ML20077D178
| ML20077D178 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 05/16/1991 |
| From: | Tremblay L VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| BVY-91-53, TAC-79442, NUDOCS 9105280053 | |
| Download: ML20077D178 (9) | |
Text
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, tVBitMONT YANKEE NUCLEAR POWEll COltPollATION JM.
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g May 16,1991 United States Nuclear Regulatory Commission avY 91-53 A'ITN: Document Control Desk Washington, DC 20555
References:
a.
License No. DPR 28 (Docket No. 50-271) i b.
Letter, VYNPC to USNRC, DVY 91-02, dated January 15,1991 c.
Letter, USNRC to VYNPC, NYY 91-56, dated April 16,1991
Subject:
Response to ".equest for Additional Infonnation -
Proposed Change No.162, Toxic Gas Monitoring System
Dear Sir:
On January 15,1991, Vennont Yankee submitted Proposed Change No.162 (Reference (b)]
to NRC for review and approval. This proposed change would eliminate the Technical Specification requirements for the Toxic Gas Monitoring System (TGMS). Upon approval,it is Vermont Yankee's intention to completely deactivate and remove from service the TGMS and the Bottled Gas Pressurization System (BGPS); however, the ability for operators to manually place the Control Room !!VAC System into the recirculation mode will remain. This proposed change, and the reasons therefore, are more fully described in Reference (b).
By Reference (c), USNRC transmitted a request for additional information regarding the subject proposed change. Reference (c) was received by Vennont Yankee on April 19,1991 and requested a response within 30 days from letter receipt.
Attached please find Vermont Yankee's response to USNRC's request for additional information (Reference (c)).
We trust that the attached information satisfactorily responds to your request; however, should you require additional infonnation, please contact this office.
Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPOR ATION 3
h' eari f
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Leonard A. Tremblay, Jr.
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Senior Licensing Engineer cc:
USNRC Region i Administrator USNRC Resident inspector - VYNPS USNRC Project Manager - VYNPS k
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ENCLOSURE RESPONSE TO Rf00EST FOR ADDITIONAL INFORMATION TECHNICAL SPECIFICATION FOR T0XIC GAS MONITORING SYSTEM (TGMS)
VERMONT YANKEE DOCKET NO. 50 271 TAC NO. 79442
References:
(a) letter, BVY 91 02, W.
P._ Murphy (VYNPS) to Document Control Desk (USNRC), " Proposed Change No. 162, Toxic Gas Monitoring System," dated January 15, 1991, (b)
Regulatory Guide (RG) 1.78, " Assumption for Evaluating the Habitability of a Nuclear Power Plant Control Room During a Postulated Hazardous Chemical Release," June 1974.
(c)
Letter, FVY 81+8, R. L. Smith (VYNPS) to D. G. Eisenhut (NRC), " Submittal of information on NUREG 0737, Item 111 D.3,4, Control Room Habitability," dated January 12, 1981.
(d)
Official Transcript of Proceedings, " Pacific Northwest Laboratory Workshop on Reactor Control Room Toxic Gas Limits,' IISNRC, Rockville, Maryland, June 19, 1990.
QUESTION'l in reference (a) the licensee states that the toxicity limits used for this analysis will be those established by National Institute of Occupational Health (IDLH) from " Pocket Guide to Chemical Hazards," y Dangerous to Life and Safety and Health (NIOSH) concentrations for immediatel NIOSH, September 1985.
The licensee considers these values which are greater concentrations than those listed in Reference (b) for chlorine, ammonia, and sulfur dioxide, acceptable.
This document is not endorsed by RG 1.78 or NRC's Standard Review Plan (SRP), Therefore, provide information to demonstrate that the proposed criteria.are at least equivalent to the SRP and RG 1.78 criteria, or provide that the SRP or RG 1.78 criteria will be used, in this demonstration, provide information Nu assure that the toxicity limits are conservative enough to
~
allow safe reactor operation without a TGMS.
t
RESPONSE
' to Reference (a) employs a four-step approach to evaluate the hauitability of the VYNPS Control Room.
Question l_ applies only to the first
' two steps.
Step 1 is to identify hazardous chemicals that have the potential
-to cause the Control Room to become uninhabitable.
Step 2 is to evaluate the
. chem ca s us ng information that is both practical and consistent with federal i
l i
guidelines, To accomplish Step 1, a list of hazardous chemicals is required.
To accomplish Step 2, a toxic concentration for each chemical on_the list is required. Table-C 1 of RG 1,78-provides a list of chemicals and a tcxic concentration-for each.
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A licensee, however, faces several problems in using Table C 1 of RG 1,78.
First, the list is small compared with other lists of potentially hazardous chemicals such as the U.S. Environmental Protection Agency's list of Extremely 1
Hazardous Substances (ENSs).
Second, RG 1.78 implies that other chemicals must be considered ("The list of chemicals given in' Table C-1 is not all inclusive..."), yet it does not specify which other lists are acceptable.
Third, RG 1.78 does not specify which toxic limits are to be used for chemicals not contained in Table C-1.
Fourth, the RG 1.78 " toxicity limits" are defined as the chemical concentrations that would cause operator l
ircapacitation within two minutes, yet as discussed below, the Table C 1 values are much lower than values quoted in other references for short term exposures.
Given the limitations of Table C 1, VYNPS adopted toxicity limits other than those specifically listed by RG 1.78.
Nevertheless, as explained below, we believe that our approach is consistent with the intent of RG 1.78.
In light of new information on toxic limits that has become available since the 1974 writing of "" 1.78, we believe that this approach is valid.
for Step 1 (identifying chemicals), VYNPS expanded the RG 1.78 list to include the U.S. Environmental Protection Agency's list of Extremely Hazardous Substances (EHSs).
This list is much more comprehensive than the list provided in Table C-1 of RG 1.78.
EHSs were developed in 1986 and are those chemicals that present toxic hazards to humans exposed to them during an accident or other emergency.
EPA specified toxicity criteria that can be used to screen chemical information sources and to identify acutely (short term) toxic chemicals.
Table C 1 of RG 1.78, on the other hand, identified both acute and chronic (long term) toxic chemicals.
For consistency in Step 2 (evaluating chemicals), VYNPS adopted the rPA approach and rationale to evaluate the effect of EHSs.
EPA. for example, establishes a level of concern if the concentrations of an EHS in air may cause serious irreversible health effects or death as a result of a single exposure for a relatively short period of time.
In principle, this is the
" toxicity limit" defined in RG 1.78.
In the past several years, various organizations have been developing DCute exposure guidelines for a limited l
number of hazardous chemicals.
The methodology, however, is still in developmental stages.
As a result, the EPA chose the NIOSH, "Immediately Dangerous to Life and Health (IDLH)," levels upon which to base its concentrations for level of concern.
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The IDLH value represents the maximum concentration of a substance in air from which healthy male workers can escape without loss of life or irreversible health effects under conditions of a maximum 30 minute exposure time.
The methodology in developing IDLHs takes into account immediate reactions that could prevent escape without injury, such as severe eye irritation or lung edema.
Practically, IDLHs are concentrations above which a highly reliable breathing apparatus is required with provisions for escape.
The EPA recognized that the IDLH is not designed as a measure of the exposure i
level required to protect general populations.
It, therefore. set a fraction of the IDLH as its level of concern.
VYNPS, on the other hand, meets the IDLH population definition of healthy male workers and, therefore, used the IDLH value as is.
The IDLH values, by definition, contain a level of conservatism when considered against the toxicity limits in RG 1.78.
As noted above, development of IDLH values is for a duration of 30 minutes at full concentration.
RG 1.78 toxic limits, however, assumes a two minute exposure to a concentration that begins low (at detection) and increases to the limit at the end of the two minutes.
As a check, NUREG/ Control Room 1741, "Models for the Estimation of Incapacitation Times following Exposures to Toxic Gases and Vapors," may be used to calculate incapacitation concentrations based on continuous exposure at full concentration. The NUREG model, for example, predicts incapacitation at two minutes for a chlorine concentration of about 60 ppm.
This is a factor of two above the IDLH value.
Similarly, the model incapacitation concentrations for ammonia and sulfur dioxide are a factor of four and seven above their IDLH values, respectivcly.
VYNPS, therefore, believes the IDLH value is sufficiently conservative to assess available emergency response times.
Lastly. VYNPS notes that a recent NRC workshop (Reference (d)) is relevant.
The workshop involved NRC personnel and expert toxicology consultants, The NRC participants noted the difficulties with spurious alarms and actuations of toxic gas monitoring systems installed at nuclear power plants.
They expressed the same concern that has led VYNPS to seek this license amendment.
--The concern is that the overly conservative limits in Regulatory Guide 1,78 have led to spurious alarms and inadvertent actuations of Control Room emergency habitability systems.
These alarms and inadvertent actuations are distracting the operators from more important concerns.
Also, the spurious l
alarms decrease the effectiveness of alarms in a real emergency.
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the workshop participants, but also of concern to VYNPS, are the safety and economic costs of maintaining the Toxic Gas Monitoring System.
The goal of the workshop was to " decide, based on your expertise. Opplication of the coherent rationale, whether or not there are other numbers ba*,ed on new data or newer insights that are better to support the licensing-reviews of NRR for these particular cnemicals that we have on the table" (Reference (d).
Page 6).
The chemicals reviewed included chlorine, ar.monia, and sulfur dioxide. Yhe experts discussed a number of different references for toxic ilmits, including RG 1,78, IDLH, and others, their conclusion was that none of the references alone were satisfactory.
This is because the effects of a chemical on humans is a function of both the concentration (ppm) and duration of exposure.
None of the references were totally consistent with the RG 1,78 assumption of a linear increase f rom detection threshold to toxic limit over a two-minute interval, Thus, the workshop relied on the experts' judgement, along with the various references, to establish a toxic limit for each chemical individually.
A consensus was reached for each chemical, in terms of either a point estimate or a range.
These results are summarized in the table below.
Note that the workshop consensus matches the IDLH exottly for chlorine and sulfur dioxide.
For ammonia, the 10LH is within the range of the workshop consensus.
Clearly, the workshop consensus supports use of the IDLH values for chlorine.
ammonia, and sulfur dioxide over the RG 1.78 values.
Comparison of Tnvir limits (ppm)
Workshop Concensus i
Chemical RG 1.78 Limit 10LH Point Estimate Range q
Ch!orlne 15 30 30
_j 300 500 Ammonia 100 500 sulfur Dioxide 5
100 100 l
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a, to reference (a) in Table 5.1, " Control Room Concentration of Hazardous Chemicals from Highway Accidents," the maximum Control Room concentration for chlorine, ammonia, and sulfur dioxide exceeds the toxic limits established in RG 1.78.
Therefore, provide information to demonstrate that these alternative limits are acceptable, or state that the RG 1.78 or SRP criteria will be used.
b.
Are control room operators trained in the detection by smell of the chemical hazards listed in Table 5.1, ard that it requires at least two minutes between the time toxic gas is dc'ected and to put on a self-contained breathing apparatus?
c.
Table 5.1 does not list the time t rom detection by operators to time at which a toxic limit (RG 1.78 limit for chemicals listed in Table C 1) is reached.
Please provide this info *mation.
Rf9PONSE a.
Please refer to the response to Question 1.
The rationale and demonstration are the same for Ouestion 2.
b.
As explained in the response to Question 1. the toxicity limits used in to Reference (a) are based on IDLH values.
Table 5.1 shows that the maximum Control Room concentrations for chlorine, ammonia, and sulfur dioxide are within the toxicity limits.
Accordingly, these chemicals were deleted from further evaluation.
Neither levels of odor detection nor the two minute screening criteria were applied.
Table 5.1, therefore, does not contain this information, end no credit was taken for Control Room operators to detect these chemicals, c,
As explained above, the IDLH values were used as the toxicity limits in Reference (a).
The analysis results in Table 5.1 show that these limits are not reached.
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=
pl[f; TION 3 i
In referente (c), the licenstfe identified anhydrous ammonia, vinyl chloride, and methanol in addition to the chemicals evaluated in reference (a) as potential toxic hazards.
Therefore, provide information as to why the above chemicals are no longer considered potential hazards, RfSPONSE The chemicals identified in Reference (c) resulted from a survey of the two adjacent railroads performed in 1980.
Since then, two important changes have
- occurred, first, the Springfield Track (formerly the Boston & Maine) railroad has rerouted rail traffic to other lines having more desirable shipping rates or interchange connections.
Second, marketing trends and new manufacturing processes that use less hazardous materials have changed the types of material transported by both the Springfield Track and Central Vermont railroads.
Those chemicals identified as being transportea during the most recent survey are summarized in Table 6.1 to Attachment 2 of Reference (a).
Vinyl chloride and methanol are no longer shipped. While anhydrous ammonia is still shipped, the frequency nf shipment (seven per year) is within the RG 1.78 limit of 30 per year.
Thus, these chemicals are not considered as potential hazards according to the criteria of RG 1.78.
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r 00fc.1104 4 In Attachment 2 to reference (a), Table 6.2, the licentee determined that the concentration of propane w0uld reach a maximum of 28,039 ppm or 2.81.
Limits af flammability percent by volume in air are 2.15 to 9.6 ftom fire Protection Handbook, 16th edition, National fire Protec+ ion Association, Quincy, Massachusetts.
Therefore, provide informat' ' regarding the acceptability of the 33,500-gallon propane tank car which was analyzed in reference (a).
Pf5PONSE Propone was evaluated using the sane screening criteria as f or toxic chemicals.
Although the maximum concentration c ? propane in the Control Room exceeds the IDLH value, it meets the two-minute limit; i.e., there is more than two minutes between the time the vapor is detected and the time the IDLH value is reathed.
The IDLH value for propane is 20,000 ppm, or 21 by volume in air.
This value is below the propane lower limit of flammability, which is 21,500 ppm.
Applying the RG 1.78 toxic limit" criterion, VYNPS assumes that the two minutes is sufficient time for a trained operator to put protective action procedures into effect.
Regardless, the likelihood that a railroad accident resulting in the release of propane could produce flammability levels in the Control room is very small.
Using the methodology outlined in Attachment 2 to Reference (a), VYNPS calculates the annual probability to be 1.8 x 10'7 This value meets the SRP 2.2.3 guidelines.
Note also that propane is not listed as a chemical to be evaluated in RG 1.78.
Nevertheless, VYNPS addressed propane and other chemicals in order to perform a comprehensive analysis of toxic chemical hazards using up-to-date informat10t'.
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a OtIE ST I ON r.
In attachment 2 to reference (a) Table 6.2 the IDLH values for carbon dioxide and chlorine exceed the limits established by RG 1.78.
Therefore, provide information to demonstrate that these limits are at least equivalent to the SRP and RG 1.78 criteria, or provide that the SRP and RG 1.78 criteria will be used.
PrMONSE Please refer to the response to Question 1.
The rationale and demonstration are the some for Question 5.
As explained, the toxicity limits used in Attachinent 2 to Ref erence (a) are based on IDlH values.
When viewed in this regard, the maximum Control Room concentration for carbon dioxide is within the toxicity limit.
Accordingly, carbon dioxide was deleted from further evaluation.
Chlorine, on the other hand, is above the toxicity limit.
Chlorine, therefore, was evaluated further to determine the probability of Control Room uninhabitability.
The resultant probability analysis, as demonstrated in Attachment 2 to Reference (a), meets the SRP 2.2.3 guidelines.
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