The Three Mile Island Accident - ACS Publications - American

15 Downloaded by EAST CAROLINA UNIV on January 3, 2018 | http://pubs.acs.org Publication Date: December 23, 1986 | doi: 10.1021/bk-1986-0293.ch015

The Recovery: A Status Report John C. DeVine, Jr. GPU Nuclear Corporation, Middletown, PA 17057

This paper provides an up-to-date synopsis of the Three Mile Island Unit 2 (TMI-2) Recovery Program. The discussion is presented within the context of the three-phase program approach that is followed by the GPU Nuclear/Bechtel Group integrated organization, in restoring safe stable conditions at TMI-2, following the March 1979 accident. In the first few weeks after the accident, efforts centered upon regaining control and assessing the damage incurred. The early recovery work centered around the new systems required to supplement or replace damaged systems and components, and the new procedures needed to deal with the damaged plant. This technical summary describes the subsequent work including Phase II, Defueling, and Phase III, Cleanup, leading to future decisions and work efforts. To date, the TMI-2 recovery program has been successful in achieving: ο A high degree of public and worker safety ο Progress in the recovery program, resulting in a vast improvement at TMI-2 Moreover, the program has proved to be a significant learning experience for the entire nuclear industry, which is enhancing the safety of nuclear plant operations. 0097-6156/86/0293-0267$06.00/0 © 1986 American Chemical Society

Toth et al.; The Three Mile Island Accident ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

Downloaded by EAST CAROLINA UNIV on January 3, 2018 | http://pubs.acs.org Publication Date: December 23, 1986 | doi: 10.1021/bk-1986-0293.ch015

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THE THREE MILE ISLAND ACCIDENT

More than s i x years have passed since the morning of March 28, 1979, when the now-famous accident at Three Mile Island Unit 2 (TMI-2) suddenly transformed the subject of nuclear safety from s c i e n t i f i c hypothesis to r e a l i t y . In that time, the TMI-2 accident and cleanup have become perhaps the most-reported and least-understood events of our time. Today, the p r e v a i l i n g public and p o l i t i c a l notion of the TMI-2 cleanup seems to be that i t i s a very hazardous venture, plagued with problems and achieving l i t t l e , i f any, success. Much press coverage of the cleanup has been negative. Within the technical community as well, f r u s t r a t i o n i s often expressed about the seemingly slow pace of the cleanup work. For these reasons, we welcome t h i s opportunity to provide an up-to-date, factual synopsis of our TMI-2 Recovery Program. In the next few pages I w i l l summarize what we have accomplished, where we stand, and what l i e s ahead i n t h i s important program. F i r s t , three points of primary importance must be made: 1. The TMI-2 accident and recovery should be (and to an extent, have been) the most s i g n i f i c a n t learning experience f o r our industry. Undoubtedly, every nuclear plant i s safer now than i t would have been had the accident not happened. And much more i s to come. For example, we are just now beginning to accumulate hard information from the damaged core i t s e l f , to serve as a basis f o r invaluable research on temperatures achieved, heat transfer and chemical processes i n the core during the accident, f i s s i o n product retention, and the l i k e . 2. The cleanup has been conducted with absolutely highest regard f o r worker and public safety, and i t has been extremely successful on that score. Despite allegations and insinuations to the contrary, that record speaks f o r i t s e l f . O f f s i t e doses have been n e g l i g i b l e , in-plant personnel exposures have been well controlled and are at very low values, i n d i v i d u a l l y and c o l l e c t i v e l y . 3. The cleanup program, although hardly problem free, has achieved r e a l progress toward i t s ultimate goal. In every respect, the plant condition i s now vastly improved over that facing the team at the program outset. With that as background, I w i l l now describe the Recovery Program.

The Starting Point. In the f i r s t few weeks a f t e r the TMI-2 accident (of March 28, 1979), an around-the-clock, emergency response mode of operation prevailed. During t h i s period p o s i t i v e control was regained, but the s i t u a t i o n which emerged—and became the s t a r t i n g point f o r the recovery e f f o r t that i s s t i l l i n process—was discouraging indeed.


The Recovery: Λ Status Report


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Although the reactor*s condition was not p r e c i s e l y known, i t was clear that massive f u e l damage had occurred. The reactor containment building was completely inaccessible because of high radiation and radioactive contamination l e v e l s , and most of the A u x i l i a r y and Fuel Handling Building (AFHB) complex was inaccessible or marginally accessible as well. Hundreds of thousands of gallons of highly contaminated water had collected i n the reactor building basement and i n A u x i l i a r y Building tanks. Because of the high contamination levels (ranging from one to more than 100 microcuries per m i l i l i t e r gross a c t i v i t y ) , plant systems were inadequate to transfer or process t h i s water. These technical d i f f i c u l t i e s were compounded by such problems as continuing public fear, regulatory uncertainty, funding l i m i t a t i o n s , and closure of commercial radwaste disposal s i t e s ( f o r TMI-2 wastes). Early Recovery Work. Work began immediately on a variety of p a r a l l e l programs to address these problems. Numerous new plant systems (including several decay heat removal systems, a new nuclear sampling system, a major RCS pressure and inventory control system, and numerous instrumentation and control systems) were designed, procured, and i n s t a l l e d on an urgent schedule to replace or supplement e x i s t i n g systems not considered suitable f o r extended use because of i n a c c e s s i b i l i t y , radiation l e v e l s , and the l i k e . New procedures were developed to deal with the plant i n i t s damaged condition. Design work began on two major l i q u i d waste processing systems, and f a c i l i t i e s were constructed to safely stage s o l i d and l i q u i d wastes f o r extended periods of time. Aggressive decontamination of the AFHB was conducted, and preparations were i n i t i a t e d for re-entry into the containment building. As work proceeded during the f i r s t few years of the recovery program, organizational and i n s t i t u t i o n a l steps were taken as well. The present organization—which combines elements of GPU Nuclear and the Bechtel Group into a unique, integrated unit structured to deal with long-term recovery—was formed i n 1982. Project funding from multiple sources, along the l i n e s i n i t i a l l y proposed by Governor Thornburg of Pennsylvania, was secured. Cooperative agreements among the U.S. Department of Energy (DOE), the U.S. Nuclear Regulatory Commission (NRC), and GPU Nuclear greatly f a c i l i t a t e d the recovery e f f o r t by providing DOE (and National Laboratory) support f o r various program a c t i v i t i e s of national interest and permitting research and disposal of TMI-2 radioactive wastes i n U.S. Government f a c i l i t i e s . Agreements among GPU Nuclear, DOE, and a group of Japanese government, u t i l i t y , and nuclear industry companies resulted i n Japanese p a r t i c i p a t i o n and funding f o r research-related aspects of the program. Also during the period, strategies and plans f o r the entire recovery e f f o r t began to take shape. The concept of a phased project, as depicted graphically i n Figure 1, was established and continues i n use today. Per t h i s concept, the recovery program consists of three d i s t i n c t (but overlapping) phases. The objective of Phase I (which i s complete) was to regain and maintain stable plant conditions f o r



PROCEED.

PERMIT

• • • • •

REACTOR CONTROL CONTAINMENT ACCESS INITIAL DECON HATER PROCESSING WASTE STORAGE

ACTIVITIES INCLUDE:

RECOVERY TO

CONDITIONS T O

REGAIN STABLE

SUPPORTING!

FUEL.

IB

-

PUBLIC

INCLUDE:

- ADDITIONAL DECON - WASTE DISPOSAL

ACTIVITIES

OR ENVIRONMENT.

N O HAZARD TO

T H A T T H E R E IS V I R T U A L L Y

SAFE CONDITION,SUCH

ACHIEVE SECURE,

CLEANUP

( P H A S E III)

Figure 1. TMI-2 recovery program phases.

CURRENT PHASE

CHARACTERIZATION DOSE REDUCTION REACTOR DISASSEMBLY WASTE MANAGEMENT

ACTIVITIES S U C H AS:

INCLUDES

ENCAPSULATE

AND

REMOVAL:

FUEL

II)

PROGRAM

[PHASE

COLLECT

STABILIZATION

(PHASE Ι )

RECOVERY


W O R K AS REQUIRED DECOMMISSION TMI-21

TO REFURBISH OR


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the extended term. This phase consisted primarily of those early a c t i v i t i e s outlined above. The objective of Phase II (the current phase) i s to remove and encapsulate the damaged f u e l from the reactor, a major project i n i t s own r i g h t . Phase III then w i l l eliminate residual radiation hazards, r e s u l t i n g i n a plant condition that i s safe and secure. A decision as to the ultimate plant d i s p o s i t i o n , which could range from recommissioning to any of several decommissioning phases, w i l l not be made u n t i l a f t e r Phase I I I . At this point, a l l safety issues w i l l have been resolved and plant conditions w i l l permit i t s thorough examination to support such a decision. Of course, TMI-2 work required a f t e r that point w i l l depend upon that determination. Phase I i s h i s t o r y , and therefore needs no further discussion. The following i s a technical summary of Phases II and I I I , and the work to be done a f t e r t h e i r completion. Phase II - Defueling. Within the o v e r a l l TMI-2 Recovery Program, reactor defueling i s the most v i s i b l e , expensive, and t e c h n i c a l l y challenging element. Preparations f o r the defueling e f f o r t — i n the form of conceptual plans, data a c q u i s i t i o n , engineering, procurement, plant refurbishment, equipment i n s t a l l a t i o n , and t r a i n i n g — h a v e been underway f o r about three years. These preparations are nearly complete. One key task of the defueling project i s data a c q u i s i t i o n and analysis to characterize the conditions of fuel and s t r u c t u r a l material inside the reactor. Because of high radiation and contamination l e v e l s , t h i s work must be done remotely. A variety of techniques have been used i n t h i s e f f o r t , including small diameter TV camera examination inside the reactor, removal and analyses of f u e l and s t r u c t u r a l material samples, internal and external ion chamber measurements, sonar p r o f i l i n g of the core void region, external p r o f i l i n g of neutron f l u x using s o l i d state track readers (SSTRs), and others. These examinations and t h e i r r e s u l t s are being described i n some d e t a i l i n other presentations. In summary, however, two points are important: From an engineering standpoint, a thorough understanding of conditions inside the reactor vessel i s a major prerequisite to reactor disassembly and defueling, both f o r safety reasons and to ensure that the chosen defueling techniques are adequate f o r t h e i r intended applications. This examination program has also produced information of great value to the s c i e n t i f i c community i n analyzing the TMI-2 accident. The examinations have been conducted i n a very d i f f i c u l t and unique environment, and have involved the development and/or refinement of innovative techniques, equipment, and a n a l y t i c a l methods. These developments have been very successful and have broad application and value to the industry. At this point, a r e l a t i v e l y c l e a r p i c t u r e of the damaged TMI-2 reactor i s emerging. Visual examination (confirmed by i t s demonstrated i n t e g r i t y over the s i x years since the accident) has shown that the reactor vessel i t s e l f i s i n t a c t and i n sound



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condition. S i m i l a r l y , the reactor vessel head and the upper reactor internals are highly contaminated but r e l a t i v e l y damage free. However, damage to the nuclear f u e l i s extreme. As o r i g i n a l l y i n s t a l l e d , the nuclear core consisted of 177 fuel rod assemblies, arranged i n a cylinder approximately 12 f t high and 12 f t i n diameter. V i r t u a l l y the entire upper f i v e feet of t h i s core region i s now a void, and the three feet below that i s a mass of loose rubble. Samples extracted from t h i s rubble bed confirm that some of the f u e l reached very high temperatures (at or approaching the melting point of uranium oxide fuel) during the accident. The lower part of the core region has not been examined d i r e c t l y but i s expected to include a spectrum of conditions; from intact f u e l rods to agglomerated material and voids. F i n a l l y , a substantial amount of core material (perhaps 10-20 tons, assumed to be f u e l and s t r u c t u r a l material) has been discovered below the core region and appears to have been once molten. Conceptual plans, detailed engineering, and design, f a b r i c a t i o n , and i n s t a l l a t i o n work have been proceeding f o r the systems and equipment needed to safely remove, encapsulate, store, and transport this damaged core material. In very b r i e f summary, the defueling process i s as follows: 1. Several methods w i l l be used to extract f u e l from the reactor, including vacuum systems, long-handled tools, and remote manipulators. 2. Using these methods under water, the f u e l w i l l be placed i n s t a i n l e s s s t e e l canisters and these w i l l be closed securely. • 3. Using s p e c i a l l y designed handling equipment, the fuel cans w i l l be moved into the TMI-2 fuel handling building, and then placed i n underwater racks f o r temporary storage i n the spent fuel pool. 4. The f u e l cans w i l l then be dewatered, placed i n s p e c i a l l y designed r a i l casks, and transported to Department of Energy f a c i l i t i e s i n Idaho f o r research, storage, and ultimate disposal. Several major reactor disassembly steps (including polar crane repair, reactor head removal, and upper plenum jacking) have already been completed i n preparation f o r the defueling e f f o r t . Numerous dose reduction tasks (such as decontamination and shielding), defueling equipment i n s t a l l a t i o n and testing, preparation of procedures, and personnel training are i n progress and nearing completion. The actual defueling work w i l l commence t h i s year, s t a r t i n g with removal of the loose rubble material i n the upper core region and then proceeding to the more d i f f i c u l t regions below. The e n t i r e job i s expected to take about two years to complete. Phase I I I and Beyond. A f t e r completion of the reactor vessel defueling, several other s i g n i f i c a n t operations are required to achieve the safe, secure, and accessible condition that i s the object of the recovery program. These include:



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C o l l e c t i o n and encapsulation of the p a r t i c l e s of fuel transported to portions of the reactor coolant system and connected a u x i l i a r y systems during the accident. While the absolute quantity of such fuel i s expected to be r e l a t i v e l y small ( i n aggregate, probably less than one percent of the core), t h i s w i l l be a d i f f i c u l t job because of access l i m i t a t i o n s , r a d i o l o g i c a l conditions, and the l i k e . Substantial additional decontamination of the reactor containment and a u x i l i a r y buildings. E a r l i e r decontamination work in these buildings was (and i s ) somewhat s e l e c t i v e , intended to reduce radiation and contamination levels i n areas where plant s t a b i l i z a t i o n and defueling work ( i . e . , Phases I and II) required frequent access. The Phase III decontamination e f f o r t has the broader objective of achieving conditions that are s a t i s f a c t o r y for the longer term i n the sense that they pose v i r t u a l l y no r i s k of release of radioactive material, and they permit access as necessary to thoroughly examine the plant for determination of i t s ultimate d i s p o s i t i o n .

A major part of this decontamination e f f o r t w i l l involve the reactor building basement. This area i s e s s e n t i a l l y inaccessible now because of high radiation levels (ranging from a few R/Hr to over 1000 R/Hr). Much work has already been done to prepare for basement decontamination, including data a c q u i s i t i o n and development of robotic equipment. As we approach Phase I I I , additional work w i l l be done to secure and i s o l a t e plant systems. Also, various systems and equipment w i l l be i n s t a l l e d to monitor and control the defueled plant. This Phase III work i s , f o r the most part, s t i l l i n the planning stages, although some a c t i v i t i e s (such as A u x i l i a r y Building Decon) are proceeding already on a not-to-interfere basis. A key element in the planning process i s the development of a l i c e n s i n g strategy, t a i l o r e d to the unique TMI-2 condition, which w i l l afford the proper balance of p r a c t i c a l i t y and plant protection. Development of this strategy along with a related set of s p e c i f i c Phase III end point conditions, i s now underway. After Phase I I I , a decision can be made as to the ultimate d i s p o s i t i o n of the plant. The obvious d i s p o s i t i o n candidates are decommissioning (either i n the near term or at some point i n the future, such as when TMI-1 i s decommissioned), or refurbishment and recommissioning. The decision w i l l require extensive study, taking into account technical economic, and regulatory factors. Such studies, p a r t i c u l a r l y those requiring assessment of the physical condition of the plant, cannot be completed u n t i l Phase III completion c r i t e r i a have been established. Therefore, a decision as to the ultimate d i s p o s i t i o n of TMI-2 i s not anticipated u n t i l 1989, or later.


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Conclusion This presentation has been necessarily b r i e f . The TMI-2 Recovery Program i s , i n a sense, a composite of a number of smaller projects—many of which are technically s i g n i f i c a n t but could not be summarized here. Questions on any aspect of the program are welcome. In conclusion, l e t me restate the obvious. The Three Mile Island accident i s an event of extraordinary impact on GPU Nuclear, on the nuclear industry, on the e l e c t r i c u t i l i t y industry, and on our energy future. There are those who would e x p l o i t the TMI-2 experience by c a l l i n g i t the f i n a l , compelling demonstration of the f a i l u r e of nuclear power and a deterrent from further nuclear power plant development. Nothing could be further from r e a l i t y . The TMI-2 accident, and the recovery that has followed, present an opportunity of inestimable value. I t i s our challenge to extract from the experience every possible benefit, to learn from our mistakes and to apply these lessons to the design, regulation, and operation of nuclear power plants. On that basis, we can proceed safely, strongly, and successfully. RECEIVED July 29, 1985


The Three Mile Island Accident - ACS Publications - American

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