ML20031D697
| ML20031D697 | |
| Person / Time | |
|---|---|
| Site: | Allens Creek File:Houston Lighting and Power Company icon.png |
| Issue date: | 10/09/1981 |
| From: | Fields M Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20031D662 | List: |
| References | |
| NUDOCS 8110140020 | |
| Download: ML20031D697 (8) | |
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- 10/09/81 f
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION BEFORE THE ATOMIC SAFETY AND LICE SING BOARD In the Matter of
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HOUSTON LIGHTING & POWER COMPANY
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Docket No. 50-466
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(Allens Creek Nuclear Generating
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Station, Unit 1)
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NRC STAFF TESTIMONY OF MEL B. FIELDS RELATIVE TO HYDROGEN MONITORING
[TexPirg Contention A-40]
Q.
Please state your name and position with the NRC.
A.
My name is Mel B. Fields.
I am employed at the U. S. Nuclear Regulatory Commission as a Containment Systems Engineer in the Contain-ment Systems Branch.
I have testified previously in this hearing on Board Question 4B, Compliance with GDC 50; Board Question 9, Bypass Leakage; and Board Question 4A, Combustible Gas Control.
Q.
What does TexPirg Contention A-40 allege?
A.
TexPirg Contention A-40 states as follows:
TexPirg contends that the Applicant monitoring of in contain-ment building events during LOCA or similar events is not adequate to detect immediately the occurrences of hydrogen explosions. That the recent Three Mile Island incident shows that current approved containment building monitoring apparatus did not bring such an event to the attention of operators immediately, and that therefore the strong possibility existed that actions which would prevent a second hydrogen explosion were not taken. There is danger that hydrogen explosions will endanger TexPirg members because the contain-i ment building during a LOCA is likely to contain radioactive l
gases which would be released from the building damaged even lightly by the explosion and in excess of 40 CFR 190 or 10 CFR 20.
8110140020 011009 PDR ADOCK.05000466 PDR T
Q.
What is the purpose of this testimony?
A.
The purpose of this testimony is to res'p'ond to board questions contained in the September 1st Order on this contention.
I will address each of the board's questions separately.
Board Question #1 Supply test results supporting the adequacy of the type and size of thermal recombiners to be used; Respo s The recombiners currently planned for installation inside the ACNGS con-tainment are Westinghouse thermal recombiners with a flos capacity of 100 scfm.
The staff has been reviewing this recombiner model since 1972 Westing-house has described this recombiner in WCAP-7709-L, Electrical Hydrogen Recombiner for Water Reactor Containments (July 1971) and in Supplements 1 through 7 to this report. Attached are three letters (R. L. Tedesco to R. C. DeYoung, dated July 15, 1974; D. B. Vassallo to C, Eicheldinger of Westinghouse, dated May 1,1975; and J. F. Stolz to T. M. Anderson of i
i Westinghouse, dated June 22, 1978) that provides the staff's detailed evaluation of Westinghouse's test program to qualify its thermal recombiner. These letters contain the type of tests run, the standards that the recombiner was required to meet, and the performance charac-teristics of the recombiner.
Board Question #2 Effects of poisoned recombiner surfaces and convective circulation in reducing recombiner effectiveness;
Response
The recombiner was exposed to severe environmen'thl effects such as steam, containment spray, radiation, temperature, and the performance of the recombiner was not degraded. The details of these tests and their results can be found in the above mentioned three letters.
The effect of convective circulation on recombiner performance has two aspects.
The first aspect is the possibility of uneven hydrogen concen-trations inside containment leading to possible unacceptably high local concentrations and reduced recombiner efficiency if the H concentration 2
around the recombiner in low.
No stratification or pocketing of hydrogen is expected because of various mixing mechanisms present inside the containment such as heat sources, heat sinks and containrent sprays.
..lso, experiments have shown that when a gas lighter than air is intro-duced at the bottom of a container, as is the case for ACNGS where the hydrogen would be introduced through the suppression pool vents, very rapid mixing occurs.
Extensive analysis on this topic is contained in section 6.2.5 of the ACNGS PSAR.
The second aspect is the possibility of convective air currents affecting the performance of the hydrogen recombiner by interferring with the con-vective air flow through the recombiner or causing recirculation of air that just left the recombiner.
Convective circulation of air throughout the containment is caused primarily 1, temperature differences. Because the temperature difference between the recombiner surface (1200'F) and the entering ai' is so much greater than the temperature differences expected between the containment atmosphere and other heat sources (or sinks), the staff expects the convective air circulation outside the
recombiner to have little or no effect on the air flow rising through the recombiner. This expectatien was verified by tests performed by Westinghouse (see page 3 of the July 24, 1974 letter reference in the l
response to Board Question #1).
Board Question #3 Sufficipa+ recombiner dynamic analysis to demonstrate that 3% concentra-tion of hydrrgen is a conservative alarm set-point;
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Response
The applicant has provided analysis, which has been confirmed by the staff, to show that the hydrogen generation rate using current regu-latory requirements (Regulatory Guide 1.7) is far less than the recom-bination capability of the recombiners once the short-term hydrogen generation from netal-water reaction is over. At the time the hydrogen concentration is reaching 3% inside the containment (approximately 8 days) the hydrogen generation ratets so low that the operator has many hours in which to get one of the two recombiners in operation.
Board Question #4 Relationship - functional and geometrical - between alarm sensor and the eight monitoring samplers;
Response
The location of eight monitoring sample points within the drywell and containment are shown on Figure 1.
The locations were determined using two different models.
The first model assumes hydrogen diffusion to be
6 identical to neutron diffusion.
Buoyancy effects were neglected in applying isotropic diffusion. The use of this model yielded locations above the suppressfon pool and at the bottom of the drywell. The second model considers the effects of free convection. The buoyancy forces lift the hydrogen from the lower regions of the containment and drywell to higher regions. The influence of trapping was also considered. This model provided five locations: 1) The top of the containment, 2) Near the top of the ~ pressure vessel, 3) Top outside of drywell, 4) Top out-side of drywell (opposite), 5) Near the Reactor Water Cleanup Pump area.
Both models which provided the sampling locations assumed that no mechanical mixing occurred.
The hydrogen monitoring system consists of sample and return lines, isolation valves, hydrogen analyzers and sample pumps. The equipment excluding the isolation valves and piping is located in the reactor auxiliary building. Each sample line can be monitored by either analyzer through a sample selection manifold. The hydrogen concentra-tion is determined in the analyzer and the volume percent is recorded in the Control Room. The analyzer has a range of 0-5 percent hydrogen with an accuracy of + 2.0 percent of full scale and a minimum sensitivity of 0.2 percent hydrogen by volume. The concentration is recorded l
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during sampling and an alarm is automatically actuated if the concen-tration at any sample point exceed:, 3.0 volume percent.
l The hydrogen monitoring system is manually actuated from the control room within 30 minutes of a safety injection signal.
If Regulatory
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Guide 1.7 assumptions are used in the generation rates of hydrogen, operator action, and thus hydrogen mon'itoring, 4,s, not needed for up to 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> after a LOCA.
Board Question #5 Ability to periodically test the operability of the monit.oring, alarm and recombiner systems;
Response
The hydrogen monitoring and alarm system can be tested and calibrated by introducing low concentration H and N mixtures for zero adjustment 2
2 and scale calibration. This calibration can be completed from the control room.
The recombiners have the capability to be periodically energized to confirm their operability requirements. These tests will be performed at the power levels needed to perform their function of recombining hydrogen with oxygen and for a long enough period to demonstrate stability of the system.
Board Question #6 Basis for confidence that pockets of high hydrogen concentration will not elude the monitoring and alarm systems; and
Response
Because of the relatively open area inside the containment and because l
of the mixing mechanisms (as detailed in the response to Board Question
- 2) there will be no pocketing of hydrogen inside containment, In addition, the location of the hydrogen monitors was based on where hydrogen could collect if it was possible to do so.
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7 Board Question #7 Nature of the backup containment hydrogen purging system that may be required to function at a time when the containment atmosphere is radioactive.
Response
The backup containment hydrogen purge system consists of a 2" supply line and a 2' exhaust line that would purge the containment atmosphere by exhausting the gas into the annulus.
After being recirculated in the annulus to allow for radioactive decay, the gas would then be released through the Standby Gas Treatment System to the environs.
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