Attachment 2
. IN 94-44
Atwood and Morrill June 16, 1994

34 Inch "Wye" Type Page 1 of 1
Main Steam Isolation Valve
(Bottom Spring Seat)

29 1/2"

pe ra

ci Bb

\

Yoke Rod
Guide

| Yoke Rod Oo

4" Diameter
Penetration Through

Lower Spring Plate
| Approx. 4 1/2" Diameter

21/2"



Attachment 1

Atwood and Morrill IN 94-44
34 Inch "Wye" Type June 16, 1994
. F Page 1
Main Steam Isolation Valve ees
(Valve Parts & Actuator)
q 1) Parts List
fox —————
ss FF ff R 1. Main Poppet
Hy ddl wy yl 2. Stem
Wy Til Wy il 3. Gasket
ij tt j i te 4. Cover Assembly
Hy Hl I} Hil 5. Yoke Rod
5 6. Cover Nuts
i iB B 7. Cover Studs
FR 8. Bushing
re) re) 9. Body
il in ia 10. Bottom Spring Seat
Hy | Tl i i 11. Top Spring Seat
Yoke rod guide on axis ij ; ij |
of main steam oe a = es
re)
) Chay. ais
Yoke rod guide on axis
perpendicular to 6
main steam line
£ T
2
3



Attachment 3

IN 94-44
June 16, 1994
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information Date of
Notice No. Subject Issuance Issued to
94-43 Determination of Primary- 06/10/94 All holders of OLs or CPs
to-Secondary Steam for pressurized water
Generator Leak Rate reactors.
94-42 Cracking in the Lower 06/07/94 All holders of OLs or CPs
Region of the Core for boiling-water reactors
Shroud in Boiling-Water (BWRs).
Reactors
94-41 Problems with General 06/07/94 All holders of OLs or CPs
Electric Type CR124 for nuclear power reactors.
Overload Relay Ambient
Compensation
94-40 Failure of a Rod Control 05/26/94 All holders of OLs or CPs
Cluster Assembly to Fully for pressurized-water
Insert Following a Reactor reactors (PWRs).
Trip at Braidwood Unit 2
94-39 Identified Problems in 05/31/94 All U.S. Nuclear Regulatory
Gamma Stereotactic Commission Teletherapy
Radiosurgery Medical Licensees.
94-38 Results of a Special NRC 05/27/94 All holders of OLs or CPs
Inspection at Dresden for NPRs and all fuel cycle
Nuclear Power Station and materials licensees
Unit 1 Following a Rupture authorized to possess spent
of Service Water Inside fuel.
Containment
94-37 Misadministration Caused 05/27/94 All U.S. Nuclear Regulatory
by a Bent Interstitial Commission Medical Licensees
Needle during Brachy- authorized to use brachy-
therapy Procedure therapy sources in high-,
medium-, and pulsed-dose-
rate remote afterloaders.
94-36 Undetected Accumulation 05/24/94 All holders of OLs or CPs
of Gas in Reactor for nuclear power reactors.
Coolant System
OL = Operating License

cP

Construction Permit


UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555

June 16, 1994

NRC INFORMATION NOTICE 94-44: MAIN STEAM ISOLATION VALVE FAILURE TO CLOSE ON
DEMAND BECAUSE OF INADEQUATE MAINTENANCE AND
TESTING

Addressees

All holders of operating licenses or construction permits for nuclear power
reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to the failure of two main steam isolation valves
at McGuire Nuclear Station to close fully on demand. It is expected that
recipients will review the information for applicability to their facilities
and consider actions, as appropriate, to avoid similar problems. However,
suggestions contained in this information notice are not NRC requirements;
therefore, no specific action or written response is required.

Description of Circumstances

On December 27, 1993, at McGuire Nuclear Station, Unit 2, the ‘B’ main steam
isolation valve (MSIV) failed to close on demand, resulting in a dryout
condition of the associated steam generator during an event initiated by a
loss of offsite power followed by a safety injection. MSIV ‘B’ closed fully
after the event when a technician working on the valve loosened one of the
yoke rod guides. In addition, analysis of transient data after the event
indicated that MSIV ‘A’ had failed to close fully at the onset of the event
and had leaked excessively. MSIV ‘A’ completed closure during the event as it
cooled down, and the steam generator associated with this MSIV did not reach a
dryout condition.

McGuire Nuclear Station Unit 2 is a four-loop pressurized-water reactor
designed by Westinghouse with nominal 34-inch Atwood & Morrill air-operated
"wye" type globe MSIVs, with the actuators mounted horizontally. The valve
actuator is constructed as follows (see attached Figures 1 and 2). The four
springs that provide the motive force for closure encase the yoke rods and
rest on a bottom spring seat. The stem of the valve passes through and is
attached to the bottom spring seat. The four yoke rods penetrate the bottom
spring seat in the corners and attach to the valve bonnet. The springs are
attached at the top to the top spring seat. As the valve is opened, the
bottom spring seat rises and compresses the springs between the bottom spring
seat and the top spring seat. Yoke rod guides are provided as part of the

9406130150


IN 94-44
June 16, 1994
Page 2 of 3

seismic qualification of the valves to minimize lateral movement of the bottom
spring seat. The guides are brass bolts that screw into the sides of the
bottom spring seat. The bolts are aligned to the centerline of the holes on
the bottom spring seat through which the yoke rods pass. Four guides prevent
deflection of the bottom spring seat along the axis of the main steam line
(vertical), and two guides prevent deflection along an axis perpendicular to
the main steam line (see Figure 2). Failure of the two MSIVs to close as
designed is attributed to inadequate setting of clearances between yoke rod
guides and yoke rods and to inadequate testing. According to the
manufacturer, clearances between the yoke rod guides and the yoke rods for a
valve should be set when the valve is closed and heated to normal operating
temperature. Also, the manufacturer indicated that the valve should be tested
at normal operating temperature. Licensee procedures specified that
clearances be set while the valve was at ambient temperature, and all testing
was done under cold conditions.

When the valve is cold, the yoke rods are essentially parallel to each other.
However, when the valve is hot, the bonnet of the valve expands slightly and
causes the lower section of the yoke rods to move laterally outward from the
centerline, forming a tapered shape. The yoke rods had formed a tapered shape
(wide at the bottom) and caused the clearance between the yoke rods and the
yoke rod guides to close. Lack of control over the yoke rod guide clearances
can cause binding in at least two ways. First, the clearances between the
yoke rod guides and the yoke rods can close completely and cause the bottom
spring seat to bind on the yoke rods. Second, when properly set (with the
valve hot), the upper yoke rod guides do not have any clearance and should
just touch the yoke rods. However, excessive torquing of these guides causes
misalignment of the bottom spring seat so that it moves the attached valve
stem off its proper line of travel, causing it to bind on the valve packing as
the valve attempts to stroke.

Discussion

The valve described in this information notice is used in safety-related
applications at both boiling-water and pressurized-water reactors. One such
application is as an MSIV. At McGuire and other domestic pressurized-water
reactors, MSIVs are required to close and remain closed after a design-basis
accident. Failure to properly set the clearances between the yoke rod guides
and the yoke rods can cause a common mode failure that will defeat the safety
function of these valves.

After the failure at McGuire, a similar failure of an MSIV was detected at the
Sequoyah Nuclear Plant during a shutdown testing program. In addition, MSIV
binding was experienced at the H. B. Robinson facility when stroke testing

was performed at normal operating temperature, even though these valves were
of a different design, i.e., check valves with air actuators.

Inservice testing (IST) for measuring the full stroke times of the MSIVs at
McGuire is performed during cold shutdown. The requirements for IST do not


IN 94-44
June 16, 1994
Page 3 of 3

include performing testing at the operating conditions that would exist at the
time a valve would be required to perform its design-basis function. The
current IST requirements, rather, are intended to establish a monitoring
program for identifying degrading trends in the operation of the tested
components. The event at McGuire illustrates an example where IST alone could
not be relied upon to ensure operability of the MSIV. The licensee determined
that additional testing, supplemental to that required by the IST program, is
necessary to verify that the valves are capable of performing their design-
basis function. One of the corrective actions taken at the Sequoyah Nuclear
Plant is to test the MSIV at approximately 286 degrees C [547 degrees F] until
an adjustment method that is not temperature dependent can be developed.

These events highlight the importance of vendor recommendations and adequate
testing programs to ensure that safety-related equipment is capable of
performing its safety function.

This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation project manager. :
é Brian K. Grimes,

Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation

Technical contacts: Jim Moorman, RII
(404) 331-5593

Eric Benner, NRR
(301) 504-1171

Attachments:
1. Figure 1 - Atwood & Morrill 34 Inch,
"Wye" Type MSIV (Valve Parts)
2. Figure 2 - Atwood & Morrill 34 Inch,
"Wye" Type MSIV (Bottom Spring Seat)
3. List of Recently Issued NRC Information Notices