CEO-88-359, Requests That SER for Amend 92 Be Revised to Extend Refueling Interval for Reactor Vessel Vent Valves to Cycle 8 Refueling Outage,But No Later than Sept 1989.Safety Analysis Encl

Requests That SER for Amend 92 Be Revised to Extend Refueling Interval for Reactor Vessel Vent Valves to Cycle 8 Refueling Outage,But No Later than Sept 1989.Safety Analysis Encl

ML20196A446
Person / Time
Site:	Rancho Seco
Issue date:	11/29/1988
From:	Firlit J SACRAMENTO MUNICIPAL UTILITY DISTRICT
To:	Knighton G NRC, NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
CEO-88-359, NUDOCS 8812060009
Download: ML20196A446 (7)

Text

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$OMUD SACRAMENTO MUNICIPAL UTluTY DISTRICT C 6201 S Street. P.o. Box 15830 Sacramento CA 95852 1830.1916) 452 3211 AN ELECTRIC SYSTEM SERVING THE HEART OF CALIFORNIA CEO 88-359 NOV 2 91938 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Hashington, DC 20555 Docket No. 50-312 Rancho Seco Nuclear Generating Station Licenso No. DPR-54 REACTOR VESSEL VENT VALVE TEST EXTENSION

Reference:

NRC letter dated December 7, 1987 (Amendment No. 92)

Attention: George Knighton The District requests that toe Safety Evaluation Report for Amendment No. 92 be revised to extend "refueling interval" for the Reactor Vessel Vent Valves (RVVVs) to the Cycle 8 refueling outage, but not later than September 1989.

A temporary extension of refueling interval until the Cycle 8 refueling outage was incorporated into Rancho Seco Technical Specificatio 1.2.8 by the issuance of Amendu nt No. 92. The Safety Evaluation Report which accompanied Amendment No. 92 extended the surveillance period of the RVVVs to "the next scheduled reactor head removal but not later than May 1989."

At the time of the original submittal of Proposed Amendment No. 145 (September 22, 1986), there was uncertainty in projecting an estimated startup date as well as an estimated date on which Cycle 8 would begin. At the time of the submittal of Proposed Amendme;.t No.145, Supplement 1 (November 25, 1987), the best projection for startup resulted in an estimated date of May 1989 for commencement of Cycle 8. The Cycle 8 refueling outage is presently scheduled for the third quarter of 1989. The District requests that the Safety Evaluation Report for Amendment No. 92 be revised to include chis new schedule.

Attached is a Safety Analysis supporting the District's request.

A prompt review of this request is necessary since planning and parts procurement for the refueling outage are highly dependent upon the scheduled outage date.

S912060009 DR S81129 ADOCK 05000 312 I \

PDC i

RANCHO SECO NUCLEAR GENERATING STATION O 14440 Twin Cities Rod. Herald, CA 95638 9799;(209) 333 2935

George Knighton CEO 88-359 Hembers of your staff with questions requiring additional information or clarification may contact Mr. Steve Crunk at (209) 333-2935, extension 4913.

Sincerely, d

Joseph F. Ftrlit

, Chief Executive fficer Nuclear Attachment cc w/atch: J. B. Martin, NRC, Halnut Creek A. D'Angelo, NRC, Rancho Seco I

'O SAFETY ANALYSIS Reactor Vessel Vent Valve Refueling Interval

. React:r Vessel Vent Valve Refueling Interval Page 1 of 4 SAFETY ANALYSIS Description The District is requesting that the Safety Evaluation Report (SER) for Amendment No. 92 be revised to extend "refueling period," for purposes of Reactor Vessel Vent Valve (RVVV) testing, to the Cycle 8 refueling outage which is presently scheduled for the third quarter of 1989.

Technical Specification Table 4.1-2 (Hinimum Equipment Test Frequency) requires a surveillance test on the Internal Vent Valves each refueling interval. Rancho Seco Technical Specifications 1.2.8. 1.9.10, and Table 1.9-1 define "refueling interval" to mean once per 18 months. Additionally, Specification 1.9 allows the interval to be extended to a maximum of +25% (4.5 months) to accommodate operations scheduling. It further states, "The total maximum combined interval time for any three consecutive intervals shall not l

exceed 3.25 times a single specified surveillance interval."

Rancho Seco received a temporary redefinition of refueling interval to "the Cycle 8 refueling outage"; however, the SER which accompanied Amendment No. 92 stated that the extension of refueling interval was to "the next scheduled reactor head removal but not later than May 1989."

Reason for Requ nt The District requested, by letters dated September 22, 1986 and November 25, 1987, an extension to the RVVV test interval to the Cycle 8 refueling outage.

This request was made to accommodate the projected operating schedule and reflected the operational history of Rancho Seco (including the extended outage commencing December 26, 1985) since the last test of the RVVVs.

Additional information in support of the original subaittal (water chemistry and metallurgical considerations) was sent to the NRC on February 2, 1987.

The NRC approved Proposed Amendment No. 145, Rev. I which a,xtended the refueling interval for RVVVs to "the Cycle 8 refueling outage"; however, on page 4 of the SER supporting Amendment No. 92 the NRC extended the surveillance period for testing the RVVVs until the next scheduled reactor head removal "but not later than May 1989."

The next scheduled reactor head removal is planned for the third quarter of 1989; therefore, an extension for the refseling interval testing for RVVVs beyond May 1989 is required, frahallon and Batis for Safety Analyill System Affected/ Safety function of Affected System:

The components affected by this request are the reactor vessel internal vent valves. The surveillance requirements for the RVVVs are addressed in Technical Specification Table 4.1-2 (Hinimum Equipment Test frequency). The valves are described in USAR Section 3.2.3.2.4 (Evaluation of Internals Vent Valve) and 3.2.4.1.2.H (Internals Vent Valves),

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- Neactor Vessel Vent Valve Refueling Interval Page 2 of 4 Internal vent valves are installed in the core support shield to prevent a  !

pressure imbalance which might interfere with core cooling following a l 1 postulated inlet pipe rupture. Under all normal operating conditions, the -

vent valve will be closed. In the event of the pipe rupture in the cold leg of the reactor loop, the valve will open to permit steam generated in the core i to flow directly to the leak and will permit the core to be rapidly re-covered '

and adequately cooled after emergency core coolant has been supplied to the i

reactor vessel.

Each valve assembly consists of a hinged disc, valve body with sealing surfaces, split-retaining ring, and fasteners. Each valve assembly is  !'

installed in a machined ring integrally welded in the core support shield

wall. The mounting contains the necessary features to retain and seal the  ;

perimeter of the valve assembly. Also, the mounting ring includes an r alignmentdevicetomagainthecorrectorientationofthevalveassemblyfor hinged-disc operation, i

Effects on Safety Function / Analysis of Effects on Safety function: [

Technical Specification Table 4.1-2, Item 13 requires inspection of the RVVVs i each refueling interval. This surveillance frequency is based on a j i

presumption that meaningful operating time will have accrued on the valves j during the interval between inspections. The RVVVs were last inspected in  ;

) April 1985. Approximately 17 months of operation (as of July 1989), much of  ;

l it at reduced power, will have accrued since the last inspection.

ASME Boiler and Pressure Vessel Code (Paragraph INA-2400(c) of Section XI)

J states:

For power units that are out of service continuously for 6 months or [

1 more, the inspection interval during which the outage occurred may be l 1 extended for a period equivalent to the outage. i j

j Rancho Seco's outage which commenced in December 1985 lasted until March 1988,  !

4 a period of 27 months. Crediting the ASME Code allowance and the +25% of the  ;

) interval, the RVVV test will be due in May 1989. The District, therefore, is l q

requesting an actual extension of less than 6 months beyond ASME allowable.  !

During the prolonged outage, the RVVVs were not exposed to the turbulent flow l which occurs during plant operation at power.

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! Surveillance of the internal vent valves requires removal of the reactor f l vessel head, estimated to result in about 25 manrem exposure. Inspection of l the internal vent valves add approximately 5 manrem exposure. The District  ;

li considers the deferral of the internal vent valves inspections a savings of f l approximately 30 manrem exposure, consistent with maintaining personnel l j exposure as low as reasonably achievable. I f

f According to site records, the surveillance of internal vent valves in the past has not rev9aled any significant abnormalities. Additionally, a survey j i performed by B&H u) has shown that RVVVs have demonstrated a high degree  ;

of reliability with no observat'le degradation in valve operability.

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Reactor Vessel Vent Valve Refueling Interval Page 3 of 4 ELMI IJSLBTERVAL TIMES TESTED # OF FAILURf5 MAX INTERVAL (s)

Oconee 1 Every Refueling 8 0 ( 22 Honths Oconee 2 Every Refueling 7 0 < 22 Henths Oconee 3 Every Refueling 8 0 < 22 Honths ANO-1 Every Refueling 6 0 23 Honths Rancho Seco Every Refueling 6 0 25 Honths Crystal River 3 18 Honths 5 0 < 22 Honths THI-1 Every Refueling 5 0 37 Honths Davis Besse 18 Honths 9 0 23 Honths The table above represents approximately 400 RVVV inspections and exercises without a failure at eight operating B&H facilities during a 10-year period.

In B&W operating reactors with an approximate total of 95 reactor years of operation, n9t)a single operability.t' RVVVofhas Inspections failed RVVVs at to demonstrate Rancho satirfactory Seco dating back to 1974 have revealed no significant abnormalities in the valves.

The District is evaluating requesting an amendment to Technical Specifications to permanently extend the interval between R"VV tests. In September 1988, Crystal River 3, a B&H facility, received Technical Specification Amendment No. 108, which p6rmanently extended the RVVV testing interval to 24 months.

This extension was requested by Florida Power Corp, to eliminate mid-cycle reactor head removals just to perform this test and to reduce the personnel radiation exposure associated with this plant evolution.t') If Rancho Seco had this NRC-approved (for Crystal River 3) interval of 24 months, plus a 6-month (+25%) window, plus the 27 month period allowed by ASME Code (for our extended shutdown), performance of the test would be due in December 1989, well beyond the date to which the District is requesting an extension.

In the SER which accompanied Amendment No. 92, the NRC Staff evsluated Rancho Seco's Reactor Coolant System (RCS) chemistry, the compatibility of mating materials and their corrosion resistance, and reactor coolant environment.

The Staff estimated that the thickness of deposited material on RVVV components to be approximately 0.15 mils / year. Since the minimum cold clearance gap dimensions vary from 3 to 60 mils, the gap would not close for this rate of corrosion.(s) The extension which the District is requesting is approximately 6 months beyond that period for which the above conclusion was drawn. The Staff also determined that the gegeral corrosion rate is less at RCS cold conditions than for hot conditions.us At least 27 months of the period since the last RVVV testing was at RCS cold shutdown conditions.

The NRC Staff also reviewed the effect of the high concentration of RCS contaminants. The Staff concluded that "...the specific type and amounts of these RCS contaminants which have been experienced at RSNGS shguld not have produced a significant amount of corrosion of RVVV materials."t5)

Sumary The District requests that the date for the Cycle 8 refueling outage in the SER for Amendment No. 92 be changed from "not later than May 1989" to "not later than September 1989."

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- Deactor Vessel Vent Valve Refueling Interval Page 4 of 4  ;

1 The components affected by this request are the reactor vessel internal vent valves. The surveillance requirements for the RVVVs (each refueling interval)  !

are addressed in Technical Specification Table 4.1-2 (Minimum Equipment Test '

Frequency). Rancho Seco Technical Specifications 1.2.8, 1.9.10, and Table 1.9-1 define "refueling interval" to mean once per 18 months. The NRC approved Proposed Amendment No. 145, Rev. I which extended the refueling interval for .VVVs o to "the Cycle 8 refueling outage."  ;

i Surveillance of the internal vent valves requires removal of the reactor vessel head, estimated to result in about 2S manrem exposure. Inspection of ,

the internal vent valves add approximately 5 manrem exposure. The District considers the deferral of the internal vent valves inspections a savings of  :

approximately 30 manrem exposure, consistent with maintaintrig personnel  ;

l exposure as low as reasonably achievable.

RWV have a high degree of reliability with no observable degradation in  !

valve operability with reactor age. [

The NRC Staff evaluated Rancho Seco's RCS chemin, the compatibility of mating materials and their corrosion resistance, and reactor coolant i environment and determined the minimum cold clearance gap would not close for this rate of corrosion. The Staff also concluded that a significant amount of cerrosion of RVVV materials should not have occurred at Rancho Seco. l The Staff's summary conclusion was that minimal amounts of corrosion of RVVV i j

materialswouldoccurovertheexten{egsurveillanceperiodandwouldnot affect the reliability of the RVVVs. s The extension beyond that period [

i l already granted by the NRC merely accounts for the length of the December 1985 t i shutdown beyond that postulated at the time of the District request in 1987.

The District feels that this extension will not:

1. Involve a significant increase in the probability or consequences of an accident !

previously evaluated, or; i

2. Create the possibility of a new or different kind of accident from any accident previously evaluated, or; j

3. Involve a significant reduction in a margin of safety.

The District considers this request to be reasonable and judged to not present any health or safety problems to the general public.

I References j

1. Rancho Seco USAR, Sections 3.2.3.2.4 and 3.2.4.1.2.H f i

2. B&W Report No. 11-1159/02-00, January 20, 1986 f I

3. Toledo Edison to NRC letter dated June 6, 1986

4. Safety Evaluation by the Office of Nuclear Reactor Regulation Supporting Amendment No. 108 to Facility Operating License No. DPR-72

5. Safety Evaluation by the Office of Nuclear Reactor Regulation Supporting Amendment No. 92 to facility Operating License No. DPR-54