ML19345E608

Responds to Questions Re Cycle 15 Reload Application. Probability of Out of Sequence Rod Drop Event Occuring Is Adequately Conservative When Applied Against Stated Criteria

ML19345E608
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	09/14/1977
From:	Bixel D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Desiree Davis Office of Nuclear Reactor Regulation
References
NUDOCS 8102050283
Download: ML19345E608 (6)

Text

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CODSum0rS 1 [J L POWCi Company General Offices 212 West Micrugan e..enue., Jackson. Micnigan 40201. Area Coce S17 788 0550 September lhi 1977

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(;_,. _ i.. L E -

6, Director of Nuclear Reactor Regulation 1

Att: ~ Mr Don K Davis, Acting Branch Chief

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3 Operating Reactor Branch No 2 i.'

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US Nuclear Regulatory Commission N. a,.

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Washington, DC '20555 DOCKET 50-155 - LICENSE DPR BIG

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RCCK POINT PLAUT - RESPONSE TO STAFF QUESTIONS FOR CYCLE 15

'In discussions with the staff concerning Consumers Power Company submittal en the Big Rock Point Cycle 15 reload application, several ite=s necessitated further evaluation. The purpose of this letter is to provide the necessar-y information.

Item Provide an analysis specifying the probability of occurrence of an out-of-sequence 1

rod drop accident.

Fesponse By letter dated November 10, 1967 Consumers Power Company submitted a reload ap-plication for Big Rock Point in which the probability analysis for the postulated out-of-sequence rod drop accident was developed. This evaluation censidered the fc11ovin6_ individual events:

a.

Rod failing to latch / rod unlatching.

b.

The unlatched rod sticks.

c.

Operator error in not identifying unlatched / stuck rod.

1 d.

The affected rod has high potential worth and it is withdrawn from an j

enhanced pattern.

d e.

The stuck rod dropping.

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j The assumptions made in etermining the individual event probability are con-tained within the November 1967 submittal and conservatively bound the parameters pertinent to the Big Rock Point Cycle 15 core.

Specifically, the control rod drive mechanism characteristics and fuel and core dimensions used in the 1967 submittal to provide the probability for rod latching failure or rod sticking are consistent for the Cycle 15 core.

However, no attempt was made to update hister-ical data upon which the probabilities ver. derived, thus no credit is taken for the approximately ten years of operaticn since 1967 without control rod drive coupling failure or rod stickin6 incidents.

Further, the maximu= out-of-sequence rod worth specified in the 1967 evaluation was 2.1% Ak/k vice the 2.03,1 ok/k rod worth for Cycle 15, and the maximum in-sequence rod worth specified in the Hovember 1967 report is 0.8% ok/k vice the Cycle 15 value of 0.7% ok/k. Table 1 is provided to sumenrize the maximum individual probability associated with each cvent as specified in the November 1967 report.

The only nu=ber in the table that is not found in the report is the rod movements per year.

The prob-ability of k x 102 assumes ten start-ups per year with 20 rods moved to obtain criticality and takes into account a factor of two to account for multiple steps involved with full withdrawal of any one rod.

Thus, the total maximum probability per year of rod drop resulting in energy deposition greater than 250 calories per gram is 4 x 10-10, By letter dated June 1, 1976, Mr B C Rusche forwarded to Mr R Fraley the staff rerort cencernin6 Generic I+em IIA-2 Control Rod Drop Accident (SWE). The attached Table 2 is a summary of the event probabilities developed in this re-port.

The report, while nct strictly applicable to Big Rock Point, contains many similar asstaptions and comparable event probabilities as those contained in our November 1967 submittal.

Further, the overall, conclusion of the report that specifies an acceptable event probability of 10-f for moaern BWR plants is certainly more limiting than the maximum probability for the event at Big Rock Point of L x 10-10 Therefore, it is concluded that the probability of an out-of-sequence rod drop event occurring at Big Rock Point is adequately conservative when applied against the stated criteria.

Item Provide the moderator temperature coefficients for Cycle 15

Response

Moderator Temperature Coefficients ak/k/ F Temperature ( F)

BOC EOC

-i,

-e 102 5 5.h96 x 10 '

2.h27h x 10 '

110 0

145 0

-5

-3 197 5

-5 158h x 10

-2.385h x 10 i

These temperatures were chosen to demonstrate the range of values and the transi-tion points up to the point boiling would begin.

~

3 i

TABLE 1 Out-of-Sequence Rod Drop Probabilities Maximum Probability Event for ERP Discussien

-6 Rod Is Disconnected 10 Propability range of 3 x 10 to 10-* for drive coupling failure.

-2

-2 Rod Sticks 10 Probability range of 10- to 10 for disconnected rod sticking.

Operator Error 10 Probability 10-for rod drive with-drawal (with the corresponding rod disconnected and stuck) of 6 notches withoutoperatordetegtion;proba-bility of 10-3 to 10-for operator error in withdrawing wrong rod (out-of-sequence).

-2

-5

-6 Rod Has High Potential 10

- Probability of 10 to 10 ggr Worth and Is Withdrawn operator error plus probability for Fro an Enhanced rod havirg worth > 2.1%.

Subtracting probability)for operator error assumed Pattern above (10-3 gives 10-2, Control Rod Drops 10-Rod Movements / Year h x 10 Assumes ten start-ups/ year; 20 blades moved to attain criticality (average of 300-18 and EOC-22); factor of two to account for cultiple steps in full withdrawal of any one rod.

-10 Maximum Probability / Year 4 x 10 of Rod Drop Resulting in

> 280 Cal /g i

a

l TABLE 2 Probabilities for Events GE

• This Report Groun Individual Groun Individual Maximum

-6 I.

Disconnect (/W) 10 2 x 10 2 x 10-A.

Disconnect 10-10-

-1 B.

Upper 1/h 3 x 10 C.

Not Discover 10-II.

Stuck (/W) 10-10 10-

-k 10-A.

Stuck 10

-1 B.

Upper 1/h 3 x 10 C.

Lower Dirve 1/3

-2 III.

Errors (/W) 8 x 10-9 10 10

-3

-3 A.

Operator Select 2 x 10 2 x 10 3.

2nd Operator 2 x 10-10-

-3

-3 or C.

R'.CI or 2 x 10 10

-3

-1 D.

Withdrav 2 x 10 10 IV.

liigh Worth Potential 7 x 10 10 L x 10

(/Ew)

-1 A.

liigh Worth 7.10-10 V.

Drop-Timing (/Dsew) 7 x 10-3 2 x 10 6 x 10-3

-3

-1 A.

Drop 1

10 B.

Crit to < 205 P 10-10-C.

Pattern Enhance 7 x 10-2 10 3

VI.

Rods / Year (W/Yr) 10 -10 7 2 x 10 2 x 10

-9

-12 4

Total ( Above 280/Yr)

N 10 s 10 s 13

(

• Staff report dated. lune 1, 19'(6 Generic Item IIA-2 Control Rod Drop Accidents (B'.G.).

5 s

Item Provide the liquid poison system vorth for Cycle 15 Resnonse The worth of the liquid poison system for Cycle 15 assuming (a) all rods out, (b) 2,000 ppa boron, and (c) core temperature of 68 F is 2~5 Ak/k. This is greater than that value of 25% ak/k specified in the FSAR Section h.5.9 uti-lizing the same assumptions.

1 i 1 A s-

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David A 31xel Iluelear Licensing Administrator CC:

JGKeppler, US:IRC i

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ac,fnu.iss u.S. NUCLE AR REautAvecay w iws mxsc aE NRd DISTRIBUTION Pon PART 50 DOCKET MATERIAL FROM:

DATE OF L OCUMENT TO *.

D K Davis Consumers Pwr Co 9 14.77 Jackson, Mi ATE RECEIVEO D A Bixal g-lg,77

$ETTER ONoToRizEo PROP INPUT FORM NUMBER OF COPtES RECEIVED W=RIGIN AL l Signen U NC LASSIPi E D DESC RIPTIO N EN CLOSU RE Response to ?!RC staff questiors concerning Cycle 15 operation......................

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Eig Rock Point 9-16-77 * * - hf SAFFTY FOR ACTION /INFORMATION BRANCH CHIEF: (7)

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