ML20151D747

IE Info Notice 81-28, Failure of Rockwell-Edward Msivs

ML20151D747
Person / Time
Issue date:	09/03/1981
From:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
To:
References
IEIN-81-28, NUDOCS 8103300413
Download: ML20151D747 (3)

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SSIN No.: 6835

• Accession No.:

8103300413 IN 81-28 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF-INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 September 3, 1981 -

IE INFORMATION NOTICE NO. 81-28: FAILURE OF ROCKWELL-EDWARD MAIN STEAM ISOLATION VALVES Description of Circumstances:

There have been several recent mechanical failures of the "Rockwell-Edward Flite Flow Stop Valve," a "Y" pattern globe valve made by Rockwell International, used for main steam isolation valves (MSIV) at some BWR facilities. Operating BWR facilities using this valve include Brunswick Unit 1 and 2, Cooper, Duane Arnold, Fitzpatrick, Hatch Unit 2, and Vermont Yankee. Of the seven total reported mechanical failures, five occurred at Brunswick Unit 2 and one each occurred at Brunswick Unit 1 and Hatch Unit 2.

The valve components that have failed are shown in Figure 1. The piston assembly is attached to the main disk (2) by thread engagement and then restrained from unwinding by pin (4). The stem disk (1) is also attached to the stem (6) by thread engagement tightened to 1050 ft-lb torque specifications with an anti-rotation restraint provided by pin (3). The valve is closed primarily by spring forces. The valve is installed so that reactor steam pressure works to seat the main disk. The stem disk provides pressure equalization action to reduce over-seat load for opening the main disk against system pressure.

The failures that have occurred involved a mechanical separation of valve internals. This separation was either at the stem-to-stem-disk threaded i

l' connection or at the main-disk-to piston threaded connection. Either failure permits the main disk to be free of the stem. The failure in either mode results from failure of the threaded connection, which in some cases is caused by vibration-induced rotation of the disk so that it becomes disconnected from its threaded mate. Such rotation is believed to be caused by or aided by the propensity of steam flow to produce vibration and to create turning forces on valve internal components when antirotation restraint is inadequate due to .

a failed or missing pin. Other contributing causes are believed to result from reassembly of the valve after disassembly at the site; such reassembly may have included inadequately torqued connections and failure to properly install the pins.

Also, an examination of spare parts at the Brunswick site showed that the thread dimensions on the stems and stem disks did not meet drawing tolerances.

The individual failures are described below in chronological order. i

1. In January 1976, the Brunswick Unit 2 "D" steam line inboard valve main disk separated from the piston. There was nc evidence that pin (4) was installed, w

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- IN 81-28 September 3, 1981 Page 2 of 2

2. On January 30, 1979, the Brunswick Unit 2 "A" steam line inboard valve stem disk separated from the stem. A square pin was used in the round hole at point (3). The corners of the pin experienced high stress, thereby causing cracking of the pin.

3. On January 15, 1981, the Brunswick Unit 2 "C" steam line outboard valve main disk separated from the piston. There was no evidence that pin (4) was

• ever inserted. This was deduced from finding the hole not deformed and no sign of a plug weld.

4. On March 5, 1981, the Hatch Unit 2 "A" steam line inboard valve stem disk separated from the stem. Pin (3) was not fully inserted.

5. On March 30, 1981, the Brunswick Unit 1 "C" steam line outboard valve stem disk separated from the stem. Pin (3) failed and was not recovered.

i 6. On July 2, 1981, the Brunswick Unit 2 "C" steam line inboard valve stem disk separated from the stem. Pin (3) was not properly installed.

7. On July 18, 1981, the Brunswick Unit 2 "D" steam line inboard valve main disk separated from the piston. Pin (4) was not fully inserted.

These failures have raised concerns regarding (1) the capability of the valve to perform its required safety function and (2) increased challenges to safety systems. However, it is noted that the failures to date have resulted in the main disk going closed (i.e., not cocking open) with some uncertainty only as to its leak tightness.

t Detailed investigation of the July failures at Brunswick Unit 2 led to the i

preliminary findings of possible excessive vibrations on valve internals from steam flow turbulences created by the piping direction changes. In addition, there was evidence of loose thread connections. Further investigations and evaluations are currently in progress. Preliminary corrective actions by the licensee include increasing the stem pin size from 5/16-inch to 3/8-inch, using three pins instead of one or two pins, and increasing the hole depth 1/8-inch into the stem. In addition, corrective actions for the main-disk-to piston connection include adding an extra pin (of the same 1/2-inch size) and increasing the hole depth by 1/8-inch.

This information is provided as notification of a potentially significant matter that is still under review by the NRC staff. In case the continuing NRC review finds that specific licensee actions would be appropriate, an IE circular or bulletin may be issued. In the interim, we expect that licensees will review this information for applicability to their facilities.

I No written response to this information is required. If you need additional information regarding this matter, please contact the Director of the appropriate i NRC Regional Office.

Attachments:

1. Figure 1

2. Recently issued IE Information Notices

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1. STEM DISK

2. MAIN DISK

3. ANTIR0TATION PIN - STEM DISK TO STEM

4. ANTIR0TATION PIN - MAIN DISK TO PISTON

5. STELLITED DISK GUIDES, 3 RIBS,120' APART (OUT OF SHOWN VIEW)

6. STEM p

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