ML20052C085
| ML20052C085 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 04/30/1982 |
| From: | Bordine T CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.B.1, TASK-TM NUDOCS 8205040349 | |
| Download: ML20052C085 (10) | |
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.?e Consumers Power Company Generes othces: 1945 West Parnail Road. Jackson, MI 49201
- 1517) 788 0550 N
April 30, 1982
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Dennis M Crutchfield, Chief s\\
Operating Reactors Branch No 5 N
m Nuclear Reactor Regulation US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT - RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION, REACTOR COOLANT (RCS) VENTS, NUREG-0737 IfEM II.B.1 By letter dated February 25, 1982, the NRC requested additional information pertaining to NUREG-0737 Item II.B.1, Reactor Coolant System (RCS) Vents for
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the Big Rock Point Plant. The attachment to this letter provides Consumers l
Power Company's specific responses to the 10 questions contained in the letter of February 25, 1982 dealing with the Reactor Coolant System at the Big Rock Point Plant.
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Thomas C Bordine Staff Licensing Engineer CC Administrator, Region III, USNRC NRC Resident Inspector-Big Rock Point Y
Attachment
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4 ADDITIONAL IhTORMATION REACTOR COOLANT SYSTEM (RCS) VENTS NUREG-0737 ITEM II.B.1 Big Rock Point Plant nu0482-0028bl42
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ATTACHMENT RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REACTOR COOLANT SYSTEM (RCS) VENTS 1.
Besides the reactor coolant system, identify any other systems, required to maintain adequate core cooling, in which the collection of a large amount of noncondensible gas would cause the loss of function of these systems. For any identified systems, provide information concerning the capability of remote venting of these systems to satisfy the requirements of NUREG-0737 Item II.B.I.
Response
The reactor vessel is continuously vented to the steam drum, thus, a collection of noncondensible gas in the reactor vessel is not possible.
The gas, if any, would collect in the emergency condenser which is the high point of the system. There is a remote chance of having to rely on the emergency condenser for heat removal under conditions where gas may be generated, therefore, vents are being installed on the tube side of the emergency condenser. No other systems requiring venting have been identified.
2.
The following items apply to the portions of the RCS high point vents that form a part of the reactor coolant pressure boundary, up to and including the second normally closed valve (reference (NUREG-0737 Item II.B.1 Clarification A.(7)):
Your design description for the RCS high point vents states that the a.
valves will be nuclear certified, Class 1.
Verify that the piping, valves, components, and supports are classified Seismic Category I and Safety Class 1.
Response
The Big Rock Point Plant RCS high point vent system is being designed and procurement is being completed. Most of the installation is complete and analysis to support the as-built condition is being conducted. For purposes of inspection and testing, the system is considered ASME Code Class 2.
Although the system constitutes part of the RCS pressure boundary, it is considered Class 2 based on the nominal three-quarter inch pipe diameter. The design and procurement associated with the system has been conducted as that of a replacement per the ASME Code Section XI IWA 7110 and 7210. The final design will consider Safe Shutdown Earthquake (SSE) loadings as evaluated to Service Level D stress limits. The final design evaluation is awaiting the determination of an appropriate seismic base response spectra for the Big Rock Point Plant site. The analysis will be based upon ANSI B31.1 with the inclusion of a 2.4 S faulted stress allowable.
nu0482-0028c142
RCS Vents, Item II.B.1 2
Big Rock Point Plant b.
Describe the instrumentation that has been provided to detect and measure RCS high point vent isolation valve seat leakage (reference Appendix A to 10 CFR Part 50, General Design Criterion 30).
Response
No specific leak detection hardware is contemplated or deemed necessary for the high point vent system. Three sets of flanges on each of the separate vent systems will be installed to facilitate system inspection and flushing. An isolation valve between each of the solenoid valve sets will also be included for system inspection and maintenance of these valves.
In addition, a visual inspection of the emergency condenser deck area each shift will help ensure detection of high point vent valve seat leakage.
c.
Verify that the materials of construction will be fabricated and tested in accordance with SRP Section 5.2.3, " Reactor Coolant Pressure Boundary Materials."
Response
Design of the RCS high point vent system will be per ANSI B31.1.'
The fabrication of the system will ensure that the design req ~uirements are met.
Procurement will be made per Section XI subsections which refer to original plant system and component specifications. Testing of the system before operation will be in accordance with ASME Code Class 2 requirements.
d.
Demonstrate that internal missiles and the dynamic effects associated with the postulated rupture of piping will not prevent the essential operation of the RCS high point vent (ie, at least one vent path remains functional) (reference Appendix A to 10 CFR Part 50, General Design Criterion 4).
Response
The design of the RCS high point vent system includes two separate essentially identical pipe routings attached to each of the six-inch l
steam supply lines which run from the main steam header to emergency condenser. The systems are therefore redundant. The physical configuration of the various piping systems supported in the very open area on the emergency condenser deck make damage of either of the high point vent piping systems from other piping systems or components highly l
unlikely. The location of the piping on the northwest corner of the deck offers very little target to other piping systems or their potential missile components.
3.
Verify that the following RCS high point vent failures have been analyzed and found not to prevent the essential operation of safety-related t
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'nu0482-0028c142 i
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i RCS Vents, Item II.B.1 3
Big Rock Point Plant systems required for safe reactor shutdown or mitigation of the consequences of a design basis accident:
a.
Seismic failure of RCS high point vent components that are not designed to withstand the safe shutdown earthquake.
Response
Due to the nature of the high point vent piping design, all structurally attached piping will be subjected to seismic design. Much of the piping will be analyzed and supported under the auspices of the SEP Topic III-6 seismic qualification program. Much of the piping which will be seismically evaluated subsequent to high point vent analysis will be evaluated to ensure that the assumptions (such as boundary conditions for decoupling) associated with the high point vent analysis are met.
The analysis of high point vent valve components will include a total acceleration limit of 3 gs in either horizontal direction and 2 gs in the vertical.
b.
Postulated missiles generated by failure of RCS high point vent components.
Response
The large solenoid valves associated with the high point vent system are supported directly by structural steel columns. The piping does not support tiiem. These large valves are not credible missiles. Based upon the proposed design, the only conceivable missiles which could possibly be postulated are the small handwheels on the normally open valve sets upstream of the solenoid valves. Because of the small size of the handwheels and their distance from safety related equipment, no failures from RCS missiles are judged credible.
c.
Fluid sprays from RCS high point vent component failures. Sprays f rom normally unpressurized portions of the RCS high point vent that are Seismic Category I and Safety Class 1, 2, or 3 and have instrumentation for detection of leakage from upstream isolation valves need not be considered.
Response
Simply because of the location of the high point vent system very high up in containment, no deleterious effects of the fluid sprays can be anticipated.
It is noted that the system discharge is at an elevation of approximatley six feet below the highest elevation of the enclosure sprays. The open nature of the containment area at this high elevation ensures good spray mixing and precludes any damage to other safety related equipoment, systems or components.
4.
Describe the design features or administrative procedures, such as key locked control switches or removal of power during normal operation, that nu0482-0028c142
RCS Vents, Item II.B.1 4
Big Rock Point Plant will be employed to prevent inadvertent actuation of the RCS high point vent (reference NUREG-0737 Item II.B.1 Clarification A.(7)).
Response
The circuit breakers for the vent valves, located in the electrical equipment room, will be left open during normal operation.
5.
Demonstrate, using engineering drawings (including isometrics) and design descriptions as appropriate, that the RCS high point vents discharge into areas:
That provide good mixing with containment air to prevent the a.
accumulation or pocketing of high concentrations of combustible gas.
Response
The vent. discharge on the highest floor level in containment directly a.
into the containment atmosphere. This location should provide good mixing with containment air.
Even assuming no mixing, the only accumulation of gas can be at the top of the sphere. This does not present a hazard as there is no equipment at all in the top of the sphere, therefore there are no ignition sources present.
b.
In which any nearby structures, systems, and components essential to safe shutdown of the reactor or mitigation of a design basic accident are capable of withstanding the effects of the anticipated mixtures of steam, liquid, and noncondensible gas discharging from the RCS vent system (reference NUREG_0737, Item II.B.1 Clarification A.(9)).
Response
Because of the location, no structures, systems, or components essential to safe shutdown of the reactor or mitigation of a design basis accident would be adversely affected by a discharge from these vents.
6.
Verify that operability testing of the RCS high point vent valves will be performed in accordance with subsection IWV of Section XI of the ASME Code for Category B valves (reference NUREG-0737 Item II.B.1 Clarification A.(11)).
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Response
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Surveillance testing will be performed to meet the requirements for Category B valves in subsection IWV of Section XI of the ASME Code.
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.7.
Submit operating guidelines for use of the RCS vent system including the following:
a.
Guidelines to determine when the operator should and should not manually initiate venting, and information and instrumentation required for this determination (reference NUREG-0737, Item II.B.1 nu0482-0028c142
RCS Vents, Item II.B.1 5
Big Rock Point Plant Clarification A.(2)).
The guidelines to determine whether or not to vent should cover a variety of reactor coolant system conditions (eg, pressures and temperatures). The effect of the containment hydrogen concentration on the decision to vent or to continue venting should be addressed considering the balance between the need for increased core cooland and decreased containment integrity due to elevated hydrogen levels.
b.
Guidelines for operator use of the vents, including information and instrumentaion available to the operator for initiating or terminating vent usage (reference Position (2)).
Response
We have two specific uses for the vents at Big Rock Point. One is during the time the ECS is being used for decay heat removal and sufficient gases have collected to impair the heat removal capability. The other use is in a case when pressure is rising to the setpoint of the safety relief valves - the vents can then be used to relieve pressure as they will be more reliable than relief valves.
In either case, the use of the vents is based on the pressure / temperature of the primary system.
If the pressure starts to rise, the guidelines will instruct the operators to check that adequate cooling water is available in the shell-side of the ECS and the inlet and outlet valves are still open.
If these conditions are satisfied but pressure continues to rise, venting may be required.
One tube bundle would then be vented until pressure begins to fall. The vent would be closed and pressure monitored to ar.sure venting was successful. The process is repeated as required Hydrogen is not considered a problem at Big Rock Point. See submittals dated May 4, 1979 and October 30, 1979 and the response to number 5-a.
Required operator actions in the event of inadvertent opening, or c.
failure to close af ter opening, of the vents including a description of the provisions and instrumentaiton necessary to detect and correct these fault conditions (reference Position (2) and Clarification A.(2)).
Response
Inadvertent opening, or failure to close after opening, of the vents is l
the same as a small steam line break. The operator may attempt to close the ECS inlet and outlet valves to isolate the open line. In any case,
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existing procedures address small steam line breaks.
8.
Verify that the 125 VDC Distribution Panel and the 120 VAC I&C Distribution Panel lY that supply the RCS high point vent valves are emergency power sources (reference NUREG-0737 Item II.B.1 Clarification l
A.(8)).
Response: The 125 VDC Distribution Panel and the 120 VAC I&C Distribution Paral 1Y are emergency power sources.
nu0482-0028c142
O RCS Vents, Item II.B.1 6
Big Rock Point Plant 9.
Verify that positive valve position indication is provided for the RCS high point vent valves (reference NUREG-0737 Item II.B.1 Clarification A.(5)).
Response
Positive valve position indication is provided.
10.
Provide a current design description and drawings of the RCS high point vents promised in your letters responding the NUREG-0737, from David P Hoffman (Consumers Power Company) to Director, Nuclear Reactor Regulation, dated December 19, 1980 and July 9, 1981.
Response
The valves are nuclear certified Class II solenoid valves. The vent capacities have been recalculated with the following results:
Hydrogen at 1000 psia, 544.6 F 1.5 RCS Vol/Hr Hydrogen at ATM pres, 100*F 0.35 RCS Vol/Hr j
The design has been modified to include. manual isolation valves upstream of the solenoid (two in series in each line) and an isolation valve between the solenoids with flange connections around them to allow flushing and leak testing. Revised design drawings are attached.
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