ML19340E776

Proposed Section 6.4 to Tech Specs

ML19340E776
Person / Time
Site:	Fort Calhoun
Issue date:	01/12/1981
From:	OMAHA PUBLIC POWER DISTRICT
To:
Shared Package
ML19340E772	List: ML19340E771 ML19340E775 ML19340E776
References
NUDOCS 8101150638
Download: ML19340E776 (11)

Text

. .

<. .s

^\

\ 6.0 INTERIM SPECIAL TECHNICAL SPECIFICATIONS 6.4 Operation With Less Than 75% of Incore Detector Strings Operable Applicability Applies to power operation during Cycle 6 and supersades Specification 2.10.3(2).

Objective To monitor kw/ft and power distribution with less than 75% of the in-core detector strings operable.

Specification (1) Theincoredetectors{stemshallbeoperabletomonitorpeak linear heat rate, F ,FRT, and the radial power distribution withlessthan75%bbtmorethan20%ofallincoredetector strings and one incore detector string per full length quadrant, where an operable string consists of three or more operable rhodium detectors, provided:

(a) The planar radial peaking factor uncertainty, Uxy, the integrated radial peaking factor uncertainty, U R, and the total peaking factor uncertainty, U q, are determined every 31 EFFD, in accordance with the reference.

(b) If UR > 6% the value of FR to be used in evalcating the approach to the limits of Specification 2.10.4(2) is F =F RM (1 + UR - 0.06)

R where FRU is determined from a power distribution map with no part length CEA's inserted and all full leagth CEA's at or above the Long Term Steady State Insertion limit for the existing Reactor Coolant Pump combination, and the integrated radial peaking factor uncertainty, Rg is the latest determined value of UR at the time U

l

! F R is determined.

(c) If U > 7% the calculated value of F xy to be used in evalNEtingtheapproachtothelimitsofSpecification 2.10.4(3) is Fxy =F xyM (1 + U xy - 0.07).

I where FxyM is determined from a power distribution map with no part length CEA's inserted and all full length CEA's at or above the Long Term Steady State Insertion l limit for the existing Reactor Coolant Pump combination l ,

and the planar radial peaking factor uncertainty, x , is

! the latest determined value of U xy at the time Fxy a determined.

l 6- AT W HMENT A 8101150[,%

x

6.0 INTERIM SPECIAL TECHNICAL SPECIFICATIONS 6.4 Operation With Less Than 75% of Incore Detector Strings Operable (Continued)

(d) If U as (qI >+ 7%

Uq ) the total shall be peaking uncertainty used in place of thefactor defined measurement-calculation factor of 1.07 in Specification 2.10.4(1).

(e) The maximum local peak linear heat rate in the core, cmax, shall be determined and the incore detector alarms shall be adjusted to no greater than the following:

Alarm Setting = C * @ allowed Smax where C = The detector signal converted to flux units when the reactor is operating at steady-state.

Callowed = Linear Heat Rate (kw/ft) allowed by Specifi-cation 2.10.4(1) and adjusted as required by Specification 6.3(1)(d).

1. max = The maximum local peak linear heat rate (kw/ft) measured at the same reactor conditions as C above.

(2) If the incore detector system is not operable within the interval specified, the peak linear heat rate shall be monitored by ex-core detectors per Specification 2.10.4(1)(c) and the surveillance requirements of Specification 3.10(5) are deleted.

Basis Operation of the incore detector system for peak linear heat rate l monitoring and surveillance of FRI and FxyT with less than 75% of the strings operable requires additional measures to compensate l for degradation of the incore instrument system. Periodic com-parisons between calculated and measured power distributions are made to confirm the core is depleting as designed. The measure-

! ment uncertainties are computed to assure the assumptions made in j the setpoint analysis are valid. The uncertainties are computed j using the methods given in the reference.

l If the determined uncertaintics exceed the uncertainties used in the setpoint and safety analysis, the measured values of FR and

! F are augmented by the appropriate uncertainty. These new values l ofFR and F x are then used to verify compliance with Specificat, ions i 2.10.4(2)and2.10.4(3). This assures that the product of the radial peaking fa.ctors and their appropriate uncertainties are '

less than the values used in determining the setpoints.

l l 6-4

$ __u - _W

4 4 6.0 INTERIM SPECIAL TECHNICAL SPECIFICATIONS 6.4 Operation With Less Than 75% of Incore Detector Strings Operable (Continued)

The minimum margin to the kw/ft limit is used to set alarms on all detectors. This imposes restraint on the power distribution as well as the peak linear heat rate and precludes the occurrence of undetected peaks larger than the limit. When incore detectors alarms are set using this method, several alarms would be re-ceived in the event of a shift in the power distribution even though the maximum local peak linear heat rate may not be exceeded.

Reference

~

INCA /CECOR Power Peaking Uncertainty - CENPD-153-P, Revision 1-P-A, May 1980.

l e

t

)

s P

4 st l

.y 6-5 o ___c... ._n_ ~

___l___--__-_______________ _______e____

DISCUSSION OF PROPOSED CHANGES TO OPERATING LICENSE The number of incore detector failures has reached Technical Specifications operability limit during operation of Cycle 6 at Fort Calhoun Station. The current status of the incore detector system is shown in Figure 1. The figure shows seven detector strings are inoperable using the operability definition of Technical Specification 2.10.3(2).

Currently, eight detector strings have, single failurce and could become inoperable if a single additional failure occurs in that string. The failures are predominantly occurring in two detector batches. The failures in the detectors inserted during Cycle 2 and at the beginning of Cycle 3 ~

are thought to be "old age" mortality. These detectors were not replaced during the last outage because excessive rhodium depletion was not expected to occur during Cycle 6. The failures occurring in the detectors inserted at the beginning of Cycle 5 are due to an unknown cause. These detectors are from our standard replacement inventory and were manufactured 'at the same time as the batches inserted at the beginning of Cycles 4 and 6.

Failures have not occurred in these batches.

Technical Specification 2.10.3(2) prohibits the use of the incore detector system for peak linear heat rate (kw/ft) monitoring and FR T and Fx I surveillance with more than seven failed incore de-tectorstr[ngs. The proposed Technical Specification will allow continued Cycle 6 operation using the incore detector system with fewer than 75% of the strings operable. To compensate for the system's degradation, several additional requirements are used to assure the core is operating within the limits of the safety analysis.

The existing limits on incore detector operability are imposed to insure the measurement uncertainties are no higher than the uncer-tainties assumed in the safety analysis and setpoint generation and to insure the incore detector system can monitor the peak linear heat rate using a level dependent alarm limit. The pro-posed Technical Specification requires determination of the planar radial peaking factor uncertainty, the integrated radial peaking factor uncertainty, and the total peaking factor uncertainty using the method described in the reference on a periodic basis. These measurement uncertainties are compared to the values assumed in the setpoint analysis and, if they exceed the assumed value, veri-fication is then made to assure the core is operating within the boundary of the setpoint analysis.

The safety and setpoint analyses used the products of the peaking factors and the peaking factor uncertainties to define the bounds of the core power distribution. The Technical Specification limits on FR and F assure the core power distribution is within the bounds ofthesafe!yy and setpoint analysis. These limits on FR and Fxy and the measured values of FR and F do not contain any uncertainty becausethesameuncertaintyisuseNyin both the setpoint and safety analysis and the measurement. However, if the measurement uncer-tainties increase, the assurance that the core power distribution is within the bounds of the setpoint and safety analysis is obtained ATTACHMENT B

by multiplying the peaking factor by the increased uncertainty and comparing it to the limit. The proposed method of calculating F R and Fx increase these values to compensate for the increased un-certainty such that the inequalities yxyLimit > p Measured

-- y (1 + Uxy - 0.07)

F Limit p Measured (1 + UR - 0.06)

R are satisfied.

Figures 2 and 3 show the measured and predicted values of FR and Fxy as a function of exposure for Cycle 6. As can be seen, there is agree-ment between the measured and predicted values, and the core is de-pleting in a predictable manner. Since the Cycle 6 core contains no burnable shims, there is no mechanism to cause the core to con-tinue the depletion in an abnormal fashion. The peaking factors can be expected to follow the predicted trend and remain within the bounds assumed in the analysis, as was seen during the Cycle 5 de-pletion, Figures 4 and 5. The District has continued its core fol-low program during Cycle 6 and the measurement uncertainties are within the values assumed in the safety and setpoint analysis. Con-sidering the large margin between the currently measured values of FR and Fxy and the Technical Specification limits, it is anticipated the proposed specification will provide sufficient operating margin for the remainder of Cycle 6. The peak allowable linear heat rate is calculated using the determined total peaking factor uncertainty if this uncertainty exceeds the value used in Specification 2.10.4(1).

The incore detector alarms are to be set using the minimum margin to the peak linear heat rate as opposed to the current procedure of setting the alarms based on a level dependent margin to the peak linear heat rate. This imposes a restriction en the core power distribution in addition to the existing restriction on peak linear heat rate. Setting the alarms in this fashion detects shifts in i the power distribution as well as approaches to the peak linear heat i rate limit.

I Although it is considered a remote possibility, sufficient failures could occur to prevent compliance with Specification 6.3(1). If this occurs, the peak linear heat rate is to be monitored on the excore detectors. Surveillance of the power distribution to date

provides sufficient assurance the core power distribution will re-main within the bounds assumed in the safety analysis. Therefore, there is no need to reduce the peak allowable linear heat rate nor T

monitor FR and FxyT. This condition also requires Tq to be monitored

by the excore detectors.

Reference

• INCA /CECOR Power Peaking Uncertainty - CENPD-153-P, Revision 1-P-A, i May 1980.

L - 3 m

CALLED NORTH CYCLE 6 OPERABLE If! CORE DETECTOR STATUS FIGURE 1

.A B C D EFGHJKLMN P R S T I I -

2 - -

2 BOC 3 BOC 3 3- -

e e e. -

3 e e ee BOC 6 MOC 2 MOC 2 B0C 5 4 -

ee ee ee ea -

4 ee--

e_. ea ea

~ ~

i 30C 3 l G- a* BOC 6 MOC 2 BOC 3

-6 7- ** ee oe ae 7 8- BOC 5 B0C 6 BOC 3 BOC 6 B0C 5 E*

ae 8 9- ea ee ee TC e3 e e ee -9 e_ p e e e e e e a 10._ - 10 11 -

BOC 3 e

a a

e e

M0C 2 e

e a3 BOC ae

-l l 12 _ BOC 6 BOC 5 _!2 13 - e e ea - 13 e e e a MOC 2 BOC 3 30C 5 BOC 5

4 -

e a ea ea e a -

i4 e e ee e e ea BOC 4 BOC 3 .

15 -

e e e . -

15 ee e e 16 - -

-16 I 17 17 A B C D EFGHJKLMN P R S T f BATCil LEVEL 1 LEVEL 3 e Closed circle indicates operable detectors.

. LEVEL 2 LEVEL 4 a Open square indicates failed detectors.

1

Figure 2 - FORT CALHOUN CYCLE 6 INTEGRATED RADIAL PEAKING FACTOR, FR '

VS CYCLE BURNUP 1.50 - O Predicted -

A Measured 1.49 -

Tech. Spec. Limit 1.52

~

1.48 -

AA 1.47 .A _

1.46 < A u."

$ 1.45 -

h A w 1.44 k AA 9

b 1.43 -

. c.

5 A AA A A J 1.42 -

$ 1.41 -

o

, # 1.40 -

5o y 1.39 -

1.38 -

1.37 -

-1.36 -

1.35 -

1.34 '

10,000 11,000 0 1000 2000 3000 4000 .5000 6000 7000 8000 9000 CYCLE BURNUP (MWD /MTU)

l Figure 3-FORT CALH0Uti CYCLE 6 PLAtlAR RA01AL PEAKIllG FACTOR,xyF VS CYCLE BURiiUP 1.52 - O Predicted

-A Measured 1.51 . A Tech. Spec. Limit 1.57 -

A l

1.50 -

a 1.49 <- A A

A 1.48 -

k A i

1.47 - A A J A A S A g ,

i. 46 -

u.

E 1.45 -

y 1.44 -

a 5 1.43 -

Ea:

g 1.42 -

i d 1.41 -

1.40 -

1.39 -

1.38 -

1.37 -

1.36 '

7000 8000 9000 10,000 11.000 2000 3000 4000 5000 6000 0 1000 CYCLE BURNUP (FrdD/MTU)

~

Figure 4 - FORT CALHOUN CYCLE 5 INTEGRATED RADIAL PEAKING FACTOR FR -

VS CYCLE BURNUP 1.50 -

O Predicted A Measured 1.49 0 Tech. Spec. Limit 1.52 1.48 g 3 1.47 -

g m 1.46 -

u-of 1.45 _

S A M

"- 1.44 -

E G 1.43 -

A b

a 1.42 - ,

5 A

$ 1.41 -

o 1.40 .

o

- 1.39 - A

- a t 1.38 .

A 1.37 - ..

~

1.36 -

1.35 -

1.04 10,000 11,000 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 CYCLE BURNUP (MWD /MTU)

Figure 5 FORT CALHOUN CYCLE 5 PLANAR RADIAL PEAKING FAC10R, Fxy VS CYCLE BURNUP 1.50 - A C) Predicted 2k A Measured 1.49 ~ A Tech. Spec. Limit 1.57 1.48 -

1.47 -

A A

1.46 -

u.

k

. 1.45 - g 8

h 1.44 -

u.

A T 1.43 -

k 1,42 -

A 1.41 -

a g g 1.40 -

a 2d 1.39 -

A 1.38 -

1.37 -

1.36 -

1.35 -

1.34 > '

10,000 11,000 4000 5000 6000 7000 8000 9000 0 1000 2000 3000 CYCLEBURNUP(MWD /NTU)

3 JUSTIFICATION FOR FEE CLASSIFICATION The proposed amendment is deemed to be Class III within the meaning of 10 CFR 170.22 since it addresses a single safety issue and does not involve a significant hazard consideration.

1 i

i I

s 1

t l

l ATTACHMENT,C

l. .

-R- _ . _ _ .

. _ . _ _ _ _ _ . . . _ _ . . _ _ . _ _ _ , _ _ . . _ . _ . _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ __ ___ __