ACCIDENT AT THE THREE MILE ISLAND NUCLEAR

POWERPLANT

MONDAY, MAY 21, 1979

HOUSE OF REPRESENTATIVES,

SUBCOMMITTEE ON ENERGY AND THE ENVIRONMENT,
COMMITTEE ON THE INTERIOR AND INSULAR AFFAIRS,

Washington, D.C. The subcommittee met at 9:55 a.m. in room 2141, Rayburn House Office Building, Hon. Morris K. Udall (chairman of the full committee and the subcommittee) presiding.

Present: Representatives Udall, Bingham, Weaver, Miller, Sharp, Markey, Vento, Edwards, Cheney, and Bereuter.

The CHAIRMAN. The subcommittee will be in session.

Our meeting today represents the first in a series of hearings and subcommittee activities conducted as part of a comprehensive inquiry into the status and the future role of nuclear power in America.

Our subcommittee investigation was triggered by the occurrence on March 28 of the most serious accident at a nuclear plant in the history of commercial atomic power. Coming on the heels of other significant events, such as the five-plant shutdown and the partial repudiation of the Rasmussen report, the Three Mile Island incident convinced me that the time had come for a serious reconsideration of the use and regulation of nuclear power.

This subcommittee is charged with primary responsibility in the House for assuring that commercial nuclear power does not present an unacceptable risk to the public's health and safety. As such, it is not only appropriate but, I believe, mandatory that this panel convene the kind of hearing we will conduct today and the full investigation into a variety of nuclear power issues we will pursue in the coming months.

Today we will hear first a report from a task force I appointed, in consultation with the minority, to inquire into the facts of the Three Mile Island accident. This group, ably chaired by our colleague Jim Weaver, has interviewed 15 witnesses over the last 2 weeks in order to gain a firsthand understanding of the accident sequence and recovery operation. The task force report includes the panel's consensus understanding of these events and identifies issues that merit further review.

Mr. Weaver and Congressman Cheney will offer the report. I want to compliment them and the other members of the task force for their hard work in completing their assignments in this short 2-week period.

Given the countless demands on a Member's time, it is a remarkable indication of these Members' attention to their responsibilities to this subcommittee and the House that they were able to carve out the time to conduct these lengthy interviews. For their important efforts, I want to thank my colleagues Mr. Weaver, Mr. Cheney, Mr. Runnels, Mr. Lujan, Mr. Carr, Mr. Marriott, Mr. Markey, Mr. Edwards, Mr. Kostmayer, Mr. Vento, and Mr. Huckaby.

Following the report of the task force, we will receive a chronology of the accident sequence from Mr. Carl Michelson, an engineer with the TVA. Mr. Michelson has been involved with the analysis of a Babcock & Wilcox reactor now under construction at the TVA. Mr. Michelson is also a consultant to the NRC's Advisory Committee on Reactor Safeguards and has spent a good part of the last 2 months analyzing the Three Mile Island accident.

I would like to note that Mr. Michelson wrote a memorandum in early 1978 which suggested that in some circumstances reactor operators might be misled into prematurely turning off the emergency core cooling system. Since this seems to have been a major part of the problem at Three Mile Island, I would like to know why it was that the Michelson analysis does not appear to have been taken more seriously and why it was not more widely distributed.

Finally, we will receive testimony from the Chairman and Commissioners of the Nuclear Regulatory Commission. While the accident is still under investigation, I am certain that the members will be interested in the Commissioners' observations about what happened at TMI and what it tells us about the way we regulate nuclear power. In addition, we will be interested in the status of the NRC's inquiry into the accident. I understand that Mr. Denton, Dr. Mattson, and other senior members of the staff are also present.

As I indicated at the outset, today's hearing is only the beginning of our efforts. We have released a tentative schedule of hearings over the summer months that will allow us to look into the full range of nuclear issues, including licensing and enforcement, nuclear waste, the economics of nuclear power, Price-Anderson, and energy needs in general.

While there are understandable and legitimate pressures on the members of this committee and the House to react immediately to the TMI accident, it is my hope that significant changes in existing policy would come only after this subcommittee carries out its hearing schedule. I reaffirm, therefore, my intention to convene sessions of the subcommittee in early fall to consider legislation affecting nuclear policy and regulation, and I hope to be drafting some proposals along those lines shortly.

We will now begin with our colleagues, Mr. Weaver and Mr. Cheney. Congressman Weaver, you can begin, sir.

[The prepared statement of Hon. James Weaver together with the report to the subcommittee by the Three Mile Island task force,

STATEMENTS OF HON. JAMES WEAVER, A U.S. REPRESENTATIVE FROM THE STATE OF OREGON; AND HON. RICHARD CHENEY, A U.S. REPRESENTATIVE FROM THE STATE OF WYOMING; AND MEMBERS OF THE SUBCOMMITTEE ON ENERGY AND THE ENVIRONMENT

Mr. WEAVER. Mr. Chairman, you established the task force to inquire into the accident at the Three Mile Island nuclear plant and the response of the licensee, Nuclear Regulatory Commission, and other officials. In closed, informal sessions, the task force interviewed representatives of the NRC, including members of its inquiry team, Metropolitan Edison, Babcock & Wilcox, and Mr. Carl Michelson, a nuclear engineer with the Tennessee Valley Authority. A list of the members of the task force and interviewees is appended to this statement.

TASK FORCE REPORT

Our purpose today is to report to the subcommittee. A definitive statement on causes and remedies of the Three Mile Island accident must await completion of the inquiry of the Presidential commission and the Nuclear Regulatory Commission. We believe it important, however, to state our preliminary observations in order to alert the subcommittee and other investigators to what we believe to be significant factors.

I will outline the significant events of the accident sequence, as the task force has been able to identify them, and a conceptual explanation of the types of failures that may have occurred. Following that. I will provide some preliminary observations of the task force. Subsequent to these comments which represent the consensus of the task force, Mr. Cheney and others will offer their personal observations. Later Mr. Michelson will explain in detail the accident sequence.

SIGNIFICANT EVENTS IN THE ACCIDENT

One: Auxiliary feedwater was blocked from the secondary cooling system by valves closed prior to the event. Whether the closure, a violation of NRC regulations, directly contributed to the exacerbation of the accident is a matter of dispute.

Two: The pilot-operated relief valve, PORV, located on top of the pressurizer opened as designed but, due to an as yet unknown mechanical failure, stuck open. Its failure to prevent leakage from the pressurizer-until a blocking valve in series with the PORV was closed at 2.3 hours-was a, if not the, major factor in the accident sequence. The reasons for the operators' failure to close a downstream block valve until well into the sequence are complicated and controversial. Three: The design of Babcock & Wilcox nuclear steam supply system results in more rapid drying out of the secondary-loop steam generator than in other manufacturers' pressurized water reactors. This may have reduced the time available for operators to respond to

the situation, although the significance of this, if any, is not clear

to us.

Four: The level indicator on the pressurizer was not an adequate indicator of reactor water level during this event. This led to misinterpretation by operators of the significance of the pressurizer water level. They relied upon it as an indicator of the reactor being full of water and consequently they limited injection of emergency core cooling water into the reactor, which led to primary coolant depletion and the uncovering of the core. Debate continues as to whether the operator had sufficient and accurate information-other than the level in the pressurizer-to infer the actual reactor water level.

Five: The operator shut off the reactor coolant pumps, RCP's possibly due to concern that pump vibrations would damage the pumps. Doing so reduced cooling of the reactor core but testimony indicates this may have been a required action.

Six: Containment isolation occurred upon pressure actuation, as designed, but after radioactive water from the primary coolant system had been automatically pumped into the auxiliary building, allowing releases to the atmosphere.

Seven: While several operators and supervisors watched a strip chart, a 28 psi pressure spike occurred in the containment building at approximately 1:50 p.m. on the day of the accident-March 28. Conflicting testimony on this event and its immediate and subsequent significance make it a controversial issue.

Eight: Throughout the early hours of the accident, the operators could not readily interpret core temperatures from the in-core thermocouples.

CATEGORIES OF FAILURE

The task force believes that it is helpful to look at the Three Mile Island accident with certain categories of types of failures in mind. We do not imply that all the possible failures contributed significantly to the events at TMI, but for the subcommittee review we present what we believe to be a breakdown of kinds of failures that can occur.

Design error would encompass plant features which allowed for insufficient safety margins, inadequate instrumentation, or systems that were not properly designed to cope with certain emergency or accident situations.

Equipment malfunction and faulty construction encompasses equipment malfunctions and construction errors that contributed to the accident.

Procedural errors are those resulting from procedures inappropriate for the circumstances. These might include such things as incomplete check lists or written instructions that cause operators to take actions that exacerbate the situation.

Operator errors includes situations where an operator acted in a manner different from that which would have been expected from a licensed operator who had sufficient information to take the appropriate action.

We have heard testimony suggesting that the reactor operators should have been made more clearly aware of the following: The tendency of the power-operated relief valve, PORV, to stick open;

the fact that there was no positive indication of closure of the PORV; that the pressurizer water level was not an indication of full primary coolant system when portions of the primary system were at temperatures in excess of the point at which boiling might occur; that in case of doubt as to the existence of a leak in the primary, high-pressure injection pumps should be left on.

We received information suggesting that the lack of instrumentation to measure and clearly indicate the following may have led to operator actions that were inappropriate for the conditions that existed: reactor pressure vessel coolant level; radiation level in containment; existence of fluid flow and the high temperature in pipe leading from pressurizer; positive indication of closure of pilot-operated relief valve, PORV; in-core temperatures indicating presence of superheated steam or chemical interactions between fuel cladding and steam; integrated measurements of coolant injected by high-pressure injection pumps, HPI; integrated measurements of reactor coolant letdown; whether steam bubbles may have developed in the reactor primary.

The subcommittee heard conflicting testimony with regard to the following: whether operators had sufficient information to know that the power-operated relief valve was stuck open; whether the operators had sufficient information to know that they should have allowed the high-pressure injection pumps to inject water into the primary at full capacity; whether the operators had sufficient information to infer that there had been a hydrogen burn or explosion at approximately 1:50 p.m. on March 28, and the impact of definite knowledge of this event upon decisions by plant managers; the time at which the operators had sufficient information to know that more than 1 percent of the fuel rods had suffered cladding failures; the extent to which there was danger on March 28 and the following several days of equipment or instrument failures that might have led to melting of fuel.

There remain many other issues which the task force was not able to explore adequately, but which are very important aspects of the accident and the events surrounding it.

One: The significance vis-a-vis Three Mile Island of incidents at other Babcock & Wilcox reactors, including the transients at Rancho Seco and Davis-Besse, and the question of whether information concerning these incidents had been adequately analyzed and disseminated-and I come to that later in my own remarks.

Two: The response of Babcock & Wilcox to TVA's April 2, 1978, letter forwarding comments of TVA engineer Carl Michelson regarding decay heat removal during a very small break loss of coolant accident in a Babcock & Wilcox reactor.

Three: The frequency of the pilot-operated relief valve-PORV'sfailing to close at TMI 2, one previous occasion, and the response by the licensee, vendor, and NRC to this problem.

Four: Concentrating on developing an understanding of the accident and recovery sequence, the working group did not explore the questions regarding the communications between, and the decisionmaking process of, the State, and the NRC. This issue, however, is a crucial one and