Information Notice 2003-17, Reduced Service Life of Automatic Switch Company (Asco) Solenoid Valves with Buna-N Material
| ML032681003 | |
| Person / Time | |
|---|---|
| Issue date: | 09/29/2003 |
| From: | Beckner W NRC/NRR/DIPM |
| To: | |
| Dozier J, NRR/IROB 415-1014 | |
| References | |
| IN-03-017 | |
| Download: ML032681003 (5) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001 September 29, 2003 NRC INFORMATION NOTICE 2003-17: REDUCED SERVICE LIFE OF AUTOMATIC
SWITCH COMPANY (ASCO) SOLENOID VALVES
WITH BUNA-N MATERIAL
Addressees
All holders of operating licenses for nuclear power reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert
addressees to potential problems caused by the hardening of Buna-N material used in
fabricating solenoid valves manufactured by Automatic Switch Company (ASCO). The NRC
expects recipients to review the information for applicability to their facilities and consider
actions, as appropriate, to avoid similar problems. However, suggestions contained in this
information notice do not constitute NRC requirements and, therefore, do not require any
specific action or written response.
Description of Circumstances
On September 1, 2002, at Dresden Nuclear Power Station, Unit 2, scram testing identified an
unexpected number of control rod drives (CRDs) that were slow to respond. As part of the
resulting troubleshooting plan, the licensee removed a set of scram solenoid pilot valves
(SSPVs) from the unit and sent them to the vendor (ASCO) for analysis. In conjunction with
General Electric (GE), ASCO tested the set of SSPVs and determined that their response times
were slow and out of specification for a new set of SSPVs. GE/ASCO further determined that
the increased response times were attributable to hardening of the exhaust port diaphragm.
Discussion
The SSPV exhaust port diaphragm is composed of Buna-N material. When exposed to heat
and air, this Buna-N material ages by becoming hard. As the diaphragm hardens, it becomes
less flexible and, therefore, does not move off of its seat as far, and thereby reduces the rate at
which the air can vent off of the scram valve actuators. This slower venting rate causes a delay
in the start of motion during scram testing, and can cause the CRD to be slow in responding.
The diaphragm will eventually harden and then fail (break), which could prevent the desired
Dresden Unit 2 and Quad Cities Nuclear Power Station have both experienced problems
resulting from premature aging of the dual ASCO SSPV exhaust diaphragms that are fabricated
using Buna-N material. In response, GE performed an evaluation of Quad Cities scram times
and the qualified lifetime of the Buna-N material. The evaluation concluded that the qualified
lifetime of Buna-N material should be reduced from 10 years to 6 years. In addition, based on a
review of the plant scram time data over the current operating cycle, GE determined that the
rate of scram time degradation is approximately .042 seconds every 120 days. Consequently, GE recommended an aggressive schedule of testing the CRD scram timing at a rate of
25 percent per week for all control rods that were not tested in 2003 to determine the actual
5 percent start of motion. This amounts to a total of 138 control rods. The alternative solution
is to replace all SSPVs within the same time period.
This information notice does not require any specific action or written response. If you have
any questions about the information in this notice, please contact either of the technical
contacts listed below or the appropriate project manager in the NRCs Office of Nuclear Reactor
Regulation (NRR).
Related Generic Communications
The NRC issued Information Notice 96-07, Slow Five Percent Scram Insertion Times Caused
By Viton Diaphragms In Scram Solenoid Pilot Valves, on January 26, 1996, to alert licensees
to slow scram insertion times associated with fluoroelastometric (Viton) diaphragms used in
SSPVs. The NRC issued Information Notice 94-71, Degradation of Scram Solenoid Pilot Valve
Pressure and Exhaust Diaphragms, on October 4, 1994, to alert licensees to embrittlement
and cracking of Buna-N diaphragms used in SSPVs.
Other operating experience associated with Buna-N aging includes NRC Information
Notice 86-109, Diaphragm Failure in Scram Outlet Valve Causing Rod Insertion which
identified a nuclear power plant experiencing a single control rod scram (insertion) when the
diaphragm in the air operator of the scram outlet valve failed. Investigation revealed that the
diaphragm failed because of an aging process that resulted in a radial crack in the rubber
(Buna-N and nylon material). Information Notice 98-31, Fire Protection System Design Deficiencies and Common-Mode
Flooding of Emergency Core Cooling System Rooms at Washington Nuclear Project Unit 2 provides an example where age hardening of an ASCO solenoid operated valve contributed to
room flooding.
/RA/
William D. Beckner, Chief
Reactor Operations Branch
Division of Inspection Program Management
Office of Nuclear Reactor Regulation
Technical Contacts: Thomas Koshy, NRR Matthew W. McConnell, NRR
(301) 415-1176 (301) 415-1597 Email: txk@nrc.gov Email: mxm4@nrc.gov
(301) 415-1176 Email: jxd@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
ML032681003 *See previous concurrence
DOCUMENT NAME: C:\MYFILES\Copies\Dozier-BunaNMaterial.IN-clean.wpd
OFFICE IROB:DIPM Tech Editor EEIB:DE EEIB:DE
NAME JDozier PGarrity* MWMcConnell* TKoshy*
DATE / /2003 09/09/2003 09/09/2003 09/09/2003 OFFICE ADIP:NRLPO BC:EEIB:DE SC:IROB:DIPM C:IROB:DIPM
NAME RVJenkins* JACalvo* TReis WDBeckner
DATE 09/11/2003 09/11/2003 09/25/2003 09/29/2003 / /2003
Attachment 1 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information Date of
Notice No. Subject Issuance Issued to
_____________________________________________________________________________________
2003-16 Icing Conditions Between Pending All 10 CFR Part 72 licensees and
Bottom of Dry Storage System certificate holders.
and Storage Pad
2003-15 Importance of Followup 09/05/2003 All holders of operating licenses
Activities in Resolving for nuclear power reactors except
Maintenance Issues those who have permanently
ceased operation and have
certified that fuel has been
permanently removed from the
reactor vessel.
2003-14 Potential Vulnerability of Plant 08/29/2003 All holders of operating licenses
Computer Network to Worm for nuclear power reactors, Infection except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor vessel.
2003-13 Steam Generator Tube 08/28/2003 All holders of operating licenses
Degradation at Diablo Canyon for pressurized-water reactors
(PWRs), except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor.
Note: NRC generic communications may be received in electronic format shortly after they are
issued by subscribing to the NRC listserver as follows:
To subscribe send an e-mail to <listproc@nrc.gov >, no subject, and the following
command in the message portion:
subscribe gc-nrr firstname lastname
______________________________________________________________________________________
OL = Operating License
CP = Construction Permit