ML19312C948
| ML19312C948 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/23/1977 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML19312C938 | List: |
| References | |
| RO-270-77-08, RO-270-77-8, NUDOCS 8001140602 | |
| Download: ML19312C948 (2) | |
Text
_.
-e DUKE p0WER COMPANY h
OCONEE UNIT 2' Report No._: R0-270/77-8 Report Date: May 23, 1977 Occurrence Date_: April 23, 1977 Facility: Oconee Unit 2, Seneca, South Carolina Identification of Occurrence: Reactor power error adjusted imbalance limit exceeded I
Conditions prior to Occurrence: Unit at 100 percent full power Description of Occurrence:
On April 23, 1977, while increasing power from 63 percent full power after the incore imbalance perforning a main turbine stop valve movement test, increased above the error adjusted incore system limits reaching a maxinum value of -14.97..
Boron concentration was increased by additions from the concentrated borated water storage tank to reduce the imbalance; however, as required by Oconce Technical Specification 3.5.2.6, a power reduction was initiated approximately two hours after exceeding the error adjusted l
imbalance limits.
j Boron additions were increased using the borated water storage tank (BWST) and approximately one hour later reactor imbalance was reduced to within the limits of Technical Specification 3.5.2.6 and the shutdown was termi-nated.
A parent Cause of Occurrence:
f The This incident resulted primarily from an unusual service condition.
condition resulted from restrictions which were placed on the movement of control rod group 7 due to a failed stator on one rod of this group.
The power reduction was made only af ter extensive preplanning which inves-tigated the restrictions necessary for operation under these ususual condi-Boron additions to the reactor coolant system appropriate to tions.
compensate for the inability to move group 7 were made during the power l
However, it is postulated that due to a ruptured oil seal, a increase.
lower than normal oil pressure existed in the concentrated boric acid storage tank (CBAST) pump. This resulted in an indication of greater flow volume from the CBAST than the volume actually added to the reactor coolant system.
i Upon evaluating the situation, the reactor operator used the borated water j
storage tank (BWST) to increase borated water additions and thus brought j
the imbalance within limits.
Analysis of Occurrence:
Technical Specification Figure 3.5.2.3B2 provides a limit for reactor.
power imbalance versus reactor power level to prevent achievement of the
- 1248 802
maxinum linear heat rate (due to local power peaking) so that maximum clad temperature will not exceed the limits given in Appendix K to 10CFR50 in The existance of the event of a postulated loss of coolant accident.
statistical and instrument errors associated with the measurement of reactor power inbalance makes it necessary to operate within an error adjusted power imbalance envelope in order to assure that the Technical is not actually being exceeded.
In this incident, Specification limit the reactor was operated for three hours outside the error adjusted power imbalance limits, and, therefore, it is possible that the limits specified in Technical Specification Figure 3.5.2.3B2 were exceeded, liowever, the bases for Technical Specification 3.5 states that all of the power distribution parameters (quadrant tilt, rod position limits and imbalance) must be at their limits while simultaneously all other engi-neering and uncertainty factors are also at their limits to produce the In this incident, although the indicated maximum allowabic heat rate.
imbalance exceeded the error adjusted value, a linear heat rate below the established limits was assured by the conservative values of the other power peak inducing parameters and the gradual power decrease.
The capability of the reactor protective system was not affected by this it is concluded that the health and safety of incident and therefore, the public was not affected.
Corrective Action _:
The CBAST pump was inspected and a ruptured oil seal on the CBAST pump was replaced. Subsequent operation has resulted in proper flow indications.
The failed stator in the group 7 control rods will be replaced during the pending refueling outage.
4