Information Notice 2003-17, Reduced Service Life of Automatic Switch Company (Asco) Solenoid Valves with Buna-N Material

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

scram of the CRD.

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

Jerry Dozier, NRR

(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