ML20235F934

Trip Rept of 870130-31 Visit to Jackson,Ms Re Safety Evaluation of Plant Reactor Core for Fuel Cycle 2,addressing thermal-hydraulic Stability Tests During Startup.Summary of Meetings Before & After Tests Also Encl

ML20235F934
Person / Time
Site:	Grand Gulf
Issue date:	06/23/1987
From:	Kintner L Office of Nuclear Reactor Regulation
To:	Office of Nuclear Reactor Regulation
References
TAC-61930, NUDOCS 8707140044
Download: ML20235F934 (9)

Text

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. . June 23, 1987 Docket No. 50-416 . DISTRIBUTION 155ciet4He- E. Jordan NRC PDR" ~ J. Partlow LICENSEE: System Energy Resources, Inc. Local PDR L. Philli PD22 Rdg. ACRS (10)ps EACILITY: Grand Gulf Nuclear Station, Unit 1 (GGNS-1) L. Rubenstein L. Kintner

SUMMARY

OF JANUARY 30 AND 31, 1987 MEETING OGC-Bethesda REGARDING FUEL CYCLE 2 CORE STABILITY (TAC No. 61930)

The NRC staff's safety evaluation of the GGNS-1 reactor core for fuel cycle 2 (Amendment 23 to the GGNS-1 Operating License dated October 24,1986) addressed thermal-hydraulic stability tests to be performed during startup of fuel cycle 2.

The reactor core for fuel cycle 2 is composed of 2/3 General Electric fuel assem-blies and 1/3 Exxon fuel assemblies. These tests were performed on January 31, I 1987. A pre-test meeting was held on January 30, 1987 and a post-test meeting  !

was held on' January 31, 1987. The staff's meeting and trip report is enclosed.

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l The tests indicated that the reactor is more stable than predicted by the pre- j test Exxon calculations in the low core coolant flow region (27% to 45i of '

rated core coolant flow). The licensee plans to submit an application for  ;

license amendment based on these test results to relax the thermal-hydraulic stability boundaries in the GGNS-1 Technical Specifications. The staff recom-mends that an application to change the Technical Specifications should address

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stability for end of core life operating conditions.

/s/

Lester L. Kintner, Project Manager Project Directorate II-2 Division of Reactor Projects-I/II

Enclosure:

As stated cc w/ enclosure:

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Mr. Oliver D. Kingsley, Jr.

System Energy Resources, Inc. Grand Gulf Nuclear Station (GGNS) l cc: l Mr. Ted H. Cloninger Mr. C. R. Hutchinson l Vice President, Nuclear Engineering GGNS General Manager t and Support System Energy Resources, Inc.

System Energy Resources, Inc. ]

Post Office Box 756  !

Post Office Box 23054 Port Gibson, Mississippi 39150 Jackson, Mississippi 39205 l 1

Robert B. McGehee, Esquire The Honorable William J. Guste, Jr.

Wise, Carter, Child, Steen and Caraway Attorney General P.O. Box 651 Department of Justice Jackson, Mississippi 39205 State of Louisiana Baton Rouge, Louisiana 70804 Nicholas S. Reynolds, Esquire Bishop, Liberman, Cook, Purcell Office of the Governor and Reynolds State of Mississippi 1200 17th Street, N.W. Jackson, Mississippi 39201 Washington, D. C. 20036 Attorney General Mr. Ralph T. Lally Gartin Building Manager of Quality Assurance Jackson, Mississippi 39205 Middle South Utilities System Services, Inc.

P.O. Box 61000 Mr. Jack McMillan, Director New Orleans, Louisiana 70161 Division of Solid Waste Management Mississippi Department of Natural Mr. John G. Cesare Resources Director, Nuclear Licensing and Safety Bureau of Pollution Control System Energy Resources, Inc. Post Office Box 10385 P.O. Box 23054 Jackson, Mississippi 39209 Jackson, Mississippi 39205 Alton B. Cobb, M.D.

Mr. R. W. Jackson, Project Engineer State Health Officer Bechtel Power Corporation State Board of Health 15740 Shady Grove Road P.O. Box 1700 Gaithersburg, Maryland 20877-1454 Jackson, Mississippi 39205 Mr. Ross C. Butcher President Senior Resident Inspector Claiborne County Board of Supervisors ,

U.S. Nuclear Regulatory Comission Port Gibson, Mississippi 39150 Route 2, Box 399 Port Gibson, Mississippi 39150 Regional Administrator, Region II U.S. Nuclear Regulatory Commission 101 Marietta Street, N.W., Suite 2900 Atlanta, Georgia 30323 Mr. James E. Cross GGNS Site Director System Energy Resources, Inc.

P.O. Box 756 Port Gibson, Mississippi 39150

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TRIP REPORT From L. PHILLIPS I

STABILITY EVALUATION O'F THE GRAND GULF 1 CYCLE 2 CORE

1.0 BACKGROUND

I The staff Safety Evaluation for Grand Gulf Unit 1 Reload 1 (Cycle 2) provided for a change to technical specification operating limits relating to core stability. The new limits are based on safety analyses using Exxon methodology for the Exxon fuel reload, and are more restrictive than the previous power flow map which defined the acceptable regions for stable operation as recomended in General Electric SIL 380. Because of an apparent discrepancy in vendor (Exxon and GE) methods for predicting the onset of core instabilities and because the licensee desires to revert to the GE SIL 380 operating boundaries (or better), the licensee agreed to perform stability tests during early Cycle 2 operation. The staff agreed to support .these tests using our Oak Ridge National Laboratory (ORNL) stability consultants to monitor the core stability with noise analysis techniques. As part of our FY87 technical assistance program, ORNL has developed an on line stability measurement system based on an algorithm which analyzes the neutron noise  !

obtained from a single APRM signal input to a personal computer. The objective of the staff /ORNL effort was:

l l (1) confirm that the technical specification boundaries for stable operation

) are suitably conservative.

(2) obtain the necessary data to properly evaluate the expected request for j

amendment to modify the power / flow operating boundaries for actions to j

assure core stability.

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(3) obtain additional benchmark data for validation of the on line system to '

qualify it for use by licensees to detect the onset of core instability, and j (4) obtain data in high decay ratio operating regions to support the evaluation of predictive methods for thermal-hydraulic instability.

2.0 TRIP REPORT On the evening of 1/30/87, I met in Jackson, Mississippi with Yosi Balas of System Energy Resources, Inc., and other members of the Grand Gulf engineering staff, members of the Exxon staff., R. G. Bernhard of NRC Region II, and D. N.

Fry and Jose March-Leuba of the ORNL staff to discuss the schedule and 3

procedures for stability tests to be performed the next morning at Grand Gulf Unit No. 1. ORNL had completed installation of the test monitoring equipment and the tests were to begin early the next morning. We discussed the planned test points on the power / flow map and the order of testing. It was expected that the least stable operating point would be TP6 which was to be monitored with both recirculation pumps at slow speed and with the flow control valves in minimum flow position. On line decay ratios were to be obtained during the tests, using the on line stability measurement system. In addition, ORNL was to record noise data from APRM C, Narrow Range Pressure LPRM 18-51 A, and Core Plate Pressure Drop in order to perform a complete offline analysis after the tests were completed.

On the morning of January 31, 1987, after some operational delays the tests were commenced and performed as planned. It soon became evident that the reactor was much more stable than expected based on the pre-test Exxon calculations. The least stable test point (TP6) was achieved at 11:30 AM at 44 percent power and 27 percent flow. The stability decay ratio measured by the on line system was approximately 0.41.

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l After completion of testing at about 2:00 PM, a meeting was held with the plant staff to discuss test results and future plans. The licensee indicated a desire to get an early technical specification change to liberalize the detect and suppress region of the power / flow map. I expressed satisfaction with the results and indicated that the staff would expedite a technical specification change justified by the test results. However, as indicated prior to the test, the justification would also need to address End of Cycle (EOC) operating conditions and explain the apparent deficiency in the Exxon l

predictive calculations versus the measured core stability decay ratio. Any l

request for less restrictive operating boundaries than those recommended by GE SIL 380 would require a much more rigorous justification of the predictive calculation results.

Yosi Balas (System Energy Resources, Inc.) indicated that the licensee expected to submit an early technical specification change request based on GE SIL 380. It was expected that an additional change would be submitted at a later date to further relax the stability boundaries after Exxon developed 1 further justification for the adequacy of their predictive results.

The staff. requested that the licensee provide core cross section data and other inputs being developed by Exxon to facilitate LAPUR audit calculations by ORNL in support of the anticipated technical specification change requests.

Figure 1 is a power / flow map with stability test points indicated on it. l Table 1 is a tabulation of on-line test results obtained by ORNL. Table 2 is I o La'uuloiiva of final test results based on the ORNL "in house" analysis of all the available data.

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5 Table 1. Online results of Grand Gulf-1 stability tests (1/31/87).

ASYMPTOTIC DECAY RATIO OSCILLATION TEST MON POWER FLOW FREQUENCY

' POINT TIME  %  % RANGE BEST ESTIMATE (Hz)

TP0 07:47 100 103 .08 - .12 .09 +/- .03 .65

. TPA --

67 53 .15 - .26 .20 +/- .06- .53 TP2 10:46 62 45 .23 - .30 .26 +/ .04 .47 TPS 11:23 44 27 .36 - .42 .41 +/ .04 .37 TPB 11:55 46 30 .20 - .37 .31 +/ .11 .36 TP4 12:45 59 39 .22 - .36 .30 +/- .08 .45 TP1 13:15 52 39 .13 - .35 .28 +/- .15 .47 Note:

(a) Time, power, and flow are taken from the MON computer printouts.

(b) Test point TPA does not have a corresponding MON printout.

(c) Test point TP6 was not properly analy=ed online due to transient reactor conditions.

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Table 2.

Results of complete analysis of Grand Gulf-1 stability tests (1/31/87).

TEST MON POWER ASYMTOTIC DECAY RATIO OSCILLATION FLOW POINT TIME  %  % FREQUENCY RANGE BEST ESTIMATE (Hz)

TP0 07:47 100 103 .08 - .12 TP2 10:46 62 .09 +/- .03 .65 45 .24 .34 TP6 11:23 44 27

.28 +/ .07 .47

.35 - .40 .38 +/- .03 TPB 11:55 46 30 .35 - .40

.37 TP4 12:45 59 .37 +/- .03 .40 39 .30 - .37 TP1 13:15 52 39

.33 +/- .07 .44

.13 - .35 .28 +/- .15 .47 Note:

(a) Time, power, (b) Test point TPA and flow are taken from the MON computer printouts.

analyzed. was not recorded on tape, and it has not been I

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3.0 pRESEPT STATUS AND RECOMMENDATIONS It is our understanding that the expected licensee request for a technical specification change has been delayed pending resolution of Advanced Nuclear Fuels Corporation (formerly Exxon) . calculation results.

ANF continues to predict an unstable core at EOC conditions. ORNL has received the ANF core data ano has also performed calculations (using LAPUR) for EOC. ORNL also '

obtains high decay ratios (greater than 0.90), though less than predicted by j Exxon.

This is partially attributed to abnonnally high bottom power peaking at E00 for the Exxon fuel and the Cycle 2 projected burnup distribution.

Based on incomplete information, it appears that additional testing (EOC) may be needed to justify technical specification changes. Such tests at EOC would also presumably accomplish the staff objective to obtain benchmark data with high decay ratio operating conditions. If an amendment request is received from the licensee, the possibility for such tests should be explored. Lacking <

such data, it still appears likely that a licensee submittal providing reasonable justification (including ANF calculations) for return to GE SIL 380

( ope' rating limits could be supported by the ORNL work.

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