ML20031F573
| ML20031F573 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 10/16/1981 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Hoffman D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| References | |
| TASK-15-03, TASK-15-04, TASK-15-3, TASK-15-4, TASK-RR LS5-81, LSO5-81, NUDOCS 8110200162 | |
| Download: ML20031F573 (10) | |
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Docket No. 50-155 5
OCTI O 19gj LS05 t u... n -,, _ [, '
G Mr. David P. Hoffman Nuclear Licensing Administrator Xs Consumers Power Company 7
f 1945 W. Parnall Road Jackson, Michigan 49201
Dear Mr. HoffMan:
SUBJECT:
BIG ROCK POINT - SEP TOPICS XV-3, XV-4 In your letter dated July 15, 1981 you submitted safety assessment reports on the above topics. The staff has reviewed your assessments and our conclusions are presented in the enclosed safety evaluation reports. Our reports complete these topic evaluations for Big Rock Point.
The enclosed safety evaluations will be basic inputs to the integrated safety assessment for your facility. The assessments may be revised in the future if your facility design is changed or if NRC criteria relating to these topics are modified before the integrated assessment is completed.
Sincerely, Dennis M. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing
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BIG ROCK POIh!, SEP TOPIC XV-3 EVALUATION Loss of External Load I.
Introduction The plant is designed to accommodate loss of external load without any significant transients felt by the reactor (Ref.1). The turbine control valves close only partially and the plant transfers to house load.
During the transfer steam is rejected to the condenser through the turbine bypass valve.
If the turbine bypass valve fails to open the reactor is tripped by high neutron flux or by high pressure.
The licensee has not analyzed the loss of external load but has identified the turbine trip vithout bypass as a bounding event (Ref. 2).
II.
Evaluation In the extreme case of corplete load rejection and failure of the bypass va?ive to open, the transient is identical to the turbine trip without bypass.
Otherwise loss of external load is a less severe event.
III.
CONCLUSION Loss of external load trar.sient is bounded by the turbine trip event which i
has been evaluated and found in conformance with the criteria of SRP Section l
15.2.1 Turbine Trip l
I.
Introduction l
A turbine trip is actuated by fast closure of the turbine stop valve which i
abruptly interrupts the steam flow to the turbine.
The stop valve closes in 0.5 seconds.
The plant is designed to accommodate a turbine trip without a reactor trip by opening the turbine bypass valve.
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urbine bypass fails to open the pressure starts to increase and the reactor is scramed from high neutron flux.
Pressure increase is buffered by a steam drum which is located on the steam flow path between the reactor vessel and the turbine.
High pressure in the steam drum actuates the emergency condenser by opening a valve in each of two redundant lines which pass the steam through the emergency condenser.
If the emergency condenser fails, the steam is relieved by six safety valves.
These are large enough to pass all steam generated in the reactor even if the reactor is not tripped.
The licensee has recently reanalyzed the turbine trip event, assuming a failure of the bypass valve to open, and has presented the results in Ref. 2.
II. Evaluation The turbine trip analysis presented in Ref. i, assumes that the bypass valve fails to open.
Thus the only protective action taken into account is tha reactor trip, actuated by high neutron flux.
The codes used in the analysis are RETRAN and a modified version of COBRA-IV-I.
These have not been formally reviewed and accepted by NRC. The plant para-rreters used as code input are conservative and the assumptions made in th'e analysis are consistent with the acceptance criteria of SRP Section 15.2.1 The calculation is continued 14 seconds into the transient. The reactor;is tripped in 0.95 seconds and the pressure reaches its maximum value in'
' 8.25 seconds.
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The nonnal operating pressure of the plant is 1350 psia and the reactor vessel design pressura is 1715 psia. The calculated maximum pressure in the reactor vessel is 1445 psia and 1432 psia in the steam drum. The initial pressure transient is tenninated by the cold feedwater added to the steam drum.
It is uncertain whether the cold feedwater would condense the steam and re-duce the pressure as predicted by the calculational model. However, we have estimated that the pressure transient would be rapidly turned down by proper operation of the emergency condenser set to actuate at 1450 psia.
In case of the emergency condenser failure the safety valves would open at 1550 psia limiting the pressure well below the design pressure.
The initial steady state CPR used in the calculation (1.68) is lower than the minimum CPR calculated for the current fuel cycle.
The lowest CPR during the transient is 1.40 while the acceptance criteria for XN-2 correlation is 1.32.
A possible inaccuracy in the modelling of the feedwater mixing in the steam drum does not significantly influence the minimum CPR which occurs early in the transient.
Thus the design limits are not exceeded.
Taking into account the margin between the calculated results and the j
acceptance criteria, and based on our experience on expected BWR behavior, we l
conclude that the turbine trip event in the Big Rock Point plant is in confor-mance with the criteria of SRP Section 15.2.5.
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III. Conclusion As part of the SEP reviews for Big Rock Point, we have evaluated the licensee's analysis of the turbine trip transient (Ref. 2), against the criteria of SRP Section 15.2.1.
Based on this evaluation we have concluded that the analysis is in conformance with the present SRP criteria.
Introduction If the condenser vacuum starts to decrease the reactor is tripped at a preset condenser pressure.
The sctting for turbine trip is somewhat higher and thus the loss of condenser vacuum is expected to be a milder transient than the turbine trip without bypass.
The licensee has not analyzed the loss of condenser vacuum but has identified the turbine trip without bypass as a bounding event (Ref. 2).
II.
Evaluation In the extreme case of sudden loss of condenser vacuum or in the dhse of failed reactor t.p at increased condenser pressure the transient is identical to the turbine trip without bypass.
Otherwise loss of condenser vacuum is a less severe event.
III.
Conclusion The loss of condenser vacuum transient is bounded by the turbine trip which has been evaluated and found in conformance with the criteria of SRP Section 15.2.1.
Closure of Main Steam Isolation Valve I.
Introduction Big Rock Point has only one steam line, and ther~e is a single isolation
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valve in that line. The isclation valve closes very slowly, with a closure time of 40 seconds while the tLrbine stop valve closes in 0.5 s'econds.
The reactor is tripped directly by isolation valve position switches
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The licensee has not analyzed the closure of the main steam isolation valve but has identified the turbine trip without bypass as a bounding event (Ref.2)
II. Evaluation Closure of the main steam isolation valve transient is tenninated by reactor trip from isolation valw position before the reactor power or steam pressure has increased.
the direct trip signal fails the reactor is tripped from the high power or the high pressure.
In this case the transient is much slower and thus less severe than the turbine trip without bypass.
III. Conclusion Closure of main steam isolation valve is bounded by the turbine trip event which has been evaluated and found in conformance with the criteria of SRP Section 15.2.1.
Steam Pressure Regulator Failure I. Introduction The steam line pressure is normally maintained at a constant value by the pressure regulator which positions the turbine control val'ves without i
l regard to the generator load.
If the pressure regulator fails and starts to inadvertantly close the control valves, the increased pressure is sensed by two independent pressure sensors which start to open the turbine bypass valve. The event induces only a mild transient in the core.
l The licensee has not analyzed the steam pressure regulator failure but has l
identified the turbine trip without bypass as a, bounding event (Ref.2).
II. Evaluation In :Se most limiting case, full closure of the control valves at maximum speed and failure of the bypass to open, the event would be similar to the
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turbine trip without bypass. Otherwise steam pressure regulator failure is a less severe evznt.
III.
Conclusion The steam pressure regulator failure ir, bounded by the turbine trip event which has been evaluated and found in conformance with the criteria of SRP Section 15.2.1 O
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LOSS OF NON-EMERGENCY A-C POWER TO THE STATION AUXILIARIES I. Introduction The plant is designed such that a loss of load can be sustained without causing reactor trip and trip of the turbine. Thus a loss of all offsite power will not necessarily cause a loss of station power, provided the turbine bypass and the turbine generator function as intended.
Even if they don't it is probable that the core power has started to decrease at the moment of tL: loss of all non-emergency A-C power.
A sudden complete loss of aon-emergency A-C power to the station auxiliaries will result in a turbine trip.
This event differs from a spurious turbine trip evaluated under topic XV-3 because with loss of jnon-emergency A-C power recirculation flow and feedwater flow will also be lost, i
The licensee has recen'.ly reanalyzed the loss of non-emergency A-C power event i
and has presented the results in Ref. 2.
D II. Evaluation The loss of non-emergen.cy A-C pawer to the station auxiliaries analysis, presented in Ref. 2, assunes that the bypass valve fails to open.
No direct reactor trip is y
assumed from loss of power but the reactor is tripped from high steam drum pressure.
The model and tho codes used in the analysis are the same ones used for the turbine trip analysis evaluated under topic XV-3.
The plant parameters used as code input are conservative and the assumptions made in the analysis are consistent with the acceptance criteria of SRP Section 15.2.1.
The calculation is continued for 6.6 seconds into the transient. At this time the i
pressure in.the steam drum has increased to 1450 psia which is actuation pressure of j
the emergency condenser. The reactor pressure reaches 1457 psia and further a
. increase is limited by the emergency cond nser.
As a backup there are six safety valves, set to open between 1550 and 1600 psia. Thus the pressure is limited well below the reactor vessel design pressure,1715 psia.
The core power starts to decrease rapidly at the beginning of the transient because of decreasing recirculation flow. At the end of the calculation the reactor has been tripped and the power has decreased to the decay heat level.
The decrease in CPR during the transient is negligible and thus the fuel design limits are not exceeded.
III. Conclusion As part of the SEP review for Big Rock Point, we have evaluated the licensee's analysis of the turbine trip transient (Ref. 2), against the criteria of SRP Section 15.2.1.
Based on this evaluation we have concluded that the analysis is in conformance with the present SRP criteria.
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REFERENCES 1.
Final Hazards Sumary Report for Big Rock Point Plant, November 14, 1961.
2.
Letter from Robert A. Vincent, Consumers Power Company, to Dennis Crutchfield NRC,
Subject:
Docket 50-155-License DPR-6-Big Rock Point Plant-SEP Design Basis Event Topics XV-1, XV-3, XV-4, XV-5, XV-7, and XV-9, dated July 15, 1981.
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