-315 SEQUENTIAL REVISION 3 OF 5 NUMBER NUMBER 1998 037 01 TEXT (Ifmore spece js reqvfred, vse addi donel copies of NRC Form 866A) I17)

With the current ice condenser design, the bottom of the ice baskets is 10 ft above the bottom of the lower plenum fioor.

When an event occurs, the air and steam enter the Ice condenser lower plenum and can pressurize the area up to 12 psi, exposing the DBS seal at the end walls to that same pressure. Due to the design of the seal, it is conservatively assumed that the seal will fail and allow the steam to bypass the ice baskets and enter into upper containment directly.

Cause Of The Event The individual bypass conditions reported in the original LER were attributed to unauthorized modifications. A tack of documented configuration and inadequate implementation of the design change control process resulted in the creation of

. bypass paths via material substitutions, original construction discrepancies, Inadequate service life, and unseating of spare penetrations during the performance of work activities. The root cause of the cumulative bypass was attributed to lack of understanding of the design basis of containment as a system, and of the divider barrier in particular. This was coupled with a lack of a comprehensive inspection program for detection of defects and damage to the divider barrier.

The apparent cause of the newly discovered ice condenser bypass is that the pressure seal required by a revised Westinghouse design was not incorporated into the AEP design. The reason for this discrepancy is unknown. According to the original Westinghouse ice condenser design, the ice baskets on the containment wall'side started at the level of the ice condenser bottom slab and extended upward 58 feet. This design was to ensure that ail steam entering the ice condenser would travel through the ice baskets before entering upper containment. With this design, only a ventilation barrier was needed to seal the end walls. Later, Westinghouse implemented a new design which located the bottoms of all ice baskets 10 ft above the ice condenser bottom slab. This is the basket design that was installed at Cook Nuclear Plant. However, when the later design was introduced, the ventilation barrier was not upgraded to a include a pressure seal capable of withstanding 24 psi.

Anal sls Of The Event The originally identified condition was determined to be reportable on August 12, 1998, in accordance with 10CFR50.72(b)(2)(i), as a degraded condition discovered white the unit is shutdown that, if found while the reactor was operating, would have resulted in the plant being in an unanalyzed condition, and an ENS notification was made at 1530 hours0.0177 days <br />0.425 hours <br />0.00253 weeks <br />5.82165e-4 months <br /> EDT. The original LER was submitted in accordance with 10CFR50.73(a)(2)(ii) as an event or condition outside the design basis of the plant. An additional ice condenser bypass condition involving the DBS identified on April 22, 1999 was also determined to be reportable pursuant to the requirements of 10CFR50.73(a)(2)(ii). The DBS ice condenser bypass condition is applicable to both units. For Unit 2, refer to LER supplement 316l98-004-01.

The known bypass flow paths summarized below represent the condition as reported on August 12, 1998:

Open Area in Ft2 Refueling Cavity Drains 2.20 Backdraft damper of air return fans 0.36 Ice Condenser Air Handling Unit line 0.005 1-CPS-209, 1-CPS-210 0.017 1-VMO-101 1.069 Divider Barrier Hatches 1.4 Glycol Lines through Ice Condenser End Wall 0.66 TOTAL 5.71 NRC FORM 366A I6.19981

NRC FORM 36BA U.S. NUCLEAR REGULATORY COMMISSION IB-1998)

LlCENSEE EVENT REPORT (LER)

T EXT CONTINUATION DOCKET Iz) LER NUMBER (Bl PAGE I31 Cook Nuclear Plant Unit 1 05000-315 YEAR SEQUENTIAL REvisioN 4 OF 5 NUMBER NUMBER 1998 037 01 The known bypass flow paths summarized below represent the current condition:

Open Area in Ft2 Refueling Cavity Drains 2.20 Backdraft damper of air return fans 0.36 Ice Condenser Air Handling Unit line 0.005 1-CPS-209, 1-CPS-210 0.0 (repaired) 1-VMO-101 0.0 (repaired)

Divider Barrier Hatches 1,4 Glycol Lines through Ice Condenser End Wall 0.66 CEQ Staiiwell and Vent Well Drain Lines 0.1 CEQ Fan Room 0.007 Divider Barrier Seal 30.78 TOTAL 35.51 The cumulative bypass has been evaluated, and it has been concluded that the safety significance of this condition is negligible. Therefore, there were no implications to the health and safety of the public. Updated Final Safety Analysis Report (UFSAR) Chapter 5, Section 5.2.2.4 states that the design basis bypass'area is 5 ft2. UFSAR Chapter 14.0 describes the accident analyses for different size pipe breaks and the allowable ice condenser bypass flow for each case.

Analysis results indicate a value of 35 ft2 as the allowable deck leakage area for the, entire spectrum of break sizes. The limiting case is an 8 inch break with one spray pump operating (2000 gpm at 80,degrees F).

A second UFSAR analysis, using a more realistic method, states that with one spray pump the deck leakage could be 56 ft2 for an 8 inch break. This analysis takes credit for passive heat sinks and additional containment spray. Thus the identified value of historical value of bypass (approximately 30.78 + 5.71 = 36.49 ft2) for Unit 1 is bounded by UFSAR analysis, but is outside of the ice condenser design basis value of 5 It2. Therefore, since the plant was not in an condition, the ENS report made August 12, 1998, in accordance with 10CFR50.72(b)(2)(i), was determined to 'nanalyzed have been unnecessary.

CORRECTIVE ACTIONS Numerous material condition waikdowns and assessments have been performed, which have increased the potential to identify bypass paths in the divider barrier. Significant degraded conditions resulting in divider barrier bypass are being corrected via corrective maintenance or design changes as they are identified. The Refueling Cavity Drains are permanent bypasses, which of course will remain open. The backdraft damper of the air return fans, ice condenser AHU fine and the CEQ stairwell and vent weil drain line bypasses are currently not scheduled for repair and represent an insignificant contribution to the cumulative ice condenser bypass. The DBS ice condenser bypass will be corrected via a design change prior to Mode 4.

To prevent unauthorized or inadvertent design changes, 12 PMI 5040.DCP.001 "Design Change Determination", has been developed and implemented. To enhance recognition of a design change, 12 PMI 2291.PLAN.001 'Work Control Planning Process," is being implemented, Additionally, the UFSAR validation project will enhance the quality of the design basis and configuration documentation. Containment is one of the selected systems. Procedure 12 EHP 6040 PER.154, "Containment Divider Barrier Walkdown," has been developed to guide inspection of the divider barrier on a refueling outage frequency for possible bypass paths. This procedure includes provisions to ensure that the design basis allowable cumulative bypass is not exceeded, through correction andlor tracking of any identified bypass paths.

NRC FORM 366A 16.1998)

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (6-1998I LICENSEE EVENT nEPORT (LER)

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

Cook Nuclear Plant Unit 1 05000-315 YEAR SEQUENTIAL NUMBER REVISION 5 QP 5 NUMBER 1998 037 01 SIMILAR EVENTS 316/98-00440 NRC FORM 366A 16.1998)