ML13308A191
| ML13308A191 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 10/05/1982 |
| From: | Rood H Office of Nuclear Reactor Regulation |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8211030458 | |
| Download: ML13308A191 (15) | |
Text
Docket No.:
50-361 LICENSEES: South California.Edison Company (SCE)
San Diego Gas and.Electric Company City of Anaheim, California City of Riv6rside, California FACILITY:
San Onofre Nuclear Generating Station, Unit 2
SUBJECT:
SUMMARY
OF MEETING TO DISCUSS NATURAL CIRCULATION TESTS On September 6-9, 1982, members of the NRC staff met with SCE at the San Onofre site to discuss the above subject and to observe natural circulation tests being conducted at low power. Enclosed is a Trip Report describing the meetin4 and listing the attendees. The Trip Report was prepared by C. Liang of the NRC staff.
Harry Rood, Project Manager Licensing Branch No. 3 Division of Licensing
Enclosure:
As stated cc:
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/82 8211030458 821005 PDR ADOCK 05000361 OFFICIAL RECORD COPY USGPO: 1981-335-960 A
San Onofre Mr. Robert Dietch Vice President Southern California Edison Company 2244 Walnut Grove Avenue P. 0. Box 800 Rosemead, California 91770 Mr. Gary D. Cotton Mr. Louis Bernath San Diego Gas & Electric Company 101 Ash Street San Diego, California 92112 cc:
Charles R. Kocher, Esq.
Mr. Mark Medford James A. Beoletto, Esq.
Southern California Edison Company Southern California Edison Company 2244 Walnut Grove Avenue 2244 Walnut Grove Avenue P. 0. Box 800 P. 0. Box 800 Rosemead, California 91770 Rosemead, California 91770.
Mr. Henery Peters Orrick, Herrington.& Sutcliffe San Diego Gas & Electric Company ATTN:
David R. Pigott, Esq.
P. 0. Box 1831 600 Montgomery Street San Diego, California 92112 San Francisco, California 94111 Ms. Lyn Harris Hicks Mr. George Caravalho Advocate for GUARD City Manager 3908 Calle Ariana
~City-of-SaClemente--
San Clemente, California 92672 100 Avenido Presidio San Clemente, California 92672 Richard J. Wharton, Esq.
University of San Diego School of Law Alan R. Watts, Esq.
Environmental Law Clinic Rourke & Woodruff San Diego, California 92110 Suite 1020 1055 North Main Street Phyllis M. Gallagher, Esq.
Santa Ana, California 92701 Suite 222 1695 West Crescent Avenue Lawrence Q. Garcia, Esq..
Anaheim, California 92701 California Public Utilities Commission 5066 State Building Mr. A. S. Carstens San Francisco, California 94102 2071 Caminito Circulo Norte Mt. La Jolla, California 92037 Mr. V. C. Hall Combustion-Engineering, Inc.
Charles E. McClung, Jr., Esq.
1000 Prospect Hill Road Attorney at Law Windsor, Connecticut 06095 24012 Calle de la Plata/Suite 330 Laguna Hills, California 92653 Mr. S. McClusky Bechtel Power Corporation Resident Inspector, San Onofre/NPS P. 0. Box 60860, Terminal Annex c/o U.S. Nuclear Regulatory Commission Los Angeles, California 90060 P. 0. Box 4329 San Clemente, California 92672 Regional Administrator-Region V/NRC 1450 Maria Lane/Suite 210 Walnut Creek, California 94596
San Onofre Unit 2 Trip Report Introduction The tests required by TMIAP Item i.G.1 (Low Power Natural Circulation tests) were witnessed by members of RSB, PTRB and IE. In addition, the RSB contractor, BNL, attended the tests and later meetings since they will be involved in the review of the later tests aimed at the demonstration of compliance with BTP RSB 5-1.
Representatives from SCE licensing and operations, and CE technical support were also present to witness and evaluate the tests. The tests were observed from the Technical Support Center (TSC) which overlooks the units 2 and *-
Control Room. The TSC has a critical functions monitor (CFM) which provides computer output, graphics and various video displays of the plant parameters. Of particular help was a member of the SONGS unit 2 startup crew who pointed out the control boards, important parameters and system aspects during the tests. The overall success of the NRC visit is a direct consequence of the extensive efforts of Mr. Fred Nandy, SCE Licensing Engineering.
The tests were conducted on Monday evening September 6 and-Tuesday morning. The meeting to discuss the tests SCE intends to perform to show compliance with BTP RSB 5-1 was held on Wednesday, September 8.
The I.G.1 tests and the subsequent meeting are discussed below.
Tests The tests were basically designed to demncstrate natural circulation.
Fission heat (i.e., a critical reactor) was used as the source of
simulated decay heat. The auxiliary feedwater system and steam generator atmospheric dump valves were used for the removal of this energy. There were three basic tests which were sequentially performed.
Each is described below, along with the observed results.
- 1.
Natural Circulation - Test Al -
This test is designed to demonstrate natural circulation with the reactor critical at about 3% power, the RCS at normal pressure (2250 psig) and both steam generators' atmospheric dump valves (ADVs) operating to remove decay heat. All four reactor coolant pumps are initially operating and the test is initiated with the simultaneous trip of all four reactor coolant pumps. The low RCS flow protective system trips are bypassed, hence a scram will not occur, and the reactor power is maintained at about 3%. The AT between hot and cold leg was increasing as natural circulation developed. (A handout, received prior to the tests, predicted a 450FAT stabilizing at 8.3 minutes.)
Results - This test was initially attempted on Sunday evening, September 5, however an unanticipated reactor scram occurred as a result of the reactor protective system low flow trip signal not be fully bypassed*.
- A circuit feature in the protective system that trips the reactor when the pump rotation completely stops was overlooked. When coastdown ended at about 8 - 9 minutes after the RCPs were tripped, a reactor scram occurred.
-3 After SCE determined the cause of the reactor trip, the low flow trip was fully bypassed and the test was again attempted on Monday evening, September 6. At 12:00 midnight, all four RCPs were simultaneously tripped, natural circulation was verified by an increase in AT and the stabilization of THOT, and a constant TCOLD. The temperature difference across the core went from an initial of <10F (with RCPs operating) to about 230 F during natural circulation. The reactor power was initially about 3%, however, as a result of the increase in TAVE (THOT increased, but TCOLD remained essentially-constant), the reactor power decreased to about 1%. (resulting in a less-than-predicted-AT) It was observed that as the operators made minor changes in the position of the
'manually controlled ADV, the cold leg temperature on that steam generator was rapidly affected. The system pressure and level remained constant at about 2250 psig and 33%, respectively.
The operators attempted to raise reactor power by withdrawing the Group C control rods a small amount. The power was initially about 1 1/2%. After the rods were withdrawn, the system temperatures
.increased and an insurge into the pressurizer was observed by an indication of pressurizer level increase.
As the pressurizer pressure increased, the operators opened the auxiliary spray valve, however the pressure went from an initial value of about 2150 psig to over 2250 psig, in about 1-2 minutes and continued to increase.
The operators, trying to avoid the high pressurizer pressure scram at 2380 psig, started a second then a third charging pump to obtain maximum auxiliary spray flow (about 130 gpm), however pressure
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continued to rise to a maximum of about 2340 psig before dropping.
When pressure did turn and begin to drop, the rate was significant.
The minimum RCS pressure was about 2100 psig before the pressure drop was slowed by securing the charging pumps.
It should be noted that this observed pressure excursion was brought on by an attempt to raise reactor power, a situation not expected to occur during natural circulation situation. However, the response df the system to a temperature change whether or not it is fission power induced, showed that pressure response can be rapid during natural circulation. Also,.the delay time associated with the use of auxiliary spray may have been due to the fact that the normal spray valve was open during some of the time when the auxiliary spray valve was open, thus providing a path that bypassed the pressurizer. After the tests, the operators commented that this flow path actually provided a means of controlling the amount of auxiliary spray flow since the auxiliary spray valve cannot be throttled the charging pumps are constant speed pump and only the main spray valve can be throttled.
- 2.
Reduced Pressure Ratural Circulation'- Test A2 - The test was designed to demonstrate that natural circulation could be maintained for a limited period of time without the use of the pressurizer heaters, and to demonstrate the rate of RCS depressurization during natural circulation with 1) loss of pressurizer heaters, and 2) loss of pressurizer heaters and using the auxiliary spray valve. The plant is initially at 1 to 3% power under natural circulation, both steam generators in operation 0@
dumping steam to the atmosphere using their ADVs and with the auxiliary feedwater system supplying feedwater. The test is initiated by turning off all pressurizer heaters.
Results - After all pressurizer heaters were turned off, the pressure began a slow decrease as the pressurizer cooled. However, because the SONGS-2 CVCS system has constant charging rate and a variable letdown rate that depends on the pressurizer level, the rate of pressure drop was not smooth. As the pressurizer cooled, the liquid contracted and pressure dropped. The pressurizer liquid contraction caused a corresponding level decrease which resulted in a decrease in 'letdown flow. As charging flow exceeded letdown
-flow, an insurge occurred that raised pressurizer level and acted to maintain or raise pressurizer pressure. This phenomenon could most easily be observed by noting the pressurizer surge line temperature which would drop as the insurge occurred. The overall rate of pressurizer pressure decrease during the first phase was very slow, about 60 psi per hour. The second phase began with the initiation of auxiliary spray to reduce RCS pressure. During this part of the test,-with only a single charging pump supplying auxiliary spray, pressure was observed to smoothly drop at about 20 psi per minute. The pressurizer level was not observed to significantly change
- 3.
Reduced Heat Removal Capacity - Test A3 -
The test was designed to demonstrate natural circulation with the main steam, feedwater, and blowdown of one steam generator isolated. The test commences with
the reactor initially critical at about 1% power, all RCPs secured, SG blowdown secured, and both steam generator ADVs in operation and feed flow from the auxiliary feedwater system. The test is initiated by simultaneously securing feedwater flow and ADV flow from one. steam generator.
Results - The test was initiated from only 1 1/2% power instead of 3% power since the power at the end of test A2 was only at 1 1/2%.
The SCE test supervisor consulted with CE and they agreed that 1 1/2% power was an acceptable power level for this test. About 1%
was called for in order to narrow the TH-TC spread. The SCE test supervisor and CE representative agreed that feed flow could not be continuously controlled from the control room at low flow rates, and that an "on-and-off" approach should be used to avoid stationing an operator locally at the feed control valves (bypass?)
to manually control flow. The SCE and CE representative agreed that the best approach for this test was the "on-and-off" approach.
When the test was actually commenced, natural circulation in the loop whose SG was isolated decreased as noted by the cold leg temperature trending towards the hot leg temperature.' The indicatedAT for the isolated SG stabilized at 160 F indicating possible isolation valve leakage and/or other heat losses from the isolated SG. The isolated steam generator pressure increased as the RCS hot leg temperature increased slightly to account for the increase in AT across the only operating steam generator. The SCE and CE representatives agreed to terminate the test before the isolated SG pressure reached the safety valve setpoint. When the
0@
- 07 isolated SG ADV was reopened, and auxiliary feed flow reinitiated, natural circulation recommenced as noted by the return of a AT across that SG, and a reduction in power from the other SG.
Mr. D. Kirsch of IE (Region V) witnessed the above described tests in the control room and found that the tests were conducted in accordance with I.G.1 requirements for Category A tests described--
in the Supplement 1 to the San Onofre SER (NUREG-0712).
Meeti no By-a letter dated April 15, 1982, the licensees submitted a test program of boron mixing and natural circulation at post-trip from 80% power, in a CE'topical report CEN-201.
Low power natural circulation tests were also included in this report. After a review of the proposed program, the staff met with SCE and CE in Bethesda on Mlay 20, 1982 to discuss the tests.
There was considerable discussion at the meeting regarding whether or not the proposed tests at 80% power will demonstrate that the plant meets the requirements of BTP RSB 5-1.
At the meeting, the staff provided the licensees with a copy of guidelines on the natural circulation test and the supporting analyses required in conformance with RSB 5-1.
At the conclusion of the meeting, the licensees agreed to provide the staff with additional information regarding how their proposed test program meets the requirements of BTP RSB 5-1.
On September 8, 1982, the staff and the RSB contractor, BNL, met with SCE and CE at San Onofre plant site to discuss the proposed boron mixing and natural circulation tests at San Onofre in compliance with RSB 5-1.
___-a-___*__*.O
-8 The licensees made a presentation describing how their proposed test program meets RSB 5-1. The following issues were discussed in the meeting.
- 1. The licensees asserted that the combination of the proposed tests identified in the CE report as Bl, B2, and B3 would satisfy the requirements of RSB 5-1. Tests B1 and B2 would be performed at a 20% power level to simulate loss of offsite power and a complete loss of AC power. Test B3 would be performed at post-trip from 80%
power level to demonstrate boron mixing and natural circulation capabilities. The staff informed the licensees that the approach of conbiningseveral different tests in regards to the compliance
-with 1.G.1 and BTP RSB 5-1 would be acceptable provided that the licensees submit sufficient justification to show that these test combinations can satisfy all the requirements of RSB 5-1.
- 2. The proposed test procedures of tests B1, B2, and 83 indicated that they all terminate at the shutdown cooling system (SCS) cut-in point. In order to demonstrate cold shutdown using SCS, the licensees agreed to perform a separate cooldown test. The licensees indicated that they may prefer to perform this cooldown tests on Unit No. 3 at a later date. The staff will evaluate the acceptability of this request.
- 3.
In test B3, the licensees proposed to use the main feedwater system during the test. The staff expressed concerns with regard to
- 1) differences in feedwater temperature effecting natural
@0
-s-
@0 circulation flow, and 2) means of estimating the total amount of condensate storage required for plant cooldown. The licensees explained that after a period of time following plant trip the main feedwater temperature is not much higher than that of the auxiliary feedwater. The slight difference in feedwater temperature will not cause a significant deviation in natural circulation phenomena.
However, the licensees have agreed to measure the amount of feedwater entering the steam generators so that the total amount of condensate required for plant cooldown can be calculated.
- 4. -
In test B3, the licensees proposed to use the non-safety grade letdown syst m during the test. The staff expressed concerns with regard to 1) the effects of utilizing the letdown system on charging fluid temperature and boron injection velocity, and 2).the possibility of delayed boron mixing due to stratification. The licensees explained that they preferred to use letdown during the natural circulation test so that they could periodically take measurements on boron concentration. In response to the staff concerns, the licensees agreed to provide additional information on why stratifications charging fluid temperature, and boron injection velocity would not significantly effect boron mixing during natural circulation. Since boron mixing is one of the most important aspects of the overall test program, the staff will carefully evaluate the licensees proposal in this regard.
- 5. In test B3, the licensees proposed to cooldown the reactor coolant system without reactor upperhead voiding. However, San Onofre 2
-1o-does not have thermocouples installed inside the vessel head for direct measurement of upperhead temperature.
Instead, voiding is indirectly predicted from pressurizer level indicators. The staff will evaluate the acceptability of this upperhead voids monitoring method.
- 6.
The staff informed the licensees that during the natural circulation test, both of the two steam generator's atmospheric steam dump valves (ADVs) may be used to release steam. However, the staff will require that the safety grade nitrogen accumulators be used during the test for operation of ADVs.
- 7.
1I test B3, the licensees proposed to use all the pressurizer heaters during the test. The staff informed the licensees that only safety grade heaters should be used during this test.
- 8. The staff informed the licensees that this test does not have to demonstrate hot standby for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> provided that the amount of condensate required to remove decay heat during these four hours has been demonstrated in a previous test, and the wate-r usage rate has been measured.
- 9.
The staff informed the licensees that two months prior to the boron mixing and natural circulation test, detailed test procedures and pretest predictions should be submitted for staff review. These pretest predictions should simulate the system transient from the plant trip to cold shutdown conditions.
In addition to the 77-.--
parameters covered in CEN-201, plots of the following parameters should be submitted.
- a. upperhead temperature vs. time
- b. charging flows vs. time
- c. heater power vs. time
- d. letdown flow vs time (if use of the letdown is permitted during the test)
- e. condensate inventory vs. time
- f. feedwater flow and auxiliary feedwater flow vs. time At the conclusion of this meeting, the staff and the licensees agreed to support the following schedule:
- 1.
Formal transmittal of SCE's position on the boron mixing and natural circulation tests during the week of September 13, 1982.
- 2.
Formal NRC response to the SCE position during the week of September 27, 1982.
- 3. Meeting during the mid-October 1982 time frame in Bethe'sda to further discuss the staff concerns.
- 4.
The licensees will submit their final commitments to the boron nixing and natural circulation test to NRC for staff review by the end of October 1982.
- 0.
MEETING AT SONGS ON NATURAL CIRCULATION TEST PROGRAM SEPTEMBER 8, 1982 LIST OF ATTENDEES Fredy Nandy SCE J.S. Iyer SCE V. B. Fisher SCE D. J. Lokker SCE W. C. Phoenix CE W. D. Bennett CE K. McQuaid CE W. C. Marsh SCE Dr. R.. Waldo SCE J. B. Droste SCE W. 0. Long NRC/PTRB C. Y. Liang NRC/RSB M. S. Lu BNL L. B. Marsh NRC/RSB
EETING
SUMMARY
Document Control (50-361).
A NRC PDR L PDR T ERA NS IC L B3 Rdg.
J. Lee Project Manager H. Rood Attorney,. 0ELD E. L. Jordon Regional. Administrator, Region V
J.. M. Taylor PARTICIPANTS (NRC):
W. 0. Long C. Y. Liang L. B. Marsh