ML19210E278
| ML19210E278 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 11/28/1979 |
| From: | Counsil W NORTHEAST UTILITIES |
| To: | Ziemann D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19210E279 | List: |
| References | |
| TASK-06-05, TASK-6-5, TASK-RR NUDOCS 7912040225 | |
| Download: ML19210E278 (5) | |
Text
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HARTFORD CONNECTICUT 06101 (203) 666-6911 c
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J November 28, 1979 Docket No.30-245 Director of Nuclear Reactor Regulation Attn:
Mr. D. L. Ziemann, Chief Operating Reactors Branch #2 U. S. Nuclear Regulatory Conmission Washington, D. C.
20555 Gentlemen:
Millstone Nuclear Power Station, Unit No. 1 SEP Topic VI-5 Combustible Gas Control In response to questions received informally from the NDC Staff, regarding SEP Topic VI-5, Combustible Gas Control, Attachment I is provided.
The responses in the attachment to this letter are based on the current method of Combustible Gas Control which is oxygen control at Millstone Unit No.1.
It is recognized that criteria evolving from TMI-2 may impact NNEC0's method for dealing with this issue; however, the attached description reflects a satis-factory method for mitigating the effects of combustible gas in the containment.
Should you have any questions, please contact us.
Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY
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. G. Counsil Vice President 1468 355 Attachment E EE 7912010
MILLSTONE UNIT NO. 1 RESPONSES TO NRC QUESTIONS ON SEP TOPIC VI-5 COMBUSTIBLE GAS CONTROL (1) NRC Question The three systems needed for combustible gas control are (1) systems to mix the containment atmosphere, (2) systems to monitor combustible gas concentrations within the containment, and (3) systems to reduce combustible gas concentrations within the containment.
For each of these three systems, provide the following information.
(a) Discuss the capability of the system to remain operable, assuming a single active failure, with or without the loss of offsite power.
(b) Discuss the capability of the system to withstand the dynamic effects, associated with a loss of coolant accic'ent, to withstand the Safe Shutdown Earthquake without loss of function, and to remain operable in the accident environment.
(c)
Discuss the codes, standards, and guides applied in the design of the systems and system components. Also, specify the functional design requirements for each component or system.
(d)
Provide piping and instrumentation diagrams of the systems.
(e) Specify the plant protection system signal (s) that actuate the systems and components.
Include a discussion of which systems or components are to be manually operated from the main control room, or from another point outside the containment and discuss the accessibility of the locatior, following an accident.
Response
A system to mix the containment atmosphere is not needed since natural convection and diffusion have been analyzed in the response to Question 6.f in Appendix B of our FTOL application and shows effective mixing is achieved.
Results of the analysis also show that oxygen concentration does not vary more than two percent throughout the containment under natural mixing conditions.
Millstone Unit No. I has an 02 analyzer and grab sample capability which are normally used to ensure Technical Specification 3.7.A.6 compliance and to test containment atmosphere prior to personnel entry. While the 02 analyzer is not designed for pressures significantly greater than atmospheric or high moisture conditions, sampling and analysis with a gas chromatigraph can be used under cur-rently analyzed post-accident conditions.
Control of combustible gas concentrations following an accident can be achieved by adding additional N2 to the containment atmosphere.
In the event that containment pressure approaches containment design pressure, containment atmosphere can be vented through the standby gas treatment system (SGTS).
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(a) Samples may be manually taken from two locations in the drywell and one location in the torus, and may be analyzed using the single gas chromato-graph (not on the emergency bus) or a portable oxygen analyzer as a backup.
Thus, samples are obtainable after a single active failure and loss of power.
The N2 system has redundant vaporizers, redundant N2 addition pathways, and redundant containment isolation valves.
Active components of the SGTS and containment isolation valves are redundant except for one air operated valve.
This valve fails open allowing venting through the SGTS.
Both the N2 addition system and SGTS are powered from emergency buses in the event of an LNP.
(b) All components of the nitrogen addition system, the SGTS, and the sampling system, except portions of the sample lines, are located outside the containment and will not be exposed to the dynamic effects of a LOCA or the accident environment.
Failure of a sample line due to pipe whip or jet impingement does not preclude obtaining a representative sample because of the previously discussed uniformity of gas concentrations.
Seismic documentation is available for all piping between the reactor building wall penetration of line 6"-AC-2 and penetrations X-26 and X-205, penetrations X-25 and X-202 and Valve V-12-10, and from HVE-5A and B up to the underground piping leading to the stack.
(c) All electrical and instrument cabling was procured to Category lE standards, containment isolation valve solenoids for the containment atmospheric sampling system were installed to IEEE-279 (1968).
Piping for the nitrogen addition system, the SGTS and the containment atmospheric sampling system was designed, manufactured and installed in accordance with ANSI B31.1.
Other equipment codes and standards are not readily available.
The functional design requirements of SGTS are in Section V-3.2.5 of the FSAR. The N2 addition system was functionally designed to purge the con-tainment volume (260,000 ft ) down to four percent (4%) 02 in four (4) hours and to provide continuous makeup of 200 - 1000 scf per day. The N2 storage vessel has a capacity of 970,000 scf and a design pressure of 64 psig.
The steam purging vaporizer has a capacity of 200,000 scfh and the makeup vaporizer has a 200 scf capacity.
(d)
Drawings 25202 - 24002 HVAC Flow Diagram Reactor & Radwaste Buildings and 25202 - 26009 Flow Diagram Atmospheric Control System (enclosed) show the N2 addition, purge exhaust, and SGTS.
(e) Containment isolation valves for the nitrogen addition systems, the SGTS and the containment atmospheric sampling system close on a containment isolation signal.
SGTS is initiated on high reactor building exhaust radiation, high refueling floor area radiation, high primary containment pressure, low reactor vessel water level, or manually from the control room. All other systems for combustible gas control except sampling are also controlled from the control room.
Containment isolation valves needed for combustible gas control can only be opened from the control room using jumpers if a containment isolation signal is present.
Samples must be manually taken in the vicinity of the standby liquid control room in the reactor building.
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. (2) NRC Question With regard to the systems that are relied on to mix the containment atmos-phere, identify the ductwork that must remain intact to mix the containment atmosphere.
Include a discussion of the design provisions that will ensure the ductwork will remain intact.
Response
Millstone Unit No.1 does not have a system to mix the primary containment post-LOCA (see response to Question 1).
(3) NRC Question For the system provided to monitor the combustible gas concentrations within the containment following an accident, provide the following information:
(a) Discuss the operating principle and accuracy of the combustible gas analyzer, and the method of readout employed (continuous or ini.armit-tent). If readout is intennittent, or samples must be taken, specify the time interval between readings or the taking of samples for analysis.
(b) Specify the locations of the multiple sampling points within the con-tainment.
(c) Discuss the capability to monitor the combustible gas concentration within the containment independent of operation of the other combustible gas control systems.
(d) Discuss the temperature limitations of the sampling gas on the analyz-ing equipment, and the effect of prolonged exposure to radiation.
Response
(a) The gas chromatograph mentioned in 1(a) above has an accuracy of +5%.
Plant procedures are being prepared that require the sampling of dry-well and torus atmospheres every two (2) hours post-LOCA.
(b) Drywell atmospheric samples can be taken from the lower level sample point and the upper level sample point adjacent to the head seal area.
There is one sample point in the torus.
(c) Sampling is completely independent of the N2 addition system or SGTS op-eration.
(d) Due to the dilution of an extremely small sample volume with argon in the gas chromatograph, temperature and radiation effects are negligible.
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(4) NRC Question In order to perfom a confirmatory analysis of the production and accumulation of combustible gases within the containment following an acci # nt, the follow-ing information is needed:
(a) The surface area and thickness of aluminum components, aluminum base paint, galvanized steel and zinc base paint.
(b) The casis (time or hydrogen concentration) for actuation of the com-bustible gas reduction system.
Specify the design flow rate and the
' low rate assumed in the analysis.
(c) The weight of the zirconium fuel cladding for Millstone Unit No.1
Response
The Millstone Unit No.1 systems used for combustible gas control are not dependent on hydrogen generation since oxygen control is utilized.
Post-acci-dent 02 and H2 curves have been generated to answer Question 6 in Appendix B to the Millstone Unit No.1 FTOL application.
Note that five percent metal-water reaction for the H2 curve was assumed per Safety Guide 7, in effect at the time. The curve also assumed an initial 02 concentration of four percent while Techrical Specification 3.7.A.6 requires a five percent maximum.
02 concentration is normally maintained below four percent during normal plant operation and a Technical Specification change to lower the limit to four per-cent was proposed to the NRC in Appendix J to the Millstone Unit No. 1 FTOL application.
The N2 addition systcm is capable of a maximum flow of 200,000 scfh which is orders-of-magnitude above the 1200 scfh required for dilution of 02 formed from radiolysi s.
N2 would be added following an accident as needed to keep 02 below five percent.
Therefore, the specific information requested in the above NRC question is not directly applicable to the current method of combustible gas control.
(5) NRC Question Describe the program for periodic operability testing of the combustible gas control systems and system components.
Discuss the scope and limitations of these tests.
Response
Containment isolation valves are tested per Technical Specifications 3/4.7A and 3/4.70. The SGTS is tested per Technical Specification 3/4.7B.
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