ML20080C706
| ML20080C706 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 08/24/1983 |
| From: | Paddleford D UNION ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20080C696 | List: |
| References | |
| ISSUANCES-OL, NUDOCS 8308290167 | |
| Download: ML20080C706 (15) | |
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80CKETED USNPC August 24 h9A5 26 N1O U1 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION BEFORE THE ATOMIC SAFETY AND LICENSING BOAR _D In the Matter of
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UNION ELECTRIC COMPANY
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Docket No. STN 50-483 OL
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(Callaway Plant, Unit 1)
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APPLICANT'S TESTIMONY OF DONALD F.
PADDLEFORD IN RESPONSE TO REED CONTENTIONS 6 AND 16 (PROTECTIVE ACTIONS AGAINST RADIOIODINES AND MESSAGES WITH INSTRUCTIONS FOR LONG-TERM SHELTERING) 8308290167 830824 PDR ADOCK 05000483 T
1 Q.1 Please state your name.
2 A.1 Donald F.
Paddleford.
3 Q.2 Mr. Paddleford, by whom are you employed?
4 A.2 Westinghouse Electric Corporation, P.O.
Box 353, 5
Pittsburgh, Pennsylvania.
The nuclear steam supply system for 6
the Standardized Nuclear Unit Power Plant System, including 7
Union Electric's Callaway Plant, is designed and supplied by 8
9 Q.3 What is your position with Westinghouse, and what are 10 your current responsibilities?
11 A.3 I am Advisory Engineer, Risk Assessment Technology, 12 in the Nuclear Safety Department of Westinghouse's Nuclear 13 Technology Division.
My responsibilities in that position 14 include the development and aaplication of probabilistic risk 15 analysis ("PRA") methods in tio safety design and licensing of 16 pressurized water reactor ("PWR") plants.
This includes both 17 system reliability assessment and accident analysis.
18 Q.4 Please summarize your professional qualifications.
19 A.4 I have B.S.
and M.S.
degrees in Nuclear Engineering 20 from Kansas State University, and have taken several post-21 graduate engineering courses at UCLA, CMU and MIT.
I have over 22 twenty years of experi'ence on the subject of reactor safety.
I 23 have participated in the conduct of six probabilistic safety 24 studies of Westinghouse designed PWRs.
I am one of the 25 technical writers of the recently issued NUREG-2300, PRA
1 Guidebook, and am currently active in a number of industry 2
organisations and technical societies involved with Light Water 3
Reactor risk criteria and standards development.
A complete 4
statement of my professional qualifications is appended as 5 to this testimony.
6 Q.5 Mr. Paddleford, what is the purpose of your testi-7 mony?
8 A.5 It is my understanding that Mr. Reed is challenging 9
the adequacy of off-site emergency response plans for the 10 Callaway Plant, in that he disagrees with the policy decision 11 made by the State of Missouri not to administer potassium 12 iodide to the general public in the 10-mile plume exposure 13 pathway Emergency planning Zone.
14 Further, I understand Mr. Reed's position to be based in 15 part on his postulation of an accident in which a significant 16 release of radioactive materials occurs in a very short time, 17 rendering evacuation undesirable and requiring resort to pro-18 longed sheltering.
19 The purpose of my testimony is to describe the extremely 20 low probability that an accident such as that postulated by Mr.
21 Reed would occur.
Since the likelihood of receiving a 22 projected dose of 25 rem or greater to the thyroid gland from 23 radiciodines released to the environment is an element in the 24 federal guidance on the use of potassium iodide as a thyroid-25 blocking agent, it is relevant to consider the probability of 1
occurrence of the event postulated by Mr. Reed.
This 2
assessment will provide a supportive foundation for the State's 3
evaluation of the relative benefits (i.e., need for) and 4
disadvantages of administering potassium iodide to the general 5
public.
6 Q.6 What is the basis for Mr. Reed's postulated event?
7 A.6 My understanding, based upon papers Mr. Reed has 8
filed with the Licensing Board, is that he relies upon 9
NUREG/CR-0388, SAND 78-0269, " Accident Descriptions for Emer-10 gency Response Exercise Scenarios" (November 1978), by Davit 11 Ericson.
In particular, he cites Accidents I, III, IV and VI 12 from that document, and has observed that large amounts of 13 radioactivity could be released to the atmosphere in as little 14 as 12 to 16 minutes.
15 In addition, while not cited by Mr. Reed, NUREG-0396 16
(" Planning Basis for the Development of State and Local 17 Government Radiological Emergency Response Plans in Support of 18 Light Water Nuclear Power Plants," December, 1978) utilizes as 19 a planning basis, a range of time values with a minimum of 20 one-half hour for:
21 (1) the time from initiating event to start of atmospheric 22 release; 23 (2) the time period over which radioactive material may be 24 continuously released; 1
(3) the time at which a major portion of the release may 2
occur; and 3
(4) the travel time for release to exposure point (time after 4
release).
5 As my testimony below will show, these planning assump-6 tions are based upon scenarios which, while possible, are ex-7 tremely improbable.
8 Q.7 How is your testimony organized?
9 A.7 My testimony is divided into four parts:
10 (1)
A discussion of potential accidents that might result 11 in radiation doses greater than 25 rem to the thyroid in the 12 10-mile plume exposure pathway Emergency Planning Zone ("EPZ").
13 The discussion will show that there is an extremely low proba-14 bility that an accident of this type will occur at the Callaway 15 Plant.
16 (2)
A summary of the results of recent technical studies, 17 performed by Westinghouse and in which I participated, which 18 show that the inference drawn from NUREG/CR-0388 and NUREG-0396 19 that large quantities of radiation are released to the atmo-20 sphere within a short time (less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />) is incorrect for 21 the most likely potential accident sequences.
Analyses of the 22 physical phenomena associated with fission product release from 23 the fuel and the containment show that in most cases many hours 24 would elapse between the initiation of an accident and signifi-25 cant radioactivity releases to the atmosphere.
_4_
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1 (3)
A brief summary of NUREG/CR-0388 scenarios I, III, IV 2
and VI and their probabilities, to illustrate that they are 3
consistent with the previous two points.
4 (4)
A description of instrumentation and facilities at 5
the Callaway Plant that enable accidents to be diagnosed early 6
and positively so that timely warnings can be provided to 7
persons within 10 miles of the plant.
8 Q.8 Please proceed with part one of your testimony.
9 A.8 In the approximately 700 Light Water Reactor plant 10 years of experience to date, there have been no accidents caus-11 ing offsite thyroid doses even approaching one rem.
Conse-12 quently, the estimation of the likelihood of accidents which 13 could result in radiation doses greater than 25 rem to the thy-14 roid in the 10-mile plume exposure pathway EPZ requires use of 15 theoretical calculations.
16 Analyses of Design Basis Accidents contained in the 17 Callaway Final Safety Analysis Report ("FSAR") and the NRC's 18 Safety Evaluation Report ("SER") (Ref. 1) show that, with the 19 exception of two cases in which unrealistic bounding assump-20 tions regarding the fission product release source have been 21 made, the offsite doses do not exceed 25 rem to the thyroid.
22 (I will return to these exceptions later.)
23 In order for significant (greater than 25 rem) offsite 24 thyroid doses to occur, it is necesary that accidents go beyond 25 the design basis, with postulated multiple failures of diverse 1
and redundant safety systems.
In particular, it is necessary
{
2 to have fuel overheating or melting, improper containment func-3 tioning, or both (Ref. 2).
Analyses of such so-called Class 9 4
accidents have not been performed for the Callaway Plant but 5
have been done for several reactor plants similar in design to 6
Callaway (Refs.
2, 3,
4, 5).
7 The results of the Reactor Safety Study ("RSS") (Ref. 2) 8 were that the frequency of core melt events in a 9
Westinghouse-designed pressurized water reactor would be less
-5 10 than 5 x 10 per year.
The Callaway Plant is a more 11 advanced Westinghouse design and has both specific design 12 features and specific surveillance procedures to reduce the 13 probability of fuel melt events relative to the RSS.
Thus, the 14 probability of an accident resulting in core melt at the
-5 15 Callaway Plant should be less than 5 x 10 per year.
It 16 is important to note that not all core melt accidents would 17 result in a major and unscrubbed airborne fission product 18 release.
In the RSS tne frequency of these major and
-5 19 unscrubbed releases were estimated to total about 1 x 10 20 per year.
These type of events are expected to be less 21 frequent at Callaway as a result of both design improvement and 22 improved phenomenological modelling.
23 For example, a dominant accident sequence in the RSS was a 24 so-called event V, in which it was postulated that (1) one of 25 two in-series isolation valves, between the reactor coolant 1
system and an interfacing low pressure system, was failed open 2
and its failure went undetected, and (2) the second valve then 3
failed.
In the Callaway Plant the probability of event V is 4
significantly reduced by requiring that any time either of two 5
in-series isolation valves between the reactor coolant system 6
and a low pressure system is caused to change position, the 7
leakage through each of the in-series valves must be tested and 8
shown to satisfy acceptance levels before the reactor can be 9
returned to power.
This essentially precludes the existence of 10 an undetected, failed isolation valve.
For event V to occur at 11 Callaway, two valves would have to fail, and the probability of 12 this is much lower.
Thus the probability of an accident re-13 sulting in both core melt and containment breach or bypass in
-5 14 the Callaway Plant should be less than 1 x 10 per year.
15 Earlier it was noted that two design basis accidents were 16 exceptions in that the Callaway FSAR/SER calculated these to 17 cause site boundary doses in excess of 25 rem to the thyroid.
18 The first of these is the design basis Loss of Coolant Accident 19
("LOCA") which, as a result of a conservative regulatory re-20 quirement, is historically analyzed with a source term equiva-21 lent to the core melt accident.
Consequently, this accident 22 when analyzed realistically using a fuel rod gap activity and 23 reactor coolant activity gives a much reduced thyroid dose and 24 is otherwise covered as a core melt event in the RSS when Emer-25 gency Core Cooling System ("ECCS") failure is addressed.
1 The second design basis case is the steam generator tube 2
rupture event.
Analyzed realistically, thyroid doses of 0.05 3
rem (Ref. 6) are calculated, which is much more in line with 4
the 0.005 rem corresponding to measured radioactivity concen-5 trations after an actual tube rupture event in a reactor 6
similar to Callaway (Ref. 7).
The point is that non-core-melt 7
events can, in some cases, be predicted to cause exposures in 8
excess of 25 rem to the thyroid when sufficient conservatisms 9
and failure contingencies are accumulated.
Such events have 10 been examined probabilistically in Ref.
8, which concludes that 11 they are bounded in terms of release magnitude and frequency by 12 the RSS study results.
Based on Ref.
8, the tube rupture 13 events causing the 72 rem (Ref. 1) site boundary thyroid dose 14 would have an approximately 10-per year frequency.
Fur-15 thermore, the dose would drop below 25 rem at a distance of 1.5 16 miles.
17 The conclusion of this portion of my testimony is that the 18 occurrence of a thyroid dose of more than 25 rem, within 10 13 miles of the Callaway Plant, is extremely unlikely.
20 Q.9 Please proceed with part two of your testimony.
21 A.9 Analyses of physical phenomena associated with 22 various core melt accident sequences and subsequent performance 23 of the containment have been performed by Westinghouse since 24 late 1978 (the time of issuance of-NUREG/CR-0388 and 25 NUREG-0396).
These analyses (Refs.
3, 4,
- 5) are for reactors I
1 similar in design to Callaway, and therefore the results can be 2
applied with a high degree of confidence to Callaway.
The con-3 clusion is that most (more than 90%) of the potential core melt 4
and containment failure sequences occur over a period of 5
several hours and that the trending of measurable plant 6
parameters provides many indications to enable the plant opera-7 tors to assess the severity of the accident.
Thus, contrary to 8
the impression which the analyses of NUREG/CR-0388 and 9
NUREG-0396 may leave, most accident sequences would develop 10 sufficiently slowly to enable residents within a 10-mile dis-11 tance of the Callaway Plant to be evacuated.
12 Q. 10 Please proceed with part three of your testimony.
13 A.
10 In order to illuntrate the preceeding points, 14 consider the four PWR scenarios Mr. Reed identified from 15 NUREG/CR-0388 (i.e.,
scenarios I,
III, IV and VI as identified 16 in Table 1 of that document).
The probabilities of these cce-17 narios are identified in Table 1 of NUREG/CR-0388 and are all 18 seen to ae very low and within the RSS totals just discussed.
19 Scenario I is a large pipe break, followed by failure of ECCS 20 (a redundant system), failure of containment spray (a redundant 21 system) and failure of the containment to isolate (a redundant 22 system).
Since a large pipe is ruptured and no safety systems 23 or containment operate, it is not surprising that a major 24 release would shortly occur.
The important point not to over-
-11 25 look, however, is that a 10 per year frequency was 26 estimated for this extraordinary scenario.
1 Scenario VI is quite similar in that a large pipe has rup-2 tured and that no core cooling or containment cooling safe-3 guards function due to a simultaneous loss of all offsite and 4
emergency onsite A.C.
electrical power.
The major difference 5
is that the containment isolates, but leaks at 10 times i's c
6 design leak rate until the concrete basemat is melted through 7
in about 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />, at which time the containment gases are 8
released via the soil filter medium.
This frequency is also
~9 9
extremely low and was estimated to be 10 per year.
10 Scenario III is a large LOCA with ruptured but not melted 11 fuel rods since the ECCS works to cool the core, but the con-12 tainment fails to isolate.
This has a higher, but still very
-7 13 low 2 X 10 per year frequency.
Note that although this 14 could cause a dose greater than 25 rem at the site boundary, it 15 would decrease to 25 rem at about two kilometers.
Hence, only 16 a very small portion of the EPZ would be impacted.
17 Scenario IV is a long duration loss of all A.C.
power 18 leading to eventual fuel melt and finally to containment
-6 19 overpressure failure.
The probability of 2 X 10 per 20 year, although very low itself, constitutes 90% of the total 21 core melt frequency on this brief list.
Recent Westinghouse 22 studies show the containment integrity would be maintained for 23 many hours in the Callaway class of reactor and containment, 24 permitting the timely evacuation of EPZ residents.
Even the 25 conservative NUREG/CR-0388 analyses show the containment 26 remaining intact for 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> and 40 minutes.
I 1
Q.11 Please proceed with part four of your testimony.
2 A.11 The Callaway Plant has many means of assessing 3
accident sequences that were not available to nuclear plants at 4
the time of the Three Mile Island accident.
Among these new 5
systems are:
6 a.
A Radiation Release Information System (RRIS) 7 that utilizes real-time meteorological data and 8
either real or postulated fission product 9
release data to calculate, continuously, real or 10 potential radiation doses outside the plant.
11 b.
A Safety Parameter Display System (SPDS), which 12 is a supervisory display of critical plant 13 parameters to aid operators to monitor plant 14 safety status.
15 c.
A Reactor Vessel Level Indication System (RVLIS) 16 which continuously indicates water level in the 17 reactor vessel.
It is impossible for fuel to 18 melt so long as it is covered with water.
19 d.
High range radiation monitors in the reactor 20 containment building that are capable of 21 indicating the amount of fission products that 22 could potentially be released to the atmosphere.
23 e.
A Technical Support Center (TSC) and Emergency 24 Operations Facility (EOF), both provided with 25 comprehensive and current data on plant status, 1
so that plant supervisory personnel (in the TSC) 2 and utility managment personnel, and local, 3
state and federal agency personnel (in the EOF) 4 can monitor the plant status during accident se-5 quences.
6 The conclusions of this portion of my testimony are that 7
many means are available for prompt assessment of the present 8
and future state of the plant during an accident sequence.
9 This will serve to minimize the time lag between a developing 10 threat to the general public and notification of the public.
11 Q.12 Mr. Paddleford, what are the implications of your 12 testimony for the off-site emergency planning issues raised in 13 this hearing?
14 A.12 In approximately 700 Light Water Reactor plant-years 15 of operating experience to date, there have been no accidents 16 in which off site thyroid doses have been in the range of even 17 one rem.
Analyses of the probability and consequences of 18 accidents beyond the design basis -- that is, those scenarios 19 which postulate multiple failures of diverse and redundant 20 safety systems -- reveal that there is an extremely low proba-21 bility of an accident occurring at the Callaway Plant that 22 might result in radiation doses greater than 25 rem to the thy-23 roid in the 10-mile plume exposure pathway EPZ.
Further, the 24 Callaway Plant has the capability to diagnose accidents early, 25 and most serious accident sequences would develop sufficiently !
)
1 slowly to enable the evacuation of nearby residents.
I believe 2
these facts support the State's policy decision that it is not 3
necessary to administer potassium iodide to the general public 4
around the Callaway Plant.,
1 REFERENCES 2
1.
NUREG-0830, Safety Evaluation Report, Callaway Plant, 3
Unit 1, USNRC, October 1981.
4 2.
WASH-1400, Reactor Safety Study, October 1975.
{
5 3.
" Zion Probabilistic Safety Study," Commonwealth 6
Edison Company, 1981.
7 4.
" Indian Point Probabilistic Safety Study," Power Au-8 thority of the State of New York and Consolidated 9
Edison Company of New York, Inc., 1982.
10 5.
" Millstone Unit 3 Probabilistic Safety Study,"
11 Northeast Utilities Service Company, 1983.
12 6.
NUREG-0921, Final Environmental Statement, Catawba 13 Nuclear Station, Units 1 and 2, USNRC, January 1983.
14 7.
NUREG-0916 Safety Evaluation Report related to the 15 restart of R.E.
Ginna Nuclear Power Plant, USNRC, May 16 1982.
17 8.
NUREG-CR/0603, A Risk Assessment of a Pressurized 18 Water Reactor for Class 3 through 8 Accidents, 19 October 1979.