05000387/LER-2011-003, HPCI Inoperability Due to Valve Packing Leak

HPCI Inoperability Due to Valve Packing Leak

ML111160599
Person / Time
Site:	Susquehanna
Issue date:	04/26/2011
From:	Rausch T Susquehanna
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
PLA-6716 LER 11-003-00
Download: ML111160599 (6)

LER-2011-003, HPCI Inoperability Due to Valve Packing Leak

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat
3872011003R00 - NRC Website

text

Timothy S. Rausch Sr. Vice President & Chief Nuclear Officer APR C 6 2011 PPL Susquehanna, LLC 769 Salem Boulevard Berwick, PA 18603 Tel. 570.542.3445 Fax 570.542.1504 tsrausch@pplweb.com 0

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,wee ppl.$I U. S. ~uclear Regulatory Commission Attn: Document Control Desk Mail Stop OP1-17 Washington, DC 20555 SUSQUEHANNA STEAM ELECTRIC STATION LICENSEE EVENT REPORT 50-3871201 1-003-00 LICENSE NO. NPF-14 PLA-6716 Docket No 50-387.

Attached is Licensee Event Report (LER) 50-3871201 1-003-00. The event involved a packing leak on the Unit 1 HPCI Steam Supply Inboard Isolation Valve that resulted in the containment isolation valve and HPCI being declared inoperable. This event was determined to be reportable under 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specification and under 10 CFR 50.73(a)(2)(v)(D) as a condition that could have prevented the fulfillment of a safety function.

There were no actual consequences to the health and safety of the public as a result of this event.

No regulatory commitments are associated with this LER.

Attachment Copy: NRC Region I Mr. P. W. Finney, NRC Sr. Resident Inspector Mr. R. R. Janati, DEP/BRP Mr. B. K. Vaidya, NRC Project Manager

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION [lo-201

0)

LICENSEE EVENT REPORT (LER)

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

APPROVED BY OMB: NO. 31 50-01 04 EXPIRES: 1 0131 1201 3

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

1. FACILITY NAME Susquehanna Steam Electric Station Unit 1

. DOCKET NUMBER 1 05000387

4. TITLE HPCl Inoperability Due to Valve Packing Leak

3. OPERATING MODE 1

5. EVENT DATE

10. POWER LEVEL 99%

MONTH 02

11. W S REPORT IS SUBMmD PURSUANT TO THE REQUIREMEWS OF 10 CFR 8 (Check all that apply)

[7 20.2201 (b)

[7 20.2203(a)(3)(i) 50.73(a)(2)(i)(C) 50.73(a) (2) (vii) 20.2201 (d)

[7 20.2203(a)(3)(ii) 50.73(a) (2) (ii)(A) 50.73(a)(2)(viii)(A) 20.2203(a)(1) 20.2203(a)(4)

[7 50.73(a)(2)(ii)(B)

[7 50.73(a) (2) (viii)(B) 20.2203(a)(2)(i) 50.36(~)(1

)(i)(A)

[7 50.73(a)(2)(iii)

[7 50.73(a) (2) (ix)(A) 20.2203(a)(2)(ii)

[7 50.36(c)(l )(ii)(A) 50.73(a) (2) (iv) (A)

[7 50.73(a)(2)0()

20.2203(a)(2)(iii)

[7 50.36(~)(2)

[7 50.73(a) (2) (v)(A)

[7 73.71 (a)(4) 20.2203(a)(2)(iv)

[7 50.46(a)(3)(ii) 50.73(a)(2)(v)(B)

[7 73.71 (a)(5)

[7 20.2203(a)(2)(v)

[7 50.73(a)(Z)(i)(A)

• 50.73(a) (2) (v)(C)

[7 OTHER [7 20.2203(a)(2) (vi) la 50.73(a)(2) (I)@)

IXI 50.73(a)(2)(v)(D)

Specify in Abstract below or in

1. FACILITY NAME Susquehanna Steam Electric Station Unit 1

1. The packing gland is a non pressure retaining component (a tool to hold the packing rings in place).

2. The brass bushing is a consumable to protect the stem from excessive wear.

2. DOCKET 05000387

3. The vendor, Anchor-Darling concurs with this change 1

4. The 118 inch bushing will not affect the integrity of the gland per Anchor-Darling.

Implementation of the changes was via action plans added to work package instructions. A brass liner was installed in HV155F002 in 1996 using this process.

3. PAGE

6. LER NUMBER In 1998, a Replacement Item Evaluation (RIE) was developed for the liner installations. An RIE is a modification mechanism utilized in the Susquehanna modification process. The RIE addressed the impact to the safety of plant operation for a "bronze" liner and recommended use of phosphor bronze. The bronze was recommended due to low Zinc content so it would have lower susceptibility to Stress Cracking Corrosion.

YEAR I In August 1998, NRC informed PPL of a valve concern. The valve concern was described as:

"The NRC has received information that during the last refueling outage, valve maintenance work on safety related Anchor Darling motor operated valves was not performed under a Design Change Package and bypassed a safety evaluation. Specifically, brass liners were slide fitted into the gland followers on safety related Anchor Darling motor operated valves and the impact on motor operated valve operation was not determined if the brass liner gets stuck between the gland follower and the valve stem."

SEQUENTIAL NUMBER As a result of the concern, Susquehanna re-evaluated material concerns with the use of brass liners given that brass had been rejected in the RIE evaluation. The re-evaluation concluded that brass was acceptable, though bronze could be considered preferred. Impacts from corrosion were judged to be a long term effect and to have the same consequences as normal packing wear. There was no consideration made of the possible failure modes or the implications of a failed liner on the packing system.

REVISION NUMBER Analvsis of the Fractured Gland Liner The fractured gland liner removed from HV155F002 was examined by In Service Inspection (ISI). Material analysis identified the liner as brass with a zinc content of 35%. IS1 identified "overload shear fracture" as the failure mechanism. The width of the fractured lip of the liner was measured as 0.049 inches. This is significant, because the recess cut into the gland to receive this lip was cut at 0.062 inches. As a result, when the liner was installed in the gland, a gap of 0.013 inches was left that exposed the sharp edge of the gland (a fulcrum point) to the top packing item.

A liner replicate was examined using a scanning electron microscope. The examiner observed what appeared to be intergranular fracture in portions of the fractured lip, which would be consistent with stress-corrosion cracking. Other areas of this fracture surface showed the dimpled rupture that normally accompanies final overload. It appears that the fracture started as a Stress Corrosion Crack but finally failed under load.

Analysis of the stress acting on the lip of the gland liner was performed for both the as-designed and as-built configurations for the gland liner. The analysis concludes that it is feasible that the as-built configuration of the gland liner could have fractured as a result of normally applied loads imposed by the packing gland. The as-built lip thickness was found to be less that that shown in the work instructions for the installation work order. Had the liner been fabricated in accordance with the action plan, this analysis shows that the gland liner would likely not have failed.

There was no indication of the liner being fractured or damaged when the valve was repacked in 2008, and the fracture is believed to have occurred sometime after this repack. In 2010, the gland follower was realigned by loosening the gland nuts one turn and tightening down on the high side to realign the follower. It is possible that gland loads exceeded normal loads during this repair.

Failure Mechanism The width of the bottom lip of the brass liner allowed a 0.013 inch gap and exposed the top packing washer to a sharp edge. Under the load of the packing, system pressure, and stroking of the valve, the washer was weakened and distorted. The lip, weakened by Stress Corrosion Cracking, is believed to have fractured completely under load possibly during attempts in 2010 to straighten the cocked packing gland and follower.

After the fracture, either as a result of system pressure or valve stroking, the liner cylinder moved axially up the gland. This resulted in loss of approximately 20% of the loading surface of the gland which increased the gap around the stem and allowed the packing to relax. Over time, as the packing displaced into the gap and the packing load on the stem was reduced below system pressure, a leak was initiated. As steam began to disintegrate the packing, the leak worsened with time.

CAUSE OF THE EVENT

The root cause was determined to be a failure to recognize the implications of gland liner failure and the failure modes and mechanisms on the packing system during changes to gland design. The gland liner function was not recognized as having a structural requirement, and this lack of understanding resulted in failure to address this event failure mode during change to the gland. This resulted in failure of the brass liner and subsequent failure of the HPCl Inboard Steam Isolation PCIV.

A causal factor was less than adequate technical rigor applied during design of the gland liner. Technical rigor did not include analysis of design considerations such as strength of material or susceptibility to stress corrosion cracking.

A second causal factor was less than adequate attention to detail during fabrication of the gland liner. When the gland liner and gland were evaluated, the liner lip dimension did not match the action plan in the work order.

ANALYSISISAFETY SIGNIFICANCE Actual Consequences:

The actual consequences were an unscheduled forced outage and accrual of HPCl system out of service time. Engineering analysis determined there was inadequate margin to assure HV155F002 would stroke closed under design basis conditions with no grease on the stem, so the valve was inoperable for primary containment isolation. The outboard HPCl steam supply isolation valve, HV155F003 was still operable to isolate the penetration.

Potential Consequences:

Each occurrence of an initiating event has the potential to increase the initiating event frequency modeled in the station Probabilistic Risk Assessment (PRA). Thus, a potential consequence of similar recurring events is a change to the initiating event frequency resulting in an increase in baseline Core Damage Frequency (CDF).

2. DOCKET 05000387

3. PAGE 6 LER NUVlBER YEAR 201 1

- 003

- 00 SEQUENTIAL NUMBER REVISION NUMBER

1. FACILITY NAME Susquehanna Steam Electric Station Unit 1

CORRECTIVE ACTIONS

The following are the key corrective action associated with this issue:

2. DOCKET 05000387

1. A review of the RIE was completed that ensured that the RIE appropriately addressed the failure of the liner material experienced on HV155F002. This review concluded that a liner constructed in accordance with the RIE would not experience the same failure mechanism.

2. The brass lined packing gland for the remaining valves will be replaced with a bronze lined packing gland for each valve with a brass liner during the 201 1 (Unit 2), 2012 (Unit I), and 2013 (Unit 2) outages.

3. A design review of the RlEs and associated instructions for installing gland liners will be reviewed to ensure that all design considerations for packing gland liners are appropriately addressed. The appropriate Engineering Change mechanism to use will be determined for any future applications after the Spring 201 1 Unit 2 refueling outage.

3. PAGE

6. LER NUMBER

PREVIOUS SIMILAR EVENTS

LER 2009-001-00, Docket No. 387License No. NPF-14 LER 2006-005-00, Docket No. 387License No. NPF-14 LER 2006-003-00, Docket No. 387kicense No. NPF-14 YEAR

4. Applicable procedures will be revised to ensure that packing gland liners are inspected during all future re-packs. Inspections will include the condition of the liner and verification that the liner is not loose and is flush with the packing gland on the surface contacting the packing. SEQUENTIAL NUMBER REVISION NUMBER