ML19208B080
| ML19208B080 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 06/21/1979 |
| From: | Mariani L AMERICAN NUCLEAR INSURERS |
| To: | Mattson R Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19208B079 | List: |
| References | |
| NUDOCS 7909190030 | |
| Download: ML19208B080 (2) | |
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UABluTY ENGINEERING CEPARTMENT
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6m June 21, 1979 g pQ g h Mr. Roger J. Mattson, Di rector Division of Systems Safety Office of Nuclear Reactor kegulation U.S. Nuclear Regulatory Commission Washington, D.C. 20202 RE:
REACTOR DOME NON-CONDENSIBLE GAS EMERGENCY VENTING SYSTEM
Dear Mr. Mattson:
The copy of NUREG-0560 you forwarded in a recent correspondence is very much app reci a ted.
The Three Mile Island accident sequence was seriously compounded by the develop-ment of a large bubble of hydrogen gas in the reactor vessel dome. The hydrogen generation which lead to formation of tnis bubble was a direct consequence of degradation of core co, ling to a sufficient extent as to cause extensive zirconium-water chemical reaction. We have due confidence that the eventual implementation of the recommendations of fered by NUREG-0560 would tend to substantia 1 N reiuce the probability of degradation of core cooling, as may be postulated to rise through the recurrence of abnormal system sequences similar to that which occurred a t TMI.
The existance of the large hydrogen bubble in the reactor vessel dome presented enormous control problems to the TMI operators. The difficulty to maintain dependable core cooling under these circumstances contributed greatly to the severity and duration of the occurrence. The long term persistance of this bubble (several days) was at the basis or a publicly announced status of continued danger to members of the public in the vicinity of TMI. There were at TMI no means in place to quickly remo,ve the bubble and to thereby avert the difficulties
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brought on by i ts presence.
It would anpear that reactor coolant system controllability subsequent to a postulated occurrence of significant zirconium water reaction would be enhanced by a suitable means to remove non-condensible hydrogen gas which may accumulate in the reactor dome.
It is also possible that ci rcumstance may arise where cover gas in the low pressure safety injection accumulators could create a ni trogen bubble in the reactor dome, wi th similar.undesi reable ef fects.
The Tedesco report was silent as to a recommendation that an emergency venting system to evacuate non-condensible gases from the reactor dome be evaluated as a possible means to acconmodate hydrogen generation which may accompany fuel damage.
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Hr., R.oger J. Mattson - Systems Safety Of fice (NRC)
June 21, 1#79 RE:
REACTOR DONE NON-CONDENSIBLE GAS EMERGENCY VENTING SYSTEM Page 2 The installation of an emergency venting system to remove and thereby accommodate the possible generation of non-trivial quantities of non-condensible gas would seem to flow directly from the defense in depth design philosophy. Conservative design philosophy would dictate that all reasonable measures be taken to preclude gas generation or deposition within the reactor vessel and further that mea.is be available to accommodate such gas as may be present due to ovc< sight or unforeseen failure.
Clearly, the availability of such a system.- TMl control room operators could only have been beneficial to mitigate and curtail the off-site consequences of the THI occurrence.
By this reasoning it is concluded that dome venting capability would be a valuable asset to safe operation.
In the event that full evaluation of this question does not uncover undesireable side effects, ANI would recognize such capability as an inducement to insureabili ty of reactor facilities so equipped.
I would be interested to learn of NRC thinking with regard to providing reactor
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doras non-condenaible gas emergency venting capabili ty.
Very truly yours,
//<hM Dr. Leo P. Ma rian
- Vice President - Liabili t, Engineering LPM:djg 86 i
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