ML20040A601
| ML20040A601 | |
| Person / Time | |
|---|---|
| Issue date: | 12/17/1981 |
| From: | Palladino N NRC COMMISSION (OCM) |
| To: | Udall M HOUSE OF REP., INTERIOR & INSULAR AFFAIRS |
| Shared Package | |
| ML20038A080 | List: |
| References | |
| SECY-81-631, NUDOCS 8201210281 | |
| Download: ML20040A601 (3) | |
Text
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o UNITED STATES 3i.
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NUCLEAR REGULATORY COMMISSION,
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December 17, 1981 CHAIRMAN D
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The Honorable Mo,rris K. Udall
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s Committee on Interior and Insular Affairs United States House of Representatives N
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Washington, D.C.
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Dear Mr. Chairman:
This is in response to your letter of July 7, 1981 requesting a statement on the Commission's rationale with regard to the consideration staff and licensing boards must give to the problem of hydrogen generation.
In your letter, you indicated your concern that a substantial part of the rationale underlying the Commission's policy on hydrogen generation may have been incorrect.
Your specific concern dealt with whether the Commission's policy was in any substantial way founded on the premise that operator error was the primary cause for the accident at Three Mile Island, and if, as a result, the corrective measures we have required are limited to those that rectify only the problem of operator error.
We have not limited our post-TMI requirements, including those for hydrogen control, to reactor operator errors.
Rather, our new measures cover reactor design as well as operation.
Even though there have been numerous changes aimed at improving the safety of reactor operations, we also are requiring that accidents that generate large amounts of hydrogen be considered in nuclear power plant designs.
Plants undergoing licensing review and those now operating are currently subject to a broad program of measures to deal with the large amounts of hydrogen that could be generated by an accident of the type that occurred at Three Mile Island.
This program, which has led to design modifications in some plants, is discussed below.
i 8201210281 811217 PDR COMMS NRCC CORRESPONDENCE PDR
2 To codify our hydrogen control program, we have recently approved interim amendments to our regulations related to hydrogen control (Enclosure 1).
We have also issued another proposed rule change related to improved hydrogen control systems for boiling water reactors with Mark III type containments and for pressurized water reactors with ice condenser type containments.
The proposed rule addresses operation of important safety systems during and following hydrogen burning (Enclosure 2).
In addition to the above rule changes, we have under consideration a final rule change for construction permits and manufacturing licenses which contains provisions for hydrogen control (Enclosure 3).
Lastly, the staff should forward to the Commission in the near future a proposed final rule change concerning TMI related requirements for operating license applications that contains provisions related to accidents which may generate significant amounts of hydrogen.
These rules address certain accidents that involve lowering of the water level in the reactor vessel to the point where the core is uncovered.
They can produce large amounts of hydrogen because of the oxidation at high temperature of the
, metal cladding surrounding the fuel.
Recovery from these accidents is possible before substantial core rearrangement or melting occurs, as the accident at TMI-2 demonstrated.
The Commission's present policy concerning hydrogen generation and control, which is reflected by the recent rulemaking activities listed above, requires the affected licensees and applicants to assure safe shutdown of the reactor and t
maintenance of containment building integrity for severe accidents that terminate prior to a meltdown of the core.
These accidents are characterized as those that could result in about 75 percent of the fuel cladding undergoing metal-water reaction without the core completely melting.
The containment and shutdown systems must be capable of coping with the hydrogen generated by such an extensive degree.of metal-water reaction.
However, in demonstrating this capa-bility we are not requiring in the near term licensees and applicants to satis fy all the usual criteria for engineered safety features for design basis accidents.
The Commission is considering a two-step approach to address qualification of essential equipment during and af ter a hydrogen burn.
As a first step, essential equipment must be demonstrated to survive the hydrogen burn and continue to be able to perform i ts safety function.
In this context, the equipment would not have to meet the more rigorous standards of the NRC's
3 equipment qualification program.
After additional i n fo rma.-
I tion is developed on equipment qualification, the Commission may propose long-term standards that are more stringent than the short-term or survivability standard being proposed.
We will continue to examine this and other aspects of our policy for hydrogen control as a part of the larger and longer term rulemaking on severe accidents that was initiated last year.
(Advanced Notice of Proposed Rulemaking on Degraded Core Accidents 45FR65474).
Our present policy presumes that accidents generating large amounts of hydrogen can happen, but it attributes a lower probability to their occurrence than for design basis accidents.
We are confident that the probability is lower because of the safety improvements implemented as a result of the lessons learned from the TMI-2 accident.
These include:
(1) staffing, training and qualification improvements designed to make the likelihood of errors in plant operation more remote; (2) improvements in operating procedures; (3) hardware changes to reduce plant vulnerability to small break loss of coolant and loss of feedwater events; and (4) improvements in the regulation of nuclear power plants, most notably in the area of feedback and analysis of operating experience.
A discussion of our new licensing requirements for hydrogen control and how they have been or will be implemented in recent operating license reviews, in near term construction permit and manufacturing license reviews, and for operating reactors, as of September 3, 1981, is provided in Enclosure 4.
If I can elaborate further or provide staff members to discuss this response to your concern, please do not hesi-tate to call on me.
Sincerely,
~.-
Nunzio J. Palladino
Enclosures:
l.
FR Notice - Final Rule 2.
FR Notice - Proposed Rule 3.
SECY-81-631 - CP/ML Rule 4.
Status of Hydrogen Control Activities dtd 9/3/81 cc:
The Honorable Manuel Lujan
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