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Radiation Safety-4.15.2020 Workshop Final
	ML20105A002
Person / Time
Site:	Nuclear Energy Institute
Issue date:	04/15/2020
From:	; Nuclear Energy Institute
To:	; Office of Nuclear Material Safety and Safeguards
	Kallan P
References
	Download: ML20105A002 (15)
	v • d • e

Radiation Safety April 15 and 16, 2020 Washington DC

Compliance with Safety Requirements Regulation and Guidance Comments on Guidance Occupational Exposure The Consequences Proposed Change to Guidance Documents (V-1)

Guidance on Modeling Details (V-2)

Discussions Agenda

©2020 Nuclear Energy Institute 3 Discuss Radiological Safety Discuss proposed reviews and revisions of guidance documents, for the purpose of ensuring activities that have no radiological safety significance are eliminated.

Goal

©2020 Nuclear Energy Institute 4 Radiological Safety Demonstration Dose Rates can be measured, and are measured Acceptance Criteria (Dose Limits) are clear Demonstrating compliance with the safety requirements is done with measurements, informed by analyses Vast amount of dose experience for dry storage of spent fuel more than 3000 systems loaded with dose rates taken and compliance demonstrated Main safety criteria Public: 25 mrem/year at the site boundary, including contribution from casks and from the plant Occupational: 5 rem/year for each person Dose Rates and Safety

Type of casks (cask vendor specific)

Distance to Site Boundary (Site Specific)

Fuel loaded into the casks (Site Specific)

Compliance with Dose at the site boundary is responsibility of the site (the licensee)

Demonstrated by measurements that are informed by calculations Dose at the Site Boundary (V-1)

Site boundary dose limits

Occupational exposure ALARA Compliance with Safety Criteria

Step 1:

Offsite dose calculations performed (typically by cask vendor) to demonstrate compliance (in calculational space)

Level of detail and sophistication can vary significantly depending on site conditions Step 2:

Calculations of dose rates on transfer cask and storage cask at locations specified in the CoC, consistent with Step 1 Step 3:

Licensee develops cask loading plans/procedures consistent with Steps 1 and 2 Compliance with Safety Criteria

Step 4 (for each cask):

Transfer cask is loaded, measurements are taken If limits are met, process continues to next step Step 5 (for each cask):

Storage casks are loaded, measurements are taken If limits are met, cask is placed on ISFSI Step 6:

After all casks of a campaign are loaded, dose rates at the site boundary are reviewed to again confirm limits are met (formal compliance demonstration).

Compliance with Safety Criteria (cont.)

§§72.104 and 72.106.

From NUREG 1536/(2215) Section 6.4 (with sections highlighted)

In general, the DSS shielding evaluation should provide reasonable assurance that the proposed design fulfills the following acceptance criteria:

1. The radiation shielding features of the proposed DSS are sufficient for it to meet the radiation dose requirements in 10 CFR 72.104 and 72.106(b). The applicant demonstrates this with:

a. A shielding analysis of the surrounding dose rates that contribute to occupational exposure and off-site doses at large distances (for a single storage and transfer cask with bounding fuel source terms at various cask locations), and

b. A shielding analysis of a single cask and a generic array of casks at large distances.

Compliance with Safety Criteria (cont.)

©2020 Nuclear Energy Institute 10 Comments on Guidance Calculated dose rates in the FSAR, around a single cask or from a cask array, provide NO indication if 72.104 regulatory requirements can be met or not for an ISFSI site, since this depends on site specific parameters For a small ISFSI far away from the site boundary, limits can be easily met even if dose rates around a cask are comparatively high But for a large ISFSI close to the site boundary, even casks with very low dose rates can be a challenge, and may require additional shielding (e.g. a berm)

Additionally, using BOUNDING source terms in the FSAR further increases the discrepancy between FSAR calculations and site-specific dose rates, which may result in erroneous conclusions drawn from the FSAR.

Compliance with Safety Criteria (cont.)

©2020 Nuclear Energy Institute 11 Occupational Exposure Crew dose (dose to the loading crew for loading a single cask) are presented in the FSAR NRC still expects update and maintenance of the FSAR information, for changes to the designs and/or content Licensees have their established RP and ALARA processes, further informed by industry experience, to plan and perform loading operations.

FSAR crew dose information does not provide any relevant information in that context.

Compliance with Safety Criteria (cont.)

The FSAR needs to maintained essentially indefinitely May also inform limits specified in the Technical Specifications Forever subject to 72.48 review Reviewed by NRC, generating a Safety Evaluation Report Used and maintained by the licensee as the licensing basis Any change to a cask design or content, even very small, triggers this cascade This should not be necessary for something that is not used or needed to demonstrate safety The Consequences

©2020 Nuclear Energy Institute 13 The licensee needs to know that the system is capable of meeting the regulatory requirements This needs to be known before the casks are loaded, i.e. before measurements can be taken to demonstrate safety.

This is achieved through site-specific site boundary dose analyses, taking into account all previously discussed site specific and cask parameters For additional verification, licensees may consult general industry experience, from the 3000+ cask loaded Dose rates reported in the FSAR play no role here Information for Licensees

©2020 Nuclear Energy Institute 14 In the FSAR, provide dose rates for a typical cask design with representative content, showing values on the surface and at various distances for a single cask. The associated analyses establish the methodology to determine site boundary dose Parameters for those calculations should be clearly specified Additionally, present qualitative discussions of the impact of any possible variations of those parameters on the results Cask type, content, ISFSI size, distance to side boundary Impact on dose rates (small, factor 2, factor 5, factor 10,.)

Occupational exposure evaluations are provided to demonstrate that worker dose can be reasonably controlled ALARA Licensee RP and ALARA programs, informed by industry experience control worker dose, not the SAR SAR presentation of off-site dose and occupational exposure are to demonstrate ability to meet site limits, and not for demonstration of compliance with the regulations.

Proposed Change to Guidance (V-1)

Without any appropriate concept on what is appropriate, the expectation often defaults to bounding.

Example: consider dimensional tolerances in shielding analyses Higher levels of details and/or bounding modeling approaches substantially increase the modeling effort See the The Consequences slide for additional discussions on the consequences of this Over 3,000 loaded systems provide measured data for comparison - typically 50%

lower than calculated.

Recommendation Review and revise the guidance on modeling, taking into consideration the industry experience on dose rates from the radiation protection programs.

Guidance on Modeling Details (V-2)

ML20105A002

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