ML20207H158

Informs of Decision Not to Plan Fuel Sipping for Upcoming Refueling Outage.Reasonable Assurance Exists That Leaking Fuel Will Be Discharged at End of Cycle 21.Search for Leaking Fuel Pins Prior to Cycle 22 Reload Not Reasonable

ML20207H158
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	12/29/1986
From:	Frisch R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 8701070471
Download: ML20207H158 (4)

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C0HSumBIS

@rewaumE MKinEnWE PanEREss Povver oeneres offices: 1945 West Parnall Hoad, Jackson, MI 49201 * (517) 788-0550 December 29, 1986 Director, Nuclear Reactor Regulation US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT - FUEL PERFORMANCE For the upcoming Cycle 22 operations Consumers Power Company has concluded that we have reasonable assurance that leaking fuel (two to three fuel pins) will be discharged at end of Cycle 21 operation and that is is not reasonable to do an exhaustive search for leaking fuel pina prior to Cycle 22 reload.

This conclusion has resulted in making the decision to not schedule any fuel sipping for the upcoming refueling outage. The decision to not plan any fuel sipping has raised concerns from the NRC which question the prudency of this decision and has resulted in several conference calls with the NRC staff. To resolve the NRCs concerns, Consumers Power Company committed to document the basis for our decision. This submittal provides the requested documentation.

The last fuel cycle at Big Rock Point to show no evidence of failed fuel was Cycle 18. During Cycle 19 the off-gas release rate started at a normal 300 pC1/sec of noble gas and climbed to approximately 30,000 pCi/see within a period of ten months. The plant chut down at that time to fix an underground leak from the condensate process monitor line. Throughout this period there was no significant increase in reactor coolant particulate radioactivity. The reactor coolant radiolodine activity increased by a factor of 10 to 100, but was.still well below the level in the Technical Specifications for required action. During this cycle plant radiation levels increased only around piping and components associated with the off-gas system. These areas are located such that the increase in dose to plant workers was negligible. The entire core was sipped upon shutdown with three leaking bundles identified. The number of leaking pins was not identified. No bundles indicating leakage were returned to the core.

Inspections indicated the failures to be enhanced waterside corrosion of a particular lot of cladding that had been manufactured by Mannesman from a 8701070471 861229 PDR ADOCK 05000155 P PDR \

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Director, Nuclear Reactor Regulation 2 Big Rock Point Plant Fuel Performance December 29, 1986 single ingot of Zircaloy. Examination of the data led both Exxon Nuclear Company and Battelle Columbus Laboratories to conclude the most likely cause to be the corrosion susceptibility of this cladding lot. Primary system chemistry was also a possible contributor. Retubing the condenser during the 18th refueling outage appears to have caused Cycle 19 to operate with a higher copper concentration than previous or subsequent cycles. All fuel containing cladding manufactured by Mannesman was discharged.

Cycle 20 also started at a normal off-gas release rate (300 pCi/sec) and proceeded to climb to a final 3000 to 4000 pCi/sec, approximately a factor of 10 less than the previous cycle. No significant increase was evident in reactor coolant iodine or particulate radioactivity. Nor was there any increase evident in the radiation levels associated with the off-gas system.

The entire core was again sipped upon shutdown with five leaking pins identified and no bundles indicating leakage were returned to the core.

Because the suspect cladding had been removed, these failures were believed to be unrelated to the corrosion problem. Reactor Engineering postulated that the design of the fuel made it susceptible to failure under higher operating levels. Thermal power was increased to near full power of 240 MWt after several cycles of operating at a maximum power of approximately 210 MWt. This change occurred after Nuclear Regulatory Commission approval of the minimum critical power ratio (MCPR) methodology for Big Rock Point. The fuel has subsequently been redesigned to account for these higher operating levels, beginning with Cycle 21 reload II. It is anticipated that once all fuel prior to Cycle 21 reload Il has been discharged, fuel failures will have been eliminated.

About mid-Cycle 21, it was predicted that there could be four to six failures located in prior to reload Il bundles having an exposure of 19 to 25 GWD/MTU.

Because of the low statistical levels involved, there was some uncertainty in this prediction. Upon startup of Cycle 21 (the current cycle), it was immediately apparent that there was some failed fuel in the core since the off-gas release rate rose to 600 pCi/sec. Either some failed fuel escaped the sipping process or some failures may have occurred during startup. The off-gas continued to climb throughout this cycle to a maximum of approximately 3000 pCi/sec. Again, no significant increase in plant radiation levels or reactor coolant iodine and particulate radioactivity was evident.

Historical data indicates that off-gas release rates of 1000 pCi/sec equates to one failed fuel pin. Actual current conditions indicate that there may be only two or three failed fuel pins. The off-gas release rates in cycle 20 were slightly higher than those present in cycle 21. Inspection during the 20th refueling indicated five failures in bundles ranging in exposure from 16 to 24 GWD/MTU.

Assuming, from past experience, that the above predictions are accurate, the failures will be in the oldest half of the core. In other words, the failed OC1286-0178-NLO4

i Director, Nucient Reactor Regulation 3

! Big Rock Point Plant i Fuel Performance i December 29, 1986 i

) fuel will either be discharged or located on the core perimeter in lower power

{ locations.

Although it is believed that sipping will find any well developed defects, it 1 is also believed that additional defects will form until all the reloads prior

, to Cycle 21 reload 11 are discharged. This causes us to question whether i sipping is worth the exposure and expense. The average dose received by plant personnel to sip the entire core is approximately four to five person-rems.

This does not include dose received by Exxon personnel in locating the failed

pin (s) and reconstituting the bundle (s), which may be higher or lower than the i

sipping process depending on the number of failures. This would mean up to ten person-reas total sipping dose. We fully expect that any leaking fuel

, pins will be discharged. If the same fuel failure rate as the previous two

cycles is assumed (in the range of 3000 to 4000 pCi/sec off-gas release rate),

prior analyses have shown that the offsite population dose (to a radius of 50 miles) would be approximately two person-rems as compared to the ten 4

person-rem total sipping. dose.

In addition to the costs incurred by Operations and Radiation Protection personnel to perform the sipping, the costs for Exxon Nuclear Company to

identify and repair the failures, and the impact on the outage schedule, there

! are additional preparatory costs, setup, and maintenance totaling about ten 1 man-days. If an assembly is repaired, an additional three man-days of l engineering is required to calculate the local peaking factors. If a le.,ker j cannot be repaired and is discharged, approximately five man-days of

engineering will be required for a new core loading.

Based on our current knowledge of the previous three cycles of fuel l performance, we believe the course of action involving the least dose

!- consequence to the total population would be not to sip any fuel during the

1987 Refueling Outage. If the entire or a partial core is sipped, it would not provide complete assurance that failed fuel is not returned to the core, as may have been apparent during the last sipping process. Since the failures we are now experiencing appear to be of the noncatastrophic type, improvements i in fuel design have been made, and for economic and ALARA considerations, we

[ believe the most prudent course of action would be to not sip fuel at the end j of Cycle 21.

The decision to not sip has been discussed with Exxon Nuclear Company and they agree with our decision. We also want to reiterate that it is not our policy to install known leaking fuel into the core.

Exxon Nuclear Company has proposed and we have scheduled inspection of two fuel bundles which contain fuel pins with beta-quenched cladding during the 1987 refueling outage. While they are on site Exxon has agreed to do some limited inspection for leaking fuel pins utilizing their ultrasonic inspection techniques. Current outage plans have a one week window available to do some UT inspection. Our current plans are to UT inspect a low exposure bundle that OC1286-0178-NLO4

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Director, Nuclear Reactor Regulation 4 l . Big Rock Point Plant l Fuel Performance l December 29, 1986

> b l was off loaded last cycle. The bundle was sipped and leakers were indicated I but eddy current resting could not locate the leaking pin (s). Results of the 4

UT inspection, person-rem expenditure and the availability of time will be considered when determining whether or not to do additional UT inspections.

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NRC Resident Inspector - Big Rock Point Plant J

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