ML17334B780

LER 98-004-02:on 980122,discovered That One of Ice Condenser Flow Passages Contained Large Amount of Frost & Ice.Caused by Inadequate Maint & Surveillance Practices.Completed Detailed Mapping & Quantification of Flow Passage Blockage

ML17334B780
Person / Time
Site:	Cook
Issue date:	05/15/1998
From:	Schoepf P INDIANA MICHIGAN POWER CO.
To:
Shared Package
ML17334B779	List: ML17334B778 ML17334B780
References
LER-98-004, LER-98-4, NUDOCS 9805220073
Download: ML17334B780 (8)

Text

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HRC FORH 366 kUCLEAR REGULATORY COMMISSIOH PPROVED BY OHB EXPIRES Ho. 3150.0104 5/31/95 ESTIMATED BURDEN PER RESPONSE To COMPLY MITH THI IHFORMATION COLLECT ION REOUEST: 50.0 HRS. FORIIAR

. LICENSEE EVENT REPORT (LER) COMMENTS REGARD lkG BURDEN ESTIMATE To TH INFORMATION AND RECORDS MANAGEMEHT BRANCH (HNB 7714), U.S. kUCLEAR REGULATORY COMMISSION/

MASHINGTON, DC 20555-0001, AND TO THE 'PAPERMOR REDUCTION PROJECT (3150.0104), OFFICE 0 MANAGEMENT AHD BUDGET MASHINGTON DC 20503.

FACILITY NAHE (1) DOCKET NUMBER (2) Page 1 of6 Donald C. Cook Nuclear Plant - Unit 1 50-315 TITLE (4)

Inadequate Maintenance and Surveillance Practices Result in Restricted Ice Condenser Flow Passages EVENT DATE 5 LER NUMBER 6 REPOR T DATE 7 OTHER FACILITIES INVOLVED 8 SEQUENTIAL REVISION FACILITY NAME DOCKET NUMBER MONTH OAY YEAR YEAR MONTH DAY YEAR NUMBER NUMBER Cook Unit 2 50-316 FACILITY NAME DOCKET HUHBER 01 22 98 98 004 02 05 15 98 OPERATING TH S REPORT IS SUBMITTED PURSUAN'I To THE REOUIREHENTS OF 10 CFR  : Check one or mar MDDE (9) 20.2201(b) 20.2203(a)(3)<<) 50 ~ 73(a)(2) << I I ) 73.71(b)

POMER 20.2203 a 1 20.2203 a 3 ii 50.73 a 2 iv 73. 710 LEVEL (10) 20.2203(a)(2)<< ) 20.2203(a)(4) 50 '3(a)(2)(v) OTHER 20.2203 a 2 ii 50.36 c 1 50.73 a 2 vii (Specify in 20.2203(a)(2)<< ii) 50.36(c)(2) 50.73(a)(2)(viii)(A) Abstract batch and in Text, 20.2203(a)(2)<<v) 50.73(a) (2) <<) 50.73(a)(2)(viii)(B) kRC Form 366A) 20.2203(a)(2)(v) X 50.73<a)<2)<<I) 50.?3(a)(2)(x)

LICENSEE CONTACT FOR THIS LER 12 HAME TELEPHONE NUMBER (Include Area Code)

Mr. Paul Schoepf, Safety Related Mechanical Engineering Superintendent 616/465-5901, x2408 COMPLETE ONE LINE FOR EACH COMPONEHT FAILURE DESCRIBED Ik THIS REPORT REPORTABLE REPORTABLE CAUSE SYSTEH COHPONEHT MANUFACTURER CAUSE SYSTEH COMPONENT MANUFACTURER To NPRDS To NPRDS

)%jw",:.Fig SUPPLEHEHTAL REPORT EXPECTED 14 EXPECTED MONTH DAY YEAR YES SUBHI SS I ON (lf yes, ccnptcta EXPECTED SUBHISSION DATE).

X Ho DATE (15)

ABS'TRACT (Limit to 1400 spaces, I:a., approximately 15 single-spaced typciiritten tines) <16)

On January 22, 1998, with Unit 2 in Mode 5, while personnel were touring the Unit 2 containment, it was noted that one of the ice condenser flow passages contained a large amount of frost and ice. A subsequent inspection of the ice condensers for both units identified that there were restricted flow passages in each unit's ice condenser bays, primarily in radial rows adjacent to the containment wall. As the Technical Specifications define more than one restricted flow passage as evidence of abnormal degradation, this was determined to constitute an unanalyzed condition. An ENS notification was made on January 28, 1998 at 1706 hours0.0197 days <br />0.474 hours <br />0.00282 weeks <br />6.49133e-4 months <br /> under 10CFR50.72(b)(2)(ii), as an unanalyzed condition found while the reactor was shutdown.

The root cause of this condition ftas been attributed to inadequate ice condenser maintenance practices which resulted in the blockage forming, in combination with an ineffective surveillance, which did not provide early detection of the blocked flow passage condition to allow timely corrective actions. A decision has been made to completely thaw both units ice condensers in order to address a variety of issues identified during the current unit outages. Flow passages will be confirmed dear at the conclusion of planned work. Maintenance and surveillance practices are being reviewed to ensure they adequately support ice condenser operability. These reviews will be completed and appropriate improvements in maintenance practices and surveillances will be implemented prior declaring either unit's ice condenser operable.

Detailed mapping and quantification of the flow passage blockage has been completed. This information was transmitted to Westinghouse for assessment of the impact on ice condenser and containment operability. It was concluded that the ice condensers in both units were considered operable relative to the 15 percent ice blockage criteria. Therefore, this condition was determined to be of minimal safety significance, and the health and safety of the public was never jeopardized.

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HRC FORK 366A U.S ~ NUCLEAR REGULATORY CDMKISSIOH PPROVED BY OMB NO. 3150.0104 EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY liITH THIS INFORMATION COLLECTION REOUEST: 50.0 NRS.

LICENSEE EVENT CONTINUATION FOR'WARD COMMENTS REGARDIHG BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMEHT BRANCH (MNBB 7714), U.S. NUCLEAR REGULATORY COMMISSION/

WASHINGTON, DC 20555 0001, AND TO THE PAPERWORK REDUCI'ION PROJECT (3150-0104), OFFICE OF MANAGEHENT AND BUDGET WASHINGTON DC 20503.

FACILITY NAME 1 DOCKET NUMBER 2 LER NUMBER 6 PAGE 3 YEAR SEOUEHTIAL REVISION Cook Nuclear Plant - Unit 2 50-315 98 004 2 OF 6 02 TEXT (if core sPace is required. use additional NRC Fons 366A's) (17)

C Unit 1 was in Mode 5, Cold Shutdown Unit 2 was in Mode 5, Cold Shutdown On January 22, 1998, with Unit 2 in Mode 5, while NRC and AEP personnel were touring the Unit 2 containment, it was noted that one of the ice condenser flow passages contained a large amount of frost and ice. A subsequent inspection of the ice condensers for both units identified that there were restricted flow passages in each unit's ice condenser bays, primarily in radial rows adjacent to the containment wall. As the Technical Specifications (T/S) define more than one restricted flow passage as evidence of abnormal degradation, this was determined to constitute an unanalyzed condition. An ENS notification was made on Janua(y 28, 1998 at 1706 hours0.0197 days <br />0.474 hours <br />0.00282 weeks <br />6.49133e-4 months <br /> under 10CFR50.72(b)(2)(ii), as an unanalyzed'condition found while the reactor was shutdown.

'ach ice condenser consists of 24 bays containing 81 ice baskets per bay, covering an arc of 300 degrees in the containment structure. Each ice basket is approximately 12 inches across and 48 feet long, filled with borated ice.

The flow passages in between the ice baskets must be kept clear of obstruction to assure even steam flow through the ice beds during a post-accident period.

T/S surveillance 4.6.5.1.b.3 requires a once per 18 month verification, "by visual inspection of at least two flow passages per ice condenser bay, that the accumulation of frost or ice on the top deck floor grating, on the intermediate deck and on flow passages between ice baskets and past lattice frames is restricted to a nominal thickness of 3/8 inches. If one flow passage per bay is found to have an accumulation of frost or ice greater than this thickness, a representative sample of 20 additional flow passages from the same bay shall be visually inspected. If these additional flow passages are found acceptable, the surveillance program may proceed considering the'single deficiency as unique and acceptable. More than one restricted flow passage per bay is evidence of abnormal degradation of the ice condenser."

The T/S surveillance of ice condenser flow passages is implemented via procedure 12 EHP 4030 STP.250, "Inspection of Ice Condenser Flow Passages." Flow passage surveillances were performed during the current unit outages at the beginning and conclusion of initial woik in each ice condenser. These inspections, performed by contract personnel, did not identify the existence any abnormal ice build up in the flow passages. An NRC inspector subsequently identified a blocked flow passage in late January, 1998. As a result of the inspector finding, a 100%

flow passage inspection was subsequently performed ln each unit. A preliminary calculation was done to estimate the flow passage blockage on a bay-by-bay basis. The average flow passage blockage was estimated to be 10.7%

in Unit 1 and 11.5% in Unit 2. Also, the 100% flow passage inspection revealed that some of the flow passages included in the earlier inspections and documented as being clear were subsequently determined to be blocked. A formal calculation was later done to determine the blockage on a bay-by-bay basis, and this information was transmitted to Westinghouse for analysis.

HRC FORM 366A U.ST NUCLEAR REGULATORY COMMISSION PPROVED BY OMB NO. 3150-0104 EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY HITN THIS INFORMATION COLLECTIO}i REQUEST: 50.0 HRS.

LICENSEE EVENT CONTINUATION FORliARD COMHEHTS REGARDIHG BURDEN ESTIMATE TO TNE IHFORHATIOH AND RECORDS MANAGEMENT BRANCH (HNBB 7714), U.S. NUCLEAR REGULATORY COMMISSION, IIASNINGTON, DC 20555.0001, AND TO THE PAPERNORK REDUCTION PROJECT (3150 0104), OFFICE OF MANAGEMEHT AND BUDGET liASHINGTON DC 20503.

FACILITY NAME 1 DOCKET NUMBER 2 LER NUMBER 6 PAGE 3 YEAR SEQUENTIAL REVISION Cook Nuclear Plant - Unit 2 50-315 98 004 02 3OF6 TEXT (if aore space is required. use additional NRC Fons 366A's) (17)

The root cause of this condition has been attributed to inadequate ice condenser maintenance practices which resulted in the formation of flow passage blockage, in combination with an ineffective surveillance which did not provide early detection of the blocked flow passage condition to allow timely corrective actions.

Inadequate ice condenser maintenance refers to practices which both contribute to formation of frost and ice in flow passages, and which do not result in effective clearing of deposits following maintenance or when otherwise identified. The following maintenance related factors are considered to be contributors to the formation of frost and ice in ice condenser flow passages.

Ice condenser doors are frequently opened for personnel or equipment access during maintenance periods, and doors which do not seal tight in the closed position, allow heat and humidity to enter the ice condenser. Lower ice condenser access doors are also left open during portions of outages, enclosed in tenting, to accommodate the passage of vacuum hoses used for ice bed maintenance. The situation is worsened by the extra humidity in containment during refueling outages, particularly during summer months. This contributes to frost and ice formation on laNcework and in the flow passages.

Ice also accumulates between ice baskets and lattices during basket filI activities, which contributes to frost and ice blockage in the flow passages. Ice may be deposited on latticework during filling of ice baskets. Plastic bags are ~

normally placed in the flow passages between adjacent baskets as a means to contain the ice in the basket being filled. However, because the basket and the lattice structure are so close together, the bags do not prevent some ice from accumulating between the basket and the lattice. Normal practice is to clear this ice following ice basket maintenance.

The ice condenser design provides for wall defrosts to clear ice and frost buildup. Ice condenser maintenance strategies have not effectively utilized defrosts to clear blockage near the ice condenser walls. Sublimation and transport of ice occurs from one area of the ice condenser to another. This generally occurs from the radial row 9, the row next to the crane wall,'oward radial row 1, the row adjacent to the outside wall of containment. Temperature gradients within the ice bed are considered to be contributors to the ice sublimation and transport. Temperature gradients occur when air handler units are not in service due to failure or planned maintenance.

Finally, maintenance of ice condenser air handler units, which help achieve uniform temperature distribution in the ice condenser, has not been optimized. The air handler units occasionally malfunction, indicating that preventive maintenance improvements are warranted. Additionally, corrective repairs to these units were not always given a high priority within the work control process.

The flow passage blockage documented in this report is considered to be the result of a combination of these factors.

For example, the priority assigned to corrective maintenance on air handler units was reviewed. It was noted that corrective maintenance on air handler units typically receive a relatively low priority for completion, given that failure of an air handler does not directly result in any Inoperability of equipment. With regard to the addition of humidity to the ice condensers, at the time the noted condition was identified, both units had been in extended outages approaching six months in duration, during which significant work was performed in the ice condensers. This work required frequent opening of ice condenser doors for personnel and equipment access, which contributes to humidity in the ice condenser. Finally, numerous ice baskets were emptied and refilled during these outages, which had the potential to result in the accumulation of ice on latticework during basket filling.

NRC FORH 366A U.S. NUCLEAR REGULATORY COMHISSIOH PPROVED BY OMB NO. 3150.0104 EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY lilTH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS.

LICENSEE EVENT CONTINUATION FORIIARD COMMENTS REGARDIHG BURDEH ESTIHATE TO THE INFORMATION AND RECORDS MANAGEMENT BRAHCH (MNBB 7714), U.ST NUCLEAR REGULATORY COMMISSIOH,

'WASHIHGTON, DC 20555.0001, AND To THE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET IIASHINGTON DC 20503.

FACILITY NAME 1 DOCKET NUMBER 2 LER NUMBER 6 PAGE 3 YEAR SEQUENTIAL REVISION Cook Nuclear Plant - Unit 2 50-315 98 004 02 4OF6 TEXT (If core space is required. use additional NRC Fons 366A's) (IT)

C I A final maintenance consideration involves the use of defrosts to control ice buildup. The ice condenser design includes provisions for both floor and wall defrosts. These design features were not effectively utilized during the current outages to control the buildup of frost and ice in areas adjacent to walls.

Surveillance activities have not been effective in consistently identifying blocked flow passages. Ineffective sulveillances contributed to this event in that they did not provide early detection of the blocked flow passage condition to allow timely corrective actions. This is supported by differing results from recent surveillances performed in proximity to one another. Ice condenser surveillance deficiencies, which contributed to this event, include lack of a T/S definition of what level of flow passage blockage results in an inoperable ice condenser. Other deficiencies included lack of guidance on required qualifications for personnel performing ice condenser flow passage sulveillances, lack of guidance on quality techniques to be used and lack of guidance on the use of lighting aids during inspections.

As previously noted the T/S surveillance of ice condenser flow passages is implemented via engineering procedure 12 EHP 4030 STP.250, "Inspection of Ice Condenser Flow Passages." Flow passage surveillances were performed during the current unit outages at the conclusion of initial work in each ice condenser. These inspections, performed by contract personnel, did not identify the existence of any abnormal ice build up in the flow passages. Subsequent inspection revealed that some of the flow passages included in the earlier inspections and documented as being clear were subsequently determined to be blocked. This points to ineffectiveness of the initial surveillances in detecting the flow passage blockage.

T/S surveillance 4.6.5.1.b.3 requires a once per 18 month verification, "by visual inspection of at least two flow passages per ice condenser bay, that the accumulation of frost or ice on the top deck floor grating, on the intermediate deck and on flow passages between ice baskets and past lattice frames is restricted to a nominal thickness of 3/8 inches. If one flow passage per bay is found to have an accumulation of frost or ice greater than this thickness, a representative sample of 20 additional flow passages from the same bay shall be visualiy inspected. If these additional flow passages are found acceptable, the surveillance program may proceed considering the single deficiency as unique and acceptable. More than one restricted flow passage per bay is evidence of abnormal degradation of the ice condenser."

While the T/S define that more than one restricted flow passage per bay is evidence of abnormal degradation of the ice condenser, the T/S do not state what amount of flow passage blockage renders the ice condenser inoperable. In response to previous instances of flow passage blockage, a blockage limit of 15% of the total upward flow area was determined based on the analysis performed for the Unit 1 Reduced Temperature and Pressure program. However, procedure 12 EHP 4030 STP.250 does not provide the detailed information necessary to determine the percentage of flow passage blockage, nor does it define the inspection acceptance criteria to ensure that the 15 percent ice condenser flow blockage limit is not exceeded.

Procedure 12 EHP 4030 STP.250 also excepts hoarfrost deposits from inspection of frost and ice buildup in the flow passages. Hoarfrost is frost that can be easily wiped away by hand.. This exception is based on a 1988 T/S Interpretation, which concluded that hoarfrost extending beyond 3/8 inches in length is not considered as blockage in the flow passage. However, T/S 4.6.5.1.b.3 states that "frost or ice" in the flow passages greater than a nominal thickness of 3/8 inches is the critical dimension for determining flow passage blockage. There is no discussion in the 7

HRC FORH 366A U.S. NUCLEAR REGULATORY COHHISSIOH APPROVED BY OHB NO. 3150-0104 EXPIRES 5/31/95 ESTIHATED BURDEN PER RESPONSE TO COHPLY MITH THIS IHFORHATIOH COLLECTIOH REQUEST: 50.0 HRS.

LICENSEE EVENT CONTINUATION FORMARD COHHENTS REGAROIHG BURDEN ESTIHATE TO THE IHFORHATION AND RECORDS HANAGEHEHT BRANCH (HNBB 7714), U.ST NUCLEAR REGULATORY COHHISSIOHg MASHIHGTON, DC 20555.0001, AND TO THE PAPERMORK REDUCTION PROJECT (3150-0104), OFFICE OF HAHAGEHENT AND BUDGET MASHINGTOH DC 20503.

FACILITY NAHE 1 DOCKET NUHBER 2 LER NUHBER 6 PAGE 3 YEAR SEQUENTIAL REVISION Cook Nuclear Plant - Unit 2 50-315 98 004 02 5OF6 TEXT (if sore space is required. use additional NC Fons 366A's) (17)

T/S permitting hoarfrost. As a result of this interpretation, condition reports were not written on hoarfrost blocked flow passages, which contributed to limited awareness of the trending toward more significant flow passage blockages.

The flow passage surveillance procedure also does not give guidance on how flow passages are selected for inspection. Past practice has been for the system engineer to select flow passages for inspection based on judgement. Procedural guidance was not available to accomplish random inspections in combination with inspection of areas most likely to exhibit problems based on past experience.

Another weakness noted in the surveillance procedure was the lack of guidance on required qualiflcations for personnel performing the flow passage inspections, and also lack of guidance on the use of quality techniques such as dual concurrent verification. The most recent surveillances were performed by contract personnel, who may have only received general training on ice condenser maintenance activities, and the procedure allowed for a single individual to perform the surveillance.

A final weakness noted in procedure 12 EHP 4030 STP.250 was the lack of detailed guidance on the use of lighting aides during the inspection. The flow passage inspection procedure states as a prerequisite that "Portable lights to inspect the ice condenser passages will be obtained as necessary." The procedure does not specify the light conditions that must be met to visually inspect the flow passages.

Following this event, both ice condenser maintenance and surveillance practices and historical information were reviewed to determine causes for the formation of the blockage, and for the failure to detect the blockage during ice condenser flow passage surveillances.

Ev This event is reportable under 10CFR50.72(b)(2)(ii), as an unanalyzed condition found while the reactor was shutdown and was reported via ENS notification on January 28, 1998 at 1706 hours0.0197 days <br />0.474 hours <br />0.00282 weeks <br />6.49133e-4 months <br />.

As a result of the 100 percent inspection, a formal calculation was performed to determine the percent blockage of

'ach of the 48 bays. This calculation indicated that the blockages for Unit 1 ranged from 6.7 percent to 18.8 percent per bay, and the blockages in Unit 2 ranged from 4.1 percent to 17.4 percent. Ten bays were found with blockage greater than 15 percent. This formal calculation replaced the preliminary calculation that had only estimated the blockage.

The results of the formal calculation were sent to Westinghouse for analysis of the impact on ice condenser and containment operability. Based on this data, and by utilizing a lumping" method, which combines several bays, Westinghouse determined that the highest calculated blockage percentage was less than 12.5 percent per lumping for Unit 1 and less than 14.0 percent per lumping for Unit 2. Therefore', Westinghouse concluded that the ice condensers in both units were considered operable relative to the 15 percent flow passage blockage criteria.

Therefore, this condition was determined to be of minimal safety significance, and the health and safety of the public was never jeopardized.

HRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION PROVED BY OMB HO. 3150-0104 EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COHPLY iiITH THIS INFORMATIOH COLLECTIOH REQUEST: 50.0 HRS.

LICENSEE EVENT'ONTINUATION FORiiARD COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AHD RECORDS MANAGEMENT BRANCH (MHBB 7714), U.S. NUCLEAR REGULATORY COMMISSIONS WASHINGTON, DC 20555-0001, AHD TO THE PAPERWORK REDUCTION PROJECT (3150 0104), OFFICE OF MANAGEMEHT AND BUDGET IIASHINGTOH DC 20503.

FACILITY NAME 1 DOCKET NUMBER 2 LER NUMBER 6 PAGE 3 YEAR SEQUEHTIAL REVISION Cook Nuclear Plant - Unit 2 50-315 98 004 02 6OF6 TEXT (if more space is required. use additional HRC Form 366A's) (17)

Both units'ce Condensers will be thawed during the current outages'to address a variety of issues. Flow passages will be confirmed clear of blockage at the conclusion of planned work.

Maintenance and surveillance practices will be reviewed and revised as necessary to ensure they adequately support ice condenser operability. These reviews will be completed and appropriate improvements in maintenance practices and surveillances will be implemented prior declaring either unit's ice condenser operable. Items, which will be specifically covered in these reviews, include consideration of possible improved methods and controls for reducing ice condenser door openings. (I.e. use of air locks for personnel passage or addition of penetrations for hoses rather than doors).

Priorities assigned to maintenance of air handler units will be revisited, to ensure this equipment receives the proper attention for corrective mainteT)ance. Preventive maintenance activities for air handlers will also be reviewed and revised as necessary to ensure appropriate activities are being pro-actively performed for these units.

Techniques for inspecting and clearing flow passages following basket filling activities will also be reviewed and revised as necessary to ensure any residual ice is removed from latticework following ice basket maintenance.

Finally, ice condenser defrosts will be revisited, to ensure there is guidance on when and how to control frost and ice accumulation before it becomes significant.

With regard to ice condenser surveillances, a wholesale review of all ice condenser surveillance procedures is being performed for both units. Items being considered in this review include the basis for procedure acceptance limits, guidance for performing surveillances, the use of margins to T/S limits, and required qualifications and quality techniques for personnel performing the surveillances. This review will be performed on all ice condenser surveillance procedures, including flow passage surveillance procedures Finally, the aforementioned T/S interpretation on what constitutes flow passage blockage will be reviewed. The basis for the T/S will be reviewed for possible revision to clarify what constitutes unacceptable flow passage blockage.

The ice condenser surveillance program reviews will be completed, and improvements incorporated into surveillance procedures prior to declaring either unit's ice condenser operable.

ail C Not applicable Ev t 315/83-099-00 315/88-007-00 316/85-013-00 316/88-005-00 315/87-013-00 316/88-015-00 315/88-002-00