ML20207K072

Safety Evaluation Re Reactor Coolant Pump Shaft Integrity Issue at Facility.Licensee Adequately Informed & Trained Operators as to Symptons & Actions to Be Taken Re Reactor Coolant Pump Sheared Shaft Event.Responses Acceptable

ML20207K072
Person / Time
Site:	Arkansas Nuclear
Issue date:	01/07/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20207K061	List: ML20207K057 ML20207K072
References
NUDOCS 8701090217
Download: ML20207K072 (3)

Text

_

[gnugyjg

- UNITED STATES

,E g NUCLEAR REGULATORY COMMISSION y ;E WASHING TON, D. C. 20555

,o$

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION CONCERNING i THE REACTOR COOLANT PUMP SPAFT INTEGRITY ISSUE -

AT ARKANSAS PORFR AND LIGHT COMPANY ARKANSAS NUCLEAR ONE, UNIT NO. 1 DOCKET NO. 50-313

1.0 BACKGROUND

On April 23, 1986, the we issued a request for information under 10 CFR 50.54(f) to the Arkansas Power and Light Company (AP&L) in response to the Reactor Coolant Pump (RCP) Shaft Failure event at Crystal River on January 1, 1986. This event was described in IE Information Notice 86-19, Reactor Coolant Pump Shaft Failure at Crystal River, which was issued on March 21, 1986.

The 50.54(f) letter requested schedules for inspecting the RCP shafts and structural components. In addition, justification for continued j operation prior to RCP inspections was also requested. This reouest included:

1. A description of those design characteristics and operational aspects of the Arkansas Nuclear One, Unit 1 (ANO-1) RCPs which are different from the design and/or operation of the Crystal River Unit No. 3, and Davis Besse Unit No. 1 RCPs.

2. The results of any analysis performed subsequent to analyses done for the FSAR which would address the consequences of a locked rotor or broken shaft event during plant operation.

3. Considering the higher probability than previously envisioned of a postulated RCP shaft failure, implemented or planned actions such as operator review and associated training concerning the specific events at Crystal River Unit No. 3, and Davis-Besse Unit No. 1, and monitoring plant parameters such as primary to secondary reactor coolant pump leakage.

AP&L responded to this reauest on May 13, 1986. v!e reviewed this response and issued a request for additional information (RAI) on July 25, 1

1986. AP&L responded to the July 25, 1986 request for additional information on September 15, 1986, and presented the results of their RCP inspections on October 23, 1986. Our evaluation of AP&L's responses and their l October 23, 1986 presentation follow:

I

%f10N P

f l

i

~

2.0 EVALUATION In the April 23, 1986 10 CFR 50.54(f) letter, we specifically requested that the licensee provide the results of any analysis performed subsequent to those done for the FSAR which would address the consequences of a locked rotor or broken shaft event during plant operation.

The licensee in its letter dated May 13, 1986 stated that the ANO-1 FSAR addressed a locked rotor accident but did not address a sheared shaft event.

In support of an earlier reload, Babcock and Wilcox was asked to perform an assessment of the locked rotor analysis and a comparison to sheared shaft event using the LYNXT code. The results indicate that the sheared shaft event is bounded by the locked rotor analysis. Minimum DNBR is greater than 1.6 in either case, and the two events are so similar that the resulting analyses are almost identical. These analyses were referenced in the -

ANO-1 cycle 7 reload report.

Following the RCP shaft failure event at Crystal River Unit No. 3, the ,

licensee formed a review group to evaluate the safety implications of a sheared shaft event at.AN0-1. The review group decided to conservatively postulate a sfinultandous' shearing of two RCP shafts in the same steam generator loop. Realistic cycle specific parameters were considered in this analysis. The resulting analysis indicated that the minimum DNRR remains above 1.0 for this case. This minimum DNBR satisfies the acceptance criteria set forth for a locked rotor accident in the original FSAR and is consistent with the licensing basis for ANO-1.

Our July 25, 1986 RAI expressed concerns with the validity of the planned Ultrasonic Examination (UT) of the RCP shafts in light of the unsatisfactory experience at Davis Besse with UT. Also, we requested additional details related to inspections and corrective actions (if required) of the impeller to shaft drive pins and capscrews. Clarification was also sought relative to planned operator actions following a sheared shaft event.

In its September 15, 1986 response AP&L also expressed concerns related to the UT examination conducted at Davis Besse. In response to those concerns, the licensee and Toledo Edison jointly funded a Babcock and Wilcnx program to develop an enhanced UT technique for inspecting RCP shafts.

In addition, the licensee has developed an examination technique to char-acterize the stiffness of the shaft to impeller joint to determine the condition of the capscrews and drive pins. The licensee also committed to perform visual inspections of the shaft, capscrews, and drive pins during pump disassembly at their upcoming outage.

During their most recent outage, examinations were performed of the RCP shafts, drive pins, and capscrews. The results of those examinations were presented to the staff at a meeting on October 23, 1986. The examin-ation included UT inspections of all RCP shafts, an assessment of the impeller to shaft joints, and an inspection of all major components of a disassembled pump, including capscrews and drive pins. The results of those examinations have shown that all four pump shafts were free nf detectable cracks. The inspection of the disassembled pump along with the evaluation of the impeller-to-shaft joint stiffnesses have confirmed the integrity of that connection for all four pumps.

I t D A memorandum was issued by the plant operations superintendent describing i the symptoms of a sheared shaft and appropriate operator action to be i

taken. AP&L also reouired that the ANO-1 operators read the LER describing the sheared shaft event at Crystal River Unit No. S. If a

, sheared shaft event occurred at ANO-1, the reactor could trip ,nn nuclear overpower based on RCS flow and axial power imbalance (as occurred at Crystal. River Unit No. 3). The ANO-1 operations staff were made aware that this could occur. However, there is no specific automatic trip

associated with this event nor is there any specific directive for the operators to manually trip the reactor. The operators would diagnose the 2

event using the pump vibration monitor, RCP seal staging pressure indications, i and RCS flow indications. Upon diagnosis of this event the operators are directed to secure the affected pump and conduct an expedited orderly shutdown to cold shutdown conditions. We find the described operator

review and training for the sheared shaft event acceptable.

1

3.0 CONCLUSION

S

) AP&L has provided their plans and the results of inspections performed on the rotating RCP assemblies at ANO-1. They have provided justification 1 for continued operation by describing the results of additional analyses.

Also, the licensee has adequately informed and trained its operators as to

the symptoms and actions to be taken related to a RCP sheared shaft event.

. Therefore, we find the licensee's responses acceptable, and has determined j that the license for ANO-1 need not be modified as a result of the sheared shaft event at Crystal River Unit No. 3.

Date

January 7,1987 j Principal Contributor:

A. Cappucci i

i J

l l

t I ,

- - . - . - , - - - . - - .. . - . - - - - - . , , - - - - . - - - - - - , -. - - . - . . - - .