ML19296B839
| ML19296B839 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 02/11/1980 |
| From: | Thomas Greene Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19296B831 | List: |
| References | |
| NUDOCS 8002220233 | |
| Download: ML19296B839 (8) | |
Text
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h UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION BEFORE THE ATOMIC SAFETY AND LICENSING BOARD In the Matter of
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SACRAliENTO MUNICIPAL UTILITY
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Docket No. 50-312 (SP)
DISTRICT
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(Rancho Seco Nuclear Generating
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Station)
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NRC STAFF TESTIMONY OF THOMAS A. GREENE ON HYDR 0 GEN RECOMBINER (Board question 20)
Q.
Please state your name and your position with the NRC.
A.
My name is Thomas A. Greene.
I am a Senior Systems Engineer in the Con-tainment Systems Branch, Division of Systems Safetv, Office of Nuclear Reactor Regulation.
Q.
Is a statement of your professional qualifications attached to this testi-mony?
A.
Yes, a copy of this statement is attached to this testimony.
Q.
What contention is addressed in your testimony?
$N 8002220
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My testimony is to respond to Board Question 20 which reads:
Board Question 20 Rancho Seco, being a Babcock & Wilcox designed reactor, does not have a hydrogen recombiner which may be neces-sary in the event of an accident caused by a loss of feedwater transient and, therefore, is unsafe and en-dangers health and safety of petitioners, constituents of petitioners, and the public.
Q.
What does a hydrogen combiner do?
A.
A hydrogen recombiner is sometimes used as part of the combustible gas control system in nuclear power plants.
The recombiner's function in this application is to cause the hydrogen and oxygen gases in the con-tainment atmosphere to react chemically to form water vapor and, thus, limit and reduce the hydrogen gas concentration inside the containment building atmosphere.
Q. 'Does the Rancho Seco facility have a hydrogen recombiner?
A.
The Rancho Seco facility does not have a hydrogen recombiner.
- However, it does have a combustible gas control system which includes a hydrogen purge system.
The combustible gas control system is described in Section 6.2.4 of the Rancho Seco FSAR.
The licensee's analyses of the effective-ness of the hydrogen purge to control the hydrogen concentration in the containment building is given in Appendix 14C of the Rancho Seco FSAR.
The NRC staff evaluation of the combustible gas control system and of the
. licensee's analysis is given in Section 6.2.4 of the Safety Evaluation Report for Rancho Seco.
In addition to hydrogen purge systems, the licensee has also made arrange-ments with another utility to borrow a hydrogen recombiner should one be requested by the licensee.
Q.
Under what conditions might a combustible gas control system or hydrogen recombiner have to be used?
A.
The design basis accident to be accommodated by the combustible gas control system is a loss-of-coolant accident in which the emergency core cooling system is assumed to be in a degraded, but not total failure, condition.
Once the primary system loses its coolant, there develops a potential for hydrogen generation that could accumulate inside the containment as a result of:
(1) a chemical reaction between the fuel rod cladding and the steam resulting from vaporization of emergency core cooling water; (2) corrosion of construction materials by the alkaline spray solutions; or (3) radiolytic decomposition of the cooling water in the reactor core and in the containment sump.
The hydrogen generated by the three sources of hydrogen can be divided into that hydrogen produced over a short time period and that produced in the longer term.
The hydrogen generated by tne core metal-water reaction occurs in the short term. This is assumed to have occurred over a two-minute time period and represents approximately one volume percent hydrogen
. concentration in the containment building.
The hydrogen concentration in the containment building continues to build up over the longer time due to the other sources of hydrogen.
When the hydrogen concentration in the containment building approaches the lower flammability limit of four volume percent, the combustible gas control system is activated.
Thus, the combustible gas control system is used to control hydrogen in the longer term.
For Rancho Seco, the hydrogen concentration in the containment will not reach the lower flammability limit of four volume percent untis about 21 days after a postulated LOCA. However, the licensee has proposed to activate the hydrogen purge system at a hydrogen concentration of 3.5 volume percent, or about 13.5 days after the start of the accident.
If the licensee has a hydrogen recombiner instead of a hydrogen purge system, then the hydrogen recombiner would probably,be activated at an earlier time after the accident than the hydrogen purge system.
At TMI-2, there was a pressure pulse that occurred in the containment building at about 9-1/2 hours after the start of the accident.
This pres-sure pulse is believed to have been caused by the burning of hydrogen.
The major source of this hydrogen was the metal-water reaction of the zirconium in the reactor core. This is believed to have occurred during the period from 1-1/2 hours to about 3-1/2 hours after the start of the accident when portions of the fuel cladding reached temperatures which were high enough to allow the Zircaloy cladding to react with steam and produce the hydrogen.
Because the hydrogen was produced over a relatively short period of time, when compared to the response time of the hydrogen recombiner system at TMI, the hydrogen concetration in the containment building would have exceeded the four volume percent limit even if the hydrogen recombiners were activated and functioning.
Because these courses
]f events at Tl11-2 indicate a need for a thorough reconsideration of the Commission's design basis for the combustible gas control system, deci-sions regarding hydrogen control will probably be deferred pending the completion of a rulemaking hearing.
Q.
Would a recombiner be required to respond to a loss of feedwater transient at Rancho Seco?
A.
A loss of feedwater transient, normally, will not result in any hydrogen being produced inside the containment building.
At Three Mile Island, the feedwater transient developed into a serious loss-cf-coolant accident due to equipment failures and operator error. Since tha Three fille Island incident, tile NRC staff has taken steps to prevent a TMI-type of feed-water transient from developing into an accident in which hydrogen could be produced.
Therefore, unless a loss-of-coolant accident occurs, there is no need for a combustible gas control system since there is no mechanism for hyrdogen to be produced or released to the containment.
Q.
Why does the Rancho Seco facility have a hydrogen purge system instead of hydrogen recombiners?
A.
The licensing requirements or standards for combustible gas control systems in light water cooled power reactors are given in 10 C.F.R. Part 50.
Paragraph 50.44(b) states, in part, that for facilities for which the notice of hearing on the application for a construction permit was published on or before December 22, 1968, only a hydrogen purging system is necessary for the combustible gas control, provided the combined radiation dose from hydrogen purging and the postulated LOCA is less than the 10 C.F.R. Part 100 guidelines. Since the notice of hearing for a construction per-mit for the Rancho Seco plant was published on July 31, 1968, and the radiation doses (3.4 REM to the thyroid and less than 1 REM to the whole body) are within 10 C.F.R. Part 100 guidelines, hydrogen recombiners are not required for the control of hydrogen.
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THOMAS A. GREENE PROFESSIONAL QUALIFICATIONS CONTAINMEfC SYSTEMS BPANCH 0FFICE OF NUCLEAR REACTOR REGULATION
'I am a senior Systems Engineer in the Containment Systems Branch, Office of Nuclear Reactor Regulation.
In this position I am responsible for the technical review, analysis and evaluation of the containment and secondary containment functional design; containment subcompartment analysis, contain-ment heat removal systems, containment isolation system, combustible gas in containment, and containment leak testing program as described in Safety Analysis Reports to assure that nuclear power plants can be built and oper-ated without undue risk to the health and safety of the public.
I also as-sist in the preparation of standards, guides, and codes for the design and operation of reactors which deal with the containment system.
From 1973 to present, I have been employed with the Atomic Energy Comission and the Nuclear Regulatory Commission which was established by the Energy Reorganization Act of 1974.
I have been the principal reviewer for a number of nuclear power plants and am a fonner member of the American Nuclear So-ciety Standard Committee 56.1, " Design Basis for Hydrogen Treatment in Con-tainments."
From 1969 to 1973 I was employed as a Nuclear Safety Engineer at Combustion Engineering, Windsor, Connecticut.
My major area of responsibility was the analysis of the thermal-hydraulic response of a nuclear power plant during
. I a hypothetical loss of coolant accident by the use of computer blowdown codes.
During this time period, I closely followed the LOFT seniscale test program at the National Reactor Testing Station, Idaho Falls, Idaho.
From 1968 to 1969, I was employed as a Nuclear Engineer at the San Francisco Bay Naval Shipyard, Vallejo, California.
My duties were in all areas of engineering related to the overhaul and refueling of nuclear power systems on naval submarines and surface vessels.
Also, at this time I taught a night course in Basic Nuclear Engineering at John F. Kennedy University, Martinez, California.
I received a Master of Science Degree in Nuclear Engineering from the University of Arizona in 1969 and a Bachelor of Science Degree in Engineer-ing Physics from the University of Oklahoma in 1966.
While at the University of Arizona, I was a graduate assistant and instructor in the radioisotopes and instrumentation course.
Since graduating from college, I have attended various courses in t eactor technology and safety.
I have been a member of the American Nuclear Society since 1965.
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