ML20117C656
| ML20117C656 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Hatch |
| Issue date: | 07/01/1983 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20114F930 | List:
|
| References | |
| FOIA-84-616 TAC-51908, NUDOCS 8505090482 | |
| Download: ML20117C656 (6) | |
Text
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't,..... f SAFETY EVALUATION FOR OPERATION WITH MISSING PIPE RESTRAINTS FOR HIGH ENERGY LINES OUTSIDE CONTAINMENT - HATCH UNIT 2 Introduction On June 23, 1983, the Georgia Power Company reported by Licensee Event Report 50-366/283-46, that eight pipe whip restraints were missing in the Edwin I. Hatch Nuclear Plant, Unit 2.
A more comprehensive discussion of the circumstances of the event, and the justification for plant operation in the present plant configuration were submitted on June 28, 1983.
Description Eight pipe whip restraints were discovered to be missing from instal-lation during a review of postulated break locations and mitigation protection in the main steam pipe chase.
The need for these restraints was identified in the Hatch 2 FSAR Sections 15A and 15A-A, but their existence was not indicated in the engineering drawings.
The individual locations, system working conditions and the nearest break location stress conditions are listed as follows:
No. of
' Pipe Pressure Break locat.
Restraints System Size Schedule Material Temp ('F)
(PSI)
Stress
- 1 RCIC 4"
120 CS 546 1000 53.6 1
RWCU 6"
80 SS 532 1191/1030 30.9 1
RWCU 4"
80 SS 532 1191/1030 31.6 3
CRD 3"
80 CS 150 1029 N/A 2
AS 10" 40 CS 450 175 89.8, 60.6 SS = Stainless Steel CS = Cuban Steel
- In precentage of the stress of which NRC Standard Review Plan, Section 3.6.2 requires a break to be postulated.
l The restraints in the RCIC and the RWCU systems were required to protect the containment outboard isolation valves from postulated breaks downstream of those valves. The restraints in the CRD system were required to protect cable trays.
The Auxiliary Steam System supplies steam to the reactor building for heafing purpose.
The need of restraints for the AS system was not described in the FSAR, although three of them were shown Fig.15.A-29.
All missing restraints are located outside of the containment, and are at intermediate break locations in those systems.
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I In a letter from L. T. Gucwa to NRC, Region II dated June 28,1983, and in subsequent discussions with the licensee, Georgia Power Company proposed the following action:
Short-Tem Plan 1.
Proceed expeditiously on design and procurement of the missing RWCU and RCIC restraints.
During operation these locations are in inaccessible areas of the plant.
2.
Proceed expeditiously to postulate pipe break locations, design and 1
procure whip restraints for the rerouted CRD return line to the Reactor Water Cleanup System.
3.
Isolate the auxiliary steam line in the reactor building so that no failures need be postulated while this line is isolated.
4.
Prior to start-up, perform a volumetric examination of several austenitic welds at the RWCU break location to insure that the welds are free of unacceptable indications.
Long-Tem Plan In accordance with the intent of the FSA'R and the requirements to maintain isolation capabilities, the design of pipe whip restraints for the RCIC steam, RWCU pump suction / discharge and the CRD return line is in progress.
The design considers the use of energy absorbing material and/or wire ropes to mechanistically address the dynamic effects of the pipe break.
The analysis follows the Bechtel Topical Report, BN-TOP-2 in conjunction with the FSAR design criteria.
The installation of all restraints will be completed at the first shutdown of sufficient duration or at the latest by December 31, 1983.
Evaluation 1.
The auxiliary steam system originally was classified as a. moderate i
energy line in accordance with the guidance provided by the December 1972 Giambusso letter.
FSAR Section 15.A.A.1 subsequently reclassified r
it~ as a high energy line operating for less than 1% of the plant l
operating line.
This line supplies heating steam to the reactor i
building and has no safety related function.
Isolation of this line in the reactor building as proposed by the licensee will remove the steam loads from this line.
1 2.
The postulated break locations near the missing restraint locations in the RCIC and the RWCU systems all have stress levels well below l
the SRP 3.6.2 criterion.
The RCIC system if nes are made of ferritic material and therefore, not susceptible to IGSCC final in sensilized estenitic materials in BWR plants.
This, plus the fact that both systems are equipped with numerous leak detectors, indicate that an j
early warning of system leak will alert operators before a break could occur..
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The RWCU system lines are made of austenitic material.
- However, the licensee will volumetrically examine welds in the break location to determine that they are free of unacceptable indications for the short term period of operation.
4.
Pipe whip restraints for Hatch 2 are not used in anyway for nonnal (non-accident) operation.
Conclusion Based on the above evaluation, we have concluded that Hatch 2 may be safely operated without the missing restraints until the long-term plan has been implemented.
Dated:
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SA7EYY EfAL41ATION FOIt OPNAfION WITii MISSING PIPE RESTRAINTS
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- FOR HIGH ENERGY LINES OUTSIDE CONTAINMENT - HATCH UNIT NO. 2 BACKGR0lMD The Hatch thit 2 licensee has reported that eight pipe whip restraints have not been installed in high energy lines outside of contaiment.
The design calls for these restraints and they are described in the FSAR but they were never installed.
The systems affected include the reactor core isolation cooling (two restraints), the contml rod drive (CRD) system return to(RCIC) system system feedwater (.three restraints) and the auxiliary steam line in the reactor building (two restraints).
DISCUSSION Auxiliary Steam Line This line comes from the auxtliary bofler and is primarily used for plant heatup prior to startup.
Until the pipe whtp restraints are installed,
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the licensee has committed to isolate this line in the reactor building.
Therefore this line will no longer be a high. energy line and we do not ne:d to assume its failure and subsequent pipe whip.
On a related note, the licensee has stated that the auxiliary boiler has been inoperatrie for i
nearly a year.
RCIC and WCU Systems i
The RCIC and WCU pipe restraints were designed to protect the outboard containment isolation valves on these systems.
If these line: were postulated to rupture and disable their respective outboard containment isolation valves, reliance can still be placed on the automatic isolation of the inboard containment isolation valve for each system.
The contain-ment isolation valves on the 4-inch RCIC and the 6-inch MCU systems automatically isolate to limit blowdown on receipt of a signal indicating a failure in the respective system line.
The isolation signals for the RCIC valves consist of high steam line space temperature, high steam line i
flow, low steam supply pressure, and high turbine exhaust pressure.
The
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WCU valves will ' isolate on high differential flow, high differential temperature between the inlet and outlet cleanup room ventilation, high ambient temperature, or high temperature downsteam of the non-regenerative heat exchanger.
The licensee has explored the possibility of the RCIC or WCU system line rupturing outside contaiment, thus disabling the outboard containment i
isolation valve as a result of the postulated pipe whip along with the j
sicultaneous single active failure of the inboard containment isolation i
valve.
This would resul.t in a loss of coolant accident outside contaiment
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through either the 4-inch RCIC system or the 6-inch WCU system.
Using i
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9 :o Ey.'O failure rate probabilities from WASH-1400 and considering pipe diameter and length of piping, the licensee has determined that the probability of the combined pipe failure along with the single active failure of the inboard containment isolatton valve for the RCIC or RWCU systems to be between 10-9 and 10-7 per year.
Although we have not verified these numbers, we agree that the probability of a pipe break in the pipe sec4 tions of interest and a failure of both the inboard and outboard isolation valve is sufficiently small to justify interim operation.
We have asked the licensee to consider the consequences of a RCIC or.RWCU pipe whip and its affect on the operability of other safety systems.
The licensee states that pfpe whip of the RCIC system could damage the safety related main steam isolation valve leakage control (MSIVLC) system.
Rupture of the MSIVLC would allow steam leakage into the secondary contain-ment, thus adding to the steam flow from the failure of the RCIC steam line.
The licensee has stated that this additional offsite release source would i
not raise the total offsite release to abot i 10 CFR Part 100 limits.
We agree that the additional failure of the M5IVLC would not be significant l
and would not be outside the plant's design basis accident analysis.
Rupture of the RWCU would not, according to the licensee, result in disabling any safety-related systems.
Control Rod Drive Return Line
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The pipe whip restraints on the CRD return line are designed to protect safety related cable trays, CRD insert and withdraw lines.
The licensee has stated that the probability of damage to essential cable to a pipe break in the CRD return line is. on the order of 10 grays due per year.
1 The licensee has examined the consequences of the CRD line disabling safety related cables.
They state that three conduits are capable of being damaged.
i lhese conduits provide power to:
1.
Main steam line condensate drain line; 2.
Main steam isolation valve leakage control system; and
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3.
Main steam isolation valve (outboard side only).
The licensee states that if any or all of conduits are damaged, the plant could still be brought to a safe cold shutdown assuming the worst single active failure for each conduit.
We have discussed these postulated events with the licensee and we concur that the loss of any or all of these conduits plus a single active failure would not prevent the plant from achieving a safe cold shutdown condition. Based on the licensee's evaluation, they have chosen not to install the pipe whip restraints on the CRD line.
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.v s-u CONCLUSION We have examined the licensee's analysis of the consequences of an unrestrained pipe whip of the affected RCIC, RWCU and CRD lines outside containment.
We conclude that the licensee has examined the appropriate areas of concern.
The probability of a pipe rupture concurrent with a single active failure of the inboard isolation valve for the RCIC and RWCU are sufficiently small to allow interim operation.
In addition, the probability and consequences of a CRD pipe rupture and resultant cable tray damage is also sufficiently small.
Based on our review of the licensee's submittal and discussions with their staff, we conclude that a reasonable basis exists to pennit plant startup.
Our review is based, in part, on the understanding that the licensee plans to install the pipe whip restraints (with the exception of the CRD systen) on or before December 31, 1983.
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