ML20212F479

Safety Evaluation Supporting Amend 131 to License NPF-2

ML20212F479
Person / Time
Site:	Farley
Issue date:	10/23/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20212F466	List: ML20212F462 ML20212F479
References
NUDOCS 9711040293
Download: ML20212F479 (4)

Text

- -

~

mg g

1 UNITED STATES J'

{

NUCLEAR REGULATORY COMMISSION o,

f W ASHINGTON, D.C. 30006 0001

~ ?,

• sse+.

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.13iTO FACILITY OPERATING LICENSE NO. NPF-2 SQUIEIERN NUCLEAR OPERATING COMPANY. INC. ET AL.

JOSEPH M. FARI FY NUCLEAR PLANT. UNIT 1 DOCKET NO. 50-348 r

1.0 INTRODUCTION

i By letter dated September 3,1997 Southem Nuclear Operating Company (SNC, the licensee),-

' inc., et al., requested changes to the Technical Specifications for Joseph M. Farley Nuclear Plant, Unit 1. These changes would reduce the number of required incore detectors necessary for continued operation for the remainder of Cycle 15 only.

The Farley Unit 1 Movable incore Detection System (MIDS) contains a total of 50 instrumentation thimbles in the core. Technical Specification (TS) 3.3.3.2 requires that at least 75% of the detector thimbles be opereble with a minimum of two detector thimbles per quadrant when performing a flux map to ensure compliance with the peaking factor requirements of TS 3.2.2. The surveilbnce requirements of TS 3.2.2 require that the peaking factors must be ~

determined to be within limits at least once per 31 effective full power days. Due to the recent increase in incore detector thimble failures at Farley Unit i during Cyc'e 15 thus far, SNC has proposed a change that will allow plant operation with the number of operable detector thimbles

- reduced to a minimum of 50% with three detector thimbles per quadrant. To compensate for the increased uncertainty as the number of operable detector thimbles is reduced, the 4

measurement uncertainty for F"aH and F"o will be increased whenever the number of detectors t

~ is between 37 and 25.

I-During the Unit 1 Cycle 14 refueling outage, the incore thimbles were inspected and cleaned and additional work was performed on the moveable incore detector system. During the start-up of Cycle 15, numerous flux maps were run dth no unusual problems. A flux map attempt on July 8,1997, was unsuccessful because 16 incore thimbles would not allow the detector to a-complete its transit. Flux maps, since that time, have been completed with 38 or 39 thimbles.

?

While the location of the detector thimbles that were unavailable has changed from map to i

map, the available detectors have remained distributed throughout the core and the thimble coverage has been adequate. Since SNC believes that this problem has the potential to

~.

L worsen throughout Cycle 15, there is concern about meeting the 75% requirement called for in the TS for future-required moveable incore detection system uses. Failure to have at least 75%

- of the thimbles accessible could result in a forced shndown.

4 16 l-9711040293 971023 PDR ADOCK 05000348 i

P POR m

t m

.me w

--r-+-m,, -,

,,,-,,r

_,,m-.

-em b-y

L l

i i

2-

- 2.0 EVALUATION

- Essentially all pressurized water reactor (PWR) TSs contain a requiremert for operability of 75% of the incore detector locations for mapping of the core power distribution. On a number

- of occasions, for various reasons, failures of detector thimbles in operating PWRs have approached or sxceeded 25%, and relaxation of the 75% requirement has been permitted for the remainder of the affected operating cycle.

Incore detector data is used to _ calculate power peaking factors that are used to verify compliance with fuel performance limits. As the number of inoperable detector thimbles -

increases, the uncerta_Inties i_n the power distribution calculation increase. The requirement for maintaining 75% of the detector thimbles available provides for a reasonable number of failures -

of the incore detectors while encouraging licensees to strive for maintaining the system as near >

to 100% available as possible The proposed TS 3.3.3.2 allows continued use of the movable incore detector system with less than 75% of the thimbles available if the measurement error allowance due to incomplete flux mapping is appropriate. The licensee submitted an analysis performed by the vendor, Westinghouse, which assessed the impacts of a reduction to a minimum of 25 of the 50 movable detector thimbles for Farley Unit 1 Cycle 15. The analysis indicated that additional uncertainties of 1.5% for FN4H and 2% for F"o are appropriate when e

the number of instrumented assemblies is reduced from 38 to 25 The additional uncertainties should be applied linearly from below 75% to greater than 50% detector thimble locations. In addition, the Westinghouse analysis assumed random deletion of the thimbles. If the thimbles were systematically deleted from use, the calculated peaking factor uncertainties would not apply. Thus, there is an additional requirement that when the number of detector locations is less than 75%, there should be a minimum of three thimbles available per quadrant, where quadrant includes both horizontal-vertical quadrants and diagonally bounded quadrants (eight quadrants in all). This requirement improves the abihty to distinguish between random and -

systemic thimble deletion events and establishes the boLoos of applicability of the peaking factor uncertainties.

SNC has provided the results of core maps for Cycle 15. These show that there is currently approximately 10% margin to the F"aH TS limit and approximately 6% margin to the FN o

TS limit. Since the peaking factors normally tend to decrease with bumup, the staff would expect the margin to increase from now till the end of the cycle.

Another safety concem relating to degradation of incore mapping ability is the ability to detect

- anomalous conditions in the core. One of these is inadvertent loading of a feel assembly into an improper position. Since this is a loading problem, it is not of concem for the remainder of the operating cycle. Fu,thermore, review of the Cycle 15 startup physics test results showed very good agreement between predictions and measurements, thus, giving more assurance that the core is as designed. Other anomalous conditions are conceived to produce either an

- axial or radial effect, which would causu either a change in quadrant tilt ratio or axial offset ratio.

These are monitored by the excore detectors and would help identify problems not fully detectable with reduced incore mapping capability. Furthermore, the core exit thermocouples in the reactor provide a useful supplement to the incore detectors to detect problems.

~ -.

v I

l

• 3-L Our review of the suitability of operation of the Farley Unit i reactor for the remainder of Cycle 15 with a reduced number of movable incore thimbles locations to as few as 50%

indicated adequate margin exists at this time in Cycle 15 and sufficiently increased uncertainty allowances have been made to ensure that TS peaking factor limits will be met. In addition, there are adequate supplementalindicators of anomalous conditions to preclude an unsafe condition from escaping detection in the absence of full incore detector mapping capability.

3.0 IECHNICAL SPECIFICATION CHANGES

. TSs 3.2.2.3.b,4.2.2.3, and 4.2.3.2 - The changes increase the measurement uncertainty by 2%

for F"o and 1.5% for F"6H when the number of operab!e incore detector thimbles is reduced to 50% (25) of the total number of duectors. The additional uncertainty is applied linearly from below 75% to greater than 50% detector thimble locations. The change in the uncertainty has been justified and is therefore acceptable.

TS 4.3.3.2 - The change adds a footnote which states that for Unit 1 Cycle 15 with greater than 50% and less than 75% detector thimbles available, three detector thimbles per quadrant are required where quadrant includes both the horizontal-vertical quadrant and four diagonally-bounded quadrants (eight individual quadrants in total). The proposed change was added to establish the bounds of applicability of the evaluation and is acesptable. The Bases have also been modified to incorporate the method for calculating the allowances for measuremant uncertainty with 25 to 37 operable detector thimbles.

On the basis of the staff's evaluation in Section 2.0 above, the staff concludes that adequate margin exists to ensure that TS peaking factors will be met for the remainder of Cycle 15.

Therefore, the proposed Technical Specification changes are acceptable. These changes are for the rema!nder of Cycle 15 only.

4.0 STATE CONSULTATION

- In accordance with the Commission's regulations, the State of Alabama official was notified of the proposed issuance of the amendments. The State official had no comments.

1

5.0 ENVIRONMENTAL CONSIDERATION

The amendment changes a requirement with respect to installation or use of a facility-component located within the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative Meu$ional radiation exposure. The Commission has previously issued a proposed finding i

that the amendment involves no significant hazards consideration, and there has been no

. public comment on such finding (62 FR 47695 dated September 10,1997). Accordingly, the smondment meets the eligibility criteria for categorical exclusion set forth in 10 CFR

--51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental.

assessment need be prepared in connection with the issuance of the amendment.

i

~ - -. -

~.

4

6.0 CONCLUSION

The Commission has concluded, based en the considerations discussed above, that (1) there is reasonable assurance that the health and safety of the public will not be endangered by-operation in the proposed mannst, (2) such activities will be coMucted in compliance with the

. Csmmission's regulations, and (3) the issuance of the amendmont will not be inimical to the common defense and security or to the health and safety of the public, g

PrincipalContributor: M. Chatterton

- Date:

October 23, 1997 P

4 3

e

_________.m_

-