ML20151N050

Recommends Denial of Util 880513 Tech Spec Change Request 169 Re Core Spray Sparger Insps.Change Would Eliminate Requirement to Document Insp Results Prior to Restarting After Each Refueling Outage

ML20151N050
Person / Time
Site:	Oyster Creek
Issue date:	07/21/1988
From:	Scott D NEW JERSEY, STATE OF
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
NUDOCS 8808080093
Download: ML20151N050 (10)

Text

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' Wad =* State of New Jersey DEPARTMENT OF ENVIRONMENTAL PROTECTION DIVISION OF ENVIRONMENTAL QUAUTY 380 Scotch Road CN 411 Trenton. N.J. 08625 (609)530 4000

,lorge H. Berkowitz, Ph.D. Gerald P. Nicholls, Ph.D., Assistant Director Director Radiation Protection July 21, 1988

{ U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:

Subject:

Oyster Creek Nuclear Generating Station Docket No. 50-219 Technical Specification Change Request No. 169 On May 13, 1988 GPU Nuclear Corporation (GPUN) submitted a Technical Specification Change Request to the NRC. This change request proposes to amend paragraph 2.C.(7) of Provisional Operating Licenso No.DPR-16 for future (12R) core spray spargar inspections. If approved the licensee would utilize a visual inspection technique and the requirement to docket inspection results before restarting after each refueling outage would be eliminated.

The Bureau of Nuclear Engineering (BNE) staff has reviewed this change request as outlined in the attached BNE review. On that basis we recommend that Change Request No.169 not be granted by the NRC.

Please feel free to contact Suren Singh or myself at (609) 530-4022 if you have any questions.

Sincere 1y,((

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ena N' David Sc t, Chief Bureau of Nuclear Engineering

c. Alexander W.Dromerick, Project Manager, NRR Michael Laggart, Licensing Manager, GPUN Suren Singh, Nuclear Engineer, BNE

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i BUREAU OF NUCLEAR ENGINEERING REVIEW OF THE OYSTER CREEK NUCLEAR GENERATING STATION TECHNICAL SPECIFICATION CHANGE REQUEST No. 169 ON CORE SPRAY SPARGER INSPECTION REQUIREMENTS  ;

l By letter dated May 13, 1988 GPU Nuclear (GPUN) Corporation, j operator of the Oyster Creek Nuclear Generating Station (OCNGS) '

requested to amend the requirements for future Core Spray Sparger inspections and to eliminate the requirement to docket ,

inspection results and to obtain NRC restart authorization from '

each refueling outage. The request to obtain NRC restart l authorization was prompted by the identification of a through-wall crack in one of the Core Spray Spargers during a 1978 inspection. In 1984 the NRC requested that an evaluation of any cracks or further progression of the existing one be identified, and determined that will not result in unacceptable degradation of the plant safety margins.

CORE SPRAY SYSTEM DESCRIPTION g The Oyrter Creek reactor vessel contains two independent Core Spray Sparger assemblies which are fed by two separate Core Spray Systems. The Core Spray System is part of the OCNGS ,

Emergency Core Cooling System (ECCS) and is an essential engineered safeguard feature which must be available for use during all modes of reactor operation. The Core Spray provides '

for removal of decay heat from the core following a Loss-of-Coolant-Accident (LOCA) so that fuel melt is prevented for the entire spectrum of postulated LOCAs. The system is provided with a 100% redundancy of active components (Attachment 1) to be able to accomplish its emergency core cooling function under the condition of a single failed component. Each sparger assembly contains spray nozzles that are designed to provide a spray pattern that will ensure that each fuel bundle receives adequate coolant flow.

REGULATORY ASPECTS The Safety Evaluation, issued in November 1978 by the office of Nuclear Reactor Regulation supporting Amendment No. 34 to Oyster Creek provisional license, agreed to the licensee's proposal to examine the spargers at the next 5 refueling outages starting with the 1979 refueling outage and then every five years thereafter.

As a result of the 1980 inspection, 29 new indications were identified as cracks in both core spray spargers and nine more clamps were installed. In the Safety Evaluation supporting Amendment No. 47 dated May, 1980, it was agreed that due to the licensee commitment to replace the existing ring core spray sparger design with a new overhead grid design, the augmented inspection program is no longer appropriate. l l

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Betueen 1980 and 1986 further inspections of accessible areas (Attachment 2) using enhanced and new inspection techniques disclosed no indications except the through-wall crack which was identified and clamped in 1978. In 1982 a License Change Request was nubmitted to defer the sparger replacement contingent upon the visual inspection results being satisf actory. In the NRC's Safety Evaluacion supporting Amendment 70 datea January 26 1984, it is stated that "future decision on... the coro spray sparger will be based or. the evide..ae that no major progression of cracking has occurred...". Ir order to facilitate this evidence "an inspection method that has the sensitivity to allow crack dimension nasurement will be necessary to evaluate crack progression IE Bulletin 80-13 was issued in May 1980 because of the concern abou*. cracking in core spray spargers at Oyster Creek and at another fa.;ility with an operating BWR.

BACKGROUND HISTORY During the 1978 refue]i1g outage, a scheduled inservice inspection identified and condirmed the existence of a through-Wall crack in the upper sparger (Core Spray System II) and a temporary repair was effected by installing a bracket arsembly over the crack. The crack, as measured in 1978, was 1/32" wide at its widest point, smaller inside the pipe than on the outside and extended approximately 200 degrees circumferential1y around the sparger. The crack appears to have initiated close to one of the spray nozzles and is adjacent to one of the support brackets (Attachment 3). Because of the location of the crack in regard to the mounting brackets, it was concluded that the sparger would have been held in place if called upon for operation in the event of core sp.ay initiation. A bracke.: assembly was fitted around the spray r.o z zle on both sides of the crack to provide axial support to the sparger in the ovent the crack propagates completely around the pipe.

The analycis of the inads assoc! 'd with the inacallation of the bracket assembly demonstrate tn-. the bracket will limit the crack opening to 1/16". The effect of leakage through a 1/16" crack had been acounted for by increasing the Technical Specification req'. ..ement on minimum flow rate for the Core Spray Soaigor II from 3eva gpm to 3640 gpm.

CIDEN'r b 'TIGATION

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ing Water Rector's Owners Group recognizes three 9ving decay haat, they are in order of preference:

' .rgence, 2. spray cooling and 3. steam cooling.

l4. ster Creek no credit is taken fOr core submergence des. -

erge LOCA. An evaluation of core cooling effect.'veness

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is presented in Oyster Creek FSAR for both large and small l break LOCAs. The Oyster Creek Spray System is designed to deliver a low pressure spray pattorn over the fuel bundles follcKing a LOCA in order to limit peak cladding temperature to less than 2200 F.

The effectiveness of the core spray in a steam environment has been evaluated and, "although the core spray distribution in the OCNGS is significantly affected by the presence of a steam environment, it has been concluded that the core spray system can deliver more than the minimum required bundle spray flow rate needed...". For large break LOCAs the reactor loses pressure rapidly, up to a pressure (55 psia) where the core spray distribution of ring spargers in steam environment had been demonstrated to be adequate. However, for small breaks the reactor blows down more slowly, and therefore there are some uncertainties in the spray distribution and effectiveness.

With the minimal amount of low pressure inventory make-up capability available at Oyster Creek and expected rapid reactor depressurization and water inventory loss following a large break LOCA (Attachment 4), the core spray system is the only system depended upon to automatically supply make-up water to reactor.

All peak cladding temperature for the worst accident scenarios are mitigated by the action of core spray heat transfer.

The Des.ign Base Accident (DBA) is defined as the complete seversnce of the largest pipe in that portion of the system which yields the highest peak cladding temperature when the most limiting single failure is assumed. The most limiting single failure for Oyster Creek is the Isolation Condenser failure.

CONCLUSION Under the assumption that no new cracks will develop and the existing crack in the Core Spray System II propagates around I the circumference therefore impacting on the ccoling effective-ness, the present FSAR does not analyzes the consequences of a DBA for a single failure of an Isolation Condensur together with  ;

the failure of the Core Spray System I. '

The closcout of Bulletin 80-13 in January 1988 was made possible doe to the fact that all licensees of operating BWRs had either replaced the core spargers, or committed to inspect its i Core Spray Spargers at every refueling outage. The fact that the i results of recent inspections at Oyster Creek did not result in i any new indication does not preclude the appearance in time of new indications. Therefore, there are no basis for waiving the requirements of Bul)etin 80-13.

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4 QUESTIONS:

Q. 1) What is the inspection method used to allow crack dimensicn measurement and if its reliability and sensitivity ,

could be used to evaluate crack progression (Amendment 70) ?

Q. 2) Due to the fact that the examination procedures lack confirmed reliability - and the accessible area to be inspected equals 50% of the total sparger area, what evidence is provided to assure that no major progression of cracking has occurred ?

Q. 3) Under the assumption that it had been "demonstrated the bracket assembly's ability to limit the crack opening to within an acceptable range should an existing crack propagate around the pipo circumference" BNE needs assurance that:

a) There will be adequate distribution of water spray to the core through the a sparger with a 360 degree crack and, b) The effect of leakage through a 360 degree through-wall crack had been accounted for, specifically a flow rate of 3640 gpm is satisfactory under this scenario.

Q. 4) Under the present design configuration there is no indication for the core spray injection line integrity. During LOCA conditions what indication can the operators rely on to positively indicate that the Core Spray flow is in fact established ?

Q. 5) GPUN estimated that the stresses in the spargar are low.

What caused the growth of a grain boundary crack (due to IGSCC) to a through wall crack extending over half the circumference ?

Q. 6) The clamp, when instalfed, will exert shear force at the extremities and compression on the remainder surface of the piping. The shear force will increase the likelihood of further cracking of the piping at the extremities of the clamp when combined with the hostile environment end the vibratory and thermal stresses already present. Due to the core Spray Sparger location !ielow the feedwater nozzle) there are additional stresses imposed due to steam-water interface.

a) Does the clamp configuration meet the fatigue design of the ASME code ?

b) What is the design life, in cycles, of a clamped joint ?

c) Will GPUN initiate a ASME code case to justify this repair since this method is not an accepted one under ASME I S2ction XI ?

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ATTACHMENTS:

1) Core Spray Diagram

2) Core Spray Piping Inspection Summary

3) Appearance of crack

4) OCFSAR figure 15.6-10 a:\ word \coresp.2

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