ML15260A242

Forwards Evaluation Criteria to Assist Licensee in Preparing Acceptable Response to NRC Bulletin 88-008, Thermal Stresses in Piping Connected to Reactor Coolant Sys

ML15260A242
Person / Time
Site:	Oconee
Issue date:	11/01/1991
From:	Wiens L Office of Nuclear Reactor Regulation
To:	Tuckman M DUKE POWER CO.
References
IEB-88-008, IEB-88-8, TAC-M69659, TAC-M69660, TAC-M69661, NUDOCS 9111190215
Download: ML15260A242 (8)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 November 1, 1991 Docket Nos. 50-269, 50-270 and 50-287 Mr. M. S. Tuckman, Vice President Nuclear Operations Duke Power Company P. 0. Box 1007 Charlotte, North Carolina 28201-1007

SUBJECT:

NRC BULLETIN 88-08, "THERMAL STRESSES IN PIPING CONNECTED TO REACTOR COOLANT SYSTEMS" (TACS 69659, 69660 AND 69661)

By letters dated October 6, 1988, March 10, July 7, December 15, and December 29, 1989, Duke Power Company responded to NRC Bulletin 88-08 for the Oconee Nuclear Station. Your response stated that a review was performed of piping connected to the reactor coolant system (RCS). You indicated that the only piping susceptible to conditions similar to those described in the bulletin was the emergency high pressure injection lines for each unit. The action taken to assure that unacceptable thermal stresses would not occur in this section of piping was to install temperature monitoring instrumentation on the Unit 1 piping. While this action, in conjunction with an acceptable monitoring program, would satisfy the recommended bulletin actions for Unit 1, it would not provide similar assurance for Units 2 and 3, even if the piping configurations were identical. Since the type of event described in the bulletin resulted from a component failure, each unit would need to be instrumented and a periodic monitoring program established in order to detect such a failure. In addition, because the fundamental precept of the actions of the bulletin is to prevent the initiation of cracks in piping, inservice inspection is not an acceptable technique identified in the bulletin for preventing such cracks. A program must be implemented to provide such assurance by means of either redesign and modification, pressure monitoring, or, as was done on Oconee Unit 1, temperature monitoring. Therefore, you are requested to review your program for each of the Oconee unit, against the bulletin recommendations and provide a response within 90 days of receipt of this letter. The evaluation criteria included as an enclosure to this letter should help you in preparing an acceptable response.

This request was covered by Office of Management and Budget Clearance Number 3150-0011, which expired June 30, 1991. The new clearance expires May 31, 1994.

Comments are still directed to Ronald Minsk, Office of Information and Regulatory Affairs (3150-0011), NEOB-3019, Office of Management and Budget, Washington, DC 20503, and to the U.S. Nuclear Regulatory Commission, Information and Records Management Branch, Division of Information Support Services, Office of Information and Resources Management, Washington, DC 20555.

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Mr. M. November 1, 1991 Although no response was required relative to Supplement 3 of the bulletin, some licensees have addressed Supplement 3 in their response to the bulletin.

Those who have not will not be required to provide a specific response to Supplement 3. However, you are reminded that having been informed of the phenomenon identified in that supplement, you are responsible for adequate review of both its applicability to your plant and any considered actions.

NRC staff may audit or inspect your implementation of Bulletin 88-08 and its supplements at a future date.

Sincerely,

/s/

Leonard A. Wiens, Project Manager Project Directorate 11-3 Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation

Enclosure:

As stated cc w/enclosure:

See next page DISTRIBUTION:

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OFICIAL RECORD COPY Document Name:

NRC BULL 8808 OCONEE

Mr. M. November 1, 1991 Although no response was required relative to Supplement 3 of the bulletin, some licensees have addressed Supplement 3 in their response to the bulletin.

Those who have not will not be required to provide a specific response to Supplement 3. However, you are reminded that having been informed of the phenomenon identified in that supplement, you are responsible for adequate review of both its applicability to your plant and any considered actions.

NRC staff may audit or inspect your implementation of Bulletin 88-08 and its supplements at a future date.

Sincerely, conard A. Wiens, Project Manager Project Directorate 11-3 Division of Reactor Projects -

I/1I Office of Nuclear Reactor Regulation

Enclosure:

As stated cc w/enclosure:

See next page

Mr. J. W. Hampton Oconee Nuclear Station Duke Power Company cc:

Mr. A. V. Carr, Esq.

Mr. M. E. Patrick Duke Power Company Compliance 422 South Church Street Duke Power Company Charlotte, North Carolina 28242-0001 Oconee Nuclear Site P.O. Box 1439 Seneca, South Carolina 29679 J. Michael McGarry, III, Esq.

Winston and Strawn Mr. Alan R. Herdt, Chief 1400 L Street, NW.

Project Branch #3 Washington, DC 20005 U. S. Nuclear Regulatory Commission 101 Marietta Street, NW., Suite 2900 Mr. Robert B. Forsum Atlanta, Georgia 30323 Babcock & Wilcox Nuclear Power Division Ms. Karen E. Long Suite 525 Assistant Attorney General 1700 Rockville Pike N. C. Department of Justice Rockville, Maryland 20852 P.O. Box 629 Raleigh, North Carolina 27602 Manager, LIS NUS Corporation Mr. R. L. Gill, Jr.

2650 McCormick Drive, 3 Floor Nuclear Production Department Clearwater, Florida 34619-1035 Duke Power Company P. 0. Box 1007 Senior Resident Inspector Charlotte, North Carolina 28201-1007 U. S. Nuclear Regulatory Commission Route 2, Box 610 Seneca, South Carolina 29678 Regional Administrator, Region II U. S. Nuclear Regulatory Commission 101 Marietta Street, NW., Suite 2900 Atlanta, Georgia 30323 Mr. Heyward G. Shealy, Chief Bureau of Radiological Health South Carolina Department of Health and Environmental Control 2600 Bull Street Columbia, South Carolina 29201 Office of Intergovernmental Relations 116 West Jones Street Raleigh, North Carolina 27603 County Supervisor of Oconee County Walhalla, South Carolina 29621

Enclosure EVALUATION CRITERIA FOR RESPONSES TO NRC BULLETIN 88-08, ACTION 3 AND SUPPLEMENT 3 1.0 OBJECTIVE To Provide continuing assurance for the life of the plant that unisolable sections of piping connected to the reactor coolant system (RCS) will not be subjected to thermal stratification and thermal cycling that could cause fatigue failure of the piping.

2.0 PURPOSE To provide guidelines for evaluation of licensee responses, including acceptable procedures and criteria to prevent crack initiation in susceptible unisolable piping.

3.0 IDENTIFICATION OF POTENTIALLY SUSCEPTIBLE PIPING (1) Sections of injection piping systems, regardless of pipe size, which are normally stagnant and have the following characteristics:

A. The pressure is higher than the RCS pressure during reactor power operation.

B. The piping sections contain long horizontal runs.

C. The piping systems are isolated by one or more check valves and a closed isolation valve in series.

D. For sections connected to the RCS:

a. Water injection is top or side entry.

b. The first upstream check valve is located less than 25 pipe diameters from the RCS nozzle.

Examples of such sections in PWRs are the safety injection lines and charging lines between the reactor coolant loop and the first upstream check valve, and the auxiliary pressurizer spray line between the charging line and the mai' )ressurizer spray line.

(2) Sections of other piping systems connected to the RCS, regardless of pipe size, which are normally stagnant and have the following characteristics:

A. The downstream pressure is lower than RCS pressure during reactor power operation.

B. The piping systems are isolated by a closed isolation valve, or a check valve in series with a closed isolation valve.

C. There is a potential for external leakage from the isolation valve.

Examples of piping containing such unisolable sections in PWRs are the residual heat removal (RHR) lines. Examples of such piping for BWRs are the RHR lines and the core spray injection lines.

4.0 ACCEPTABLE ACTIONS The following actions are considered as acceptable responses to Bulletin 88-08, Action 3 and Supplement 3, as applicable, provided that the requirements of Bulletin 88-08, Action 2 have been satisfied.

(1) Revision of system operating conditions to reduce the pressure of the water upstream of the isolation valve below the RCS pressure during power operation.

(2) Relocation of the check valves closest to the RCS to be at a distance greater than 25 pipe diameters from the nozzle.

(3) Installation of temperature monitoring instrumentation for detection of piping thermal cycling due to valve leakage.

A. Type and location of sensors.

a. Temperature sensors should preferably be resistance temperature detectors (RTDs).

b. RTDs should be located between the first elbow (elbow closest to the RCS), and the first check valve (check valve closest to the RCS).

c. For the auxiliary pressurizer spray line, RTDs should be installed near the "tee" connection to the main pressurizer spray line or on the cold portion (ambient temperature) of the line.

d. RTDs should be located within six inches of the welds.

e. At each pipe cross section, one RTD should be positioned on the top of the -ipe and another RTD on the bottom of the pipe.

B. Determination of baseline temperature histories.

After RTD installation, temperature should be recorded during normal plant operation at every location over a period of 24

-3 hours. The resulting temperature versus time records represent the baseline temperature histories at these locations. Baseline temperature histories should meet the following criteria:

a. The maximum top-to-bottom temperature difference should not exceed 50*F.

b. Top and bottom temperature time histories should be in-phase.

c. Peak-to-peak temperature fluctuations should not exceed 600F.

C. Monitoring time intervals.

a. Monitoring should be performed at the following times:

1. At the beginning of power operation, after startup from a refueling shutdown

2.

At least at six-month intervals thereafter, between refueling outages

b. During each monitoring period, temperature readings should be recorded continuously for a 24-hour period.

0. Exceedance Criteria.

Actions should be taken to modify piping sections or to correct valve leakage if the following conditions occur:

a. The maximum temperature difference between the top and the bottom of the pipe exceeds 500F.

b. Top and bottom temperature histories are in-phase but the peak-to-peak fluctuations of the top or bottom temperatures exceed 60oF.

c. Top and bottom temperature 1..

tories are out-of-phase and the bottom peak-to-peak temperature fluctuations exceed 500F.

d. Temperature histories do not correspond to the initially recorded baseline histories.

-4 (4) Installation of pressure monitoring instrumentation for leakage detection in injection lines.

(Pressure monitoring is not the preferred method since pressure measurements cannot provide a measurement of thermal cycling in the unisolable pipe sections.)

A. Type and location of sensors.

a. Pressure sensors should preferably be pressure transducers.

b. Pressure transducers should be installed upstream and downstream of the first check valve.

c. For systems having a pressure higher than the RCS pressure, pressure transducers may be installed upstream and down stream of the first closed isolation valve. (The downstream section is the pipe segment between the isolation valve and the check valve.)

B. Monitoring time intervals.

a. Monitoring should be performed at the following times:

1. At the beginning of power operation, after startup from a refueling shutdown

2. At least at six-month intervals thereafter, between refueling outages

b. Pressure readings should be recorded continuously for a 24-hour period.

C. Exceedance criteria.

Actions should be taken to modify piping sections or to correct valve leakage if the following conditions occur:

a. For pressure measurements across a check valve, the downstream pressure (RCS pressure) is equal to or less than the upstream pressure at any time during power operation.

b. For pressure measurements across a closed isolation valve, the downstream pressure is equal to or greater than the upstream pressure at any time during power operation.